OPERATIONAL SAFETY

OF NUCLEAR POWER PLANTS

P R O C E E D IN G S OF A SY M PO SIU M , M A R SE IL L E S, 2 - 6 M AY 1 9 8 3VOL. 11I N T E R N A T I O N A L A T O M I C E N E R G Y A G E N C Y , V I E N N A , 1 9 8 4

O P E R A T I O N A L S A F E T Y

O F N U C L E A R P O W E R P L A N T S

V O L . II

T h e fo llow ing S ta te s a re M em bers o f th e In te rn a tio n a l A to m ic E nergy A gency :

AFGHANISTANALBANIAALGERIAARGENTINAAUSTRALIAAUSTRIABANGLADESHBELGIUMBOLIVIABRAZILBULGARIABURMABYELORUSSIAN SOVIET

SOCIALIST REPUBLIC CANADA CHILE CHINA COLOMBIA COSTA RICA CUBA CYPRUSCZECHOSLOVAKIA DEMOCRATIC KAMPUCHEA DEMOCRATIC PEOPLE’S

REPUBLIC OF KOREA DENMARKDOMINICAN REPUBLICECUADOREGYPTEL SALVADORETHIOPIAFINLANDFRANCEGABONGERMAN DEMOCRATIC REPUBLICGERMANY, FEDERAL REPUBLIC OFGHANAGREECEGUATEMALAHAITI

HOLY SEEHUNGARYICELANDINDIAINDONESIAIRAN, ISLAMIC REPUBLIC OFIRAQIRELANDISRAELITALYIVORY COASTJAMAICAJAPANJORDANKENYAKOREA, REPUBLIC OF KUWAIT LEBANON LIBERIALIBYAN ARAB JAMAHIRIYALIECHTENSTEINLUXEMBOURGMADAGASCARMALAYSIAMALIMAURITIUSMEXICOMONACOMONGOLIAMOROCCONAMIBIANETHERLANDSNEW ZEALANDNICARAGUANIGERNIGERIANORWAYPAKISTANPANAMAPARAGUAY

PERUPHILIPPINESPOLANDPORTUGALQATARROMANIASAUDI ARABIASENEGALSIERRA LEONESINGAPORESOUTH AFRICASPAINSRI LANKASUDANSWEDENSWITZERLANDSYRIAN ARAB REPUBLICTHAILANDTUNISIATURKEYUGANDAUKRAINIAN SOVIET SOCIALIST

REPUBLIC UNION OF SOVIET SOCIALIST

REPUBLICS UNITED ARAB EMIRATES UNITED KINGDOM OF GREAT

BRITAIN AND NORTHERN IRELAND

UNITED REPUBLIC OF CAMEROON

UNITED REPUBLIC OF TANZANIA

UNITED STATES OF AMERICA URUGUAY VENEZUELA VIET NAM YUGOSLAVIA ZAIRE ZAMBIA

The Agency’s Statute was approved on 23 October 1956 by the Conference on the Statute of the IAEA held at United Nations Headquarters, New York; it entered into force on 29 July 1957. The Headquarters of the Agency are situated in Vienna. Its principal objective is “to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world”.

© IAEA, 1984

Permission to reproduce or translate the information contained in this publication may be obtained by writing to the International Atomic Energy Agency, Wagramerstrasse 5, P.O. Box 100, A-1400 Vienna, Austria.

Printed by the IAEA in Austria March 1984

P R O C E E D I N G S S E R I E S

O P E R A T I O N A L S A F E T Y

O F N U C L E A R P O W E R P L A N T S

PRO CEEDING S OF A N IN T E R N A T IO N A L SYMPOSIUM ON O PER A TIO N A L S A FE T Y O F N U C LEA R POWER PLA N TS

O R G A N IZ E D BY THE IN T E R N A T IO N A L ATOMIC E NER G Y A G ENC Y

A N D H ELD IN M A RSEILLES, 2 - 6 M AY 1983

In two volum es

V O L . I I

IN T E R N A T IO N A L ATOM IC E NER G Y AG ENC Y V IE N N A , 1984

O PE R A T IO N A L SA FE T Y O F N U C L E A R POWER PLA N TS IA E A , V IE N N A , 1984

S T I/P U B /648 ISBN 9 2 - 0 - 0 2 0 1 8 4 - 9

F O R E W O R D

Im provem ent o f the safety o f nuclear pow er is a continu ing process. In spite o f d ifficu lties w hich have been faced w ith public acceptance, the design, construction and operation o f nuclear pow er plants have been successfu lly carried ou t. S ince the nuclear industry has experience o f nearly 3 0 0 0 reactor years o f op eration , it can be considered to have reached m aturity . T he n ex t phase w ill n o doubt see the u tiliza tion o f nuclear pow er on a greater scale in an increasing num ber o f countries and a broadening o f the areas o f application (i.e . use as a source o f heat as w ell as o f e lectricity ).

C om m ercial nuclear pow er has a very good safety record, m aintained by its long tradition o f a tten tion to sa fety , and it com pares very favourably w ith other industries in this regard. D esigners and operating organizations are still devoting considerable e fforts to achieving even higher levels o f safety .

A m ong the various m easures and actions taken to im prove the safety o f nuclear pow er plants, those that are related to operation are o f special im portance, because it is during the operational phase that the com p eten ce o f designers, the diligence o f m anufacturers, and the care and discip line o f operating personnel are tested . Errors in these various spheres o f hum an activity cou ld at this stage n ot on ly have significant safety im plications but also involve serious econ om ic penalties.

It was therefore judged opportune for an International Sym posium on O perational Safety in N uclear P ow er Plants to be convened by the IA EA. The m eeting to o k p lace in M arseille, France, from 2 to 6 May 1983 . It consisted o f nine sessions and tw o panel discussions, w ith a num ber o f poster displays. T he panel d iscussions w ere concerned w ith hum an factors and the m an/m achine in terface, and future activities to im prove operational safety .

T he International A tom ic Energy A gency is m ost grateful to the G overn­m en t o f France for h osting the sym posium and acknow ledges in particular the assistance and co-operation o f the C om m issariat à l ’énergie atom ique and E lectricité de France in the preparation and running o f th e m eeting.

EDITORIAL NOTE

The papers and discussions have been edited by the editorial staff o f the International Atomic Energy Agency to the extent considered necessary for the reader's assistance. The views expressed and the general style adopted remain, however, the responsibility o f the named authors or participants. In addition, the views are not necessarily those o f the governments o f the nominating Member States or o f the nominating organizations.

Where papers have been incorporated into these Proceedings without resetting by the Agency, this has been done with the knowledge o f the authors and their government authorities, and their cooperation is gratefully acknowledged. The Proceedings have been printed by composition typing and photo-offset lithography. Within the limitations imposed by this method, every effort has been made to maintain a high editorial standard, in particular to achieve, wherever practicable, consistency o f units and symbols and conformity to the standards recommended by competent international bodies.

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C O N T E N T S O F V O L U M E II

D ESIG N IM PROVEM ENT F O R SA FE O PER A TIO N (Session IV )

Управление энергораспределением и безопасность реактора ВВЭР-1000при работе в маневренном режиме (IA E A -S M -268 /75) .......................Е.В. Филипчук, В. Г. Дунаев, И. А. Лукьянец,П. Т. Потапенко, Е. С. Тимохин, В. А. Вознесенский, В. И. Митин

(C o n tr o l o f p o w e r d is tr ib u tio n a n d th e s a fe ty o f a W W E R -1000 rea c to r du rin g o p era tio n in a lo a d -fo llo w in g regim e:E. V. F il ip c h u k e t a l.)

\ f N ouvelles d ispositions de p rotection contre les surpressions deschaudières nucléaires REP de 9 0 0 et 1300 MW (IA E A -SM -268/62) J.-L . C abannes, R . P e tit, M. O livon

Влияние некоторых нейтронно-физических характеристик активной зонына безопасную работу реактора типа ВВЭР (I A E A -SM -268/76) ............М. А. Л укьянов, В. А. Вознесенский, А .К . Горохов,В. П. Спасское, Н. С. Филь( E f fe c t o f certa in n e u tro n p h y s ic s characteris tics o f th e core o n th e sa fe o p era tio n o f a W W ER reactor: M .A . L u k y a n o v e t a l.)

U ltim ate heat sink for PHWRs: evaluation o f existing m ethod sand alternative proposals (IA E A -S M -268 /22) ..........................................A .K . G hosh, S .K . B a n d y o p a d h y a y , L .G .K . M u r th y ,N . R a m a m o o r th y

Post loss o f coo lan t accident m anagem ent (IA E A -S M -268 /32) .........A . N a ta liz io , J.G . C om eau , D .W . B la c k

•^ /l /a p p r o c h e par état: une n ouvelle con cep tion des procéduresde con d u ite p ost-accidentelle (IA E A -S M -268 /53) ...............................H. Sureau , G. D ep o n d , A . O lio t

Poster presentations

F eedback o f operating experience and its u tiliza tion forim proved safe perform ance (IA E A -SM -268/21P ) ...............................B .K . B hasin

\ / L ’approche probabiliste et le retour d ’expérience(I AE A -S M -268/51 P) ..........................................................................................C. A n c e lin , J .F . B a rb e t, A . V illem eu r

\ / E xpérience acquise dans la surveillance des structures internes et m oyen s m is en œ u vre sur les paliers REP 9 0 0 et 1300 MW(IA E A -SM -268/52P ) ..................................................................................................... 96C. P u ya l

\ / Mise en oeuvre des am éliorations des salles de com m ande destranches REP 9 0 0 MW (IA E A -SM -268/57P ) .................................................... 98P. R o lla n d

Sum m ary o f Session IV ..................................................................................................... 99

FEED BA C K O F O PE R A T IN G EXPERIENCE (Session V)

Organizational and technical aspects o f operating experience reviewand feedback activ ities (IA E A -S M -268 /23) ...................................................... 103M. N o b ile , I. T r ip p u ti

E xam ples o f evaluations o f incidents in nuclear pow er plants andlessons learned (IA E A -S M -268 /81) ..................................................................... 113H. H au n h o rst, K. K o t t h o f f F. S ch le ifer , M. S im o n

y / E nseignem ents généraux tirés des incidents survenus sur les centralesnucléaires françaises (IA E A -S M -268 /43) .......................................................... 121Y. D roulers, C. F e ltin , B. F o u re s t

V L ’analyse des incidents à Fram atom e (IA E A -S M -268 /47) ............................... 135A . C alam and, A . O lio t

N uclear pow er plant reliability data co llection system in Japan(IA E A -S M -268 /13) ..................................................................................................... 151S. M iya o ka , H. F u k u m o to , S. Sasaki

Processing o f data generated at Paks nuclear pow er p lant forcentralized use and operational feedback (IA E A -S M -268 /25) ............... 163P. R ésch , J. T a llósy, J. V alkó , L . Vôrôss, I. C zoch

Evaluation o f events reported to CNEN during startup phase o fAngra I (IA E A -S M -268/7) .................................................................................... 173J.M . d e L im a

Опыт безопасной эксплуатации АЭС с быстрыми реакторами в СССР(IA E A -S M -268 /74) .......................................................................................................... 183Ю.Е. Богдасаров, И. А . Кузнецов, В.Н. Иваненко, И. А. Ефимов (U S S R exp erien ce o f th e sa fe o p era tio n o f nuc lear p o w e r p la n ts w ith fa s t reactors: Y u .E . Bagdasarov e t a l.)

R eview o f operational experience w ith the gas-cooled M agnox reactors o f the U n ited K ingdom Central E lectr icity G eneratingBoard (IA E A -S M -268 /30) .................................................................................... 197L. Cave, A .W . C larke

International experience in the im plem entation o f the lessons learned from the T hree M ile Island incident: report on an IA EAtechnical com m ittee (IA E A -S M -268 /49) .......................................................... 215R .J . Palabrica

\ / Arrêts d ’urgence survenus sur les tranches REP 9 0 0 du parc E D F de1979 à 1982 (1A E A -S M -268 /42) ......................................................................... 227P. C assette , K. Park, A . C ayo l

Segu im ien to , en un p a ís im portador, de la exp lo tac ión de una central nuclear con problem as de diseño: central nuclear deAlm araz (IA E A -S M -268 /90) ..................................................................................... 241J. R e ig

A nticipated transient w ith ou t scram events at Salem : anotherlesson in operating experience (IA E A -S M -268 /91) ...................................... 259W.D. b a n n in g

Sum m ary o f Session V ..................................................................................................... 275

IN T E R N A T IO N A L ACTIVITIES TO IM PROVE SA FE T Y (Session VI)

v / Les actions des autorités de sûreté françaises en m atière de coopération internationale sur la sûreté d ’ex p lo ita tion descentrales nucléaires (IA E A -S M -268 /39) .......................................................... 281M. L avérie

N E A incident reporting system : three years’ experience(IA E A -S M -268 /71 ) ..................................................................................................... 291Y. O tsuka , W. H àusserm ann

IA E A activ ities aim ed at im proving th e feedback o f experience inoperational safety o f nuclear pow er plants (IA E A -S M -268 /72) ............... 301H. W right, V.S. O sm a ch kin

International guidance on the qualifications o f nuclear pow er plantoperations personnel (IA E A -S M -268 /33) .......................................................... 315B.J. C sik

A ssuring nuclear safety from the p o in t o f v iew o f standardization(I A E A -S M -268/7 7 ) ..................................................................................................... 325V. K re tt, L. J a n ík , F. Ya. O vch in n ik o v , V. C h ebo ta rev

IA EA-assisted research w ork in the field o f operational safety forH ungary’s first nuclear pow er p lant (IA E A -S M -268 /68) ............................ 333I. T ó th , L . S za b a d o s

Poster presentations

C om puterized personnel dosim etry m onitoring and m anagem entsystem (IA E A -SM -268/1 OP) ..................................................................................... 345A . Yanagisawa, M. T akayam a, Y. K im ura , A . K aw am ura

E ffect o f external decontam ination o f persons contam inated w ith radionuclides at an operating nuclear pow er plant(I A E A -SM -268 /27P ) ..................................................................................................... 3 4 8D. S to ja n o v ic , Z. D ju k ic , M. T ra jkovic , D. V eljkovic ,K. M ilivo jev ic , B. A le k s ic

Sum m ary o f Session V I ..................................................................................................... 3 4 9

EM ERGENCY PR E PA R E D N ESS (Session VII)

J Organisation des plans d’urgence en cas d’accident dans une centrale nucléaire à eau sous pression — D ispositions prises parl’exp lo itan t et les pouvoirs publics (IA E A -S M -268/63) ............................... 353M. L avérie, L . B er tro n

\y Plan d ’urgence et expérience d ’exp lo ita tion (IA E A -S M -268 /37) ............... 365O. H alpern , J. B ren ière

E m ergency plans for civil nuclear installations in theU nited K ingdom (IA E A -S M -268 /85) ................................................................. 373W. S. G ro n o w

E m ergency preparedness in the CEGB: d evelopm ent o f em ergency arrangem ents fo llow in g th e T hree Mile Island accident(IA E A -S M -268 /31) ..................................................................................................... 38 7T.P. H aire

Im portance o f the con tro l room during a nuclear em ergencysituation (I A E A-SM -26 8 /2 8 ) .................................................................................. 403K. N o w a k , H. S c h n a d t

D evelop m ent o f BWR com puterized operator support system forem ergency con d ition s (IA E A -S M -268 /20) ....................................................... 415F. M u ra t a, K. K a to , S. H a sh im o to

Sum m ary o f Session VII ................................................................................................. 42 7

Panel: F uture activ ities to im prove operational safety ............................... 429

L ist o f Chairm en o f Sessions and Secretariat o f th e Sym posium ............... 433

List o f Participants and D esignating M em ber States and O rganizations .... 435

A uthor Index ..................................................................................................................... 453

Index o f Papers by N um ber .................................................................................... 455

D E S I G N I M P R O V E M E N T F O R S A F E O P E R A T I O N

( S e s s io n I V )

Chairman

W. ROEHNSCHGerm an D em ocratic R epublic

lAEA-SM-268/75

У П РАВЛ ЕН И Е ЭН ЕРГО РАС П РЕДЕЛ ЕН И ЕМ И

Б Е ЗО П А С Н О С Т Ь РЕА К Т О РА В В Э Р -1 0 0 0 ПРИ

РА Б О Т Е В М АНЕВРЕН НОМ РЕЖИМЕ

Е.В. ФИЛИПЧУК, В. Г. ДУНАЕВ, И.А. ЛУКЬЯНЕЦ,П.Т. ПОТАПЕНКО, Е.С. ТИМОХИН Инженерно-физический институт,Москва

В.А. ВОЗНЕСЕНСКИЙ, В.И.МИТИН Институт атомной энергии им.И.В. Курчатова,Москва,

Союз Советских Социалистических Республик

Д оклад представлен Г. Н. Полетаевым

• Abstract-Аннотация

CONTROL OF POWER DISTRIBUTION AND THE SAFETY OF A WWER-1000 REACTOR DURING OPERATION IN A LOAD-FOLLOWING REGIME.

An important task in ensuring the operational safety of a nuclear power plant with a vessel-type water-cooled, water-moderated reactor is the development of algorithms for controlling power distribution in base-load and load-following regimes. The control strategy must ensure that the form of power distribution is maintained within the permissible limits in the case of situations presenting a nuclear hazard and of xenon fluctuations when there are variations in power output. The task of controlling power distribution can be broken down into an axial problem and a radial-azimuthal problem. For maintenance of the form of axial power distribution an algorithm of optimum fast-action control is proposed; for maintenance of the radial-azimuthal form, an algorithm of optimum (i.e. best) approximation to the given distribution of control. The two control problems are solved by using a single computerized procedure based on mathematical programming. The algorithms are designed for use in computerized control. The paper presents the results of algorithm simulation. The authors propose that in the first stage, activation of the control systems should involve the operator, who can view the sequence of actions on a display screen.

УПРАВЛЕНИЕ ЭНЕРГОРАСПРЕДЕЛЕНИЕМ И БЕЗОПАСНОСТЬ РЕАКТОРА ВВЭР-1000 ПРИ РАБОТЕ В МАНЕВРЕННОМ РЕЖИМЕ.

Важной задачей обеспечения эксплуатационной безопасности АЭС с корпусным водо-водяным реактором является разработка алгоритмов управления энергораспределением в базовом и манев­ренном режимах. Стратегия управления должна обеспечивать сохранение формы энергораспределения в допустимых пределах в случаях возникновения ядерно-опасных ситуаций, ксеноновых колебаний, при изменениях мощности. Задача управления энергоснабжением разбита на аксиальную и радиально­азимутальную задачи. Для поддержания формы аксиального энергораспределения предложен алго­ритм оптимального по быстродействию управления, для поддержания формы радиально-азимуталь­ного энергораспределения - алгоритм оптимального, в смысле наилучшего, приближения к заданно­

3

4 ФИЛИПЧУК и др.

му распределению управления. Обе задачи управления решены в рамках единой вычислительной процедуры, построенной на основе математического программирования. Алгоритмы ориентированы на использование для управления ЭВМ. Приведены результаты моделирования алгоритмов. Авторы предполагают на первом этапе воздействовать на органы регулирования через оператора, которому указывается последовательность действий на экране дисплея.

ВВЕДЕНИЕ

Увеличение размеров и мощности реакторов требует качественно нового подхода к реактору, к ак к объекту управления с распределенными параметрами [ 1 ]. Достиже­ния в общей теории распределенных систем, разумеется, применимы и в приложении к ядерному реактору.

В докладе излагается один из возможных подходов к управлению энергораспре­делением применительно к реактору ВВЭР-1000 [2] на основе современной теории управления. Результаты моделирования, приводимые в докладе, показывают, что рас­сматриваемый алгоритм управления может быть эффективным как для базового режи­ма работы, так и для режимов изменения нагрузки. Необходимость изменения мощнос­ти АЭС может быть связана как с отказами отдельных систем и оборудования (аварий­ные реж имы ), так и с работой АЭС в переменном графике нагрузок (маневренный режим) . Маневрирование мощностью реактора может осуществляться изменением по­ложения органов регулирования (ОР) и работой системы борного регулирования (СБР)

Стратегия управления при изменениях мощности и в стационарных режимах долж­на обеспечить сохранение заданной формы энергораспределения в допустимых пределах. Алгоритм управления энергораспределением, рассчитанный на использование ЭВМ, дол­жен учитывать возможность возникновения ксеноновых колебаний нейтронного поля, изменение коэффициента реактивности в процессе кампании, близость основных тепло­технических параметров реактора к предельно-допустимым значениям.

При управлении энергораспределением воздействие на органы регулирования и систему борного регулирования наиболее целесообразно осуществлять через оператора, путем указания на экране дисплея оптимальной последовательности управляющих воз­действий.

СИСТЕМА УПРАВЛЕНИЯ

Автоматизированная система управления реактора ВВЭР-1000 должна включать в себя информационно-измерительный комплекс с системой внутриреакторного конт­роля, человека-оператора, средства воздействий на реактивность (ОР и СБР) и, собст­венно, реактор — объект управления с распределенными параметрами.

Система внутриреакторного контроля в качестве первичных источников инфор­мации имеет датчики температуры воды на выходе из кассет и нейтронные измеритель­

IAEA-SM-268/75 5

ные зонды. Каждый измерительный зонд оснащен несколькими равномерно разме­щенными по высоте зонда родиевыми ^-эмиссионными детекторами. Часть нейтронных измерительных зондов равномерно распределена по активной зоне, остальные установ­лены в кассетах из различных групп симметрии. Чувствительные части ^-эмиссионных детекторов выполнены из родия. В состав системы внутриреакторного контроля вхо­дят также аппаратура, предназначенная для сбора, предварительной обработки и пере­дачи в информационно-вычислитеьлный комплекс сигналов датчиков, и специальное математическое обеспечение информационно-вычислительного комплекса, обеспечива­ющего обработку сигналов датчиков и представление на дисплей оператору необходи­мой информации.

Задача системы контроля — обеспечение оператора полной и точной информацией о нейтронно-физических и теплогидравлических процессах в объеме активной зоны. В частности, в информационно-вычислительной системе блока вычисляется распределение энерговыделения по объему активной зоны, запасы до кризиса теплообмена, регистри­руются положения регулирующих органов и другие параметры.

Плотность потока нейтронов в точках установки /3-эмиссионных детекторов опре­деляется путем умножения величин токов детекторов на соответствующие весовые коэффициенты. Матрица весовых коэффициентов хранится в памяти информационно­вычислительного комплекса. В течение кампании весовые коэффициенты корректи­руются. Распределение энерговыделения определяется как линейная комбинация извест­ного набора опорных функций. Амплитуда (коэффициенты линейной комбинации) вы­числяются по величинам измеренных плотностей потоков нейтроной. Подобный подход при использовании шести опорных функций позволяет получить среднеквадратичную погрешность вычисления распределения энерговыделения менее одного процента.

Совместное использование информационно-вычислительного комплекса и системы внутриреакторного контроля дает оператору средство как для контроля реакторной установки в режиме нормальной эксплуатации, так и для предупреждения возмущений, связанных с ядерно-опасными ситуациями в реакторной установке.

К ак показывают исследования, имеющиеся на реакторе ВВЭР-1000 средства воз­действия на реактивность — ОР и СБР — достаточны для эффективного управления энергораспределением [ 3 ]. При работе на мощности практически все ОР, за исключе­нием ОР автоматического регулятора мощности (АРМ) , находятся в крайнем верхнем положении во избежание искажения энергораспределения. Система борного регулиро­вания реактора способна обеспечивать компенсацию не только выгорания топлива в процессе кампании, но и эффектов отравления.

При разработке и исследовании различных подходов и алгоритмов управления авторами использовалась математическая модель [ 4 ] , содержащая двухгрупповые диффузионные уравнения для расчета распределения плотности нейтронного потока, уравнения для концентраций ксенона и иода, уравнения баланса массы и энергии в I контуре. Модель учитывает основные обратные связи в активной зоне реактора и вы­горание топлива, позволяет определить аксиальное и радиально-азимутальное распреде­ление энерговыделения, распределения концентраций ксенона и иода в активной зоне.

6 ФИЛИПЧУК и др.

Для сокращения времени счета в модели используются различного рода аппрокси­мации и рекуррентные формулы. Требуемые коэффициенты определяются заранее и, по мере необходимости, пересчитываются в течение кампании по результатам внутри- реакторных измерений.

В активной зоне ВВЭР-1000 при определенных условиях может возникать неста­бильность аксиального распределения мощности — ксеноновые колебания с периодом 21-24 ч. Колебания аксиального распределения мощности могут сопровождаться зату­хающими радиально-азимутальными колебаниями. Наибольшие деформации энерго­распределения возникают в переходных режимах с умеренным снижением мощности или нагрузки (до 40-50%) и последующим (через несколько часов) восстановлением номинального ее значения.

Эффективность использования информационно-вычислительной системы для по­вышения эксплуатационной безопасности реакторной установки возрастает при введе­нии в программное обеспечение модели реактора. Наличие модели в пакете оператив­

ных программ позволит вычислять целый ряд важных неизмеряемых переменных состояния реактора, прогнозировать изменения состояния реактора при любых наруше­ниях нормального режима эксплуатации блока, выявлять ошибки оператора в процессе управления реактором.

АЛГОРИТМ УПРАВЛЕНИЯ

Перейдем теперь непосредственно к описанию исследовавшихся алгоритмов опти­мального управления. В соответствии со сказанным ранее, цель управления состоит в поддержании энергораспределения в активной зоне в стационарных и нестационарных режимах с минимально возможной погрешностью вблизи заданного оптимального энергораспределения с учетом технологических ограничений.

Основной вклад в отклонение нейтронного поля от заданных значений вносят фундаментальная и первая высотная гармоники. Фундаментальная гармоника опреде­ляет заданное оптимальное энергораспределение и контролируется автоматическим регулятором мощности. Первая высотная гармоника вносит дисбаланс мощности меж­ду верхней и нижней половинами активной зоны. С учетом сказанного, сформулирован­ная цель управления может быть достигнута при эффективном подавлении фундамен­тальной и первой высотной гармоник в отклонениях энергораспределения от заданного. Целесообразность такого подхода к управлению обусловлена использованием двух различных средств воздействия на реактор — ОР и СБР. Амплитуды регулируемых гармоник измеряются информационно-вычислительной системой. Математическая фор­мулировка задачи управления, рассматриваемая авторами, состоит в следующем.

Формируется вектор состояния S , состоящий из отклонений распределений плот­ности нейтронного потока, концентраций ксенона и иода от стационарных распределений в дискретные моменты времени. Тогда задача управления конечным состоянием сос­тоит в нахождении последовательности управляющих воздействий, которая переводит

IAEA-SM-268/75 7

динамическую систему из начального состояния S (О) в нулевое конечное состояние S (N) за определенное (минимальное) число интервалов времени N с учетом техноло­гических ограничений, а именно:

— удельного энерговыделения в ТВЭЛах;— ограничения на величину и скорость изменения первой аксиальной гармоники,

определяемые требованиями к теплотехнической надежности активной зоны;— ограничения на величину и скорость управляющих воздействий, связанных с

конечной реактивностью, вносимой ОР и конечной скоростью введения и разбавления борной кислоты в теплоносителе;

— условия поддержания требуемой общей мощности реактора.При выборе критерия качества в виде квадратичной целевой фукнции J = S T(N) S(N )

исходная задача управления сводится к последовательности задач квадратичного про­граммирования, численное решение которых хорошо разработано [ 5 ] . .

По нашему мнению, все наиболее важные задачи управления энергораспределе­нием могут быть сведены к описанной задаче. Приведем здесь наиболее характерные примеры решения этих задач:

1. Маневрирование мощностью со скоростью 1% в минуту при больших запасах реактивности, скомпенсированных СБР. Этот режим характерен для начала кампании.

В этом случае с помощью борного регулирования можно поддерживать заданный темп изменения мощности, оставляя за группой автоматического регулятора мощности функции корректировки высотного энергораспределения. Стабилизация с заданной точностью первой аксиальной гармоники практически исключает возможность возник­новения ксеноновых колебаний.

На рис. 1 показаны результаты моделирования алгоритма прямого управления мощностью и аксиальным энергораспределением при циклических изменениях нагрузки. В процессе регулирования мощность реактора изменялась от 100% до 50% со скоростью 1% в минуту с помощью системы борного регулирования. Для управления аксиальным энергораспределением использовалась группа АРМ. При этом отклонение амплитуды первой аксиальной гармоники надежно удерживалось в диапазоне ± 5% от номинального значения.

2. Маневренные режимы со скоростями, превышающими динамические возмож­ности СБР (до 5% в минуту) .

В этом случае для управления необходимо использовать органы регулирования и группу АРМ. В работе [6 ] предлагается обеспечить минимальные искажения высотного энергораспределения путем объединения ОР в легкие группы, полностью погружаемые (извлекаемые) при изменении мощности. Однако, для реактора ВВЭР-1000 со сравни­тельно тяжелым ОР подобная стратегия привела бы к значительным искажениям ради­ально-азимутального энергораспределения.

В рассматриваемом алгоритме допускается искажение высотного энергораспреде­ления на пониженной мощности из-за значительного перемещения группы АРМ и, если необходимо, дополнительной группы ОР. Стратегия управления на пониженной мощ ­ности направлена на исключение ксеноновых колебаний после выхода на номинальный уровень.

8 ФИЛИПЧУК и др.

о 2 S

4 ? Ш <

? < X û.О о

1.0

л _ г \ _ г

о 20 40 60 80 100 ВРЕМЯ (Ч)

Рис. 1. Прямое управление мощностью и аксиальным энергораспределением при изменениях мощности со скоростью до 1% в минуту.

IAEA-SM-268/75 9

Результаты моделирования алгоритма отслеживания суточного цикла нагрузки при скорости изменения мощности, равной 5% в минуту, показаны на рис.2. При мо­делировании мощность реактора снижалась до 70% от номинальной за 6 минут, и после выдержки в течение 5 часов поднималась до номинального уровня с той же скоростью. Пунктирной линией показаны временные зависимости при отсутствии управления аксиальным энергораспределением, сплошной линией — переходные процессы, полу­ченные в результате управления. В качестве управляющих органов использовались система борного регулирования и группа ОР, связанная с автоматическим регулятором мощности реактора. Из полученных результатов видно, что требуемое состояние дос­тигается сразу после возврата к полной мощности вследствие прогнозируемых воз­действий системы управления.

3. Внеплановые быстрые сбросы мощности к ак по требованию энергосистемы, так и в результате срабатывания аварийной защиты.

При этом из-за случайного характера возмущений отсутствует возможность целе­направленного воздействия на энергораспределение до выхода на номинальный уро­вень мощности. Естественно, что в такой ситуации возможно возникновение ксеноно- вых колебаний, требующее мер для их эффективного подавления.

На рис.З показаны результаты моделирования подавления аксиальных ксеноно- вых колебаний, возникающих в результате быстрого уменьшения мощности реактора до уровня 10% от номинальной и после четырехчасовой выдержки увеличения ее до номинального значения. Сразу же после подъема мощности инициировалась программа вычисления оптимальной по быстродействию стратегии подавления ксеноновых коле­баний. На рисунке показан полученный закон управления, а также переходные про­цессы для основных переменных состояния реактора. Штриховой линией показаны процессы в реакторе при отсутствии управления.

Стабилизация высотного энергораспределения — важнейшая, но не единственная задача, с которой сталкивается оперативный персонал при управлении энергораспреде­лением реактора ВВЭР-1000. Хотя принятый регламент направлен на исключение воз­можности деформации радиально-азимутального энергораспределения, она все же оста­ется, к ак следствие различных нештатных ситуаций, например, отклонения от номиналь­ного режима в одной или нескольких циркуляционных петлях.

Большая устойчивость радиально-азимутального энергораспределения водо-водя- ных реакторов, небольшие возмущения этого распределения в процессе эксплуатации и быстро затухающий характер радиально-азимутальных ксеноновых колебаний позво­ляют сформулировать задачу управления радиально-азимутальным энергораспределе­нием как статическую задачу оптимального приближения энергораспределения к задан­ному профилю с учетом системы ограничений. В качестве технологических ограничений задачи управления должны быть учтены стандартные ограничения на диапазон управля­ющих воздействий, поддержание требуемой общей мощности реактора, непревышение предельно-допустимых значений плотности нейтронного потока во всех топливных сборках.

ГЛУБИНА

ПОГРУЖЕНИЯ

КОНЦЕНТР

АЦИЯ ЙОДА

КОНЦЕНТРАЦИЯ КСЕ

НОН А

ОРГАНОВ

РЕ ГУ ЛИРОВА-

В ВЕРХНЕЙ ЧАСТИ

30-

В ВЕРХНЕЙ ЧАСТИ

АКТИВ-

АМПЛИТУДА

ПЕРВОЙ АК

СИАЛ

ЬНОЙ

МО

ЩНОС

ТЬНИЯ

(ОТН.ЕД.)

НЫ ЮТН.ЕД.I

НОЙ

ЗОНЫ ЮТН.ЕД.)

ГАРМОНИКИ

(%]

ЮТН.ЕД.)

1 0 ФИЛИПЧУК и др.

Рис. 2. Управление энергораспределением при изменении мощности со скоростью до 5% в минуту:

................. без управления аксиальным энергораспределением;----------- с управлением аксиальным энергораспределением.

ГЛУБИНА

ПОГРУЖЕНИЯ

КОНЦЕНТРАЦИЯ ЙОДА

КОНЦЕН

ТРАЦИЯ КСЕНОНА

АМПЛИТУДА

ПЕРВОЙ АК-

МОЩН

ОСТЬ

ОРГАНОВ

РЕ ГУЛИРОВА-

В ВЕРХНЕЙ

ЧАСТИ

АК-

В ВЕРХНЕЙ ЧАСТИ

АКТИВ-

СИАЛЬНОЙ ГАРМОНИКИ

(ОТН.ЕД.)

НИЯ

(ОТН.ЕД.)

ТИВНОЙ ЗОНЫ (ОТН.ЕД.)

НОЙ

ЗОНЫ (ОТН.ЕД.)

(%)

IAEA- SM * 268/75 И

Рис.З. Ксеноновые колебания энергораспределения:................. свободные;------ управляемые.

12 ФИЛИПЧУК и др.

• — органы автоматического регулятора мощности.— 0.0— - отклонение энергораспределения от заданного, %.

Кроме этих ограничений при решении задачи оптимизации, по нашему мнению, необходимо обеспечить выполнение условия равенства мощностей по половинам реак­тора, что позволит исключить возможность возбуждения первой азимутальной гармони ки, которая является наиболее неустойчивой по отношению к радиально-азимутальным ксеноновым колебаниям. Выполнение этого условия позволит также обеспечивать в процессе работы одинаковые температурные условия для разных тепловых контуров реактора.

IAEA-SM-268/75

Рис. 5. Конечное радиальное энергораспределение после управления.

• — органы автоматического регулятора мощности.V////A — органы регулирования радиального энергораспределения.

— 0.0— — отклонение радиального энергораспределения от заданного, %>.

В качестве органов управления радиально-азимутальным энергораспределением реактора ВВЭР также могут быть использованы ОР и СБР. Однако, перемещения ОР, осуществляемые в процессе управления радиальным полем, оказывают воздействие на высотное энергораспределение, искажая его. Для того, чтобы избежать искажения высотного энергораспределения при управлении радиальным распределением энерго­выделения необходимо учитывать также ограничения на поддержание амплитуды первой аксиальной гармоники в заданных пределах. Сформулированная задача управ­ления также сводилась нами к канонической задаче квадратичного программирования

14 ФИЛИПЧУК и др.

и решалась с помощью той же вычислительной процедуры, что и задачи управления высотным энергораспределением.

Результаты моделирования алгоритма управления радиальным энергораспреде­лением реактора ВВЭР-1000 показаны на рис.4, 5. В качестве исходного возмущения радиального профиля мощности реактора было использовано изменение на 10% от но­минальной величины расхода теплоносителя в одной циркуляционной петле I контура. Картограмма изменения радиального энергораспределения, вызванного возмущением, показана на рис. 4. Линиями на картограмме соединены топливные каналы с одинако­выми отклонениями мощностей от эталонных значений. Кружками обозначены места расположения ОР группы АРМ. Картограмма изменения радиального поля мощности, полученного в результате компенсации возмущения по расходу теплоносителя, пока­зана на рис. 5. При этом в качестве органов управления использовались СБР и ОР спе­циально выбранной группы ОР, расположение которых показано на картограмме рис. 5.

ВЫВОДЫ

1. В описанном алгоритме основные операции по управлению в маневренном режиме завершаются на пониженном уровне мощности. При выходе на номинальный уровень мощности все ОР устанавливаются в номинальное положение.

2. Показано, что решение основных задач управления энергораспределением мо­жет быть проведено в рамках единой вычислительной процедуры методом квадратич­ного программирования.

3. При введении в состав математического обеспечения информационно-вычисли­тельной системы рассмотренных алгоритмов в сочетании с предсказанием на цифровой модели последствий реализации оптимальных управляющих воздействий можно ожи­дать повышения эффективности работы оперативного персонала и, в конечном итоге, безопасности эксплуатации АЭС.

ЛИТЕРАТУРА

[1] ФИЛИПЧУК, Е.В., ПОТАПЕНКО, П.Т.,ПОСТНИКОВ, В.В., Управление Нейтронным Полем Ядерного Реактора. М., Энергоиздат, 1981.

[2] ВИХОРЕВ, Ю.В., ВОЗНЕСЕНСКИЙ, В.А., ДЕНИСОВ, В.П. и др., Реакторная установка ВВЭР-1000 - особенности проекта, итоги пуска 5-го блока Нововоронежской АЭС и пути дальнейшего совершенствования установки, Ат. Энерг.50 2 (1981).

[3] СИДОРЕНКО, В. А., Вопросы Безопасной Работы Реакторов ВВЭР, М., Атомиздат, 1977.[4] ТИМОХИН, Е.С., "Нелинейная распределенная модель большого водо-водяного реактора”,

в кн. Управление Ядерными Энергетическими Установками, вып.5, М., Энергоиздат, 1981.[5] DANTZIG, G., COTTLE, R., Positive (semi -) Definite Programming. -In Nonlinear Programming,

J. Abadie (ed), Amsterdam, 1968.[6] ПОТАПЕНКО, П.Т., ДУНАЕВ, В.Г., ТИМОХИН, Е.С., Управление нейтронным полем

водо-водяных реакторов в режиме следования за нагрузкой, Ат. Тех. Рубежом 5 (1979).

I IAEA-SM-268/62

N O U V E L L E S D I S P O S I T I O N S D E P R O T E C T I O N

C O N T R E L E S S U R P R E S S I O N S D E S C H A U D I E R E S

N U C L E A I R E S R E P D E 9 0 0 E T 1 3 0 0 M W

J.-L. C A B A N N E S, R. PETIT R égion d ’équipem ent Alpes-M arseille,E lectricité de France,Marseille

M. OLIVONService E tudes et projets therm iques et nucléaires,E lectricité de France,Paris La D éfense,

France

Abstract-Résu mé

NEW ARRANGEMENTS FOR PROTECTING AGAINST EXCESS PRESSURE IN 900 MW AND 1300 MW PWR NUCLEAR BOILERS.

A number of operating incidents at PWR plants in operation or undergoing trials which were caused by the failure or faulty operation of mechanisms to protect against excess pressure in the main primary circuit or the shut down cooling circuit have led Electricité de France (EDF) to take the following actions: (1) To carry out a series of loop tests on a large number of discharge and safety valves within a loop. Among other things, these tests revealed the lack of reliability of most of these components in the various temperature, pressure and fluid regimes typical of real conditions, and enabled their failure modes to be analysed; and (2) To study, and then apply to the main primary circuit, the shut down cooling circuit and, to some extent, the volumetric and chemical control circuit of 900 MW and 1300 MW PWR nuclear boilers, new arrangements to protect against excess pressure. These new arrangements, which are described in the paper and whose implementation was made possible following their recent acceptance by the French authorities, will lead to increased safety in nuclear power stations by replacing conventional spring-type mechanical valves by controlled valves of the SEBIM type whose reliability and suitability for use in both the steam and water phases have been demonstrated through numerous tests, by making available to the operator various means of obtaining reliable information on the state of the circuits and equipment, and, lastly, by reducing through rapid isolation the risk of breaks resulting from the failure of a protective device. These arrangements, which have led to a reduction in operating and maintenance constraints (which are quite considerable with existing equipment), also take account of new concerns based largely on studies carried out since the Three Mile Island accident. These have led to consideration of the possibility of the controlled opening of safety valves in certain accident sequences.

1 5

NOUVELLES DISPOSITIONS,DE PROTECTION CONTRE LES SURPRESSIONS DES CHAUDIERES NUCLEAIRES REP DE 900 ET 1300 MW.

Un certain nombre d’incidents d’exploitation sur des centrales REP en fonctionnement ou en cours d’essais, causés par la défaillance ou le mauvais fonctionnement des organes de protection contre les surpressions du circuit primaire principal ou de refroidissement à l’arrêt ont conduit Electricité de France: 1) à réaliser sur un grand nombre de vannes de décharge et soupapes de sûreté des campagnes d’essais sur boucle qui ont permis, en particulier, de mettre en valeur le manque de fiabilité de la plupart de ces matériels utilisés dans les différentes conditions de température, pression et nature de fluide représentatives des conditions réelles, ainsi que d’analyser leurs modes de défaillance; et 2) à étudier puis mettre en oeuvre, sur le circuit primaire principal, celui de refroidissement à l’arrêt et, en partie, celui de contrôle volumétrique et chimique des chaudières nucléaires REP 900 et 1300, de nouvelles dispositions de protection contre les surpressions. Ces nouvelles dispositions, présentées dans ce mémoire et rendues possibles par une acceptation récente de l’administration française, permettront d’améliorer la sûreté des centrales nucléaires en utilisant, à la place des soupapes mécaniques classiques à ressort, des soupapes pilotées de type SEBIM dont la fiabilité et l’aptitude à fonctionner à la fois en phase vapeur et en phase eau ont été démontrées par de nombreux essais, en m ettant à la disposition de l’exploitant un certain nombre de moyens d’information fiables sur l’état des circuits et des matériels, et, enfin, en réduisant, par une possibilité d’isolement rapide, le risque de brèches causées par la défaillance d’un organe de protection.Par ailleurs, la prise en compte de préoccupations nouvelles, liées en particulier aux études post-TMI, et conduisant à envisager dans certaines séquences accidentelles l’ouverture commandée des soupapes de sûreté, est rendue possible par ces dispositions qui conduisent à une réduction des contraintes d’exploitation et d’entretien importantes pour les matériels existants.

16 | i CABANNES et al.

Les nouvelles d ispositions retenues par E lectricité de France (E D F ) sur les circuits primaire principal (R CP) et de refroid iseem ent à l’arrêt (R R A ) des chaudières nucléaires REP consisten t à protéger ces circuits par des soupapes p ilotées SEBIM isolables à l’aval par des soupapes identiques. Pour le circuit de contrôle chim ique et volum étrique (R C V ), com p te tenue d ’une part de la possib ilité d’isoler la ligne de décharge sur laquelle est installée la soupape RCV 201 VP et, d’autre part, du faible d-ebit évacué par cette soupape ( < 5 0 t /h ), une seule soupape SEBIM sans iso lem en t aval a été installée.

1. PRINCIPE DE LA PROTECTION ACTUELLE (R CP ET R R A , TRA NC H E9 0 0 MW)

La régulation de pression des circuits RCP et R R A fait appel à d ifférents systèm es ou m atériels d on t la description ne fa it pas l’objet de cette présentation. Sont seuls décrits ci-après les organes de robinetterie participant à la régulation- p ro tection de ces deux circuits. Le schém a de la figure 1 présente l’agencem ent des ces organes.

IAEA-SM-268/62 1 7

( ) = Valeuyde Tarage (bar)

FIG .l. Schema de principe de la protection actuelle (RCP e t RRA).

1.1. Circuit primaire principal

Les so u p a p es d e sû re té , qui ne son t so llic itées que dans les situations de 3 e e t 4 e catégories, son t de typ e classique, m écaniques à ressort. Elles sont chacune reliées au dôm e supérieur du pressuriseur par une tuyauterie en form e de col de cygne, non calorifugée, ce qui perm et la form ation par cond ensation d’un bou ch on d’eau en am ont des soupapes.

Ces soupapes de sûreté son t tarées à 172 bar abs perm ettant un espacem ent suffisant entre leurs p o in ts de tarage et celu i des vannes de décharge (1 6 2 bar abs).

Les vannes d e décharge, au nom bre de trois, on t un p oin t de consigne réglé à 162 bar abs. Ces vannes son t à m otorisation pneum atique assistée e t ouverture to u t ou rien; leur p osition de sécurité est ferm ée sur m anque d’air. En cas de perte d ’étanchéité de l’une de ces vannes de décharge, son iso lem en t est nor­m alem ent assuré par la ferm eture de la vanne m otorisée électrique placée en am ont. C om m e pour les soupapes de sûreté, le tracé des tuyauteries perm et la form ation par condensation d’un b ou ch on d’eau à l ’am ont des vannes de décharge.

18 CABANNES et al.

D eux so u p a p es de sû re té protègent le circuit R R A . A l’origine, ces deux soupapes de typ e m écanique à ressort on t connu un certain nom bre d ’incidents conduisant E D F à m ettre en oeuvre, sur tou tes les tranches en exp lo ita tion , une so lu tion transitoire. C elle-ci consiste à rem placer l’une des soupapes à ressort par une soupape p ilo tée de typ e SEBIM, tarée à 39 bar abs, qui, en cas de surpression, d oit fon ction n er en priorité. L’autre soupape à ressort, m aintenue après m od i­fication pour adjonction d’un am ortisseur hydraulique, est tarée à une valeur supérieure (4 4 bar abs).

1.2. Circuit R R A

2. LES R A ISO N S A Y A N T C O NDUIT E D F A M O D IFIER LE SYSTEM E DEPRO TECTION A CTUEL

2.1 . Problèm es liés au fon ction n em en t des soupapes m écaniques à ressort

Bien que la capacité de ces m atériels (d on t le type est largem ent répandu) à assurer sur des installations courantes leur fon ction de soupape de sûreté ne puisse être m is en d oute, ils présentent néanm oins les défauts inhérents à leur conception: fon ction n em en t instable à certains régim es, risque de dérive des p o in ts de tarage ou perte d’étanchéité.

Un certain nom bre d’incidents du type de ceu x cités ci-dessus on t fait apparaître la nécessité d ’effectuer, sur ces m atériels, des contrôles et un entretien périodique particu lièrem ent lourds et pénalisants.

Par ailleurs, concernant les soupapes du pressuriseur, un nom bre im portant d’essais effec tu és par E D F sur la bou cle Indira ont m ontré qu’un fon ction n em en t en eau ou, sim plem ent, le passage du bou ch on d’eau conduisaient à un fon ction ­nem en t instable de la soupape engendrant des battem ents.

En conséquence, aucune garantie sérieuse du fon ction n em en t correct de ces m atériels dans leur état actuel ne peut être donnée et E D F, dans l’atten te de la m ise en oeuvre des nouvelles protection s présentées dans cette n ote , a engagé sur les tranches nucléaires en fon ction n em en t une m od ification consistant en la suppression du bou ch on d’eau des soupapes à ressort classique du pressuriseur.

2 .2 . Problèm es liés au fo n ction n em en t de la ligne de décharge

Tel que prévu à la con cep tion , le fon ction n em en t des m atériels de la ligne de décharge éta it relativem ent sim ple. C ependant, pour lim iter les conséquences d’une dépressurisation par ouverture intem pestive, ou non ferm eture, des vannes

IAEA-SM-268/62 19

de décharge, E D F a au tom atisé la ferm eture des vannes d’iso lem en t de la décharge en dessous du seuil de pression P 11 qui est le seuil de pression (1 3 8 bar) utilisé dans les p rotection s de la chaudière. Pour éviter ensu ite de détériorer par un fo n ctio n n em en t in term itten t ces vannes d’iso lem ent, une nouvelle m od ifica tion pour m aintenir ferm ée la vanne de la ligne en défaut est intervenue.

A ctu ellem en t, outre ce tte com p lica tion dans le con trô le com m ande de la décharge, des problèm es liés au fo n ction n em en t m êm e des vannes d’iso lem ent et de décharge rendent la so lu tion d’origine m oins satisfaisante.

Il faut rappeler, enfin , qu’EDF, ne pouvant accepter à titre d é fin itif la servitude d’ex p lo ita tion que représente la nécessité d’u ne expertise des vannes d’iso lem en t après chaque fon ction n em en t sous plein déb it, s’est engagé à rem placer les vannes ex istan tes par des organes qualifiés sur to u tes les tranches m ises en

service ju squ’à présent.

2 .3 . Iso lem ent d’une brèche primaire

Le risque de défaillance à la referm eture des soupapes de p rotection du pressuriseur est pris en com p te dans les étu des de sûreté.

Pour des installations classiques, les conséquences d’un tel accident peuvent être considérées com m e m ineures vis-à-vis de la fo n ctio n principale qui privilégie l’ouverture.

C ependant, si un tel accident intervenait sur des soupapes assurant la protec­tion du circuit prim aire principal, il aurait du p o in t de vue de l’exp lo ita tion et de la d isp on ib ilité de la tranche des conséquences su ffisam m ent graves pour que la possib ilité d’iso lem en t de ces soupapes so it sérieusem ent exam inée bien que l’iso lem en t d’une soupape de sûreté ne so it pas actuellem ent accepté par la réglem entation française.

2 .4 . A streintes nouvelles

E D F s’est engagé à prendre en com p te, par l’application des procédures, des cas de fon ction n em en t hors dim ensionnem ent:— procédures H2 pour l’évacuation d’énergie su ite à une perte to ta le des alim enta­tions G V (il en est de m êm e en cas de p etite brèche primaire, GV ind isponib le);— évacuation des incondensables su ite à un accident ayant en traîné la détériora­tion partielle du com bustib le.

L’application de ces procédures nécessite, entre autres, la qualification à un fo n ction n em en t en eau et dans des con d ition s post-accidentelles de tem pérature et d’irradiation des m atériels équipant la ligne de décharge. Ces ex igences sem blent plus aisées à satisfaire avec un nouveau m atériel.

2 0 CABANNES et al.

P = Soupape de Protection I = Soupape d'isolement ( ) = Valeurs de Tarage (bar)

FIG.2. Schéma de principe de la nouvelle solution.

3. N O U V E L L E S D ISPO SITIO NS

Le principe retenu par E D F (fig .2 ) sur les circuits RCP et R R A des tranches REP de 9 0 0 et 13 0 0 MW consiste à protéger ces circuits contre les surpressions uniqu em ent par des lignes de soupapes p ilo tées de marque SEBIM isolables à l’aval par d’autres soupapes SEBIM identiques.

P o u r le pressuriseur, trois lignes de soupapes (déb it par ligne: 170 t/h de vapeur) son t ainsi équipées. U ne des ces lignes, b ien qu’identique aux autres, sera spécialisée (par un tarage à 162 bar au lieu de 172) afin d ’assurer le rôle de régulation-décharge.

En cas de défaillance à la referm eture d’une soupape de p rotection (P), la soupape d’iso lem en t (I) ouverte pendant le fon ction n em en t norm al (P = 155 bar) se referm era autom atiquem ent dès que la pression deviendra inférieure à 135 bar.

P o u r le c ircu it R R A , les deux lignes de soupapes (d éb it par ligne: 3 0 0 t/h en eau) seront équ ipées de d ispositifs analogues.

IAEA-SM-268/62 21

Détecteur pilote

FIG.3. Schéma de la soupape de sûreté p ilotée SEBIM.

Ces nouvelles d ispositions se caractérisent essen tiellem ent par les trois parti­cularités suivantes présentées sous 3 .1 , 3 .2 et 3 .3 :— utilisation de soupapes p ilo tées SEBIM (en rem placem ent des soupapes classiques);— m ise en p lace de soupapes d’iso lem en t à l’aval de chaque soupape de p rotection ;— am élioration des m oyen s d’in form ations à d isposition de l’exp lo itan t.

3 .1 . La soupape de sûreté p ilo tée SEBIM

A ccep tée par l’adm inistration française, au titre de l’A rticle 9 du décret de 1926 , par décision 16761 du 14 février 1980, la soupape SEBIM est une soupape de sûreté p ilo tée et au ton om e à d étection hydraulique. Pour son p ilotage elle fait appel à la pression du flu ide con ten u dans la capacité à protéger. L’ensem ble de l’insta llation com prend (fig .3 ): 1) la soupape proprem ent dite, e t 2 ) le détecteu r de pression et d isp ositif de p ilotage.

La soupape, le détecteur p ilo te et la capacité à protéger son t reliées par des tuyauteries d’im pulsion de p etit diam ètre (3 /4 in ) et de forte épaisseur chem inant

2 2 CABANNES et al.

FIG.4. Schéma de principe de fonctionnement. Phase 1: Si P < PI (pression intermédiaire d ’ouverture) le clapet R I est ouvert, R 2 est fermé. La soupape est maintenue ferm ée par la pression (P) du fluide du circuit. Phase 2: Quand P augmente e t a tte in t PI le clapet R I se ferme, le vérin V n ’est plus en communication avec le fluide du circuit cependant la pression PI est maintenue e t la soupape reste fermée. Phase 3: Lorsque P attein t Pt (pression de tarage) le clapet R 2 s ’ouvre e t provoque la mise à l ’atmosphère du fluide contenu au-dessus du piston (V). La soupape s ’ouvre. Phase 4: Lorsque P diminue e t a tte in t P2 (pression inter­médiaire de ferm eture) le clapet R 2 se referme, la soupape reste ouverte. Phase 5: Quant P attein t la pression P f de la fermeture, R I s ’ouvre e t le fluide sous pression du circuit rem plit le vérin de la soupape conduisant celle-ci à se refermer.

dans des zon es protégées. C ette précaution est indispensable car la soupape SEBIM est à p osition de sécurité «ouverte» et to u te rupture de ligne d’im pulsion condu it à l’ouverture de la soupape.

1 ) L a so u p a p e se m onte directem ent sur la capacité à protéger. Elle se com pose de:- un corps com portant le siège et le clapet (c);- un en sem ble cylindre-piston (V ) form ant vérin dans sa partie supérieure;- une tige (T ) reliant entre eu x le clapet et le p iston.

IAEA-SM-268/62 23

Lorsque la soupape est ferm ée, le clapet est appliqué sur le siège par l’effort fourni sur le p iston par le flu ide de la capacité à protéger. La surface S du p iston étan t environ double de celle s du clapet, la force d’appui résultante du clapet sur son siège est, dans le cas des soupapes du pressuriseur, supérieure à 5 0 0 0 daN, conférant ainsi à la soupape une étan ch éité parfaite. Lorsque, par l’interm édiaire du p ilo te , la partie supérieure du p iston V est m ise à l ’atm osphère, l’ouverture de la soupape est assurée par la poussée du flu ide sous le clapet P X s.

2 ) L e d é te c te u r p i lo te est con stitu é de:- un p iston (p ) d on t la face supérieure est en perm anence en com m unication avec le flu ide du circuit à protéger;- un ressort (R ) d on t l’e ffort est ajustable agit sur la face inférieure du p iston;- une tige centrale (D ) actionnant deux clapets R l et R2.

Le fo n ction n em en t de ces ensem bles est décrit sur la figure 4.

3.1 .1 . U tilisa tion d e la so u p a p e S E B IM en vanne d e décharge

En plus de la fon ction «soupape de sûreté», la soupape SEBIM offre la possib ilité, par adjonction dans le co ffret p ilo te d’une électrovanne 3 voies, d’assurer le rôle de régulation autom atiqu e d’une vanne de décharge, ou de per­m ettre l’ouverture volon ta ire par l’opérateur depuis la salle de com m ande (fig .5 ).

L’électrovanne 3 vo ies d isposée sur la tuyauterie reliant la tê te de la soupape aux clapets R l e t R 2 perm et, par son basculem ent, de m ettre à l’atm osphère le vérin de la tê te de soupape et, ainsi, déclenche son ouverture quelle que so it la p osition des clapets R l et R2. L’électrovanne est com m andée par un signal électrique élaboré so it à partir d’un capteur de pression, so it par un ordre volontaire depuis la salle de com m ande.

Ces possib ilités de fon ction n em en t («régulation autom atique» ou «ouvertures volontaires») sont u tilisées dans les nouvelles dispositions:1) Sur RCP, tou tes les soupapes son t équ ipées de com m ande électrique perm ettant leur ouverture volontaire par l’opérateur (procédures hors d im ensionnem ent, m ise en p osition «ouvert» des soupapes d’iso lem en t, réalisation des essais de m anoeuvrabilité).2) Sur RCP, une des lignes est en plus com m andée au tom atiquem ent à partir d ’un signal électrique, conférant à cette ligne le rôle de régulation actuellem ent jou é par la ligne de décharge équipée des trois vannes pneum atiques. L’ouverture de la soupape SEBIM à partir du signal électrique se produit à 162 bar abs. En cas de défaillance du signal électrique l’ouverture de la soupape interviendrait alors hydrauliquem ent à partir de son p ilo te à 166 bar abs évitant ainsi, sur des transi­to ires de I e ou 2 e catégorie, la so llic ita tion des deux autres lignes de p rotection tarées à 172 bar abs.

24

Détecteur pilote

CABANNES et al.

FIG.5. Schéma de principe de la soupape SEBIM équipée d'une commande électrique.

3) Sur R R A , seules les soupapes d ’iso lem ent son t équipées de com m ande électrique perm ettant à l’opérateur de les placer en p osition «ouverte» requise lors du fon ction n em en t de la chaudière.

3 .1 .2 , P ro te c tio n à fr o id d u c ircu it prim aire

Si le signal électrique u tilisé pour com m ander l ’ouverture de la soupape SEBIM est élaboré à partir d’un autom atism e logique classique ou par un calcu­lateur en fon ction du coup le pression-tem pérature (éventuellem ent gradient de tem pérature), la p rotection du circuit primaire (e t de la cuve en particulier) peut être alors assurée quelle que so it la tem pérature.

C ette p rotection qui, sur des chaudières récentes, ne présente pas un caractère d’urgence (en e ffe t la tem pérature de transition a peu évolué), figure dans le program m e des actions engagées par E D F pour les cinq années à venir.

IAEA-SM-268/62 25

Le fon ction n em en t décrit sur la figure 4 con fère aux soupapes SEBIM les caractéristiques suivantes:1) Stabilité, quel que so it le régim e de l’écou lem en t, la nature e t les caracté­ristiques du flu ide évacué. C ontrairem ent aux soupapes classiques à ressort en état d’équilibre perm anent (la force du ressort s’opposant à la p oussée du fluide sous le c lapet) et, de ce fait, susceptib les d’in stab ilité, la soupape SEBIM est, lors de son fon ction n em en t, en état stable perm anent (bascu lem ent d ’un état stable ferm é à un autre éta t stable ouvert).2 ) E tanchéité parfaite jusqu’à la pression d’ouverture. La force d’appui du clapet sur le siège augm ente en e ffe t avec la pression pour atteindre son m axim um juste avant l’ouverture de la soupape (le p h énom ène est inverse sur une soupape classique).3 ) F idélité des pressions d’ouverture et ferm eture. L’armoire de pilotage séparée de la soupape est d isposée à l’écart des phénom ènes m écaniques et therm iques v io len ts qui apparaissent lors du fon ction n em en t d’une soupape.4 ) In fluence négligeable des pertes de charge. La possib ilité du ch o ix de l’em placem ent de la prise de pression du p ilo te perm et de placer celle-ci en un p oin t du circuit à protéger jud icieusem ent choisi et, en particulier, peu in flu en cé par les pertes de charge engendrées lors de l’écou lem en t du fluide.5) A m élioration des contraintes d’exp lo ita tio n et d ’essais périodiques. En particulier, le réglage e t la vérification de la valeur des p o in ts de tarage son t effectu és «soupapes en place»-.

3 .2 . F on ction n em en t de d eu x soupapes en série (p ro tection , iso lem en t)

Par la m ise en p lace en aval de chaque soupape d ’une soupape d ’iso lem en t,E D F a vou lu se prém unir contre les risques suivants:— les cas de brèches con sécu tifs au fo n ction n em en t d ’une soupape et résultant du blocage entre siège et clapet d’une im pureté ou d’un corps étranger dans le circuit;— la m ise en p osition de sécurité ouverte d ’une soupape SEBIM consécutive à la rupture d’une tuyauterie d’im pulsion .

En outre, ce tte d isposition rend p ossib le les essais réglem entaires de manoeuvra- bilité des soupapes en p lace en n ’évacuant pratiquem ent pas de flu ide primaire (au m axim um le volum e com pris entre les d eux soupapes).

L’analyse de fon ction n em en t.p résen tée ci-après concerne les soupapes du pressuriseur. Pour le circuit R R A , le principe est iden tique, seules les pressions d’ouverture et de ferm eture des soupapes d iffèrent.

Sur le schém a de principe (fig. 6 ), les deux soupapes d ’une m êm e ligne son t p ilo tées par deux détecteurs d istincts à lignes d’im pulsion séparées. C ette d ispo­sition perm et d ’éviter le défaut de m ode com m un que constituerait la rupture d ’une prise d ’im pulsion si elle éta it unique pour les deux soupapes de la m êm e ligne.

3 .1 .3 . C a ra c té r is t iq u e s d u fo n c t io n n e m e n t des soup ap e s S E B IM

26 CABANNES et al.

SOUPAPED'ISOLEMENT(PILOTE)

(PO SITIO N NORMALE O U V E R T E ’

FIG.6. Schéma de principe d ’une ligne de protection de pressuriseur (deux soupapes SEBIM en série).

IAEA-SM-268/62 27

L e s d e u x d é t e c t e u r s r e p r é s e n t é s s u r l e s c h é m a n e d i f f è r e n t q u e p a r l e u r s

p r e s s i o n s d e t a r a g e : 1 7 2 b a r ( o u v e r t u r e ) p o u r l e s s o u p a p e s d e s l i g n e s d e s û r e t é

( 1 6 2 b a r p o u r l a s o u p a p e d e l a l i g n e s p é c i a l i s é e s p o u r l a d é c h a r g e ) , e t 1 3 5 b a r ( f e r ­

m e t u r e ) p o u r l e s s o u p a p e s d ’i s o l e m e n t . A l ’i n t é r i e u r d e s s e u i l s d e t a r a g e , l e

d i s p o s i t i f m a n u e l o u é l e c t r i q u e d e c o m m a n d e p e r m e t d e c h o i s i r l a p o s i t i o n o u v e r t e

o u f e r m é e d e l a s o u p a p e . A u - d e s s u s d u s e u i l d e t a r a g e , l a c o m m a n d e h y d r a u l i q u e

d u d é t e c t e u r d e v i e n t p r i o r i t a i r e . D a n s c e s c o n d i t i o n s , o n n o t e q u ’ a u - d e s s u s d e

1 3 8 b a r , l a c o n f i g u r a t i o n d e l a l i g n e a i n s i é q u i p é e e s t : s o u p a p e d e p r o t e c t i o n

d i s p o n i b l e e t s o u p a p e d ’i s o l e m e n t o u v e r t e e t p r ê t e à i s o l e r s i l a p r e s s i o n d e v e n a i t

i n f é r i e u r e à 1 3 5 b a r , s u r u n e d é f a i l l a n c e d e l a s o u p a p e d e p r o t e c t i o n p a r e x e m p l e .

D a n s c e c a s d e n o n - r e f e r m e t u r e d e l a p r e m i è r e s o u p a p e , l a s o u p a p e d ’i s o l e ­

m e n t f e r m é e d e v i e n d r a i t l a s o u p a p e d e l a l i g n e , e t s ’i l n ’y a v a i t p a s u n r é g l a g e

p a r t i c u l i e r , o n a u r a i t , d u f a i t d e l a r é g u l a t i o n p r e s s u r i s e u r , u n e r é g u l a t i o n d e

p r e s s i o n p a r l a s o u p a p e a u t o u r d e 1 3 5 b a r c o m m e i n d i q u é s u r l e s c h é m a f o n c t i o n n e l

d e l a f i g u r e 7 . P o u r é v i t e r c e p o m p a g e e t p e r m e t t r e à l a p r e s s i o n d e r e j o i n d r e

l a v a l e u r n o m i n a l e d e f o n c t i o n n e m e n t , o n i n t r o d u i t p a r u n r é g l a g e m é c a n i q u e

s i m p l e u n e p l a g e m o r t e d e 2 5 b a r ( e n t r e s e u i l d ’ o u v e r t u r e e t d e f e r m e t u r e d e l a

s o u p a p e d ’i s o l e m e n t ) . L a r e m i s e à z é r o d e l a f o n c t i o n ( c ’e s t - à - d i r e r e t o u r à

l a p o s i t i o n o u v e r t e ) n e d o i t ê t r e é f f e c t u é e q u e d a n s l a m e s u r e o ù l e d é f a u t s u r

l a p r e m i è r e s o u p a p e a é t é é l i m i n é . E n t o u t é t a t d e c a u s e , s i c e t t e r e m i s e à z é r o

é t a i t o m i s e , l ’i s o l e m e n t s e r a i t r é o u v e r t a u t o m a t i q u e m e n t d è s l o r s q u e l e s e u i l d e

1 6 0 b a r s e r a i t p a s s é l o r s d ’u n t r a n s i t o i r e c o n d u i s a n t s o i t à l a d é c h a r g e s u r l a l i g n e

s p é c i a l i s é e e t t a r é e à 1 6 2 b a r , s o i t à l a d é c h a r g e s u r l e s l i g n e s d e s û r e t é t a r é e s à

1 7 2 b a r s ’i l s ’a g i s s a i t d ’u n d é f a u t s u r u n e d e c e s l i g n e s .

E n c e q u i c o n c e r n e l a m o n t é e e n p r e s s i o n s u i v a n t l e d i a g r a m m e ( P , T ) , i l e s t

n é c e s s a i r e , e n t r e 0 e t 1 3 8 b a r , d e c o m m a n d e r l ’o u v e r t u r e d e l a s o u p a p e d ’i s o l e m e n t

p o u r r e s t e r d a n s l ’ e s p r i t d e l ’ a r r ê t é d e s m i n e s d e 1 9 2 6 . L o r s q u e l a p r e s s i o n

p r e s s u r i s e u r c o r r e s p o n d r a à u n e p r e s s i o n e n c a d r é e p a r l e s b o r n e s d e l a p l a g e

m o r t e d e l a s o u p a p e d ’ i s o l e m e n t ( 1 3 5 — 1 6 0 b a r ) , c e t t e a c t i o n « v o l o n t a i r e »

d ’o u v e r t u r e n e s e r a p l u s n é c e s s a i r e ( l e s d e u x c l a p e t s d u p i l o t e é t a n t f e r m é s ) e t i l

s e r a a l o r s p o s s i b l e d ’a n n u l e r a u t o m a t i q u e m e n t l ’a c t i o n v o l o n t a i r e a u p a s s a g e d u

s e u i l P I 1 ( 1 3 8 b a r ) .

P o u r l e s d é c h a r g e s v o l o n t a i r e s n é c e s s i t a n t l e n o n - i s o l e m e n t à 1 3 5 b a r p a r S 2 ,

i l f a u t u n e c o m m a n d e m a n u e l l e m o n o s t a b l e g a r a n t i s s a n t l ’o u v e r t u r e d e S 2 s u r t o u t e

l a p l a g e d e f o n c t i o n n e m e n t d e S I . B i e n q u e c e s y s t è m e d e d é c h a r g e n e s o i t

e s s e n t i e l l e m e n t c o n ç u q u e p o u r d e s i n t e r v e n t i o n s e n s i t u a t i o n h o r s d i m e n s i o n -

n e m e n t , i l e s t p r é v u d ’é q u i p e r l e s d e u x l i g n e s d e s û r e t é d e c e d i s p o s i t i f d ’o u v e r t u r e

c o m m a n d é e ( a c t i o n é l e c t r i q u e e n v o i e B ) e n p l u s d e l a l i g n e d e d é c h a r g e d o n t

l ’a c t i o n é l e c t r i q u e s e r a i t t r a i t é e e n v o i e A . C e t t e d i s p o s i t i o n e s t u n e r e d o n d a n c e

d e l a f o n c t i o n d é c h a r g e v o l o n t a i r e a v e c s é p a r a t i o n d e s v o i e s é l e c t r i q u e s d e

c o m m a n d e d e s d i s p o s i t i f s d ’ o u v e r t u r e .

28 CABANNES et al.

P * Soupape de Protection I ~ Soupape d'isolement { ) = Valeurs de Tarage (bar)

FIG. 7. Protection du pressuriseur: schéma fonctionnel.

IAE A-SM-268/62 29

L e b u t p r i n c i p a l d e s n o u v e l l e s d i s p o s i t i o n s e s t d ’ a m é l i o r e r l a f i a b i l i t é d e s

m o y e n s d e p r o t e c t i o n , e t p a r l à m ê m e d ’a c c r o î t r e l a c o n f i a n c e q u ’a c c o r d e

l ’ o p é r a t e u r a u x m a t é r i e l s p a r t i c i p a n t à l a r é g u l a t i o n - p r o t e c t i o n .

C e p e n d a n t , i l e s t t r è s i m p o r t a n t d e p e r m e t t r e à c e t o p é r a t e u r d e c o n n a î t r e

l ’é t a t e t d e s ’a s s u r e r à t o u t m o m e n t d u b o n f o n c t i o n n e m e n t d e s d i s p o s i t i f s d e

p r o t e c t i o n . D a n s c e b u t l e s a m é l i o r a t i o n s s u i v a n t e s o n t é t é r é a l i s é e s :

— a m é l i o r a t i o n s d e s i n d i c a t i o n s d e m e s u r e d e l a p r e s s i o n p r i m a i r e ( é c h e l l e s m i e u x

a d a p t é e s , i n d i c a t e u r s n u m é r i q u e s , e t c . ) ;

— a l a r m e s e n s a l l e d e c o m m a n d e , s u r g r a d i e n t é l e v é d e p r e s s i o n p r i m a i r e , p r e s s i o n

é l e v é e a u r é s e r v o i r d e d é c h a r g e d u p r e s s u r i s e u r , e t c . ;

— a m é l i o r a t i o n d e s m o y e n s d e d é t e c t i o n t h e r m o m é t r i q u e ( d e f u i t e s o u d u

f o n c t i o n n e m e n t d e s s o u p a p e s ) : p o u r c h a q u e l i g n e d e s o u p a p e , u n c a p t e u r t h e r m o ­

m é t r i q u e d é l i v r e u n e i n f o r m a t i o n e n r e g i s t r é e e t a c t i o n n e u n e a l a r m e e n s a l l e d e

c o m m a n d e s i l a t e m p é r a t u r e à l ’a v a l d e s s o u p a p e s d é p a s s e 7 0 ° C ;

— m i s e e n p l a c e s u r c h a q u e s o u p a p e d ’u n i n d i c a t e u r d e p o s i t i o n d e t i g e . U n

c a p t e u r m é c a n i q u e m e s u r a n t l a p o s i t i o n d e l a t i g e d e c h a q u e s o u p a p e i n f o r m e

l ’o p é r a t e u r d e l ’é t a t d e l a s o u p a p e ( e t n o n d e l ’o r d r e t r a n s m i s p a r l e p i l o t e à l a

s o u p a p e .

3.3. Amélioration des moyens d’information à la disposition de l’exploitant

4 . P R O G R A M M E D E Q U A L I F I C A T I O N E T M I S E E N O E U V R E

4 . 1 . C i r c u i t p r i m a i r e

L e s r é s u l t a t s p o s i t i f s d e s é t u d e s d e f a i s a b i l i t é d e l a s o l u t i o n d e b a s e e f f e c t u é e s

e n 1 9 8 2 , a i n s i q u e d e s e s s a i s d e v a l i d a t i o n r é a l i s é s d a n s d e s c o n d i t i o n s r e p r é ­

s e n t a t i v e s d e p r e s s i o n e t t e m p é r a t u r e s u r l a b o u c l e I n d i r a d ’E D F , n o u s o n t p e r m i s

d ’e n g a g e r , a u c o u r s d u d e u x i è m e s e m e s t r e 1 9 8 2 , l a m i s e e n o e u v r e d e c e s n o u v e l l e s

d i s p o s i t i o n s s u r t o u t e s l e s t r a n c h e s n u c l é a i r e s R E P d e 9 0 0 e t 1 3 0 0 M W .

4 . 1 . 1 . P r o g r a m m e d e q u a l i f i c a t i o n

E n p l u s d e s e s s a i s f o n c t i o n n e l s d ’u n e s o u p a p e S E B I M d u p r e s s u r i s e u r c i t é s

c i - d e s s u s , l e p r o g r a m m e d e q u a l i f i c a t i o n c o m p o r t e l e s p h a s e s s u i v a n t e s :

— e s s a i s f o n c t i o n n e l s e t d e m e s u r e d e s c a r a c t é r i s t i q u e s p h y s i q u e s ( d é b i t s , t e m p s

d e r é p o n s e , e t c . ) d ’u n e l i g n e d e p r o t e c t i o n e n t i è r e m e n t é q u i p é e ( r é a l i s é s e n f é v r i e r

1 9 8 3 s u r l a b o u c l e I n d i r a d ’ E D F ) ;

— e s s a i s d e v a l i d a t i o n d ’e n s e m b l e e t e s s a i s d e f o n c t i o n n e m e n t r é p é t é s s u r l a

t r a n c h e n u c l é a i r e t ê t e d e s é r i e d e C r u a s 2 , l o r s d e s e s s a i s à c h a u d d e c e t t e t r a n c h e

( m a i 1 9 8 3 ) ;

30 CABANNES et al.

— e s s a i s d e q u a l i f i c a t i o n d é f i n i t i f s s u r l a b o u c l e d ’e s s a i s e n c o u r s d e c o n s t r u c t i o n

s u r l a c e n t r a l e t h e r m i q u e c l a s s i q u e d ’ E D F à P r o c h e v i l l e .

4 . 1 . 2 . P r o g r a m m e d e m i s e e n o e u v r e

L ’i n s t a l l a t i o n d e s s o u p a p e s S E B I M e s t e n c o u r s s u r l e s t r a n c h e s n u c l é a i r e s d e

9 0 0 M W e n c o n s t r u c t i o n d e C r u a s 2 e t 3 , G r a v e l i n e s 5 e t 6 e t C h i n o n 3 e t 4 , a i n s i

q u e s u r l e s t r a n c h e s 1 3 0 0 M W à p a r t i r d e P a l u e l 3 .

E n c e q u i c o n c e r n e l e s a u t r e s t r a n c h e s d e 9 0 0 e t 1 3 0 0 M W a y a n t d é j à

d é m a r r é , l ’i n s t a l l a t i o n d e s n o u v e l l e s d i s p o s i t i o n s s e r a e f f e c t u é e a u c o u r s d e s a n n é e s

1 9 8 4 e t 1 9 8 5 , l o r s d e s a r r ê t s a n n u e l s p o u r r e c h a r g e m e n t d e c e s d i f f é r e n t e s

t r a n c h e s .

4 . 2 . C i r c u i t d e r e f r o i d i s s e m e n t à l ’a r r ê t

L e r e m p l a c e m e n t d ’u n e s o u p a p e à r e s s o r t p a r u n e s o u p a p e S E B I M s u r l e

c i r c u i t R R A a y a n t é t é d é c i d é e n 1 9 8 1 e t r é a l i s é s u r t o u t e s l e s t r a n c h e s n u c l é a i r e s

R E P d ’ E D F , l e p r o g r a m m e d e q u a l i f i c a t i o n d e s n o u v e l l e s d i s p o s i t i o n s e s t d e c e

f a i t m o i n s c o n s é q u e n t q u e c e l u i d e s s o u p a p e s d u p r e s s u r i s e u r .

I l c o m p r e n d e s s e n t i e l l e m e n t :

— d e s e s s a i s r é a l i s é s s u r l a b o u c l e I n d i r a a u c o u r s d e l ’a n n é e 1 9 8 2 , v i s a n t à

c o m p l é t e r l a q u a l i f i c a t i o n p a r t i e l l e d é j à e f f e c t u é e e n 1 9 8 0 e t 1 9 8 1 . C e c o m p l é ­

m e n t d e q u a l i f i c a t i o n a p o r t é e n p a r t i c u l i e r s u r l e s p o i n t s s u i v a n t s : d é b i t s e t

e s s a i s f o n c t i o n n e l s d e d e u x s o u p a p e s e n s é r i e , e s s a i s d e v a l i d a t i o n d u c a p t e u r d e

d é p l a c e m e n t , e t c . ;

— d e s e s s a i s d e v a l i d a t i o n d ’e n s e m b l e d e l ’ i n s t a l l a t i o n c o m p l è t e a u x c o n d i t i o n s

r e p r é s e n t a t i v e s s o n t p r é v u s s u r l a b o u c l e I n d i r a e n m a i 1 9 8 3 .

L a p r e m i è r e m i s e e n o e u v r e i n t e r v i e n d r a s u r l a t r a n c h e n u c l é a i r e d e C r u a s 3 .

L a p o u r s u i t e d u p r o g r a m m e s e r a r é a l i s é e s u r t o u t e s l e s t r a n c h e s 9 0 0 M W d a n s l e s

m ê m e s c o n d i t i o n s q u e c e l l e s d é c r i t e s c i - d e s s u s p o u r l e p r e s s u r i s e u r . P o u r l e R R A ,

l e s n o u v e l l e s d i s p o s i t i o n s n ’ o n t p a s é t é r e t e n u e s s u r l e s t r a n c h e s d e 1 3 0 0 M W p o u r

l e s r a i s o n s s u i v a n t e s :

— c o m p t e t e n u d e l ’ e x p é r i e n c e a c q u i s e d è s 1 9 8 0 e t 1 9 8 1 s u r l e s t r a n c h e s d e

9 0 0 M W , l e s p r o t e c t i o n s d u R R A d e s t r a n c h e s d e 1 3 0 0 M W o n t é t é c o n ç u e s à

p a r t i r d e s o u p a p e s S E B I M u n i q u e m e n t ;

— l e s c h é m a R R A d u 1 3 0 0 M W e s t d i f f é r e n t d e c e l u i d u 9 0 0 M W e t , e n p a r t i c u l i e r ,

c o m p o r t e d e u x f i l e s s é p a r é e s p e r m e t t a n t l ’é v e n t u e l i s o l e m e n t d e l ’u n e d e s f i l e s .

5 . C O N C L U S I O N S

L e s n o u v e l l e s d i s p o s i t i o n s p r é s e n t é e s p r é c é d e m m e n t , d o n t l a m i s e e n o e u v r e

a é t é d é c i d é e s u r t o u t e s l e s t r a n c h e s n u c l é a i r e s d e 9 0 0 e t 1 3 0 0 M W d ’ E D F , v o n t

p e r m e t t r e e n p a r t i c u l i e r ( d è s 1 9 8 4 p o u r l e s p r e m i è r e s t r a n c h e s ) :

IAEA-SM-268/62 31

— l ’a m é l i o r a t i o n d e l a s û r e t é d e f o n c t i o n n e m e n t d e s c e n t r a l e s n u c l é a i r e s , e n

a s s u r a n t u n e p r o t e c t i o n c o n t r e l e s s u r p r e s s i o n s p l u s f i a b l e , r é d u i s a n t e n p a r t i c u l i e r

l e s r i s q u e s d e b r è c h e c o n s é c u t i f s a u f o n c t i o n n e m e n t d e s o r g a n e s d e p r o t e c t i o n ;

— l a r é d u c t i o n d e s c o n t r a i n t e s d ’e x p l o i t a t i o n ( m a t é r i e l f i a b l e n e n é c e s s i t a n t p l u s

d ’a r r ê t p o u r e x p e r t i s e a p r è s f o n c t i o n n e m e n t , s i m p l i f i c a t i o n d e s r é g l a g e s e t d e s

e s s a i s p é r i o d i q u e s , m a t é r i e l s i d e n t i q u e s s i m p l i f i a n t l e s p r o b l è m e s d ’e n t r e t i e n , e t c . ) ;

— l ’a m é l i o r a t i o n d e l a d i s p o n i b i l i t é d e s t r a n c h e s n u c l é a i r e s .

P a r a i l l e u r s , c e s n o u v e l l e s d i s p o s i t i o n s , e t e n p a r t i c u l i e r l ’u t i l i s a t i o n d e

s o u p a p e s p i l o t é e s S E B I M f o n c t i o n n a n t e n « p r o t e c t i o n » e t « r é g u l a t i o n » v o n t

p e r m e t t r e à m o y e n t e r m e , s a n s m o d i f i c a t i o n d e s m a t é r i e l s , d ’ a s s u r e r d e f a ç o n

e n t i è r e m e n t s a t i s f a i s a n t e l a p r o t e c t i o n à f r o i d d e l a c h a u d i è r e n u c l é a i r e à p a r t i r

d e s s o u p a p e s d u p r e s s u r i s e u r . C e t t e p r o t e c t i o n e s t a c t u e l l e m e n t r é a l i s é e , d e f a ç o n

i n d i r e c t e e t c o m p t e t e n u d ’u n n o m b r e i m p o r t a n t d e c o n t r a i n t e s , p a r l e s s o u p a p e s

d u R R A .

B I B L I O G R A P H I E

BESSOU , F., C A B A N N E S, J.L., CH AN TO T, H., M odification des dispositifs de protection des circuits R R A et R C V , Note ED F E/REAM /R/82-015 (1982).

G E R R Y , A., PETIT, R., CH A N TO T, H., C R A N S A C , J., C A BA N N E S, J.L., Protection du circuit primaire principal contre les surpressions, Note ED F E/REAM PWR 900/1300 MW (19 8 1).

Notice de présentation des soupapes de sûreté pilotées SEBIM, SEBIM Z.I., La Palunette, Châteauneuf-les-Martigues.

IAEA-SM-268/76

ВЛИЯНИЕ НЕКОТОРЫХ НЕЙТРОННО-ФИЗИЧЕСКИХ ХАРАКТЕРИСТИК АКТИВНОЙ ЗОНЫ НА БЕЗОПАСНУЮ РАБОТУ РЕАКТОРА ТИПА ВВЭР

М. А . Л У К ЬЯ Н О В, В. А . ВОЗН ЕСЕНСКИ Й, А .К . ГО РО Х О В,

В .П . С П А С С К О В , Н .С. ФИЛЬ

Государственны й ком итет по использованию

атомной энергии СССР,

М осква,

Сою з С оветски х Социалистических Республик

Д о к л а д представлен Г .Н . Полетаевым

A b s t r a c t - А н н о т а ц и я

EFFE C T O F C E R T A IN N EU TR O N PH YSICS C H A R A C T E R IST IC S O F THE C O R E ON THE SA FE O PER A T IO N O F A WWER R E A C TO R .

The paper discusses the effect o f reactivity coefficients and other neutron physics parameters o f the core on the safe operation o f water-cooled, water-moderated (WWER)

power reactors. The discussion is based on the example o f a WWER-1000 reactor design having a (gross) capacity o f 1000 MW(e), the main characteristics o f which are given in the paper.

In the discussion o f the influence o f the physical characteristics on operational safety, the following matters are considered: the conditions governing the magnitude andsign o f the temperature coefficient o f reactivity Эр/ЭТн Q and the density coefficient o f

reactivity др /ду o f the coolant; the effect o f the reactivity coefficients on the course o f regimes involving operational failures and o f accident processes; ways and means o f influencing the magnitude and sign o f 9p/9TH j0 .

ВЛИЯНИЕ НЕКОТОРЫХ НЕЙТРОННО-ФИЗИЧЕСКИХ ХАРАКТЕРИСТИК АКТИВНОЙ ЗОНЫ НА БЕЗОПАСНУЮ РАБОТУ РЕАКТОРА ТИПА ВВЭР.

В настоящем докдаде рассматривается влияние коээфициентов реактивности и других нейт­ронно-физических параметров активной зоны на безопасную работу водо-водяных энергетических реакторов (типа ВВЭР). Рассмотрение проводится на примере проекта реактора ВВЭР-1000 энерге­тической мощностью (брутто) 1000 МВт, основные характеристики которого приводятся в докладе. При рассмотрении влияния физических характеристик на безопасность работы представляют интерес следующие вопросы: условия формирования величины знака и коэффициента реактивности по температуре теплоносителя, , и по плотности теплоносителя, 4 -; влияние коэффициентовреактивности на протекание режимов с эксплуатационными нарушениями и аварийных процессов; пути и способы воздействия на величину и знак

6 ÍHjO

33

34 ЛУКЬЯНОВ и др.

1. УСЛ О ВИ Я ФОРМ ИРОВАНИЯ ВЕЛИЧИНЫ И ЗН А К А КОЭФФИ ЦИЕНТА

РЕАКТИ ВН О СТИ ПО ТЕМ П ЕРАТУРЕ ТЕП Л ОН О СИ ТЕЛ Я

На рис. 1, 2 представлены зависимости коэффициента размножения бесконечной

реш етки Коо от воДо-уранового отношения при различных состояниях активной зоны

и разных концентрациях бора в теплоносителе (среднее обогащение по 235U — р 5 = 2,5%) .

Расчет проводился по програм ме POP [2].

Полученные зависим ости Коо = S (со) показываю т, что оптим ум коэффициента

размножения при повышении концентрации бора в теплоносителе снижается и сдвигает­

ся влево.

Т аки м образом , при выбранном водо-урановом отношении, обеспечивающем

м аксимальную глубину выгорания топлива, определяющ им параметром, от которого

зависит величина и знак коэффициента реактивности , является критическая

концентрация борной кислоты и ее эфф ективность. Н2°

Действительно, если взять реш етку твэлов реактора В В Э Р -1000 (основны е хар ак­

теристики реактора В В Э Р -1000 приведены в табл.1) с водо-урановы м отношением

со = 2,1 (соответствует оптимальной области со [3 ]) , то из рис. 1, 2 видно, что снижение

со при определенных концентрациях бора в воде, а это равнозначно разогреву теплоно­

сителя и уменьшению его плотности, приводит к росту коэффициента размножения Коо .

Ниже в табл.II для реактора В В Э Р -1000 приводятся коэффициенты реактивности

по температуре теплоносителя для различных состояний реактора на начало и конец

первого года выгорания для одного из вариантов первой топливной загрузки без исполь­

зования выгораю щ их поглотителей.

Из рассмотрения табл. II и анализов результатов расчетов следует, что при достаточ­

но больш их концентрациях бора в теплоносителе, которы е имеют место в начале цикла

выгорания при полностью извлеченных органах системы управления и защиты (СУ З) в

горячем состоянии на нулевой мощ ности и други х состояниях реактора, коэффициент

реактивности ~ может иметь положительное значение. О днако на величину ~° 1н2о d 1 н2о

и его знак можно воздействовать. Например, введение д в у х групп органов регулирова­

ния в горячем состоянии приводит к снижению концентрации бора и изменению знака ЭрЗТН;2о

Следует подчеркнуть, что при рабочем состоянии реактора на полной мощ ности

с равновесны м отравлением ксеноном температурный коэффициент реактивности

становится отрицательным даже при полностью извлеченных органах С У З. Д ля такого

же состояния реактора, но без отравления ксеноном , | о с т а е т с я слегка поло-O 'H jO

жительным.

Расчеты показы ваю т, что по мере выгорания топлива примерно через 60 эф ф ек­

тивны х с ут о к работы реактора критическая концентрация бора в воде снижается до

величины, при которой обеспечивается отрицательное значение коэффициента реактив­

ности во всей области регулирования реактора до конца кампании топливной загрузки.

Наиболее отрицательное значение ~ имеет в конце цикла вы горания, когда крити-

ческая концентрация бора в теплоносителе приближается к нулю.

IAEA-SM-268/76 35

Рис. 1. Зависимость коэффициента размножения от водо-уранового отношения

ш при

различных значениях концентрации бора в теплоносителе Св.

36 ЛУКЬЯНОВ и др

Рис. 2. Зависимость коэффициента размножения от водо-уранового отношения

w при различных значениях

концентрации бора в теплоносителе

Т А Б Л И Ц А I. ОСНОВНЫЕ Х А РА КТЕРИ СТИ КИ РЕ А К Т О РА В В Э Р -1000 [1]

IAEA -SM -268/76 37

Наименование параметра Величина

Тепловая мощность, МВт 3000Давление теплоносителя, МПа 15,7Средняя температура теплоносителя, °С 306Расход теплоносителя через реактор, м 3/ч 80 000Эквивалентный диаметр активной зоны, см 316Высота активной зоны в рабочем состоянии, см 356Удельная мощность активной зоны, кВт/л 107Число топливных кассет 163Форма и тип топливной кассеты Шестигранник

без чехлаВодо-урановое отношение 2,1Размер кассеты под ключ, мм 234Загрузка топлива в активную зону (UO,), т 80Наружный диаметр и шаг расположения твэлов, мм 9,1/12,75Средний тепловой поток, Вт/см 166Число органов регулирования 61Число поглощающих элементов в органе регулирования 18Число главных циркуляционных насосов (ГЦН) 4

2. ВЛИЯНИЕ КОЭФФИ ЦИЕН ТА РЕАКТИ ВН ОСТИ П О ТЕПЛОНОСИТЕЛЮ Н А

П РОТЕКАН И Е АВАРИ Й Н О ГО РЕЖИМА С БОЛЬШ ОЙ ТЕЧЬЮ I КО Н ТУРА

Ниже рассматривается влияние положительного коэффициента реактивности по

температуре теплоносителя и отрицательного по плотности теплоносителя на протека­

ние постули руем ого аварийного режима с разры вом главного циркуляционного тр уб о ­

провода диаметром 850 мм.

Принимается разрыв трубопровода на входе в реактор с 2 -х сторонним истечением

теплоносителя.

В расчете рассматривалось 2 канала активной зоны: канал с максимальным энерго­

выделением (общий объемный коэффициент неравномерности K v = 2,44) и канал со

средним значением энерговыделения.

Анализ проводится для 2 -х зависим остей реактивности от плотности теплоноси­

теля, представленных на рис. 3, где кривая 1 соответствует наличию отрицательного

коэффициента реактивности по плотности теплоносителя в определенном диапазонео Эр7н2о > а кривая 2 соответствует н улевом у значению ~ в том же диапазоне 7H î0 .

38 ЛУКЬЯНОВ и др.

Т А Б Л И Ц А II. КОЭФФИЦИЕНТЫ РЕАКТИ ВН О СТИ

Состояние реактора . 1/°С° *н3о

1. Начало цикла выгорания :а) холодное, Т = 20°С, неотравленное,

органы СУЗ извлечены, СцР = 1,55 г/кг; +1,3 - 10 s

6) горячее, Т = 278°С, нулевая мощность, неотравленное, органы СУЗ извлечены, С*р = 1,61 г/кг;

+ 9,0 ■ 10_s

в) горячее, Т = 278 °С, нулевая мощность, неотравленное, полностью погружена одна группа органов СУЗ, CgP = 1,57 г/кг;

+1,7 • 10~5

г) то же, что и в), но погружено две группы СУЗ, CgP = 1,48 г/кг; - 2,1 10‘s

д) то же, что и в), но погружено три группы СУЗ, CgP = 1,39 г/кг; - 6,9 10's

е) рабочее, Т = 306 °С, неотравленное, органы СУЗ извлечены, CgP = 1,40 г/кг; + 1,3 - 10"s

ж) рабочее, Т = 306 °С, равновесное отравление ксеноном, органы СУЗ извлечены,CgP= 1,13 г/кг.

- 4,3 • 10"5

2. Конец цикла выгорания:а) холодное, Т = 20°С, CgP - 0,76 г/кг; - 2,0 -lO-7б) горячее, Т = 278°С, нулевая мощность,

отравленное Sm, органы СУЗ извлечены, Cgp = 0,52 г/кг;

-2.5-10'4

в) рабочее, Т = 306°С, отравление Хе и Sm, органы СУЗ извлечены, CgP = 0. -6,1 io-"

Расчет аварийного процесса с большой течью проводился по програм м ам ” ТЕЧ Ь-М ”

и "К А Н А Л ” [4].

На рис. 4 представлено изменение плотности теплоносителя и нейтронной мощ нос­

ти в о времени.

На рис. 5 приведено изменение температуры топлива и оболочки для максимально

напряженного твэла; на р и с.6 - температура оболочки для средненапряженного твэла.

Рассмотрение этих кр и вы х показы вает, что наличие отрицательного значения коэф ­

фициента реактивности по плотности теплоносителя для максимально напряженного

твэла приводит к сущ ественном у повышению максимальной температуры оболочки

IAEA -SM -268/76 39

Рис. 3. Используемая в расчетах с большой течью зависимость реактивности от плотности теплоносителя:

Ъ р >1 - при < О,

2 -при > О.

(приблизительно на 15 0 оС) по сравнению с тем , когда активная зона не имеет отрица- Ьр

тельного значенияо у

Этот ф акт имеет больш ое значение при удовлетворении требований по безопаснос­

ти по критерию недопущ ения интенсивной паро-циркониевой реакции (непревышение

м аксимальной температуры оболочки твэлов выш е 1200 ° С ) .

Н еобходим о такж е отм етить, что температура оболочки средненапряженного

твэла в данной аварии такж е сущ ественно зависит от знака и величины ^ (см . рис. 6 ).

Хотя разница в тем пературах оболочки в этом случае меньше ( ~ 100 ° С ) , однако

она м ож ет иметь принципиальное значение.

Действительно, характерной температурой разгерметизации оболочек твэлов с

учетом перепада давлений под оболочкой твэлов и в I кон тур е является температура,

равная приблизительно 700 °С [5 ] .

К а к видно из рис. 6, максимальные температуры оболочек при > 0 ниже, а Эр - - о Упри отрицательном значении выш е этой характерной температуры , что является

сущ ественны м с точки зрения вы хода радиоактивности в этой аварии.

40 ЛУКЬЯНОВ и др.

У, кг/м3 N, отн.ед.

Рис. 4. Изменение параметров в аварии с разрывом главного циркуляционного трубопровода Ду 850 на входе в реактор:

7 — изменение плотности теплоносителя (при < 0) ;N- изменение относительной нейтронной мощности;

1 - при < 0;

2-при >0.

IAEA-SM-268/76 41

П редставленный краткий анализ влияния коэффициента реактивности по тепло­

носителю на протекание аварии с больш ой течью показы вает на необходимость приня­

тия мер по исключению режимов работы реактора с положительным коэфф ициентом

реактивности по тем пературе теплоносителя (отрицательным по плотности) .

3. ВЛИЯНИЕ КОЭФФИ ЦИЕН ТА РЕАКТИ ВН О СТИ ПО ТЕПЛОНОСИТЕЛЮ

Н А ПРОТЕКАН И Е РЕЖИМА С ОБЕСТОЧИ ВАН И ЕМ ГЛ АВН Ы Х

ЦИРКУЛЯЦИОННЫ Х Н АСОСОВ

На примере данного режима рассматривается влияние положительного коэф ф и­

циента по тем пературе теплоносителя на протекание процесса применительно к реактору

В В Э Р -1000 5-го блока Н ововоронеж ской А ЭС.

Этот режим с обесточиванием ГЦН и потерей расхода среди предполагаемы х

эксплуатационных нарушений является наиболее опасным с точки зрения надежности

охлаждения активной зоны.

Критерием надежности отвода тепла от твэлов активной зоны является коэф ф и­

циент запаса до кризиса теплообмена.

Расчетный анализ выполнен для д в у х значений коэффициента реактивности по

теплоносителю:

% = + 4,50 • 10 ~5 1/°С и = — 4 • 1 0 -5 1/°С.d 1 Н20 О 1 н2о

На р и с.7 представлены зависим ости коэфф ициентов запаса до кризиса теплооб­

мена от времени.

К а к следует из рассмотрения кр и вы х, наличие положительного коэффициента

заметно снижает запас до кризиса теплообмена, т .е. в этом случае надежностьd l H jOохлаждения активной зоны ухудш ается.

4. ВЛИЯНИЕ З Н А К А КО ЭФФИ Ц ИЕНТА РЕАКТИ ВН ОСТИ ПО ТЕМ П ЕРАТУРЕ

ТЕП Л О Н О СИ ТЕЛ Я Н А П РОТЕКАН И Е АВАРИ И С НЕУПРАВЛЯЕМЫ М

ИСТЕЧЕНИЕМ П А РА ИЗ II К О Н ТУРА

В проекте В В Э Р -1000 в качестве максимальной аварии с истечением пара расс­

матривается разрыв главного парового коллектора.

В такой аварии наруш ается тепловой баланс м еж ду I и II контурам и и происхо­

дит интенсивное охлаждение теплоносителя, поступающ его в реактор, что при наличии

отрицательного коэффициента реактивности по температуре теплоносителя приводит

к увеличению реактивности активной зоны.

Одной из мер обеспечения безопасности для такой аварии является закрытие

отсечных клапанов на паропроводах. П редполагается, что один из четырех имеющихся

ЛУКЬЯНОВ и др.

Рис.5. Изменение максимальной температуры топлива и оболочки для твэла с максимальной мощностью:

Тт - изменение температуры топлива;То6 - изменение температуры оболочки;

IAEA -SM -268/76 43

Рис. 6. Изменение максимальной температуры оболочки твэла со средней мощностью:

1 - при -2- < 0;Ъу

2 - при > 0.ду

отсечных клапанов м ож ет не закры ться, и авария с разры вом парового ко л л ек то­

ра сводится к истечению пара из одного парогенератора.

В дальнейш ем считаются возм ож ны м и два варианта развития аварии:

1) по б лок и р овке отключается главный циркуляционный насос петли с незак-

рывающ имся отсечным клапаном, охлажденный теплоноситель из неотсеченного па­

рогенератора поступает в верхнюю кам ер у реактора и смеш ивается с потокам и от

петель с работающими насосами;

2) одновременно с разры вом парового коллектора наступает полная потеря

энергоснабжения от внешней систем ы , охлаждение реактора осущ ествляется естествен­

ной циркуляцией теплоносителя через парогенератор с течью по пару.

В дальнейш ем обсуж даю тся результаты расчетов по програм ме М ОСТ - 10 [16]

для последнего варианта, в к о тор ом поведение параметров реакторной установки

является более неблагоприятным.

В качестве и сходного состояния было принято, что реактор работает на номи­

нальной мощ ности в конце кампании, к огд а коэффициент реактивности по темпера­

туре теплоносителя отрицателен и имеет максимальное значение.

При срабатывании аварийной защиты учитывается застревание в верхнем поло­

жении одного сам ого эф ф ективного из 49 органов регулирования (здесь рассмотрен

44 ЛУКЬЯНОВ и др.

Рис. 7. Изменение коэффициента запаса до кризиса теплообмена в режиме обесточивания четырех ГЦН:

1 -при If = -4,0.1<Г* 1/°С;д *нао

2 - при = +4,5-10-* 1/°С°l H J 3

вариант активной зоны с 49 органами регулирования). Учитывалось такж е неполное

перемешивание п отоков теплоносителя, поступающ их из различных петель и сек то ­

ров активной зоны.

Значение коэффициента перемешивания, определенного к а к доля расхода теп­

лоносителя из расхолаж иваемой петли, заменяемая теплоносителем из други х петель,

для обеих кам ер реактора принималось равны м 20%.

Кривы е изменения основны х параметров реакторной установки при разрыве

паропровода представлены на рис. 8 ,9 . К а к следует из ри сунк ов, увеличение энерго­

выделения в кассете, в котор ую не вводится орган регулирования, начинается на 10-й

секун де и достигает к 35 -й секун де значения 36% от исходной величины. К этом у

м ом ен ту времени расход теплоносителя через кассету снижается до 19% от номиналь­

ного, а тем пература на ее вхо д е — до 210 °С. В период времени м еж ду 2 -й и 3 -й ми­

нутой от начала процесса происходит повторный вы ход реактора в критическое сос­

тояние. О днако, в течение всей аварии сохраняется достаточный запас до возникно­

вения кризиса теплообмена на поверхности твэлов.

IAEA-SM-268/76 45

Рис. 8. Изменение мощности в активной зоне при аварии с разрывом главного парового коллектора при наличии отключения всех главных циркуляционных насосов:1 - относительное изменение энерговыделения в активной зоне;2 - относительное изменение тепловой мощности, переданной теплоносителю;3 — относительное изменение среднего энерговыделения в кассете с застрявшим органом СУЗ;4 - относительное изменение тепловой мощности, переданной теплоносителю, в кассете с застрявшим

органом СУЗ.

На основании анализа спектра аварий с неуправляем ы м истечением пара из па­

рогенераторов был внесен ряд дополнений в проект реакторной установки В В Э Р -1000:

повыш ено количество органов регулирования с 49 до 6 1 , расширены возм ож ности в в о ­

да в активную зону концентрированного раствора борной кислоты .

Эти мероприятия позволяю т обеспечить сохранение подкритичности реактора

после срабатывания аварийной защиты, требуем ое действующ ими в СССР Правила­

ми обеспечения ядерной безопасности [7].

5. ПУТИ В О ЗД ЕЙ СТВИ Я Н А ВЕЛИЧИНУ И ЗН А К КОЭФФИ Ц ИЕНТА

РЕАКТИ ВН О СТИ ПО ТЕМ П ЕРАТУРЕ ТЕП Л ОН О СИ ТЕЛ Я

П о ск о л ьк у при наличии положительной величины коэффициента реактивности

g Y (отрицательной ~ ) значительно усугуб л я ется протекание аварийных режимов,

необходим о в проекте предусматривать меры воздействия на величину и знак Ш -d i H20

46 ЛУКЬЯНОВ и др.т , °с

Рис. 9. Изменение температуры теплоносителя в Iконтуре в аварии с разрывом главного парового коллектора при наличии отключения всех главных циркуляционных насосов:1 — средняя температура в нижней камере смешения;2 - средняя температура в верхней камере смешения;3 - средняя температура на выходе из кассеты с застрявшим органом СУЗ;4 - температура теплоносителя на выходе из петель с отсеченным парогенератором;5 - температура теплоносителя на выходе из петли с течью парогенератора по пару.

К а к бы ло отмечено выш е, основным параметром, влияющ им на формирование

величины и знака ^ , является критическая концентрация борной кислоты ,d l H20

используемой для компенсации эфф ектов реактивности (разогрев и расхолаживание

реактора, отравление ксен оном и самарием, вы ход реактора на мощ ность, запас на

вы гор ан и е).

П оэтом у, основны м способом воздействия на величину и знак являетсяd J H20

снижение величины критической концентрации борной кислоты . Это может быть д о с­

тигнуто нескольким и путям и, рассматриваемыми ниже.

5 .1 . Использование органов регулирования

Этот способ является наиболее оперативным и л егко реализуемы м на практике.

На рис. 10 для активной зоны без вы гораю щ их поглотителей показана зависимостьЭ р-jîj; от числа вводи м ы х групп органов регулирования и температуры теплоносителяd l H20

IAEA-SM-268/76 47

ТЕП ЛО НО СИ ТЕЛЯ. °C

Рис. 10. Зависимость коэффициента реактивности по температуре теплоносителя от средней температуры теплоносителя в процессе разогрева в начале первого цикла выгорания при критической концентрации бора.

48 ЛУКЬЯНОВ и др.

для начала топливного цикла. К ак следует из рис. 10, введение в активную зону 2-3 групп

органов регулирования при одновременном уменьшении критической концентрации бо-Эрра в теплоносителе снижает величину ^ и делает ее отрицательной при достижении

о н 2 °температуры теплоносителя 278 °С, которая является характерной для начала вы вода

реактора в критическое состояние и последую щ его вы хода на мощ ность.

При медленном вы воде реактора на номинальную мощ ность за счет извлечения

органов С У З при соответствую щ ем отравлении ксеноном можно поддерживать наибо­

лее низкое значение критической концентрации бора в теплоносителе, при которой темпе­

ратурный коэффициент — , находится вблизи нулевого значения или является слегка ó í н2о

отрицательным. По мере выгорания топлива критическая концентрация бора снижается

и через примерно 60 эфф ективны х суто к достигает значения, при к отор ом коэффициент

реактивности по температуре теплоносителя становится отрицательным в лю бы х состо­

яниях реактора.

Н есмотря на практическую приемлемость данного способа воздействия на величину

и знак коэффициента реактивности , он не решает данную проблем у кардинально.d l H20

5 .2 . Применение вы гораю щ их поглотителей

Величина критической концентрации борной ки слоты в активной зоне может

быть понижена путем применения выгораю щ его поглотителя (либо в виде отдель­

ны х пучков-стержней с вы гораю щ им поглотителем, либо за счет введения в топлив­

ные элем ен ты ).

Расчетный анализ показы вает, что для топливного цикла с трехгодичной кам па­

нией топлива применение 54 пучков стержней с вы гораю щ им поглотителем (С В П ),

вы полненны х аналогично п уч ку поглотителей органов С У З (с использованием бора)

и разм ещ аем ы х в свободны х каналах топливны х кассет, позволяет обеспечить отри­

цательное значение коэффициента (и соответствую щ ую положительную величинуЭр d l H2o- ^ ) в о всей области режимов работы реактора.

В качестве примера для некоторы х характерны х состояний реактора при пол­

ностью извлеченных органах СУЗ для начала топливного цикла активной зоны с в ы го­

рающим поглотителем в виде 54 пучков СВП коээфициенты реактивности приведены

в табл. III.

5 .3 . Изменение топливного цикла

Снижение критической концентрации борной кислоты можно обеспечить за

счет уменьш ения запасов на выгорание топлива, что связано, естественно, с ум еньш е­

нием продолжительности топливного цикла меж ду перегрузками. Этого можно до­

биться путем уменьш ения обогащ ения топлива подпитки при сохранении количест-

IAEA-SM-268/76 49

ТАБЛИЦА III.

Состояние реактора - Ю ' М Г с3 !н2о -Vе- • КГ1 , — I-., О у г • см 5

Горячее, Т = 278 °С, без мощности, неотравленное; -3,58 +2,96

Рабочее, Т = 306 °С, номинальная мощность, стационарное отравление ксеноном и самарием. -25,4 +11,9

ва перегруж аем ы х кассет или за счет уменьш ения количества перегруж аем ы х кассет

при сохранении обогащ ения подпиточного топлива.

Расчетный анализ показы вает, что более рациональным путем является ум ень­

шение количества перегруж аем ы х кассет при сохранении обогащ ения подпитки.

Д ля рассм атриваем ого реактора с 163 кассетам и в двухгодичном топливном

цикле перегружается примерно 80 кассет ежегодно. П ереход на учащенный цикл пе­

р егр узок топлива, а именно 2 перегрузки в год (око л о 40 кассет за пер егр узку) ,

позволяет уменьшить критическую концентрацию бора в теплоносителе на 50-70%,

при этом величина температурного коэффициента реактивности становится. э т н2о

отрицательной во всех режимах работы реактора.

Коэффициент неравномерности энерговыделения в активной зоне при реализа­

ции так ого топливного цикла такж е становится более благоприятным.

Данный способ влияния на величину и знак коэффициента реактивности 4 =d i H20

является предпочтительным и эконом ически целесообразным [ 1 ] (обеспечивает сни­

жение топливной составляющ ей стоим ости энергии на 8-9%) ; его реализация на прак­

тике требует сокращ ения времени на все технологические операции, связанные с пере­

гр узк ой топлива.

6. ВЫВОДЫ

6 .1 . А ктивная зона реактора типа ВВЭР больш ой мощ ности (примерно 1000 МВт

(э л .)) при использовании в качестве поглотителя нейтронов раствора борной кислоты

для компенсации эф ф ектов реактивности при определенных состояниях реактора без

принятия специальных мер может иметь положительную величину коэффициента ре­

активности по температуре (и соответствую щ ее отрицательное значение по плотности)

теплоносителя, что может неблагоприятно отражаться на услови я безопасной работы

реактора.

Д ля исключения этого в проекте ВВЭР - 1000 изменение величины и знака коэф ­

фициента реактивности достигается следующ ими путями:

50 ЛУКЬЯНОВ и др.

— использованием в начале цикла выгорания нескольки х групп органов р егу­

лирования (введением их в активную зону с последую щ им вы водом ) ;

— применением вы гораю щ их поглотителей (в виде отдельных пучков или путем

добавления в топливны е элем енты ).

В качестве эф ф ективного способа влияния на знак коэффициента реактивности

следует такж е рассматривать изменение топливного цикла с переходом на учащенный

режим перегрузок (например, две перегрузки в год) ; этот способ наряду с воздей­

ствием на величину и знак коэффициента реактивности дает сущ ественный выигры ш

в топливной составляющ ей (8 -9 % ).

6 .2 . Наличие больш ого отрицательного коэффициента реактивности по темпе­

ратуре теплоносителя в конце каж дого цикла вы горания в аварийных режимах с течью

паропроводов за счет бы строго расхолаживания после срабатывания аварийной защи­

ты м ож ет приводить к п овторном у в ы хо ду в критическое состояние и повышению

мощ ности в отдельны х областях активной зоны. Х отя кризиса теплосъема не возни­

кает, в проекте реализованы меры по исключению в этих режимах вы хода реактора

в критическое состояние (удовлетворение требований ядерной безопасности) за счет

повыш ения эф ф ективности систем воздействия на реактивность: увеличено число

органов регулирования до 6 1, предусм отрен вво д концентрированного раствора бора.

Эфф ективной мерой, уменьшающей неблагоприятные последствия неравномер­

ного расхолаживания петель в этих режимах, является увеличение степени перемеш и­

вания теплоносителя в о входной и вы ходной кам ерах реактора.

Л И ТЕРАТУРА

[1] ВИХОРЕВ, Ю.В. и др., Ат. Энерг. SO 2 (1981) 92.[2] СИДОРЕНКО, В. Д., Расчет критичности и выгорания решеток со слабообогащенным топливом

и легководным замедлителем, Препринт ИАЭ-1437, 1970.[3] ВОЗНЕСЕНСКИЙ, В.А. и др., Ат. Энерг. 43 6 (1977) 445.[4] СПАССКОВ, В. П. и др., в сб. ’’Вопросы атомной науки и техники”, серия ’’Физика и техника

ядерных реакторов”, 7 (20) (1981) 72.[5] ГОЛОВНИН, И.С., НОВИКОВ, В.В., Ат. Тех. Рубежом, 5 (1982) 6.[6] МЫСЕНКОВ, А.И., ’’Программа для расчета аварийных ситуаций на АЭС с ВВЭР”, Доклад

ТФ-82/85 на семинаре ”Теплофизика-82”, Карловы Вары, ЧССР, май 1982.[7] Правила Ядерной Безопасности Атомных Электростанций (ПБЯ-04-74), М., Атомиздат, 1977.

IAEA-SM-268/22

U L T I M A T E H E A T S I N K F O R P H W R s :

E V A L U A T I O N O F E X I S T I N G M E T H O D S

A N D A L T E R N A T I V E P R O P O S A L S

A . K . G H O S H , S . K . B A N D Y O P A D H Y A Y ,

L . G . K . M U R T H Y

R e a c t o r A n a l y s i s a n d S t u d i e s S e c t i o n ,

B h a b h a A t o m i c R e s e a r c h C e n t r e ,

D e p a r t m e n t o f A t o m i c E n e r g y ,

B o m b a y

N . R A M A M O O R T H Y

P o w e r P r o j e c t s E n g i n e e r i n g D i v i s i o n ,

D e p a r t m e n t o f A t o m i c E n e r g y ,

B o m b a y

I n d i a

A b s t r a c t

U LTIM A TE H E AT SIN K FO R PHWRs: E V A L U A T IO N O F EX ISTIN G M ETHODS AND A L T E R N A T IV E PR OPOSALS.

The PHWRs currently in operation in India use the main steam generators and a shutdown cooling system as ultim ate heat sinks under loss o f mains supply. The primary heat transport system pressure control, w hich is a feed and bleed system, is not adequate to prevent voiding due to insufficient injection capability on standby power. The shutdown cooling system is intended to be cut in only after the main coolant temperature is brought down to 149°C. In certain em ergency conditions this is done by blowing steam from the steam generators, which tends to cause large shrinkage in the main coolant circuit and consequent loss o f circulation.The present paper examines the therm osyphon cooling perform ance o f the reactor system and suggests m odifications to cut in the shutdown cooling directly after the loss o f main power to improve dependability o f the ultim ate heat sink.

1 . I N T R O D U C T I O N

T h e P H W R s o f p r e s e n t d e s i g n i n I n d i a d e p e n d o n t h e m a i n s t e a m g e n e r a t o r s

( S / G ) a n d a s t a n d b y c o o l i n g s y s t e m ( S C S ) f o r r e m o v a l o f t h e h e a t g e n e r a t e d i n

t h e r e a c t o r . A s c h e m a t i c o f t h e p r i m a r y h e a t t r a n s p o r t ( P H T ) s y s t e m i s s h o w n i n

F i g . 1 . T h e S C S i s s p e c i f i e d [ 1 ] t o b e c u t i n t o o p e r a t i o n o n l y a f t e r t h e P H T

t e m p e r a t u r e i s b r o u g h t d o w n t o 1 4 9 ° C b y b l o w i n g s t e a m f r o m t h e S / G s a t p r e ­

s e l e c t e d r a t e s . T h e P H T s y s t e m i s d e s i g n e d t o b e a ‘s o l i d ’ s y s t e m , i . e . t o a l w a y s

b e b e l o w s a t u r a t i o n t e m p e r a t u r e u n d e r v a r i o u s m o d e s o f o p e r a t i o n , t h e p r e s s u r e

51

52 GHOSH et al.

NOTE: 1. VSG open and VSCS closed in normaloperation and thermosyphon cooling

2. VSG closed and VSCS open when SCS in operation

3. Stations 1—6 external circuit4. Stations 6— 11 internal circuit

F IG .l . Schematic diagram o f P H T circuit.

i n t h e s y s t e m b e i n g m a i n t a i n e d b y f e e d a n d b l e e d c o n t r o l . H o w e v e r , l o s s o f c l a s s I V

p o w e r s u p p l y , w h i c h is n o t t o o i n f r e q u e n t i n t h e l o c a l c o n d i t i o n s , a n d s i m u l t a n e o u s

l a c k o f a d e q u a t e p r i m a r y i n j e c t i o n c a p a c i t y c r e a t e c o n d i t i o n s w h i c h c o u l d r e s u l t i n

v o i d i n g o f t h e s y s t e m , l e a d i n g t o u n c e r t a i n t y i n h e a t s i n k c a p a b i l i t y . T h e v o i d i n g

i n t h e P H T s y s t e m a n d c o n s e q u e n t l o s s o f n a t u r a l c i r c u l a t i o n d u e t o s h r i n k a g e i s

a c c e n t u a t e d i n c r a s h c o o l i n g . T h e p r e s e n t p a p e r d e a l s w i t h a n a n a l y s i s o f t h e r m o ­

s y p h o n p e r f o r m a n c e o f t h e P H T s y s t e m a n d s u g g e s t i o n s f o r i m p r o v e d a n d m o r e

d e p e n d a b l e h e a t s i n k c a p a b i l i t y .

2 . T H E R M O S Y P H O N P E R F O R M A N C E

W i t h l o s s o f c l a s s I V p o w e r , t h e i n e r t i a o f t h e f l y w h e e l s o n t h e m a i n P H T

p u m p s m a i n t a i n s f l o w f o r a b o u t 9 0 s e c o n d s , a f t e r w h i c h t h e o n l y m o d e o f t r a n s ­

f e r r i n g h e a t f r o m t h e r e a c t o r t o t h e s t e a m g e n e r a t o r w o u l d b e t h e t h e r m o s y p h o n

c i r c u l a t i o n . N o r m a l l y , i t i t p r e s u m e d t h a t t h e s y s t e m i s b o t t l e d u p , b u t a c e r t a i n

a m o u n t o f s t e a m i s t a k e n o f f f o r t u r b i n e g l a n d s , e j e c t o r s , e t c . a n d a s l o w d e c a y

o f t h e S / G p r e s s u r e a s w e l l a s t h e P H T p r e s s u r e t a k e s p l a c e .

IAEA-SM-268/22 53

T h e p r i m a r y p r e s s u r e i s m a i n t a i n e d b y a f e e d a n d b l e e d s y s t e m . T h e m a i n

p r e s s u r i z i n g p u m p f o r f e e d i n g l i q u i d t o t h e P H T i s o p e r a b l e o n l y o n c l a s s I V p o w e r .

I n t h e c a s e o f f a i l u r e o f t h e c l a s s I V p o w e r s u p p l y , f e e d i s p r o v i d e d b y a n a u x i l i a r y

f e e d p u m p w i t h a c a p a c i t y o f o n e q u a r t e r t h a t o f t h e m a i n p r e s s u r i z i n g p u m p .

E v e n o u t o f t h i s , t h e f u e l t r a n s f e r s y s t e m c o n s u m e s a l a r g e p a r t a n d e f f e c t i v e l y

t h e r e i s a f e e d c a p a c i t y o f o n l y a b o u t 4 . 5 L p e r m i n u t e p e r o p e r a t i n g p u m p

a v a i l a b l e t h r o u g h p u m p g l a n d i n j e c t i o n f o r m a i n t a i n i n g t h e p r e s s u r e a t t h e i n i t i a l

d e s i g n l e v e l . I f t h e s y s t e m w e r e o p e r a t i n g o n t w o p u m p s o n e i t h e r s i d e , o n l y

1 8 L / m i n o f i n j e c t i o n w o u l d b e a v a i l a b l e , w h i c h i s h i g h l y i n a d e q u a t e f o r k e e p i n g

t h e s y s t e m s o l i d .

A s a n i m m e d i a t e m e a s u r e , a d i r e c t c o n n e c t i o n f r o m t h e a u x i l i a r y f e e d p u m p s

t o t h e P H T l i n e h a s b e e n m a d e t o s u p p l y a b o u t 1 0 0 L / m i n o f w a t e r , w h i c h i s t h e

a v a i l a b l e s p a r e c a p a c i t y a f t e r c a t e r i n g f o r t h e n e e d s o f t h e f u e l l i n g m a c h i n e s .

A l s o , u n d e r c e r t a i n a c c i d e n t c o n d i t i o n s s u c h a s L O C A a n d b r e a k o f f e e d w a t e r

p i p e t o t h e S / G , t h e P H T s y s t e m h a s t o b e c r a s h c o o l e d b y b l o w i n g s t e a m f r o m t h e

s t e a m g e n e r a t o r s : t h i s a g a i n r e s u l t s i n l a r g e s h r i n k a g e o f t h e P H T f l u i d a n d v o i d i n g .

T h e s e c o n s i d e r a t i o n s l e d t o t h e i n v e s t i g a t i o n o f h e a t r e m o v a l c a p a b i l i t y

t h r o u g h t h e r m o s y p h o n .

2 . 1 . M e t h o d o f t h e r m o s y p h o n a n a l y s i s

T o u n d e r s t a n d t h e b e h a v i o u r o f t h e s y s t e m u n d e r v a r i o u s c o n d i t i o n s , s t e a d y -

s t a t e t h e r m o s y p h o n a n a l y s i s h a s b e e n c a r r i e d o u t [ 2 ] f o r v a r i o u s s t e a d y - s t a t e

c o n d i t i o n s . T h e S / G p r e s s u r e a n d t h e P H T p r e s s u r e a r e i n d e p e n d e n t l y c o n t r o l l a b l e

a n d h e n c e d i s c r e t e c o m b i n a t i o n s o f t h e s e t w o p a r a m e t e r s h a v e b e e n s t u d i e d . T h e

f o l l o w i n g a s s u m p t i o n s h a v e b e e n m a d e i n t h e s t u d y :

( a ) T h e s y s t e m i s b o t t l e d u p i n a s t e a d y s t a t e , i . e . j u s t e n o u g h s t e a m i s r a i s e d a n d

l e d o u t t o m a i n t a i n r e a c t o r c o n d i t i o n s c o n s t a n t .

( b ) A o n e - d i m e n s i o n a l f l o w i n t h e s y s t e m h a s b e e n c o n s i d e r e d .

( c ) T h e t e m p e r a t u r e p r o f i l e i n t h e s t e a m g e n e r a t o r h a s b e e n a s s u m e d t o b e l i n e a r

a l o n g t h e l e n g t h . T h i s i s a m a j o r a s s u m p t i o n [ 3 ] .

( d ) T h e f l o w r e s i s t a n c e f a c t o r s i n t h e c h a n n e l f e e d e r s a r e e v a l u a t e d o n t h e b a s i s

o f f l o w r a t e a n d d e n s i t y v a r i a t i o n s f r o m t h e f u l l f l o w v a l u e s . E x a m i n a t i o n

o f t h e f e e d e r p r e s s u r e l o s s c o m p o n e n t s r e v e a l e d t h a t a v e r y l a r g e p a r t o f t h e

f l o w r e s i s t a n c e i s m a d e u p o f s t r a i g h t l e n g t h s a n d b e n d s o n l y a n d t h e a b o v e

a s s u m p t i o n i s f u l l y j u s t i f i a b l e .

T h e f l o w i s e s t i m a t e d b y i t e r a t i n g t h e l i n e a r m o m e n t u m e q u a t i o n a r o u n d t h e

l o o p f o r c o n v e r g e n c e o f t h e n e t d r i v i n g f o r c e d u e t o d e n s i t y d i f f e r e n t i a l a n d t h e

t o t a l s y s t e m r e s i s t a n c e l o s s e s . F o r p a r a l l e l f l o w p a t h s , e n d - t o - e n d i t e r a t i o n f o r

e q u a l p r e s s u r e l o s s i s a l s o c a r r i e d b e t w e e n t h e c o n n e c t i n g p o i n t s .

FLOW

(% OF

FULL FL

OW)

GHOSH et al.

POWER (% OF FULL POWER)

F IG .2 . Converged thermosyphon flo w as a function o f power.

232° С

254° С

262° С

F IG .3 . Shrinkage o f prim ary coolant as a function o f S /G and P H T pressures fo r constant inventory.

IAEA-SM-268/22 55

270

265

260

ш 255ос

S 2 50UJQ_5ш 245

240

125*

118

ASSUMED LINEAR DISTRIBUTION OF PRIMARY TEMPERATURE CALCULATED PRIMARY TEMPERATURE

CALCULATED SECONDARY TEMPERATURE

STEAM TEMPERATURE - 257.4°C PRIMARY FLOW - 4.69 X 105 kg/h POWER TRANSFERRED - 13.22 M W

■120 I I I I _L _L _L0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

NORMALIZED LENGTH

F IG .4. Typical temperature profiles o f prim ary and secondary flu ids in S/G.

2 . 2 . R e s u l t s o f a n a l y s i s

F i g u r e 2 i n d i c a t e s t h e r e s u l t s o f t h e s e e s t i m a t e s . I t s h o w s t h a t t h e r m o s y p h o n

f l o w c a n b e s u s t a i n e d f r o m 2 % t o 1 0 % o f r e a c t o r p o w e r i f t h e s y s t e m c a n b e m a i n ­

t a i n e d s o l i d . R e s u l t s h a v e a l s o b e e n o b t a i n e d f o r c o n v e r g e d f l o w c o n d i t i o n s f o r

d i f f e r e n t c o m b i n a t i o n s o f S / G a n d p r i m a r y p r e s s u r e s . F i g u r e 3 i n d i c a t e s t h e

s h r i n k a g e i n t h e P H T v o l u m e w i t h c o n s t a n t m a s s i n t h e s y s t e m , f o u n d o n t h e b a s i s

o f a w e i g h t e d m e a n c i r c u i t t e m p e r a t u r e . T h i s r e v e a l s o n l y t h a t a s p e c i f i c c o m b i n a ­

t i o n o f b o i l e r a n d P H T p r e s s u r e s m i g h t r e s u l t i n t h e r m o s y p h o n b e i n g s u s t a i n e d .

2 . 3 . S t e a m g e n e r a t o r p e r f o r m a n c e

F u r t h e r d e t a i l e d t e m p e r a t u r e p r o f i l e s h a v e b e e n g e n e r a t e d i n t h e s t e a m

g e n e r a t o r t o c h e c k t h e a s s u m p t i o n o f l i n e a r t e m p e r a t u r e d i s t r i b u t i o n i n t h e s t e a m

g e n e r a t o r b u n d l e s . F i g u r e 4 i n d i c a t e s t h e r e s u l t s f o r 2 % p o w e r t r a n s f e r r e d f r o m

t h e P H T a n d 4 3 . 4 b a r p r e s s u r e i n t h e S / G . I t c a n b e s e e n i m m e d i a t e l y t h a t t h e

f i r s t f e w a s s u m p t i o n s l i s t e d i n S e c t i o n 2 . 1 a r e n o t r i g o r o u s . A l s o , i f a x i a l c o n ­

d u c t i o n i n t h e s t e a m g e n e r a t o r t u b e i s t a k e n i n t o a c c o u n t , t h e t e m p e r a t u r e p r o f i l e

i t s e l f m i g h t c h a n g e . T h i s l e a d s t o t h e c o n c l u s i o n t h a t t h e r m o s y p h o n c o o l i n g i s a

v e r y c o m p l e x p h e n o m e n o n a n d a c r i t i c a l a s s e s s m e n t i s n e c e s s a r y .

56 GHOSH et al.

T h e a s s e s s m e n t o f t r a n s i e n t t h e r m o s y p h o n c o o l i n g a n d s y s t e m p e r f o r m a n c e

w h e n s t e a m i s b l o w n f r o m t h e S / G s c a u s i n g c r a s h c o o l i n g o f t h e P H T s y s t e m i s

m u c h m o r e c o m p l i c a t e d a n d r e q u i r e s c o n s i d e r a t i o n o f d e t a i l e d u V u T ( u n e q u a l -

v e l o c i t y , u n e q u a l - t e m p e r a t u r e ) m o d e l s a n d p h e n o m e n a s u c h a s s t e a m b i n d i n g a n d

f l o o d i n g i n t h e s t e a m g e n e r a t o r t u b e s . C u r r e n t l y , b a s i c m o d e l l i n g e f f o r t s a r e u n d e r

w a y . A l s o , e x p e r i m e n t a l m e a s u r e m e n t s o f t h e t h e r m o s y p h o n f l o w s i n t h e r e a c t o r

u n d e r c o n t r o l l e d s t e a d y / q u a s i - s t e a d y o p e r a t i n g c o n d i t i o n s a r e b e i n g p l a n n e d ,

i n c l u d i n g a s s e s s m e n t o f i n s t r u m e n t a t i o n f o r m e a s u r i n g t h e r m o s y p h o n r a n g e

o f f l o w s .

2.4. Steam blowing from S/Gs

3 . A L T E R N A T I V E T O T H E R M O S Y P H O N - T H E S C S

I n v i e w o f w h a t h a s b e e n s t a t e d a b o v e r e g a r d i n g t h e i n a d e q u a c y o f m o d e l l i n g

t e c h n i q u e s a s w e l l a s l a c k o f r e q u i s i t e s i g n a l s f o r t h e o p e r a t o r f r o m i n s t r u m e n t a t i o n

f o r j u d g i n g t h e e x i s t e n c e a n d a d e q u a c y o f t h e r m o s y p h o n c o o l i n g , a p r o p o s a l h a s

b e e n e v a l u a t e d f o r c u t t i n g i n t h e s e c o n d c o m p o n e n t o f t h e u l t i m a t e h e a t s i n k , i . e .

t h e s h u t d o w n c o o l i n g s y s t e m , d i r e c t l y o n l o s s o f c l a s s I V p o w e r . T h e S C S c o n s i s t s

o f a p u m p ( F i g . 1 ) w h i c h t a k e s P H T w a t e r f r o m t h e r e a c t o r o u t l e t h e a d e r , p u t s i t

t h r o u g h a s t a n d b y c o o l i n g h e a t e x c h a n g e r ( H X ) a n d a d m i t s t h e c o l d w a t e r i n t o

t h e i n l e t h e a d e r t o c o m p l e t e t h e c i r c u i t t h r o u g h t h e r e a c t o r c o r e t o t h e o u t l e t

h e a d e r o n t h e o t h e r s i d e o f t h e f i g u r e - o f - e i g h t c o n f i g u r a t i o n . T h e h e a t e x c h a n g e r

i s c o o l e d b y p r o c e s s w a t e r .

3 . 1 . S C S e v a l u a t i o n

T h e c u r r e n t p r o p o s a l i s t o r e g u l a t e t h e f l o w o f P H T w a t e r t h r o u g h t h i s s y s t e m

t o b e a b l e t o r e j e c t a d e s i r e d p o w e r t o t h e p r o c e s s w a t e r s u c h t h a t e i t h e r t h e P H T

s y s t e m p r e s s u r e c a n b e m a i n t a i n e d o r c a n b e c o o l e d a t a d e s i r a b l e r a t e . T h e p e r ­

f o r m a n c e o f t h e s h u t d o w n c o o l i n g s y s t e m a n d h e a t e x c h a n g e r h a s b e e n e v a l u a t e d

a n d t h e r e s u l t s a r e g i v e n i n F i g . 5 . I t c a n b e o b s e r v e d t h a t t h e p o w e r t r a n s f e r r e d

b y t h e s y s t e m i s a f u n c t i o n o f t h e p r i m a r y f l o w a n d t h e r e a c t o r o u t l e t t e m p e r a t u r e

a n d b y c o n t r o l l i n g t h e f l o w t h e p o w e r i s t r a n s f e r r e d , a n d h e n c e t h e s y s t e m

s h r i n k a g e a s w e l l a s p r e s s u r e c a n b e m a i n t a i n e d i n a m u c h b e t t e r m a n n e r .

T h e c u r r e n t d e s i g n p e r m i t s o p e r a t i o n [ 1 ] o f t h e s h u t d o w n c o o l i n g s y s t e m

o n l y w h e n t h e P H T t e m p e r a t u r e h a s b e e n b r o u g h t d o w n t o 3 0 0 ° F ( 1 4 8 . 9 ° C )

b e c a u s e o f t h e l i m i t a t i o n o f s e a l c o o l i n g o f t h e S C S p u m p a n d p o s s i b l e f a t i g u e

f a i l u r e d u e t o s t r e s s c y c l i n g . I t i s p r o p o s e d t o i n c r e a s e t h e s e a l c o o l i n g c a p a c i t y

b y a u g m e n t a t i o n a n d t o c a r r y o u t m i n o r c h a n g e s o n t h e p r o c e s s w a t e r s i d e o f t h e

h e a t e x c h a n g e r s o t h a t n o b o i l i n g t a k e s p l a c e o n t h e s e c o n d a r y s i d e u n d e r c o n ­

t r o l l e d c o o l i n g c o n d i t i o n s .

IAEA-SM-268/22 57

D20 FLOW RATE (L/min)

F IG . 5. Steady-state performance o f SCS-HX.

A d e t a i l e d s t r e s s a n a l y s i s o f t h e S C S h e a t e x c h a n g e r h a s a l s o b e e n , p e r f o r m e d ,

i n c l u d i n g c o n s i d e r a t i o n o f t h e f a t i g u e s t r e n g t h o f t h e t u b e , t u b e s h e e t a n d s h e l l ,

a n d i t h a s b e e n f o u n d t h a t t h e m i n i m u m n u m b e r o f c y c l e s t h a t a f f e c t t h e t u b e

s h e e t i s 1 2 0 0 , w h i c h i s q u i t e a d e q u a t e f o r t h e f r e q u e n c y o f t h e n e e d t o c u t i n t h e

s y s t e m d u r i n g t h e l i f e t i m e o f t h e p l a n t .

4 . P R O B L E M S O F D I R E C T O P E R A T I O N O F S C S

T h e p o s s i b i l i t y o f t h e p r o c e s s w a t e r b o i l i n g o n t h e s e c o n d a r y s i d e o f t h e S C S

h e a t e x c h a n g e r h a s b e e n m e n t i o n e d . I t i s p r o p o s e d t o o v e r c o m e t h i s b y m a i n t a i n i n g

a d e q u a t e p r e s s u r e t o s u p p r e s s b o i l i n g o n t h e s e c o n d a r y s i d e .

T h e m a i n p r o b l e m , h o w e v e r , c e n t r e s o n p r e v e n t i o n o f c a v i t a t i o n o f t h e S C S

p u m p . T h i s p u m p s t a y s a h e a d o f t h e h e a t e x c h a n g e r s o t h a t i t s s u c t i o n l i f t i s u s e d

58 GHOSH et al.

SCS-HX

SCHEME I

SCHEME II

F IG . 6. Suggested schemes fo r SCS operation.

f o r m a i n t a i n i n g h e a d e r l e v e l c o n t r o l d u r i n g P H T s y s t e m m a i n t e n a n c e . T h e s y s t e m

o f t r a n s f e r r i n g t h e p u m p a f t e r t h e h e a t e x c h a n g e r b y v a l v i n g a n d p i p i n g a n d

b r i n g i n g i t b a c k a h e a d f o r h e a d e r l e v e l c o n t r o l r e q u i r e m e n t s p o s e s s e v e r e l i m i t a t i o n s

o n s p a c e a n d m a i n t a i n a b i l i t y . T w o a l t e r n a t i v e s a r e b e i n g s e r i o u s l y c o n s i d e r e d f o r

i m p r o v i n g t h e p u m p p e r f o r m a n c e a n d a v o i d i n g c a v i t a t i o n . T h e s u g g e s t e d s c h e m e s

a r e s h o w n i n F i g . 6 . B y p a s s i n g o f p a r t o f t h e f l o w f r o m t h e o u t l e t o f t h e h e a t

e x c h a n g e r t o t h e p u m p i n l e t o r p r o v i s i o n o f a c o l d - w a t e r a c c u m u l a t o r a h e a d o f t h e

p u m p a r e b o t h b e i n g c o n s i d e r e d a n d d e t a i l s a r e n o w b e i n g w o r k e d o u t .

5 . C O N C L U S I O N S

1 . T h e t h e r m o s y p h o n p e r f o r m a n c e o f P H W R s y s t e m s i s a c o m p l e x

p h e n o m e n o n b e c a u s e o f t h e c i r c u i t g e o m e t r y ( h o r i z o n t a l c h a n n e l s ) . C r a s h c o o l i n g

IAEA-SM-268/22 59

c o n d i t i o n s c r e a t e v o i d i n g i n h o r i z o n t a l c h a n n e l s t h u s a c c e n t u a t i n g t h e u n c e r t a i n t i e s

i n t h e s y s t e m p e r f o r m a n c e .

2 . T h e r e i s a l a r g e d i f f e r e n c e o f o v e r 5 m o f h e i g h t b e t w e e n t h e t o p - m o s t a n d

t h e b o t t o m - m o s t c h a n n e l s i n t h e r e a c t o r c o n n e c t e d t o t h e s a m e i n l e t a n d o u t l e t

h e a d e r s . M o d e l l i n g u n c e r t a i n t i e s c r e a t e f u r t h e r d i f f i c u l t i e s i n t h e a s s e s s m e n t o f

t h e s i t u a t i o n .

3 . T h e d e s i g n o f t h e s y s t e m i n v o l v e s l i m i t a t i o n s o f s p a c e a n d m a i n t a i n a b i l i t y .

C o n s i d e r a t i o n i s t o b e g i v e n t o d e l i n k i n g t h e S C S f r o m o t h e r n e e d s s o t h a t e f f e c t i v e

u s e c a n b e m a d e o f i t s c a p a b i l i t y .

4 . C r a s h c o o l i n g b y c e r t a i n s p e c i f i e d r a t e s o f s t e a m b l o w i n g r e s u l t s i n

t h e r m a l s h o c k s t o t h e e q u i p m e n t a n d q u e n c h i n g o f t h e P H T s y s t e m w i t h l o s s o f

c i r c u l a t i o n . T h i s c a n b e e l i m i n a t e d b y p r o p e r l y d e s i g n e d c o n t r o l l e d c o o l i n g w i t h

t h e u s e o f t h e S C S .

A C K N O W L E D G E M E N T S

T h e a u t h o r s w i s h t o t h a n k t h e i r c o l l e a g u e s R . N . R a y , B . F . C h a m a n y a n d

S . K . C h a k i f o r v a l u a b l e d i s c u s s i o n s .

R E F E R E N C E S

[1] Rajasthan A tom ic Power Station Safety Report, V ol. 1, Department o f Atom ic Energy, Governm ent o f India.

[2] RAO, S.B., et al., “ Therm osyphon analysis o f Rajasthan atom ic power stations primary heat transport system” , Paper (H M T-101-81) presented at 6th National Heat and Mass Transfer Conference, Madras, India, 1981.

[3] ZV IRIN , Y ., A review of natural circulation loops in pressurized w ater reactors and other systems, Nucl. Eng. Des. 67 (1 9 8 1 )2 0 3 -2 2 5 .

IAEA-SM-268/32

P O S T L O S S O F C O O L A N T

A C C I D E N T M A N A G E M E N T

A . N A T A L I Z I O * , J . G . C O M E A U * * , D .W . B L A C K *

* A t o m i c E n e r g y o f C a n a d a L i m i t e d ,

M i s s i s s a u g a , O n t a r i o

* * N e w B r u n s w i c k E l e c t r i c P o w e r C o m m i s s i o n ,

L e p r e a u , N e w B r u n s w i c k

C a n a d a

A b s t r a c t

POST LO SS O F C O O L A N T A C C ID E N T M ANAGEM ENT.In Canada, it is the responsibility o f the licensee, w ith the assistance o f the designer o f

nuclear pow er plants, to ensure that the nuclear plant design with its administrative procedures provides adequate protection for the health and safety o f operating staff and the public. A de­tailed post loss o f coolant (LO C) accident management study is one o f the procedures used to support assurances given to the A tom ic Energy Control Board, the Canadian regulatory agency, on this point. The paper describes a m ethodology to assess the effectiveness o f post- LOC accident procedures and the plant design. Some results and recommendations from recent studies on CAN D U reactors are discussed. The m ethodology and com puter codes developed as part o f this review process are general and are applicable to other nuclear plants as well as to CANDU.

1. INTRODUCTION

Under the Canadian regulatory process, the licensee of a nuclear power plant has the responsibility to implement design features or to institute emergency procedures as necessary to ensure that plant staff and the general public are protected from the consequences of plant accidents.

As a part of the effort to carry out this responsibility, studies have been undertaken by utilities with nuclear plants under construction to demonstrate that the main control room would be habitable in the event of a loss-of-coolant (LOC) accident.More recently, this activity has been extended to include all operating plants and the scope has been expanded. All nuclear power plants operating or under construction are now required to perform a plant-wide post-LOC operations review.

61

62 NATALIZIO et al.

This review, prompted by an increased focus on the operational aspects of post-accident management by the industry in general, is additional to the reviews required to assess and assure the environmental qualification of equipment needed to keep the plant in a safe state following an accident.

The purpose of the review is to demonstrate a workablepost-accident operations capability by ensuring that:

the main control room remains habitable under the "worst case" LOC accident

the operating staff can carry out essential functions required to place and maintain the plant in a safe state, thereby protecting the public

the plant emergency procedures can be implemented and personnel can be evacuated safely if required

the design of the plant is such that the operating staff hasthe flexibility to respond as appropriate to a real accident situation, and that they are not hampered in so doing by procedures which might be included only to cater to "worst case" scenarios.

2. ACCIDENT MANAGEMENT PHILOSOPHY

Accident management is an in-depth process which begins at the design stage, at which time design decisions are made to minimize or reduce the potential for an accident. The design basis is established in the safety design guides which specify requirements for environmental qualification, redundancy, diversity, separation, etc. These requirements ensure that essential plant components and systems are capable of responding to accident conditions.

Throughout the design and construction stages design basis accident analyses are performed, and reported in the plant safety report, to demonstrate that the plant design meets the site release guidelines. These analyses confirm the capability of the plant safety systems to respond to accidents. During the latter stages of construction a further set of analyses are performed. These are event sequences/fault tree analyses which give an independent check of the plant accident management/recovery capability. These analyses assist the preparation of plant procedures. The adequacy of these procedures and the "as built" plant is then further confirmed by a post-LOC operations review.

IAEA-SM-268/32 63

The overall purpose of this post-LOC accident operations review is to provide adequate assurances of the plant capability to handle an accident. The process involves a review of emergency plans and plant operating procedures to identify all the required operator actions. Generally, emergency plans are those procedures which detail the emergency preparedness and radiological protection aspects of the station, such as response groups, communications, resources, evacuation procedures, and emergency procedures. In general, there are two types of plant operating procedures: event-specific procedures and system-specific procedures.

Event-specific procedures are those produced to enable the operator to respond to plant transients or accidents on a plant-wide basis. These procedures define the short and long- teAn actions necessary to place and maintain the plant in a safe state. They consider the interaction of the various plant systems.

System-specific procedures refer to the detailed operating procedures related to a single system; for example, valving sequences for that system.

It is important that in addition to the above procedures, proper plant maintenance, equipment testing and operator training programs are implemented. Equally important is a program to collect, collate and feed back relevant information on reactor incidents which could point out the need for changes to existing plant design and/or procedures.

The post-LOC accident management review is performed with source terms derived from a "worst case" LOC accident. By necessity this assumption provides a very conservative approach when assessing radiation fields that might be encountered in various areas of the plant after a real accident. If emergency procedures are planned entirely on the basis of the "worst case" scenario results, some areas of the plant could be designated as inaccessible after a LOC accident. However, in the event of an actual LOC accident, these very same areas could in fact be safe and access to them might help to mitigate the accident consequences. It is therefore very important in assessing "worst case" LOC accident results to ensure that the decision to render specific areas accessible or inaccessible is made only after radiation fields are verified by radiation monitors, after a real accident has occurred.

An important aspect of the post-LOC study is that it can be readily used to evaluate the relative merits of alternative emergency evacuation routes and staff assembly areas or the relative merits of alternative design changes (if required).Such studies are also important in determining the most effective location for radiation monitors and alarms.

NATAUZIO et al.

FIG.l. Post-LOCaccident management methodology.

IAEA-SM-268/32 65

In Canada, the maximum permissible whole body dose to an individual at the plant boundary arising from a "worst case"LOC accident is 250 mSv[l], Although, for such severe accident conditions, a cumulative dose of 250 mSv would also be permissible for operating staff, considerable effort is made to keep predicted accumulated doses to operating staff below 100 mSv. This general guideline as well as the ALARA (As Low As Reasonably Achievable) principle serve as criteria for assessing the results of the radiation study.

3. POST-ACCIDENT OPERATIONS REVIEW PROCESS

During and after a LOC accident the major efforts of plant staff are directed to ensuring that the following conditions are established and maintained, namely;

reactor shutdown fuel coolingcontainment of radioactive materials monitoring of key plant parameters.

These conditions are essential to ensure the safety of both the public and the operating staff, and set the prioritiesfor the post-accident operations review.

The process generally applied in Canada is illustratedin Figure 1. The process is an iterative one and is describedbelow.

3.1 Identification of Operator Actions/Emergency Procedures

A review of safety assessment documentation (safety reports and event sequence/fault tree analyses), emergency planning procedures, and plant operating procedures is conducted to identify operator actions for essential plant functions and emergency planning functions during and after an accident. The result is a list of operator actions and staff emergency actions whose practicability must be verified.

At this point in the process, actual field locations of equipment, control panels, valves, etc. are inspected for accessibility by several plant walkthroughs. This is generally done at the end of the construction p h a s e . For each operator action identified above the following items are considered:

Feasibility of performing actions from the control room.Location of field station at which action must be carried out.

66 NATALIZIO et al.

OPERATOR ACTION PLANT LOCATION TIME AFTER LOC DURATION

1 A TA ДТАВ TB ДТВС TC ДТС

2 - • - -

3 - - -

••••

N - - -

F IG .2 . Operator action matrix.

Route to get to field station.Emergency evacuation routes and assembly areas.Time or times action is to be performed.Expected duration of action.

These generate a matrix of operator actions as illustrated in Figure 2.

It is possible, at this stage, to identify the need, if it exists, for design and/or procedural changes based on considerations other than radiation. Hence, such modifications can be implemented before the radiation study is completed.

3.2 Radiation Study Parameters

As indicated in Figure 1, the next step is to identify all of the radiation sources which could affect each plant location listed in the operator action matrix. These are described in detail in Section 4.1. Doses and dose rates are then calculated for each of the plant locations. To facilitiate what is an iterative process a computer program was developed to do thesecalculations. This program is described in Section 4.3. Doserates and doses are calculated for different times after a LOC

IAEA-SM-268/32 67

accident; hence, the end product is a three-dimensional matrix giving the contribution of each radiation source, at different times, for each plant location.

3.3 Study Review and Recommendations

Finally, the acceptability of individual operator actions and assembly areas, given the respective radiation doses/fields, is established. A final list of required design and/or procedural changes is produced and implementation of these changes is initiated. It is at this final stage that significant interaction between operating staff, health physics staff and plant designers is required.

4. POST-LOC RADIATION STUDY

4.1 Post-LOC Radiation Sources

In the standard 600 MW(e) CANDU plants, moderator and primary coolant system components are located inside containment. Hence, after a LOC accident, the potentially contaminated locations (radiation sources) outside containment are generally limited to parts of the emergency core cooling (ECC) system and reactor building ventilation system.

ECC System

CANDU reactors have a multi-stage ECC system consisting of a high and/or medium pressure injection stage, and a low pressure stage which recirculates water from the reactor building sump. The pumps and heat exchanger of the low pressure stage are located outside containment and after a LOC accident these components and associated piping become sources of radiation outside containment.

Reactor Building Ventilation System

In the standard 600 MW(e) plants components of the reactor building ventilation system are located inside the service building. These consist of vapour recovery driers, filter trains with the associated ducting, and a stack. After a LOC accident, these components would be isolated from containment on high containment pressure or high activity level. Hence, they do not become major sources of radiation, unless there is a failure of containment isolation. In Canadian licensing practice, failure of containment to isolate is a design basis accident.

68 NATALIZIO et al.

The wall thickness of the containment boundary provides shielding against radioactivity within containment. Therefore, most of the dose rates from activity inside containment are due to active material located at or near penetrations in the containment building wall. The equipment airlock and personnel airlock are the largest of these penetrations. In one plant (a prototype CANDU), the reactor building dome is a relatively thin steel hemisphere, rather than thick concrete, as is the case for all subsequent plants. For this prototype reactor, scattering of radiation in the air above the dome was also considered a source for the study.

4.2 Radiation Source Terms

In these studies, the LOC is assumed to be aggravated further by functional failure of one of the special safety systems, (ECC or containment systems). This means in effect that consideration is given to possible magnitude, and to release point. In practice, post-LOC radiation fields are based on radiation source terms taken from "worst case" LOC accidents analyzed in the safety report. The "worst case" LOC accident is bounded by a LOC coincident with failure of the ECC system.Hence, fission product source terms based on a LOC coincident with loss of the ECC system provide a conservative estimate of radiation doses for the "worst case" LOC accident.

In addition to the above, source terms based on a LOC accident in which ECC is assumed to operate properly, coincident with failure of containment to isolate, are also considered.

The "worst case" LOC accident gives the largest releases of radioactivity to containment. Although the ECC system has been assumed unavailable, the same accident is used to define source terms for the ECC system piping located outside the reactor building. This assumption covers the possibility that an operator might initiate the low pressure ECC stage, after failure of the automatic high and/or medium pressure injection stages.

The other accident allows a transfer of activity to process equipment located outside containment; for example, to the reactor building ventilation system equipment and the vapour recovery system equipment.

Containment Envelope

Radioactive Releases From Fuel

Typical releases of radioactivity from the fuel for these accidents are given below (numbers are in percent of total

IAEA-SM-268/32 69

core inventory). These estimates are based on fuel behaviour and figsion product release codes appropriate to accident analysis.

"Worst case" LOC - Halogens - 10%- Noble gases - 10%- Particulates - 3%

LOC + Loss of Containment - Halogens - 0.04%Isolation (ECC assumed to - Noble Gases - 0.04%operate properly) - Particulates - 0.02%

It should be noted that although the above fission product releases are given as percentages of the total core inventory, in the standard 600 MW(e) CANDU reactors, only half of the core is affected in a "worst case" LOC accident. The reason is that the primary heat transport system is divided into two separate heat transport loops which automatically isolate during a LOC accident. Hence, only the loop in which the LOC occurswill have the potential for fuel failures.

Another aspect worthy of note is that even for a "worst case" LOC accident, bounded by a LOC coincident with a loss of ECC, the fission product releases are relatively small. The reason is that CANDU reactors have a cool moderator which acts as a large heat sink. Hence, gross fuel melting is prevented and fission product releases are small fractions of total inventory.

The radioactivity releases for the LOC and loss of containment isolation event result from fuel failure in a high power channel. For this event, the fuel bundles are assumed to be ejected from the channel and to fracture on impact, resultingin a release of a significant portion (10%) of the total channelfission product inventory.

Distribution of Radioactivity

Although there is much evidence to indicate that fission products, especially the halogens, are trapped in significant fractions within the reactor components after they are released from the fuel, it is assumed, in these studies, that they are transported from the fuel to containment without any such retention

Furthermore, the assumed distribution of fission products within containment depends on the radiation source being considered For example, if photon transmission through the containment structure is being considered as the source of radiation, then the amount of particulate and halogen plateout on the containment walls is maximized. Similarly, if the ECC system piping is being considered as the radiation source then the amount of washout of particulates and halogens into the ECC sump water is maximized.

70 NATALIZIO et al.

T A B L E I . T Y P I C A L D I S T R I B U T I O N O F A C T I V I T Y A S S U M E D F O R

T H E S E S T U D I E S

Radiation sourceDistribution (percent o f activity released from fuel)

Halogens Noble gases Particulates

EC C piping (in water) 50 0 100

Containment (on walls) 50 0 50

Containment (airborne) 50 100 50

Totals 150 100 200

Table 1 summarizes the assumed distribution of radioactivity commonly used in such studies. It is clear from the totals in Table I that the approach used is conservative.

4.3 Computational Methodology

The computational methodology for radiation doses and dose rates is shown in Figure 3. There are four inputs:

(1) The fission product source terms and distribution of activity, which are obtained from the safety report accident analysis.

(2) The source strength of a unit quantity of radioactive material (MeV/s) obtainable from an isotope generation and depletion code, such as ORIGEN [2].

(3) Plant geometry - location of radiation sources, location of dose point, location of shielding walls or material.

(4) The dose rate per unit source strength which can be obtained from a radiation transport code such as QAD-5K [3].

Each input to the overall computation is either from a standard package such as ORIGEN or QAD-5K, or has been verified in-house. As an example of the in-house verification work on radiation codes, Figure 4 illustrates code capability by comparing gamma air-scattering code predictions against dose rate measurements taken at Douglas Point N.G.S.

IAEA-SM-268/32 71

KEY

P - dose po i nt locations - sourc e locationt - time after accident9 - chemi cal element groupe - gamma ray energy

F IG .3 . B lock diagram o f com puter method.

The dose rates outside the Douglas Point plant containment building, shown in Figure 4, are from argon-41 in the containment atmosphere. The double peak curve demonstrates that the total dose rate has two contributions: direct radiation from thecontainment building dome, and radiation scattered in the air surrounding the dome. The code has captured the trends of the measured data very well.

72 NATALIZIO et al.

F IG .4. Comparison o f code predictions to measurement.

5. RESULTS OF OPERATIONS REVIEW

The purpose of the operations review is to provide a final check on the plant "as built", and the procedures "as written". It may reveal a need for further changes in equipment and procedures but is the last iteration in a long design process. To date, post-LOC operations reviews have been performed for domestic CANDU reactors. These reviews were confirmatory in nature. That is, the "as built" plant, and its operating procedures, were reviewed to confirm their adequacy. For the most part, their adequacy was confirmed. In some areas, however, recommendations for additional shielding, remote control operation of valves and/or procedural changes have resulted from the review.

IAEA-SM-268/32 73

F IG .5. Installation o f a shielding wall beside the main airlock to protect the main control room.

74 NATALIZIO et al.

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.

IAEA-SM-268/32 75

The study reconunendations are categorized into two classes: design changes and procedural changes. In each ofthese categories the reason for the change was one or more of the following:

improve access to specific locationsallow operability of equipment in inaccessible locations (i.e. eliminate the need for access)allow monitoring and/or maintenance of essential equipment allow plant assembly and evacuation ensure confinement of contamination.

The following design/procedural changes are typical examples intended to illustrate the nature of the changes arising from a number of post-LOC operations reviews. These reviews were done on plants that were already in operation or at the final stages of construction.

Design Changes

A shielding wall was installed along the side of the Gentilly-2 N.G.S. main airlock, to protect the main control room from radiation passing through the airlock penetration. Figure 5 shows this wall. (Accessibility improvement, allow control room operations)

A shielding wall was installed beside the Point Lepreau N.G.S. reactor building ventilation system exhaust filter, to protect the main control room from the potentially active filter. Figure 6 shows this wall. (Accessibility improvement, ensure continued control room operations capability)

Remotely-operated isolation of instrument air to the Gentilly-2 reactor building has been adopted, because the isolation valves are in a high dose rate area beside a reactor building wall penetration. (Permit operability of equipment)

At Point Lepreau the ECC pump switchgear was relocated from the vicinity of the ECC pump pit to an accessible location in the secondary control room. (Permit operability and maintenance of equipment)

Procedural Changes

To cater to the requirement to isolate service air to the reactor building (valves are in inaccessible area), the service air operating manual for Point Lepreau G.S. now requires these valves to be normally locked closed. (Eliminate need for access)

76 NATALIZIO et al.

- A recommendation in the Point Lepreau review was that theReactor Building Underdrainage Operating Manual incorporate a procedure for periodic sampling subsequent to а Ю С accident. (Allow monitoring)

An assembly area on the upper floor of the Douglas Point N.G.S. administration building could potentially receive significant dose rates from radioactivity present in the reactor building dome after a LOC accident. A high dose rate alarm has been installed in the assembly area. Should the alarm be set off as a result of a LOC accident, operating staff would not enter the area and would go to an alternate assembly area on a lower floor. (Allow plant assembly and evacuation).

A post-LOC operations review is a tool which can and will identify even minute plant/procedural deficiencies; hence, it should not be surprising that the method gives rise to changes. What is surprising is that, given the conservative assumptions incorporated in the radiation study, and the use of loss of ECC sóurce terms, the number of design changes have been few.

It is very important, when assessing the need for changes, to also recognize the need for operating staff flexibility to respond as appropriate to a real accident; and that they are not hampered in so doing by procedures which might be included only to cater to "worst case" accidents.

A key result of the radiation calculations performed for these post-LOC operations reviews is that the major contribution to the predicted dose rates, at short times, is from the halogens, specifically iodine. At longer times (several weeks and beyond) the iodines decay to very low levels and the long-lived particulates become dominant. However, the dose rates at longer times are not a large fraction of the total dose. This is an important result because present research indicates that iodine source terms are much lower than previously assumed, due to chemical reactions that occur within the reactor core. This would lead to lower dose estimates.

6. CONCLUSION

A relatively simple methodology has been developed to assist plant operators in verifying the adequacy of emergency procedures. It also allows plant personnel to be better prepared to cope with post-LOC accident management, should the situation arise. The methodology and computer code developed for this purpose are general and are applicable to other nuclear plants, as well as to CANDU.

IAEA-SM-268/32 77

A post-LOC operations review is the final stage of a long and exhaustive review process, to ensure the safety of plant personnel and the general public. It is, however, in our opinion, an essential part of this review process. In the past, the post- LOC operations review has been performed either at the operating stage or just prior to it. In our view, such reviews should, in future, be done in two stages: an initial review at the earlystages of a project and a final confirmatory review at the final stages of the project.

ACKNOWLEDGEMENTS

The authors wish to acknowledge the efforts of all people associated with the initiation and implementation of the various post-LOC accident operations reviews for CANDU plants. Particular thanks are due to J.D. Sommerville, J.R. Humphries and L. Pease for their helpful comments and encouragement in writing this paper. Thanks are also due to M. Lombardo who typed the manuscript.

REFERENCES

1. HURST, D.G., BOYD, F.C., "Reactor Licensing and Safety Requirements", Atomic Energy Control Board Report No. AECB- 1059, (1972).

2. BELL, M.J., "ORIGEN - The ORNL Isotope Generation and Depletion Code", ORNL-4628, Oak Ridge, Tennessee, U.S.A. (1973).

3. SMITH, T.W., KNIES, R.J., "QAD-5K Operating Manual", Technical Note RL-251, Brown Engineering Company Inc., Huntsville, Alabama, U.S.A. (1967).

L ’A P P R O C H E P A R E T A T :

U N E N O U V E L L E C O N C E P T IO N

D E S P R O C E D U R E S D E C O N D U I T E

P O S T - A C C I D E N T E L L E

H . S U R E A U , G . D E P O N D

S e r v i c e E t u d e s e t p r o j e t s t h e r m i q u e s e t n u c l é a i r e s ,

E l e c t r i c i t é d e F r a n c e ,

P a r i s L a D é f e n s e

A . O L I O T

S o c i é t é F r a m a t o m e ,

P a r i s L a D é f e n s e ,

F r a n c e

V~~--" IAEA-SM-268/53

A b s t r a c t - R é s u m é

PL A N T STA T E A PPRO ACH : A NEW CON CEPT IN PO ST-ACCID EN T O PER A TIO N

PROCED U RES.

Normal accident procedures are based on a diagnosis o f the accident-initiating incident and on a predetermined succession o f events in the most probable sequences. This ‘event’ approach does not allow all conceivable accident situations to be taken into account or the diagnosis to be reviewed and updated in the event that the system deviates from the pattern predicted by the first diagnosis. These shortcomings can be overcome by a ‘state’ approach based on the observation o f physical parameters, analysis o f the thermohydraulic status o f the system and definition o f operator action. This is done continuously throughout the post-accident phase. Studies carried out have identified all the cooling states o f a PWR boiler, revealed the need for additional instrum entation to give a comprehensive description o f these states and indicated that it is possible to establish a direct relationship between a state and the appropriate action. The procedures used in French pow er plants have benefited from this work: a number o f important mechanisms such as the safety injection system have been made independent o f accident- initiating events and accident sequences through the use o f continuous plant state criteria.A further application o f the state approach, which is still restricted by existing instrumentation, is effected by the safety engineer who exercises continuous post-incident surveillance. Based on very precise plant state criteria, this approach makes it possible either to confirm the main safety measures dictated by the sequential procedure being applied or to decide to use the emergency procedure which defines the action required as a function o f the state o f the boiler and the available systems and is used where the normal procedures are no longer valid. Work is continuing to achieve more system atic application o f the state approach with additional instrumentation.

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80---------- / SUREAU et al.

L ’APPROCH E P A R ET A T : UNE N O U V E L LE CONCEPTIO N DES PR O CED U RES DE

CON D U ITE PO ST-ACCID EN TELLE.Les procédures accidentelles habituelles sont basées sur un diagnostic de l ’incident initiateur

et sur un déroulement prédéterminé des séquences les plus probables. Cette approche «par événement» ne permet pas de couvrir toutes les situations accidentelles imaginables et de réactualiser le diagnostic pour une évolution du système non conform e aux prévisions du premier diagnostic. Ces lacunes peuvent être comblées par une approche «par état», basée sur l ’obser­vation des paramètres physiques, l’ analyse de l’ état therm ohydraulique du système et la défini­tion des actions de l ’opérateur, et ceci d’une manière permanente pendant toute la phase post­accidentelle. Les études effectuées ont permis d’identifier l ’ensemble des états de refroidissement d’une chaudière REP, de faire apparaître la nécessité d’une instrumentation complémentaire par la caractérisation com plète de ces états, et de montrer la possibilité d’établir une relation directe état-actions. Les procédures utilisées dans les centrales françaises bénéficient, entre autres, de ces travaux: certaines actions importantes, par exem ple sur l’injection de sécurité, ont été rendues indépendantes des événements initiateurs et des séquences accidentelles, par utilisation de critères permanents d’états. Une autre application de l ’approche par état, encore limitée par l’instrum entation actuelle, est confiée à l ’ingénieur de sûreté qui exerce une surveillance permanente après incident. A partir de critères très précis d’états, elle permet soit de confirmer les principales actions de sûreté demandées par la procédure séquentielle en cours d’application, soit de décider d’utiliser la procédure d’urgence qui définit les actions requises en fonction de l’ état de la chaudière et des systèmes disponibles, au-delà du domaine de validité des procédures habituelles. Les travaux se poursuivent pour une utilisation plus systématique de l ’approche

par état avec une instrumentation complémentaire.

1 . L ’ I N T E R A C T I O N H O M M E - M A C H I N E E N S I T U A T I O N A C C I D E N T E L L E

L a s û r e t é d u r e f r o i d i s s e m e n t d e s p r o d u i t s r a d i o a c t i f s d u c o m b u s t i b l e n u c l é a i r e

e n s i t u a t i o n a c c i d e n t e l l e r e p o s e , a u - d e l à d e s p r e m i è r e s m i n u t e s r e d e v a b l e s a u x

a u t o m a t i s m e s , s u r u n e b o n n e c o n c e p t i o n d e l ’ i n t e r a c t i o n h o m m e - m a c h i n e .

L e s é v é n e m e n t s p e r t u r b a t e u r s i n d u i s e n t u n e d é g r a d a t i o n d e l ’é t a t d u s y s t è m e

q u i e s t a p p r é h e n d é e p a r l ’ o p é r a t e u r g r â c e a u x i n f o r m a t i o n s d é l i v r é e s p a r d e s

c a p t e u r s e t p r é s e n t é e s , a p r è s t r a i t e m e n t , e n s a l l e d e c o m m a n d e . L ’o p é r a t e u r d o i t

a l o r s e f f e c t u e r u n d i a g n o s t i c e t e n g a g e r l e s a c t i o n s r e q u i s e s p o u r r a m e n e r l e s y s t è m e

d a n s u n é t a t s û r .

L e s p r o c e s s u s d e d i a g n o s t i c e t d ’a c t i o n c o r r e s p o n d a n t s s o n t p r é c i s é s d a n s d e s

p r o c é d u r e s p o s t - a c c i d e n t e l l e s é c r i t e s . U n e c o n c e p t i o n c o h é r e n t e d e l ’e n s e m b l e d e

c e s p r o c é d u r e s p e r m e t d e s t r u c t u r e r l e s a u t r e s é l é m e n t s d e l ’i n t e r a c t i o n h o m m e -

m a c h i n e : c a p t e u r s e t a c t i o n n e u r s n é c e s s a i r e s e t l e u r q u a l i f i c a t i o n a u x c o n d i t i o n s

p o s t - a c c i d e n t e l l e s , t r a i t e m e n t s e t p r é s e n t a t i o n d e s i n f o r m a t i o n s e t d e s c o m m a n d e s

e n s a l l e d e c o m m a n d e , o r g a n i s a t i o n d e l ’é q u i p e d e c o n d u i t e , f o r m a t i o n e t e n t r a î ­

n e m e n t d e s o p é r a t e u r s s u r s i m u l a t e u r s , e t c .

L a n é c e s s i t é d ’ a m é l i o r e r l ’e n s e m b l e d e c e s é l é m e n t s e n s i t u a t i o n a c c i d e n t e l l e

e s t a p p a r u e d e p u i s 1 9 7 9 a p r è s l ’ a c c i d e n t d e T h r e e M i l e I s l a n d , l a m i s e e n s e r v i c e

d e n o m b r e u s e s t r a n c h e s e t l ’ a n a l y s e d e s i n c i d e n t s r é e l s e t d e s t e s t s e f f e c t u é s s u r

IAEA-SM-268/53 81

s i m u l a t e u r : s i l e s y s t è m e R E P s e m b l e b i e n d o t é d e s m o y e n s p o t e n t i e l s d e s o r t i r

c o r r e c t e m e n t d ’u n t r è s g r a n d n o m b r e d e s i t u a t i o n s d é g r a d é e s , l e p r o b l è m e e s t d e

s a v o i r q u a n d e t c o m m e n t l e s m e t t r e e n o e u v r e . L a c o n c e p t i o n d u p r o c e s s u s d e

d i a g n o s t i c d e s s i t u a t i o n s e t d e d é c i s i o n d e s a c t i o n s s ’e s t a v é r é e ê t r e l e p o i n t e s s e n t i e l

à a m é l i o r e r , l e s m o y e n s m a t é r i e l s e t h u m a i n s p e r m e t t a n t u n e a p p l i c a t i o n c o r r e c t e

d e c e p r o c e s s u s d e v a n t e n s u i t e ê t r e a d a p t é s à c e t t e c o n c e p t i o n .

2 . I N S U F F I S A N C E D E S P R O C E D U R E S P O S T - A C C I D E N T E L L E S P A R

E V E N E M E N T

L e s p r o c é d u r e s p o s t - a c c i d e n t e l l e s à l a d i s p o s i t i o n d e l ’ o p é r a t e u r é t a i e n t

b a s é e s , j u s q u ’e n 1 9 8 0 , s u r u n e a n a l y s e s é q u e n t i e l l e p e s s i m i s t e d e s a c c i d e n t s

« e n v e l o p p e » s e r v a n t a u d i m e n s i o n n e m e n t d e s p r o t e c t i o n s e t d e s s y s t è m e s d e s a u v e ­

g a r d e .

C e s p r o c é d u r e s p a r é v é n e m e n t o n t é t é d e p u i s a m é l i o r é e s , d a n s l e u r c o n t e n u

t e c h n i q u e , à p a r t i r d ’é t u d e s p o s t - a c c i d e n t e l l e s p l u s r é a l i s t e s , e t , d a n s l e u r f o r m e , à

p a r t i r d u r e t o u r d ’e x p é r i e n c e d e s c e n t r a l e s e t d e s t e s t s s u r s i m u l a t e u r s .

L e d i a g n o s t i c d e l ’ é v é n e m e n t i n i t i a t e u r d o i t ê t r e e f f e c t u é e n t r e 5 e t

1 5 m i n e n v i r o n a p r è s l e d é c l e n c h e m e n t d ’u n e p r o t e c t i o n d u r é a c t e u r o u d ’u n e

a l a r m e , d é l a i n é c e s s a i r e à u n e p r e m i è r e « s t a b i l i s a t i o n » d e l ’é t a t d u s y s t è m e a p r è s

f o n c t i o n n e m e n t d e s a u t o m a t i s m e s d e s é c u r i t é d o n t l e b o n d é r o u l e m e n t e s t v é r i f i é .

L e d i a g n o s t i c d e l ’ é v é n e m e n t i n i t i a l c o n d u i t a u c h o i x d ’u n e p r o c é d u r e

s é q u e n t i e l l e d ’a c t i o n s p r é d é f i n i e s c o r r e s p o n d a n t a u d é r o u l e m e n t d ’u n e s é q u e n c e

a c c i d e n t e l l e p r é é t u d i é e .

C e t t e a p p r o c h e s é q u e n t i e l l e p a r é v é n e m e n t a c o n d u i t à u n j e u d e p r o c é d u r e s

a c c i d e n t e l l e s , d i t e s I , A o u H , c o u v r a n t l ’e n s e m b l e d e s s é q u e n c e s p r i s e s e n c o m p t e

d a n s l a c o n c e p t i o n d e s t r a n c h e s R E P .

M a i s l a r é a l i t é à l a q u e l l e p e u t ê t r e c o n f r o n t é l ’o p é r a t e u r n e s e c o n f o r m e r a p r o ­

b a b l e m e n t à a u c u n e d e s s é q u e n c e s p r é é t u d i é e s . E n e f f e t , u n e p r o c é d u r e s p é c i f i q u e

à u n é v é n e m e n t i n i t i a t e u r p e u t d i f f i c i l e m e n t c o l l e r d e m a n i è r e r é a l i s t e à l ’e n s e m b l e

d e s s i t u a t i o n s p o u v a n t r é s u l t e r à m o y e n t e r m e d e d i f f é r e n c e s d a n s l ’é t a t i n i t i a l d e

l a t r a n c h e , d a n s l e c o m p o r t e m e n t d e s m a t é r i e l s o u d a n s l e s d é l a i s d ’a c t i o n d e s

o p é r a t e u r s . I l e n r é s u l t e r a u n f l o u c r o i s s a n t d a n s l ’a p p l i c a t i o n d e l a p r o c é d u r e a u

c o u r s d u d é v e l o p p e m e n t d e l ’ i n c i d e n t . L ’ o p é r a t e u r r i s q u e d e s e p e r d r e s a n s s a v o i r

c e q u ’i l d o i t f a i r e e t l ’i n c i d e n t r i s q u e d e d é g é n é r e r e n a c c i d e n t p l u s s é r i e u x .

P a r a i l l e u r s , l e s p r o c é d u r e s p a r é v é n e m e n t n e p e u v e n t p a s c o u v r i r t o u t e s l e s

c o m b i n a i s o n s p o s s i b l e s d ’é v é n e m e n t s c o r r e s p o n d a n t à d e s c u m u l s d e d é f a i l l a n c e s

m a t é r i e l l e s e t / o u h u m a i n e s , s i m u l t a n é e s o u é t a g é e s d a n s l e t e m p s , t e l l e s q u e , p a r

e x e m p l e , l ’e r r e u r d e d i a g n o s t i c i n i t i a l , l a m a u v a i s e a p p l i c a t i o n d ’u n e p r o c é d u r e ,

l e c u m u l d e p l u s i e u r s a c c i d e n t s , l a p e r t e t o t a l e d ’u n s y s t è m e d e s a u v e g a r d e , e t c .

L a t e n t a t i o n d e m u l t i p l i e r l e s s é q u e n c e s p r é é t u d i é e s c o n d u i r a i t à m u l t i p l i e r

82 SUREAU et al.

c o r r é l a t i v e m e n t l e n o m b r e d e s p r o c é d u r e s d e c o n d u i t e e t r e n d r a i t l e d i a g n o s t i c ,

e t d o n c l e c h o i x d e l a b o n n e p r o c é d u r e , p r a t i q u e m e n t i m p o s s i b l e s .

L ’a p p r o c h e s é q u e n t i e l l e p a r é v é n e m e n t , q u i p e r m e t d ’o p t i m i s e r l a c o n d u i t e

s p é c i f i q u e à c e r t a i n s é v é n e m e n t s a c c i d e n t e l s , c o n d u i t à u n e i m p a s s e r e l a t i v e :

i m p o s s i b i l i t é d e r é a c t u a l i s e r l e d i a g n o s t i c e n c a s d ’é v o l u t i o n d u s y s t è m e n o n c o n ­

f o r m e a u x p r é v i s i o n s d u p r e m i e r d i a g n o s t i c e t i m p o s s i b i l i t é d e c o u v r i r t o u t e s l e s

s i t u a t i o n s a c c i d e n t e l l e s i m a g i n a b l e s .

C e t t e c r i t i q u e e s t b i e n i l l u s t r é e p a r l ’a c c i d e n t d e T h r e e M i l e I s l a n d e n 1 9 7 9 :

l ’e r r e u r d e d i a g n o s t i c i n i t i a l , f a i t e p a r l ’ o p é r a t e u r s u r l a b a s e d ’u n e i n s t r u m e n t a t i o n

d é l i v r a n t d e s i n f o r m a t i o n s a m b i g u ë s e n s i t u a t i o n p e r t u r b é e , a c o n d u i t à d e s a c t i o n s

i n a d é q u a t e s e t t r a n s f o r m é u n a c c i d e n t m i n e u r e n a c c i d e n t m a j e u r . L ’o p é r a t e u r ,

p r i s à c o n t r e - p i e d p a r d e s r é a c t i o n s i n a t t e n d u e s d u s y s t è m e à s e s a c t i o n s , a a p p l i q u é

s u c c e s s i v e m e n t s e p t p r o c é d u r e s d i f f é r e n t e s e t j a m a i s l a b o n n e . C e n ’e s t q u ’a p r è s

p l u s i e u r s h e u r e s q u e l ’e x p l o i t a n t p r i t c o n s c i e n c e d u f a i t q u e l e f l u i d e p r i m a i r e d e

r é f r i g é r a t i o n é t a i t p a s s é à l a s a t u r a t i o n p u i s e n d i p h a s i q u e a v e c d é n o y a g e e t

d é g r a d a t i o n d u c o e u r d u r é a c t e u r .

S u i t e à c e t t e e x p é r i e n c e m a l h e u r e u s e , l a p r e m i è r e i d é e a é t é d ’a j o u t e r

r a p i d e m e n t e n s a l l e d e c o m m a n d e u n e i n f o r m a t i o n s u r l a m a r g e à l a s a t u r a t i o n ,

p r e m i è r e m a n i f e s t a t i o n d ’u n d i a g n o s t i c p e r m a n e n t d ’ é t a t , p u i s d ’ e s s a y e r d e

g é n é r a l i s e r u n e s u r v e i l l a n c e d e s é t a t s d u s y s t è m e e n s i t u a t i o n p o s t - a c c i d e n t e l l e .

E n e f f e t , s i l e s s é q u e n c e s a c c i d e n t e l l e s p e u v e n t ê t r e m u l t i p l i é e s à l ’i n f i n i , l e s

é t a t s d e r e f r o i d i s s e m e n t e t d e c o n f i n e m e n t p o s s i b l e s d u s y s t è m e p e u v e n t p a r c o n t r e

ê t r e d é n o m b r é s . D e p l u s , l e s a c t i o n s r e q u i s e s d e l ’o p é r a t e u r , à u n i n s t a n t d o n n é

e t à l ’é c h e l l e d e t e m p s d e s o n i n t e r v e n t i o n , p e u v e n t e n g é n é r a l ê t r e d é d u i t e s d e

l a c o n n a i s s a n c e d e c e t é t a t d u s y s t è m e s a n s q u e l ’e n c h a î n e m e n t d e s é v é n e m e n t s

a n t é r i e u r s y a y a n t c o n d u i t a i t n é c e s s a i r e m e n t é t é i d e n t i f i é . U n e a p p r o c h e p a r é t a t

d e l a c o n d u i t e p o s t - a c c i d e n t e l l e d e v r a i t d o n c p e r m e t t r e d e s o r t i r d e l ’i m p a s s e

r e l a t i v e d e l ’a p p r o c h e s é q u e n t i e l l e p a r é v é n e m e n t .

3 . D E V E L O P P E M E N T D E L ’A P P R O C H E P A R E T A T

3 . 1 . O b j e c t i f

L ’o b j e c t i f d e l ’a p p r o c h e p a r é t a t e s t d ’e x p l i c i t e r u n e r e l a t i o n d i r e c t e

é t a t s - ^ a c t i o n s d e l ’o p é r a t e u r , c ’e s t - à - d i r e :

1 ) I d e n t i f i e r t o u s l e s é t a t s d e r e f r o i d i s s e m e n t p o s s i b l e s d e l a c h a u d i è r e , l e u r s

d o m a i n e s d e s t a b i l i t é , l e u r s t r a n s i t i o n s , e n r e c h e r c h a n t u n e e x h a u s t i v i t é q u ’i l

n ’e s t p a s p o s s i b l e d ’a t t e i n d r e p a r l ’a p p r o c h e s é q u e n t i e l l e p a r é v é n e m e n t e t

i n d é p e n d a m m e n t d e l e u r p r o b a b i l i t é d ’o c c u r e n c e .

2 ) C a r a c t é r i s e r c e s é t a t s p a r d e s g r a n d e u r s p h y s i q u e s m e s u r a b l e s .

IAEA-SM-268/ S3 83

F IG .l . Analyse des états de refroidissement du coeur et de la chaudière.

3 ) I d e n t i f i e r p o u r c h a c u n d e c e s é t a t s l e s a c t i o n s c o r r e c t i v e s e t / o u r é p a r a t r i c e s

r e q u i s e s d e l ’o p é r a t e u r .

4 ) C o n s t r u i r e u n e s y n t h è s e d e s p o i n t s p r é c é d e n t s o ù n e s o n t p l u s d i s c r i m i n é s

l e s u n s d e s a u t r e s q u e l e s s o u s - e n s e m b l e s d ’é t a t s n é c e s s i t a n t d e s a c t i o n s d i f f é r e n t e s .

5 ) E x p l i c i t e r l e p r o c e s s u s d e d i a g n o s t i c d ’é t a t c o r r e s p o n d a n t e t l e s r è g l e s d e

c o n d u i t e a s s o c i é e s .

6 ) I d e n t i f i e r l e s m e s u r e s p h y s i q u e s c o m p l é m e n t a i r e s e t l e s t r a i t e m e n t s

d ’i n f o r m a t i o n e n s a l l e d e c o m m a n d e n é c e s s a i r e s à l a m i s e e n o e u v r e d e c e p r o c e s s u s

d e d i a g n o s t i c d ’é t a t e t d ’a c t i o n .

84 SUREAU et al.

L e f o n c t i o n n e m e n t d ’u n e c h a u d i è r e n u c l é a i r e e s t a n a l y s é à p a r t i r d e s b i l a n s

f o n d a m e n t a u x d e m a s s e , é n e r g i e , i m p u l s i o n a p p l i q u é s a u x d i f f é r e n t s é l é m e n t s d e

c e l l e - c i e t q u i f o n t a p p a r a î t r e :

— l e c h e m i n e m e n t d e l ’é n e r g i e : p r o d u c t i o n , e x t r a c t i o n d u c o m b u s t i b l e , t r a n s p o r t ,

t r a n s f e r t h o r s c i r c u i t p r i m a i r e ;

— l e s t o c k a g e , d é s t o c k a g e d ’é n e r g i e d a n s l e s c i r c u i t s p r i m a i r e e t s e c o n d a i r e ;

— l e s t o c k a g e , d é s t o c k a g e d e s m a s s e s d ’ e a u d a n s l e s c i r c u i t s p r i m a i r e e t s e c o n d a i r e .

C e s d i f f é r e n t e s « c a t é g o r i e s » p h y s i q u e s s o n t a n a l y s é e s . P o u r c h a c u n e d ’e l l e s

d i f f é r e n t e s c o n f i g u r a t i o n s s o n t r e t e n u e s , c o u v r a n t l ’e n s e m b l e d e s p o s s i b i l i t é s , e t

i d e n t i f i é e s p a r d e s p a r a m è t r e s m e s u r a b l e s ( p r e s s i o n , n i v e a u , t e m p é r a t u r e e t l e u r s

d é r i v é e s , e t c . ) .

L e s c o m b i n a i s o n s p o s s i b l e s d e c e s c o n f i g u r a t i o n s s o n t r e g r o u p é e s e t m o n t r e n t

q u e ( f i g u r e 1 ) :

— l e s t o c k d e m a s s e d u f l u i d e p r i m a i r e ( M P ) e t l ’e x t r a c t i o n d e c h a l e u r d u c i r c u i t

p r i m a i r e d é f i n i s s e n t l e c o m p o r t e m e n t d e l a c h a u d i è r e , e n p a r t i c u l i e r l a c i r c u l a t i o n

d u f l u i d e p r i m a i r e e t l ’e x t r a c t i o n d e c h a l e u r d u c o m b u s t i b l e ;

— l ’e x t r a c t i o n d e c h a l e u r d u c i r c u i t p r i m a i r e e s t f o n c t i o n d e l a p r é s e n c e é v e n t u e l l e

d e g a z i n c o n d e n s a b l e s d a n s l e c i r c u i t , i d e n t i f i é e p a r l e p i n c e m e n t p r i m a i r e -

s e c o n d a i r e ( A T P S ) , e t d e l ’ é t a t d u c i r c u i t s e c o n d a i r e ( S ) ;

— l ’é t a t d u s e c o n d a i r e ( S ) d é p e n d l u i - m ê m e d e l ’é t a t d e c h a c u n d e s g é n é r a t e u r s d e

v a p e u r d é f i n i à p a r t i r d e l a m a s s e d u f l u i d e s e c o n d a i r e ( M S ) , d e l a p r e s s i o n v a p e u r

( P S ) e t d u n i v e a u d e r a d i o a c t i v i t é é v e n t u e l d u f l u i d e s e c o n d a i r e ( A C ) .

3.2. Analyse des états de refroidissement de la chaudière

3 . 3 . S y n t h è s e : g r i l l e é t a t s / a c t i o n s ( f i g u r e 2 )

L e s r é s u l t a t s d e l ’a n a l y s e p r é c é d e n t e p e r m e t t e n t d e c o n s t r u i r e u n e g r i l l e

d ’é t a t s p o u r l a c h a u d i è r e e t u n e g r i l l e d ’é t a t s p o u r c h a q u e g é n é r a t e u r d e v a p e u r .

C h a q u e é t a t d é f i n i d a n s c e s g r i l l e s e s t i d e n t i f i é à p a r t i r d e p a r a m è t r e s p h y s i q u e s

m e s u r é s e t d e l e u r é v o l u t i o n : m a s s e d e f l u i d e p r i m a i r e ( t a u x d e v i d e , n i v e a u c u v e ) ,

t e m p é r a t u r e s e t p r e s s i o n s p r i m a i r e e t s e c o n d a i r e , n i v e a u x d ’e a u , p r e s s i o n v a p e u r ,

r a d i o a c t i v i t é d e s g é n é r a t e u r s d e v a p e u r . C h a q u e é t a t r e q u i e r t d e s a c t i o n s d e s û r e t é

s p é c i f i q u e s s u r l e s d i f f é r e n t s a c t i o n n e u r s e n f o n c t i o n d e l e u r d i s p o n i b i l i t é ( i n j e c t i o n

d e s é c u r i t é , c i r c u i t d e c h a r g e e t d é c h a r g e , a s p e r s i o n e t d é c h a r g e p r e s s u r i s e u r , e a u

a l i m e n t a i r e d e s e c o u r s d e s g é n é r a t e u r s d e v a p e u r , d é c h a r g e v a p e u r a u s e c o n d a i r e ,

i s o l e m e n t v a p e u r e t e a u d u s e c o n d a i r e , e t c . ) . C e s a c t i o n s s o n t à o p t i m i s e r a f i n d e

s t a b i l i s e r e t s i p o s s i b l e r e s t a u r e r l e s y s t è m e a f i n d e r e t r o u v e r d e s é t a t s d e m o i n s e n

m o i n s d é g r a d é s .

IAEA-SM-268/53

G R I L L E S E T A T S A C T I O N S D E S G V :

A L I M E N T A T I O N ,

I S O L E M E N T , P U R G E !

(GV1 ) (GV2) (GV3)

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4 sM P \ 1 2 3 . . .

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A C T I O N S S U R :

- I N J E C T I O N D E S E C U R I T E

- P O M P E S P R I M A I R E S

- D E C H A R G E V A P E U R D E S G V

- D E C H A R G E P R E S S U R I S E U R

M E S U R E S P H Y S I Q U E S

F IG .2 . Synthèse: grilles états/actions.

86 SUREAU et al.

P o u r ê t r e t o t a l e m e n t o p é r a n t e , e t n o t a m m e n t p e r m e t t r e d e s r i p o s t e s g r a d u é e s

m ê m e a p r è s p a s s a g e e n r é g i m e d i p h a s i q u e , u n e t e l l e a p p r o c h e n é c e s s i t e u n e

i n s t r u m e n t a t i o n c o m p l é m e n t a i r e à c e l l e e x i s t a n t a c t u e l l e m e n t s u r n o s r é a c t e u r s :

d e s m e s u r e s d e t a u x d e v i d e d a n s l e s b r a n c h e s c h a u d e s e t d e n i v e a u d a n s l a c u v e ,

p l u s p a r t i c u l i è r e m e n t d a n s l e p l é n u m s u p é r i e u r . E n e f f e t , l e s m e s u r e s e x i s t a n t e s

( p r e s s i o n e t t e m p é r a t u r e p r i m a i r e , n i v e a u p r e s s u r i s e u r ) n e s o n t p a s s u f f i s a n t e s

p o u r c o n n a î t r e l a m a s s e d ’ e a u p r i m a i r e e t s a t e n d a n c e e n s i t u a t i o n d i p h a s i q u e .

L e s a c t i o n s d e d é v e l o p p e m e n t d e c e t t e i n s t r u m e n t a t i o n c o m p l é m e n t a i r e o n t

é t é e n g a g é e s e n l i a i s o n a v e c F r a m a t o m e e t l e C E A . D e s m e s u r e s d e n i v e a u c u v e

p a r p o i d s d e c o l o n n e s e r o n t o p é r a t i o n n e l l e s p o u r l e d é m a r r a g e d u p r e m i e r o u d u

d e u x i è m e r é a c t e u r 1 3 0 0 M W e d e P a l u e l . L e s é t u d e s d e f a i s a b i l i t é d e m e s u r e s d e

t a u x d e v i d e e n b r a n c h e c h a u d e s e p o u r s u i v e n t a v e c d e s t e s t s d e c a p t e u r s à u l t r a ­

s o n s h a u t e f r é q u e n c e s u r u n e t r a n c h e d u B l a y a i s e t s u r l a b o u c l e d ’e s s a i d i p h a s i q u e

S u p e r M o b y D i c k à G r e n o b l e . D e s c o n c l u s i o n s s e r o n t t i r é e s a v a n t l a f i n d e 1 9 8 3 .

C e p e n d a n t , s a n s a t t e n d r e l e s r é s u l t a t s d e s d é v e l o p p e m e n t s d e c e t t e i n s t r u m e n t a ­

t i o n c o m p l é m e n t a i r e e t d e s p r o c é d u r e s p a r é t a t s a s s o c i é s , l ’ a p p r o c h e p a r é t a t a

d é j à é t é u t i l i s é e d a n s l e c a d r e d e l a f o r m a t i o n d u p e r s o n n e l d e c o n d u i t e , e t p o u r

a m é l i o r e r e t c o m p l é t e r l e s p r o c é d u r e s a c t u e l l e s p a r é v é n e m e n t .

3.4. Mesures physiques complémentaires

4 . P R E M I E R E S A P P L I C A T I O N S D E L ’A P P R O C H E P A R E T A T

4 . 1 . A m é l i o r a t i o n d e s p r o c é d u r e s p a r é v é n e m e n t

L e s a m é l i o r a t i o n s a p p o r t é e s d a n s l a r é v i s i o n e n c o u r s d e s p r o c é d u r e s I , A e t H

e t p r o v e n a n t d e l ’ a p p r o c h e p a r é t a t v i s e n t :

1 ) D ’u n e p a r t , à r e n d r e l e s c r i t è r e s d ’a c t i o n d e s p r i n c i p a u x s y s t è m e s d e s a u v e ­

g a r d e a u s s i i n d é p e n d a n t s q u e p o s s i b l e d e s s é q u e n c e s . P o u r c e l a , o n a s s u r e u n e

s u r v e i l l a n c e c o n s t a n t e d e s p r i n c i p a u x p a r a m è t r e s , o u c o m b i n a i s o n s d e p a r a m è t r e s ,

q u i p e r m e t t e n t d e d i s c r i m i n e r à c h a q u e i n s t a n t l e s a c t i o n s d ’a c t i v a t i o n e t d e

d é s a c t i v a t i o n d e c e s s y s t è m e s . C e t y p e d ’a m é l i o r a t i o n p o r t e s u r l e s a c t i o n s d e

d é m a r r a g e e t d ’ a r r ê t d e s p o m p e s d ’i n j e c t i o n d e s é c u r i t é , s u r l a m i s e e n s e r v i c e d e

l ’ a s p e r s i o n d e l ’ e n c e i n t e d e c o n f i n e m e n t , s u r l ’ i s o l e m e n t d e s g é n é r a t e u r s d e v a p e u r

c o n t a m i n é s e t , d a n s u n e m o i n d r e m e s u r e , s u r l ’ a r r ê t d e s p o m p e s p r i m a i r e s .

2 ) D ’a u t r e p a r t , é t a n t d o n n é l e c o n s t a t d e n o n - e x h a u s t i v i t é d e s p r o c é d u r e s

a c t u e l l e s , à l e s c o m p l é t e r p a r d e s g a r d e - f o u s , q u i c o n f i r m e n t o u r e d é f i n i s s e n t l e s

a c t i o n s e s s e n t i e l l e s , i n d é p e n d a m m e n t d u d i a g n o s t i c i n i t i a l e t d e l ’é v o l u t i o n q u i

e n é t a i t a t t e n d u e ( c e q u i p e r m e t d e c o u v r i r l e s s é q u e n c e s h o r s p r o c é d u r e s ) . C e

d e u x i è m e t y p e d ’ a m é l i o r a t i o n c o n c e r n e d e s r e n v o i s e n t r e p r o c é d u r e s e t s u r t o u t

IAEA-SM-268/S3 87

l a s u r v e i l l a n c e p e r m a n e n t e a p r è s i n c i d e n t ( S P I ) e t l ’é l a b o r a t i o n d ’u n e n o u v e l l e

p r o c é d u r e d ’u r g e n c e ( U l ) .

A t i t r e d ’e x e m p l e d u p r e m i e r t y p e d ’ a m é l i o r a t i o n , l a c o n d u i t e d e l ’ i n j e c t i o n

d e s é c u r i t é e s t p r é c i s é e d a n s l e p a r a g r a p h e s u i v a n t .

4 . 2 . C o n d u i t e d e l ’ i n j e c t i o n d e s é c u r i t é ( I S )

L ’ i n j e c t i o n d e s é c u r i t é s e r t e s s e n t i e l l e m e n t à c o m p e n s e r l e s p e r t e s d ’e a u d u

c i r c u i t p r i m a i r e l o r s q u e l e c i r c u i t d e c h a r g e n ’e s t p l u s s u f f i s a n t p o u r a s s u r e r c e t t e

f o n c t i o n .

L a c o n d u i t e d e l ’ i n j e c t i o n d e s é c u r i t é d é p e n d d o n c d ’u n e é v a l u a t i o n d u s t o c k

d ’e a u q u i e s t s û r e e t d é n u é e d ’ a m b i g ü i t é . L e c r i t è r e p o u r é v a l u e r c e s t o c k e s t l e

n i v e a u p r e s s u r i s e u r r e p r é s e n t a t i f d u v o l u m e l i q u i d e , v a l i d é t o u t e f o i s p a r u n e c o n ­

d i t i o n d e s o u s - s a t u r a t i o n e n s o r t i e c o e u r ( A T s a t ) , p o u r c o u v r i r l e c a s d e s b r è c h e s e n

p h a s e v a p e u r d u p r e s s u r i s e u r ( y c o m p r i s l e s o u v e r t u r e s i n t e m p e s t i v e s d e s o u p a p e s

d u p r e s s u r i s e u r ) . L e p r i n c i p e g é n é r a l d e l a c o n d u i t e d e l ’ I S e s t l ’a r r ê t p r o g r e s s i f

d e s f i l e s s i l e s t o c k e s t s u f f i s a n t , o u e x c e s s i f , e t l a ( r e ) m i s e e n s e r v i c e s i l e s t o c k

e s t i n s u f f i s a n t .

L a g r i l l e é t a t s / a c t i o n s d e l ’ i n j e c t i o n d e s é c u r i t é p r é s e n t e u n e c o m b i n a i s o n

d e s s e u i l s d e n i v e a u p r e s s u r i s e u r e t d e A T s a t d e m a n i è r e à é v i t e r d a n s l a p l u p a r t d e s

c a s l e s p o m p a g e s e n t r e a r r ê t e t r e d é m a r r a g e d e s p o m p e s . D e p l u s l e d é p l a c e m e n t

d u p o i n t r e p r é s e n t a t i f d e l ’é t a t ( n i v e a u , A T s a t ) d a n s c e t t e g r i l l e p e r m e t d e s u i v r e

e t m i e u x c o m p r e n d r e l ’é v o l u t i o n d e l a s i t u a t i o n , e t d o n c d e v é r i f i e r l a c o h é r e n c e e t

l ’e f f i c a c i t é d e s a c t i o n s d e s a u v e g a r d e e n t r e p r i s e s p a r a i l l e u r s .

C e t t e g r i l l e d e c o n d u i t e , i n d é p e n d a n t e d e l a s é q u e n c e a c c i d e n t e l l e e s t

i n c o r p o r é e d a n s t o u t e s l e s p r o c é d u r e s ( v e r s i o n 1 9 8 2 ) o ù l ’i n j e c t i o n d e s é c u r i t é

i n t e r v i e n t .

L e s i m a g e s c o r r e s p o n d a n t e s s e r o n t p r é s e n t é e s s u r l e s p a n n e a u x d e s û r e t é e n

c o u r s d ’i n s t a l l a t i o n ( v o i r l e m é m o i r e I A E A - S M - 2 6 8 / 5 6 , p r é s e n t s c o m p t e s r e n d u s ,

v o l u m e I ) .

4 . 3 . P r o c é d u r e s d e s u r v e i l l a n c e p e r m a n e n t e e t d ’u r g e n c e

L a p r o c é d u r e d e s u r v e i l l a n c e p e r m a n e n t e a p r è s i n c i d e n t ( S P I ) , b a s é e s u r

l ’a p p r o c h e p a r é t a t , p e r m e t d e r é a c t u a l i s e r c o n t i n u e m e n t l e d i a g n o s t i c i n i t i a l e t

é v e n t u e l l e m e n t d ’a d o p t e r l a p r o c é d u r e d ’u r g e n c e ( U l ) q u i s e r t d e « g a r d e - f o u » a u x

p r o c é d u r e s p a r é v é n e m e n t .

L a p r o c é d u r e U l e s t p r é v u e p o u r a s s u r e r l e s m e i l l e u r e s c o n d i t i o n s p o s s i b l e s

d e r e f r o i d i s s e m e n t d e l a c h a u d i è r e e t d e s a u v e g a r d e d u c o e u r d a n s d e s s i t u a t i o n s o ù

l e s p r o c é d u r e s I , A o u H , p r o p r e s à d e s s é q u e n c e s a c c i d e n t e l l e s b i e n i d e n t i f i é e s ,

s ’ a v è r e n t i n a d a p t é e s e t i n e f f i c a c e s . L ’ o b j e c t i f d e c e t t e p r o c é d u r e U l e s t d ’é v i t e r ,

o u d e l i m i t e r , o u d e r e t a r d e r l ’e n d o m m a g e m e n t d u c o e u r e t s e s c o n s é q u e n c e s

88 SUREAU et al.

---------- , ---------------------- . v---------------------- , ---------------------> -----------------------„---------------------- »

M A C H I N E O P E R A T E U R ( S ) I N G E N I E U R D E S U R E T E

F IG .3 . In teraction homme-machine en situation accidentelle.

r a d i o l o g i q u e s , s e l o n l a g r a v i t é d e l a s i t u a t i o n e t l ’i m p o r t a n c e d e s m o y e n s r e s t a n t

d i s p o n i b l e s .

P a r q u e l p r o c e s s u s p e u t - o n a r r i v e r à l a d é c i s i o n d ’a b a n d o n n e r u n e p r o c é d u r e

I , A o u H e n c o u r s d ’ a p p l i c a t i o n a u p r o f i t d e l a p r o c é d u r e U l ? C ’e s t - à - d i r e

c o m m e n t d é t e c t e r , à n ’ i m p o r t e q u e l m o m e n t e t q u e l l e s q u ’e n s o i e n t l a o u l e s

c a u s e s , q u e l e s y s t è m e n e s u i t p a s o u n e s u i t p l u s l a s é q u e n c e a c c i d e n t e l l e

i n i t i a l e m e n t d i a g n o s t i q u é e , e t / o u q u e l a p r o c é d u r e a p p l i q u é e p a r l ’o p é r a t e u r n ’e s t

p a s o u n ’e s t p l u s e f f i c a c e ?

I l e s t a p p a r u i n o p p o r t u n d ’e f f e c t u e r c e p r o c e s s u s à l ’i n t é r i e u r d e s p r o c é d u r e s

« s é q u e n t i e l l e s » I , A e t H p o u r t r o i s r a i s o n s :

1 ) D i f f i c u l t é d e c o n c e v o i r l e s c r i t è r e s p r é c i s à l ’i n t é r i e u r d e c h a q u e p r o c é d u r e

e t à c h a q u e é t a p e d e l e u r d é r o u l e m e n t p e r m e t t a n t d e d é t e c t e r u n e é v o l u t i o n n o n

c o n f o r m e à l ’a t t e n t e e t p o t e n t i e l l e m e n t d a n g e r e u s e .

2 ) D i f f i c u l t é d e d e m a n d e r à l ’ o p é r a t e u r u n p r o c e s s u s d ’a u t o - c o n t r ô l e e t l a r e m i s e

e n q u e s t i o n c o n s t a n t e d e s e s d é c i s i o n s e t d e s e s a c t i o n s a n t é r i e u r e s .

3 ) D i f f i c u l t é d ’i n t r o d u i r e c e p r o c e s s u s d a n s l e s p r o c é d u r e s a c t u e l l e s d o n t l a

c o n c e p t i o n e t l a r é d a c t i o n d e v r a i e n t a l o r s ê t r e r e p r i s e s e n t i è r e m e n t .

I l e s t p a r c o n t r e a p p a r u p l u s i n t é r e s s a n t e t t e c h n i q u e m e n t p o s s i b l e d e

p r o c é d e r à u n d i a g n o s t i c p e r m a n e n t :

— s e l o n u n e l o g i q u e i n d é p e n d a n t e , r e d o n d a n t e e t e x t é r i e u r e a u x p r o c é d u r e s

e x i s t a n t e s , q u i r e s t e n t a l o r s i n c h a n g é e s e t q u i p o u r r o n t é v o l u e r u l t é r i e u r e m e n t d e

f a ç o n a u t o n o m e s i b e s o i n e s t ;

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IAEA-SM-268/53 89

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90 SUREAU et al.

— e n f a i s a n t a p p e l à l ’ i n g é n i e u r d e s û r e t é e t d e r a d i o p r o t e c t i o n ( I S R ) , c e q u i a s s u r e

u n e r e d o n d a n c e h u m a i n e p a r r a p p o r t à l ’ o p é r a t e u r ;

— e n s ’ a p p u y a n t s u r l ’ a n a l y s e d e s é t a t s d e r e f r o i d i s s e m e n t d e l a c h a u d i è r e ,

c o m p l é t é e p a r l ’a n a l y s e d e l a d i s p o n i b i l i t é d e s s y s t è m e s d e s a u v e g a r d e u t i l i s é s , e t

m i s e e n o e u v r e a v e c l ’ i n s t r u m e n t a t i o n a c t u e l l e .

C e t t e l o g i q u e c o n d u i t Г I S R à e x e r c e r u n e s u r v e i l l a n c e p e r m a n e n t e a p r è s

i n c i d e n t ( S P I ) q u i p e r m e t , à p a r t i r d e c r i t è r e s t r è s p r é c i s d ’é t a t ( f i g u r e 3 ) :

— s o i t , s i l e s y s t è m e s u i t la s é q u e n c e i n i t i a l e m e n t d i a g n o s t i q u é e , d e s u i v r e , e t

é v e n t u e l l e m e n t d e c o n f i r m e r à l ’ o p é r a t e u r , a v e c u n l é g e r d é c a l a g e d a n s l e t e m p s ,

l e s p r i n c i p a l e s a c t i o n s d é j à d e m a n d é e s p a r l a p r o c é d u r e s é q u e n t i e l l e e n c o u r s

d ’a p p l i c a t i o n ;

— s o i t , d a n s c e r t a i n s c a s d e d é f a i l l a n c e s c u m u l é e s n o n p r i s e s e n c o m p t e d a n s l e s

s é q u e n c e s , d e d e m a n d e r à l ’ o p é r a t e u r d e s a c t i o n s c o m p l é m e n t a i r e s l i m i t é e s ( i s o ­

l e m e n t d ’u n G V ) s a n s p o u r a u t a n t a b a n d o n n e r l a p r o c é d u r e e n c o u r s ;

— s o i t , d a n s c e r t a i n e s s i t u a t i o n s e n c o r e p l u s d é g r a d é e s , d e p r e n d r e l a d é c i s i o n

d ’a b a n d o n n e r l a p r o c é d u r e e n c o u r s e t d e p a s s e r à l ’a p p l i c a t i o n d e l a p r o c é d u r e U 1

q u i d é f i n i t a l o r s l e s a c t i o n s r e q u i s e s e n f o n c t i o n d e l ’é t a t d u s y s t è m e e t d e s m o y e n s

d i s p o n i b l e s à c h a q u e i n s t a n t .

U n l o g i g r a m m e t r è s s i m p l i f i é d e l a s u r v e i l l a n c e p e r m a n e n t e a p r è s i n c i d e n t

( S P I ) e s t p r é s e n t é f i g u r e 4 . L a S P I p o r t e s u r l e s p a r a m è t r e s s u i v a n t s :

— d i s p o n i b i l i t é d e c h a q u e g é n é r a t e u r d e v a p e u r , c ’e s t - à - d i r e s a c a p a c i t é à é v a c u e r

l a p u i s s a n c e r é s i d u e l l e s a n s q u e l a v a p e u r é v a c u é e s o i t c o n t a m i n é e ;

— l e s t o c k d ’e a u p r i m a i r e e t l a t e m p é r a t u r e s o r t i e c o e u r ;

— l ’ e f f i c a c i t é g l o b a l e d u s e c o n d a i r e s u r l e p r i m a i r e , c ’e s t - à - d i r e s a c a p a c i t é à

r e f r o i d i r e t d é p r e s s u r i s e r l e p r i m a i r e ;

— l a m i s e e n s e r v i c e e f f e c t i v e d e s s y s t è m e s d e s a u v e g a r d e a p p e l é s ( A S G , I S H P ,

I S B P , E A S , e t c . ) ;

— l a p r e s s i o n , l a t e m p é r a t u r e e t l ’a c t i v i t é d a n s l ’e n c e i n t e d e c o n f i n e m e n t ;

— l a c r i t i c i t é d u c o e u r ( f l u x n u c l é a i r e , p o s i t i o n d e s b a r r e s d e c o n t r ô l e , c o n c e n t r a ­

t i o n e n b o r e , e t c . ) .

L a p r o c é d u r e U 1 e l l e - m ê m e p e r m e t , e n f o n c t i o n d e l ’é v o l u t i o n d e s t e m p é ­

r a t u r e s s o r t i e c o e u r e t d e l a d i s p o n i b i l i t é d e s g é n é r a t e u r s d e v a p e u r e t d e l ’i n j e c t i o n

d e s é c u r i t é , d e p r é c o n i s e r l e s m e i l l e u r e s a c t i o n s p o u r :

— l ’u t i l i s a t i o n d e s g é n é r a t e u r s d e v a p e u r ,

— l ’i n j e c t i o n d e s é c u r i t é ,

— l e s s o u p a p e s d e d é c h a r g e d u p r e s s u r i s e u r ,

— l e s p o m p e s p r i m a i r e s ,

p o u r a r r ê t e r , a t t é n u e r o u r e t a r d e r l e s é v o l u t i o n s d a n g e r e u s e s ( d o n n a n t a i n s i d u

t e m p s p o u r r e t r o u v e r d e s s y s t è m e s d é f a i l l a n t s ) .

L e s l o g i g r a m m e s d e s p r o c é d u r e s S P I e t U 1 s o n t p r o g r a m m é s s u r l e s p a n n e a u x

d e s û r e t é e n c o u r s d ’ i n s t a l l a t i o n d a n s t o u t e s l e s t r a n c h e s R E P ( v o i r l e m é m o i r e

I A E A - S M - 2 6 8 / 5 6 , p r é s e n t s c o m p t e s r e n d u s , v o l u m e I ) .

IAEA-SM-268/S3 91

C e t t e s u r v e i l l a n c e p a r é t a t a m è n e u n e d o u b l e r e d o n d a n c e :

— r e d o n d a n c e d u m o d e d e r é f l e x i o n : c o n d u i t e p a r é t a t c o n j o i n t e m e n t a v e c la

c o n d u i t e n o r m a l e p a r c o n s i g n e s l i é e s a u x é v é n e m e n t s ;

— r e d o n d a n c e h u m a i n e : I S R c o n j o i n t e m e n t a v e c l ’é q u i p e n o r m a l e d e c o n d u i t e .

5 . C O N C L U S I O N

L a d é m a r c h e e n g a g é e p a r E D F — c o n j o i n t e m e n t a v e c l e c h a u d i è r i s t e F r a m a t o m e

e t l e s a u t o r i t é s d e s û r e t é — p o u r i n t r o d u i r e l ’a p p r o c h e p a r é t a t d e r e f r o i d i s s e m e n t

d e l a c h a u d i è r e d a n s l a c o n c e p t i o n d e l a c o n d u i t e p o s t - a c c i d e n t e l l e a d é j à

p e r m i s u n e a m é l i o r a t i o n q u a l i t a t i v e m e n t d é c i s i v e d e l a s û r e t é d ’e x p l o i t a t i o n d u

p a r c n u c l é a i r e E D F .

L a p o u r s u i t e d e s t r a v a u x s e s i t u e m a i n t e n a n t s u r t r o i s p l a n s :

1 ) L e d é v e l o p p e m e n t d e l ’i n s t r u m e n t a t i o n c o m p l é m e n t a i r e p o u r m i e u x

a p p r é h e n d e r l ’i n v e n t a i r e e n m a s s e d e f l u i d e p r i m a i r e e n c o n d i t i o n d i p h a s i q u e :

i n s t a l l a t i o n i m m é d i a t e d e m e s u r e d e n i v e a u c u v e s u r l e s t r a n c h e s 1 3 0 0 M W , é t u d e

d e f a i s a b i l i t é d e m e s u r e d e t a u x d e v i d e e n b r a n c h e c h a u d e q u i d o i t d é b o u c h e r s u r

u n e d é c i s i o n f i n 1 9 8 3 .

2 ) L ’i n t r o d u c t i o n d e l ’a p p r o c h e p a r é t a t s u r l e s p a n n e a u x d e s û r e t é a v e c m i s e

a u p o i n t d e s t r a i t e m e n t s e t p r é s e n t a t i o n s d e s i n f o r m a t i o n s a s s o c i é e s .

3 ) E n f i n , e t p r i n c i p a l e m e n t , l ’a p p l i c a t i o n p l u s s y s t é m a t i q u e d e l ’a p p r o c h e p a r

é t a t u t i l i s a n t l ’i n s t r u m e n t a t i o n c o m p l é m e n t a i r e , d e m a n i è r e à g é n é r a l i s e r l e s

p r o c é d u r e s p a r é t a t p o u r c o u v r i r l e d o m a i n e m a x i m u m d e s s i t u a t i o n s a c c i d e n t e l l e s

o u i n c i d e n t e l l e s p o s s i b l e s e t r é d u i r e d ’a u t a n t l e c h a m p d ’a p p l i c a t i o n d e s c r i t è r e s e t

a c t i o n s g a r d e - f o u s d e l a p r o c é d u r e d ’ u r g e n c e U l .

P a r a i l l e u r s , u n e n s e m b l e d ’o u t i l p e r m e t t a n t l a v a l i d a t i o n d e c e t t e n o u v e l l e

a p p r o c h e d e l a c o n d u i t e p o s t - a c c i d e n t e l l e , p u i s l ’e n t r a î n e m e n t d e s o p é r a t e u r s , e s t

e n c o u r s d ’é l a b o r a t i o n . C e s o u t i l s s o n t l e c o d e C a t h a r e , l e s i m u l a t e u r S I P A e t

l a b o u c l e s y s t è m e B e t h s y .

P o ste r P re se n ta tio n s

IAEA-SM -268/21P

F E E D B A C K O F O P E R A T I N G E X P E R I E N C E A N D

I T S U T I L I Z A T I O N F O R I M P R O V E D S A F E

P E R F O R M A N C E

B . K . B H A S I N

T a r a p u r A t o m i c P o w e r S t a t i o n ,

D i s t r i c t T h a n a , I n d i a

O p e r a t i n g e x p e r i e n c e g a i n e d o v e r t h e p a s t t w e l v e y e a r s h a s b e e n v e r y u s e f u l

i n t h e a n a l y s i s o f a b n o r m a l o c c u r r e n c e s a n d i n d e t e r m i n i n g t h e a r e a s r e q u i r i n g

d e s i g n c h a n g e s t o s a f e t y - r e l a t e d s y s t e m s f o r i m p r o v e d p l a n t p e r f o r m a n c e .

T h e p a p e r e n u m e r a t e s m o d i f i c a t i o n s c a r r i e d o u t t o t h e r e a c t o r p r o t e c t i o n

s y s t e m , r a d i a t i o n m o n i t o r s , r e a c t o r f e e d w a t e r c o n t r o l s y s t e m , r e a c t o r i n t e r n a l s

a r r a n g e m e n t , s t a n d b y p o w e r s u p p l i e s t o a u x i l i a r i e s , e t c . i n t h e t w i n - u n i t ( 2 1 0 M W ( e )

e a c h ) B W R a t T a r a p u r A t o m i c P o w e r S t a t i o n . S o m e o f t h e m o d i f i c a t i o n s a r e

b r i e f l y d e s c r i b e d b e l o w .

R E A C T O R P R O T E C T I O N S Y S T E M

( a ) P r o v i s i o n o f b l o c k i n g d i o d e s o n t h e o u t p u t o f b a t t e r y c h a r g e r s t o a v o i d

d i s c h a r g e o f b a t t e r y d u r i n g l o s s o f A C p o w e r a n d t h u s p r e v e n t t r i p s t o s a f e t y

c h a n n e l s .

( b ) I n s t a l l a t i o n o f d i s c h a r g e r e s i s t o r s a c r o s s t h e D C s o l e n o i d s t o a v o i d d a m a g e t o

d r y w e l l p e n e t r a t i o n p l u g s c o n t a i n i n g t h e c o n n e c t o r s t o t h e D C s o l e n o i d s o f

i s o l a t i o n v a l v e s .

( c ) I n s t a l l a t i o n o f a d d i t i o n a l l i m i t s w i t c h e s t o a v o i d f u l l c l o s u r e o f i s o l a t i o n

v a l v e s d u r i n g t e s t c l o s i n g .

( d ) I n t r o d u c t i o n o f 8 0 m i l l i s e c o n d t i m e d e l a y i n t r i p l o g i c t o a v o i d s p u r i o u s

t r i p s f r o m r a d i a t i o n m o n i t o r s d u e t o p o w e r s u p p l y f l u c t u a t i o n s .

R E A C T O R F E E D W A T E R C O N T R O L S Y S T E M

( e ) C h a n g e o f p o w e r s u p p l y t o G E M A C c o n t r o l o f f e e d w a t e r r e g u l a t o r s f r o m

a u x i l i a r i e s t o i n v e r t e r a n d s e g r e g a t i o n o f t h e p o w e r s u p p l y t o p r i m a r y a n d

s e c o n d a r y f e e d w a t e r c o n t r o l v a l v e s . T h i s h e l p e d i n i m p r o v i n g t h e p e r f o r m a n c e

a n d t h e ‘f a i l a s i s ’ f e a t u r e .

93

9 4 POSTER PRESENTATIONS

( f ) M o d i f i c a t i o n s t o h o l d - d o w n d e v i c e o f t h e g u i d e t u b e s w h i c h w e r e f o u n d

d i s p l a c e d u p w a r d s i n t h e c o r e d u r i n g t h e i n i t i a l y e a r s o f o p e r a t i o n .

( g ) M o d i f i c a t i o n s i n t h e t o p f u e l g u i d e s p a c e r s t o p r e v e n t t h e m f r o m g e t t i n g

d i s l o c a t e d d u r i n g o p e r a t i o n .

R E A C T O R I N T E R N A L S

S T A N D B Y S U P P L Y T O A U X I L I A R I E S

( h ) M o d i f i c a t i o n s t o t h e p o w e r s u p p l y a r r a n g e m e n t s t o t h e c o n t r o l r o d

h y d r a u l i c p u m p s a n d t h e t u r b i n e t u r n i n g g e a r o i l p u m p s . T h e p o w e r c a n

n o w b e s u p p l i e d b y e m e r g e n c y d i e s e l g e n e r a t o r s s o t h a t t h e p u m p s a r e

a v a i l a b l e d u r i n g l o s s o f o f f - s i t e p o w e r t o t h e s t a t i o n .

E M E R G E N C Y V E N T I L A T I O N S Y S T E M

( i ) M o d i f i c a t i o n t o t h e c i r c u i t a n d t h e p r o v i s i o n o f a i r a c c u m u l a t o r s .

I m p r o v e m e n t s t o t h e d r y w e l l C a r d o x S y s t e m t o p r o v i d e a c c e s s i b i l i t y

f o r m a i n t e n a n c e a n d f u n c t i o n a l c h e c k s .

IAEA-SM -268/51P

L ’ A P P R O C H E P R O B A B I L I S T E

E T L E R E T O U R D ’ E X P E R I E N C E

C l a u d e A N C E L I N , J . F . B A R B E T , A . V I L L E M E U R

D é p a r t e m e n t P h y s i q u e d e s r é a c t e u r s ,

D i r e c t i o n d e s é t u d e s e t r e c h e r c h e s ,

E l e c t r i c i t é d e F r a n c e ,

C l a m a r t , F r a n c e

C ’e s t t o u t d ’ a b o r d d a n s l ’é l a b o r a t i o n d e d o n n é e s d e f i a b i l i t é c o n c e r n a n t l e s

d i f f é r e n t s c o m p o s a n t s d u s y s t è m e q u e l e r e t o u r d ’e x p é r i e n c e i n t e r v i e n t d i r e c t e m e n t .

M a i s i l i n t e r v i e n t é g a l e m e n t a u n i v e a u d e la r e c h e r c h e d e s c o m b i n a i s o n s d e d é f a i l ­

l a n c e s c o n d u i s a n t à u n ( o u p l u s i e u r s ) é v é n e m e n t ( s ) i n d é s i r a b l e ( s ) . Q u e l l e q u e s o i t

l a m é t h o d e u t i l i s é e à c e t e f f e t , a u s s i e x h a u s t i v e s o i t - e l l e , i l e s t p a r f o i s t r è s d i f f i c i l e

POSTER PRESENTATIONS 95

d e m e t t r e e n é v i d e n c e c e r t a i n s f a c t e u r s q u e s e u l l e r e t o u r d ’e x p é r i e n c e p e r m e t

d e r é v é l e r . O n p e u t a i n s i c i t e r l e s d é f a u t s d e m o d e c o m m u n e t l e s d é f a i l l a n c e s

d ’ o r i g i n e h u m a i n e .

A t i t r e d ’e x e m p l e , l e s é t u d e s d e s i n c i d e n t s r e l a t i f s a u x s y s t è m e s d ’i n j e c t i o n

d e s é c u r i t é e t d ’a l i m e n t a t i o n d e s e c o u r s d e s g é n é r a t e u r s d e v a p e u r d e s c e n t r a l e s

R E P a u x E t a t s - U n i s ( é t u d e s q u i p o r t e n t p o u r c h a c u n e d ’e n t r e e l l e s s u r l ’ a n a l y s e

d ’e n v i r o n 6 0 a n n é e s - r é a c t e u r s d ’e x p é r i e n c e ) o n t n o t a m m e n t p e r m i s d e m e t t r e e n

é v i d e n c e l ’i m p o r t a n c e d e s d é f a u t s d e m o d e c o m m u n . C e s d é f a u t s o n t é t é c l a s s é s

e n c i n q c a t é g o r i e s : e f f e t s d e l ’e n v i r o n n e m e n t , e r r e u r s d e c o n c e p t i o n , e r r e u r s d e

f a b r i c a t i o n , e r r e u r s d e m o n t a g e , e r r e u r s h u m a i n e s e n e x p l o i t a t i o n .

E n f i n , l e r e t o u r d ’e x p é r i e n c e p e r m e t d e c o n f r o n t e r d e u x c h i f f r e s : d ’u n e

p a r t , l a f i a b i l i t é p r é v i s i o n n e l l e , c a l c u l é e à p a r t i r d e l a d é m a r c h e d é c r i t e p r é c é d e m ­

m e n t e t d ’ a u t r e p a r t , l a f i a b i l i t é o p é r a t i o n n e l l e , r é s u l t a t d ’u n e o b s e r v a t i o n

s t a t i s t i q u e d u c o m p o r t e m e n t e n e x p l o i t a t i o n d u s y s t è m e é t u d i é .

C ’ e s t a i n s i q u ’u n e é t u d e p r é v i s i o n n e l l e d e l a f i a b i l i t é d ’u n s y s t è m e é l e c t r o ­

n i q u e a n a l o g i q u e d e r é g u l a t i o n d ’ a l t e r n a t e u r s a é t é r é a l i s é e . C e t t e é t u d e e s t b a s é e

s u r l ’ a n a l y s e d e s m o d e s d e d é f a i l l a n c e e t d e l e u r s e f f e t s ( F M E A ) e t l e s a r b r e s d e

d é f a i l l a n c e c o m m e m é t h o d e s c o m p l é m e n t a i r e s d ’ a n a l y s e q u a l i t a t i v e . L ’a n a l y s e

q u a n t i t a t i v e a u t i l i s é l e s d o n n é e s d e f i a b i l i t é d u C e n t r e n a t i o n a l d ’é t u d e d e s t é l é ­

c o m m u n i c a t i o n s c o n c e r n a n t l e s c o m p o s a n t s é l e c t r o n i q u e s .

P a r a i l l e u r s , t r o i s d e c e s r é g u l a t e u r s , o b j e t s d e l ’é t u d e p r é v i s i o n n e l l e , o n t é t é

e s s a y é s p e n d a n t p l u s i e u r s m o i s , e n e x p l o i t a t i o n , s u r d e s a l t e r n a t e u r s d e c e n t r a l e s

t h e r m i q u e s e t n u c l é a i r e s . L ’o b s e r v a t i o n s t a t i s t i q u e d e l e u r c o m p o r t e m e n t a p e r m i s

d e c o m p a r e r l e u r s f i a b i l i t é s o p é r a t i o n n e l l e s e t p r é v i s i o n n e l l e s . L e s r é s u l t a t s d ’e x p l o i ­

t a t i o n c o n c o r d e n t a v e c l e s p r é v i s i o n s .

T o u t e f o i s , l e f a i b l e n o m b r e d e s y s t è m e s e s s a y é s e t l a d u r é e l i m i t é e d e

l ’o b s e r v a t i o n n e f o u r n i s s e n t m a l g r é t o u t q u ’u n é c h a n t i l l o n d e t a i l l e l i m i t é e . I l s e r a

i n t é r e s s a n t d e c o n t i n u e r à s u i v r e l e s r é g u l a t e u r s d é f i n i t i f s q u i s e r o n t i n s t a l l é s s u r

l e s c e n t r a l e s e t d e v é r i f i e r s i , l a t a i l l e d e l ’é c h a n t i l l o n g r a n d i s s a n t , l a f i a b i l i t é

o p é r a t i o n n e l l e c o n f i r m e l e s r é s u l t a t s d e l ’a n a l y s e p r é v i s i o n n e l l e . D a n s l e c a s

c o n t r a i r e , l a r e c h e r c h e d e s c a u s e s d e s d i f f é r e n c e s c o n s t a t é e s s e r a t r è s f r u c t u e u s e

p o u r l e s a n a l y s e s d e f i a b i l i t é e n p a r t i c u l i e r p o u r j u g e r d e l ’i m p o r t a n c e d e s f a c t e u r s

d ’e n v i r o n n e m e n t , d e c o n d u i t e e t d e m a i n t e n a n c e .

O u t r e c e s t r o i s a p p l i c a t i o n s p r i n c i p a l e s d u r e t o u r d ’e x p é r i e n c e , i l e s t é g a l e m e n t

p o s s i b l e d e c i t e r l e c a s d e s y s t è m e s p o u r l e s q u e l s l ’a n a l y s e q u a n t i t a t i v e , t e l l e

q u ’e l l e e s t d é f i n i e c i - d e s s u s , e s t d i f f i c i l e m e n t r é a l i s a b l e p a r l e s t e c h n i q u e s p r o b a -

b i l i s t e s u s u e l l e s . A i n s i , p o u r c e r t a i n s c o m p o s a n t s , t e l l e s l e s p i è c e s m é c a n i q u e s ,

l e s t a u x d e d é f a i l l a n c e s o n t t r è s d i f f i c i l e s à é v a l u e r : i l s p e u v e n t e n e f f e t d é p e n d r e

d e s c o n d i t i o n s d e t r a v a i l d e l a p i è c e e t f o n t s o u v e n t i n t e r v e n i r l e s l o i s d e l a

m é c a n i q u e d e l a r u p t u r e . L ’o b s e r v a t i o n s t a t i s t i q u e d u c o m p o r t e m e n t e n

e x p l o i t a t i o n d u s y s t è m e é t u d i é e s t a l o r s l e s e u l m o y e n d ’e n q u a n t i f i e r l a f i a b i l i t é .

U n e r e c h e r c h e d ’i n c i d e n t s c o n c e r n a n t l e s s o u p a p e s d e s û r e t é d e s s y s t è m e s d ’u n e

96 I POSTER PRESENTATIONS

c e n t r a l e R E P d e 9 0 0 M W e , c e l l e s d e l a c e n t r a l e t h e r m i q u e d e L o i r e - s u r - R h ô n e e t

c e l l e s , e n f i n , d e s i n s t a l l a t i o n s d ’e s s a i s d e s R e n a r d i è r e s , a a i n s i p e r m i s l a c o m p a ­

r a i s o n s u r l e p l a n f i a b i l i t é e t m a i n t e n a b i l i t é d ’u n e s o u p a p e à r e s s o r t c l a s s i q u e e t

d ’u n e s o u p a p e t h e r m o h y d r a u l i q u e d e t y p e S E B I M .

B i e n q u e d é j à b e a u c o u p u t i l i s é p a r l ’a p p r o c h e p r o b a b i l i s t e , l e r e t o u r d e

l ’ e x p é r i e n c e d ’ e x p l o i t a t i o n d e v r a i t ê t r e d e p l u s e n p l u s u n e a i d e p o u r l e f a i b i l i s t e .

N o n s e u l e m e n t u t i l e a u x é t u d e s d e s y s t è m e s , i l d e v r a i t é g a l e m e n t , p a r e x e m p l e ,

f a c i l i t e r l ’é l a b o r a t i o n d e s é q u e n c e s a c c i d e n t e l l e s p o u r u n e c e n t r a l e n u c l é a i r e p a r

l ’ é t u d e a p p r o f o n d i e d e s « d é b u t s d e s é q u e n c e s » o u i n c i d e n t s i n i t i a t e u r s q u i p e u v e n t

s e p r o d u i r e e n e x p l o i t a t i o n .

IAEA-SM -268/52P

E X P E R I E N C E A C Q U I S E

D A N S L A S U R V E I L L A N C E D E S S T R U C T U R E S

I N T E R N E S E T M O Y E N S M I S E N O E U V R E

S U R L E S P A L I E R S R E P 9 0 0 E T 1 3 0 0 M W

C . P U Y A L

D i v i s i o n S u r v e i l l a n c e e t d i a g n o s t i c ,

D i r e c t i o n d e s é t u d e s e t r e c h e r c h e s ,

E l e c t r i c i t é d e F r a n c e

C h a t o u , F r a n c e

D è s l a f i n d e s a n n é e s 1 9 6 0 , d e s i n c i d e n t s d ’ o r i g i n e v i b r a t o i r e o n t a f f e c t é

l e s s t r u c t u r e s i n t e r n e s d e s r é a c t e u r s à e a u s o u s p r e s s i o n ( R E P ) d e l a p r e m i è r e

g é n é r a t i o n ( C h o o z , T r i n o ) : e n p a r t i c u l i e r , d e s d é b r i s m é t a l l i q u e s o n t é t é v é h i c u l é s

p a r l e f l u i d e e t o n t f o r t e m e n t e n d o m m a g é l e s p a r o i s d u c i r c u i t p r i m a i r e . D è s l o r s

e s t a p p a r u e l a n é c e s s i t é d ’u n e s u r v e i l l a n c e e n s e r v i c e d e s s t r u c t u r e s i n t e r n e s e t

d ’u n e d é t e c t i o n p r é c o c e d e p i è c e s v a g a b o n d e s , e t u n p r e m i e r s y s t è m e a é t é

i n s t a l l é a u r e d é m a r r a g e d e C h o o z . L e s y s t è m e d e s u r v e i l l a n c e a c t u e l l e m e n t m i s e n

p l a c e s u r p l u s d e 2 2 t r a n c h e s d e 9 0 0 M W u t i l i s e l e s s i g n a u x d ’a c c é l é r o m è t r e s m o n t é s

s o u s l a c u v e e t l e s g é n é r a t e u r s d e v a p e u r ( 9 v o i e s ) e t l e s s i g n a u x d e b r u i t n e u t r o n i q u e

i s s u s d e s c h a m b r e s d ’ e x p l o i t a t i o n ( 8 v o i e s ) .

A f i n d ’a s s u r e r u n e s u r v e i l l a n c e c o r r e c t e d e s s t r u c t u r e s i n t e r n e s , u n e c a r a c t é ­

r i s a t i o n d e l e u r é t a t v i b r a t o i r e n o r m a l e s t n é c e s s a i r e . E l l e e s t b a s é e s u r d e s é t u d e s

f o n d a m e n t a l e s ( m o d é l i s a t i o n d e s t r u c t u r e s ) a s s o r t i e s d ’ e s s a i s s u r m a q u e t t e ( S a f r a n )

POSTER PRESENTATIONS 97

e t s u r d e s e s s a i s d e q u a l i f i c a t i o n v i b r a t o i r e e n v r a i e g r a n d e u r e f f e c t u é s a u d é m a r r a g e

d e s t r a n c h e s n u c l é a i r e s t ê t e d e s é r i e ( F e s s e n h e i m 1 , T r i c a s t i n 1 ) . D e p u i s F e s s e n h e i m 1

e n 1 9 7 6 , u n s u i v i d e s s i g n a t u r e s v i b r a t o i r e s d e t o u t e s l e s t r a n c h e s a é t é r é a l i s é ,

p e r m e t t a n t d e d é f i n i r u n c o m p o r t e m e n t s t a t i s t i q u e d ’e n s e m b l e . L ’i n s t r u m e n t a t i o n

m i s e e n p l a c e e s t e n m e s u r e d e d é t e c t e r :

— d e s c o r p s e r r a n t s ( p a r d e s m o y e n s d e s o n o r i s a t i o n e t v i s u a l i s a t i o n ) ;

— d e s a n o m a l i e s v i b r a t o i r e s d e s s t r u c t u r e s i n t e r n e s , p a r a n a l y s e s p e c t r a l e : d é g r a d a ­

t i o n d e l ’a n n e a u d e c a l a g e ( i n c i d e n t t y p e P a l i s a d e s ) , v i b r a t i o n s d e b a r r e s d e

c o m m a n d e , d ’ a s s e m b l a g e s c o m b u s t i b l e s , j e t s d ’e a u à t r a v e r s l e c l o i s o n n e m e n t

c o e u r ; l e d i a g n o s t i c d a n s c e c a s s ’a p p u i e e n o u t r e s u r l ’a n a l y s e d e s s i g n a u x d e s

c h a m b r e s « i n c o r e » .

D e s e x e m p l e s s o n t d o n n é s d e s i g n a t u r e s n o r m a l e s e t a n o r m a l e s e t d e u x c a s d e

d é t e c t i o n d e c o r p s m i g r a n t s s o n t r e p o r t é s .

L e s y s t è m e e s t c o m p l è t e m e n t p r i s e n c h a r g e p a r l e p e r s o n n e l d e s c e n t r a l e s

a v e c l ’ a p p u i d ’u n e u n i t é s p é c i a l i s é e . P r o g r e s s i v e m e n t , l ’e x p é r i e n c e a c q u i s e e t u n e

m e i l l e u r e q u a l i f i c a t i o n d u p e r s o n n e l a i n s i q u e l ’é v o l u t i o n t e c h n i q u e o n t p e r m i s

d ’ i n t r o d u i r e d e s m o y e n s i n f o r m a t i q u e s e t d e s u r v e i l l a n c e e n c o n t i n u . L e p e r s o n n e l

e s t a l o r s d é g a g é d e s c o n t r ô l e s r o u t i n i e r s e t p e u t s e c o n s a c r e r d a v a n t a g e a u s u i v i d e s

p h é n o m è n e s p h y s i q u e s . C i t o n s u n d i s p o s i t i f s e m i a u t o m a t i q u e d e c o l l e c t e d e

d o n n é e s , p o u v a n t ê t r e u t i l i s é e n a u t o m a t i q u e l o r s d ’a n o m a l i e s e t u n d é t e c t e u r d e

v i b r a t i o n s a n o r m a l e s o u d e t r a n s i t o i r e s p o u r l a s u r v e i l l a n c e d e s g é n é r a t e u r s d e

v a p e u r .

S u r l e s t r a n c h e s 1 3 0 0 M W , u n p a s d e p l u s a é t é f r a n c h i d a n s l a v o i e d e

l ’a u t o m a t i s a t i o n e t d u s u i v i e n c o n t i n u , g r â c e à l a m i s e e n p l a c e d ’u n e c e n t r a l e d e

c o m m u t a t i o n c o u p l é e à u n c a l c u l a t e u r m u n i d ’u n é c r a n e t d e d i v e r s p é r i p h é r i q u e s

d e s t o c k a g e d e d o n n é e s . C e t e n s e m b l e a s s u r e r a l e s u i v i d e l ’h i s t o r i q u e v i b r a t o i r e e t

l ’e n r e g i s t r e m e n t d e s s i g n a u x d ’a c c é l o r o m è t r e s e t d e b r u i t n e u t r o n i q u e e n c a s

d ’a l a r m e . L ’a u g m e n t a t i o n d u n o m b r e d e c a p t e u r s ( 4 e n f o n d d e c u v e , 3 p a r

g é n é r a t e u r d e v a p e u r ) , l ’i n t r o d u c t i o n d e m o y e n s d e s t o c k a g e d e d o n n é e s e t d e

p e r t u r b o g r a p h i e , u n s u i v i e n c o n t i n u d e s s i g n a u x d o i v e n t p e r m e t t r e d e r é d u i r e la

d u r é e d e f o n c t i o n n e m e n t e n s i t u a t i o n i n c i d e n t e l l e e t u n e p r i s e d e d é c i s i o n p l u s

r a p i d e , d a n s l e b u t d ’a c c r o î t r e l a s û r e t é d e f o n c t i o n n e m e n t d e s r é a c t e u r s .

98 POSTER PRESENTATIONS

M I S E E N O E U V R E D E S A M E L I O R A T I O N S

D E S S A L L E S D E C O M M A N D E

D E S T R A N C H E S R E P 9 0 0 M W

P . R O L L A N D

S e r v i c e d e l a p r o d u c t i o n t h e r m i q u e ,

E l e c t r i c i t é d e F r a n c e ,

P a r i s , F r a n c e

IAEA-SM-268/57P

L ’o r i g i n a l i t é d e c e t t e o p é r a t i o n r é s i d e m o i n s d a n s l a n a t u r e d e s s o l u t i o n s

t e c h n i q u e s q u i s o n t b a n a l e s q u e d a n s l ’ a m p l e u r d e l ’a p p l i c a t i o n , t a n t d u p o i n t d e

v u e d u n o m b r e d ’ o r g a n e s d e c o n t r ô l e - c o m m a n d e d é p l a c é s q u e d u p o i n t d e v u e

d u n o m b r e d e t r a n c h e s c o n c e r n é e s ( 2 8 ) d o n t c e r t a i n e s f o n c t i o n n e n t a v e c l ’a n c i e n n e

c o n f i g u r a t i o n d e p u i s p l u s i e u r s a n n é e s .

C e t t e m i s e e n o e u v r e c o n c r è t e r e q u i e r t l ’o b t e n t i o n d ’u n e d o u b l e a s s u r a n c e :

1 ) L ’a s s u r a n c e d ’u n e c o n s e r v a t i o n p a r f a i t e d u f o n c t i o n n e m e n t d e l ’e n s e m b l e d e s

s y s t è m e s e t d e s c h a î n e s d e t r a n s m i s s i o n d ’i n f o r m a t i o n ; d ’o ù u n e p r é p a r a t i o n e t

u n e p l a n i f i c a t i o n r i g o u r e u s e s d e s r e q u a l i f i c a t i o n s n é c e s s a i r e s .

2 ) L ’a s s u r a n c e d ’u n e a d a p t a t i o n b o n n e e t r a p i d e d e s o p é r a t e u r s à l a n o u v e l l e

c o n f i g u r a t i o n ; d ’ o ù l a p r é p a r a t i o n d ’u n e a c t i o n e n 3 v o l e t s d e s t i n é e a u x o p é r a t e u r s :

— u n v o l e t d e s e n s i b i l i s a t i o n e t d e m o t i v a t i o n s ’a p p u y a n t s u r l ’i n t é r ê t q u e r e v ê t

l ’ a m é l i o r a t i o n a u - d e l à d e l ’ e f f o r t d e r é a d a p t a t i o n d e m a n d é à c h a c u n ;

— u n v o l e t d ’a d a p t a t i o n p r o p r e m e n t d i t e u t i l i s a n t p r i n c i p a l e m e n t u n e m a q u e t t e à

g r a n d e é c h e l l e t r a n s p o r t a b l e d e c e n t r a l e e n c e n t r a l e ;

— u n v o l e t d ’e n t r a î n e m e n t s p é c i f i q u e d e s o p é r a t e u r s s u r l a t r a n c h e e l l e - m ê m e a u

c o u r s d e s o p é r a t i o n s d e r e m i s e e n s e r v i c e a p r è s l ’ a r r ê t a u c o u r s d u q u e l a é t é r é a l i s é e

l a m o d i f i c a t i o n .

D a n s l e p l a n n i n g p r é v i s i o n n e l d e r é a l i s a t i o n s u r l ’e n s e m b l e d e s t r a n c h e s , l e s

s i m u l a t e u r s s o n t é v i d e m m e n t i n c l u s ; l e u r u t i l i s a t i o n o b l i g a t o i r e p o u r l ’ a d a p t a t i o n

i m m é d i a t e d e s o p é r a t e u r s a p r è s m o d i f i c a t i o n e s t c e p e n d a n t e x c l u e e n r a i s o n d e s

c o n t r a i n t e s q u ’e n t r a î n e r a i t u n t e l c h o i x v i s - à - v i s d e s t r a n c h e s m o d i f i é e s m a i s , a u s s i ,

v i s - à - v i s d e l a f o r m a t i o n d u p e r s o n n e l d e s t r a n c h e s n o n e n c o r e m o d i f i é e s . P a r

a i l l e u r s , l e f o n c t i o n n e m e n t e t l e s y s t è m e d ’i n f o r m a t i o n d e m e u r a n t i n c h a n g é s ,

l a v a l e u r a j o u t é e a p p o r t é e p a r l e s i m u l a t e u r p o u r c e t t e o p é r a t i o n e s t r e l a t i v e m e n t

f a i b l e .

L e b é n é f i c e a t t e n d u e s t d ’a c c r o î t r e l ’ i m p r o b a b i l i t é d ’é v é n e m e n t s d é j à t r è s

i m p r o b a b l e s e t l a n a t u r e m ê m e d e c e b é n é f i c e r e n d t o u t e e s t i m a t i o n i n f i n i m e n t

d é l i c a t e .

I

SUM M ARY O F SE SSIO N IV

C h a i r m a n : W . R o e h n s c h

T w o p a p e r s i n t h i s s e s s i o n d e a l t w i t h t h e p h y s i c s o f t h e W W E R - 1 0 0 0

r e a c t o r , a n d o t h e r p a p e r s c o v e r e d d e s i g n i m p r o v e m e n t s .

O n e o f t h e U S S R p a p e r s d i s c u s s e d r e a c t o r e n e r g y d i s t r i b u t i o n c o n t r o l

u n d e r v a r i a b l e l o a d c o n d i t i o n s , p a r t i c u l a r l y i n t h e c a s e o f a l l c o n t r o l r o d s e x c e p t

t h e a u t o g r o u p b e i n g w i t h d r a w n f r o m t h e r e a c t o r . T h e o n l y u n s t a b l e m o d e i s

a x i a l , a n d t h i s i s c o n t r o l l e d b y b o r o n c o n c e n t r a t i o n . T h e s e c o n d U S S R p a p e r

c o n s i d e r e d m e t h o d s o f c o n t r o l l i n g r e a c t i v i t y c h a n g e s d u e t o b u r n u p o r x e n o n

p o i s o n i n g . I t i s p r o p o s e d t o u s e b u r n a b l e p o i s o n s a n d u n d e r t a k e f u e l c h a n g i n g

t w i c e a y e a r , a s t h i s i s c o n s i d e r e d e c o n o m i c . T h e s e m e t h o d s w o u l d m a i n t a i n

t h e t e m p e r a t u r e c o e f f i c i e n t s o f r e a c t i v i t y n e g a t i v e ; s o t h a t f u e l c l a d d i n g t e m p e r a t u r e

t r a n s i e n t s a r e n o t s e v e r e .

I n F r a n c e a t t e n t i o n i s b e i n g p a i d t o i m p r o v e m e n t s i n t h e r e l i a b i l i t y o f

c o m p o n e n t s f o r o v e r p r e s s u r e p r o t e c t i o n o f t h e p r i m a r y p r e s s u r e c i r c u i t a n d s h u t ­

d o w n c o o l i n g s y s t e m . T h e m a i n s t e p s r e p o r t e d f o r s o l v i n g t h i s p r o b l e m a r e t o

u s e p i l o t e d s a f e t y v a l v e s o f t h e S E B I M t y p e w h i c h a r e s u i t a b l e f o r s t e a m a n d

w a t e r d i s c h a r g e , t o p r o v i d e m e a n s o f c l o s i n g t h e d o w n - s t r e a m s i d e o f t h e s a f e t y

v a l v e i n t h e e v e n t o f s a f e t y v a l v e f a i l u r e , a n d t o s u p p l y i n f o r m a t i o n t o t h e o p e r a t o r

o n t h e s t a t e o f t h e p r e s s u r e r e l i e f s y s t e m c o m p o n e n t s .

T h e p r o b l e m o f r e m o v i n g d e c a y h e a t a f t e r a r e a c t o r s c r a m t o a m e l i o r a t e

c o n d i t i o n s w h i c h a r i s e i f t h e r m o s i p h o n c o o l i n g i s r e l i e d u p o n h a s b e e n c o n s i d e r e d

i n I n d i a . T h e s o l u t i o n h a s b e e n t o i n s t a l l a c o n t r o l l e d b y - p a s s a c r o s s t h e m a i n

p r i m a r y f l o w a t a l o w p r e s s u r e t o p r e v e n t b o i l i n g .

C a n a d i a n a u t h o r s d e s c r i b e d t h e i r p o s t - a c c i d e n t r e v i e w p r o c e d u r e s . T h e

p u r p o s e o f t h e r e v i e w i s t o e n s u r e t h a t t h e o p e r a t o r s w o u l d b e a b l e t o c o n t i n u e

t h e i r d u t i e s i n a c c i d e n t c o n d i t i o n s i n a c c o r d a n c e w i t h e m e r g e n c y p r o c e d u r e s . A s

a r e s u l t o f t h e r e v i e w s o m e a d d i t i o n a l m e a s u r e s h a v e b e e n t a k e n . F o r e x a m p l e ,

a s h i e l d i n g w a l l h a s b e e n b u i l t t o r e d u c e r a d i a t i o n l e v e l s i n t h e c o n t r o l r o o m f r o m

a p o t e n t i a l l y r a d i o a c t i v e f i l t e r a n d e m e r g e n c y c o r e c o o l i n g p u m p s w i t c h g e a r h a s

b e e n r e l o c a t e d s i n c e i t w o u l d o t h e r w i s e b e i n a c c e s s i b l e a s a r e s u l t o f h i g h r a d i a t i o n

l e v e l s . P r o c e d u r e s h a v e a l s o b e e n c h a n g e d . T h e la r g e a m o u n t o f d e t a i l w h i c h i s

r e q u i r e d f o r t h e s e r e v i e w s w a s s t r e s s e d b y t h e a u t h o r s .

I t w a s c l a i m e d t h a t a l l t h e c o o l i n g s t a t e s o f a P W R p l a n t c a n b e i d e n t i f i e d a n d

a d i r e c t r e l a t i o n c a n b e e s t a b l i s h e d b e t w e e n a n y o f t h e s e s t a t e s a n d t h e a p p r o p r i a t e

a c t i o n s t o b e t a k e n , p r o v i d e d s u i t a b l e i n s t r u m e n t a t i o n i s a v a i l a b l e . T h e p r o c e d u r e s

99

100 SUMMARY OF SESSION IV

t o b e f o l l o w e d n e e d t o b e u s e d i n c o n j u n c t i o n w i t h t h e s a f e t y p a n e l s ( d e s c r i b e d i n

t h e F r e n c h p a p e r I A E A - S M - 2 6 8 / 5 6 i n S e s s i o n I I I ) . T h e o p e r a t o r i s e x p e c t e d t o

d i a g n o s e t h e s i t u a t i o n , a s s u r e h i m s e l f t h a t t h e a u t o m a t i c a c t i o n s h a v e b e e n t a k e n

a n d f o l l o w t h e a p p r o p r i a t e p r o c e d u r e ; i n c e r t a i n s i t u a t i o n s t h e s a f e t y e n g i n e e r

w o u l d b e c a l l e d i n .

T h e p a p e r s a n d d i s c u s s i o n s i n t h i s s e s s i o n h i g h l i g h t e d t h r e e i m p o r t a n t p o i n t s .

T h e f i r s t i s t h a t t h e s a f e t y v a l v e s a n d o t h e r c o m p o n e n t s p r o v i d e d a s p r o t e c t i o n

a g a i n s t o v e r p r e s s u r e i n t h e p r i m a r y c o o l a n t c i r c u i t d e m a n d m o r e f u n c t i o n a l

i n t e g r i t y t h a n s i m i l a r c o m p o n e n t s u s e d i n o t h e r i n d u s t r i e s ; s t e p s t a k e n t o m e e t

t h i s r e q u i r e m e n t a r e w e l l a d v a n c e d . T h e s e c o n d i s t h a t a r e v i e w s h o u l d b e u n d e r ­

t a k e n i n c o n s i d e r a b l e d e t a i l i n o r d e r t o e n s u r e t h a t p l a n t c o n d i t i o n s f o l l o w i n g a n

a c c i d e n t h a v e b e e n t a k e n i n t o a c c o u n t i n t h e r e c o v e r y a c t i o n s t h a t a r e p l a n n e d . T h e

t h i r d i s t h a t t h e p r o b l e m o f l o s s o f i n s t r u m e n t a t i o n m u s t b e c o n s i d e r e d . I n s o m e c a s e s ( e . g .

l o s s o f i n s t r u m e n t s u p p l i e s ) t h e o p e r a t o r m a y n o t k n o w w h a t i n f o r m a t i o n p r e s e n t e d

t o h i m i s c o r r e c t a n d w h a t i s f a l s e ; a l t h o u g h t h e a u t o m a t i c e q u i p m e n t m a y f u n c t i o n

c o r r e c t l y , s o m e o f i t m a y b e r e s p o n d i n g t o f a u l t y i n s t r u m e n t s . I t a p p e a r s t o b e

p o s s i b l e t o p r o v i d e r e d u n d a n c y o f i n s t r u m e n t a t i o n s u p p l i e d f r o m d i f f e r e n t s o u r c e s ,

b u t c o n t i n u o u s m o n i t o r i n g o f i n s t r u m e n t a t i o n o r s o m e o t h e r m e t h o d i s n e e d e d t o

t e l l t h e o p e r a t o r w h i c h i n s t r u m e n t s a r e o u t o f o r d e r . T h i s a p p e a r s t o b e a u s e f u l

f i e l d o f s t u d y .

F E E D B A C K O F O P E R A T I N G E X P E R I E N C E

(S e ss io n V )

C h a i r m e n

F . Y a . O V C H I N N I K O V

U S S R

T . P . H A I R E

U n i t e d K i n g d o m

IAEA-SM-268/23

O R G A N I Z A T I O N A L A N D T E C H N I C A L

A S P E C T S O F O P E R A T I N G E X P E R I E N C E

R E V I E W A N D F E E D B A C K A C T I V I T I E S

M . N O B I L E , I . T R I P P U T I

E n t e N a z i o n a l e p e r l ’E n e r g i a E l e t t r i c a ,

R o m e , I t a l y

Abstract

O R G A N IZ A T IO N A L AN D T EC H N IC A L ASPECTS OF O PER A TIN G EXPERIENCE REVIEW

AN D F E E D B A C K A C TIV ITIES.The screening and in-depth evaluation o f operating experience and the implementation o f the

lessons learned from it are approaches being used more and more by the nuclear com m unity, especially after the Three Mile Island accident, as an aid not only to reliable operation, but also to further improvement o f safety. Ente Nazionale per l’Energia Elettrica (EN EL) has come to the conclusion that evaluating a wider data and inform ation base and sharing operational inform ation with as many operating plants as possible is to be highly recommended. It has therefore set up an ad hoc W orking Group whose aims are the collection, screening and integration o f data, and preliminary analysis and distribution o f relevant experience and abnormal events. A fter discussing the constitution and the interfaces o f the W orking Group with other EN EL units, the paper outlines the principal problems encountered in perform ing each o f the tasks. In particular, the abnormal event screening and analysis criteria adopted by the W orking Group and a summary o f the first trial period o f experience are reported.

I N T R O D U C T I O N

O n e o f t h e m o s t g e n e r a l l y a g r e e d l e s s o n s l e a r n e d f r o m t h e T M I a c c i d e n t i s

t h e i n c r e a s i n g a t t e n t i o n t h a t n e e d s t o b e d e v o t e d t o t h e r e v i e w o f o p e r a t i n g

e x p e r i e n c e .

O n t h e b a s i s o f t h i s c o n s i d e r a t i o n , E n t e N a z i o n a l e p e r l ’E n e r g i a E l e t t r i c a

( E N E L ) , t h e I t a l i a n S t a t e - o w n e d U t i l i t y , d e c i d e d t o i m p r o v e i t s a c t i v i t i e s r e l a t e d

t o t h e e v a l u a t i o n a n d a n a l y s i s o f o p e r a t i n g e x p e r i e n c e . A s E N E L i s r e s p o n s i b l e

b o t h f o r t h e e n g i n e e r i n g a n d o p e r a t i o n o f i t s n u c l e a r p o w e r p l a n t s i n I t a l y , i t

s e e m e d n e c e s s a r y t o d e v o t e t h e s a m e a t t e n t i o n t o t h e u t i l i z a t i o n o f t h i s i m p o r t a n t

t o o l d u r i n g p l a n t o p e r a t i o n a s d u r i n g t h e d e s i g n a n d c o n s t r u c t i o n p h a s e s .

A l s o t h e I t a l i a n s a f e t y a u t h o r i t y , E N E A , f o r m a l l y i d e n t i f i e d t h e n e e d t o t a k e

i n t o a c c o u n t , i n a c o m p r e h e n s i v e a n d s y s t e m a t i c w a y , t h e o p e r a t i n g e x p e r i e n c e

b o t h o f I t a l i a n a n d f o r e i g n p l a n t s .

103

T A B L E I . I T A L I A N N U C L E A R P O W E R P L A N T D A T A

104 NOBILE and TRIPPUTI

Latina Trino Caorso A lto Lazio Cirene PUNa

Reactor type G CR PWR W BWR mark 2 BWR mark 3 SGHWR PWR W

Electric power(MW(e)) 160 270 894 2 X 980 40 2 X 1000

Com mercialoperation 1964 1965 1981 — —

a Progetto unificato nucleare (standardized project for future pressurized nuclear power

plants to be built in Italy).

T h e f i r s t p r o b l e m t h a t E N E L h a d t o s o l v e w a s t o c h o o s e t h e b e s t o r g a n i z a t i o n a l

a p p r o a c h b e t w e e n t h e f o l l o w i n g a l t e r n a t i v e s :

( a ) C r e a t i o n i n e a c h n u c l e a r p o w e r p l a n t i n o p e r a t i o n a n d i n e a c h d e s i g n c e n t r e

o f a n a u t o n o m o u s u n i t p r o v i d i n g d i r e c t l y f o r t h e c o l l e c t i o n , s c r e e n i n g a n d

a n a l y s i s o f i n t e r n a l a n d e x t e r n a l o p e r a t i n g e x p e r i e n c e a n d f o r i m p l e m e n t a t i o n

o f t h e l e s s o n s l e a r n e d .

( b ) C r e a t i o n o f a c e n t r a l i z e d w o r k i n g g r o u p w i t h t h e s a m e f u n c t i o n s , r e q u i r i n g

o f t h e p e r i p h e r a l u n i t s o n l y t h e i m p l e m e n t a t i o n o f i t s r e c o m m e n d a t i o n s

r e l a t e d t o p o s s i b l e c o r r e c t i v e m e a s u r e s .

A f t e r a c a r e f u l e v a l u a t i o n o f t h e p r o b l e m , E N E L d e c i d e d t h a t t h e b e s t a p p r o a c h

w a s p r o b a b l y t o p r o c e e d w i t h a n i n t e r m e d i a t e s o l u t i o n t h a t c a n b e s u m m a r i z e d

a s f o l l o w s :

( a ) C o n s t i t u t i o n o f a c e n t r a l i z e d O p e r a t i n g E x p e r i e n c e R e v i e w ( O E R ) W o r k i n g

G r o u p w i t h t h e p a r t i c i p a t i o n o f r e p r e s e n t a t i v e s o f t h e C e n t r a l D e p a r t m e n t s

f o r d e s i g n a n d c o n s t r u c t i o n , p r o d u c t i o n a n d t r a n s m i s s i o n , a n d r e s e a r c h a n d

d e v e l o p m e n t . T h e s p e c i f i c a i m i s t o c o l l e c t s c r e e n , i n t e g r a t e , a n a l y s e i n a

p r e l i m i n a r y w a y a n d d i s t r i b u t e t h e r e l e v a n t e x p e r i e n c e a n d a b n o r m a l e v e n t

n o t i f i c a t i o n r e l a t i v e t o E N E L a n d o v e r s e a s p l a n t s .

( b ) D e v e l o p m e n t o f o r g a n i z a t i o n a l a n d s t a f f i n g m e a s u r e s i n t h e p e r i p h e r a l u n i t s

i n o r d e r t o p e r f o r m d e t a i l e d a n a l y s e s , e n h a n c i n g i n t h i s w a y , o n t h e b a s i s

o f i n f o r m a t i o n r e c e i v e d b y t h e O E R W o r k i n g G r o u p , t h e c a p a b i l i t y o f

d e f i n i n g p o s s i b l e c o r r e c t i v e a c t i o n s i n t h e c o n t e x t o f e a c h s p e c i f i c s i t u a t i o n .

A s a m a t t e r o f f a c t t h i s a p p r o a c h h a s b e e n o r i g i n a t e d m a i n l y b y t h e s p e c i a l I t a l i a n

s i t u a t i o n i n t h e n u c l e a r f i e l d ( s e e T a b l e I ) , w i t h m a n y d i f f e r e n t k i n d s o f r e a c t o r s .

IAEA-SM-268/23 105

T h i s , o n t h e o n e h a n d , d i s c o u r a g e s d e t a i l e d a n a l y s i s i n a c e n t r a l i z e d W o r k i n g G r o u p ,

b e c a u s e i t w o u l d r e q u i r e t o o m a n y d i f f e r e n t k i n d s o f e x p e r t i s e , b u t o n t h e o t h e r

h a n d p r o v i d e s t h e o p p o r t u n i t y t o s c r e e n i n a d v a n c e a l l o p e r a t i n g e x p e r i e n c e

i n f o r m a t i o n s o a s t o s e n d t o t h e p e r i p h e r a l u n i t s f o r f u r t h e r e x a m i n a t i o n o n l y

t h o s e j u d g e d a p p l i c a b l e t o t h e m . I n t h i s w a y i t i s p o s s i b l e t o r e d u c e d r a s t i c a l l y

t h e w o r k l o a d o f t h e p e r i p h e r a l u n i t s ( a d m i n i s t r a t i v e d u t i e s , l o g g i n g , e x a m i n i n g , e t c . ) .

T h e s e a d v a n t a g e s a p p e a r e v e n m o r e s i g n i f i c a n t i n v i e w o f t h e f a c t t h a t a l l

t h e s e a c t i v i t i e s m u s t b e p e r f o r m e d i n t h e n e a r f u t u r e u n d e r t h e r e q u i r e m e n t s o f a n

o v e r a l l q u a l i t y a s s u r a n c e p l a n .

O R G A N I Z A T I O N A L A S P E C T S

F i r s t o f a l l i t i s w o r t h u n d e r l i n i n g t h a t t h e m a i n a i m o f t h e i n f o r m a t i o n

p r o c e s s i n g p e r f o r m e d b y t h e O E R W o r k i n g G r o u p i s n o t t o h a v e s t a t i s t i c a l l y

s i g n i f i c a n t d a t a o n p l a n t a n d c o m p o n e n t b e h a v i o u r , b u t r a t h e r t o d i s s e m i n a t e

n a r r a t i v e , i n t e g r a l , c o m p r e h e n s i v e a n d t e c h n i c a l l y v a l i d d e s c r i p t i o n s o f a b n o r m a l

e v e n t s w i t h p a r t i c u l a r e m p h a s i s o n t h e i r s a f e t y s i g n i f i c a n c e . T h i s i n f o r m a t i o n i s

d i s t r i b u t e d t o g e t h e r w i t h a n ‘E v e n t E v a l u a t i o n S h e e t ( E E S ) ’ ( s e e F i g . 1 ) , d e s i g n e d

f o r l i s t i n g a l l t h e r e f e r e n c e s r e l a t e d t o a p a r t i c u l a r a b n o r m a l e v e n t a n d , a t t h e

s a m e t i m e , p r e s e n t i n g i n a m a t r i x f o r m t h e r e s u l t s o f w o r k i n g g r o u p e v a l u a t i o n s

i n t e r m s o f a p p l i c a b i l i t y t o a s p e c i f i c p l a n t , s a f e t y s i g n i f i c a n c e a n d o p p o r t u n i t y

f o r d e e p e r a n a l y s i s o r i n t e g r a t i o n .

A c o m p l e t e n a r r a t i v e s e c t i o n i s a l s o a t t a c h e d t o e a c h E E S a n d d i s s e m i n a t e d .

A s m e n t i o n e d a b o v e , s i n c e t h e p r i n c i p a l s c o p e o f t h e O E R W o r k i n g G r o u p

i s t o s e l e c t a b n o r m a l e v e n t s o n t h e b a s i s o f t h e i r s a f e t y s i g n i f i c a n c e a n d n o t t o

o b t a i n r e l i a b i l i t y d a t a , a l l t h e p e o p l e i n c h a r g e o f t h e s e a c t i v i t i e s b e l o n g t o t h e

s a f e t y d i v i s i o n o f t h e i r r e s p e c t i v e C e n t r a l D e p a r t m e n t s .

T h e n u m b e r o f W o r k i n g G r o u p m e m b e r s h a s b e e n l i m i t e d , a t l e a s t i n t h i s

f i r s t p h a s e , t o a f e w e x p e r t s i n s a f e t y a n a l y s i s . T h i s c h o i c e h a s o n t h e o n e s i d e t h e

d i s a d v a n t a g e s o f a h i g h l e v e l o f w o r k i n g l o a d o n i n d i v i d u a l m e m b e r s a n d a n

o b v i o u s l a c k o f e x p e r t i s e i n s o m e s p e c i f i c a r e a s , b u t o n t h e o t h e r t h e a d v a n t a g e

o f a s m o o t h e r o p e r a t i o n a n d e a s e o f d e c i s i o n m a k i n g .

T o m a k e u p f o r p o s s i b l e l a c k o f e x p e r t i s e , s p e c i a l i s t s i n s p e c i f i c a r e a s c a n b e

c a l l e d u p o n b y W o r k i n g G r o u p m e m b e r s , a n y t i m e a n i n - d e p t h a n a l y s i s i s d e e m e d

n e c e s s a r y .

A f t e r t h e W o r k i n g G r o u p h a s d i s s e m i n a t e d t o t h e p r o p e r p e o p l e t h e p e r t i n e n t

i n f o r m a t i o n , i n c l u d i n g p o s s i b l y i t s o w n o r o t h e r ’s r e c o m m e n d a t i o n s , t h e E N E L

u n i t s r e s p o n s i b l e f o r e a c h p l a n t i n o p e r a t i o n , c o n s t r u c t i o n o r d e s i g n t a k e

r e s p o n s i b i l i t y f o r i m p l e m e n t i n g a n y l e s s o n s t h a t c a n b e d e r i v e d f r o m t h e

i n f o r m a t i o n .

106 NOBILE and TRIPPUTI

E V E N T

E V A L U A T I O N

S H E E T

C O M P I L A T I O N D A T E N U M B E R

R E V I S I O N

N U C L E A R P O W E R P L A N T E V E N T

n a m e D E S C R I P T I O N

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IAEA-SM-268/23 107

F e e d b a c k t o t h e W o r k i n g G r o u p o f i n f o r m a t i o n r e l a t i v e t o a n y a c t i o n

p e r f o r m e d b y t h e r e s p o n s i b l e u n i t s i s r e q u i r e d i n o r d e r t o c o m p l e t e t h e f i l e .

F i n a l l y i t i s p e r h a p s w o r t h s a y i n g t h a t t h e W o r k i n g G r o u p d o e s n o t

c o n s t i t u t e a u n i t i n d e p e n d e n t f r o m o t h e r E N E L C e n t r a l D e p a r t m e n t s , s i n c e i t

m u s t o p e r a t e w i t h i n t h e f r a m e w o r k o f t h e c o r p o r a t e o r g a n i z a t i o n a n d u t i l i z e

e x i s t i n g s t r u c t u r e s a n d r e s o u r c e s .

P R O C E S S I N G O F E X T E R N A L O P E R A T I N G E X P E R I E N C E

I n f o r m a t i o n c o l l e c t i o n

W i t h t h e e x c e p t i o n o f t h e L a t i n a a n d C i r e n e p l a n t s ( s e e T a b l e I ) , b o t h

e x i s t i n g a n d f u t u r e n u c l e a r p o w e r p l a n t s i n I t a l y u s e t e c h n o l o g y f r o m t h e U S A .

T h e r e f o r e a t t e n t i o n h a s f i r s t b e e n d e v o t e d t o U S p l a n t e x p e r i e n c e s . R e c o g n i z i n g

t h e i m p o r t a n c e o f t h e w o r k p e r f o r m e d i n t h i s f i e l d b y s o m e n e w u t i l i t y o r g a n i z a ­

t i o n s , E N E L d e c i d e d t o j o i n N S A C ( N u c l e a r S a f e t y A n a l y s i s C e n t e r ) i n J u l y 1 9 8 1

a n d I N P O ( I n s t i t u t e f o r N u c l e a r P o w e r O p e r a t i o n s ) i n J a n u a r y 1 9 8 2 .

T h e s e m e m b e r s h i p s p r o v i d e E N E L w i t h t h e r e s u l t s o f t h e s c r e e n i n g a n d

e v a l u a t i o n o f t h o u s a n d s o f U S L i c e n s e e E v e n t R e p o r t s ( L E R s ) e a c h y e a r a n d

a l l o w p a r t i c i p a t i o n i n N O T E P A D , a v e r y v a l u a b l e c o m p u t e r - a i d e d i n t e r c o m m u n i c a ­

t i o n s y s t e m b e t w e e n u t i l i t i e s . T h e O E R W o r k i n g G r o u p m o n i t o r s a l m o s t d a i l y

t h e f o l l o w i n g N O T E P A D a c t i v i t i e s :

— E m e r g e n c y H o t L i n e ( i n f o r m a t i o n r e g a r d i n g a c t u a l e m e r g e n c i e s )

— O p e r a t i n g P l a n t E x p e r i e n c e s ( t e c h n i c a l d e s c r i p t i o n o f o f f - n o r m a l e v e n t s )

— I N P O S i g n i f i c a n t E v e n t R e p o r t s ( d e s c r i p t i o n o f t h e e v e n t s s c r e e n e d b y I N P O

a n d t h e r e a s o n s t h e y a r e o f c o n c e r n )

A d d i t i o n a l l y , I N P O S i g n i f i c a n t O p e r a t i n g E x p e r i e n c e R e p o r t s a n d I N P O / N S A C

c a s e s t u d i e s , b o t h o f t h e m r e c e i v e d b y m a i l , a r e e v a l u a t e d .

O t h e r i m p o r t a n t s o u r c e s o f i n f o r m a t i o n a r e t h e r e s u l t s o f N R C o p e r a t i n g

e x p e r i e n c e e v a l u a t i o n s , i n p a r t i c u l a r :

— I n s p e c t i o n a n d E n f o r c e m e n t B u l l e t i n s

— I n s p e c t i o n a n d E n f o r c e m e n t C i r c u l a r s

— I n s p e c t i o n a n d E n f o r c e m e n t I n f o r m a t i o n N o t i c e s

— N R C G e n e r i c L e t t e r s

— N R C P o w e r R e a c t o r E v e n t s ( N U R E G / B R - 0 0 5 1 )

— A E O D r e p o r t s ( O f f i c e f o r A n a l y s i s a n d E v a l u a t i o n o f O p e r a t i o n a l D a t a ) .

T h e O E R W o r k i n g G r o u p a l s o h a s t h e p o s s i b i l i t y o f e x a m i n i n g t h e p u b l i c a t i o n

‘N u c l e a r P o w e r E x p e r i e n c e ’ , m a i n l y u s e d t o c o l l e c t a d d i t i o n a l i n f o r m a t i o n o n

1 08 NOBILE and TRIPPUTI

e v e n t s a l r e a d y c o v e r e d b y o t h e r d o c u m e n t s a n d t o i d e n t i f y r e l a t e d f a i l u r e s o r

e v e n t s e q u e n c e s w h i c h c a n g i v e f u r t h e r i n s i g h t i n t o a n e v e n t u n d e r c o n s i d e r a t i o n .

A s r e g a r d s t h e L a t i n a a n d C i r e n e p l a n t s , t h e a b o v e d o c u m e n t s a r e n o t

g e n e r a l l y u s e f u l f o r i m p l e m e n t i n g t h e o p e r a t i n g e x p e r i e n c e r e v i e w ; t h e r e f o r e

i t i s p l a n n e d i n t h e n e a r f u t u r e t o c a r r y o u t a c t i o n s i n o r d e r t o g u a r a n t e e o t h e r

u t i l i z a b l e i n f o r m a t i o n s o u r c e s .

S c r e e n i n g o f a b n o r m a l e v e n t s

T h e n e x t s t e p a n d , p e r h a p s t h e m o s t i m p o r t a n t o n e i n t h e r e s p o n s i b i l i t i e s

o f t h e O E R W o r k i n g G r o u p , i s t h e e v e n t s c r e e n i n g p r o c e s s . T h e a i m i s t o i d e n t i f y

w h a t i s r e a l l y i n t e r e s t i n g f o r o u r p l a n t s a n d d e t e r m i n e h o w i m p o r t a n t i t i s .

T h e f i r s t p h a s e i s t h e s e t t l e m e n t o f e v e n t a p p l i c a b i l i t y o r n o n - a p p l i c a b i l i t y

o n t h e b a s i s o f t h e s p e c i f i c c r i t e r i a l i s t e d i n t h e A p p e n d i x . T h e e v e n t a p p l i c a b i l i t y

i s v e r i f i e d f o r e a c h E N E L p l a n t a n d t h e r e l e v a n t i n f o r m a t i o n i s s e n t t o p l a n t s o r

t o d e s i g n c e n t r e s o n l y w h e n j u d g e d a p p l i c a b l e .

T h e d i f f i c u l t y o f d e c i s i o n r a n g e s f r o m t h e a p p a r e n t l y t r i v i a l t o t h e v e r y

c o m p l e x a n d u n c e r t a i n . G e n e r a l l y s p e a k i n g t h e W o r k i n g G r o u p d o e s n o t d e f i n e

a s a p p l i c a b l e a n e v e n t c a u s e d b y f a i l u r e o f a s p e c i f i c c o m p o n e n t n o t p r e s e n t i n

o u r p l a n t s . H o w e v e r , i t i s n e c e s s a r y t o g i v e a t t e n t i o n t o s u c h c a s e s i n o r d e r t o

i d e n t i f y w h e t h e r t h e e v e n t s e q u e n c e f o l l o w i n g a c o m p o n e n t f a i l u r e m a y h a v e a

g e n e r a l s i g n i f i c a n c e , o r w h e t h e r t h e f a i l u r e m o d e m a y a p p l y t o d i f f e r e n t v e n d o r s

o f t h e s a m e c o m p o n e n t .

I n p r a c t i c e i t i s o f t e n t r o u b l e s o m e t o d e t e r m i n e t h e p r e s e n c e o f a s p e c i f i c

c o m p o n e n t i n o u r p l a n t s , i n p a r t i c u l a r w h e n i t i s a s u b c o m p o n e n t o f a m a j o r

i t e m o f e q u i p m e n t . M o r e o v e r , m a t e r i a l l i s t s o f t e n r e f e r t o t h e I t a l i a n v e n d o r

n a m e a n d c l a s s i f i c a t i o n a n d n o t t o t h e o r i g i n a l U S ( o r o t h e r s ) m a n u f a c t u r e r s .

T h e s e c o n d p h a s e o f t h e s c r e e n i n g i s t h e d e f i n i t i o n o f s a f e t y r e l e v a n c e o n

t h e b a s i s o f s p e c i f i c c r i t e r i a l i s t e d i n t h e A p p e n d i x . T h e s a f e t y r e l e v a n c e i s

e s t a b l i s h e d e s s e n t i a l l y o n t h e b a s i s o f t h e c a u s e s a n d t h e e v o l u t i o n o f e a c h e v e n t .

O n e m a j o r f e a t u r e o f t h i s s t e p , a s w e i n t e n d i t , i s t h e a t t e m p t n o t t o i d e n t i f y t h e

s a f e t y r e l e v a n c e o f t h e e v e n t i n t h e p l a n t w h e r e i t h a p p e n e d , b u t t h e r e l e v a n c e

o f t h e s a m e e v e n t i f i t h a p p e n e d i n o n e o f o u r p l a n t s . S o , f o r e x a m p l e , t h e l o s s

o f t w o d i e s e l s i s a n u n a c c e p t a b l e d e g r a d a t i o n o f s a f e t y i n a p l a n t w h e r e o n l y t w o

d i e s e l s a r e i n s t a l l e d , w h i l e t h e s a m e e v e n t p r o v e s n o t t o b e r e l e v a n t f o r t h e C a o r s o

p l a n t w h e r e t h e r e a r e f o u r d i e s e l s , o f w h i c h o n e a l o n e i s s u f f i c i e n t .

I n s o m e c a s e s t h i s a n a l y s i s i s d i f f i c u l t , b e c a u s e i t i m p l i e s a r a t h e r d e t a i l e d

k n o w l e d g e b o t h o f t h e o r i g i n a l a n d o f t h e E N E L p l a n t . H o w e v e r i t i s b e l i e v e d

t h a t i t i s a v e r y i m p o r t a n t p i e c e o f i n f o r m a t i o n b e c a u s e p l a n t p e r s o n n e l h a v e n o t

g e n e r a l l y t h e o p p o r t u n i t y o f a n a l y s i n g p o t e n t i a l e v o l u t i o n s a n d c o n s e q u e n c e s o f

e v e n t s v e r y o f t e n d i f f e r e n t f r o m t h o s e c o n s i d e r e d i n t h e s a f e t y r e p o r t s o r i n t h e

b a s i c t r a i n i n g c o u r s e s .

IAEA-SM-268/23 109

T h e t h i r d p h a s e i s t h e d e f i n i t i o n o f s a f e t y p r i o r i t y o n t h e b a s i s o f t h e s p e c i f i c

c r i t e r i a g i v e n i n t h e A p p e n d i x . T h e s a f e t y p r i o r i t y i s d e f i n e d f r o m a n e x a m i n a t i o n

o f t h e p o t e n t i a l c o n s e q u e n c e s o f t h e e v e n t a s a p p l i e d t o o u r p l a n t s . A n e v e n t is

c l a s s i f i e d i n a s a f e t y p r i o r i t y c l a s s w h e n i t h a s t h e p o t e n t i a l t o c a u s e t h e d i r e c t l o s s

o f a s a f e t y b a r r i e r ( f u e l c l a d d i n g , p r i m a r y s y s t e m , c o n t a i n m e n t , e t c . ) o r a l a r g e

d o s e t o p e r s o n n e l . I n t h i s c a s e t h e i n f o r m a t i o n i s c o m m u n i c a t e d t o t h e p l a n t s a s a

m a t t e r o f u r g e n c y a s s p e c i f i e d b e l o w .

D a t a i n t e g r a t i o n

I n o r d e r t o o v e r c o m e p r o b l e m s r e l a t e d t o l a n g u a g e ( m o s t o f t h e i n f o r m a t i o n

i s a v a i l a b l e o n l y i n E n g l i s h ) a n d , m o r e i m p o r t a n t , t o c o m p l e t e t h e i n f o r m a t i o n

w i t h g e n e r a l a n d d e t a i l e d d e s c r i p t i o n s o f t h e p l a n t , a c o m p r e h e n s i v e r e p o r t i s

p r e p a r e d b y t h e W o r k i n g G r o u p w h e n j u d g e d n e c e s s a r y . T h e r e p o r t m a y a l s o

h a v e a s e c t i o n c o n t a i n i n g r e f e r e n c e s t o s i m i l a r e v e n t s i n o r d e r t o g i v e a c o m p l e t e

p i c t u r e o f a r e c u r r i n g p r o b l e m i n t h e n u c l e a r i n d u s t r y .

P r e l i m i n a r y a n a l y s i s

W h e n a n e v e n t i s v e r y s i g n i f i c a n t a n d t h e p l a n t r e s p o n s e m a y b e u n c e r t a i n ,

a s p e c i f i c s t u d y i s p e r f o r m e d . T h e s t u d y m a y r a n g e f r o m a s i m p l e c a l c u l a t i o n

( f o r e x a m p l e , a s u p p r e s s i o n p o o l h e a t - u p r a t e ) t o t h e u s e o f c o m p l e x c o m p u t e r

c o d e s l i k e R E T R A N - 0 2 a n d C O N T E M P T . T h e f i r s t p l a n t t o b e m o d e l l e d o n

R E T R A N - 0 2 i s C a o r s o a n d t h e c o d e i s n o w o p e r a t i o n a l . I n a d d i t i o n , w h e n , a t

t h e e n d o f t h i s y e a r , a p r o b a b i l i s t i c r i s k a s s e s s m e n t f o r t h e E N E L s t a n d a r d P W R

p l a n t i s p r e p a r e d , a n a t t e m p t w i l l b e m a d e t o u s e f a u l t t r e e s a n d e v e n t t r e e s t o

a s s e s s t h e s a f e t y r e l e v a n c e o f a s p e c i f i c e v e n t r e l a t i v e t o o u r p l a n t s .

D i s s e m i n a t i o n

T h e f i n a l t a s k i s t o k e e p t h e k e y p e o p l e o f t h e r e s p o n s i b l e u n i t s i n f o r m e d

a b o u t t h e m a j o r a p p l i c a b l e e v e n t s ; t h e r e f o r e t i m e l y a n d c o r r e c t d i s t r i b u t i o n i n a

c o n t r o l l e d w a y i s v e r y i m p o r t a n t .

G e n e r a l l y t h e i n f o r m a t i o n i s s e n t b y m a i l . O n l y w h e n a n e v e n t i s c l a s s i f i e d

i n a s a f e t y p r i o r i t y c l a s s i s i t s e n t b y t e l e x o r t e l e c o p i e r , o r e v e n a n t i c i p a t e d b y a

p h o n e c a l l .

P R O C E S S I N G O F A B N O R M A L E V E N T S O C C U R R I N G I N E N E L P L A N T S

W i t h r e f e r e n c e t o t h e p l a n t s l i s t e d i n T a b l e I , T r i n o i s s t i l l s h u t d o w n f o r

m a j o r m o d i f i c a t i o n s a n d L a t i n a e v e n t s h a v e n o t b e e n s y s t e m a t i c a l l y e v a l u a t e d u p

110 NOBILE and TRIPPUTI

t o n o w , s o t h e b u l k o f I t a l i a n o p e r a t i n g e x p e r i e n c e i s d e r i v e d f r o m t h e C a o r s o

p l a n t . T h e W o r k i n g G r o u p e x a m i n e s t h e f o l l o w i n g d o c u m e n t s :

— P r o m p t N o t i f i c a t i o n s t o S a f e t y A u t h o r i t y ( E N E A )

— E v e n t s h e e t s ( n o t r e s t r i c t e d t o s a f e t y - r e l a t e d e v e n t s ; p l a c e d o n c o m p u t e r i z e d

f i l e )

— M o n t h l y r e p o r t s ( f o l l o w - u p o f p r o m p t n o t i f i c a t i o n s )

— S e m i - a n n u a l r e p o r t s ( s y n t h e s i s o f t h e o p e r a t i o n a l d a t a )

— S p e c i f i c e v e n t r e p o r t s p r e p a r e d b y p l a n t p e r s o n n e l .

A l l t h e s e s o u r c e s o f i n f o r m a t i o n , b e s i d e s o f c o u r s e d i r e c t c o m m u n i c a t i o n s

w i t h p l a n t p e r s o n n e l , a r e t r e a t e d g e n e r a l l y i n t h e s a m e w a y a s e x t e r n a l i n f o r m a t i o n

in o r d e r t o g u a r a n t e e f e e d b a c k t o t h e d e s i g n c e n t r e s a n d t o o t h e r E N E L p l a n t s .

D e s c r i p t i o n s o f t h e m o s t s i g n i f i c a n t e v e n t s a r e d i s s e m i n a t e d a b r o a d t h r o u g h

t h e a p p r o p r i a t e i n t e r n a t i o n a l o r g a n i z a t i o n s .

S U M M A R Y O F O E R W O R K I N G G R O U P A C T I V I T I E S

T h e f o l l o w i n g d a t a s u m m a r i z e t h e a c t i v i t i e s p e r f o r m e d b y t h e O E R W o r k i n g

G r o u p i n t h e p e r i o d 1 M a y 1 9 8 2 t o 2 8 F e b r u a r y 1 9 8 3 .

E v e n t s e v a l u a t e d 2 0 0

E v e n t s e v a l u a t e d a s a p p l i c a b l e t o a t l e a s t o n e p l a n t 1 5 4

E v e n t s a p p l i c a b l e t o f u t u r e p l a n t s 9 8

E v e n t s a p p l i c a b l e t o C a o r s o p l a n t 9 4

E v e n t s a p p l i c a b l e t o T r i n o p l a n t 9 2

T h e f i l t e r i n g f u n c t i o n o f t h e W o r k i n g G r o u p a p p e a r s t o b e l i m i t e d f o r e a c h

p l a n t t o a b o u t o n e h a l f o f t h e t o t a l e v e n t s . T h i s i s b a s i c a l l y f o r t w o r e a s o n s :

( a ) T h e i n c o m i n g i n f o r m a t i o n h a s g e n e r a l l y b e e n a l r e a d y s c r e e n e d b y o t h e r

o r g a n i z a t i o n s a n d j u d g e d t o b e o f g e n e r a l i n t e r e s t ;

( b ) M o r e e x p e r i e n c e a n d m o r e t u n e - u p o f t h e s c r e e n i n g c r i t e r i a a r e n e e d e d t o

p r e p a r e a f i n e r m e s h f i l t e r .

H o w e v e r t h e r e s u l t s o f t h i s f i r s t t r i a l p e r i o d o f a c t i v i t i e s a r e j u d g e d t o b e

v a l u a b l e a n d p r o m i s i n g i n t e r m s o f a f u r t h e r r e d u c t i o n o f a n u n n e c e s s a r y b u r d e n

o n p e r i p h e r a l u n i t s .

C O N C L U S I O N S

T h e s y s t e m a t i c e v a l u a t i o n o f n a t i o n a l a n d o v e r s e a s n u c l e a r p o w e r p l a n t

o p e r a t i o n a l e x p e r i e n c e i s q u i t e a d i f f i c u l t t a s k . M a n y p r o b l e m s f a c e t h e s t a f f

IAEA-SM-268/23 111

i n v o l v e d : l a n g u a g e p r o b l e m s , l a c k o f k n o w l e d g e o f o v e r s e a s p l a n t d e s i g n s , a n d

d e f i c i e n c i e s i n c o m p o n e n t l i s t s a n d r e a l i s t i c a n a l y s e s o f p l a n t b e h a v i o u r i n d e g r a d e d

c o n d i t i o n s .

T h e O E R W o r k i n g G r o u p , e v e n i n a s i t u a t i o n o f p a r t i a l l a c k o f r e s o u r c e s , i s

t r y i n g t o f a c e t h e p r o b l e m i n a n i n t e g r a l m a n n e r , b e i n g c o n v i n c e d o f t h e i m p o r t a n c e

o f t h e t a s k . I n m o s t c a s e s i n f a c t t h e p r o b l e m s i n s i m i l a r p l a n t s a r e t h e s a m e w o r l d ­

w i d e a n d i t i s v e r y l i k e l y t h a t a p r o b l e m b e i n g f a c e d t o d a y h a s a l r e a d y b e e n s o l v e d

s u c c e s s f u l l y b y o t h e r s i n t h e p a s t . T h e p r o b l e m i s t o k n o w b y w h o m a n d h o w .

A P P E N D I X

A P P L I C A B I L I T Y C R I T E R I A

A . I . A c c i d e n t s c e n a r i o t h a t c o u l d b e r e p e a t e d i n a n o t h e r p l a n t b e c a u s e o f i t s

s i m i l a r d e s i g n a n d / o r t e c h n o l o g i c a l c h a r a c t e r i s t i c s

A . 2 . T h e p r e s e n c e o f c o m p o n e n t s ( m a t e r i a l s ) a n d e n v i r o n m e n t a l c o n d i t i o n s

s i m i l a r t o t h o s e i n v o l v e d i n t h e a b n o r m a l e v e n t

A . 3 . T h e e x i s t e n c e o f s i m i l a r o p e r a t i n g , e m e r g e n c y o r m a i n t e n a n c e p r o c e d u r e s

t h a t c o u l d l e a d p e r s o n n e l t o m a k e t h e s a m e e r r o r s

A . 4 . T h e u s e o f c a l c u l a t i o n a l a n d / o r a n a l y s i s m e t h o d o l o g i e s s i m i l a r t o t h o s e

r e v e a l e d a s i n s u f f i c i e n t o r e r r o n e o u s i n t h e e v e n t

A . 5 . N e w a n d r e l e v a n t l e s s o n w i t h g e n e r a l v a l i d i t y t o b e d r a w n f r o m t h e e v e n t .

S A F E T Y R E L E V A N C E C R I T E R I A

R . l . T w o o r m o r e f a i l u r e s i n r e d u n d a n t s y s t e m s , i n d e p e n d e n t o r d u e t o a c o m m o n

c a u s e

R . 2 . F a i l u r e s t h a t w o u l d h a v e e a s i l y e s c a p e d d e t e c t i o n b y t e s t i n g o r e x a m i n a t i o n

R . 3 . E v e n t s c e n a r i o s n o t e n v e l o p e d b y t h e p l a n t d e s i g n b a s e s

R . 4 . E v e n t s t h a t p r o c e e d i n a s i g n i f i c a n t l y d i f f e r e n t w a y f r o m w h a t w o u l d b e

e x p e c t e d

R . 5 . E v e n t s t h a t c o u l d h a v e b e e n m o r e r e l e v a n t i f t h e y h a d h a p p e n e d i n o t h e r

o p e r a t i n g c o n d i t i o n s , o r w i t h t h e a d v e n t o f a n o t h e r c r e d i b l e o c c u r r e n c e o r

w i t h a d i f f e r e n t p r o g r e s s i o n o f o c c u r r e n c e s

R . 6 . E v e n t s c a u s e d b y d é f i c i e n c e s i n p r o c e d u r a l o r a d m i n i s t r a t i v e c o n t r o l o r b y

o p e r a t i o n a l e r r o r s

R . 7 . D e s i g n o r c o n s t r u c t i o n d e f i c i e n c i e s

R . 8 . A n e v e n t w h i c h h a p p e n s w i t h a n u n a c c e p t a b l e f r e q u e n c y o r w h i c h a p p e a r s t o

h a p p e n m o r e a n d m o r e f r e q u e n t l y .

112 NOBILE and TRIPPUTI

A n e v e n t i s i n a s a f e t y p r i o r i t y c l a s s i f i t m a y i m p l y :

P . 1 . F u e l d e g r a d a t i o n

P . 2 . L o s s o f u l t i m a t e h e a t s i n k

P . 3 . L o s s o f s c r a m c a p a b i l i t y a n d / o r a b i l i t y t o m a i n t a i n t h e c o r e s u b c r i t i c a l

P . 4 . L a r g e f i s s i o n p r o d u c t r e l e a s e i n t o t h e e x t e r n a l e n v i r o n m e n t

P . 5 . P e r s o n n e l e x p o s u r e b e y o n d a c c e p t a b l e l i m i t s .

S A F E T Y P R I O R I T Y C R I T E R I A

R E F E R E N C E S

[1] K E M E N Y , J.G. (Chairman), Report of the President’s Commission on the Accident at

Three Mile Island, Commission Recommendations, B.l.b, US Government Printing Office

(October 1979) p. 68.

[2] U N I T E D STATES N U C L E A R R E G U L A T O R Y COMMISSION, Clarification of TMI

Action Plan Requirements, Rep. NUREG-0737, USNRC, Washington, D C (November 1980);

Item I, C.5.

[3] Significant Event Evaluation and Information Network (SEE-IN) Program Description

INPO (February 1983).

[4] ELECTRIC P O W E R R E S E A R C H INSTITUTE, Using P R A to Assess Nuclear Power Plant

Operating Events, Rep. NSAC-54, EPRI, Palo Alto (August 1982).

[5] U N I T E D STATES N U C L E A R R E G U L A T O R Y COMMISSION, Use of INPO SEE-IN

Program, Generic Letter No. 82-04, USNRC, Washington, D C (1982).

IAEA-SM-268/81

E X A M P L E S O F E V A L U A T I O N S O F

I N C I D E N T S IN N U C L E A R P O W E R

P L A N T S A N D L E S S O N S L E A R N E D

H . H A U N H O R S T , K . K O T T H O F F ,

F . S C H L E I F E R , M . S I M O N

G e s e l l s c h a f t f ü r R e a k t o r s i c h e r h e i t

( G R S ) m b H ,

C o l o g n e ,

F e d e r a l R e p u b l i c o f G e r m a n y

A b s t r a c t

E X A M P L E S O F E V A L U A T I O N S O F INCIDENTS IN N U C L E A R P O W E R P L A N T S A N D

LESSONS L E A R N E D .

The paper gives a survey on the evaluation of incidents experienced in nuclear power plants

in the Federal Republic of Germany (FRG) and other countries. In the F R G the evaluation of

incidents is performed by several institutions. The aim of the activities of the Gesellschaft fiir

Reaktorsicherheit in this special area are: feedback of operating experience; screening and

evaluation of important events; and dissemination of conclusions and recommendations.

Examples are given of important incidents and the conclusions which were directly drawn

from them, and an example for general analysis, which was stimulated by a certain incident.

These examples relate to: defective control pipes in pressure relief valves; pilot valve failure

of pilot-operated main steam safety valves; loss of offsite power; problems with closed-circuit

DC-contactors; steam generator tube rupture.

1 . I N T R O D U C T I O N

T h e e v a l u a t i o n o f i n c i d e n t s e x p e r i e n c e d i n n u c l e a r p o w e r p l a n t s ( N P P s ) i n

t h e F e d e r a l R e p u b l i c o f G e r m a n y ( F R G ) i s p e r f o r m e d b y s e v e r a l i n s t i t u t i o n s :

f o r s i n g l e e v e n t s b y t h e u t i l i t i e s , t h e a u t h o r i t i e s o f t h e i n d i v i d u a l s t a t e s a n d t h e i r

e x p e r t o r g a n i z a t i o n s ; a n d w i t h r e g a r d t o t h e c o l l e c t i o n a n d e v a l u a t i o n o f a l l

o p e r a t i n g e x p e r i e n c e i n N P P s b y t h e G e s e l l s c h a f t f i i r R e a k t o r s i c h e r h e i t m b H ( G R S ) .

T h e c o l l e c t i o n a n d a n a l y s i s i s d o n e b y G R S o n b e h a l f o f t h e F e d e r a l M i n i s t r y o f

t h e I n t e r i o r . A n i n s t r u m e n t f o r t h i s w o r k i s t h e ‘a b n o r m a l o c c u r r e n c e r e p o r t i n g

s y s t e m ’, w h i c h w a s i n t r o d u c e d i n t h e F R G i n 1 9 7 5 . T h e a c t i v i t i e s o f t h e G R S i n

t h i s s p e c i a l a r e a i n c l u d e f e e d b a c k o f o p e r a t i n g e x p e r i e n c e , s c r e e n i n g a n d e v a l u a t i o n

o f i m p o r t a n t e v e n t s , a n d d i s s e m i n a t i o n o f c o n c l u s i o n s a n d r e c o m m e n d a t i o n s .

E x a m p l e s a r e g i v e n b e l o w f o r t w o t y p e s o f r e a c t i o n s t o i n c i d e n t s : c o n s e ­

q u e n c e s w h i c h a r e d i r e c t l y d r a w n f r o m s i n g l e i n c i d e n t s , a n d g e n e r a l a n a l y s e s

s t i m u l a t e d b y c e r t a i n i n c i d e n t s .

1 1 3

114 HAUNHORST et aL

Pilot Valve

Main Steam SR-Valve

AfromMainSteamLine

^ Corrosion

п т

ITo Pressure

Suppression Pool

Pulse Line

Control Pipe(X 10 Cr Ni Ti 18 9)

FIG.l. Defective control pipes.

2 . D E F E C T I V E C O N T R O L P I P E S O F P R E S S U R E R E L I E F V A L V E S

D u r i n g s h u t d o w n o f a b o i l i n g w a t e r r e a c t o r ( B W R ) , i n s p e c t i o n s o f t h e p i l o t

v a l v e s o f t h e s a f e t y r e l i e f v a l v e s w e r e c a r r i e d o u t . S e v e r a l c o n t r o l l i n e s ( D N 1 5 )

w h i c h a r e m a d e o f t h e a u s t e n i t i c C r N i - s t e e l X 1 0 C r N i T i 1 8 9 ( m a t e r i a l N o . 1 . 4 5 4 1 )

w e r e f o u n d d e f e c t i v e t o d i f f e r e n t e x t e n t s . O n e p i p e b r o k e d u r i n g d i s a s s e m b l y

b e c a u s e i t w a s t o o w e a k . I m m e d i a t e l y b e f o r e t h e s h u t d o w n f u n c t i o n a l t e s t s o f t h e

s a f e t y r e l i e f v a l v e s h a d b e e n p e r f o r m e d . A l l v a l v e s h a d w o r k e d p r o p e r l y .

L i q u i d p e n e t r a n t e x a m i n a t i o n s , v i s u a l i n s p e c t i o n s a n d m e t a l l o g r a p h i c e x a m i n a ­

t i o n s r e v e a l e d d e f e c t s a t s e v e n o u t o f s i x t e e n c o n t r o l p i p e s c a u s e d b y t r a n s g r a n u l a r

s t r e s s - a s s i s t e d c o r r o s i o n . T h e d e f e c t s w e r e p a r t i a l l y t h r o u g h - w a l l c r a c k s ( F i g . 1 ) .

T h e c o r r o s i o n o r i g i n a t e d o n t h e i n n e r s u r f a c e o f t h e p i p e s a n d w a s l i m i t e d t o s m a l l

a r e a s o f a b o u t 5 0 — 7 0 m m l e n g t h . T h e s e a r e a s w e r e l o c a t e d a b o u t 1 0 0 - 2 0 0 m m

b e h i n d t h e o u t l e t s a n d w e r e c o v e r e d w i t h c o a t i n g c o n t a i n i n g a b o u t 3 0 0 p p m

c h l o r i d e . C r a c k s w e r e o n l y f o u n d i n t h e a r e a s c o v e r e d w i t h t h e s e s e d i m e n t s . T h e

c o r r o s i o n d e v e l o p e d o v e r a n o p e r a t i n g p e r i o d o f 2 . 5 y e a r s .

T h e f o l l o w i n g c i r c u m s t a n c e s c o n t r i b u t e d t o t h e c o r r o s i o n :

( a ) T h e p r e s e n c e o f c h l o r i d e . T h e a s b e s t o s p a c k i n g s a s w e l l a s t h e p r e s e r v a t i o n

m e d i u m f o r t h e p i l o t v a l v e s c o n t a i n e d c h l o r i d e .

( b ) T h e t e m p e r a t u r e r a n g e . T h e c o n t r o l p i p e s w e r e i n s u l a t e d . T h e t e m p e r a t u r e

i n t h e a f f e c t e d a r e a s w a s a b o u t 1 0 0 ° C . A s t h e r e w e r e s m a l l s t e a m l e a k a g e s

a t t h e v a l v e s e a t , c h l o r i d e w a s t r a n s p o r t e d f r o m t h e p a c k i n g i n t o t h e p i p e ,

c a u s i n g l o c a l d e p o s i t i o n a n d c o n c e n t r a t i o n .

IAEA-SM-268/81 1 1 5

( a ) T h e a s b e s t o s p a c k i n g s w e r e r e p l a c e d b y g r a p h i t e p a c k i n g s w h i c h c o n t a i n e d

m u c h l e s s c h l o r i d e .

( b ) T h e c o n t r o l l i n e s w e r e r e p l a c e d . L a b o r a t o r y i n v e s t i g a t i o n s s h o w e d t h a t n o

c h a n g e o f t h e p i p e m a t e r i a l w a s n e c e s s a r y . E x p e r i e n c e w i t h o t h e r p i p e s

s h o w e d t h a t t h e m e r e e x c h a n g e o f t h e p a c k i n g i s n o t s u f f i c i e n t , b e c a u s e

c o r r o s i o n c o n t i n u e s i f o n c e s t a r t e d .

( c ) T h e c o n t r o l l i n e s i n o t h e r B W R s w e r e i n s p e c t e d . S i m i l a r f i n d i n g s w e r e

o b t a i n e d a n d t h e s a m e a c t i o n s t a k e n .

R e c e n t l y t h e s a m e c o r r o s i o n m e c h a n i s m w a s d e t e c t e d i n t h e c o n t r o l U n e s o f

m a i n s t e a m s a f e t y v a l v e s i n P W R s a n d i n t h e e x h a u s t l i n e s o f g l a n d a n d o t h e r s e a l i n g s .

T h e a s b e s t o s p a c k i n g s w e r e r e p l a c e d b y g r a p h i t e p a c k i n g s a n d t h e a f f e c t e d U n e s

r e p l a c e d a s w e l l .

T h e f o l l o w i n g a c t i o n s w e r e t a k e n :

3 . P I L O T V A L V E F A I L U R E O F P I L O T - O P E R A T E D M A I N S T E A M

S A F E T Y V A L V E S

T h e p H o t v a l v e s o f t h e m a i n s t e a m s a f e t y v a l v e s ( M S S V s ) o f a P W R w e r e

t e s t e d o u t s i d e t h e p l a n t i n a t e s t i n g d e v i c e . D u r i n g t h i s t e s t t w o o u t o t t w e l v e

p i l o t v a l v e s d i d n o t o p e n a t t h e m a x i m u m p r e s s u r e o f t h e t e s t i n g d e v i c e ( 1 3 b a r

a b o u t s e t p o i n t ) , s i x o t h e r s o p e n e d a t p r e s s u r e s u p t o 3 b a r a b o v e t h e s p e c i f i e d

t o l e r a n c e s . A l l M S S V s w o u l d h a v e o p e n e d o n d e m a n d a t t h e s p e c i f i e d p r e s s u r e

s i n c e t h e f o u r M S S V s a r e e q u i p p e d w i t h t h r e e p i l o t v a l v e s i n p a r a l l e l ( 1 o f 3

c o n d i t i o n ) ( F i g . 2 ) .

T h e r e a s o n f o r t h e f a i l u r e t o o p e n p r o p e r l y i s t h e c l a m p i n g o r g r o w i n g - t o g e t h e r

o f t h e t w o c o r r o s i o n c o a t s o f t h e p i l o t v a l v e s e a t a n d d i s c ( c o n t a c t c o r r o s i o n ) .

B o t h s e a t a n d d i s c c o n s i s t e d o f c h r o m i u m a l l o y e d f e r r i t i c s t e e l X 3 5 C r M o 1 7

( m a t e r i a l N o . 1 . 4 1 2 2 ) w h i c h i s n o t s t a b l e i n a h i g h - t e m p e r a t u r e s t e a m a t m o s p h e r e .

A s a r e s u l t , c o a t s a r e f o r m e d i n t h e r e g i o n o f t h e s e a l i n g s u r f a c e . T h e c o a t s c o n s i s t

o f m a g n e t i t e ( F e 3 0 4 ) i n t h e s t e a m a r e a a n d o f h e m a t i t e ( F e 2 0 3 ) i n t h e a t m o s p h e r e

a r e a .

D u r i n g o p e r a t i o n t h e r e i s c o n d e n s a t e p r e s e n t i n t h e s e a t . I r o n i s d i s s o l v e d i n

t h e c o n d e n s a t e a n d t h e e x t r a c t e d i r o n o x i d e p r o d u c e s a c o n n e c t i o n b e t w e e n t h e

c o r r o s i o n c o a t s ( e s p e c i a l l y t h e m a g n e t i t e ) . T h i s l e a d s t o c l a m p i n g .

T h e m e c h a n i s m i s a g g r a v a t e d b y t h e u s e o f i d e n t i c a l m a t e r i a l s f o r s e a t a n d

d i s c o f t h e v a l v e . I n t h i s c a s e t h e s t r u c t u r e s o f t h e s u r f a c e m a t e r i a l s a r e i d e n t i c a l

a n d t h i s f a c i l i t a t e s t h e g r o w i n g - t o g e t h e r o f i r o n o x i d e c r y s t a l s b e t w e e n t h e p o l i s h e d

s u r f a c e s . T h e r a t e a t w h i c h c l a m p i n g d e v e l o p s i s r a t h e r v a r i a b l e b u t s t i c k i n g c a n

o c c u r w i t h i n a r e l a t i v e l y s h o r t t i m e .

116 HAUNHORST et al.

( 2 6 0 ° C )

FIG. 2. Pilot valve disc and seat arrangement.

C o r r e c t i v e a c t i o n s

T h e d i s c s w e r e r e p l a c e d b y o t h e r s m a d e o f a n a u s t e n i t i c m a t e r i a l ( X 5 N i C r T i

2 6 1 5 , m a t e r i a l N o . 1 . 4 9 8 0 ) , g i v i n g a f e r r i t i c - a u s t e n i t i c c o m b i n a t i o n f o r s e a t a n d

d i s c . A s a u s t e n i t i c m a t e r i a l s a r e r e s i s t a n t a g a i n s t c o r r o s i o n a t t h e t e m p e r a t u r e s

p r e v a i l i n g i n t h e m a i n s t e a m s y s t e m , s t i c k i n g o f t h e p i l o t v a l v e s w i l l b e p r e v e n t e d .

T h e s a m e a c t i o n w a s t a k e n w i t h v a l v e s i n t h e o t h e r s y s t e m s w h e r e s i m i l a r

c o n d i t i o n s p r e v a i l . T h e e x c h a n g e w a s a l s o m a d e i n o t h e r p l a n t s .

4 . L O S S O F O F F S I T E P O W E R

A f t e r a l o s s o f o f f s i t e p o w e r i n a P W R , c o o l d o w n o f t h e p r i m a r y c i r c u i t w i t h

5 0 K / h w a s i n i t i a t e d 1 8 m i n a f t e r s c r a m . D u r i n g c o o l d o w n a s t e a m b u b b l e f o r m e d

u n d e r t h e v e s s e l h e a d , s i n c e t h e h e a d i s i n s u f f i c i e n t l y c o o l e d u n d e r n a t u r a l c i r c u ­

l a t i o n c o n d i t i o n s ( F i g . 3 ) . T h e p r e s s u r i z e r l e v e l t h e r e f o r e i n c r e a s e d o w i n g t o t h e

b u b b l e f o r m a t i o n a n d t h e r e w a s a m a l f u n c t i o n o f t h e m a k e - u p s y s t e m , w h i c h

l i m i t e d t h e l e t d o w n r a t e s t i l l f u r t h e r .

A f t e r 2 h 3 0 m i n , t h e o f f s i t e p o w e r s u p p l y w a s r e s t o r e d . S i n c e t h e p r o d u c t i o n

o f d e m i n e r a l i z e d w a t e r t h e r e f o r e w a s a v a i l a b l e a g a i n , t h e c o o l d o w n w a s s t o p p e d a t

5 3 b a r w i t h i n l e t a n d o u t l e t t e m p e r a t u r e s a t 1 9 6 ° С a n d 2 1 8 ° С r e s p e c t i v e l y .

I n o r d e r t o c o m p r e s s t h e b u b b l e a n d r e d u c e t h e t e m p e r a t u r e d i f f e r e n c e

b e t w e e n p r i m a r y c o o l a n t a n d v e s s e l h e a d , t h e p r i m a r y p r e s s u r e a n d t e m p e r a t u r e

IAEA-SM-268/81 117

F I G . 3 . F o r m a t i o n o f a s t e a m b u b b l e i n t h e r e a c t o r v e s s e l .

w e r e i n c r e a s e d . S i n c e t h e h e a t i n g o f t h e p r e s s u r i z e r w a s t e m p o r a r i l y n o t a v a i l a b l e

o w i n g t o a n i n t e r l o c k , t h e p r e s s u r e i n c r e a s e w a s a c h i e v e d b y f e e d i n g w i t h t w o

m a k e - u p p u m p s . A s a c o n s e q u e n c e , t h e p r e s s u r i z e r l e v e l i n c r e a s e d a n d w e n t

o u t s i d e t h e m e a s u r i n g r a n g e , b u t t h e p r e s s u r i z e r w a s n o t t o t a l l y f i l l e d u p .

A t 7 h 3 0 m i n a f t e r l o s s o f o f f s i t e p o w e r , t h e p r e s s u r i z e r l e v e l w a s r e d u c e d

t o n o r m a l v a l u e s . T h e p l a n t r e m a i n e d i n t h i s c o n d i t i o n u n t i l s t a r t u p a d a y la t e r .

S a f e t y s i g n i f i c a n c e

T h e i n c i d e n t s h o w s t h a t i n t h e c a s e o f r a p i d c o o l d o w n w i t h n a t u r a l c i r c u l a t i o n

a s t e a m b u b b l e i s t o b e e x p e c t e d b e l o w t h e v e s s e l h e a d . T h e b u b b l e d o e s n o t

h i n d e r t h e c o o l d o w n . B u t t h e i n c i d e n t a l s o s h o w s t h a t i t i s d e s i r a b l e t o h a v e

w r i t t e n i n s t r u c t i o n s o n h o w t o p r o c e e d w i t h s u c h a b u b b l e . T h e m o s t i m p o r t a n t

p o i n t i s t h a t t h e m a i n c o o l a n t p u m p s m u s t n o t b e r e s t a r t e d w h e n a b u b b l e i s

p r e s e n t i f s u d d e n c o n d e n s a t i o n o f t h e b u b b l e i s t o b e a v o i d e d . A p p r o p r i a t e

i n s t r u c t i o n s w e r e i n c l u d e d i n t h e p r o c e d u r e s f o r P W R s .

5 . P R O B L E M S W I T H C L O S E D - C I R C U I T D C - C O N T A C T O R S

A s h r i n k i n g o f t h e c o i l f o r m w a s r e p e a t e d l y o b s e r v e d i n t h e c o i l s o f c o n t a c t o r s

w h i c h a r e n o r m a l l y c l o s e d . T h i s i m p a i r e d t h e m o t i o n o f t h e m o v a b l e c o r e a n d

11 8 HAUNHORST et al

F I G . 4 . D С - c o n t a c t o r a r r a n g e m e n t .

Accumulator Converter

F I G . 5 . R e a c t o r t r i p s y s t e m .

c a u s e d t h e c o n t a c t o r s t o f a i l t o o p e n o n d e m a n d ( F i g . 4 ) . T h e s h r i n k i n g w a s

c a u s e d b y t h e e l e v a t e d t e m p e r a t u r e o f t h e c o i l f o r m s d u e t o t h e p e r m a n e n t c u r r e n t .

T h e s y n t h e t i c m a t e r i a l u s e d w a s a p p a r e n t l y i n a p p r o p r i a t e f o r t h e s e c o n d i t i o n s .

T h i s p h e n o m e n o n w a s o b s e r v e d w i t h t h e c o n t a c t o r s o f t h e a d d i t i o n a l s o l e n o i d

l o a d o f s a f e t y v a l v e s o n t h e p r e s s u r i z e r o f a P W R , t h e c o n t a c t o r s f o r t h e a c t u a t i o n

o f c o n t a i n m e n t i s o l a t i o n v a l v e s a n d t h e c o n t a c t o r s i n t h e c o n t r o l r o d d r i v e s y s t e m .

I n t h i s c a s e a n a u x i l i a r y c o n t a c t o r w h i c h i n t e r r u p t s t h e p o w e r s u p p l y t o a s i n g l e

c o n t r o l r o d w a s a f f e c t e d . T h e r o d d i d n o t d r o p w h e n a r e a c t o r t r i p o c c u r r e d ( F i g . 5 ) .

IAE A-SM-268/81 1 1 9

( a ) I n s t a l l a t i o n o f s p e c i a l c o n t a c t o r s e q u i p p e d w i t h a r e s i s t a n c e w h i c h i s

c o n n e c t e d i n s e r i e s w i t h t h e s o l e n o i d a f t e r t h e c o n t a c t o r h a s a t t r a c t e d ;

( b ) U t i l i z a t i o n o f c o n t a c t o r s w i t h a g e d f o r m s ;

( c ) I m p r o v e m e n t o f t h e r e a c t o r t r i p s y s t e m . I n a d d i t i o n t o t h e e x i s t i n g d e v i c e s

f o r i n t e r r u p t i n g t h e p o w e r s u p p l y t o t h e s i n g l e c o n t r o l r o d s , a n u m b e r o f

b r e a k e r s a r e a u t o m a t i c a l l y o p e n e d . T h i s i n t e r r u p t s t h e c o m m o n s u p p l y t o

t h e c o n t r o l r o d s b y d i s c o n n e c t i o n o f t h e a s s o c i a t e d b u s b a r .

6 . S T E A M G E N E R A T O R T U B E R U P T U R E

A n e x a m p l e o f a m o r e e x t e n s i v e e v a l u a t i o n o f o p e r a t i n g e x p e r i e n c e i s a s t u d y

o n s t e a m g e n e r a t o r t u b e r u p t u r e s . T h e r e a s o n f o r t h i s s t u d y w a s a s t e a m g e n e r a t o r

t u b e r u p t u r e w h i c h o c c u r r e d i n t h e B e l g i a n p l a n t D o e l 2 . T h e m a j o r a i m s o f t h e

s t u d y a r e t h e s e :

( a ) D e s c r i p t i o n o f t h e s t a t u s o f t h e s y s t e m s t o c o p e w i t h s t e a m g e n e r a t o r t u b e

r u p t u r e s i n F e d e r a l G e r m a n n u c l e a r p o w e r p l a n t s ;

( b ) S u r v e y o f t h e p r o b l e m s w h i c h w e r e o b s e r v e d w i t h a c t u a l s t e a m g e n e r a t o r

t u b e r u p t u r e s ;

( c ) E v a l u a t i o n o f t h e s e p r o b l e m s w i t h r e s p e c t t o t h e i r r e l e v a n c e t o F e d e r a l

G e r m a n p l a n t s ;

( d ) D e t e c t i o n a n d i d e n t i f i c a t i o n o f p o s s i b l e w e a k p o i n t s i n t h e F e d e r a l G e r m a n

d e s i g n t o c o p e w i t h s t e a m g e n e r a t o r t u b e r u p t u r e s .

W o r k o n t h e f i r s t t w o i t e m s h a s b e e n c o n c l u d e d . T h e o t h e r t w o r e q u i r e v e r y

d e t a i l e d i n v e s t i g a t i o n o f t h e d y n a m i c b e h a v i o u r o f t h e p l a n t . T h e r e l e v a n t c a l c u ­

l a t i o n s a r e c u r r e n t l y b e i n g m a d e .

T h e r e a r e s o m e p r o f o u n d d i f f e r e n c e s i n t h e c o n t r o l o f s t e a m g e n e r a t o r t u b e

r u p t u r e s b e t w e e n F e d e r a l G e r m a n a n d o t h e r P W R s . W h i l s t i n o v e r s e a s p l a n t s

t h e y a r e d e a l t w i t h l i k e a l o s s o f c o o l a n t a c c i d e n t i n t e r m s o f p r o t e c t i v e a c t i o n ,

F e d e r a l G e r m a n p l a n t s h a v e a r e a c t o r p r o t e c t i o n c r i t e r i o n w h i c h i s s p e c i f i c f o r

t h e s e r u p t u r e s - a m e a s u r e m e n t o f t h e 1 6 N - a c t i v i t y i n t h e m a i n s t e a m l i n e b e h i n d

t h e s t e a m g e n e r a t o r s . F r o m t h i s c r i t e r i o n a u t o m a t i c m e a s u r e s a r e d e r i v e d w h i c h

a i m a t t h e p a r t i c u l a r r e q u i r e m e n t s o f t h e c o n t r o l o f s t e a m g e n e r a t o r t u b e r u p t u r e s .

T h e m o r e i m p o r t a n t o f t h e s e a r e :

— r e a c t o r s c r a m

— a c t i v a t i o n o f t h e a u x i l i a r y p r e s s u r i z e r s p r a y

— d e l a y e d t u r b i n e t r i p

— s w i t c h - o f f o f t h e p r e s s u r i z e r h e a t e r s

— r e d u c t i o n o f t h e s e t p o i n t o f t h e m a i n s t e a m m a x i m u m p r e s s u r e c o n t r o l w h i c h

c o n t r o l s t h e o p e n i n g o f t h e t u r b i n e b y - p a s s s t a t i o n .

T h e a c t i o n s t a k e n w e r e :

120 ükuNHORST et aL

— c l o s i n g o f t h e l e t d o w n o r i f i c e v a l v e s t o m i n i m u m f l o w

— s t a r t i n g o f t h e s e c o n d c h a r g i n g p u m p .

T h r o u g h t h e s e m e a s u r e s t h e p r i m a r y p r e s s u r e i s l o w e r e d i n a s h o r t t i m e b e l o w

t h e s e t p o i n t o f t h e m a i n s t e a m s a f e t y v a l v e s a n d t h e p r e s s u r e d i f f e r e n c e b e t w e e n

t h e p r i m a r y a n d s e c o n d a r y c i r c u i t d e c r e a s e s s o f a r t h a t t h e v o l u m e c o n t r o l s y s t e m

k e e p s t h e w a t e r l e v e l o f t h e p r e s s u r i z e r a b o v e t h e l i m i t i n g v a l u e f o r s a f e t y i n j e c t i o n

a n d c o n t a i n m e n t i s o l a t i o n a c t u a t i o n .

T h i s e n s u r e s t h a t a l l o p e r a t i n g s y s t e m s r e m a i n f u n c t i o n a l , a l l e v i a t i n g a c c i d e n t

c o n t r o l r e m a r k a b l y . I n t h e p a s t , a t o t a l o f f i v e i n c i d e n t s c a u s e d b y l a r g e r s t e a m

g e n e r a t o r t u b e l e a k s h a v e o c c u r r e d . A l l h a v e t h o r o u g h l y b e e n e v a l u a t e d o n t h e

b a s i s o f t h e a v a i l a b l e d o c u m e n t s . P a r t i c u l a r e m p h a s i s w a s d e v o t e d t o p r o b l e m s

w h i c h e i t h e r o c c u r r e d i n t h e c o u r s e o f t h e a c c i d e n t o r s h o w e d a p o t e n t i a l o f

d e v e l o p i n g . T h e f o l l o w i n g m a y s e r v e a s e x a m p l e s :

( a ) B y d e s i g n i n t h e p l a n t s c o n c e r n e d , s a f e t y i n j e c t i o n i s a c t i v a t e d i n t h e e v e n t

o f a s t e a m g e n e r a t o r t u b e r u p t u r e w h i c h i m p o s e s a r e l a t i v e l y h i g h p r e s s u r e

o n t h e p r i m a r y c i r c u i t c o m p a r e d t o t h a t o f t h e d e f e c t s t e a m g e n e r a t o r . T h i s

c a u s e s a f a i r l y h i g h l e a k r a t e u n t i l t h e s a f e t y i n j e c t i o n i s t u r n e d o f f . W i t h o n e

e x c e p t i o n t h i s h a s l e d t o p r o b l e m s w i t h t h e f l o o d i n g o f t h e d e f e c t s t e a m

g e n e r a t o r .

( b ) T h e s a f e t y i n j e c t i o n a c t u a t e s c o n t a i n m e n t i s o l a t i o n w h i c h a s a c o n s e q u e n c e

l e a d s t o t h e l o s s o f i m p o r t a n t o p e r a t i n g s y s t e m s ( e . g . p r i m a r y c o o l a n t p u m p s ,

v o l u m e c o n t r o l s y s t e m ) .

( c ) T h e l o w e r i n g o f t h e p r i m a r y p r e s s u r e m a y c a u s e d i f f i c u l t i e s s u c h a s t h e

f l o o d i n g o f t h e p r e s s u r i z e r w i t h t h e s a f e t y i n j e c t i o n p u m p s r u n n i n g .

( d ) T h e r e s p o n s e o f t h e m a i n s t e a m s a f e t y v a l v e s w i t h a f l o o d e d s t e a m g e n e r a t o r

m a y r e s u l t i n t h e d i s c h a r g i n g o f t w o - p h a s e f l o w , c a u s i n g d i s t u r b a n c e s o f t h e

v a l v e s .

I n s u m m a r y , t h e e v a l u a t i o n o f t h e p r o b l e m s d e r i v e d f r o m t h e a c t u a l s t e a m

g e n e r a t o r t u b e f a i l u r e s d o e s n o t r e v e a l a n i m m e d i a t e t r a n s f e r a b i l i t y t o F e d e r a l

G e r m a n P W R s . T h i s m a y b e e x p l a i n e d b y t h e d i f f e r e n t d e s i g n m e n t i o n e d a b o v e

w h i c h , f o r e x a m p l e , d o e s n o t n o r m a l l y f o r e s e e a s a f e t y i n j e c t i o n . O n t h e o t h e r

h a n d , s i n g l e f a i l u r e s o r d i s t u r b a n c e s c a n n o t b e e x c l u d e d . I n s u c h a c a s e s i m i l a r

d i f f i c u l t i e s m a y o c c u r w i t h F e d e r a l G e r m a n p l a n t s . T h e p r o b l e m o f f i n d i n g u n d e r

w h i c h c i r c u m s t a n c e s t h i s m a y b e t h e c a s e r e q u i r e s v e r y d e t a i l e d i n v e s t i g a t i o n s a n d

c o m p u t e r c a l c u l a t i o n s w h i c h h a v e n o t y e t b e e n c o m p l e t e d .

T h e d r o p p i n g o f t h e p r e s s u r i z e r w a t e r l e v e l a u t o m a t i c a l l y c a u s e s :

í IAEA-SM -268/43

E N S E I G N E M E N T S G E N E R A U X

T I R E S D E S I N C I D E N T S S U R V E N U S

S U R L E S C E N T R A L E S N U C L E A I R E S F R A N Ç A I S E S

Y . D R O U L E R S , C h r i s t i n e F E L T I N , B . F O U R E S T

D é p a r t e m e n t d ’a n a l y s e d e s û r e t é ,

C E A , I n s t i t u t d e p r o t e c t i o n e t d e s û r e t é n u c l é a i r e ,

F o n t e n a y - a u x - R o s e s , F r a n c e

Abstract-Résu mé

G E N E R A L LESSON S LE A R N E D FROM INCIDENTS T H A T H A V E O CCU R R E D A T FREN CH N U C L E A R POWER PLAN TS.

This paper highlights some o f the main lessons to be learned from the first years o f operation o f the French pressurized-water reactor programme. A study is made o f significant incidents which occurred between 1 January 1981 and 30 June 1982, and the concept o f “ significant incident” is defined. A ll these incidents are examined in the light o f the factors involved in their causes and their consequences: operating conditions o f the unit, plant components involved, human factors, generic or isolated nature o f the incident and actual consequences. Quantitative results are presented and comm ented on. The consequences o f the “ series effect” which constitutes a main feature o f the French nuclear programme, its advantages and its disadvantages, are discussed. The importance o f high standards in operating procedures is stressed. The actual consequences o f the incidents considered show that the results o f these first years o f operation can be considered positive. Future trends in this type o f study are indicated.

ENSEIGNEM ENTS G E N E R A U X TIRES DES INCIDENTS SU R VEN U S SUR LES C E N TR A LE S N U C LEA IR ES F R A N Ç A ISE S.

Ce mémoire met en évidence certains des enseignements importants qui peuvent être tirés des premières années d’exploitation du programme français de réacteurs à eau sous pression. Il présente une étude des incidents significatifs survenus au cours de la période 1er janvier 19 8 1—30 juin 1982. On donne la définition d’un «incident significatif». On examine tous ces incidents à la lumière de facteurs intervenant dans leurs causes et leurs conséquences: condi­tions de fonctionnem ent de la tranche, matériel impliqué, facteur humain, caractère générique ou ponctuel de l ’incident, conséquences réelles. Des résultats quantitatifs sont présentés et commentés. Les conséquences de «l’e ffet palier», base du programme nucléaire français, ses avantages et ses inconvénients sont présentés. L ’importance de la qualité des procédures d’exploitation est soulignée. Les conséquences réelles des incidents examinés permettent de qualifier de positif le bilan de ces premières années d’exploitation. Les orientations futures de l’étude engagée sont indiquées.

121

> !1 2 2 ’ D R O U LER S et al.

1 . I N T R O D U C T I O N

P o u r t i r e r t o u s l e s e n s e i g n e m e n t s d e s i n c i d e n t s s u r v e n a n t s u r l e s c e n t r a l e s

n u c l é a i r e s , o n p e u t , e t o n d o i t , e n v i s a g e r p l u s i e u r s d é m a r c h e s f a i s a n t a p p e l à d e s

é t u d e s d e t y p e d i f f é r e n t . N o u s e n m e n t i o n n e r o n s t r o i s .

L a p r e m i è r e c o n s i s t e à a n a l y s e r d e f a ç o n a p p r o f o n d i e l e s i n c i d e n t s

p a r t i c u l i è r e m e n t s i g n i f i c a t i f s a y a n t u n i m p a c t d i r e c t s u r l a s û r e t é . L e b u t d e s

é t u d e s d e c e t y p e e s t d e m e t t r e e n é v i d e n c e l e s c a u s e s p r o f o n d e s d e t e l s i n c i d e n t s

e t d e d é f i n i r l e s d i s p o s i t i o n s p r o p r e s à é v i t e r q u ’i l s n e s e r e p r o d u i s e n t . C o m p t e

t e n u d e l ’a m p l e u r d u t r a v a i l q u e s u p p o s e n t c e s a n a l y s e s , e l l e s n e p e u v e n t ê t r e

c o n d u i t e s q u e p o u r u n n o m b r e r e s t r e i n t d ’i n c i d e n t s . C e p e n d a n t , d e s e n s e i g n e m e n t s

i n t é r e s s a n t s p e u v e n t s e t r o u v e r c a c h é s d a n s d e s i n c i d e n t s q u i a p r i o r i p a r a i s s e n t

p e u s i g n i f i c a t i f s .

L a s e c o n d e d é m a r c h e c o n s i s t e à s e p e n c h e r s u r d e s f a m i l l e s d ’i n c i d e n t s

s u r v e n a n t f r é q u e m m e n t . A t i t r e d ’e x e m p l e n o u s c i t e r o n s l e s é t u d e s e f f e c t u é e s

o u e n c o u r s s u r l e s s o l l i c i t a t i o n s d u s y s t è m e d ’i n j e c t i o n d e s é c u r i t é , l e s s o l l i c i t a ­

t i o n s d e l ’a r r ê t d ’u r g e n c e , l e s f u i t e s p r i m a i r e s o u l e s p r o b l è m e s r e n c o n t r é s s u r

c e r t a i n s t y p e s d e v a n n e s . C h a c u n d e c e s i n c i d e n t s p r i s i s o l é m e n t n e j u s t i f i e r a i t p a s

q u e s o i e n t p r i s e s d e s d i s p o s i t i o n s c o r r e c t i v e s ; p a r c o n t r e , l ’a n a l y s e s t a t i s t i q u e d e

f a m i l l e s p e u t m e t t r e e n é v i d e n c e c e r t a i n s d é f a u t s à c a r a c t è r e g é n é r i q u e e t m o n t r e r

l ’i n t é r ê t d ’a m é l i o r a t i o n s c o n c e r n a n t l a f i a b i l i t é o u l a d i s p o n i b i l i t é d e t e l o u t e l

s y s t è m e ; c o m m e l a s û r e t é e s t é t r o i t e m e n t l i é e à c e s d e u x f a c t e u r s , e l l e e n b é n é f i c i e

p a r c o n t r e - c o u p .

T o u t e f o i s , d a n s l a m e s u r e o ù e l l e s s e l i m i t e n t à c e r t a i n s p o i n t s p a r t i c u l i e r s ,

c e s d e u x d é m a r c h e s n e s o n t p a s s u f f i s a n t e s l o r s q u ’i l s ’a g i t , c o m m e e n F r a n c e

a u j o u r d ’h u i , d ’é v a l u e r l a s û r e t é d ’u n g r a n d n o m b r e d e c e n t r a l e s e n e x p l o i t a t i o n .

I l f a u t a u s s i p r o c é d e r à l ’e x a m e n g l o b a l d e s i n s t a l l a t i o n s , i d e n t i f i e r l e s p r i n c i p a u x

p r o b l è m e s r e n c o n t r é s , é v a l u e r l e s r e m è d e s a p p o r t é s e t l ’i m p a c t d e s é v e n t u e l l e s

m o d i f i c a t i o n s d é c i d é e s . I l f a u t e n f i n s u i v r e l ’é v o l u t i o n d a n s l e t e m p s d e s c a u s e s

p r o f o n d e s d e s i n c i d e n t s . C e c i d o i t p e r m e t t r e d e d é g a g e r l e s p o i n t s f a i b l e s s u r

l e s q u e l s u n e f f o r t p a r t i c u l i e r d e v r a ê t r e f a i t . C ’e s t d a n s c e b u t q u ’a é t é e n t r e p r i s e

l ’é t u d e f a c t o r i e l l e d e s i n c i d e n t s d o n t l e s p r e m i e r s r é s u l t a t s e t l e s p r e m i è r e s

c o n c l u s i o n s s o n t p r é s e n t é s i c i .

2 . D E F I N I T I O N D E S I N C I D E N T S

C e t t e é t u d e p o r t e s u r l a p é r i o d e d u 1 er j a n v i e r 1 9 8 1 a u 3 0 j u i n 1 9 8 2 ; e n

e f f e t , a u p a r a v a n t , u n g r a n d n o m b r e d e t r a n c h e s é t a i t e n c o r e e n e s s a i s a v a n t

d é m a r r a g e . A u c o u r s d e c e t t e p é r i o d e , s i x t r a n c h e s o n t é t é c o u p l é e s a u r é s e a u :

s e u l s s o n t a l o r s p r i s e n c o m p t e l e s i n c i d e n t s s u r v e n u s a p r è s l a p r e m i è r e d i v e r g e n c e .

C e c i r e p r é s e n t e e n v i r o n 3 0 a n n é e s - r é a c t e u r d e f o n c t i o n n e m e n t .

P o u r e f f e c t u e r u n e t e l l e é t u d e , i l f a l l a i t d i s p o s e r d ’u n e n s e m b l e d ’i n c i d e n t s

c o h é r e n t s q u a n t à l e u r c a r a c t è r e s i g n i f i c a t i f v i s - à - v i s d e l a s û r e t é p o u r l e s d i f f é r e n t e s

c e n t r a l e s ; i l f a l l a i t a u s s i q u e l e s i n f o r m a t i o n s s u r c e s i n c i d e n t s s o i e n t s u f f i s a m m e n t

p r é c i s e s . N o u s a v o n s d o n c d é c i d é d ’é t u d i e r l e s i n c i d e n t s d é c l a r é s o f f i c i e l l e m e n t

a u x a u t o r i t é s d e s û r e t é , d a n s l e c a d r e r é g l e m e n t a i r e .

C e s i n c i d e n t s , a p p e l é s « i n c i d e n t s s i g n i f i c a t i f s » , r é p o n d e n t à u n e n s e m b l e d e

c r i t è r e s n o t i f i é s o f f i c i e l l e m e n t p a r l e S e r v i c e c e n t r a l d e s û r e t é d e s i n s t a l l a t i o n s

n u c l é a i r e s à E l e c t r i c i t é d e F r a n c e e n a v r i l 1 9 8 2 ; t o u t e f o i s , c e s c r i t è r e s é t a i e n t

d é j à a p p l i q u é s , à t i t r e d ’ e s s a i , d e p u i s l e d é b u t d e 1 9 8 1 e t o n t é t é p r é s e n t é s d a n s

u n e a u t r e c o m m u n i c a t i o n à c e c o l l o q u e ( I A E A - S M - 2 6 8 / 4 7 , p r é s e n t s c o m p t e s

r e n d u s ) . L e n o m b r e d e s i n c i d e n t s a i n s i s é l e c t i o n n é s s ’é l è v e à 2 8 6 .

A c e s t a d e , i l c o n v i e n t d e f a i r e u n e p r e m i è r e r e m a r q u e : l e c r i t è r e n ° 1

d e m a n d e q u e s o i e n t d é c l a r é s a u x a u t o r i t é s d e s û r e t é t o u s l e s a r r ê t s d ’u r g e n c e d u

r é a c t e u r , à l ’e x c e p t i o n d e c e u x d u s à u n d é c l e n c h e m e n t d e l a t u r b i n e . B i e n q u e

l e s a r r ê t s d ’u r g e n c e s o i e n t , l e p l u s s o u v e n t , m o i n s s i g n i f i c a t i f s q u e l e s i n c i d e n t s

r é p o n d a n t a u x a u t r e s c r i t è r e s , l e u r d é c l a r a t i o n n e s ’e s t p a s r é v é l é e i n u t i l e ; e l l e a

n o t a m m e n t p e r m i s d ’e f f e c t u e r d e s é t u d e s s t a t i s t i q u e s d u t y p e d e c e l l e s é v o q u é e s

d a n s l ’ i n t r o d u c t i o n e t d e p r e n d r e d e s m e s u r e s v i s a n t à d i m i n u e r l e n o m b r e d e s

p r i n c i p a u x i n i t i a t e u r s d e c e r t a i n s d e c e s t r a n s i t o i r e s .

L ’é t u d e p r é s e n t é e c i - d e s s o u s n e p o r t e q u e s u r l e s i n c i d e n t s a u t r e s q u e l e s

a r r ê t s d ’u r g e n c e , s o i t 1 5 8 s u r l a p é r i o d e c o n s i d é r é e .

L ’é t u d e s p é c i f i q u e d e s a r r ê t s d ’u r g e n c e s u r v e n u s e n 1 9 8 0 , 1 9 8 1 e t 1 9 8 2 s u r

l e s c e n t r a l e s f r a n ç a i s e s f a i t l ’o b j e t d u m é m o i r e I A E A - S M - 2 6 8 / 4 2 d a n s l e s p r é s e n t s

c o m p t e s r e n d u s .

IAEA-SM-268/43 j 123

3 . D E F I N I T I O N S D E S F A C T E U R S E X A M I N E S D A N S L ’E T U D E

P o u r c a r a c t é r i s e r l e s d i f f é r e n t s a s p e c t s d ’u n i n c i d e n t , n o u s a v o n s e x a m i n é

q u a t r e t y p e s d e f a c t e u r s :

— l e s c o n d i t i o n s i n i t i a l e s d e l a t r a n c h e e t l e s c i r c o n s t a n c e s d e l ’i n c i d e n t ,

— l e s c a u s e s ,

— l e s c o n s é q u e n c e s ,

— l e s m a t é r i e l s o u s y s t è m e s i m p l i q u é s .

L a l i s t e d e l ’e n s e m b l e d e c e s f a c t e u r s e s t d o n n é e a u t a b l e a u I .

C o m m e u n i n c i d e n t p e u t a v o i r d e s c a u s e s o u d e s c o n s é q u e n c e s m u l t i p l e s e t

d e n a t u r e d i f f é r e n t e , l e s f a c t e u r s d e s c r i p t i f s n e s o n t p a s i n d é p e n d a n t s . P a r e x e m p l e ,

u n d é f a u t d e l ’a s s u r a n c e d e la q u a l i t é e n e x p l o i t a t i o n ( A Q ) p e u t c o n s i s t e r e n

l ’ o u b l i d ’u n e é t a p e d a n s u n e p r o c é d u r e e t a v o i r p o u r c o n s é q u e n c e u n e e r r e u r

h u m a i n e : l ’ i n c i d e n t e s t a l o r s d é c r i t p a r l e s t r o i s f a c t e u r s , d é f a u t d ’a s s u r a n c e

q u a l i t é , d é f a u t d e p r o c é d u r e , f a c t e u r h u m a i n .

1 2 4 DROULERS et al.

T A B L E A U I . F A C T E U R S P R I S E N C O M P T E D A N S L ’ E T U D E

1. Conditions initiales et circonstances

— Fonctionnem ent en puissance— Différents états d’arrêt

— Conditions initiales de la tranche indifférentes pour les causes et le déroulement de l’ incident

— Incident découvert au cours d’un arrêt à l ’occasion d’opérations de maintenance ou d’entretien

2. Causes

— Causes à caractère générique— Défaillance aléatoire ou spécifique de la tranche— Défaut de conception— Défaut de fabrication ou de montage— Qualification insuffisante— Incident lié au facteur humain— Assurance de la qualité en exploitation— Défaut de procédure

3. Conséquences

— Gaine du combustible— Enveloppe primaire— Enceinte de confinem ent

— Perte d’une fonction de sûreté— Dispersion incontrôlée de radioactivité

4. Systèmes impliqués

— 23 systèmes ou groupes de systèmes

T o u s l e s i n c i d e n t s p r i s e n c o m p t e d a n s l ’é t u d e o n t é t é e x a m i n é s à l a l u m i è r e

d e s f a c t e u r s d o n t l a l i s t e f i g u r e a u t a b l e a u I . L ’a f f e c t a t i o n d e t e l f a c t e u r à u n

i n c i d e n t d é p e n d é v i d e m m e n t d e l a q u a l i t é e t d e l a p r é c i s i o n d e s i n f o r m a t i o n s

c o n t e n u e s d a n s l e s r a p p o r t s d ’i n c i d e n t ; e l l e p o u r r a i t d o n c , d a n s c e r t a i n s c a s ,

ê t r e d i s c u t é e , n o t a m m e n t p a r l e s p e r s o n n e s q u i o n t v é c u l ’i n c i d e n t , o u p a r d ’a u t r e s

a n a l y s t e s ; n o u s n e p e n s o n s p a s , t o u t e f o i s , q u e c e l a s o i t d a n s d e s p r o p o r t i o n s t e l l e s

q u e l e s c o n c l u s i o n s d e l ’ é t u d e p u i s s e n t ê t r e r e m i s e s e n c a u s e .

IAEA-SM-268/43 1 2 5

L ’ é t u d e n ’é t a n t p a s t e r m i n é e d a n s s o n e n s e m b l e , n o u s n e d o n n e r o n s i c i q u e

l e s r é s u l t a t s c o n c e r n a n t c e r t a i n s f a c t e u r s p o u r l e s q u e l s l e s r é s u l t a t s d é j à d i s p o n i b l e s

o n t p e r m i s d e t i r e r d e s e n s e i g n e m e n t s i n t é r e s s a n t s ; n o u s i n d i q u e r o n s , l e c a s

é c h é a n t , l e s d i s p o s i t i o n s m i s e s e n o e u v r e o u l e s d é c i s i o n s p r i s e s p a r l ’e x p l o i t a n t ,

E l e c t r i c i t é d e F r a n c e , p o u r r é s o u d r e l e s p r o b l è m e s é v o q u é s .

4 . 1 . L ’e f f e t p a l i e r

O u t r e s e s a v a n t a g e s é c o n o m i q u e s é v i d e n t s , l e p r o g r a m m e n u c l é a i r e f r a n ç a i s ,

c o n s t i t u é d ’e n s e m b l e s d e r é a c t e u r s R E P à c o n c e p t i o n i d e n t i q u e o u p a l i e r s , p r é s e n t e

d u p o i n t d e v u e d e l a s û r e t é u n i n t é r ê t c e r t a i n : i l p e r m e t d ’e f f e c t u e r d e s é t u d e s

a p p r o f o n d i e s , a p p l i c a b l e s à u n g r a n d n o m b r e d e t r a n c h e s , e t l ’e x p é r i e n c e a c q u i s e

g r â c e a u x p r o b l è m e s r e n c o n t r é s s u r l ’u n e d ’e n t r e e l l e s p e u t ê t r e m i s e à p r o f i t s u r

l ’e n s e m b l e d u p a r c .

E n r e v a n c h e , c e p r o g r a m m e e s t v u l n é r a b l e c a r t o u t d é f a u t d e c o n c e p t i o n

o u d e f a b r i c a t i o n p e u t a f f e c t e r u n g r a n d n o m b r e d ’ i n s t a l l a t i o n s . L e s 1 5 8 i n c i d e n t s

e x a m i n é s m e t t e n t e n é v i d e n c e c e t r a i t c a r a c t é r i s t i q u e :

— 8 4 d ’e n t r e e u x , s o i t 5 3 % , o n t e n e f f e t d e s c a u s e s à c a r a c t è r e g é n é r i q u e ;

— 3 9 d ’e n t r e e u x , s o i t 2 5 % , o n t p o u r o r i g i n e u n e d é f a i l l a n c e a l é a t o i r e o u s p é c i f i q u e

d e l ’i n s t a l l a t i o n o ù i l s s e s o n t p r o d u i t s ;

— l e s a u t r e s , c ’e s t - à - d i r e 3 5 , s o i t 2 2 % , n e p e u v e n t ê t r e c l a s s é s d a n s l ’u n e o u l ’a u t r e •

c a t é g o r i e : c e s o n t e n g é n é r a l d e s i n c i d e n t s d o n t l e s c a u s e s r e l è v e n t d e f a c t e u r s

h u m a i n s ; c e u x - c i p e u v e n t a v o i r d e s a s p e c t s g é n é r i q u e s , n o t a m m e n t l o r s q u ’i l s ’a g i t

d e p r o b l è m e s d ’ a s s u r a n c e q u a l i t é ; t o u t e f o i s n o u s n ’a v o n s q u a l i f i é d e « g é n é r i q u e s »

q u e l e s i n c i d e n t s a y a n t p o u r o r i g i n e d e s d é f a i l l a n c e s d e m a t é r i e l s r e c o n n u e s c o m m e

t e l l e s , o u r é p é t i t i v e s ( m ê m e d é f a i l l a n c e d e m a t é r i e l o b s e r v é e s u r p l u s i e u r s t r a n c h e s ,

p a r e x e m p l e f u i t e s a u x v a n n e s d ’a s p e r s i o n d u p r e s s u r i s e u r ) .

N o u s a v o n s c l a s s é e n d e u x c a t é g o r i e l e s i n c i d e n t s à c a r a c t è r e g é n é r i q u e : c e u x

q u i r e l è v e n t d e p r o b l è m e s l i é s à l a f a b r i c a t i o n e t a u m o n t a g e e t c e u x q u i r e l è v e n t

d e p r o b l è m e s l i é s à l a c o n c e p t i o n ; p a r m i c e s d e r n i e r s , n o u s a v o n s t e n t é d e d i s t i n g u e r

l e s d é f a u t s q u e l ’o n a u r a i t p u d é t e c t e r p l u s t ô t , à l ’a i d e d e p r o g r a m m e s d e q u a l i f i ­

c a t i o n p e r m e t t a n t d ’a s s u r e r q u e l e c o m p o s a n t o u l e s y s t è m e i n c r i m i n é é t a i t b i e n

a p t e à r e m p l i r l a f o n c t i o n q u i l u i é t a i t a s s i g n é e . L e s r é s u l t a t s c o r r e s p o n d a n t s s o n t

p r é s e n t é s d a n s l e t a b l e a u I I .

C o m p t e t e n u d e l a p l a c e o c c u p é e p a r l e n u c l é a i r e d a n s l a p r o d u c t i o n d ’é l e c ­

t r i c i t é e n F r a n c e , l a s t a n d a r d i s a t i o n e x i g e , d e l a p a r t d ’ E l e c t r i c i t é d e F r a n c e e t

d e s a u t o r i t é s d e s û r e t é , u n e l i g n e d e c o n d u i t e s t r i c t e g a r a n t i s s a n t l a d é t e c t i o n

p r é c o c e d e t o u t d é f a u t d e c o n c e p t i o n o u d e f a b r i c a t i o n q u i p o u r r a i t a f f e c t e r u n e

p a r t i e , v o i r l ’e n s e m b l e , d u p a r c d e c e n t r a l e s . C e c i s i g n i f i e n o t a m m e n t q u e , p o u r

é v i t e r l ’e x t e n s i o n d e s e f f e t s n é f a s t e s d ’u n t e l d é f a u t , i l f a u t t r è s r a p i d e m e n t p r e n d r e

4 . P R E M I E R S R E S U L T A T S E T C O N C L U S I O N S

126 DROULERS et al.

T A B L E A U I L I N C I D E N T S A C A R A C T E R E G E N E R I Q U E : R E P A R T I T I O N

D E S C A U S E S

Fabrication ou montage

Conception

Nombre total d’incidents

de ce type

Qualificationinsuffisante

Nombre 9 74 29

Pourcentage 11 89 35

d e s m e s u r e s p a l l i a t i v e s , i n s p e c t i o n o u t r a v a u x p r é v e n t i f s , m ê m e a u p r i x d ’u n e

i n d i s p o n i b i l i t é d ’u n e c e r t a i n e d u r é e .

L e s d é f a i l l a n c e s d e s b r o c h e s d e c e n t r a g e d e s t u b e s g u i d e s d e b a r r e d e c o m ­

m a n d e c o n s t i t u e n t u n b o n e x e m p l e d ’u n d é f a u t d e c e t y p e ; c i n q t r a n c h e s e n o n t

c o n n u : G r a v e l i n e s 1 , F e s s e n h e i m 1 , B u g e y 2 , 3 e t 4 . M ê m e s i c e s d é f a i l l a n c e s n e

c o n s t i t u e n t p a s u n p r o b l è m e d e s û r e t é m a j e u r , e l l e s o n t f a i t b a i s s e r d e f a ç o n

s i g n i f i c a t i v e l e t a u x d e d i s p o n i b i l i t é d e s t r a n c h e s f r a n ç a i s e s F e s s e n h e i m e t B u g e y ,

c o n s t i t u e n t u n d é f a u t à c a r a c t è r e g é n é r i q u e . D ’a u t r e s e x e m p l e s s e r o n t d o n n é s

p l u s l o i n , s o u s 4 . 3 .

C e t e x a m e n d e s a s p e c t s l i é s à l a s t a n d a r d i s a t i o n m o n t r e a u s s i q u e , p o u r l e s

f u t u r s p a l i e r s , u n e a t t e n t i o n t o u t e p a r t i c u l i è r e d e v r a ê t r e a p p o r t é e a u x m o d i f i c a ­

t i o n s d e c o n c e p t i o n o u d e f a b r i c a t i o n d e s s y s t è m e s o u d e s c o m p o s a n t s ; c h a c u n e

d ’e n t r e e l l e s d e v a n t ê t r e j u s t i f i é e p a r u n e q u a l i f i c a t i o n c o m p l è t e .

4 . 2 . I n c i d e n t s l i é s a u x f a c t e u r s h u m a i n s

S u r 1 5 8 i n c i d e n t s , 5 6 , s o i t 3 5 % , r e l è v e n t d e c e t t e c a t é g o r i e . N o u s a v o n s

t e n t é d e d i s t i n g u e r t r o i s a s p e c t s :

1 ) D é f a u t s d ’a s s u r a n c e q u a l i t é e n e x p l o i t a t i o n : d a n s c e t t e r u b r i q u e o n t é t é

a f f e c t é s l e s i n c i d e n t s l i é s à l ’a b s e n c e d e p r o c é d u r e , à d e s c o n d i t i o n s d ’e x p l o i t a t i o n

i n c o m p a t i b l e s a v e c l a c o n c e p t i o n , à d e s i n t e r v e n t i o n s p o u r r é p a r a t i o n o u

m a i n t e n a n c e m a l p r é p a r é e s o u m a l c o o r d o n n é e s , à d e s e s s a i s i n c o m p a t i b l e s a v e c

l ’é t a t d e l a t r a n c h e d a n s l e q u e l i l s o n t é t é r é a l i s é s , e t c .

2 ) D é f a u t s d e p r o c é d u r e s : d a n s c e t t e r u b r i q u e f i g u r e n t l e s i n c i d e n t s l i é s à d e s

p r o c é d u r e s , g a m m e s d ’e s s a i s o u c o n s i g n e s d e c o n d u i t e s i n c o m p l è t e s o u e r r o n é e s ;

d a n s c e d e r n i e r c a s , i l s ’a g i t e n g é n é r a l d e p r o c é d u r e s n o n r é v i s é e s a p r è s q u ’u n e

m o d i f i c a t i o n s o i t i n t e r v e n u e s u r l e c i r c u i t c o r r e s p o n d a n t , o u d e p r o c é d u r e s

n ’e n v i s a g e a n t p a s c e r t a i n s é t a t s d e l a t r a n c h e ( p r o l o n g a t i o n d u c y c l e p a r e x e m p l e ) .

IAEA-SM-268/43

T A B L E A U I I I . I N C I D E N T S L I E S A U F A C T E U R H U M A I N

1 2 7

Assurance qualité en exploitation

Défaut de procédure

Autres

Nombre 25 15 30

Pourcentage dunombre total 16 9 19d’incidents

3 ) A u t r e s c a u s e s : d a n s c e t t e r u b r i q u e f i g u r e n t n o t a m m e n t l e s i n c i d e n t s l i é s à

d e s p r o b l è m e s e r g o n o m i q u e s , à l ’i n s u f f i s a n c e d e f o r m a t i o n d u p e r s o n n e l o u à d e s

e r r e u r s h u m a i n e s c a r a c t é r i s é e s ; l e s c h i f f r e s o b t e n u s p o u r c h a c u n d e c e s c a s n e

n o u s o n t p a s p a r u s u f f i s a m m e n t s i g n i f i c a t i f s p o u r ê t r e d i s t i n g u é s : i l s s o n t d o n c

r e g r o u p é s d a n s l a m ê m e c a t é g o r i e .

L e s r é s u l t a t s o b t e n u s s o n t d o n n é s d a n s l e t a b l e a u I I I .

L e n o m b r e r e l a t i v e m e n t é l e v é d ’i n c i d e n t s d o n t l ’ o r i g i n e e s t l i é e à u n e

d é f a i l l a n c e d e l ’o r g a n i s a t i o n d e l a q u a l i t é e n e x p l o i t a t i o n s ’e x p l i q u e p a r l e f a i t q u e ,

d u r a n t l a p é r i o d e c o n s i d é r é e , l e s d i s p o s i t i o n s p r i s e s p a r E l e c t r i c i t é d e F r a n c e d a n s

c e d o m a i n e a c h e v a i e n t d ’ê t r e f o r m a l i s é e s e t s e m e t t a i e n t e n p l a c e s u r l e s d i f f é r e n t s

s i t e s . U n e f f o r t i m p o r t a n t a é t é f a i t , e t l e n o m b r e d e c e s i n c i d e n t s d e v r a i t d o n c

d é c r o î t r e d a n s l ’a v e n i r .

E n c e q u i c o n c e r n e l e s d é f a u t s d e p r o c é d u r e , i l c o n v i e n t d e s o u l i g n e r q u e , à

l a s u i t e d e l ’a c c i d e n t s u r v e n u à T M I - 2 , u n v a s t e p r o g r a m m e d e r é v i s i o n e t d ’a m é l i o ­

r a t i o n d e s p r o c é d u r e s a é t é l a n c é ; c e t r a v a i l p o r t e t a n t s u r l e u r p r é s e n t a t i o n q u e

s u r l e u r c o n t e n u t e c h n i q u e . I l e s t m a i n t e n a n t t e r m i n é p o u r l e s p r o c é d u r e s

c o r r e s p o n d a n t a u x s i t u a t i o n s a c c i d e n t e l l e s e t i n c i d e n t e l l e s q u i s o n t i d e n t i q u e s s u r

t o u s l e s s i t e s : a u c u n d e s d é f a u t s é v o q u é s d a n s l e t a b l e a u I I I n e m e t e n c a u s e l ’u n e

d e c e s p r o c é d u r e s a m é l i o r é e s . L e m ê m e t r a v a i l e s t p r é v u s u r l e s p r o c é d u r e s q u i

o n t t r a i t à l a c o n d u i t e e n f o n c t i o n n e m e n t n o r m a l , à l a m a n u t e n t i o n d u c o m b u s t i b l e ,

a u x e s s a i s p é r i o d i q u e s , e t c . A c t u e l l e m e n t , c e l l e s - c i s o n t r é d i g é e s p a r c h a q u e

c e n t r a l e : u n e p r e m i è r e é t a p e c o n s i s t e r a à é t a b l i r d e s g u i d e s d e r é d a c t i o n s t a n d a r d i s é s

a u x q u e l s d e v r o n t s e c o n f o r m e r l e s r e s p o n s a b l e s c o n c e r n é s .

4 . 3 . I n c i d e n t s l i é s à d e s d é f a i l l a n c e s d e s y s t è m e s o u d e m a t é r i e l s

S u r 1 5 8 i n c i d e n t s , 1 2 7 , s o i t 8 0 % , a p p a r t i e n n e n t à c e t t e c a t é g o r i e ; i l s o n t

d o n n é l i e u à 1 3 9 d é f a i l l a n c e s d e m a t é r i e l . N o u s a v o n s d i s t i n g u é t r o i s g r a n d e s

r u b r i q u e s c o r r e s p o n d a n t à d e s g r o u p e s d e s y s t è m e s :

1 ) C i r c u i t p r i m a i r e e t i n t e r n e d e c u v e .

128 DROULERS et al.

- C i r c u i t p r i m a i r e

i - F u i t e s

4 3 3 1 %

- C i r c u i t s c o n n e c t é s a u c i r c u i t

p r i m a i r e e t c i r c u i t s d e s û r e t é 4 9 3 5 % —

R I S

3 2 7 4 %

L - A u t r e s

I- R R A

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11 2 6 %

1 5 3 1 %

1 3 2 7 %

3 1 %

T u b e s d e

g é n é r a t e u r s d e v a p e u r

J o i n t s d e p o m p e s p r i m a i r e s .....................

S o u p a p e s d e s û r e t é V a n n e s d e d é c h a r g e

I . . . p r e s s u r i s e u r : 4

V a n n e s - P r e s s e - é t o u p e : 1 0

- A u t r e s I 5 I L A u t r e s : 5

E c h a n g e u r s ............................................................

- V a n n e s ...................................................................

m

L A u t r e s ....................................

V a n n e s ............................

L A u t r e s ....................................

C i r c u i t d e b o r i c a t i o n

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1

10

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D ie s e l s e t

t a b l e a u x s e c o u r s

1 2 %

5 1 0 %

- A ir c o m p r i m é

- C i r c u i t s s e c o n d a i r e e t

a u x i l i a i r e ; s y s t è m e s s u p p o r t s 4 7 3 4 % '

E f f l u e n t s

- S e c o n d a i r e

8 1 7 %

4 9 %

1 8 3 8 %

1 7 3 6 %

F IG . l . Défaillances de systèmes ou de composants (139 défaillances pour 1 2 7 incidents).

2 ) P r i n c i p a u x s y s t è m e s e n l i a i s o n d i r e c t e a v e c l e c i r c u i t p r i m a i r e ( c i r c u i t d e

c o n t r ô l e v o l u m é t r i q u e e t c h i m i q u e R C V , c i r c u i t d e r e f r o i d i s s e m e n t à l ’a r r ê t R R A )

e t s y s t è m e s i m p o r t a n t s p o u r l a s û r e t é ( i n j e c t i o n d e s é c u r i t é R I S , a s p e r s i o n d e

l ’e n c e i n t e E A S , g r o u p e s é l e c t r o g è n e s d e s e c o u r s e t t a b l e a u x é l e c t r i q u e s a s s o c i é s ) .

3 ) C i r c u i t s e c o n d a i r e , c i r c u i t s a u x i l i a i r e s e t s y s t è m e s s u p p o r t s .

M i s à p a r t l e s i n c i d e n t t e l s q u e l e s j e t s a u x j o i n t s d e b a f f l e o u l e s r u p t u r e s d e

b r o c h e s d e t u b e g u i d e , l ’e s s e n t i e l d e s d é f a i l l a n c e s a f f e c t a n t l e c i r c u i t p r i m a i r e

( 3 2 , s o i t 7 4 % ) e s t c o n s t i t u é p a r d e s f u i t e s d ’e a u p r i m a i r e . Q u a t r e f u i t e s , o b s e r v é e s

a u n i v e a u d e s t u b e s d e g é n é r a t e u r d e v a p e u r , o n t d é p a s s é l a l i m i t e f i x é e d a n s l e s

s p é c i f i c a t i o n s t e c h n i q u e s d ’e x p l o i t a t i o n ( 7 0 L / h ) e t o n t n é c e s s i t é l ’a r r ê t d u r é a c t e u r .

IAEA-SM-268/43 1 2 9

P a r a i l l e u r s , l e s t r a n c h e s f r a n ç a i s e s o n t c o n n u d e s d é f a i l l a n c e s d e j o i n t s d e

p o m p e s p r i m a i r e s ( 4 ) : c e l l e s - c i s e s o n t t r a d u i t e s p a r u n e a u g m e n t a t i o n s i g n i f i c a t i v e .

d u d é b i t d ’ i n j e c t i o n , m a i s d a n s a u c u n d e s c a s , l a d é f a i l l a n c e d u j o i n t n ’a é t é

c o m p l è t e .

I l r e s t e q u e l a p l u p a r t d e s f u i t e s p r i m a i r e s o b s e r v é e s s o n t d u e s à d e s d é f a i l l a n c e s

d e l a r o b i n e t t e r i e , p a r m i l e s q u e l l e s o n p e u t d i s t i n g u e r :

a ) D e s f u i t e s a m o n t - a v a l s u r l e s s o u p a p e s d e s û r e t é e t l e s v a n n e s d e d é c h a r g e d u

p r e s s u r i s e u r ( 4 ) .

b ) D e s f u i t e s a u p r e s s e - é t o u p e d ’ a u t r e s v a n n e s ( 1 0 ) .

C o m m e d e s p r o b l è m e s a u t r e s q u e c e l u i d e s f u i t e s c o n d u i s a i e n t à s ’i n t e r r o g e r

s u r l a f i a b i l i t é d e s s o u p a p e s d e s û r e t é e t d e s v a n n e s d e d é c h a r g e , l e s y s t è m e d e

p r o t e c t i o n d u c i r c u i t p r i m a i r e c o n t r e l e s s u r p r e s s i o n s a é t é e n t i è r e m e n t r e p e n s é .

U n n o u v e a u s y s t è m e a é t é i n s t a l l é s u r l a t r a n c h e C r u a s 2 q u i d e v r a i t d é m a r r e r l ’é t é

p r o c h a i n : s i l e s r é s u l t a t s d ’e x p l o i t a t i o n s o n t p o s i t i f s , E l e c t r i c i t é d e F r a n c e e n v i s a g e r a

d e l ’i n s t a l l e r s u r l ’e n s e m b l e d e s t r a n c h e s .

L e s p r o b l è m e s d e f u i t e s a u x p r e s s e - é t o u p e d e r o b i n e t t e r i e n e s o n t p a s e n c o r e

r é s o l u s d e m a n i è r e s a t i s f a i s a n t e , b i e n q u e d e s a m é l i o r a t i o n s r é c e n t e s s o i e n t i n t e r ­

v e n u e s . I l s c o n s t i t u e n t u n e b o n n e i l l u s t r a t i o n d e s d é f a i l l a n c e s à c a r a c t è r e g é n é r i q u e ,

q u e n o u s a v o n s é v o q u é e s p l u s h a u t e t q u i a u r a i e n t p u ê t r e é v i t é e s p a r l a m i s e e n

o e u v r e d e p r o g r a m m e s d e q u a l i f i c a t i o n m i e u x a d a p t é s .

P a r m i l e s i n c i d e n t s a f f e c t a n t l a s e c o n d e c a t é g o r i e d e s y s t è m e s , i l c o n v i e n t

d e c i t e r :

a ) L e s p r o b l è m e s r e n c o n t r é s s u r l e c i r c u i t d e r e f r o i d i s s e m e n t d u r é a c t e u r à l ’a r r ê t

( R R A ) : 1 5 d é f a i l l a n c e s o n t é t é r e c e n s é e s , 9 s u r d e s v a n n e s , q u i e n g é n é r a l n e

f o n c t i o n n e n t p a s c o r r e c t e m e n t , e t 5 f u i t e s a u n i v e a u d e s é c h a n g e u r s . C e s o n t a u s s i

d e s i n c i d e n t s à c a r a c t è r e g é n é r i q u e t o u c h a n t l a c o n c e p t i o n ; i l s o n t s u s c i t é d e s

é t u d e s e t d e s m e s u r e s c o r r e c t i v e s v o n t ê t r e p r i s e s .

b ) L e s p r o b l è m e s r e n c o n t r é s s u r l e c i r c u i t d ’i n j e c t i o n d e s é c u r i t é ( R I S ) e t q u i

a f f e c t e n t , p o u r l a p l u p a r t , l e s y s t è m e d e b o r i c a t i o n e n r a i s o n d e l a f o r t e c o n ­

c e n t r a t i o n e n a c i d e b o r i q u e ( 2 1 0 0 0 p p m ) d u f l u i d e q u ’i l v é h i c u l e . C e s y s t è m e

n ’e s t p a s r e d o n d a n t , s i b i e n q u ’u n e d é f a i l l a n c e , m ê m e m i n e u r e , p e u t l e r e n d r e

i n d i s p o n i b l e e t c o n d u i r e à l ’ a r r ê t d u r é a c t e u r , c o n f o r m é m e n t a u x c o n d i t i o n s l i m i t e s

d e f o n c t i o n n e m e n t f i x é e s p a r l e s s p é c i f i c a t i o n s t e c h n i q u e s d ’ e x p l o i t a t i o n . P o u r

l e s t r a n c h e s d e 1 3 0 0 M W e , E l e c t r i c i t é d e F r a n c e a a p p o r t é l a d é m o n s t r a t i o n q u e

c e s y s t è m e n ’é t a i t p a s i n d i s p e n s a b l e p o u r l a s û r e t é , e t l ’a d o n c a b a n d o n n é .

D a n s l e m ê m e t e m p s , d e s é t u d e s v i s a n t à d i m i n u e r s e n s i b l e m e n t l a c o n c e n t r a t i o n

d ’a c i d e b o r i q u e s u r l e s t r a n c h e s d e 9 0 0 M W e o n t é t é e n t r e p r i s e s .

c ) L e s p r o b l è m e s r e n c o n t r é s s u r l e c i r c u i t d e c o n t r ô l e v o l u m é t r i q u e e t c h i m i q u e

s o n t , p o u r l a p l u p a r t , c o m m e s u r l e c i r c u i t p r i m a i r e , d e s f u i t e s a u p r e s s e - é t o u p e

d e v a n n e s ( 1 0 ) .

L a t r o i s i è m e c a t é g o r i e d ’i n c i d e n t s d é f i n i e p l u s h a u t c o n c e r n e l e c i r c u i t

s e c o n d a i r e , l e s c i r c u i t s a u x i l i a i r e s e t l e s s y s t è m e s s u p p o r t s . U n e r e m a r q u e s ’i m p o s e :

130 DROULERS et al.

I l n o u s p a r a î t p a r t i c u l i è r e m e n t r é v é l a t e u r q u ’u n e é t u d e , q u i n e p o r t e q u e s u r

l e s i n c i d e n t s s i g n i f i c a t i f s p o u r l a s û r e t é e t n o n s u r l ’e n s e m b l e d e s é v é n e m e n t s

s u r v e n u s s u r l e s t r a n c h e s , m o n t r e q u e l e t i e r s e n v i r o n d e c e s i n c i d e n t s a f f e c t e d e s

s y s t è m e s c o n s i d é r é s a p r i o r i c o m m e p e u i m p o r t a n t s p o u r l a s û r e t é . C e r é s u l t a t

e s t d ’ a u t a n t p l u s i n t é r e s s a n t q u e c ’ e s t d a n s c e t t e c a t é g o r i e q u e s e t r o u v e n t l e s

i n c i d e n t s a u x c o n s é q u e n c e s p o t e n t i e l l e s l e s p l u s g r a v e s , c ’e s t - à - d i r e d e s i n c i d e n t s

q u i a u r a i e n t p u c o n d u i r e à d e s s i t u a t i o n s n o n p r i s e s e n c o m p t e d a n s l e d i m e n s i o n -

n e m e n t .

A c e t é g a r d , i l c o n v i e n t d e c i t e r l e s s y s t è m e s d e t r a i t e m e n t d ’e f f l u e n t s e t

s u r t o u t l e s y s t è m e d ’ a i r c o m p r i m é . A t i t r e d ’e x e m p l e , r a p p e l o n s l ’i n c i d e n t s u r ­

v e n u e n a o û t d e r n i e r s u r l a c e n t r a l e d e T r i c a s t i n : l a d é f a i l l a n c e d ’u n d é t e n d e u r

s u r l e c i r c u i t d ’a i r a c o n d u i t à l a p e r t e d e l ’a l i m e n t a t i o n d e s d e u x j o i n t s d u s a s

d u b â t i m e n t r é a c t e u r e t d o n c à l a p e r t e t o t a l e d e l ’i s o l e m e n t d e l ’e n c e i n t e . C e c i

n o u s a m è n e à p e n s e r q u ’i l v a u d r a i t m i e u x n e p a s f a i r e d e d i f f é r e n c e a u s s i n e t t e

q u ’a c t u e l l e m e n t e n t r e l e s s y s t è m e s i m p o r t a n t s p o u r l a s û r e t é e t l e s a u t r e s . B i e n

q u ’i l n e p u i s s e ê t r e q u e s t i o n d ’ a p p l i q u e r a u x s y s t è m e s a u x i l i a i r e s l e s m ê m e s

c r i t è r e s d e c o n c e p t i o n o u d e f o n c t i o n n e m e n t q u ’ a u c i r c u i t p r i m a i r e o u a u c i r c u i t

d ’ i n j e c t i o n d e s é c u r i t é , i l c o n v i e n d r a i t n é a n m o i n s d ’e x a m i n e r d e m a n i è r e

a p p r o f o n d i e l e s c o n s é q u e n c e s d e l e u r d é f a i l l a n c e s u r l a s û r e t é d e l ’i n s t a l l a t i o n .

C ’e s t d ’ a i l l e u r s c e q u i d o i t ê t r e f a i t , e n F r a n c e , d a n s l ’a n a l y s e d u r a p p o r t

p r o v i s o i r e d e s û r e t é d e s t r a n c h e s d e 1 3 0 0 M W e , q u i e s t e n c o u r s a c t u e l l e m e n t .

4 . 4 . E t a t d e l a t r a n c h e a u m o m e n t d e l ’ i n c i d e n t

L e t a b l e a u I V d o n n e l a r é p a r t i t i o n d e s i n c i d e n t s e n f o n c t i o n d e l ’é t a t d e

l a t r a n c h e a u m o m e n t o ù i l s s o n t s u r v e n u s ; n o u s a v o n s d i s t i n g u é q u a t r e c a s :

— t r a n c h e e n f o n c t i o n n e m e n t ;

— t r a n c h e à l ’a r r ê t ( c h a u d , i n t e r m é d i a i r e , f r o i d o u a r r ê t p o u r r e c h a r g e m e n t ) ;

— i n c i d e n t s o u a v a r i e s d é c o u v e r t s a u c o u r s d ’u n a r r ê t ( à l ’ o c c a s i o n d e s e s s a i s o u

d e c o n t r ô l e s s y s t é m a t i q u e s ) ;

— i n c i d e n t s q u i a u r a i e n t p u s u r v e n i r d a n s n ’ i m p o r t e q u e l l e a u t r e c o n d i t i o n d e

f o n c t i o n n e m e n t , l ’é t a t d e l a t r a n c h e n ’i n t e r v e n a n t e n r i e n s u r s e s c a u s e s o u s o n

d é r o u l e m e n t .

C o m p t e t e n u d u n o m b r e r e l a t i v e m e n t é l e v é d ’ i n c i d e n t s s u r v e n u s a u c o u r s d e s

p é r i o d e s d ’a r r ê t , n o u s a v o n s p o u s s é p l u s l o i n n o t r e i n v e s t i g a t i o n :

— 8 d e c e s i n c i d e n t s f o n t i n t e r v e n i r l e s s y s t è m e s d e m a n u t e n t i o n o u d e s t o c k a g e

d u c o m b u s t i b l e ;

— 1 2 d e c e s i n c i d e n t s o n t c o n d u i t à u n e p e r t e p a r t i e l l e o u t o t a l e ( d a n s 2 c a s ) d u

r e f r o i d i s s e m e n t d u c o e u r ; p a r m i c e s 1 2 , 5 o n t c o n s i s t é e n d e s p e r t e s t o t a l e s d u

R R A ;

— 1 9 d e c e s i n c i d e n t s é t a i e n t l i é s à d e s a c t i v i t é s d e m a i n t e n a n c e o u d ’e s s a i s .

C e s r é s u l t a t s n o u s s u g g è r e n t l e s r é f l e x i o n s s u i v a n t e s .

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131

Puissance Arrêt Découvert à l ’arrêt

Etatindifférent

Nombre 64 53 30 11

Pourcentage du nombre total d’incidents

41 34 19 7

D a n s l e s c e n t r a l e s n u c l é a i r e s , i l e s t i n d é n i a b l e q u e c ’e s t l o r s q u e l a t r a n c h e e s t

e n p u i s s a n c e q u ’e x i s t e n t l e s r i s q u e s l e s p l u s i m p o r t a n t s . T o u t e f o i s , l o r s q u ’e l l e e s t

à l ’a r r ê t , i l f a u t q u e s o i t t o u j o u r s m a i n t e n u e l a f o n c t i o n d e r e f r o i d i s s e m e n t d u

c o e u r , c e q u i e x i g e n o t a m m e n t l a d i s p o n i b i l i t é d e s s o u r c e s é l e c t r i q u e s . D e p l u s ,

p e n d a n t c e s p é r i o d e s d ’ a r r ê t , l a p r e s s i o n e t l a t e m p é r a t u r e d u c i r c u i t p r i m a i r e

p e u v e n t ê t r e e n c o r e é l e v é e s , d e t e l l e s o r t e q u e l e s r i s q u e s d e d é p r e s s u r i s a t i o n

d e m e u r e n t , a l o r s q u e d e s i n t e r v e n t i o n s p e u v e n t n é c e s s i t e r l a p r é s e n c e d e p e r s o n n e l

d a n s l e b â t i m e n t r é a c t e u r . E n f i n , c ’e s t p e n d a n t c e s p é r i o d e s d ’ a r r ê t q u e s o n t

e f f e c t u é e s l e s o p é r a t i o n s d e m a n u t e n t i o n d u c o m b u s t i b l e e t q u e l a p i s c i n e d e

d é s a c t i v a t i o n c o n t i e n t l e p l u s d e p r o d u i t s a c t i f s .

P a r c o n s é q u e n t , s i l e r i s q u e à l ’a r r ê t e s t m o i n s i m p o r t a n t q u ’e n p u i s s a n c e ,

i l e s t t o u t e f o i s l o i n d ’ ê t r e n é g l i g e a b l e . U n e a t t e n t i o n p l u s g r a n d e d e v r a i t d o n c y

ê t r e a p p o r t é e d a n s l e s a n a l y s e s d e s û r e t é . E n e f f e t , c ’e s t a u c o u r s d e s a r r ê t s q u e

s o n t e f f e c t u é s l a p l u p a r t d e s m o d i f i c a t i o n s , d e s t r a v a u x d ’e n t r e t i e n , d e s e s s a i s

p é r i o d i q u e s : c e s i n t e r v e n t i o n s c o n d u i s e n t à r e n d r e v o l o n t a i r e m e n t i n d i s p o n i b l e s

c e r t a i n s s y s t è m e s , p a r t i e l l e m e n t o u t o t a l e m e n t , e t c e c i a u g m e n t e l a p r o b a ­

b i l i t é d e p e r t e t o t a l e d ’u n e f o n c t i o n d e s û r e t é .

P a r a i l l e u r s , l e s o p é r a t i o n s d e m a n u t e n t i o n d u c o m b u s t i b l e n e s o n t p a s

a u t o m a t i s é e s ; e l l e s s o n t t r è s r é p é t i t i v e s ; l e s p r o c é d u r e s u t i l i s é e s n ’o n t p a s f a i t

l ’o b j e t d ’ a n a l y s e s d e s û r e t é a p p r o f o n d i e s e t n e r é p o n d e n t p a s t o u j o u r s à d e s r è g l e s

p r é c i s e s d ’a s s u r a n c e d e l a q u a l i t é ; c e c i a c c r o î t d o n c l a p r o b a b i l i t é d ’e r r e u r

h u m a i n e ( 1 4 ) .

L e s r é s u l t a t s p r é s e n t é s d a n s l e t a b l e a u V c o n f i r m e n t l ’ i m p o r t a n c e d u f a c t e u r

h u m a i n d a n s l e s c a u s e s d e s i n c i d e n t s s u r v e n a n t p e n d a n t l e s a r r ê t s ; c e t a b l e a u

p r é c i s e l e s r é s u l t a t s d o n n é s d a n s l e t a b l e a u I I I , e n f o n c t i o n d e l ’é t a t d e l a t r a n c h e .

D i f f é r e n t e s m e s u r e s , d ’o r e s e t d é j à d é c i d é e s o u p r é v u e s , d e v r a i e n t p e r m e t t r e

d ’a m é l i o r e r l a s i t u a t i o n . E n e f f e t :

— à l a d e m a n d e d e s a u t o r i t é s d e s û r e t é , E l e c t r i c i t é d e F r a n c e d e v r a c o m p l é t e r l e s

s p é c i f i c a t i o n s t e c h n i q u e s d ’e x p l o i t a t i o n a f i n d e c o u v r i r a u s s i l e s é t a t s d ’a r r ê t

d u r é a c t e u r ;

13 2 DROULERS et al.

T A B L E A U V . I N C I D E N T S L I E S A U F A C T E U R H U M A I N S E L O N L ’E T A T

D E L A T R A N C H E

Puissance Arrêt

Nombre % a Nombre % a

Assurance-qualité en exploitation

7 13 15 27

Défaut de procédures

6 11 9 16

Autres 17 30 13 23

a Le pourcentage est exprim é en fonction du nom bre total d’incidents liés au facteur humain.

— à l ’ o c c a s i o n d e l ’ e x a m e n d e s o p t i o n s d e s û r e t é d u f u t u r p a l i e r N 4 , i l a é t é

d e m a n d é q u e l e s é t u d e s d ’a c c i d e n t p r e n n e n t e n c o m p t e l e s s i t u a t i o n s d ’ a r r ê t c o m m e

c o n d i t i o n s i n i t i a l e s ;

— E l e c t r i c i t é d e F r a n c e d é v e l o p p e u n p r o g r a m m e d e g e s t i o n i n f o r m a t i s é e d e s

i n d i s p o n i b i l i t é s v o l o n t a i r e s d e c o m p o s a n t s o u d e s y s t è m e s ; c e c i , a s s o c i é à l ’a m é ­

l i o r a t i o n d e s s p é c i f i c a t i o n s t e c h n i q u e s d ’e x p l o i t a t i o n , d e v r a i t p e r m e t t r e d e v o i r

d i m i n u e r n o t a b l e m e n t l e n o m b r e d e s i n c i d e n t s s u r v e n a n t p e n d a n t l e s a r r ê t s ;

— e n f i n , E l e c t r i c i t é d e F r a n c e e n v i s a g e d e s p é c i a l i s e r l e s é q u i p e s c h a r g é e s d ’e f f e c t u e r

l e s o p é r a t i o n s d e m a n u t e n t i o n d u c o m b u s t i b l e .

4 . 5 . C o n s é q u e n c e s r é e l l e s d e s i n c i d e n t s

N o u s a v o n s p e n s é q u e , p o u r a v o i r u n e v u e c o m p l è t e d u n i v e a u d e s û r e t é

d e s t r a n c h e s e n e x p l o i t a t i o n , i l é t a i t i n d i s p e n s a b l e d e d i s p o s e r d ’u n e c l a s s i f i c a t i o n

d e s i n c i d e n t s e n f o n c t i o n d e l e u r s c o n s é q u e n c e s .

E n f a i t , i l f a u d r a i t e x a m i n e r à l a f o i s l e s c o n s é q u e n c e s r é e l l e s e t l e s c o n s é ­

q u e n c e s p o t e n t i e l l e s ; n o u s a v o n s c o m m e n c é p a r l e s p r e m i è r e s , c a r e l l e s s o n t m o i n s

s u j e t t e s à c o n t r o v e r s e . N o u s a v o n s d i s t i n g u é c i n q s o r t e s d e c o n s é q u e n c e s r é e l l e s :

p e r t e d ’i n t é g r i t é d e l ’u n e d e s b a r r i è r e s , p e r t e d ’u n e f o n c t i o n d e s û r e t é , d i s p e r s i o n

i n c o n t r ô l é e d e r a d i o a c t i v i t é ; l e s r é s u l t a t s d ’e n s e m b l e s o n t d o n n é s d a n s l e t a b l e a u V I .

1 ) R u p t u r e d e g a i n e ( p e r t e d ’i n t é g r i t é d e la p r e m i è r e b a r r i è r e ) . N o u s n ’a v o n s

o b s e r v é q u e t r o i s f o i s u n n i v e a u d ’a c t i v i t é d e l ’e a u p r i m a i r e i m p o s a n t u n e d é c l a ­

r a t i o n f o r m e l l e a u x a u t o r i t é s d e s û r e t é ; u n e s e u l e f o i s , c e n i v e a u a d é p a s s é l a v a l e u r

l i m i t e f i x é e d a n s l e s s p é c i f i c a t i o n s t e c h n i q u e s d ’e x p l o i t a t i o n e t a d o n c c o n d u i t à

IAEA-SM-268/43 1 3 3

T A B L E A U V I . C O N S E Q U E N C E S R E E L L E S D E S I N C I D E N T S

Ruptures de gaine

Défauts de confinem ent primaire

Pertes partielles de l’isolement de l ’enceinte

Perte totale d’une fonction de sûreté

Dispersion incontrôlée

Total

3

39 a

5

134

64

a 10 ont dépassé le seuil fixé dans les spécifications techniques d’exploitation.

l ’a r r ê t d e l a t r a n c h e . D e u x d e c e s i n c i d e n t s a v a i e n t p o u r o r i g i n e d e s j e t s a u x j o i n t s

d e b a f f l e . C e s r é s u l t a t s t é m o i g n e n t d u b o n c o m p o r t e m e n t d u c o m b u s t i b l e .

2 ) D é f a u t d e c o n f i n e m e n t p r i m a i r e ( p e r t e d ’i n t é g r i t é d e la d e u x i è m e b a r r iè r e ) .

L e n o m b r e é l e v é d ’i n c i d e n t s d a n s c e t t e c a t é g o r i e e s t d i r e c t e m e n t l i é a u p r o b l è m e

d e s u i t e s d é j à é v o q u é p l u s h a u t . I l f a u t t o u t e f o i s n o t e r q u e l e d é b i t m a x i m u m

o b s e r v é a é t é d e 1 0 m 3 / h , v a l e u r t r è s e n d e ç à d u s e u i l n é c e s s i t a n t l a m i s e e n r o u t e

d e l ’i n j e c t i o n d e s é c u r i t é . E n o u t r e , p o u r d i x i n c i d e n t s s e u l e m e n t , l e d é b i t d e f u i t e

a d é p a s s é l a v a l e u r d u s e u i l l i m i t e f i x é p a r l e s s p é c i f i c a t i o n s t e c h n i q u e s d ’e x p l o i t a ­

t i o n e t i m p o s a n t l ’a r r ê t d u r é a c t e u r .

3 ) E t a n c h é i t é d e l ’e n c e i n t e d e c o n f i n e m e n t ( p e r t e d ’i n t é g r i t é d e la t r o i s i è m e

b a r r i è r e ) . A u c o u r s d e l a p é r i o d e e x a m i n é e , a u c u n e p e r t e t o t a l e d u c o n f i n e m e n t

o u f u i t e s i g n i f i c a t i v e n ’e s t s u r v e n u e s u r l e s t r a n c h e s f r a n ç a i s e s . L e s i n c i d e n t s

m e n t i o n n é s d a n s l e t a b l e a u V I c o r r e s p o n d e n t à d e s p e r t e s p a r t i e l l e s d e l ’i s o l e m e n t

d e l ’e n c e i n t e d u e s à d e s d é f a i l l a n c e s d e l ’u n e d e s v a n n e s d ’i s o l e m e n t , q u i ,

r a p p e l o n s - l e , s o n t r e d o n d a n t e s .

4 ) P e r t e t o t a l e d ’u n e f o n c t i o n d e s û r e t é . I l c o n v i e n t d e f a i r e , à c e t é g a r d , l e s

c o m m e n t a i r e s s u i v a n t s : s e p t d e s i n c i d e n t s e n c a u s e c o r r e s p o n d e n t à d e s i n d i s p o ­

n i b i l i t é s d u r é s e r v o i r d e b o r e à 2 1 0 0 0 p p m o u d u c i r c u i t a s s o c i é ; i l n e m e t t e n t p a s

g r a v e m e n t e n c a u s e l a s û r e t é d e l ’ i n s t a l l a t i o n . C i n q a u t r e s i n c i d e n t s o n t c o n s i s t é

e n l a p e r t e t o t a l e d u R R A , e t o n t d é j à é t é é v o q u é s p l u s h a u t ; d a n s t o u s l e s c a s ,

d ’a u t r e s s y s t è m e s é t a i t d i s p o n i b l e s e t o n t p e r m i s d ’a s s u r e r l e r e f r o i d i s s e m e n t d u

c o e u r . L e d e r n i e r i n c i d e n t d e c e t t e c a t é g o r i e e s t l e p l u s s i g n i f i c a t i f : a u c o u r s d ’u n e

s é q u e n c e d ’i n j e c t i o n d e s é c u r i t é s u r a b o n d a n t e , l e s d e u x p o m p e s b a s s e p r e s s i o n

o n t d é c l e n c h é a u s s i t ô t a p r è s l e u r s o l l i c i t a t i o n . U n e m o d i f i c a t i o n a é t é m i s e e n

o e u v r e s a n s d é l a i p o u r c o r r i g e r l a s i t u a t i o n .

5 ) R e j e t s i n c o n t r ô l é s d ’a c t i v i t é . T o u s c e s i n c i d e n t s f o n t i n t e r v e n i r l e s s y s t è m e s

d e t r a i t e m e n t e t d e s t o c k a g e d ’e f f l u e n t s . N o u s a v o n s i n c l u s d a n s c e t t e c a t é g o r i e

d e s i n c i d e n t s t e l s q u e f u i t e d e r é s e r v o i r s d ’e f f l u e n t s l i q u i d e s o u c o n t a m i n a t i o n d e

134 \ J>ROULERS et al.

l ’a t m o s p h è r e d ’u n b â t i m e n t s a n s q u e l e r e j e t a t t e i g n e f o r c é m e n t l ’e n v i r o n n e m e n t .

I l c o n v i e n t d e n o t e r n é a n m o i n s q u e , d a n s t o u s l e s c a s , l e s a c t i v i t é s r e j e t é e s s o n t

r e s t é e s t r è s e n d e ç à d e s s e u i l s l i m i t e s f i x é s d a n s l e s a u t o r i s a t i o n s d e r e j e t a n n u e l .

E n c o n c l u s i o n , c o m p t e t e n u d e la d é f i n i t i o n q u e n o u s a v o n s a d o p t é e p o u r

l e s c o n s é q u e n c e s r é e l l e s d e s i n c i d e n t s , i l a p p a r a î t q u ’u n p e t i t n o m b r e s e u l e m e n t

( 1 2 % d u t o t a l ) a a f f e c t é l e s p r i n c i p a u x s y s t è m e s m i s e n p l a c e p o u r g a r a n t i r l a

s û r e t é d e s i n s t a l l a t i o n s n u c l é a i r e s ; c e c i p e u t ê t r e c o n s i d é r é c o m m e u n b o n r é s u l t a t

p o u r l e s p r e m i è r e s a n n é e s d e f o n c t i o n n e m e n t d u p r o g r a m m e P W R f r a n ç a i s .

5 . D E V E L O P P E M E N T U L T E R I E U R

L e p r e m i e r o b j e c t i f d e c e t t e é t u d e é t a i t d e c o n f i r m e r , p a r d e s r é s u l t a t s

q u a n t i t a t i f s , l e s j u g e m e n t s q u a l i t a t i f s d e s i n g é n i e u r s q u i e x a m i n e n t q u o t i d i e n n e m e n t

l e s i n c i d e n t s s u r v e n a n t s u r l e s c e n t r a l e s .

L ’é v o l u t i o n d a n s l e t e m p s d e s r é s u l t a t s o b t e n u s d e v r a i t p e r m e t t r e d e v é r i f i e r

l ’e f f i c a c i t é d e s m e s u r e s c o r r e c t i v e s m i s e s e n o e u v r e e n m a t i è r e d ’a s s u r a n c e d e

l a q u a l i t é o u d ’e s s a i s p é r i o d i q u e s p a r e x e m p l e ; e l l e d e v r a i t a u s s i m o n t r e r u n e

d i m i n u t i o n d u n o m b r e d e s « d é f a u t s d e j e u n e s s e » . E l l e d e v r a i t e n f i n p e r m e t t r e d e

d é t e c t e r l e s p r o b l è m e s n o u v e a u x e t l ’i n f l e x i o n d e c e r t a i n e s t e n d a n c e s d é n o t a n t ,

p a r e x e m p l e , l e v i e i l l i s s e m e n t d e s c o m p o s a n t s .

C e t t e é t u d e d e v r a i t , p a r a i l l e u r s , d é b o u c h e r s u r u n e m e i l l e u r e é v a l u a t i o n d e

l a g r a v i t é d e s i n c i d e n t s . P o u r c e l a , e l l e d e v r a p r e n d r e e n c o m p t e n o n s e u l e m e n t

l e u r s c o n s é q u e n c e s r é e l l e s , m a i s a u s s i l e u r s c o n s é q u e n c e s p o t e n t i e l l e s : c e c i

s u p p o s e q u e , d a n s c h a q u e c a s , s o i t e s t i m é e l a p r o b a b i l i t é p o u r q u e l ’i n c i d e n t a i t

c o n d u i t à d e s r e j e t s i n a c c e p t a b l e s .

E n f i n , n o u s p e n s o n s q u ’e n p o u r s u i v a n t c e t t e é t u d e à l ’a i d e d e m o y e n s

i n f o r m a t i q u e s , e n t r a i t a n t u n p l u s g r a n d n o m b r e d ’ i n c i d e n t s e t e n e x a m i n a n t u n

p l u s g r a n d n o m b r e d e f a c t e u r s , q u i s e r o n t a l o r s m i e u x p r é c i s é s , n o u s p o u r r o n s

é v e n t u e l l e m e n t d é c o u v r i r d e s c o r r é l a t i o n s e n t r e d i v e r s e s c a u s e s , c o n s é q u e n c e s ,

é t a t s d e t r a n c h e , o u s y s t è m e s i m p l i q u é s .

C e t t e c o n n a i s s a n c e p l u s a p p r o f o n d i e p o u r r a i t c o n d u i r e à d e s e s t i m a t i o n s

d e c o û t / b é n é f i c e e t é c l a i r e r l e s d é c i s i o n s à p r e n d r e p o u r a m é l i o r e r l a s û r e t é d e s

t r a n c h e s e n f o n c t i o n n e m e n t o u e n p r o j e t .

i IAEA-SM-268/47

L ’A N A L Y S E D E S I N C I D E N T S A F R A M A T O M E

A . C A L A M A N D , A . O L I O T

S o c i é t é F r a m a t o m e ,

P a r is l a D é f e n s e , F r a n c e

Abstract-Résumé

A N A L Y S IS O F INCID ENTS A T FRA M A TO M E.Pursuing the organizational arrangements set up after the Three Mile Island accident,

Framatom e is building up a centralized system atic analysis o f significant incidents. The analyses are perform ed in accordance with the following m ethodological principles: selection o f incidents for detailed analysis, critical analysis o f the course o f incidents, research on and analysis o f ‘reduced’ initiating events, description and analysis o f reduced operating conditions and lessons learned. Examples o f significant incidents analysed on this basis are presented and demonstrate the value o f the method. The lessons derived from these analyses apply to the follow ing four main areas: design principles, operating conditions, operating rules and plant components.

L ’ A N A L Y S E DES IN CID EN TS A FRAM ATO M E.Prolongeant l ’organisation mise sur pieds après l ’accident de Three Mile Island, Framatome

développe une activité centralisée d’analyse systématique des incidents significatifs. Ces analyses sont menées en suivant les éléments de m éthodologie suivants: sélection des incidents retenus pour une analyse détaillée, analyse critique du déroulement des incidents, recherche et analyse des initiateurs «réduits», caractérisation et analyse des conditions de fonctionnem ent réduites, enseignements. Des exemples d’incidents significatifs analysés sur ces bases sont présentés et montrent l ’intérêt de la m éthode. Les enseignements extraits de ces analyses sont répartis dans les quatre grands domaines suivants: bases de conception, conditions de fonction­nem ent, règles de conduite, matériel.

1 . I N T R O D U C T I O N

L a c o n c e p t i o n d e s î l o t s n u c l é a i r e s c o m p o r t a n t u n r é a c t e u r à e a u

p r e s s u r i s é e e s t f o n d é e s u r d e s r è g l e s q u i t i e n n e n t c o m p t e d e

l ' o c c u r r e n c e p o s s i b l e o u h y p o t h é t i q u e d ' u n c e r t a i n n o m b r e d ' i n ­

c i d e n t s o u d ' a c c i d e n t s d é n o m m é s c o n d i t i o n s d e f o n c t i o n n e m e n t d e

c o n c e p t i o n .

C e t t e d é m a r c h e e s t c a r a c t é r i s t i q u e d e l ' i n d u s t r i e n u c l é a i r e e t

l a d i f f é r e n c i e d e l a p l u p a r t d e s a u t r e s a c t i v i t é s i n d u s t r i e l l e s .

A v e c l ' a u g m e n t a t i o n d u n o m b r e d e t r a n c h e s é l e c t r o n u c l é a i r e s e n

e x p l o i t a t i o n e t d o n c l ' i n é l u c t a b l e a c c r o i s s e m e n t d e s d i v e r s

i n c i d e n t s , i l d e v i e n t i n d i s p e n s a b l e d e c o m p l é t e r l ' a p p r o c h e

1 3 5

136 t ALAMAND et OLIOT

t h é o r i q u e p a r u n e v é r i f i c a t i o n " e x p é r i m e n t a l e " d e s o n b i e n -

f o n d é , b a s é e s u r l ' e x p l o i t a t i o n r a t i o n n e l l e d e c e s i n c i d e n t s . A

c e t t e f i n , i l e s t n é c e s s a i r e d e p r o c é d e r à l ' a n a l y s e s y s t é ­

m a t i q u e e t a p p r o f o n d i e d e s i n c i d e n t s d ' e x p l o i t a t i o n . C e t t e

a n a l y s e p e r m e t p a r a i l l e u r s d e t i r e r d e n o m b r e u x e n s e i g n e m e n t s

d o n t l ' i m p o r t a n c e a u p l a n d e l a s û r e t é p e u t ê t r e t r è s v a r i a b l e

e t q u i c o u v r e n t d e s d o m a i n e s t r è s d i f f é r e n t s .

C e s e n s e i g n e m e n t s p e r m e t t e n t e n p a r t i c u l i e r :

- d e c o n f o r t e r o u d ' i n f i r m e r l e s s o l u t i o n s r e t e n u e s p a r 1 e c o n ­

c e p t e u r e t e n p a r t i c u l i e r d a n s d e s d o m a i n e s o ù l e s r è g l e m e n t s ,

c o d e s e t n o r m e s n ' o n t p a s u n d e g r é d e r é s o l u t i o n s u f f i s a n t o u

s o n t i n e x i s t a n t s ;

- d e c o m p a r e r l e c o m p o r t e m e n t r é e l d e l a c h a u d i è r e a v e c l e c o m ­

p o r t e m e n t p r é d i t . C e t t e c o m p a r a i s o n n ' e s t p o s s i b l e q u e p o u r

l e s p l u s f r é q u e n t s d e s i n c i d e n t s c o n s i d é r é s à l a c o n c e p t i o n .

E l l e p e r m e t d a n s c e r t a i n s c a s d ' a m é l i o r e r l a c o n d u i t e p o s t -

i n c i d e n t e l l e ;

- d e c o m p a r e r l e s p r o b a b i l i t é s o b s e r v é e s ( c ' e s t - à - d i r e d é r i v a n t

d e s t a t i s t i q u e s ) a v e c l e s p r o b a b i l i t é s e s t i m é e s d e s é v é n e m e n t s

i n i t i a t e u r s c o n s i d é r é s d a n s l a c o n c e p t i o n .

- d ' i d e n t i f i e r d e s i n c i d e n t s p r é c u r s e u r s d ' i n c i d e n t s p l u s g r a ­

v e s .

L a m u l t i p l i c i t é d e s i n c i d e n t s m i n e u r s , l a d i v e r s i t é d e s d i s c i ­

p l i n e s t e c h n i q u e s c o n c e r n é e s a i n s i q u e l a p l u r a l i t é d e s e n s e i ­

g n e m e n t s q u i p e u v e n t e n ê t r e t i r é s s o n t l e s p r i n c i p a l e s r a i s o n s

q u i c o n d u i s e n t d i v e r s o r g a n i s m e s n a t i o n a u x - A u t o r i t é s d e S û ­

r e t é , E x p l o i t a n t s , C o n s t r u c t e u r s - o u i n t e r n a t i o n a u x , à r e c u e i l ­

l i r e t à a n a l y s e r l e s i n c i d e n t s . D a n s c e t t e o p t i q u e , FRAM ATOM E -

d o n n a n t u n e s u i t e à l ' o r g a n i s a t i o n t e m p o r a i r e m i s e s u r p i e d s

p o u r a n a l y s e r l ' i m p a c t d e l ' a c c i d e n t d e T h r e e M i l e I s l a n d -

d é v e l o p p e u n e a c t i v i t é c e n t r a l i s é e d ' a n a l y s e s y s t é m a t i q u e d e s

i n c i d e n t s s i g n i f i c a t i f s s u s c e p t i b l e s d ' a v o i r d e s r é p e r c u s s i o n s

s u r l a c h a u d i è r e .

2 . E L E M E N T S D E M E T H O D O L O G I E

L a m é t h o d o l o g i e e m p l o y é e p a r FRAM ATOM E p o u r e x t r a i r e t o u s l e s

e n s e i g n e m e n t s d e s i n c i d e n t s s i g n i f i c a t i f s r e p o s e s u r l e s p r i n c i ­

p e s s u i v a n t s :

IAEA-SM-268/47 ¡ 137

U n g r a n d n o m b r e d ' i n c i d e n t s s u r v e n a n t s u r d e s r é a c t e u r s à e a u

l é g è r e s o n t i d e n t i f i é s d a n s d i v e r s e s s o u r c e s d ' i n f o r m a t i o n ^ i l

n ' e s t é v i d e m m e n t p a s p o s s i b l e d e l e s a n a l y s e r t o u s e n d é t a i l .

U n e s é l e c t i o n s ' a v è r e d o n c i n d i s p e n s a b l e p o u r r e t e n i r c e u x q u i

f e r o n t l ' o b j e t d ' u n e a n a l y s e a p p r o f o n d i e . O n s ' e f f o r c e d e r e t e ­

n i r e n p r i o r i t é l e s i n c i d e n t s p r é s e n t a n t u n e n c h a î n e m e n t ( p a r ­

f o i s c o m p l e x e à d é m ê l e r ) d ' é v é n e m e n t s e t d o n t l ' a n a l y s e r e v ê t u n

c a r a c t è r e m u l t i - d i s c i p l i n a i r e . P o u r c e s i n c i d e n t s - q u ' o n q u a ­

l i f i e d ' i n c i d e n t s d e " f o n c t i o n n e m e n t " p a r o p p o s i t i o n a u x i n c i ­

d e n t s d i t s d e " m a t é r i e l " - , i l p e u t y a v o i r u n l o n g c h e m i n e m e n t

e n t r e l e s p r e m i e r e t d e r n i e r m a i l l o n s d e l a c h a î n e d e s é v é n e ­

m e n t s .

A i n s i , d a n s l e c a s d e l ' i n c i d e n t s u r v e n u l e 2 0 m a r s 1 9 7 8

s u r l a t r a n c h e d e R A N C H O S E C O , l e c o u r t - c i r c u i t p r o v o q u é

p a r l a c h u t e d ' u n e a m p o u l e é l e c t r i q u e d a n s u n p u p i t r e e n

s a l l e d e c o m m a n d e l o r s d ' u n e b a n a l e o p é r a t i o n d e m a i n t e ­

n a n c e a c o n d u i t à u n e c a s c a d e d ' é v é n e m e n t s s e t r a d u i s a n t

e n f i n d e c o m p t e p a r u n c h o c f r o i d p r e s s u r i s é s u r l a c u v e .

P a r c o n t r e , p o u r l e s i n c i d e n t s d i t s d e " m a t é r i e l " , l a d é f a i l ­

l a n c e i n i t i a l e r e s t e l i m i t é e a u s e u l m a t é r i e l d é f a i l l a n t e t n e

d é c l e n c h e p a s u n e c a s c a d e d ' é v é n e m e n t s ( a v é r é s o u p o t e n t i e l s ) .

C e s i n c i d e n t s d e " m a t é r i e l " n ' a p p e l l e n t à p r i o r i p a s d ' a u t r e s

a n a l y s e s q u e c e l l e s l i m i t é e s a u s e u l m a t é r i e l c o n c e r n é ; e l l e s

i n c o m b e n t a u x c o n c e p t e u r s e t / o u a u x c o n t r u c t e u r s d e c e s m a t é ­

r i e l s . I l e s t d o n c e s s e n t i e l q u ' i l s s o i e n t d e s t i n a t a i r e s d u

r e t o u r d ' e x p é r i e n c e p o u r e n t i r e r e u x - m ê m e s t o u s l e s e n s e i ­

g n e m e n t s a u p l a n d e l a c o n c e p t i o n , d e l a f a b r i c a t i o n , o u d u

c o n t r ô l e .

L e s i n c i d e n t s d e " f o n c t i o n n e m e n t " r e t e n u s p o u r u n e a n a l y s e

a p p r o f o n d i e s o n t c h o i s i s s e l o n c e r t a i n s c r i t è r e s a u n o m b r e

d e s q u e l s f i g u r e n t :

- l e s d e m a n d e s é v e n t u e l l e s d e s c l i e n t s r e l a t i v e s à c e r t a i n s

i n c i d e n t s ( c e l a p e u t - ê t r e l e c a s p o u r l e s i n c i d e n t s a y a n t u n e

c e r t a i n e n o t o r i é t é ) ;

- l ' i m p a c t p r é s u m é d e l ' i n c i d e n t s u r l a s û r e t é d e l ' i n s t a l l a ­

t i o n . L e j u g e m e n t d e l ' i n g é n i e u r , l ' e x p é r i e n c e a c q u i s e d a n s

d e s a n a l y s e s a n t é r i e u r e s a i n s i q u e l e s d i v e r s e s i n f o r m a t i o n s ,

d o n t s u r t o u t l e s é v e n t u e l l e s a n a l y s e s d e c e t i n c i d e n t q u a n d

e l l e s e x i s t e n t d é j à , g u i d e n t d a n s l ' e s t i m a t i o n d e c e t i m p a c t

p r é s u m é ;

- l a d i s p o n i b i l i t é e t l a p e r t i n e n c e d e s i n f o r m a t i o n s d i s p o n i ­

b l e s .

2 . 1 . C h o i x d e s i n c i d e n t s r e t e n u s p o u r l ’a n a l y s e

138 CALAMAND et OLIOT

2 . 2 . A n a l y s e c r i t i q u e d u d é r o u l e m e n t d e l ’i n c i d e n t

L e s i n c i d e n t s d e f o n c t i o n n e m e n t d o n t l ' a n a l y s e a p p r o f o n d i e a é t é

r e t e n u e , f o n t d ' a b o r d l ' o b j e t d ' u n e a n a l y s e c h r o n o l o g i q u e p a s à

p a s d e s d i f f é r e n t s m a i l l o n s d e l a c h a î n e d e s é v é n e m e n t s . Q u a n d

l ' i n c i d e n t n e s ' e s t p a s p r o d u i t s u r u n e c h a u d i è r e d e c o n c e p t i o n

FR A M A T O M E , l ' a n a l y s e p a s à p a s c o m p o r t e u n e c o m p a r a i s o n d u d é ­

r o u l e m e n t e f f e c t i f d e l ' i n c i d e n t r é e l a v e c l e d é r o u l e m e n t p r é ­

s u m é d e l ' i n c i d e n t t e l q u ' i l s e s e r a i t p r o d u i t s u r u n e c h a u d i è r e

FR A M A T O M E . L e s é v e n t u e l l e s d i f f é r e n c e s d e c o n c e p t i o n s o n t a i n s i

m i s e s e n é v i d e n c e . Q u a n d l ' i n c i d e n t s ' e s t p r o d u i t s u r u n e c h a u ­

d i è r e FR A M A T O M E , d e s s i m u l a t i o n s c h e r c h a n t à r e p r o d u i r e l e

f o n c t i o n n e m e n t i n c i d e n t e l e f f e c t i f s o n t p a r f o i s r é a l i s é e s . E l l e s

p e r m e t t e n t l e c a s é c h é a n t d e m i e u x v a l i d e r c e r t a i n s m o d è l e s

p h y s i q u e s o u d ' a m é l i o r e r l e s r è g l e s d e c o n d u i t e p o s t - i n c i d e n -

t e l l e .

L ' a n a l y s e c r i t i q u e c o n s i s t e é g a l e m e n t à s ' i n t e r r o g e r s u r l e s

e f f e t s q u ' a u r a i e n t e u s d ' é v e n t u e l l e s d é f a i l l a n c e s q u i n e s e s o n t

p a s p r o d u i t e s l o r s d e l ' i n c i d e n t r é e l . E l l e c h e r c h e a i n s i à m e t ­

t r e e n é v i d e n c e l e s p o i n t s f o r t s o u f a i b l e s e t e n p a r t i c u l i e r

l e s l i g n e s d e d é f e n s e s u b s i s t a n t a v a n t l e f r a n c h i s s e m e n t d e s

l i m i t e s d e s û r e t é c o n s i d é r é e s d a n s l a c o n c e p t i o n .

A p a r t i r d e c e t t e a n a l y s e c r i t i q u e d u d é r o u l e m e n t d e l ' i n c i d e n t ,

o n p e u t p r o c é d e r a u x d e u x é t a p e s s u i v a n t e s d é v e l o p p é e s d a n s l e s

d e u x p r o c h a i n s p a r a g r a p h e s :

- l a r e c h e r c h e e t l ' a n a l y s e d e s i n i t i a t e u r s " r é d u i t s " ;

- l a c a r a c t é r i s a t i o n e t l ' a n a l y s e d e s c o n d i t i o n s d e f o n c t i o n ­

n e m e n t " r é d u i t e s " .

2 . 3 . R e c h e r c h e e t a n a l y s e d e s i n i t i a t e u r s « r é d u i t s »

L ' é t a p e q u i s u i t l ' a n a l y s e c r i t i q u e d u d é r o u l e m e n t d e l ' i n c i d e n t

c o n s i s t e à i d e n t i f i e r d a n s l a c h a î n e d e s é v é n e m e n t s t e l s q u ' i l s

s e s o n t e f f e c t i v e m e n t p r o d u i t s , u n m a i l l o n p a r t i c u l i e r d o n t o n

p e n s e a p r i o r i q u e l ' e x a m e n s e r é v é l e r a f é c o n d d u p o i n t d e v u e

d e s e n s e i g n e m e n t s q u e l ' o n p e u t e n e x t r a i r e . L a p a r t i c u l a r i t é d e

c e m a i l l o n e s t q u ' i l p e u t ê t r e c o n s i d é r é i n d é p e n d a m m e n t d e s

m a i l l o n s s i t u é s e n a m o n t d a n s l a c h a î n e d e s é v é n e m e n t s : L ' i n c i ­

d e n t a n a l y s é c o n d u i t à c e m a i l l o n p a r u n e n c h a î n e m e n t d ' é v é n e ­

m e n t s q u i p o u r r a i t ê t r e t o u t a u t r e e t a b o u t i r n é a n m o i n s à c e

m a i l l o n l à o u à u n m a i l l o n d e m ê m e n a t u r e .

I l i m p o r t e e n e f f e t d e m e t t r e e n é v i d e n c e , a u - d e l à d e s c a u s e s

a v é r é e s d e l ' i n c i d e n t a n a l y s é , l a c l a s s e d ' é v é n e m e n t s i n i t i a ­

t e u r s d e m ê m e n a t u r e à l a q u e l l e c e s c a u s e s s o n t r é d u c t i b l e s . C e t

IAEA-SM-268/47 139

i n i t i a t e u r " r é d u i t " a i n s i i d e n t i f i é p e u t - ê t r e c o n s i d é r é c o m m e

r e p r é s e n t a t i f d e t o u t e u n e f a m i l l e d e s é q u e n c e s d ' é v é n e m e n t s

d o n t l e s c a u s e s i n i t i a l e s a p p a r a i s s e n t p a r f o i s c o m m e é t a n t t r è s

é l o i g n é e s d e l ' i n i t i a t e u r " r é d u i t " .

A i n s i , d a n s l e c a s d é j à c i t é d e R A N C H O S E C O , l e c o u r t - c i r ­

c u i t i n i t i a l a c o n d u i t à l a p e r t e d e l ' a l i m e n t a t i o n é l e c ­

t r i q u e d ' u n d e s d e u x g r o u p e s d e r é g u l a t i o n ( i n i t i a t e u r

" r é d u i t " ) .

O n c o n ç o i t l ' i n t é r ê t q u ' i l y a à t r a n s p o s e r l ' i n i t i a t e u r

" r é d u i t " d e R A N C H O S E C O a u c a s d e s c h a u d i è r e s FR A M A TO M E e t

à e x a m i n e r p l u s e n d é t a i l l e u r c o m p o r t e m e n t s u i t e à l a

p e r t e d e l ' a l i m e n t a t i o n é l e c t r i q u e d ' u n d e s q u a t r e g r o u p e s

d e r é g u l a t i o n ( i n i t i a t e u r " r é d u i t " t r a n s p o s é a u c a s d e s

c h a u d i è r e s FR A M A TO M E d e 9 0 0 M W e ) .

L ' a n a l y s e d é t a i l l é e d e c e s i n i t i a t e u r s " r é d u i t s " e s t s u s c e p t i b l e

d e m e t t r e e n é v i d e n c e d e s p r é c u r s e u r s d ' i n c i d e n t s a u x c o n s é q u e n ­

c e s p l u s s é r i e u s e s q u e l ' i n c i d e n t r e e l q u i a é t é a n a l y s é .

S e l o n l e s c a s p e u v e n t ê t r e c o n s i d é r é s c o m m e d e s p r é c u r s e u r s ,

s o i t l ' i n i t i a t e u r " r é d u i t " d i r e c t e m e n t e x t r a i t d e l ' a n a l y s e d e

l ' i n c i d e n t , s o i t l ' i n i t i a t e u r " r é d u i t " t r a n s p o s é a u c a s d e s

c h a u d i è r e s F R A M A T O M E , s o i t e n c o r e u n i n i t i a t e u r " r é d u i t " d e m ê m e

n a t u r e d o n t 1 ' o c c u r e n c e e s t c o n c e v a b l e .

A i n s i , e n r e p r e n a n t l ' e x e m p l e d e R A N C H O S E C O , u n i n i t i a ­

t e u r " r é d u i t " d e m ê m e n a t u r e d o n t l ' o c c u r r e n c e e s t c o n c e ­

v a b l e c o n s i s t e e n l a p e r t e d e l ' a l i m e n t a t i o n é l e c t r i q u e

d e s d e u x g r o u p e s d e r é g u l a t i o n . D e c e p o i n t d e v u e l à ,

R A N C H O S E C O a e f f e c t i v e m e n t é t é l e p r é c u r s e u r d e C R Y S T A L

R I V E R 3 .

2 . 4 . C a r a c t é r i s a t i o n e t a n a l y s e d e s c o n d i t i o n s d e f o n c t i o n n e m e n t « r é d u i t e s »

L ' i d e n t i f i c a t i o n d e s i n i t i a t e u r s " r é d u i t s " p e r m e t d e d é c o u p l e r

c o m m o d é m e n t l ' a m o n t d e l ' a v a l d a n s l a c h a î n e d e s é v é n e m e n t s .

E l l e p e r m e t d e f o c a l i s e r l ' a n a l y s e s u r c e t i n i t i a t e u r " r é d u i t "

q u i e s t d o n c d é b a r r a s s é d ' u n h i s t o r i q u e u n i q u e m e n t s p é c i f i q u e d e

l ' i n c i d e n t r é e l e t d ' e n t i r e r p a r c o n s é q u e n t l e s e n s e i g n e m e n t s

l e s p l u s g é n é r i q u e s .

L a m ê m e d é m a r c h e s ' a p p l i q u e a u ( x ) d e r n i e r ( s ) m a i l l o n ( s ) d e l a

c h a î n e d e s é v é n e m e n t s : c e l u i ( c e u x ) q u i r e p r é s e n t e ( n t ) l e s

c o n s é q u e n c e s d e l ' i n c i d e n t s u r l a c h a u d i è r e . I l e s t i n t é r e s ­

s a n t d e t e n t e r d e c a r a c t é r i s e r c e s c o n s é q u e n c e s e n t e r m e s d e

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c o n d i t i o n s d e f o n c t i o n n e m e n t v u e s p a r l a c h a u d i è r e o u p a r d e s

m a t é r i e l s p a r t i c u l i e r s . P a r a n a l o g i e a v e c l e c o n c e p t d ' i n i ­

t i a t e u r " r é d u i t " , o n l e s d é s i g n e p a r c o n d i t i o n s d e f o n c t i o n ­

n e m e n t " r é d u i t e s " .

A i n s i , t o u j o u r s d a n s l e m ê m e e x e m p l e d e l ' i n c i d e n t d e

R A N C H O S E C O , l e s c o n s é q u e n c e s s o n t r é d u c t i b l e s a u x c o n d i ­

t i o n s d e f o n c t i o n n e m e n t s u i v a n t e s :

- u n c h o c f r o i d p r e s s u r i s é c ô t é p r i m a i r e ,

- u n r e m p l i s s a g e e x c e s s i f d e s g é n é r a t e u r s d e v a p e u r .

L a f i g u r e 1 i l l u s t r e s c h é m a t i q u e m e n t l e s c o n c e p t s d ' i n i t i a t e u r

" r é d u i t " e t d e c o n d i t i o n s d e f o n c t i o n n e m e n t " r é d u i t e s " a v e c a p ­

p l i c a t i o n à l ' i n c i d e n t d e R ANCHO S E C O .

2 . 5 . E n s e i g n e m e n t s t i r é s d e l ’a n a l y s e

L e s a n a l y s e s d ' i n c i d e n t s o n t p o u r o b j e c t i f p r i n c i p a l d ' e x t r a i r e

t o u s l e s e n s e i g n e m e n t s p o s s i b l e s e t , p l u s p a r t i c u l i è r e m e n t - p o u r

l e s i n c i d e n t s d e f o n c t i o n n e m e n t q u i n o u s i n t é r e s s e n t i c i - d e

t e n t e r d e p o r t e r u n j u g e m e n t a u p l a n d e l a s û r e t é . C e t t e d é m a r ­

c h e c o n s i s t e à s e p r o n o n c e r , e n g é n é r a l d ' u n e m a n i è r e i m p l i c i t e ,

s u r l e c a r a c t è r e a c c e p t a b l e o u n o n d u c o u p l e [ p r o b a b i l i t é ( a v é ­

r é e o u p o t e n t i e l l e ) d e l ' i n i t i a t e u r " r é d u i t " , c o n d i t i o n s d e

f o n c t i o n n e m e n t " r é d u i t e s " ( a v é r é e s o u p o t e n t i e l l e s ) ] . R e m a r q u o n s

à c e s u j e t q u e d e u x c a s p e u v e n t s e p r é s e n t e r . D a n s l e p r e m i e r ,

i l y a c o r r e s p o n d a n c e b i u n i v o q u e e n t r e l ' i n i t i a t e u r " r é d u i t " e t

l a c o n d i t i o n d e f o n c t i o n n e m e n t " r é d u i t e " r é s u l t a n t e ( c ' e s t p a r

e x e m p l e l e c a s d e s f u i t e s o u r u p t u r e s d e t u b e d e g é n é r a t e u r d e

v a p e u r ) : i l s u f f i t a l o r s d e c o m p t a b i l i s e r l e n o m b r e d ' o c c u r ­

r e n c e s . D a n s l e d e u x i è m e c a s , d e m u l t i p l e s i n i t i a t e u r s " r é d u i t s "

p e u v e n t c o n d u i r e à l a m ê m e c o n d i t i o n d e f o n c t i o n n e m e n t " r é d u i ­

t e " : i l c o n v i e n t a l o r s d e s ' a s s u r e r q u e l a f r é q u e n c e c u m u l é e d e

c e s i n i t i a t e u r s " r é d u i t s " n ' e s t p a s i n c o m p a t i b l e a v e c l e c l a s ­

s e m e n t d e l a c o n d i t i o n d e f o n c t i o n n e m e n t .

C e j u g e m e n t d e s û r e t é , p o u r i m p o r t a n t q u ' i l s o i t , n ' e s t q u ' u n

e n s e i g n e m e n t p a r m i c e u x d e d i f f é r e n t e n a t u r e m e n t i o n n é s d a n s

l ' i n t r o d u c t i o n d e c e m é m o i r e e t i l l u s t r é s c i - d e s s o u s a u c h a p i ­

t r e 4 .

2 . 6 . D o c u m e n t a t i o n

C h a q u e a n a l y s e , q u i p e u t p a r f o i s c o n d u i r e à d e l o n g s d é v e l o p p e ­

m e n t s s i l ' i n c i d e n t e s t c o m p l e x e , f a i t s y s t é m a t i q u e m e n t l ' o b j e t

d ' u n e f i c h e r é s u m é d ' u n e p r é s e n t a t i o n s t a n d a r d , d e s t i n é e à

r a t i o n a l i s e r l ' i n f o r m a t i o n e t à f a c i l i t e r l a p r i s e d e d é c i s i o n .

T A B L E A U I . E X E M P L E S D ’I N C I D E N T S A N A L Y S E S

142 CALAMAND et OLIOT

Nom de la tranche affectée

Date de l'incident

Nombre de boucles/ Puissance électrique

(MWe)Concepteur de la chaudière

Point Beach 1 26/02/75 2 boucles/497 MWe WestinghouseSurry 2 16/09/76 3 boucles/822 MWe WestinghouseDoel 2 25/06/79 2 boucles/390 MWe Westinghouse

Prairie Island 1 02/10/79 2 boucles/530 MWe WestinghouseGinna 1 25/01/82 2 boucles/490 MWe WestinghouseRancho Seco 20/03/78 2 boucles/883 MWe Babcock & Wilcox

Crystal River 3 26/02/80 2 boucles/825 MWe Babcock & Wilcox

Tihange 1 31/05/80 3 boucles/825 MWe Framatome

Gravelines 1 09/04/80 3 boucles/920 MWe Framatome

North Anna 1 25/09/79 3 boucles/907 MWe Westinghouse

Fessenheim 09/01/80 3 boucles/890 MWe Framatome

Blayais 2 30/10/81 3 boucles/910 MWe Framatome

Bugey 5 12/02/81 3 boucles/900 MWe Framatome

North Anna 1 23/05/80 3 boucles/907 MWe Westinghouse

Sainte Lucie 1 11/06/80 2 boucles/810 MWe CombustionEngineering

Blayais 1 30/12/80 3 boucles/910 MWe Framatome

Indian Point 2 17/10/80 4 boucles/873 MWe Westinghouse

3 . E X E M P L E S D ’A N A L Y S E S

U n c e r t a i n n o m b r e d ' i n c i d e n t s s u r v e n u s s u r d e s r é a c t e u r s à e a u

p r e s s u r i s é e e t c o n s i d é r é s c o m m e s i g n i f i c a t i f s o n t é t é a n a l y s é s

s e l o n l e s b a s e s m é t h o d o l o g i q u e s p r é c i t é e s . L e t a b l e a u I e n i d e n ­

t i f i e q u e l q u e s e x e m p l e s p a r t i c u l i è r e m e n t r e p r é s e n t a t i f s . P o u r

c h a c u n d ' e u x , l e t a b l e a u II p r é s e n t e l a c a u s e i n i t i a l e , l ' i n i t i a ­

t e u r " r é d u i t " e t l e s c o n d i t i o n s d e f o n c t i o n n e m e n t " r é d u i t e s "

r e t e n u s a i n s i q u e l e s p r i n c i p a u x d o m a i n e s c o n c e r n é s p a r l e s e n ­

s e i g n e m e n t s . U n e p r e m i è r e c o n s t a t i o n s ' i m p o s e .

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146 CALAMAND et OLIOT

S i , d a n s c e r t a i n s c a s ( e s s e n t i e l l e m e n t l e s i n c i d e n t s d e f u i t e s o u

r u p t u r e s d e t u b e d e g é n é r a t e u r d e v a p e u r ) , l ' i d e n t i f i c a t i o n

d ' i n i t i a t e u r s " r é d u i t s " e t d e c o n d i t i o n s d e f o n c t i o n n e m e n t

" r é d u i t e s " p e u t p a r a î t r e s t é r i l e , i l e n e s t b i e n d ' a u t r e s ( p a r

e x e m p l e , l e s i n c i d e n t s d e p e r t e s d ' a l i m e n t a t i o n é l e c t r i q u e ) o ù

e l l e s e r é v è l e f é c o n d e e t c o n f o r t e l ' i n t é r ê t d e l a d é m a r c h e .

O n c o n s t a t e é g a l e m e n t q u e l a " d i s t a n c e " e n t r e l a c a u s e i n i t i a l e

e t l ' i n i t i a t e u r " r é d u i t " e s t t r è s v a r i a b l e :

P r a t i q u e m e n t n u l l e d a n s l e c a s d e s f u i t e s o u r u p t u r e s d e

t u b e d e g é n é r a t e u r d e v a p e u r , e l l e d e v i e n t t r è s g r a n d e

d a n s l e c a s d é j à c i t é d e R A N C H O S E C O o u d e C R Y S T A L R I V E R 3

I l e s t c l a i r q u e l ' a n a l y s e d é t a i l l é e d e s i n i t i a t e u r s " r é d u i t s "

e s t b i e n p l u s f é c o n d e q u e c e l l e , q u ' i l n e f a u t n é a n m o i n s p a s

n é g l i g e r , d e s s e u l e s c a u s e s i n i t i a l e s .

E n c e q u i c o n c e r n e l e s c o n d i t i o n s d e f o n c t i o n n e m e n t " r é d u i t e s " ,

o n o b s e r v e q u ' e l l e s s e r é p a r t i s s e n t e n d e u x g r a n d e s c a t é g o r i e s :

- d e s c o n d i t i o n s d e f o n c t i o n n e m e n t e n g é n é r a l p r i s e s e n c o m p t e à

l a c o n c e p t i o n , c ' e s t - à - d i r e c e l l e s q u i c o r r e s p o n d e n t a u x

d i f f é r e n t e s c l a s s e s d ' i n c i d e n t s o u d ' a c c i d e n t s a i n s i q u ' a u x

d i f f é r e n t e s c a t é g o r i e s d e s i t u a t i o n s r e l a t i v e s a u x e n c e i n t e s

s o u s p r e s s i o n d u c i r c u i t p r i m a i r e e t d e s a u t r e s c i r c u i t s ;

- d e s c o n f i g u r a t i o n s p a r t i c u l i è r e s d e f o n c t i o n n e m e n t p o u r l e s

s y s t è m e s o u l e s m a t é r i e l s .

O n r e t r o u v e p a r e x e m p l e d a n s c e t t e c a t é g o r i e l ' i s o l e m e n t

i n t e m p e s t i f d e l ' a s p i r a t i o n d e s p o m p e s d e c h a r g e

( B L A Y A I S 2 , l e 3 0 / 1 0 / 8 1 ) o u l ' i n o n d a t i o n d u b â t i m e n t

r é a c t e u r e t d u p u i t s d e c u v e ( I N D I A N P O I N T 2 , l e 1 7 / 1 0 / 8 0 ) .

4 . E N S E I G N E M E N T S

L e s p r i n c i p a u x e n s e i g n e m e n t s d é c o u l e n t d e l ' e x a m e n a p p r o f o n d i

d e s i n i t i a t e u r s " r é d u i t s " e t d e s c o n d i t i o n s d e f o n c t i o n n e m e n t

" r é d u i t e s " , q u e c e s o i e n t c e u x o u c e l l e s d i r e c t e m e n t o b s e r v é s

l o r s d e s i n c i d e n t s a n a l y s é s o u i n d i r e c t e m e n t o b t e n u s , p a r t r a n s ­

p o s i t i o n a u x c h a u d i è r e s d e c o n c e p t i o n FR A M A T O M E . P o u r l e c o n c e p ­

t e u r , l e s p r i n c i p a u x e n s e i g n e m e n t s s e r é p a r t i s s e n t d a n s l e s

d o m a i n e s s u i v a n t s :

- b a s e s d e c o n c e p t i o n ,

- c o n d i t i o n s d e f o n c t i o n n e m e n t ,

IAEA-SM-268/47 1 4 7

- r e g l e s d e c o n d u i t e ,

- p e r f o r m a n c e d u m a t é r i e l .

L e s e n s e i g n e m e n t s c o n c e r n e n t é g a l e m e n t d ' a u t r e s d o m a i n e s q u i

s o n t m o i n s d i r e c t e m e n t d u r e s s o r t d u c o n c e p t e u r m a i s d o n t l ' i m ­

p o r t a n c e e s t é g a l e m e n t t r è s g r a n d e ; à c e t t e c a t é g o r i e a p p a r ­

t i e n n e n t l e s e n s e i g n e m e n t s r e l a t i f s a u x c o m p o r t e m e n t s h u m a i n s

a u x q u e l s c e c o l l o q u e a c c o r d e u n e l a r g e p l a c e .

4 . 1 . B a s e s d e c o n c e p t i o n

D ' u n e f a ç o n g é n é r a l e , l e s e n s e i g n e m e n t s t i r é s d e s i n c i d e n t s n e

r e m e t t e n t p a s e n c a u s e l e s g r a n d s p r i n c i p e s d e s û r e t é s u r l e s ­

q u e l s r e p o s e n t l e s b a s e s d e c o n c e p t i o n , c e q u i c o n s t i t u e e n s o i

u n e n s e i g n e m e n t t r è s i m p o r t a n t . P a r c o n t r e , i l s a p p o r t e n t u n e

p l u s g r a n d e " r é s o l u t i o n " m e t t a n t e n é v i d e n c e c o m m e n t l e s d é t a i l s

d e l a c o n c e p t i o n - q u i r e s p e c t e n t l e s g r a n d s p r i n c i p e s p r é c i ­

t é s - " r é s i s t e n t " à l ' é p r e u v e d e s i n c i d e n t s . I l s s u g g è r e n t d e

c e t t e f a ç o n u n c e r t a i n n o m b r e d ' a m é l i o r a t i o n s p o s s i b l e s d e l a

c o n c e p t i o n .

A i n s i , l ' e x a m e n d e s p e r t e s p a r t i e l l e s o u t o t a l e s d e s

a l i m e n t a t i o n s é l e c t r i q u e s d e s g r o u p e s d e r é g u l a t i o n m o n ­

t r e , d ' u n e p a r t , q u e c e s i n i t i a t e u r s c o n d u i r a i e n t s u r l e s

c h a u d i è r e s FR A M A TO M E à d e s c o n s é q u e n c e s e n g é n é r a l m o i n s

s é v è r e s q u e c e l l e s e f f e c t i v e m e n t c o n s t a t é e s l o r s d e s

i n c i d e n t s a v é r é s (R A N C H O S E C O e t C R Y S T A L R I V E R 3 ) . I l

s u g g è r e d ' a u t r e p a r t d e p o s s i b l e s a m é l i o r a t i o n s d a n s l a

c o n c e p t i o n d e c e s a l i m e n t a t i o n s é l e c t r i q u e s . P o u r l e s

n o u v e a u x p r o j e t s , l e r a p p o r t c o û t - b é n é f i c e d e c e s a m é l i o ­

r a t i o n s p e r m e t d e c o n c l u r e f a v o r a b l e m e n t à l e u r m i s e e n

o e u v r e .

C e d e r n i e r p o i n t m e t e n é v i d e n c e u n e d i f f i c u l t é q u ' i l n e f a u t

p a s s e d i s s i m u l e r : d u p o i n t d e v u e d e l a s û r e t é , o ù p a s s e l a

d é m a r c a t i o n e n t r e l ' e x i g i b l e e t l e s o u h a i t a b l e ? L ' a p p r o c h e

c o û t - b é n é f i c e c o n s t i t u e u n e r é p o n s e p o s s i b l e q u i n ' e s t p a s

t o u j o u r s d ' u n e m i s e e n o e u v r e f a c i l e .

4 . 2 . C o n d i t i o n s d e f o n c t i o n n e m e n t

C ' e s t u n d o m a i n e o ù l e s a n a l y s e s d ' i n c i d e n t s m e t t e n t e n é v i d e n c e

d e s e n s e i g n e m e n t s s i g n i f i c a t i f s d ' u n e f a ç o n p l u s d i r e c t e m e n t

e x p l o i t a b l e . S c h é m a t i q u e m e n t , l e s e n s e i g n e m e n t s c o n c e r n e n t d ' u n e

p a r t l a f r é q u e n c e d ' o c c u r r e n c e d e s c o n d i t i o n s d e f o n c t i o n n e m e n t

d e c o n c e p t i o n , d ' a u t r e p a r t l ' é v o l u t i o n d e l e u r s p a r a m è t r e s

p h y s i q u e s . L e s i n c i d e n t s d e f u i t e s o u r u p t u r e s s u r v e n u e s s u r d e s

t u b e s d e g é n é r a t e u r d e v a p e u r i l l u s t r e n t b i e n c e d o u b l e a s p e c t .

1 4 8 CALAMAND et OLIOT

D u p o i n t d e v u e d e l a f r é q u e n c e d ' o c c u r r e n c e e t d o n c d e s

c a u s e s i n i t i a l e s , l ' i n c i d e n t d e G I N N A 1 a r e n f o r c é l a

l e ç o n t i r é e d e c e l u i d e P R A I R I E I S L A M ) 1 :

l e s p l u s g r o s s e s f u i t e s , a s s i m i l a b l e s e n p r e m i è r e a p p r o x i ­

m a t i o n à d e s r u p t u r e s g u i l l o t i n e d e t u b e d e g é n é r a t e u r d e

v a p e u r , s o n t p r o v o q u é e s p a r d e s o b j e t s é t r a n g e r s l o c a l i s é s

d a n s l a p a r t i e s e c o n d a i r e d e s g é n é r a t e u r s . E n d é p i t d e s

p r é c a u t i o n s p r i s e s a u n i v e a u d e s p r o c é d u r e s d e m o n t a g e o u

d ' i n t e r v e n t i o n s u r l e s g é n é r a t e u r s d e v a p e u r , i l n ' e s t

p l u s p o s s i b l e , c o m p t e t e n u d u n o m b r e t o t a l d ' a n n é e s - r é a c -

t e u r s , d e m a i n t e n i r e n 4 è m e c a t é g o r i e u n e c o n d i t i o n d e

f o n c t i o n n e m e n t q u i s ' e s t t r o u v é e a v é r é e à d e u x r e p r i ­

s e s . P a r a i l l e u r s , l a m ê m e c a u s e p o u r r a i t c o n d u i r e à l a

r u p t u r e d e p l u s d ' u n t u b e . L e s A u t o r i t é s d e S û r e t é f r a n ­

ç a i s e s o n t d o n c é t é a m e n é e s à d e m a n d e r p o u r l e n o u v e a u

p a l i e r 1 4 0 0 M W e, l e " d é c l a s s e m e n t " d e l a r u p t u r e d ' u n s e u l

t u b e d e l a 4 è m e à l a 3 è m e c a t é g o r i e e t s o n r e m p l a c e m e n t e n

4 è m e c a t é g o r i e p a r l a r u p t u r e d e d e u x t u b e s .

L e s i n c i d e n t s p e r m e t t e n t p a r f o i s d e v é r i f i e r q u e l e s c o m p o r t e ­

m e n t s r é e l s r e c o u p e n t b i e n l e s c o m p o r t e m e n t s p r é d i t s . I l n ' e s t

p a s q u e s t i o n i c i d e r e c a l e r o u d e v a l i d e r u n c o d e d e c a l c u l .

P o u r c e l a , i l f a u d r a i t u n e i n s t r u m e n t a t i o n s p é c i a l e e t u n e

c o n n a i s s a n c e p a r f a i t e d e t o u s l e s p a r a m è t r e s , c e q u i n ' e s t

é v i d e m m e n t p a s l e c a s . L e s e n r e g i s t r e m e n t s n o r m a u x d ' e x p l o i t a ­

t i o n p e r m e t t e n t n é a n m o i n s d e p r o c é d e r à d e s c o m p a r a i s o n s i n t é ­

r e s s a n t e s .

A i n s i , d a n s l e c a s d e s i n c i d e n t s t r è s s i m i l a i r e s d e b l o ­

c a g e e n p o s i t i o n o u v e r t e d ' u n e v a n n e d u c o n t o u r n e m e n t

v a p e u r a u c o n d e n s e u r , s u r v e n u s à N O R T H A N N A ( 2 5 / 0 9 / 7 9 ) e t

à F E S S E N H E I M 1 ( 0 9 / 0 1 / 8 0 ) , o n a p u p r o c é d e r à u n e t e l l e

c o m p a r a i s o n e t r e t r o u v e r l ' a l l u r e g é n é r a l e d e s t r a n s i t o i ­

r e s . C e t t e c o m p a r a i s o n p e r m e t e n p a r t i c u l i e r d e v a l i d e r l e

m o d è l e d e c o m p o r t e m e n t d u p r e s s u r i s e u r .

4 . 3 . R è g l e s d e c o n d u i t e

I l s ' a g i t l à d ' u n d o m a i n e o ù l e s a n a l y s e s d ' i n c i d e n t s s e r é v è ­

l e n t l e p l u s r i c h e d ' e n s e i g n e m e n t s . U n e p a r t i e i m p o r t a n t e d u

d é r o u l e m e n t d e l ' i n c i d e n t d é p e n d e n e f f e t d e s r è g l e s d e c o n d u i t e

p o s t - i n c i d e n t e l l e e t d e l a f a ç o n d o n t l e s o p é r a t e u r s l e s s u i ­

v e n t : l a s a n c t i o n p a r l ' e x p é r i e n c e e s t d o n c t r è s d i r e c t e e t l e s

c o n f i r m a t i o n s d u b i e n - f o n d é d e c e r t a i n e s d i s p o s i t i o n s d e c e s

r è g l e s s o n t a u s s i i m p o r t a n t e s q u e l e s i n f i r m a t i o n s o u l e s l a c u ­

n e s q u i s o n t a i n s i r é v é l é e s .

IAEA-SM-268/47 149

S a n s e n t r e r d a n s l e s d é t a i l s , o n p e u t r e t e n i r q u e l e s

i n c i d e n t s o n t p e r m i s d ' a p p o r t e r d e s a m é n a g e m e n t s p r é c i e u x

à l a c o n d u i t e d e l ' i n j e c t i o n d e s é c u r i t é , a u x r è g l e s d e

c o n d u i t e c o n c e r n a n t l e s r u p t u r e s d e t u b e d e g é n é r a t e u r d e

v a p e u r a i n s i q u e l e s d é p r e s s u r i s a t i o n s d u p r i m a i r e e t d u

s e c o n d a i r e .

L ' i n c i d e n t d e S A I N T E L U C I E 1 a t r è s l a r g e m e n t c o n t r i b u é à

a t t i r e r l ' a t t e n t i o n s u r l a p o s s i b i l i t é d e f o r m a t i o n d ' u n e

b u l l e s o u s l e c o u v e r c l e d e l a c u v e q u a n d o n p r o c è d e a u

r e f r o i d i s s e m e n t d e l a c h a u d i è r e e n c i r c u l a t i o n n a t u r e l l e ;

d e s p r é c a u t i o n s e x p l i c i t e s p e u v e n t m a i n t e n a n t ê t r e p r i s e s

a u n i v e a u d e s r è g l e s d e c o n d u i t e p o u r é v i t e r q u e l e s

o p é r a t e u r s s e l a i s s e n t s u r p r e n d r e p a r d e s r é a c t i o n s i n a t ­

t e n d u e s d e l a c h a u d i è r e d a n s u n e t e l l e s i t u a t i o n .

4 . 4 . P e r f o r m a n c e d u m a t é r i e l

N o u s a v o n s v u q u e l e s a n a l y s e s d o n t i l e s t q u e s t i o n d a n s c e t t e

c o m m u n i c a t i o n s o n t d e s a n a l y s e s d e " f o n c t i o n n e m e n t " . C e c i n ' e m ­

p ê c h e q u e , d a n s b o n n o m b r e d e s c a s é t u d i é s , d e s d é f a i l l a n c e s d e

m a t é r i e l s o i e n t à l ' o r i g i n e d e l ' i n c i d e n t e t / o u q u e l ' i n c i d e n t

s e t r a d u i s e p a r d e s s o l l i c i t a t i o n s p a r t i c u l i è r e s s u r l e m a t é ­

r i e l . D e m u l t i p l e s e n s e i g n e m e n t s p e u v e n t d o n c e n ê t r e t i r é s s u r

l e s p e r f o r m a n c e s - a u s e n s l a r g e - d u m a t é r i e l .

5 . C O N C L U S I O N

A l ' i n t é r i e u r d u r e s p e c t d e s p r e s c r i p t i o n s r é g l e m e n t a i r e s d e

s û r e t é , l e c o n c e p t e u r p e u t d é v e l o p p e r u n c e r t a i n n o m b r e d e

s o l u t i o n s t e c h n i q u e s p o u r l a c o n c e p t i o n d e s s y s t è m e s o u d e s

m a t é r i e l s . L e s s o l u t i o n s r e t e n u e s f o n t e n s u i t e l ' o b j e t d ' a n a l y ­

s e s d e c o n f o r m i t é a u x p r e s c r i p t i o n s r é g l e m e n t a i r e s d e s û r e t é

é d i c t é e s e n a m o n t d e l a c o n c e p t i o n .

L e s e n s e i g n e m e n t s t i r é s d e s i n c i d e n t s a p p o r t e n t u n c o m p l é m e n t

i m p o r t a n t à c e s a n a l y s e s d e c o n f o r m i t é . S ' i l s r e m e t t e n t r a r e m e n t

e n c a u s e l e s c r i t è r e s d e b a s e f i g u r a n t d a n s l e s p r e s c r i p t i o n s d e

s û r e t é , i l s p e r m e t t e n t p a r c o n t r e d e v a l i d e r o u d ' i n f i r m e r l e s

c h o i x t e c h n i q u e s r e t e n u s p a r l e c o n c e p t e u r p a r m i l e s c h o i x

p o s s i b l e s . I l s a c c r o i s s e n t l a f i n e s s e d e r é s o l u t i o n d e s a n a l y ­

s e s .

I l s c o n t r i b u e n t à u n e m e i l l e u r e c o n n a i s s a n c e d u c o m p o r t e m e n t d e

l a c h a u d i è r e d a n s d e s s i t u a t i o n s i n h a b i t u e l l e s e t p e r m e t t e n t

d a n s c e r t a i n s c a s d ' a p p r é c i e r l e s m a r g e s d a n s l e s c o n d i t i o n s

r é a l i s t e s .

150 CALAMAND et OLIOT

L a d i v e r s i t é d e s d o m a i n e s c o n c e r n é s p a r l e s e n s e i g n e m e n t s m i l i t e

e n f a v e u r d ' a n a l y s e s m e n é e s i n d é p e n d a m m e n t p a r d i f f é r e n t s o r g a ­

n i s m e s d o n t c h a c u n e s t p a r n a t u r e p l u s p a r t i c u l i è r e m e n t a t t e n t i f

à s o n m é t i e r : C o n c e p t e u r , C o n s t r u c t e u r , E x p l o i t a n t , A u t o r i t é d e

S û r e t é .

C e s d i v e r s e s a n a l y s e s e t l e u r c o n f r o n t a t i o n c o n s t i t u e n t u n e d e s

v o i e s d e l ' a m é l i o r a t i o n d e l a s û r e t é .

IAEA-SM-268/13

N U C L E A R POWER PLANT RELIABILITY D A T A COLLECTION SYSTEM IN JA PA N

S. M IYAOKA, H. FUKUMOTO Central Research Institute of

Electric Power Industries,Tokyo

S. SASAKITokyo Electric Company,Tokyo

Japan

Abstract

NUCLEAR POWER PLANT RELIABILITY DATA COLLECTION SYSTEM IN JAPAN.Since 1977, the Central Research Institute of Electric Power Industries (CRIEPI) has been

developing a nuclear power plant reliability data collection system (RDCS) under the sponsor­ship of the Japanese Federation of Electric Power Companies. The aims of the RDCS are to obtain reliability data on components which are directly related to the safe and reliable operation of nuclear power plants and to statistically analyse the failure trends of these components.To fulfil these purposes, 14 kinds of components have been selected. The data consist of three categories: component engineering data, component failure data and plant operating data. The engineering and plant operating data are used to estimate the total operating time of components for calculating the reliability data. The component failure data are reported to MITI with information such as cause, mode and effects. The reports will be stored in a computerized data base and be used to calculate reliability data. Statistical trend analysis will be also performed.

1. INTRODUCTION

The collection, analysis and assessment of reliability data for nuclear power equipment are essential for improving the utilization factor and safety by preventing failures of nuclear power plants, as well as for probabilistic safety assessments.Since 1977, the Central Research Institute of Electric Power Industries (CRIEPI) has been developing a nuclear power plant reliability data collection system (RDCS) in Japan under the sponsorship of the Federation of Electric Power Companies (FEPCO). As a pilot study, CRIEPI developed an RDCS for major valves from specified nuclear power plants and monitored its performance for three years in order to confirm the possibility of data collection from many plants using a standardized format.

151

152 MIYAOKA et ai.

The accident which occurred at Three Mile Island Unit 2 in March 1979 demonstrated that a more structured RDCS is required to ensure safe operation of nuclear power plants in Japan. For this reason, CRIEPI has been developing an improved RDCS to collect reliability data for components directly related to the safe and reliable operation of nuclear power plants.

The two main objectives are as follows:

(a) To obtain equipment reliability data (mean failure interval, mean repair time, etc.) from the operating track record of commercial plants, to provide the basis for reliability assessments of systems and their components; and

(b) To analyse and evaluate component failure data in order to utilize the results for

— improvement in the reliability of nuclear power plant systems— improvement in the utilization factor of nuclear power plants— improvement in system design— rationalization of inspection, test and repair intervals— analysis of secular changes of failures— prevention of similar failures.

In October 1981, the improved RDCS was completed: CRIEPI has since been operating the system under the control of the committee on Nuclear. Power Plant Reliability, consisting of general managers from the utilities and CRIEPI’s nuclear power division. Since October 1981, component failure data from nuclear power plants throughout the country have been collected and stored in a data base.

2. DATA COLLECTION

In view of the expectations for higher reliability of nuclear power generation and of the importance of understanding component failure trends, it is planned in the improved RDCS to report failure data of equipment for which engineering data have not been registered, but for which failures are expected to produce a large impact. In this way, it is intended to extend the coverage by adding failure analysis to the pilot RDCS approach with its emphasis on reliability analysis.

In the RDCS, 14 kinds of components have been selected; the names of these components, the comparison with the nuclear power reliability data system (NPRDS) classification, and the frequencies of failure in comparison with overseas data are listed in Table I.

The coverage is limited, in principle, to the components inside the contain­ment and to the components that are directly related to the operation and safety of the nuclear reactors (safety class 1, kind 2).

TABLE I. COMPARISON OF THE RDCS W ITH OTHER SYSTEMS

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RDCS NPRDS Significant number of failures reported NPRDS LER WASH 1400

Diesel generator Combustion engine • • •

Heat exchanger Heat exchanger •

Motors Motors •

Pumps Pumps • • •

Turbine Turbine •

Valves Valves • • •

Valve operator Valve operator • •

M-G set M-G set

Battery Battery • •

Blower Blower •

Circuit breaker Circuit breaker • •

CRD mechanism CRD mechanism • •

Support Support • •

Instrument Instrument

Accumulator

Air dryer

Annunciator

Control rod

Demineralizer

Filter

Fuel assembly •

Generator • • •

Heater

Mechanical trans. • •

Penetration •

Piping • • •Recombiner •

Relay • •Transformer •Vessel

154 MIYAOKA et al.

The RDCS will cover all of the light water power generating units in commercial operation in Japan. Currently, 23 nuclear power plants are being operated by the seven electric power companies.

Collecting data are divided into three categories:

(a) Component engineering data(b) Component failure data(c) Plant operating data

2.1. Component engineering data

The component engineering data are used in generating statistical populations that will provide the basis for the reliability survey and the maintenance work survey. Components registered will be sorted according to items (type, function and size), summarized and stored in a memory as populations. When a failure of a registered component is reported, its engineering data will be retrieved according to its registration number, and data on its reliability will be summarized by com­paring the failure data with the populations.

The registered engineering data will be updated whenever a design change of component is effected. I f trouble with a component has been registered before the updating of its engineering data, the older engineering data will be maintained together with the failure data.

Survey items fo r engineering data

The survey items for the respective components have been selected as shown in Table II. The classification of the particulars of each survey item may be fairly extensive, depending on the scope of the reportable components. As the reportable components are limited in number, the classification has been selected for each component with due consideration given to the actual form of the technical specification.

The designation, the system to which a component belongs and the name of the manufacturer are survey items common to all components. The difference in survey items between a PWR and a BWR is limited to the systems to which the components belong.

Engineering data input sheet

The data collecting method for these survey items involves entering code numbers for appropriate classification items printed on the data input sheet. The same method is used as for the pilot RDCS for valve reliability.

TABLE II. COMPONENTS AND ENGINEERING DATA TO BE REPORTED

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Component Engineering data items

Diesel generators Type, power, rotation speed, generator capacity, voltage of generators per diesel engine

Heat exchangers Name, system, major type, sub-type, structure, heat transfer area

Pumps Name, system, major type, sub-type, driving method, fluid, pressure head, flow rate

Motors Power, voltage

Turbine Power

Valves ID No., name, system, function, type, pipe size, pressure, temperature, valve operating method

Valve operators Type

MG Set Name, capacity, voltage, rotation speed, motor power

Batteries No. o f cell, bus voltage, type and no. of charger

Fans Name, system, type, structure, capacity, m otor capa­city, motor voltage

Breakers Name, arc suppressor, voltage rating, ampere rating

Control rod drive mechanism Type, No. of CRD mechanism

Support Load capacity, no. o f supports

Sensors Name, system, major type, sub-type, function

2.2. Failure data

The coverage of the failure data collection is not limited to components for which engineering data have been registered. Failure data on a significant failure of any component of which engineering data have not been registered are reportable.

To summarize:

(a) All failures of any component registered in the data bank are to be reported;(b) In the following cases, failures of any component which has not been

registered in the data bank are to be reported to the data centre:

(i) Failures of components directly related to the safety of the reactor;(ii) Component failures which resulted in a loss or drop of plant output.

In this context, a failure is defined as a component state where the component cannot execute its required function at the appropriate time (switching failure,

TABLE III . FA ILURE DATA ITEMS TO BE REPORTED

1 5 6 MIYAOKA et al.

No. Item No. Item

1 Registered or not registered 10 Effects

2 ID Number 11 Method o f failure detection

3 Component name in Japanese 12 Failure mode ( 1 )

Component name in English 13 Failure mode (2)

4 Component 14 Failure cause

5 System 15 Repair method

6 Event data 16 System condition

7 Date repair work started 17 Radioactivity release

8 Date repair work completed 18 Reported or no t reported

9 Parts

defective control, failure to operate at the specified set point, and so on), or where the component is not normal (occurrence of abnormal phenomenon such as leakage, excessive speed, vibration, etc., or where the component is not as safe as prescribed by the specification).

The above-mentioned component failure is not limited to the main body of the component itself. A loss of the function of a component due to failure of a special accessory indispensable to the proper functioning of the component is to be reported as a failure of the component itself. For example, when a pump fails to operate owing to a valve failure in the lubricating system, the pump failure as well as the valve failure are to be reported. When one root cause results in failures of two or more components (a broken coupling results, say, in failures of a pump and its motor), the failure is to be reported for each component. Provided that when a failure of an accessory common to several components (say a failure of a control air system) results in a loss of the functions of several components, the components themselves are not considered to have failed.

Failure data survey items

For convenience in the analysis of a component failure and its repair, it is desirable to record the failure data in as much detail as possible. However, the particulars of failure data have been selected as shown in Table I II , with due con­sideration given to the difficulty in acquiring failure data, the track record of the pilot RDCS, the actual situation of overseas RDCSs, and the survey items of other domestic RDCSs.

IAEA-SM-268/13 157

The major differences from the pilot RDCS include the addition of the following items: system to which component is belongs; condition at the time of failure; presence of leakage of radioactivity; and report to other systems. Other changes include the adoption of a descriptive approach as a result of the great number of parts, and the division of the conditions at the time of failure into dynamic and static conditions.

As for the cause and conditions of failure, their causal relationship, generally speaking, tends to be uncertain and the reportable phenomena are complicated in many cases. Accordingly, the format is designed to accept up to three classifica­tions for each. Furthermore, the causes and conditions o f a failure are not readily understandable from the classified descriptions and so larger spaces are provided for description of the cause, conditions and repair requirements for convenience in later analysis.

Failure data input sheet

As with the engineering data ledger, the data collecting method for the survey items is to enter code numbers according to the classification printed on the data input sheets. In order to assist the detailed analysis of failure and to compensate for possible uncertainties in the coded classification, descriptive columns are pro­vided for the conditions of failure, findings at the time of repair and matters con­cerning radioactivity (on the back of the input data sheet).

2.3. Plant operating data

To determine the reliability of a component, it is necessary to find its total operating hours. However, the operation of the component and the operation of the plant or reactor do not necessarily correspond with each other. Hence, the operating hours of the reactor'are to be considered as equal to the component operating hours, with the justification that all components are required to perform their respective functions properly whenever the reactor is in operation. The requisite time data (reactor criticality, parallelization and deparallelization of the generators, and full withdrawal of control rods) are to be collected.

3. PROCESS OUTPUTS

A variety of documents may be prepared from the survey data, depending on the intended application. In the improved RDCS, the process outputs were examined in the light of findings of the pilot system, and it was decided to prepare a total of eleven kinds of output document: four kinds of Table A for recording

158 MIYAOKA et al.

TABLE IV. RDCS OUTPUT LISTS

Output data name Objective Explanation

Al Component engineer­ing data (E-data)

A2 Component failure data

A3 Reactor operating data

A4 Component ID-number

To check and record the input engineering data

To check and record the input failure data

To check and record the input operating track record

To list the name of each component registered

To show the entire E-data of each component registered

To show the contents of the failure survey table and of the E-data of failed components

To show the contents of the reported operating track record

To arrange registered components in order of ID-number and show the system and component name

B1 Total number of To determine the populations Number of each registeredE-data so as to examine reliability

as well as maintainabilitycomponent’s E-data

B2 Total number of To ascertain the number of Number o f failures forreported failures failures each classification item

of E-data of registered components

B3 Component reliability To ascertain the reliability To show the componentdata of each component reliability (number of

failures per 104 hours)

B4 Component maintainabi­ To ascertain the importance To show the mean failurelity data of component failure time and mean repair time

Cl Summarized reliability data

C2 System reliability

C3 Component failure and entry number

To compare the reliability of each component

To compare the reliability of each system

To compare the failure rate o f registered components

To summarize the reli­ability data for each component from B4

To summarize the reli­ability data for each system on the basis of failure data

To summarize the number of failures for each com­ponent obtained in B2

IAEA-SM-268/13 159

F I G . l . F l o w d i a g r a m o f n u c l e a r p o w e r p l a n t r e l i a b i l i t y d a t a c o l l e c t i o n s y s t e m ( R D C S ) .

and showing the input data and seven kinds of Table В and Table С for showing the results of statistical treatments of the input data.

A list of the designations, objectives, inputs, etc. for each of these output tables is shown in Table IV.

4. THE RDCS

The computer process flow of the RDCS is shown in Fig. 1. Engineering data, failure data and plant operating data transmitted from electric power companies are transferred to the input processing program of a large computer. This program checks the data for input errors (engineering, failure and plant operating data) and accumulates only error-free data in the respective data files. The program can handle not only the addition of input data but also updating and deletion of the contents of old engineering, failure and plant operating data files.

The output processing program executes various statistical treatments on the new engineering, failure and plant operating master files prepared by the input processing program.

1 6 0 MIYAOKA et al.

A special feature of the present input and output processing programs are that they have an input control table and an output control table for easy modifi­cation of the input data format. For example, if the coverage of components is extended or the number of survey items is increased, it is sufficient to modify the input and output tables. No modification of the processing program is required.

5. RDCS OPERATING RESULTS

A summary of the reports from various power companies in Japan in the period from October 1981 to September 1982 shows that during this period, the total number of reports was about 100 (75% for BWRs and 25% for PWRs). From these failure data and from the engineering and plant operating data, the reliability of each component was determined. Although the number of failure reports is not sufficient to make a definite reliability assessment, the reliability figures obtained seem to be better than those of the NPRD system.

As for causes, natural deterioration, defective maintenance and defective manufacture are frequent and account for 59% of the total causes. On the other hand, misoperations are few and less frequent than in overseas data. As for effects, no effects cases are frequent at 54%; trip or manual shutdown account for about 19%.

Data collection conditions are also examined. The detection o f the faults occurred mainly during operation; alarms, protective system activation and periodic inspection account for 48% of the events that led to detection. Replace­ment of parts is the most frequent repair method and accounts for 64% of cases.

6 . CONCLUSIONS

On the basis of the pilot RDCS, an improved reliability collecting system was developed. This system has a size about one half that of overseas systems in operation in terms of classified kinds of equipment and the number of components. The contents of the system, however, have been carefully arranged for future expansion and the system has many features that will enable it to acquire, analyse and assess data:

(a) Reportable components include not only those directly related to the reactor operation but also those directly related to the plant operation;

(b) As for failure data, significant failures of components not registered in the populations are to be reported where necessary to make it possible to deter­mine the failure trend of whole components;

(c) The work load involved in the preparation of a large volume of engineering data has been reduced by extensive use of computer processing;

IAEA-SM-268/13 161

(d) The component classification and the particulars o f various survey items are co-ordinated with those of NPRD so that they can be easily compared with NPRD system data;

(e) The system is also arranged to acquire failure data during periodic inspections.

On the other hand, it is essential to review the system from time to time on the basis of the track record of its operation. An extension of the RDCS is now under consideration. The items to be expanded or enforced include:

- piping, joints, etc.- valves of 2 inches and under, and the major valves around the turbine; and- instrumentation and control equipment.

In addition, the need for expanding the descriptive columns to include the failure conditions as well as repair findings has been pointed out.

IAEA-SM-268/25

PR O C ESSIN G O F D A T A G E N E R A T E D AT PAKS N U C L E A R POWER PLA N T F O R C E N TR A LIZED U SE A N D O PE R A T IO N A L FEED BA C K

P. RÉSCHHungarian Company for Electric Energy Supply, Budapest

J. TALLOS YNuclear Power Plant, Paks

J. VALKÓCentral Research Institute for Physics,Budapest

L. VÔROSSInstitute for Electric Power Research,Budapest

Ildiko CZOCHNational Atomic Energy Commission,Budapest

Hungary

Abstract

PROCESSING OF DATA GENERATED AT PAKS NUCLEAR POWER PLANT FOR CENTRALIZED USE AND OPERATIONAL FEEDBACK.

Hungarian conventional power stations collect operational and technical data and report them to a central data collection system. Collection of data on off-normal events is regulated by special instructions which classify these events according to their effect on the operational state of the power station. In the Paks NPP, off-normal situations are recorded in three docu­ments: event reports, investigation records and data sheets. In the case of an off-normal situation the most important parameters are recorded by computers. A part of these records can be displayed in the control room. The display shows up to 30 events preceding the off- normal situation, the events during it, and the protective actions taken. In addition, the plant is provided with a R 55 type computer for a back-up data logging system. This system will enable post-mortem evaluation and modelling of off-normal situations. Going beyond traditional power plant practice, it seems reasonable for nuclear plants to introduce an additional system of reports covering operational status. Investigations have been initiated to establish a data bank for normal operation (status data, operational data, data on maintenance and repair work, data from check-up and periodic testing). The collection and evaluation of availability and reliability data is a prerequisite for probabilistic risk assessment. Apart from this field of utilization there

163

1 6 4 RÉSCH et al.

are two more tasks based on data evaluation which are now under investigation in Hungary: cause-consequence analysis, and noise diagnostics. The former is based on the fault-tree/event- tree method and will function at first off-line in Paks. In 1980 a joint R & D programme was started to develop a plant diagnostic system for WWER-440 units. The first results of this work at Paks Unit 1 are an automated vibration monitoring system and a diagnostic system based on neutron flux and pressure pulse signals.

DATA COLLECTION SYSTEM FOR CONVENTIONAL POWER STATIONS

According to existing regulations, power plants of the Hungarian electric power company (MVMT) have to collect and report daily operational and technical data to the Central Data Collection System (CDCS) and have to prepare monthly technical reports.

Daily data collection and reporting involves three data groups in the field of production, performance and plant status. Data on production contain the quantity of produced and supplied electric energy and heat. Data on perform ance

show the daily values entering the demand and load distribution balance calculated by MVMT. The plant status data describe the main operational events related to essential equipment and to certain auxiliary systems, whether or not the operational event (startup, shutdown, power reduction) was planned.

The processing of daily reports is carried out on a central computer. The data from the CDCS are accessible via a terminal system individually and also in the form of cumulative and averaged values. A detailed event data bank system has been initiated and plants are required to provide the full set of data according to specified formats.

The instructions on the preparation of the monthly reports prescribe how to calculate from the primary operational values those parameters to be reported (specific heat consumption, efficiency, losses, etc.). Consistent application of this procedure has been essentially achieved.

At larger units all the work on data collection is done by computers.The scheduling of the maintenance of power station systems takes place

centrally at MVMT level. Research work is under way in MVMT to create the possibilities for condition-dependent maintenance and to introduce it by adopting up-to-date diagnostic methods.

Diagnostics in power stations is also carried out within the framework of the Council for Mutual Economic Assistance (CMEA). Good results have been already achieved by applying vibration diagnostics, thermovision techniques and material testing methods. Further results have been obtained in the determination of residual machine life expectancy. A prerequisite for the introduction of condition- dependent maintenance is a system containing records on all significant changes, events and observations related to the operation and behaviour of equipment (both qualitatively and quantitatively, and in chronological order).

IAEA-SM-268/2S 165

The Maynard system is now being introduced experimentally in one Hungarian thermal power plant and a significant increase of productivity is hoped for.

The collection of data on off-normal events is regulated by a special MVMT instruction. It deals with unexpected events — so called off-normal situations (ONS) - which alter the planned operational status of systems in major power generating units. The instruction classifies off-normal situations according to the change in the operational status of the power station - limiting or breaking off the electric energy supply to the consumers.

U T IL IZA TIO N OF NPP OPERATIONAL EXPERIENCE

In Paks, off-normal events are recorded in three documents: event reports, investigation records and data sheets for ONS registration.

Should an off-normal event occur, the shift supervisor prepares the event report in accordance with Annex I. He has to take responsibility for the decision whether further investigation is necessary. I f it is, the investigation record gives further information.

The data sheet for ONS registration summarizes the previous two documents and completes them with a description of the failure (Annex II) .

In the Paks plant the most important parameters are recorded by computers in a set of records called an ONS journal. Recording is automatically initiated at present values of certain parameters and the system assures preservation of all essential data which entered the computer during a specific period before the event — as well, of course, as the input created during the event and its aftermath. The frequency of reading of analog and digital signals is geared to their rate of change, thus avoiding overload of the computer.

To achieve completeness of the ONS journal, all triggering signals from the reactor protection system are connected to the computer. The ONS journal contains the sequence of values characterizing the plant conditions and showing how the event evolved.

A part of the ONS journal can be reproduced in the control room on display. The display shows up to 30 events preceeding the ONS, the events of the ONS itself and the protective actions taken. Thus, operators can follow both the antecedents and the full history of the ONS. In most cases they can determine its cause and the possibility of further operation.

In addition to the real-time computer system, the plant is provided with a back-up data logging system with an R 55 type computer. Its data base consists mainly but not exclusively of data collected and partly processed by the unit computer. This system will enable the post-mortem evaluation of ONS and modelling of ONS phenomena.

1 6 6 RÉSCH et al.

As an extension to traditional power plant practice, it seems reasonable for nuclear plants to introduce an additional system of records covering operational conditions. Similarly, data on plant unavailability and its causes, and especially on safety-related events, are also of great importance for improving operational safety. Accordingly, investigations have been initiated to establish a data bank which should contain both ONS data and data on normal operation. These latter would be grouped as follows:

Status data

This group of data is to reflect the as-existing state of the plant (derived from drawings, specifications, QA records, pre-operational and startup test records, operational procedures, etc.) It forms the framework for assessing the technical condition of the plants.

Operational data

Operational data describe the actual status of the plant, based as far as possible on directly measured parameters. For the reactor these parameters are, for example:

— actual values of in-core temperature and neutron flux measurements— control rod positions— ion-chamber measurements— boron concentration— pressures, pressure differences— temperatures— position of each active component in the reactor-related systems— condition of the automatic systems operating and controlling the reactor, etc.

The retrieval of data can be achieved through detailed recording. However, for a general survey it is better to use a more comprehensible form with a graphical display indicating derived parameters such as heat output, distribution of power density (and its maximum value), control rod worth, output of fuel bundles and loops, burnout, etc.

The Central Research Institute for Physics (CRIP) has developed a special computer code to monitor the functioning of the reactor, taking into account the problems of reactor physics, thermohydraulics and fuel economy. The code permits the collection, processing and classification of operational data and allows retrieval of any data from the data bank, compiled according to different points of view.

Operational data help in the evaluation of the efficiency of the nuclear power plant and in the assessment of achievable economical parameters and the causes of

IAEA-SM-268/2S 167

deviations from these. They are of value for decisions on operational strategy and for finding the optimal place of the nuclear power plant in the electric energy production system.

Data on maintenance and repair work

The main purpose of collecting this data group is to develop an optimal maintenance strategy and to update the status record. It also makes it possible to:

— monitor contamination and the result of decontamination work— determine the life expectancy of major equipment and items, and to establish

optimal reserve supplies— decrease the quantity of radwaste— discover hidden failures— verify the planned maintenance schedules— establish an optimum available set of repair equipment and tools— determine the optimum maintenance staff.

Data from check-up and periodic testing

The results can be used to:

— obtain reliability data for important systems which do not function in normal operation but are activated during off-normal events (diesel units, relief valves, etc.)

— determine the condition of important equipment by monitoring characteristic parameters and comparing them with those measured for diagnostic purposes to provide reference levels

— assess residual working life expectancy for major equipment items— reveal operational reserves.

R & D POSSIBILITIES BASED ON DATA COLLECTION AND EVALUATION

Some of the aims considered in the discussion on normal operation data are best achieved by evaluation of a data bank through simple methods.

The situation is quite different with availability and reliability data. This is a new territory not yet fully elaborated but still under development all over the world.

One of the possible aims is probabilistic risk assessment. The greatest problem with the fault-tree/event tree method is that a broad data base — a reliability data bank — is required. Examination of an NPP as a whole is an enormous task going beyond the capabilities of a small country. Countries with

1 6 8 RÉSCH et al.

modest possibilities can set themselves the aim of investigating the reliability of certain systems and components with the aid of parametric studies. With suitably pruned event trees it is possible to explore the fault expectancy of selected systems.

Beyond this field of utilization there are two more tasks based on data evaluation which are now under investigation in Hungary: cause-consequence analysis and noise diagnostics.

Cause-consequence analysis by fault-tree method

Investigations have been carried out to develop this method in CRIP and in the Institute for Electric Power Research (V E IK I) since 1978.

Apart from design data, the data on ONS are the most important source for the analysis of equipment fault properties. The method takes into account the failure mode, its cause and consequences, and the possibility of recognizing it.For quantitative results the probabilities of occurrence, i.e. the frequency of repairs and the average time for repairs, are also needed as input.

The procedure is based on the fault-tree/event-tree method, and it can be realized both off-line and on-line. It will function at first off-line in the Paks NPP.

The usefulness of the planned reliability data bank is enhanced by the use of dynamic simulation to verify fault transfer models in addition to the fault trees and event trees. Therefore it will require a very large data base.

Noise diagnostics in the Paks NPP

In 1980, a joint R & D programme was started by CRIP and VE IK I to develop a plant diagnostic system for WWER-440 units. The first result of this work is an automated vibration monitoring system developed by VE IK I. It is composed of two essential parts:

— an automatically operated on-line system for early failure detection— an intermittently activated off-line system for detailed failure cause evaluation.

To provide proper information, one primary coolant loop is more widely instrumented and sensors are attached on the shaft bearings of turbine/generator units. The system contains 74 accelerometers and 9 pressure fluctuation measuring chains.

The other system installed by CRIP at the first unit of the Paks NPP consists of a number of in-core neutron flux detectors and out-of-core ionization chambers with specially designed amplifiers to measure the fluctuations in neutron flux and power.

Detailed cross-spectral analysis between the various detector signals, nuclear and non-nuclear (neutronic and pressure, neutronic and vibration, etc.) is used to

IAEA-SM-268/25 169

get a better understanding of the processes inside the reactor and the primary circuit. This should of course in turn help to evaluate anomalous situations.

During the commissioning of the Paks NPP Unit I, detailed measurements were carried out to define reference levels and to identify spectrum changes under different working conditions with both systems.

Collecting information on safety-related events is a prerequisite to utilizing operational experience. However, feedback of operational experience cannot be effective if the problem of the assessment and dissemination of information is not solved. A recent IAEA document on such a national system gives considerable help towards achieving this goal in Hungary [1 ]. Moreover, we consider the inter­national exchange of relevant experience in this field to be of great importance and are convinced that it will greatly enhance the improvement of plant safety and availability.

REFERENCE

[ 1 ] INTERNATIONAL ATOMIC ENERGY AGENCY, Guide on a National System forCollecting, Assessing and Disseminating Information on Safety-Related Events in Nuclear Power Plants, TECDOC No. 278, IAEA, Vienna (1983).

170 RÉSCH et al.

Annex I EVENT REPORT DETAILS

PLANT NAME E V E N T R E P O R T REPORT No.

Title

Unit: Shift:

Decrease of power

Start of event End of event Duration

Operational state before the event

UA Impact on working conditions UH

Full load Power reduction caused by the failure

Reduced load on command Power reduction on command

Reduced load because of failure

Shutdown in cold stand-by on command

No-load run Reactor scram

Startup from cold condition Turbine trip

Startup from half warm condition

Interruption of startup or shutdown

Startup from warm condition after incident

Normal shutdown with cooling down

Scram

Load transient at normal operation

Refuelling and annual revision System

METHOD OF DISCOVERING UE

Alarm

Instrument indication

Main steam system

High-pressure preheaters

Low-pressure preheaters

RA

RD

RH

IAEA-SM-268/25 171

Annex I (cont.)

METHOD OF DISCOVERING UE (cont.)

System(cont.)

Computer output С Feedwater system RL

Action of protective system D Main condensate system RM

Automatic testing E Turbine SA

Periodical control F Condenser SD

Functional test G Generator SP

Adjustment H Reactor protection system (instrumental)

SUZ

Inspection I Intermediate cooling system TF

Maintenance К Emergency core cooling system TH

Repair of another failure L Water supply and boron regulation

TK

Other Z Ventilation system TL

Condenser cooling system VE

No.of equipment No. of item Primary circuit YA

Steam generators YB

Reactor vessel YC

Main coolant circulation pumps YD

Volume compensation system YP

Reactor protection system (mechanical)

YS

Reactor protection system YZ

172 RESCH et al.

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IAEA-SM-268/7

E V A L U A T IO N O F E V E N T S REPO RTED TO CN EN D U R IN G ST A R T U P PH ASE O F A N G R A I

J.M. de LIMANational Nuclear Energy Commission,Rio de Janeiro, Brazil

Abstract

EVALUATION OF EVENTS REPORTED TO CNEN DURING STARTUP PHASE OF ANGRA I.

During the startup of Angra I, the first Brazilian nuclear power plant (PWR of 626 MW(e)), various operational events occurred, several of which are important to plant safety. From September 1981 until June 1982, the utility reported 49 such events in accordance with the technical specifications and norms of the regulatory body - the Brazilian National Nuclear Energy Commission (CNEN). The paper describes in detail the two events which most affected safety. The first, which occurred on 15 December 1981, was an electronic component failure in the reactor protection system, where breaker A failed to open, although breaker В tripped the reactor normally. The second event, on 17 April 1982, was a plant blackout.The failure of an auxiliary feedwater pump as the result of a short circuit in the insulating cables (muffles) brought about the transference of power from the service transformer (TI A2) to the auxiliary transformer (T1A1). In turn, this last was tripped by its protective relay. According to administrative procedures, the plant was declared to be in a local emergency condition (blackout plus fire risk potential) during a short period until the operators could handle the emergency. All reports were reviewed and analysed by the CNEN staff. Except for the modifications suggested by the utility, no requirements were imposed by CNEN.Checking of the modifications introduced in consequence of these events has been made through on-site audits and the review of the training programme. Neither of these events had any impact on either the public or the environment. However, the lessons learned will serve to improve the operational procedures and give further training to the plant operators. They will also demonstrate the necessity for a closer contact between the utility and the vendors and suppliers in order to maintain reliability of the equipment during this vital startup phase.

1. INTRODUCTION

During startup of a nuclear power plant (NPP) it is almost certain that some kinds of operational events will occur, some of which will affect safety. Although design and construction programmes are subject to rigorous quality assurance criteria, pre-operational tests are performed for verification of all equipment and systems. During this period operator errors may occur, due to inaccurate operational procedures, inability to perform tests and surveillance or to handle unforeseen events which may require previous experience.

173

174 DE LIMA

U N IV E R S A LB O A R DIN PU TS

C T 2

MT1

MT2

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F 1 G . 1 . U V o u t p u t c i r c u i t .

IAEA-SM-268/7 175

Angra I, the first Brazilian NPP, is a 626 MW(e) PWR. It experienced several operational incidents between its core loading in September 1981 and the completion of the 30% power integrated tests.

During this period, the utility (Furnas S.A.) reported to the regulatory body (the Brazilian National Nuclear Energy Commission — CNEN) 49 events according to the technical specifications [1] and CNEN regulations [2], i.e.24-hour and 30-day reportable occurrences. The most frequent were related to a reactor trip owing to steam generator level control and flow mismatch (nine events) and diesel generator inoperability for various reasons (seven events).

In the paper, we will describe the two most significant events from the point of view of the safety of the plant. The first was a solid state reactor protection system (RPS) electronic component failure in which breaker A failed to open, although there was a valid trip reactor signal. The second one was a plant blackout, due to loss of one auxiliary feedwater pump, thus causing a short circuit in the cable insulation of the safety power bus. In consequence, the station service and auxiliary transformers were tripped.

We will also discuss the status of the steam generator modification of Angra I.None of the events reported has had any adverse impact on the public or

the environment.

2. SIGNIFICANT SAFETY ISSUES

2.1. Electronic component failure of reactor protection system (UV output card)

Prior to the event the reactor was in cold shutdown. On 12 and 13 December 1981, maintenance work had been carried out on two reactor trip breakers. On December 14, surveillance tests were performed on the solid state protection system, and both breakers tripped without any problem.

2.1.1. D escription o f event (D ecem ber 1981)

On December 15, a failure occurred in the electronic component of the reactor protection system (RPS) following a reactor trip caused by starting one of the main coolant pumps. Breaker A failed to open, although breaker В opened correctly and the reactor trip was performed successfully. Investigations carried out showed that the cause of the failure was an accidental short circuit in the UV output card, where the Q3 transistor and CR9 diode were short circuited (Fig. 1 ).

Once the UV output card was replaced, investigations were carried out both upstream and downstream of this system to verify any abnormal conditions which might be causing a short circuit in the electronic component of the SPR.

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IAEA-SM-268/7 177

Site personnel made inspections, checks and voltage measurements in the following UV card interfaces: 1) reactor trip switchgear; 2) main control board; 3) solid state protection system cabinets; 4) 48 V DC power supplies 1 and 2; and 5) ground system. No abnormalities were found.

It was concluded that the failure of the Q3 transistor and CR9 diode was almost certainly caused by an accidental short circuit or by an overvoltage storage during testing and checking performed on the reactor trip breakers two days before the incident.

2.1.2. Corrective actions

After lengthy discussions with Westinghouse and the utility, it was requested that an engineer specializing in this system be sent to the site to perform a detailed checkout on the entire reactor protection system in order to determine the causes of the component failures in the UV output card.

No project failure was identified in the whole system as a result of the investigations.

After replacement of the faulty UV output card, the entire reactor protection system was retested and checked, and all functions performed correctly.

Administrative procedures were reviewed and improved with regard to inspection and tests of circuits involved in this system. Additional surveillance requirements were set up to control access of personnel to the switchgear cubicles.

Since then, no abnormalities have been observed, which means that the system demonstrates high reliability.

2.2. Plant blackout

2.2.1. D escription o f event

On Saturday, 17 April 1982, the reactor was in hot shutdown condition,12 hours after its scram, having been operated for two days at 24% power.

At 11.44 a.m. the alarm of the 64-2/T1A2 relay of the T1A2 station service transformer was actuated, indicating a short circuit to the grounding system. Inspection of the locale showed a release of smoke due to overheating in the Y isolation grounding transformer of this T1A2 transformer.

In this event, the operator decided to transfer the power supply manually to the unit auxiliary transformer T I A l and to isolate the damaged T I A2.

At 12.04 p.m., power feeding to the safety bus 1A3 was completed, and one minute later the same exchange was made to bus 1 A4, by the T I A l transformer (Fig.2).

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Immediately after the conclusion of these manoeuvres, phase В and С of the 87/T1 A l differential relay was tripped, causing all connections to open (4160 V buses) and leading to a blackout condition.

Actuation of the 87/T1 A l relay was due to insulation cable (muffle) problems in the T I A 1-4 breaker.

This was due to an overcurrent caused by actuation of the AF-1B pump when the sequencer put it in the safety bus. At that time, the T I A l auxiliary transformer was tripped and the automatic transfer to the T I A2 service trans­former did not take place, since it was isolated.

Following this sequence of events, the auxiliary feedwater pump AF-1B was tripped by its own protection system.

This entire problem therefore was caused by the faulty pump.

2.2.2. A ctio n taken during the blackout

As a result of the event, the following measures were taken:

(a) Verification of the primary system parameters (temperature, pressure, pressurizer level and stopping of the PSPs).

(b) Verification of the secondary system (temperature, pressure steam generator level and auxiliary feedwater alignment). The auxiliary feedwater pump AF-1B was disconnected but the turbine-driven pump came on normally.The AF-1A pump was blocked. Later on, this pump was unblocked manually and came on, and the turbine-driven pump was tripped.

(c) An operator was sent to the switchgear in the 4160 V cubicles to inspect the AF-1 В pump. (The overcurrent 50/51 relays in the two phases were actuated.) The presence of smoke was observed in the electrical cable insulation (muffle) of this pump, with scorching inside the cubicle.

(d) The fire risk potential of this cubicle, combined with the loss of off-site power, characterized a local emergency according to the plant procedures, and the emergency plan was activated.

(e) At 12.21 p.m. the T I A2 service transformer was put into service again, as well as the service bus (1A2). The end of the blackout was declared.

2.2.3. A ction s taken after the blackout

Following a blackout, the core is usually cooled by natural circulation, when enough residual heat generation exists. In the present case this did not occur because the plant was shutdown. The primary system temperature was stabilized throughout the event and the pressure was 156 kg/cm2.

As soon as the off-site power supply came on in the T I A2 station transformer, the non-essential 4160 V buses (1 A l and 1A2) were reconnected and a reactor coolant pump, RCP2, started.

IAEA-SM-268/7 179

This pump start-up provoked a small surge line in the pressurizer, which went up to 159 kg/cm2. However, this increasing pressure was enough to open a pressurizer relief valve (PCV-431C), discharging water into the pressurizer relief tank. In consequence, the primary system pressure dropped slightly and stabilized at 155 kg/cm2.

The secondary system pressure remained almost constant and when the condensor vacuum became available, the plant was cooled down to cold shut­down condition, using the steam dump process.

At 9.46 p.m., after the analysis and conclusion of the causes of the incident, the safeguard bus (1 A3) was reconnected to the T I A2 station transformer and the diesel generators were tripped.

At 8.00 a.m. on the next day, 20 hours later, the plant was in the cold shutdown condition.

2.2.3. Corrective actions

The fire risk potential disappeared as soon as the AF-1B pump was tripped and the T I A l-4 breaker opened. Both sets of equipment showed scorching in their cubicles, owing to damaged muffles.

All these safety bus, motor, and transformer muffles were inspected and tested. In some of them, the cable termination and muffles were deficient.These were remade and tested.

The incident caused no damage to either the reactor or the safety-related systems. All parameters behaved in the manner foreseen in the design. The opening of the pressure relief valve (PCV-431C) was due to its proportional/ integral response. It functioned in accordance with the specifications of the Final Safety Analysis Report (FSAR) [1].

Once the muffle and cable termination were rebuilt and tested, the utility followed up with the integrated power test.

2.3. Steam generator modifications

The viewpoint of the regulatory body (CNEN) concerning the complex safety issues applicable to the Westinghouse D-3 steam generator tube vibration, is under discussion with the utility. At the present time, all integrated tests have been performed with main feedwater through the auxiliary feedwater line in the upper nozzle o f the steam generator. We have had the opportunity to exchange information with Swedish, Spanish and U.S. regulatory bodies, where this problem was pointed out.

Recently, the CNEN received the documents describing the SG modifications, which are scheduled to be started in May 1983. These documents are under review and analysis by CNEN.

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In September 1982, the diesel generators were considered inoperable because of the plastic deformation of the piston sleeves. Manufacturer’s representatives were called to analyse and correct the problem.

After replacement of the damaged jackets, pistons and stems, an extensive test programme was initiated. These engines were put into operation for 30 hours, and then disassembled, but the problem continued.

The manufacturer decided to initiate a comprehensive programme of parameter measurements, such as vibration frequency, combustion chamber pressure variation, analysis and specification of lube oil, injection nozzle pressure calibration, etc.

At the conclusion of the investigations it was decided to upgrade the quality of the lube oil. A new period of tests was initiated, after which the diesel generators were considered operable. The tests ended in February 1983.

Other administrative procedures taken were: the precaution of hand turning the engine crank before each starting of the motor for test and surveillance, and running the pre-lube pump before each scheduled starting.

2.4. Diesel generator inoperability

3. CNEN EVALUATION OF OPERATIONAL EVENTS

The Commission has two on-site resident inspectors. They remain on call at all times. These two representatives of the regulatory body have followed all incidents occurring at the power plant. They are the primary contacts with headquarters on these occasions. When the two events described here occurred, they were able to follow, at close quarters, all inspections, checks and tests during the incidents, and furnish all the information they had noted and the conclusions taken from direct discussions with the plant superintendent.

The headquarters staff reviewed and analysed these two incidents, as well as the corrective measures taken. The Commission accepted the utility’s proposed measures, especially those referring to modifications of operational procedures.

No new requirements were imposed by the regulatory body. The checking of these modifications has been made through audits of the training and retraining of plant personnel — licensed and non-licensed. The lessons learned from these events have since then been made part of the operator examination for licensed personnel.

Finally, the experience acquired in the analysis of these safety-related events might be considered a step toward establishing a system of storage and dissemina­tion of information on similar events.

IAEA-SM-268/7 181

The two incidents described provoked no adverse effects on either the public or the environment. However, their consequences for the operation of the plant lead to the following conclusions:

(a) The necessity for perfecting maintenance, testing and operational procedures each time a problem occurs must be borne in mind.

(b) The operational QA programme should be updated to identify changes necessary for improving performance.

(c) An active training and retraining programme must be enforced for the plant staff (licensed and non-licensed personnel) incorporating modifications of operating procedures and other lessons learned.

(d) Strict co-operation should be maintained with vendors and suppliers so as to acquire the manufacturers’ know-how and have reliable equipment.

The electronic component failure of the SPR on train A did not impair the adequate tripping of the reactor by train B. However, reliability in this system is vital for safe operation of the power plant. Recently [3, 4] another event of this nature occurred in Salem-1 (USA), when the automatic scram system was triggered but neither of the breakers opened, and the operators had to scram the plant manually. The failure was caused by improper maintenance of the relays, which stuck because they had not been properly lubricated.

The blackout incident caused by an internal short circuit in the plant was well handled by the operators and caused no adverse consequences for the safe operation of the plant. As pointed out previously, this incident has the indication of an important precursory event, the analysis of which deserves attention in view of the possibility of some other potential breakdown.

4. CONCLUSION

REFERENCES

[1] FURNAS CENTRAIS ELÉTRICAS S.A., Final Safety Analysis Report (FSAR) of Angra 1, Rev. 10, Rio de Janeiro (1978).

[2] BRAZILIAN NATIONAL NUCLEAR ENERGY COMMISSION (CNEN), Relatório de Operaçâo de Usinas Nucleares, Norma CNEN-NE.1.14, CNEN, Rio de Janeiro (January 1983).

[3] INSIDE NRC, Vol.5, No.5, McGraw Hill (March 7, 1983).[4] UNITED STATES NUCLEAR REGULATORY COMMISSION, NRC IE Bulletin

No.83-01, USNRC, Washington, D.C. (March 1983).

IAEA-SM-268/74

ОПЫТ БЕЗОПАСНОЙ ЭКСПЛУАТАЦИИ АЭС С БЫСТРЫМИ РЕАКТОРАМИ В СССР

Ю.Е. БАГДАСАРОВ, И.А. КУЗНЕЦОВ,В.Н. ИВАНЕНКО, И.А. ЕФИМОВ

Физико-энергетический институт,Обнинск, Калужская область,Союз Советских Социалистических Республик

Abstract- Аннотация

USSR EXPERIENCE OF THE SAFE OPERATION OF NUCLEAR POWER PLANTS WITH FAST REACTORS.

Experience of the operation of nuclear power plants with fast reactors in the USSR is based on the results of work with BN-350 and BN-600 reactors. This experience affords, evidence of extremely satisfactory safety characteristics from the point of view both of reliable heat removal from the reactor cores and of the hazard to plant personnel, the environment and the population at large from exposure to radiation. The paper gives information concerning the power regime at which the facility is operated and about the most characteristic and dangerous situations which have occurred during operation. A comparison is made between a list of the most dangerous initiating events which are analysed in connection with the design of nuclear power stations with fast reactors (in accordance with USSR standards documents now in force) and the events which were observed in the process of operation. Reference is made to the important role of the more probable initiating events in the overall problem of ensuring the safety of nuclear power plants, especially when this is related to action by the staff which is not provided for in instructions and to possible errors on the part of personnel.

ОПЫТ БЕЗОПАСНОЙ ЭКСПЛУАТАЦИИ АЭС С БЫСТРЫМИ РЕАКТОРАМИ В СССР.Опыт эксплуатации АЭС с быстрыми реакторами в СССР основан на результатах работы

реакторов БН-350 и БН-600. Этот опыт свидетельствует о весьма удовлетворительных характе­ристиках безопасности как с точки зрения обеспечения надежного теплоотвода от активной зоны реакторов, так и с точки зрения опасности радиационного воздействия на персонал станций, окру­жающую среду и население. В докладе приведены данные по мощностному режиму эксплуатации установок и наиболее характерным или опасным ситуациям, которые имели место за время экс­плуатации. Проводится сравнение между перечнем наиболее опасных исходных событий, которые анализируются при разработке АЭС с быстрыми реакторами (в соответствии с действующими в СССР нормативными документами) и событиями, которые наблюдались в процессе эксплуатации. Отмечается важная роль более вероятных исходных событий в общей проблеме обеспечения безо­пасности АЭС, в особенности, когда это связано с непредусмотренными в инструкциях действиями персонала и его возможными ошибками.

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1 8 4 БАГДАСАРОВ и др.

В настоящее время в СССР успешно эксплуатируются 4 быстрых реактора:

БР-5(10) БОР-60 БН-350 БН-600

введен в 1958 г. введен в 1968 г. введен в 1973 г. введен в 1980 г.

Несмотря на то, что первые 2 реактора имеют небольшую мощность и являются экспериментальными, опыт эксплуатации их систем и оборудования с радиоактивным натрием является чрезвычайно важным с точки зрения оценки безопасности будущих АЭС с быстрыми натриевыми реакторами. Это тем более важно, что они работали при существенно более ’’грязных” условиях по примесям в теплоносителе (в том чис­ле продуктов деления горючего, продуктов коррозии конструкционных материа­лов и д р .) .

Общая наработка реакторов на быстрых нейтронах в СССР составила таким об­разом более 50 реакторолет. В настоящее время разработан проект реактора БН-800, разрабатывается проект АЭС с реактором Б Н -1600.

1. БЕЗОПАСНОСТЬ АЭС В СВЯЗИ С ОСОБЕННОСТЯМИ БЫСТРЫХ НАТРИЕВЫХ РЕАКТОРОВ

Как известно, подавляющая часть АЭС эксплуатируется и сооружается с реакто­рами на тепловых нейтронах с водяным теплоносителем. Поэтому, естественно, необ­ходимо, по возможности, более четко очертить то новое, что вносят быстрые натрие­вые реакторы в вопросы безопасной эксплуатации АЭС по сравнению с водяными реакторами на тепловых нейтронах.

Если сгруппировать и очень коротко охарактеризовать эти особенности, то они сводятся к следующему:

— отличающиеся от реакторов на тепловых нейтронах динамические характерис­тики активной зоны быстрого реактора и 1 контура реактора в целом;

— химическая активность натрия по отношению к кислороду воздуха и воде.Отсутствие замедлителя, примерно в 10 раз большие тепловые нагрузки в еди­

нице объема активной зоны по сравнению с водо-водяными реакторами приводят к более жестким требованиям с точки зрения допустимых перерывов энергоснабжения насосов (постоянная времени топливных элементов активной зоны — 1,5- 2 с ).

В то же время энергетические реакторы на быстрых нейтронах лишены такого малоприятного явления, как отравление продуктами деления; они имеют отрицатель­ный температурный и мощностной эффекты реактивности во всем диапазоне измене­ния мощности при ведущей роли эффекта Допплера; в быстром реакторе отсутствуют пространственные неустойчивости распределения нейтронных потоков во всех стацио­нарных и предполагаемых переходных режимах с перемещением различных стержней управления реактивностью [ 1 ].

IAE A-SM -268/74 185

Свойства натрия позволяют осуществить охлаждение активной зоны при относи­тельно высокой температуре до 550°С на выходе из активной зоны и при очень низком рабочем давлении. При этом необходимо отметить, что для надежного отвода тепла от активной зоны требуются умеренные скорости теплоносителя через реактор и дос­таточно малые мощности на его прокачку по контуру. Опыт подтвердил, что исклю­чительно высокий коэффициент теплоотдачи, эффективный и высокий расход естест­венной циркуляции позволяют обеспечить безопасность реактора при наиболее небла­гоприятных аварийных ситуациях, связанных с полной потерей электропитания насо­сов. Особо следует отметить большой запас внутренней теплоемкости натриевых контуров. При аварийных ситуациях, связанных с прекращением отвода тепла в окру­жающую среду, вынос остаточного тепловыделения из активной зоны и его аккумуля­ция в натрии и стальных элементах оборудования I контура приводит, как показали эксперименты, к росту температуры со скоростью примерно 1(Н40°С/ч, в зависимости от исходного состояния установки.

Отметим при этом, что запас до температуры кипения в самых опасных точках активной зоны составляет свыше 400°С.

Таким образом, комплекс динамических характеристик активной зоны и I кон­тура быстрого натриевого реактора в целом способствуют достижению большей безо­пасности АЭС по сравнению с водо-водяными реакторами на тепловых нейтронах.

Второй комплекс особенностей, наоборот, приводит к более сложному решению вопросов безопасности АЭС.

В процессе эксплуатации быстрого реактора с натриевым теплоносителем сущест­вует возможность аварийного вылива натрия в технологические боксы.

При натриевом пожаре подвергаются тепловым воздействиям строительные и технологические конструкции. Это, в принципе, может привести к их повреждению. Однако более реальную опасность представляют аэрозольные продукты горения натрия.

При попадании аэрозольных продуктов горения натрия на слизистую оболочку глаз, носоглотки и в легкие происходит разрушение слизистой оболочки и тканей. Допустимая массовая концентрация натриевых аэрозолей в воздухе обслуживаемых помещений в Советском Союзе принята равной 0,5 мг/м 3 [2 ].

В случае горения радиоактивного натрия опасность натриевого дыма возрастает. Допустимая концентрация для персонала радионуклида натрий-24 в воздухе рабочих помещений равна 1,4- Ю~10Ки/л [3]. Этому значению соответствует массовая концент­рация приблизительно 0,007 мг/м 3 (если в момент перехода в аэрозоль теплоноситель имел удельную радиоактивность по натрию-24, равную 20 К и /кг).

Заметим, что допустимая концентрация для населения радионуклида натрий-24 в атмосферном воздухе в Советском Союзе принята равной 4 ,9-10~ 12 Ки/л [3 ,4 , 5].

Учитывая эти данные, были проанализированы аварии в технологических поме­щениях с различными характеристиками. В результате было выработано некоторое общее требование к герметичности боксов натриевых систем: утечка из них не должна превышать 1% объема в час при избыточном давлении 100 Па.

Эксперименты показали принципиальную возможность допущения горения боль­ших количеств натрия (до 1000 кг) при начальной температуре до 550°С в помещениях,

186 БАГДАСАРОВ и др.

заполненных воздухом. Было доказано, что при герметичности помещения, характе­ризующейся натеканием количества воздуха, равного одному объему помещения в час при разрежении в помещении 50 мм вод.ст., наступает самогашение натрия вслед­ствие выгорания кислорода. Длительность горения составляла 10-12 мин. Температу­ра газа в боксе не превышала 300°С. Температура бетона пола бокса на глубине 20 и 50 мм через 1ч после начала эксперимента была равна 450 и 230°С, соответственно.На глубине 100 мм температура бетона в ходе экспериментов не превышала 100°С. Максимальная массовая концентрация аэрозолей в боксе была равна ~20-^25 г/м 3.

После проведения серии таких экспериментов повреждения помещения оказа­лись незначительными.

При разработке и эксплуатации быстрых реакторов (в том числе БН-350 и БН-600) локализация утечек натрия производится путем облицовки помещений (где могут в принципе возникнуть большие проливы) листовой углеродистой сталью, уста­новки специальных поддонов с гидрозатворами и специальных трапов в дренажные баки большой емкости. Основными способами тушения возникшего натриевого по­жара являются самотушение (за счет выгорания кислорода в помещении) , тушение газовыми смесями на основе азота, порошковое тушение. Широко внедряются порош­ки типа МГС и брикеты на той же химической основе с эффективностью 3 кг на квад­ратный метр площади горения.

Особо необходимо остановиться на вопросе о нарушениях герметичности тепло­передающей поверхности парогенератора и последствиях контакта натрия и воды. Многочисленные специальные экспериментальные исследования этой проблемы и име­ющийся опыт эксплуатации установок показал, что даже при имеющихся еще недоста­точно совершенных приборах индикации протечек воды в натрий и системах защиты парогенераторов не возникает непосредственной угрозы с точки зрения радиационной или ядерной безопасности АЭС.

2. ОПЫТ ЭКСПЛУАТАЦИИ РЕАКТОРА БН-350

Как известно, реактор БН-350 имеет специальное предназначение. Он эксплуати­руется около 10 лет на полуострове Мангышлак Каспийского моря в режиме выдачи электроэнергии и тепла для дистилляции морской воды:

— тепловая мощность реактора 700 Мвт,— электрическая мощность 125 Мвт,— количество производимого дистиллята 85 000 т/сут.

Все последние годы реактор работал устойчиво с коэффициентом использования установленной мощности около 0,88. Имелось незначительное количество внеплано­вых остановок основного оборудования [ 6 ] (см. табл. I).

Причинами отключений и остановок являются, в основном, ошибки персонала и отказы приборов контроля. За весь период эксплуатации не было ни одного случая отказа оборудования I контура.

IAEA-SM -268/74 187

ТАБЛИЦА I.

Год 1978 1979 1980 1981 1982

Количество неплановых отключений оборудования 4 2 1 - -

1 0 -летний опыт эксплуатации систем, оборудования и механизмов показал их высокие надежностные характеристики. В первые годы эксплуатации вследствие технологических дефектов изготовления имели место несколько случаев выхода из строя испарительных модулей парогенератора с трубками Фильда. Но после проведен­ного ремонта с заменой рабочих труб выходы из строя испарителей прекратились. Сле­дует заметить, что один из первоначально установленных модулей испарителя без каких-либо замечаний проработал около 60 ООО ч на рабочих режимах с тепловыми потоками около 1 • 1 0 6 ккал/м 2 ч; его вырезка из контура и проверка показали весьма хорошее состояние.

Корпус реактора, вращающиеся пробки, механизмы перегрузки, элеваторы и другие внутрикорпусные устройства — каждое из них без каких-либо замечаний отра­ботали весь период от пуска реактора до настоящего времени.

Ресурс основных насосов I и II контуров, задвижек I контура диаметром 500 мм и 600 мм, основных теплообменников, трубопроводов, пароперегревателей, фильтр- ловушек и др. совпадает с ресурсом работы установки (т.е. ~ 1 0 лет) .

Все это оборудование продолжает эксплуатироваться и пока не видно причин, по которым их ресурс пришлось бы ограничивать.

Радиационная обстановка на БН-350 и выбросы в окружающую среду в течение всего периода эксплуатации были весьма низкими даже при работе реактора с пример­но 100 негерметичными твэлами. Мощность дозы гамма-излучения в обслуживаемых помещениях практически близка к естественному фону (~10 мкР/ч), в полуобслужи- ваемых — меньше 0,8 мкР/с. Радиоактивные выбросы в атомосферу полностью опре­деляются аргоном-41 (из системы воздушного охлаждения биологической защиты).

Наведенная равновесная активность натрия составляет около 10 Ки/кг по нат­рию-24.

После остановки реактора остаточная активность теплоносителя определяется долгоживущим натрием-22 (~0,75 К и /кг), продуктами деления из дефектных твэлов (цезий-137, цезий-134), а также продуктами коррозии конструкционных материалов.

Дренирование натрия существенно улучшает радиационную обстановку для производства работ по замене выемных частей оборудования. За время эксплуатации установки получен большой опыт подобных работ: замена выемных частей насосов, обратных клапанов I контура, установка в реактор устройств для измерения расходов через тепловыделяющиеся сборки (ТВС) и т.д. С целью создания необходимой степени

188 БАГДАСАРОВ и др.

ТАБЛИЦА II.

№ № Дата Место течи Потери натрияПричина кг Тушение

1. Октябрь Отверстие под Неправильные1973 г. уровнемер в

петле II контура при ремонте

действия 20ремонтногоперсонала

Местное,глиноземом

2. Декабрь1974 г.

Усиковый шов вентиля на вспомогательной системе

Неправильныйразогрев 10 участка

Местное,глиноземом

3. Февраль Образование Скопление продуктов Слив в металлические1975 г. отверстия в реакции, возникших

из-за аварии в парогенераторе

ящики с глиноземом струбе II контура плотнозакрывающимися

крышками

герметизации в процессе разуплотнения натриевого контура использовались мягкие и жесткие герметизирующие скафандры.

Активность защитного газа I контура определяется главным образом количест­вом негерметичных твэлов. В наиболее неблагоприятные периоды работы установки активность газовой подушки достигала 0,1 КИ/л.

За прошедшее 10-летие было несколько утечек натрия из нерадиоактивных кон­туров. Наиболее значительные из них характеризуются данными, приведенными в табл.II.

Имел место также ряд более мелких утечек нерадиоактивного натрия, которые не приводили к возникновению пожаров.

Хорошая, надежная работа оборудования, в частности задвижек I контура диамет­ром 500 мм и 600 мм, освоение натриевой технологии, низкие рабочие давления в I контуре позволили эксплуатационному персоналу БН-350 осуществить смелый экспе­римент. В 1978 г. при работе реактора на полной мощности было осуществлено пере­крытие одной из петель I контура задвижками на всасе и напоре и заменена выемная часть насоса.

За время эксплуатации установки выбросы радиоактивности в окружающую среду держались постоянно на уровне, примерно в 100 раз ниже допустимых. Суммар­ная доза, получаемая персоналом при проведении работ на реакторе, не превышает 2 ,0 бэр/год.

IAEA-SM-268/74 189

ТАБЛИЦА III. ОСНОВНЫЕ ПОКАЗАТЕЛИ РЕАКТОРА БН-600

Тепловая мощность 1470 МвтЭлектрическая мощностьРасход энергии на собственные нуждыКПД, бруттоТемпература острого пара Давление острого пара Давление пара промперегрева

490° С 120 кгс/см2 25 кгс/см2

40,5%

600 Мвт

6,4%

3. ОПЫТ ЭКСПЛУАТАЦИИ РЕАКТОРА БН-600

Реактор БН-600 был введен в эксплуатацию на Белоярской АЭС 8 апреля 1980 г ., когда он дал 30% мощности от номинальной. На этой мощности блок проработал до июня 1980 г. с кратковременными остановками для испытаний и экспериментов, инспек­ции оборудования, измерения напряженного состояния в узлах и элементах, измерения расходов через тепловыделяющие сборники и др.

В июне 1980 г. мощность была поднята до 50% от номинала, а в сентябре — до 80% от номинальной при средней температуре натрия на выходе из реактора — 520°С, средней температуре на выходе из ТВС — 550°С и максимальной температуре на выходе из наибо­лее напряженных ТВС — 570°С.

В течение 1981 г. продолжалось освоение установки, проведение экспериментов и испытаний. 2 октября мощность была повышена до 90%, а 18 декабря впервые полу­чена проектная мощность 600 Мвт (эл .) . В 1981 г. было проведено 4 перегрузки ядер- ного горючего, к одной из перегрузок был приурочен плановый капитальный ремонт одного из турбогенераторов. Основные показатели реактора БН-600 приведены в табл. III.

Как и на установке БН-350 при эксплуатации БН-600 наибольшие трудности вызвали парогенераторы. За время эксплуатации (до 1981 г.) возникло 4 отказа нер­жавеющих модулей пароперегревателей и промпароперегревателей. Однако, последст­вия этих отказов с точки зрения влияния на мощностной режим установки были в корне отличны от наблюдавшихся на БН-350. Дело в том, что парогенератор каждой петли БН-600 состоит из 8 параллельных секций, каждая из которых включает модуль испарителя, перегревателя и промперегревателя. После того как фиксировались утеч­ка воды в натрий в данной секции, последняя отсекалась от остального контура зад­вижками по натрию и воде-пару. Дальнейшие операции с дефектной секцией произ­водились независимо от действий на установке. Благодаря наличию запасов в поверх­ностях теплоотдачи парогенератора, отключение одной из 8 секций практически не приводило к необходимости изменения мощности установки; производилась лишь

1 9 0 БАГДАСАРОВ и др.

5 7 0 -

3 М Е С Я Ц Ы , ГО Д Ы

Р и с . 1 . Г р а ф и к р а б о т ы у с т а н о в к и Б Н - 6 0 0 .

небольшая регулировка числа оборотов насосов по петлям. Отметим, что из 72 моду­лей (48 из них имеют нержавеющие теплопередающие трубки, а 24 — из стали ОХ2М) разуплотнение наблюдалось только в 4-х. В целом парогенераторы работали хорошо.

Они устойчиво эксплуатировались при тепловых потоках в испарителях 0,9 Мвт/м2, пароперегревателях — 0,2 Мвт/м2, промпароперегревателях - 0,13 Мвт/м2.

Все механическое оборудование реактора и натриевых контуров показало весьма удовлетворительную работоспособность. На сегодняшний день отработанный ресурс оборудования можно охарактеризовать следующими цифрами:

— реактор, внутриреакторные механизмы и элементы — 2 1 0 0 0 ч,— парогенераторы — 16 0 0 0 ч,— турбогенераторы — 16 0 0 0 ч,— натриевые насосы — 2 1 0 0 0 ч.В 1982 г. и начале 1983 г. реактор БН-600 работал весьма успешно. График рабо­

ты в течение последних двух кампаний представлен на рис. 1. За исключением несколь­ких кратковременных изменений мощности (главным образом, определяемых отклю­чением одной петли), реактор эксплуатировался на постоянном уровне мощности 570 Мвт (эл .) .

В течение всего периода после энергопуска радиационная обстановка на установке характеризовалась очень низким уровнем дозовых нагрузок на эксплуатационный пер­сонал и окружающую среду, в 1 0 - 1 0 0 раз ниже уровней, допустимых для нормальных режимов эксплуатации АЭС по НРБ-76 и СП АЭС-79 [3, 4].

ТАБЛИЦА IV. ОБЩАЯ ХАРАКТЕРИСТИКА РАБОТЫ РЕАКТОРА В 1959-1979 гг.

IAEA-SM -268/74 191

Период(годы)

Топливо Максимальнаямощность

К В Т

Температуранатрия

вход в выход из реактор реактора

Максимальное выгорание топлива % т.а.

Среднийкоэффициентнагрузки

1959-1964 PuOj 5000 430 500 6,7 0,311965-1971 UC 5000 430 500 6 , 1 0,551973-1979 Ри02 7500 350 470 14,1 0,65

4. ОПЫТ ДЕМОНТАЖА И ЗАМЕНЫ ЗАГРЯЗНЕННОГО ОБОРУДОВАНИЯ И ТРУБОПРОВОДОВ I КОНТУРА УСТАНОВКИ БР-10

К важнейшему комплексу проблем безопасности АЭС относится комплекс, включающий:

— последствия работы с негерметичными твэлами;— выход из активной зоны, распространение по контуру, увод из него осколков

деления и радиоактивных продуктов коррозии конструкционных материалов ;— возможности проведения операций по замене оборудования на загрязненном

контуре;— проблемы демонтажных работ после длительной эксплуатации I контура

АЭС и др.Несмотря на относительно малый масштаб установки Б Р -10, ее опыт является

уникальным для оценки указанных проблем. Данные, характеризующие работу реак­тора Б Н -10 в 1959-1979 гг., приведены в табл.IV.

К сентябрю 1979 г. флюенс нейтронов на корпусе реактора достиг значения 8 ,4 -1022 нейтр /см2. Было принято решение о демонтаже и замене корпуса реактора для обеспечения дальнейших исследований.

4.1. Радиоактивное загрязнение I контура продуктами деления и коррозии

В связи с тем, что большую часть времени реактор работал с дефектными твэлами, I контур имел радиоактивное загрязнение продуктами деления. При работе холодной ловушки более 90% активности йода, цезия и трития переходят в нее. Распределение цезия мевду стенками контура и теплоносителем зависит от температуры натрия: при 150-200°С 80-90% цезия находится на стенках контура, а при температуре 350°С толь­ко 20-25% цезия остается на стенках. Значительная часть цезия находится на поверхнос­ти раздела натрий-газ и высаживается на холодных поверхностях в газовых объемах

192 БАГДАСАРОВ и др.

контура. Активность цезия по отношению к активности нуклида 22 Na в натрии, скон­денсировавшемся из паров натрия (например, в ловушках паров) в сотни раз выше, чем в циркулирующем натрии. Обнаружено концентрирование цезия в тупиковых участ­ках контура и увеличение активности на трубопроводах I контура при остановленной циркуляции.

4.2. Очистка I контура от радиоактивных продуктов деления

Радиационную обстановку I контура определяли радионуклиды цезия-137, цезия -134 вместе с продуктами коррозии, а в газовых полостях — радионуклиды ксенона и криптона.

Очистка 1 контура с помощью холодных ловушек окислов (ХЛО) проводилась при полном расходе натрия по I контуру, объем которого составляет 1,7 м3. Объем натрия в ХЛО — 0,2 м3, расход через нее — 0,8 м3/ч. В первых экспериментах по очист­ке ХЛО накапливала 130-200 Ки цезия -137, оставляя в I контуре 2,5-8 Ки цезия-137.При этом за 10 ч концентрация цезия-137 снижалась в 8 раз. Равновесная концентра­ция цезия -137 в контуре зависела от температуры внутри ХЛО. Подтверждением эффек­тивной работы ХЛО являлся высокий уровень мощности дозы гамма-излучения (6000 мкР/с) на ее поверхности после распада натрия-24 и относительно низкий (200 мкР/'с) — на поверхностях I контура. Гамма-сканирование по высоте ХЛО через два месяца после ее демонтажа из контура показало, что активность ее определялась цезием-137 и натрием-22 и сосредоточена в основном в отстойнике. В дальнейшем ресурс работы ХЛО определялся не емкостью по окислам, а допускаемой мощностью дозы гамма-излучения на ее поверхности.

Объем газовых полостей I контура в сумме составляет 0,5 м 3 и состоит их газовых полостей 2-х насосов по 220 л и газовой полости в реакторе, объемом 50 л. Очистка газа осуществлялась системой очистки газа (СОГ), которая представляла собой замкну­тый циркуляционный контур с угольным адсорбентом. СОГ поочередно подключалась к газовым полостям баков насосов.

Очистка газа проводилась на заглушенном реакторе при отключенном и макси­мальном расходе натрия, а также при максимальном расходе натрия на мощности реак­тора 5000 кВт. Было установлено, что имеется существенная разница в очистке аргона от ксенона в зависимости от режима циркуляции натрия. Для режима с остановленной циркуляцией натрия достигнутый коэффициент очистки газа (отношение начальной концентрации ксенона в аргоне к конечной) за сравнительно короткое время, измеряе­мое часами, при кратности обмена газа 1,5-2 ч ' 1 составлял 100-200, а на работающем реакторе с максимальным расходом натрия — лишь 20-100. СОГ была сооружена и эксплуатировалась в исследовательских целях. Для нужд эксплуатации газовой систе­мы I контура Б Р -10 достаточно было адсорбера с активированным углем, установлен­ного на линии сброса аргона в спецвентиляцию.

Особый интерес представляет улавливание трития холодной ловушкой окислов. Очевидная связь активности трития в натрии с режимом работы холодной ловушки и эффективность такой очистки хорошо видны на рис. 2 .

IAEA-SM -268/74 193

ЭНЕРГОВЫРАБОТКА, м ли.кВ т.ч

Р и с . 2 . А к т и в н о с т ь т р и т и я в н а т р и и I к о н т у р а р е а к т о р а Б Р - 1 0 .

4.3. Дезактивация I контура

За 20 лет работы реактора в связи с необходимостью снижения мощности дозы гамма-излучения и удаления остатков натрия для проведения ремонтных работ на кон­туре трижды проводилась пароводяная промывка I контура. В 1961 г. и в 1971 г. после паро-водяной промывки проводилась кислотная дезактивация. В 1980 г. паро­водяной промывке предшествовала вакуумная отгонка натрия из I контура. При паро-водяной промывке пар и азот подавались в верхнюю часть контура через газовые линии и удалялись через дренажные трубопроводы в конденсатор и далее в монжюсы. Промывка велась последовательно по всем ветвям контура. Контроль за ходом про­мывки осуществлялся по концентрации водорода и температуре контура. Объемная концентрация водорода в процессе отмывки не превышала 3% и лишь в отдельные моменты достигала 8-10%. В сливном монжюсе поддерживалась инертная атмосфера. Реакция взаимодействия натрия с паром проходила спокойно, без хлопков и ударов и без значительного разогрева контура. Далее промывка контура осуществлялась, последовательно, водой, 5% раствором азотной кислоты (HNO3) , 1% раствором щаве­левой кислоты (Н2 С20 4) и раствором марганцевокислого калия (КМн04) с последую­щей промывкой водой. Сушка контура осуществлялась разогревом до 250°С и вакуу- мированием до прекращения заметного выделения влаги в холодной ловушке.

Изменение мощности дозы гамма-излучения в мкР/с на трубопроводах и обору­довании I контура при дезактивации представлено в табл. V.

Паровая и водяная промывки снимали основную активность продуктов деления. Кислотная дезактивация снимала альфа-активность, обусловленную загрязнением кон­тура делящимися веществами, а также активность продуктов коррозии (54Мп, 60С о ,58Со).

194 БАГДАСАРОВ и др.

ТАБЛИЦА V.

Этап дезактивации 1961 г. 1971 г. 1980 г.

Контур заполнен натрием 4000-14 000 250-3000 70-380(500*)Натрий сдренирован 4000-15 000 80-3000 20-300 (500*)После вакуумной отгонки натрия не проводилась не проводилась 20-200(7000*)

После паровой и водяной промывок 200-2000 30-600 8-40

После кислотной промывки 10-20 12-60 не проводилась

* - на уровнемерах натрия и фланцах насосов.

В процессе демонтажа и замены корпуса реактора из 20 участков основных трубо­проводов I контура были вырезаны и обследованы образцы. Исследования показали, что толщина науглероженного слоя со стороны натрия находится в пределах 100-200 микрон и обладает большей на 50% твердостью, чем основной металл трубы. В целом же прочностные характеристики стали и ее пластичность оказались близкими к исход­ным значениям.

5. ОБЕСПЕЧЕНИЕ БЕЗОПАСНОСТИ АЭС С БЫСТРЫМИ НАТРИЕВЫМИ РЕАКТОРАМИ

Несмотря на существенно меньшую по сравнению с реакторами на тепловых нейтронах долю быстрых реакторов, вся деятельность, связанная с переработкой дей­ствующих или разработкой новых нормативных документов по АЭС направлена в русло учета и отражения в этих документах особенностей натриевых быстрых реакто­ров. Поэтому как правило подход к обеспечению безопасности АЭС с быстрыми реак­торами принципиально аналогичен подходу к обеспечнию безопасности АЭС с реакторами на тепловых нейтронах и основывается на одних и тех же общесоюзных документах.

Основным принципом, положенным в основу обеспечения безопасности дейст­вующих и будущих АЭС в СССР, является обеспечение защиты персонала и населения от внешнего и внутреннего облучения, а окружающей среды — от загрязнения радио­активными веществами в пределах, допускаемых ’’Нормами радиационной безопаснос­ти” [3] при длительной нормальной эксплуатации и в аварийных ситуациях, вызван­ных экстремальными природными явлениями и деятельностью человека.

Проектом АЭС должны быть предусмотрены технические меры и средства, на­правленные на обеспечение безопасности при любом единичном возможном нарушении

IAEA-SM - 268/74 195

нормальной эксплуатации устройств (систем) (являющемся исходным событием аварии), которое может совпасть с необнаруженным длительным нарушением эксплуатации друго­го неконтролируемого при эксплуатации АЭС устройства; одновременно с выходом из строя устройств (систем) нормальной эксплуатации рассматривается выход из строя одного из независимых активных или пассивных элементов устройств (систем) безо­пасности, имеющих механические движущиеся части [7].

Безопасность АЭС с реакторами на быстрых нейтронах, как и АЭС с другими типа­ми реакторов, обеспечивается за счет следующих мероприятий:

— выбора благоприятных природных условий расположения АЭС и выбора необ­ходимых размеров санитарно-защитной зоны [4] ;

— обеспечения АЭС защитными и локализующими системами;— размещения оборудования I контура в герметичных помещениях;— качественного выполнения устройств нормальной эксплуатации;— контроля качества при изготовлении, ремонте и передаче оборудования в

эксплуатацию;— правильной эксплуатации АЭС;— обеспечения наблюдения и периодического контроля состояния оборудования

в ходе эксплуатации;— обеспечения профилактических противоаварийных мер по всем системам.В качестве максимальных проектных аварий для быстрого натриевого реактора

в [7] предписывается рассматривать:— аварийное разуплотнение трубопровода I контура, не имеющего страховочного

кожуха;— аварийное сужение или перекрытие проходного сечения в отдельной ТВС за

счет распухания, попадания примесей теплоносителя или посторонних предметов, при­водящее к понижению расхода теплоносителя через эту ТВС и к повреждению, разру­шению или плавлению твэлов в ней с распространением повреждений на один ряд окру­жающих ТВС.

Следует заметить, что при разработке реакторов, в том числе и быстрых с натрие­вым теплоносителем, в СССР центр тяжести исследований безопасности лежит в области подробного рассмотрения прежде всего наиболее вероятных отказов, аварий или ошибок персонала, которые при дополнительных сопутствующих отказах или ошибках могут привести к опасным последствиям.

Если проанализировать имевшие место исходные неисправности оборудования и систем на БН-350 и БН-600, то на первое место по количеству выходит III контур.Это всевозможные разуплотнения паровых и водяных трубопроводов и арматуры, неисправности в системе водоочистки, отказ арматуры, непосадка предохранительных клапанов, незапуск резервных агрегатов, отказ приборов и т.д. Наиболее характерные неисправности по натриевым контурам (незначительное по количеству по сравнению с III контуром) связаны с электрообогревом, малыми утечками натрия в помещения.Как правило, большие затруднения вызывают системы регулирования различных пара­метров ; особенно это касается систем регулирования питательной воды на входе в

196 БАГДАСАРОВ и др.

парогенератор при глубоких возмущениях по мощности (например, отключении петли, быстром снижении мощности).

В этой связи в общей задаче обеспечения безопасности данной атомной станции большая роль отводится экспериментальной проверке на стадии пуска всех характе­ристик, важных с точки зрения обеспечения безопасности. При этом комплексно получаются ответы на вопросы о правильности заложенных технических решений по системам, о правильности выбранных эффективностей органов управления реактив­ностью, достаточности перечня аварийных сигналов, их уставках и задержках и т.д.

ЛИТЕРАТУРА

[1 ] БАГДАСАРОВ, Ю. Е. и др., ’’Опыт эксплуатации и подход к оценке безопасности будущих быстрых реакторов в СССР”, Доклад на Международную конференцию по безопасности быстрых реакторов, Франция, Лион, 19-23 июля 1982 г.

[2] Вредные Вещества в Промышленности, J1., Химия, 1976.[3] Нормы Радиационной Безопасности (НРБ-76), М., Атомиздат, 1978.[4] Санитарные Правила Проектирования и Эксплуатации Атомных Электростанций (СП АЭС-79),

М., Энергоиздат, 1981.[5] Допустимые Выбросы Радиоактивных и Вредных Химических Веществ в Приземный Слой Ат­

мосферы, М., Атомиздат, 1980.[6] ВАСИЛЕНКО, К.Т. и др., ’’Некоторые аспекты безопасной эксплуатации реактора БН-350”,

Доклад на Международную конференцию по безопасности быстрых реакторов, Франция,Лион, 19-23 июля 1982 г.

[7 ] Основные положения обеспечения безопасности АЭС при проектировании, строительстве и эксплуатации, Ат. Энерг.2 (1983).

IAEA-SM-268/30

REVIEW O F O PER A TIO N A L EX PER IENC E WITH TH E G AS-CO OLED M A G N O X REAC TO RS OF T H E U N IT E D K INGDOM C E N T R A L ELECTRICITY G EN E R A TIN G BO A R D

L. CAVERisk Assessment Limited,Eridge, Tunbridge Wells, Kent

A.W. CLARKENuclear Operations Support Group,Central Electricity Generating Board,London

United Kingdom

Abstract

REVIEW OF OPERATIONAL EXPERIENCE WITH THE GAS-COOLED MAGNOX REACTORS OF THE UNITED KINGDOM CENTRAL ELECTRICITY GENERATING BOARD.

The paper provides a review, which is mainly of a statistical nature, of 260 reactor years of operating experience which the (United Kingdom) Central Electricity Generating Board (CEGB) has obtained with its gas-cooled, graphite moderated Magnox reactors. The main emphasis in the review is on safety rather than on availability. Data are provided on the overall incidence and frequencies of faults and it is shown that the plant items which are predominantly responsible for recorded faults are the gas circulators and the turbo-alternators. Analysis of the reactor trip experience shows that the incidence of events which necessitate an automatic shutdown of the reactor has been about one per reactor year and that of other events leading to a reactor trip has not been much higher (1.4 per reactor year). As would be expected from the length of the operating experience, some relatively rare events have occurred (expected frequency 1СГ2 per reactor year, or less) but on each occasion the reactor shutdown system and decay heat removal systems functioned satisfactorily. No overheating of, or damage to, the fuel occurred as a result of these rare events or of other, more frequent, faults. Analysis of the trend of failure rates has shown an improvement with time in nearly all safety-related items and external inspection of the primary coolant circuits has shown no significant deteriora­tion with time. However, some derating of the reactors has been necessary to reduce the effects of oxidation of mild steel in C 02, in order to obtain optimum service lives. In spite of major differences between the systems, a comparison of the failure rates of analogous systems and plant items in PWRs and the Magnox reactors shows a considerable similarity. Overall, the review of CEGB’s operational experience with its Magnos reactors has shown that the frequencies of faults in systems and plant items has been satisfyingly low.

197

198 CAVE and CLARKE

1. INTRODUCTION

The Central Electricity Generating Board (CEGB) is responsible for virtually all electricity generation in England and Wales; it has been operating 8 twin reactor stations (embodying the gas-cooled, graphite moderated Magnox type of reactor) for periods of between 10 and 20 years on a commercial basis and has now accumulated some 270 reactor years of operating experience with this type of reactor.

The CEGB reviews periodically its operating experience and has reported its experience with these stations in the open literature on several occasions (see Refs [1, 2], for example). The present paper provides a review of that experience up to October 1982 and covers a total of 260 reactor years. The main emphasis is on safety rather than availability, e.g. on the causes of outages, their frequency and the trends in frequency, rather than on the extent to which loss of availability is attributable to particular types of fault. It should be noted that none of the events included in this review has caused overheating of, or damage to, the fuel.

As a starting point for this review the more readily available information for each station was consolidated into a ‘Chronological Record’ for that station under 14 separate headings. The creation of a record of this type facilitates examination of the trend in plant behaviour with time in each of the 14 groups and also facilitates cross-comparison between stations. In view of their specialized nature both the fuel and the on-load fuel handling machinery have been omitted from the review presented here.

In addition to the grouping on a ‘type-of-plant’ basis, the events in the Chronological Record have also been subdivided, within each group, into ‘Categories’ based on the outcome of the event (e.g. reactor trip, turbine trip or significant loss of output). The details of the various groups and categories are given in the Appendix.

2. METHOD OF ANALYSING THE DATA

The basic data in the Chronological Records can be analysed in a variety of ways. For presentation in this brief review the aspects selected are as follows:

— Fault response category on a station-by-station basis (Table I)— Fault response category on a plant group basis (Table II)— Reactor trip experience, by plant group and by station (Table I I I )— ‘Rare events’ (see below) leading to reactor trips (Table IV )

In Tables I, I I and II I , the frequency of events (per reactor or per station year) is of interest. The maximum net capacity (MNC) in MW(e) and load factor are shown in Table V by station and by year. From these a better approximation

IAEA-SM-268/30 199

to the actual operating time can be obtained, leading to a more accurate estimate of the frequencies. To supplement Table V, the major outages (i.e. those lasting more than 12 reactor weeks) are listed by station, cause and year in Table V I. In order that frequency rates per plant item can be derived, if required, the numbers of major components per station are listed in Table V II.

3. DISCUSSION OF THE DATA

3.1. Overall incidence and frequency of faults

Table I shows that the predominant category of fault has been that leading to a significant reduction in output (more than 5 per cent of MNC) without a reactor or turbine trip — 53 per cent of the 2962 recorded events. The frequency of faults, taken over all the categories, has been similar in all the stations, ranging from 0.7 of the mean (16 incidents per reactor year) to 1.6 times the mean.

The second largest class (reactor trips and uncontrolled shutdowns) has contributed only 15 per cent of the total. The data relating to this type of fault are discussed in more detail in Section 3.3 below.

As noted in the Introduction, in none of these events has there been any overheating of, or damage to, the fuel.

3.2. Predominant plant items subject to faults

Table I I shows that the plant items predominantly responsible for recorded faults, irrespective of severity, have been the gas circulators and the turbo­alternators. These have each contributed 20 per cent of the total; none of the other plant items has contributed more than 10 per cent. However, the gas circulator faults have led to fewer reactor trips than faults in the reactor shutdown system itself.

3.3. Causes of reactor trips

The frequency of reactor trips is an important parameter in reactor safety studies, as it has a major influence on the reliability required from the reactor shutdown system, if the trips result from a genuine demand for a shutdown, and from the shutdown heat removal systems. In the latter case both genuine and spurious trips are important.

From Table I I I it can be seen that, in general, the frequency of the genuine, automatic trips is lower than that of the spurious trips. However, the overall frequency of the latter, 1.4 per reactor year, is substantially less than is often assumed for design purposes, e.g. in the United Kingdom a value of 1 per reactor

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IAEA-SM-268/30 205

TABLE IV . SUMMARY OF RARE EVENTS, RESULTING IN REACTOR TRIPS, EXPERIENCED IN THE OPERATION OF CEGB MAGNOX REACTORS

Faultgroup

Nature of fault Station Date

1 (a) Uncontrolled withdrawal o f sector rods; reactor at power

Bradweil Sep 67

(b) Uncontrolled withdrawal of a coarse Trawsfynydd Jun 67control rod group; reactor at power

2 Lifting of primary circuit safety valve and Hinkley A May 65failure to re-seat Hinkley A

TrawsfynyddJan 70 Jul 75

3 Inadvertent, rapid closure of a main gas isolation valve

Trawsfynydd Oct 65

4 Failure of rc-settable safety valves of LPHinkley A Jan 67

steam system to operate

8 Complete loss of ‘guaranteed’ (non-interruptible) DC supplies Hinkley A Jan 66

6 Loss of sufficient proportion of reactorauxiliary cooling water system to cause Wylfa Apr 80a reactor trip Aug 81

8 Loss of electrical supplies due to a fire on air blast contact breaker of a station board

Hinkley A Dec 81

8 Loss of part of guaranteed supplies (generalinstrumentation supplies), due to an invertor Wylfa Jul 80fault, leading to a trip of both reactors

8 Maloperation of gas circulators led to a fireon the guaranteed supplies board feeding Wylfa Jul 82two of the DC pony motors

11 Loss of 400 kV line, in blizzard conditions, followed by maloperation of the auto-close system led to a severe current surge on onephase, causing all turbines and both Wylfa Jan 82reactors to trip and a partial loss ofguaranteed supplies, resulting in loss of thestation computer

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IAEA-SM-2 68/30 2 0 7

TABLE V I. PROLONGED OUTAGES (MORE THAN 3 MONTHS) OF MAGNOX REACTORS IN ANY ONE YEAR

S ta tio n YearO utage (w eeks)

R eacto r R eacto r 1 2

Percentage o f s ta tio n o u tp u t lost

P rim e cause o f ou tage

B erkeley 80 52 50 9881 52 4 9 a 97 B o th reac to rs sh u t dow n82(40 w ks)

3 8 a nU 36 fo r de ta iled in spec tion o f prim ary circu it

Bradweil 80 52 46 9481 52 52 100 B o th reac to rs sh u t dow n82(40 w ks)

6“ 3 8 a 42 fo r de ta iled inspec tion o f p rim ary circu it

H inkley P t A 69 See P rim e cause 18 D isin tegration o f a m ain70 o f ou tage 58 tu rb ine and subsequen t

m od ifica tion to the o th e r sets led to e n fo rced red u c tio n in reac to r o u tp u t fo r over a y ea r

T raw sfynydd 66 16 15 Rl sh u t dow n due to d isp lacem ent o f charge pan during refuelling

73

80

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26 32

41

56

B o th reac to rs shu t dow n fo r rep lacem en t o f in s tru m en ta tio n w ith in th e reac to r vessels

81 2 8 a nil 27 R l, sh u t dow n due to large ingress o f w a te r fo llow ing a boiler tube failureR 2 , sh u t dow n fo r de ta iled in spec tion o f prim ary circu it d u c ts and bellow s

D ungeness A 80 52 50 9881 52 4 8 a 96 B o th reac to rs sh u t dow n82(40 w ks)

26 nil 25 fo r detailed in spec tion o f p rim ary circu it

W ylfa 72 See P rim e cause o f 17 F req u en t shu tdow ns73 outage 15 to p lug leaking boiler

tubes in b o th reac to rs74 29 28 R2 shu t dow n fo r75 2 6 5 2 a 75 periods show n, for76 13a 12 repairs to boilers

R l sh u t dow n in ’75 fo r pro longed b iennial overhaul

a O utage co n tin u ed from prev ious year.

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IAEA-SM-268/30 209

year is usually used for the frequency of genuine trips on GCRs, which is in accordance with the operating experience, and a value of 10 per reactor year is usually used for spurious trips. Thus the operating experience suggests that the latter value is highly conservative for GCRs.

3.4. ‘Rare events’ leading to reactor trips

Another factor of importance in reactor safety studies is the completeness of the spectrum of faults which is examined in the analysis. Table IV provides an indication of the more unusual faults that have been encountered in the operation of the Magnox reactors; the faults listed have a frequency of order 10~2 per reactor year or less.

In each of the 13 cases listed in Table IV , the reactor shutdown system and the decay heat removal systems functioned satisfactorily, thereby preventing any damage to the fuel or to other plant items.

In all cases where these ‘rare events’, or other unusual occurrences not covered by this definition, could have affected reactor safety they were thoroughly investigated and appropriate measures were taken to prevent their recurrence.

3.5. Frequency of events leading to a significant reduction in output

An analysis of the data for ‘Category I I ’ faults on a station-by-station and plant item basis has been made. This analysis shows that the dominant causes of a ‘significant loss of output’ have been gas circulator faults (25 per cent), turbo-alternator faults (22 per cent), boiler tube leaks (18 per cent) and secondary circuit defects, such as steam leaks (15 percent). The pattern of predominant faults varies somewhat from one station to another but in nearly all the stations three of these four fault groups provide the three predominant types. The greatest variability from station to station is shown by Group 14 (i.e. boiler tube leaks); the mean frequency has been 1.5 per reactor year, but the frequency ranges from 0.04 per reactor year to 7.3 per reactor year; the median value is0.6 per reactor year, i.e. the distribution is approximately a log-normal one.

3.6. Analysis of the trend of failure rates with time

The data for three Categories of faults (I, I* and II) have been analysed, by plant item and by station, to determine the way in which failure rates have been changing with time. In order to obtain adequate sample sizes the data were examined on a quinquennial basis.

In nearly all cases the reliability of the equipment which is most relevant to reactor safety has been high and has been improving with time. In the case of two stations the fault rate for Group 9 (Control and Instrumentation) plant

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IAEA-SM-268/30 211

items has shown some increase with time. However, in the case of equipment more relevant to availability than to safety the trend has been less uniform; at a higher proportion of stations the frequency of faults affecting availability has been increasing slightly.

3.7. Trends of availability with time

It will be seen from Table V that from 1970 the maximum net capacity of most of the stations was reduced by about 10 per cent. This reflects a reduction in reactor gas outlet temperature which was made in order to reduce the rate of oxidation of certain mild steel reactor internal components. By this means a useful extension of service life should be achieved.

In addition to this derating there has also be a noticeable drop in availability of the reactors since 1979. It can be seen from Table V I that this has been due to the prolonged shutdown of some of the stations for detailed inspection of their primary circuits. This inspection has revealed a few minor defects in the ductwork but metallographic examination has shown that these defects had been present since the reactors were constructed and had not grown in service.

3.8. Comparison with the failure rates encountered in other reactor systems

Although much of the equipment in a GCR is different from that in water reactors, some comparisons can be made. These are shown in Table V III; in this table the water reactor data are based on the frequencies for initiating faults used in a recent probabilistic risk assessment carried out by Westinghouse, and on the values used by CEGB and NNC for design purposes (see Ref.[3 ]). The Westinghouse set reflects US operating experience whereas the CEGB/NNC set reflects their view on what should be attainable in a modern design. It will be seen from Table V I I I that in general there is no very marked difference between the three sets of data.

4. UNCERTAINTY OF THE DATA

The sources of uncertainty in the data used to obtain failure rates for running items not directly related to reactor safety may have been omitted from the reports on which the Chronological Records are based; i.e. the failure rates reported here could be optimistic. However, consideration of the mode of operation of most of the stations suggests that the method used in this paper to correct the total operating time may have led to an underestimate of the running

212 CAVE and CLARKE

time accumulated by plant items such as gas circulators, so that there would be an error in the estimated failure rates in the opposite direction.

Overall it is considered that the failure rates quoted are unlikely to be in error by more than ±20 per cent.

5. CONCLUSIONS

The principal conclusion to be drawn from the summary of CEGB’s operational experience with Magnox reactors is that the frequency of faults in systems and in plant items has been satisfyingly low, particularly in the case of those whose failure could require a response from the reactor protection systems.

It can also be concluded that, with the few exceptions noted in Section 3.6 above, there are no indications of any deleterious trend in the reliability of systems or components.

With relatively few exceptions, the fault frequencies for the various fault groups show relatively little variation from one station to another; typically the observed range is encompassed by a factor 1.5 on either side of the mean. Boiler tube leaks are the most notable exception; in this case the variation about the median is a factor of 12 on one side and 15 on the other (i.e. the distribution is approximately log-normal).

Comparison of the incidence of failures in analogous systems and plant items in PWRs shows that, in general, there is no very marked difference between the values obtained from the operating experience with Magnox reactors and those currently in use in the design and assessment of PWRs.

Appendix

DESCRIPTION OF EQUIPMENT GROUPS AND OF FAULT CATEGORIZATION SYSTEM

1. Description of the equipment groups

The data are subdivided into the following Groups:

Group 1. Plant items relating to the control of reactivity, e.g. control rods and their drives; reactor protection systems, electrical supplies for the CQntrol rod drives and protection systems. The automatic reactor control system, embodying the ‘sector control rods’, has been included in this Group but the burst cartridge detector (BCD) system is covered in Group 9.

IAEA-SM-268/30 213

G ro u p 3.

G ro u p 4.

G ro u p 5.

G ro u p 6 .

G ro u p 7.

G ro u p 8.

G ro u p 9 .

G ro u p 10.

G ro u p 11.

Group 2. F a u lts in w hich som e loss o f p rim ary c o o la n t h as o cc u rre d acc id en ta lly , e.g. f ra c tu re o f sm all-bo re p ip in g an d in a d v e r te n t lif tin g o f sa fe ty valves.

F a u lts a ffec tin g th e flow o f p rim a ry co o la n t (o th e r th a n gas c irc u la to r fau lts , w h ich are covered in G ro u p 14), e.g. ch an n e l b lo ck ag e ; inadver­te n t o p e ra tio n o f iso la tio n o r th ro tt le valves.

F a u lts a ffec tin g th e in te g rity o f th e seco n d a ry c o o la n t c irc u it, covering an ana logous ran g e o f fau lts to th o se in G ro u p 2. T his g ro u p in c lu d es th e w ho le o f th e seco n d a ry c ircu it fro m c o n d en sa te su c tio n p u m p s to tu rb in e in let.

F a u lts a ffec tin g th e c o n tin u ity o f flow o f seco n d ary co o la n t, in c lud ing th e b o ile r feed p u m p s , feed reg u la to rs an d s team iso la tio n valves.

F a u lts a ffec tin g th e te r tia ry coo ling sy s tem s, e.g. th e m a in coo ling w a te r (CW ) system an d th e sm aller sy s tem s u sed fo r co o lin g item s su ch as tu rb in e an d gas c irc u la to r lu b r ic a tio n sy s tem s and th e p rim ary lin er co o lin g sy s tem s o f p re -stressed c o n c re te p ressu re vessels. M ajor c o n d e n se r fa ilu res, lead ing to gross ingress o f sea w a te r in to th e feed sy s tem o r loss o f tu rb in e vacuum have b een re c o rd e d , b u t fa ilu res o f a few co n d en se r tu b es a t an y one tim e have n o t b een in c lu d ed .

F a u lts a ffec tin g th e tu rb o -a lte rn a to rs , o rig in a tin g b e tw e e n tu rb in e in le t an d th e a lte rn a to r o u tp u t te rm in a ls , in c lu d in g th e tu rb in e g overno r system .

F a u lts a ffec tin g the s ta tio n e lec trica l sy s tem s in c lu d in g th e m a in , essen tia l (o r ‘in te r ru p tib le em ergency su p p lie s ’) and ‘g u a ra n te e d ’(o r n o n -in te rru p tib le em erg en cy supp lies) w h ich o rig in a te w ith in th e s ta tio n o r o n th e s ta tio n side o f th e sw itch -yard . H ow ever, th e supp lies fo r th e c o n tro l ro d drives a n d th e r e a c to r tr ip sy s tem are in c lu d ed in G ro u p 1.

F a u lts a ffec tin g th e c o n tro l an d in s tru m e n ta t io n sy s tem , ex c lud ing th e c o n tro l sy s tem s w h ich can d irec tly a ffec t re a c tiv ity (e.g. th e a u to m a tic se c to r c o n tro l sy s tem ) an d th e tu rb in e g o v ern o r sy s tem . I tem s such as c en tra l d a ta p ro cesso rs an d th e BCD system are in c lu d ed in th is G ro u p .

M iscellaneous fau lts , o f a re la tive ly ra re n a tu re (f req u en cy o f o rd e r 10-2 p e r re a c to r y e a r) w h ich d o n o t fa ll in to any o f th e o th e r 14 G ro u p s b u t m ay be o f in te re s t (e.g. loss o f lo ad fro m cranes, u n u su a l ac tiv ity in re a c to r co o lan t) .

R esponse o f th e s ta tio n to d is tu rb an ce s in th e ex te rn a l grid sy s tem , in c lu d in g c o m p le te loss o f c o n n ec tio n .

214 CAVE and CLARKE

G ro u p 12 . F a u lts a ffec tin g gas c ircu la to r.

G ro u p 13. F a u lts o n th e ‘M ulsify re ’ sy s tem ; th ese are in c lu d ed to p ro v id e som e in d ic a tio n o f th e freq u en cy w ith w h ich sp u rio u s o p e ra tio n o f th is ty p e o f fire p ro te c tio n sy s tem has led to e lec trica l fau lts .

G ro u p 14. F a u lts lead ing to seco n d ary c o o la n t leakage w ith in th e boilers.

In a n u m b e r o f cases w h ere th e fa u l t b eh av io u r w as co m p lex th e in c id e n t co u ld have b een re c o rd e d in tw o o r m o re G ro u p s b u t in o rd e r to avoid d o u b le co u n tin g th e in c id e n t has b een re c o rd e d in one G ro u p on ly .

2. P re lim in a ry c a te g o riz a tio n o f d a ta

In o rd e r to p ro v id e an in itia l in d ic a tio n o f th e fre q u e n c y an d severity o f theind iv idua l G ro u p s o f fa u lts th e d a ta in th e C h ro n o lo g ica l R eco rd have b eenca te g o rized , b y s ta tio n an d by ca len d ar y ea r, acco rd in g to th e fo llow ing schem e:

C a teg o ry I. F a u lts lead ing to a tr ip , o r u n c o n tro lle d sh u td o w n o f th e re a c to r , in c lu d in g cases w h e re th e re a c to r p o iso n s o u t.

C a teg o ry I*. F a u lts lead in g to th e tr ip o f a m ain tu rb in e .

C a teg o ry II. F a u lts lead ing to a s ign ifican t (i.e. g rea te r th a n 5 p e r c e n t) en fo rcedre d u c tio n in e lec trica l o u tp u t o f th e p la n t, o th e r th a n a sh u td o w n .

C a teg o ry II* . F a u lts lead ing to an e n fo rced b u t c o n tro lle d sh u td o w n o f th e re ac to r.

C a teg o ry III. F a u lts w h ich do n o t lead to an en fo rced and sign ifican t re d u c tio n in e lec trica l o u tp u t o f th e p lan t.

C a teg o ry IV . F a u lts caused b y m a lfu n c tio n o f a p p a ra tu s u sed fo r ro u t in e , o n ­line , te s tin g o f p la n t (e.g. tu rb in e em ergency tr ip devices o r re a c to r g u a rd lines) o r fa u lts n o t p rev iously revea led in o p e ra tio n , w h ich are d iscovered in th e cou rse o f sch ed u led sh u td o w n in sp ec tio n s , o r ro u t in e testing .

R E F E R E N C E S

[1] DIXON, F., SIMONS, H.K., CEGB’s nuclear power stations: A review of the first 10 years of Magnox plant performance and reliability, British Nuclear Energy Society, 13 1 (1974)9 .

[2] BROOM, T., CLARKE, A.W., Operational Experience with Gas Cooled Reactors in the CEGB and SSEB Power Systems, NUCLEX, Basle 1978.

[3] CENTRAL ELECTRICITY GENERATING BOARD, Sizewell ‘B’ Power Station Public Inquiry: CEGB Statement of Case. Appendix M. Degraded Core Analysis, CEGB(1 July 1982).

IAEA-SM-268/49

I N T E R N A T I O N A L E X P E R I E N C E I N T H E

I M P L E M E N T A T I O N O F T H E L E S S O N S L E A R N E D

F R O M T H E T H R E E M I L E I S L A N D I N C I D E N T

R e p o r t o n a n I A E A T e c h n i c a l C o m m i t t e e

R .J . PA L A B R IC AIn te rn a tio n a l A to m ic E n erg y A gency ,V ien n a

Presented by H. Wright

Abstract

INTERNATIONAL EXPERIENCE IN THE IMPLEMENTATION OF THE LESSONS LEARNED FROM THE THREE MILE ISLAND INCIDENT: REPORT ON AN IAEA TECHNICAL COMMITTEE.

In an effort to assess the worldwide status of implementation of the lessons learned from the TMI incident, the IAEA convened a Technical Committee in October 1982. Representatives from eleven countries and two international organizations discussed their experiences, the difficulties they had encountered and future action plans. The Committee presented recommendations in ten areas in nuclear power plant safety where improvements could be made. These areas include: licensing and regulation; plant design; conduct of operations; operator qualification and training; review and feedback of operational experience; emergency planning and preparedness; man-machine interaction; probabilistic risk assessment; safety research and studies; and international co-operation. The technical document resulting from the meeting should be useful to countries with existing nuclear power programmes in that it will provide a means for comparing their actions with others. For countries which are embarking on their first nuclear power projects, the document should provide a useful reference for specific TMI-related issues that need to be considered in their nuclear programmes. The paper summarizes worldwide experiences and recommendations on the implementation of TMI lessons learned. The highlights of country-specific responses and post-TMI actions in each of the ten subject areas mentioned are also presented.

I . INTRODUCTION

A l i t t l e over four year s have now elapsed s ince the occurrence of the nuc lea r Inciden t on 29 March, 1979 a t the Three Mile I s l and (TMI) - Unit 2 nuclea r power p lant in Har r i sburg , Pennsylvania, USA. The inc ide n t has had

impl i ca t ions in the nuc lea r power indus t ry not only In the USA but a l so worldwide. Various review groups have been formed in the af te rmath of the

inc iden t to s tudy i t s causes, i d e n t i f y lessons to be learned and draw up recommendations fo r improving the l e v e l of s a fe ty of nuc lea r power p la n t s .

215

216 PALABRICA

Most of the post TMI-related ac t io ns taken by cou n t r i e s with nuclear

power programmes are a l ready under way, al though se ve ra l more years w i l l

e l apse before o the r s can be f u l l y implemented. The I n te r n a t io n a l Atomic Energy Agency (IAEA) deemed i t t imely and app rop r ia t e to convene a meeting

of a Technical Committee from 18 to 22 October 1982 to a s sess the worldwide s t a t u s n f the implementation of the TMI l e ssons l earned . Representat ives

from eleven cou n t r i e s and two in te r n a t i o n a l o rganizat ions d iscussed th e i r

experi ence, the d i f f i c u l t i e s they had encountered and t h e i r fu tu re ac t ion p lans . These coun t r i e s and o rganiza t ions were: Belgium, Braz i l ,

Czechoslovakia, Fin land, the Federal Republic of Germany, Hungary, the Republic of Korea, Mexico, Ph i l i pp in e s , Spain, Yugoslavia, the Commission of

the European Communities and the IAEA.

The Technical Committee discussed the general responses and ac t io ns

taken worldwide with r e sp ec t to the l e ssons l earned , in accordance with the

fol lowing sub ject grouping:

1 . Licensing and r eg u l a t io n of nuc lea r power p lan t s ;2 . Plant design;3. Conduct of ope ra t ions;A. Operator q u a l i f i c a t i o n and t r a in in g ;

5. Feedback of ope ra t ing exper ience from o the r p la n t s

6. Emergency planning and preparedness;7. Man-machine i n te r a c t io n ;8 . P r o b a b i l i s t i c r i s k assessment methodology;9. Safety r esearch and study;

10. I n te r n a t io n a l co -opera t ion .

Towards the conclusion of the meeting, the Technical Committee a l so drew up recommendations r egarding the implementation of the l e ssons learned in the ten a reas given above.

A t ec h n ic a l document r e s u l t in g from the meeting w i l l be published th i s yea r . I t w i l l c o n s i s t of two pa r t s and an Appendix. Par t I w i l l provide a summary of worldwide exper iences and recommendations r egarding the

implementation of the l e ssons l earned . Par t I I w i l l g ive , in a summary fashion , cou n t ry - and -o rg an i za t i on - sp ec i f i c responses and ac t io ns ca tegor ized

in to the ten subject , a r eas . Relevant informat ion from published repo r t s

w i l l be incorporated in P a r t s I and I I for a number of cou n t r i e s with nuc lea r power programmes which were not r epresented in the Technical

IAEA-SM-268/49 217

Commit t ee . The Appendix of the document, on the o ther hand, w i l l conta in d e t a i l e d de s c r ip t i o n s of the exper ience of four c o u n t r i e s : Bra z i l , the

Federal Republic of Germany, Hungary and the P h i l ip p in e s . The examples of

Br az i l , Hungary and the Ph i l i pp i ne s w i l l give an in s i g h t in to the post-TMI ac t i o n s of co u n t r i e s which were a t d i f f e r e n t s tages of t h e i r nuclea r power programmes when the TMI in c id en t occur red. The example of the Federal Republic o f Germany w i l l i l l u s t r a t e the response of a country with a l a rge number of nuc l ea r power p la n t s , some of which had a l r eady been in opera t ion for many yea r s before the in c id e n t .

I I . SUMMARY STATUS OF WORLDWIDE IMPLEMENTATION OF TMI LESSONS LEARNED

A summary of the genera l responses and a c t io ns taken worldwide with

r e spec t to the l e s sons learned in the t en sub jec t a reas are presented below. Mentioned in the d i sc uss ion s under each a rea a re the r e l ev an t sa fe ty i s s ues tha t were considered by d i f f e r e n t coun t r i e s in developing t h e i r

responses to the TMI in c id e n t .

1. Licensing and Regulat ion

Most of the co u n t r i e s have repor ted th a t TMI did not cause a majorchange in t h e i r r eg u la to ry approach or in the l i c en s in g process i t s e l f as a

d i r e c t outcome of the in c id e n t . The l e ssons learned were transformed in to

more or l e s s d e t a i l e d requirements or r eg u l a t io n s depending on ind iv idua l

co un t r i e s . Addi t ional s t u d i e s and analyses were r equested from the l i c ens ees and new repor t ing requirements fo r ope r a t ion a l da ta were e s t a b l i s h e d . To

eva lua te the responses to these r equirements , new groups a l so had to be

e s t a b l i sh ed in the r eg u la to ry bodies ( to ana lyse human f a c to r s and op er a t ion a l d a t a , fo r example). Several r egu la to ry bodies have a l so e s t a b l i sh ed the pol icy of ma in ta in ing a t l e a s t one re s i d e n t inspe c to r a t

each nuclea r power p lant s i t e .

2 . P lan t Design

Plan t eva lua t ions conducted in a number of coun t r i e s with r e spec t to

the TMI inc ide n t i d e n t i f i e d des ign d e f i c i e n c ie s which prompted requirements for ad d i t i on s to or modif i ca t ions in:

a) Ins t rumenta t ion fo r acciden t d iagnosi s and monitoring; and

b) The mode of ope ra t ion of s a fe ty systems.

218 PALABRICA

Examples of the f i r s t kind Include subcooling me ter s , a u x i l i a r y

feedwater f lowmeters, valve pos i t i on i n d ic a t o r s and high-range

thermocouples. On the o the r hand, modi f ica t ions in s a fe ty systems opera t ion inc lude ac tu a t i o n of s a fe ty i n j e c t i o n based only on low p re ss u r i z e r p ressu re , automat ic I n i t i a t i o n of the a u x i l i a r y feedwater system and new containment i s o l a t i o n c r i t e r i a . Beyond these, the f a c t t h a t an acciden t

occurred wi th consequences to the p lant worse than a n t i c i p a te d through previous ana lyses showed the ne c es s i t y of ad d i t i o n a l equipment to mi t iga te the consequences of and to recover from more severe a c c i de n t s . This i s t rue

in the case , for example, of hydrogen recombiners and high point vent s; and

of high r a d i a t i o n monitoring and/or r ad io ac t i ve m a te r i a l sampling systems and a d d i t i o n a l sh ie ld ing fo r support equipment. New f a c i l i t i e s for b e t t e r management of emergency s i t u a t i o n s a l so had to be e s t a b l i sh ed in opera t ing

p l an t s and w i l l he designed i n to new p l a n t s . Examples of these f a c i l i t i e s are the t ec h n i c a l support and the emergency co n t ro l ce n t r es .

Some of the problems i d e n t i f i e d by the TMI inc ide n t r equi red

enginee ring s o lu t i o n s which were not r ea d i ly a v a i l a b le . In v es t i g a t io n s and s tu d i e s are s t i l l under way to f ind app ropr ia t e so lu t io n s , such as in the

case of water l e v e l in d i c a t io n in PWR pressure v es se l s .

3. Conduct of Operat ions

An enhancement of the sa fe t y a spec ts of ope ra t ion a c t i v i t i e s has been achieved e i t h e r through the c re a t ion of new s t a f f p o s i t i ons / r ev i ew groups or a b e t t e r d e f i n i t i o n of r e s p o n s i b i l i t i e s of e x i s t i n g ones. The

ad m in i s t r a t ion of ope ra t ion a c t i v i t i e s has a l so been reviewed to improve s a fe ty through the development or modif i ca t ion of turnover procedures and co n t ro l room acc ess , s t a f f i n g , working hours c o n t ro l , e t c .

P lan t emergency opera t ion procedures have been reviewed in the l ig h t of the problems observed dur ing the TMI in c id en t . Improved d iagnosi s

procedures have been developed and sp e c i a l i n s t r u c t i o n s concerning the opera t ion o f sa fe ty equipment have been provided. Special a t t e n t i o n has been given to e s t a b l i s h in g n a t u r a l c i r c u l a t i o n and recognizing t h a t i t has been achieved, and to o the r a l t e r n a t i v e core cool ing methods ( e . g . feed and

bleed) .

IAEA-SM-268/49 219

Maintenance and t e s t procedures have a l so been c a r e f u l l y reviewed, e s p e c ia l l y with r espect to the removal of s a f e t y - r e l a t e d equipment fo r

se rv ice and assur ing proper r e - es t ab l i shm ent of system oper a t ion a l s t a t u s a t

the end of th i s a c t i v i t y .

4. Q u a l i f i c a t io n and Training of Operators

Surveys conducted a f t e r the TMI In c iden t on i n i t i a l q u a l i f i c a t i o n for

s e l e c t i o n of ope ra to r s showed varying requirements from country to coun try .

Evaluat ion of t h i s s i t u a t i o n i s s t i l l under way, and poss ib le s o lu t i on s may

have been adopted, such as r eq u i r ing an engineer ing degree for the s h i f t superv iso r and the use of psychological t e s t i n g .

A common conclusion was tha t the re should be people in the con t ro l room who are b e t t e r prepared to ana lyse unforeseen s i t u a t i o n s . This has

been accomplished through a d d i t i o n a l t r a i n i ng o f e x i s t i n g personnel or e s t a b l i s h in g a standby group/person. Also, more s t r i n g e n t requirements have been imposed on the examination of p lant personnel who need to be l i ce n se d .

The use of s imulato r s on r e t r a i n i n g has been s p e c i a l l y emphasized; t h e i r number i s Inc reasing and t h e i r c a p a b i l i t i e s a r e being expanded.

5. Review and Feedback of Operat ional Experience

Systems have been e s t a b l i s h ed or improved to c o l l e c t , eva lua te and

disseminate op e ra t iona l d a t a . The I n s t i t u t e f o r Nuclear Power Operat ions/Nuclear Safety Analysis Center (INPO/NSAC) i s a ty p ic a l example, but o the r na t io n a l systems have a l so been es t a b l i s h ed . I n te r n a t io n a l e f f o r t s have been a l so made in t h i s f i e l d , f o r example, by the Organisa t ion f o r Economic Co-operat ion and Development/Nuclear Energy Agency (OECD/NEA),

Commission of the European Communities (CEC) and the IAEA. Owners' groups, a l ready ex i s t in g before the TMI in c id e n t , have gained inc reased importance.

Th^re have been st rong e f f o r t s to a s su re th a t the informat ion gathered and evaluated i s taken in to con s i de ra t ion In p lan t ope ra t ion , in

des ign (whether of p l an t s under co ns t ru c t ion or in ope ra t ion) and in the t r a i n in g and r e t r a i n in g of op e ra to r s .

220 PALABRICA

Licensing a u t h o r i t i e s have a l s o e s t a b l i sh ed groups for review of ope r a t ion a l exper ience and take th i s exper ience i n to cons ide ra t ion in the

l i ce ns ing process whenever necessary.

6 . Rnergency Planning and Preparedness

In most co u n t r i e s emergency plans have been reviewed and modified both o n - s i t e and o f f - s i t e . On-s i te , new f a c i l i t i e s have been es t ab l i she d for b e t t e r management of emergency s i t u a t i o n s . Minimum equipment

requirements have been spe c i f i e d and new and more so p h i s t i ca te d equipment i s under development. Engineering c a p a b i l i ty with in the p lant or ava i l a b l e a t shor t no t i ce i s now provided to help manage a c r i s i s .

With r e sp ec t to o f f - s i t e emergency planning, the s i t u a t i o n can vary g r e a t l y depending on the p a r t i c u l a r s t r u c t u r e of emergency response in each coun try . There has been a d e f i n i t e move towards the in te g r a t i o n of

emergency plans under a wel l defined lead o rgan iza t ion , sometimes even with

modi f i ca t ion of the ex i s t in g s t r u c t u r e . There has a l so been a d e f i n i t e move towards an expansion of the r egion to be considered in planning and in some

cases t h i s has led to the need fo r co -o rd ina t ion with a u t h o r i t i e s of neighbouring co un t r i e s .

The l in k between o n - s i t e and o f f - s i t e plans has been improved, for ins t ance through more p rec i se n o t i f i c a t i o n requirements and b e t t e r

communications systems.

7. Man-machine I n te r a c t i o n

A review of the c on t r o l room s i t u a t i o n with r e sp ec t to man-machine i n t e r a c t i o n s has been ca r r i e d out in many p l a n t s . Because t h i s aspec t had not been considered in a sys temat ic way in the des ign and eva lua t ion of nu c lea r power p l a n t s , no sp e c i f i c guidance ex i s t e d fo r these eva lua t ions , and the exten t of modi f ica t ions var ied from p lant to p la n t . Standards are

now under development and new groups a re being e s t a b l i s he d both on the d e s ig n e r /o p e ra to r ' s s ide as wel l as in the r egu la to ry bodies.

IAEA-S М-268/49 221

8 . P r o b a b i l i s t i c Risk Assessment

P r o b a b i l i s t i c r i s k assessment (PRA), a technique which was in inc reas ing use even before the TMI in c id en t , has been employed in the an a ly s i s of systems and systems modi f ica t ions ( a u x i l i a r y feedwater system,

for example). In some spe c ia l cases ( e . g . Zion, Indian Po int , Limerick) , p l a n t an a ly s i s has been performed using PRA methodology in order to support l i c e n s in g d ec i s i ons .

The PRA methodology i t s e l f has undergone some changes a f t e r the TMI in c id e n t , such as inc reased importance given to the ro le of the opera to r and

the in t r odu c t ion of new emergency planning cons id e ra t i ons ( e . g . evacua t ion) .

9. Safety Research and Studies

Several s tu d i es have been and a re being ca r r i e d out as a d i r e c t r e s u l t of the TMI inc iden t in a number of a re as such as acc ident and po s t - acc iden t behaviour of systems and components ( e . g . valve t e s t i n g , hydrogen g en er a t io n) , degraded core cond i t ions ( e . g . Super Sara p ro jec t , core ca tche r s ) and human f a c to r s enginee ring ( e . g . performance under s t r e s s ) .

Some o the r s tu d i e s , a l ready under development before the in c i d en t , have been re o r i e n t e d . One example i s the s h i f t from la rge -b reak LOCA to small breaks in both exper imental and code development a reas .

In order to e s t a b l i s h p r i o r i t i e s in r e a c t o r sa fe ty , se ve ra l s t ud ie s a re under way in a reas such as eva lua t ion of PRA methodology, c o s t / b e n e f i t an a ly s i s , q u a n t i f i c a t i o n of s a fe ty goal s and publ ic percep t ion of r i s k .

10. I n te r n a t io n a l Co-operat ion

The exchange of o pe ra t io na l exper ience on an i n t e r n a t i o n a l bas i s has

seen a s i g n i f i c a n t inc rea se as a r e s u l t of the TMI in c id e n t . B i l a t e r a l agreements have been implemented and an i n t e r n a t i o n a l system has been es t a b l i sh ed by OECD/NEA. Another system, involving the p a r t i c i p a t i o n of a

l a r g e r number of c o u n t r i e s , i s under development by the IAEA.

The same inc rease in the exchange of in format ion was a l s o noted in

the a rea of s a fe ty r esearch through o rganiza t ions such as OECD/NEA, CEC, the

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Council f o r Mutual Economic Assis t ance (CMEA) and the IAEA. The World

Health Organizat ion (WHO) i s co -o rdina t ing a system to c o l l e c t and eva lua te data on radiopa thology.

Provi s ions for render ing emergency a s s i s t a n c e on an i n t e r n a t i o n a l b as i s a re being e s t a b l i s h ed through the IAEA and WHO.

The s tandards development programme a t the IAEA (NUSS) and other o rgan izat ions has not been fundamental ly changed, but some guides have been reviewed and modif ied, such as those on emergency planning.

I n te r n a t io n a l co -opera t ion on the decontaminat ion and recovery of the TMI-2 nuc lea r power plant has been requested by the USA and i s being

considered by many coun t r i e s and o rgan iza t ions .

I I I . TECHNICAL COMMITTEE RECOMMENDATIONS

The TMI inc ide n t has shown tha t al though no fundamental change in the general approach to nuclear power plant sa fe ty was necessary , severa l

improvements are being made in the a reas of l i c e n s in g , des ign and op era t ion . Based on the exper ience gained in the implementation of these improvements, s evera l recommendations could be made.

1. Licensing and Regulat ion

The review of the des ign, con s t ruc t ion and opera t ion of a nuclear

power p lant by an independent body (e . g . a r egula to ry body) has been a c h a r a c t e r i s t i c of the commercial nuclea r indus t ry s ince I t s beginning. As a consequence of the TMI in c id e n t , s evera l new as pec t s have been id e n t i f i e d which may r e s u l t i n a d d i t i o n a l eva lua t ion by the appro pr ia t e des igner , cons t ru c t o r or ope ra to r as wel l as the r egula tory body. In t h i s r egard, the cu r ren t r e gu la t io ns and l i cen s i ng procedures should be reviewed for the purpose of determining poss ible changes tha t need to be made to accommodate requirements der ived from these new aspec t s .

2. Plant Design

A bas ic concept In the design of nuc lea r power p la n t s i s th a t of defence- in-dep th (preven t ion, p r o tec t ion and m i t ig a t io n ) . Although the TMI

IAEA-SM-2 68/49 223

i nc ide n t r ea ff i rmed the v a l i d i t y of t h i s approach, the event did i d e n t i f y

des ign a reas tha t could be improved in a l l p l a n t s . For ope ra t ing p lant s and those under con s t ru c t io n , an an a ly s i s should be conducted to determine the

need f o r modi f ica t ions of or ad d i t io n s to the ins t rume nta t ion , equipment and support f a c i l i t i e s which a re necessary to prevent , diagnose and monitor an

ac c i d e n t , m i t ig a t e i t s consequences and a id in long- term recovery a c t i o n s .

At the nrevent ion l e v e l , s teps should be taken to improve equipment r e l i a b i l i t y and to provide b e t t e r ins t rumenta t ion . At the p ro tec t io n l e v e l ,

one should a s su re core c o o l a b i l i t y in a l l c i rcumstances. Emphasis should be placed on an accura te knowledge of the p lant s t a t u s a t a l l t imes. This may a l s o r equ i re a d d i t i o n a l ins t rumenta t ion and d i s p l a y s . At the m i t ig a t io n l e ve l , i t should be v e r i f i e d th a t e s s e n t i a l equipment and ins t rumenta t ion

needed dur ing the course of and a f t e r an acc ident have been q u a l i f i e d for acc iden t con d i t ions . Improved s o lu t i on s to these ma t t e r s should be included fo r p lant s s t i l l under des ign.

3 . Conduct o f O p e ra tio n s

I t i s recognized t h a t the o rgan iz a t i on and the a v a i l a b le too l s ( e . g . procedures , r u l e s , e t c . ) which govern the conduct of ope ra t ions have an in f luence on re a c t o r opera tor performance. The o rg an iz a t io n a l s t r u c t u re

should emphasize p lan t s a fe ty without s a c r i f i c i n g ope ra t iona l

e f f e c t i v e n e s s . This concept should a l so be r e f l e c t e d in the d e f i n i t i o n of s t a f f and s h i f t personnel d u t i e s and r e s p o n s i b i l i t i e s . Procedures and/or r u le s should be e s t ab l i sh ed to spec i fy , among o t h e r s , s h i f t personnel

requirements , co n t ro l room acc ess , s h i f t and r e l i e f tu rnover , working hours and maintenance a c t i v i t i e s . Procedures should be adequate and w r i t t e n in such a manner as to prevent m is i n t e r p r e t a t i o n by the oper a t o r .

4. Operator Q ua l i f i ca t io ns and Training

The TMI inc iden t has shown th a t the r e a c t o r op e ra to r s play a key ro le in ensur ing o v e r a l l plant s a f e ty . As such, t h e i r s e l e c t i o n and t r a i n in g should be given ca r e f u l a t t e n t i o n , wel l in advance of p lant opera t ions .

Basel ine c r i t e r i a should be e s t a b l i sh ed fo r the q u a l i f i c a t i o n , t r a i n in g and l i c e n s in g /a u t h o r i z a t io n of ope ra to r s . These op era to r s should have

s u f f i c i e n t a b i l i t y to diagnose and respond to off-normal even ts , inc lud ing those which have not been s p e c i f i c a l l y covered by t h e i r t r a i n i ng programmes

224 PALABRICA

or the opera t ing procedures. Provi s ions should be made to ensure tha t op e ra to r s mainta in t h e i r s k i l l s and knowledge through re t r a i n in g

programmes. In the t r a i n in g and r e t r a i n in g of ope ra to r s the use of

s imulato r s i s s t r ong ly recommended s ince they have proven to be e f f e c t i v e .

5. Review and Feedback of Operat ional Experience

An important f ind ing a f t e r the TMI inc iden t was t h a t previous s im i la revents had occurred but t h e i r p o te n t i a l s ig n i f i c an c e had not been recognized

and adequately acted upon. Therefore, enhanced systems fo r the c o l l e c t i o n ,

eva lua t ion and d is semina t ion of opera t ing data should be provided.Prov is ions should be made to a s su re t h a t t h i s informat ion i s made ava i l a b l e

and reviewed a t each f a c i l i t y and tha t appropr ia t e i s su es are r e f l e c te d in

the p lant design and/or included in the opera t ing procedures and t r a i n in g programme. S ign i f i ca n t f ind ings should be considered in the des ign,

l i c en s in g and r eg u l a t io n of o the r f a c i l i t i e s . The exchange of appropr ia t e

data on a b i l a t e r a l or i n t e r n a t i o n a l ba s i s I s a l so recommended.

6 . Emergency Planning and Preparedness

The TMI inc iden t a l s o i d e n t i f i e d the need for improved emergency planning and preparedness . An in t eg ra ted emergency plan should be developed and implemented before p lant opera t ions . The plan should c l e a r l y speci fy the l eading o rganiza t ion and the ro les of lo c a l and n a t io n a l a u t h o r i t i e s

( including those of neighbouring co u n t r i e s , where a p p r o p r ia t e ) . Emergency ex e r c i se s should be p e r i o d i c a l l y conducted. On-s i te , s u f f i c i e n t engineer ing support should be a v a i l a b le on shor t no t i ce and the re should be appropr ia t e ce n t r a l i ze d f a c i l i t i e s and equipment, i nc luding adequate communications c a p a b i l i t i e s . O f f - s i t e t e ch n ic a l support should be av a i l a b le sh o r t l y a f t e r an event .

Regulatory a u t h o r i t i e s should a l so be prepared to provide increased response to an emergency s i t u a t i o n .

7. Man-machine I n t e r a c t i o n

The response to the TMI inc iden t emphasized the need to have a

co n t ro l room from which the opera tor s could s a fe ly and e f f i c i e n t l y con t ro l

IAEA-SM-268/49 225

the p lant under a l l con d i t ions . Control rooms in opera t ing p la n t s and those under cons t ru c t ion should be sub jected to human f a c to r s (ergonomics)

eva lua t ion by q u a l i f i e d exper t s and those modi f ica t ions th a t s i g n i f i c a n t l y improve rea c to r sa fe t y should be made. For new p la n t s , ergonomics should form a par t of the design and s a fe ty eva lua t ion cons ide ra t ion s , including

c on t r o l room layout , panel a c c e s s i b i l i t y , i nformat ion d i sp la y , e t c .

Furthermore, se r ious con s i de ra t ion should be given to the use of

dedica ted panels to supply informat ion and t r ends on parameters abs o lu te ly

necessary to mainta in the p la n t in a safe condi t ion .

8 . P r o b a b i l i s t i c Risk Assessment

P r o b a b i l i s t i c r i s k assessment techniques a re recognized as a use fu l tool which gained inc reas ing importance a f t e r the TMI in c id e n t . I t s use in plant an a ly s i s can help i d e n t i f y c r i t i c a l systems or ope ra t ions r equ i r ing

improved r e l i a b i l i t y . Analysis of a sp e c i f i c c r i t i c a l system or ope ra t ion would help in the decision-making process for poss ib le a l t e r n a t i v e s o lu t io n s . The q u a n t i t a t i v e r e s u l t s obtained from comprehensive p lant

an a ly s i s should s t i l l be regarded with caut ion because of the l a rge u n c e r t a i n t i e s involved. However, the cont inued development of PRA techniques i s encouraged. I t s expanded use in the l i c en s i ng process should

cont inue to be in v e s t ig a te d . The use of PRA techniques to ana lyse opera t ing exper ience and i d e n t i f y precursor s to more severe events should a l so cont inue to be developed.

9. Research and Studies

The inc iden t a t TMI i d e n t i f i e d se ve r a l a reas fo r ad d i t i o n a l r esearch

and s t u d i e s in nuc lea r s a f e t y , a l l of which a re now being in v e s t i g a te d . I t i s recommended th a t not only should these s t u d i es cont inue but o the r s which

may be d ic t a t e d by f u r t h e r ope r a t ion a l exper ience should be conducted. An increased and more open exchange of informat ion among research workers i s

a l so recommended in order to improve the ov er a l l l e v e l of nuc lea r sa fe ty .

An important outcome from the conduct of sa fe ty r e search should be

the implementation of new and /o r advanced knowledge i n to the des ign and opera t ion of new and e x i s t i n g p la n t s .

226 \PALABRICA

1 0 . I n t e r n a t io n a l Со-o pera t lon

The TMI Inciden t has demonstrated th a t a nuclea r Incident In one country may have i n t e r n a t i o n a l im pl i ca t ions . The exchange of s a f e t y - r e l a t e d

op er a t ion a l da ta along with sa fe t y and research informat ion should be enhanced through i n t e r n a t i o n a l co -opera t ion . Provis ions fo r rendering

a s s i s t a n c e in case of a nuclea r emergency should a l s o be e s t a b l i s h e d .

The eva lua t ion and formulat ion of appropr ia t e responses to the l e ssons learned from the TMI inc iden t r equ i re a d d i t i o n a l r esources and

s tu d ie s by a l l coun t r i e s wi th nuclear power programmes. In th i s regard, ad d i t i o n a l t e ch n ic a l a s s i s t a n c e for developing coun t r i e s from the IAEA may

be needed. This a s s i s t a n c e should take the form of informat ion exchange (meet ings, symposia and seminars) on appropr ia t e nuc lea r sa fe t y topics and

the conduct of missions and expert assignments.

The decontaminat ion and recovery of the TMI-2 nuclea r power p lant i s recognized as a p o t e n t i a l source of nuclea r s a fe ty informat ion which should

he valuable to a l l coun t r i e s with nuclea r power programmes.

IV. CONCLUDING REMARKS

The inc ide n t a t Three Mile I s land and the r e l a t e d follow-up

a c t i v i t i e s had a s i g n i f i c a n t impact in the r e a c t o r s a f e t y f i e l d throughout the world. Cert a in a reas where Improvements could be made to enhance rea c to r sa fe ty were i d e n t i f i e d .

The IAEA Technical Committee meeting provided an ex c e l l e n t oppor tun i ty fo r cou n t r i e s wi th nuclea r power programmes to exchange t h e i r TMI-related exper ience and to compare t h e i r a c t i on s . The t e chn ic a l document^ r e s u l t in g from the meeting should be o f p a r t i c u l a r i n t e r e s t for cou n t r i e s embarking on t h e i r f i r s t nuclea r power p r o je c t s , in terms of providing a u se fu l r e f e rence fo r s p e c i f i c TMI-related i s su es th a t need to be

considered in t h e i r nuclear programmes.

1 International Atomic Energy Agency, International Experience in the Implementation of the Lessons Learned from the Three Mile Island Incident, Technical Document № 294(1983).

/\

A R R E T S D ’U R G E N C E S U R V E N U S

S U R L E S T R A N C H E S R E P 9 0 0

D U P A R C E D F D E 1 9 7 9 A 1 9 8 2

P. C A S SE T T E , K. P A R K D é p a rte m e n t d ’ana ly se de sû re té ,C EA , In s t i tu t de p ro te c tio n e t de sû re té n u c léa ire , F o n ten ay -au x -R o ses

A. C A Y O LService de la p ro d u c tio n th e rm iq u e ,E le c tr ic ité de F ran ce ,Paris,

F ran ce

^ IAEA-SM-268/42

Abstract-Résumé

EMERGENCY SHUT-DOWNS OF THE 900 MW PWRs OF ELECTRICITE DE FRANCE FROM 1979 TO 1982.

Emergency shut-downs triggered by a reactor’s protection system give rise to transient safety conditions in the fuel and the primary circuit and their frequency serves as one indicator of the level of development of the unit and of the quality of its operation. On the basis of data collected from 1979 to 1982 on a total of 55 reactor-years accumulated with fairly new units in Electricité de France’s network of plants, a study was performed which showed the develop­ment of the average number of emergency shut-downs per unit as a function of the age of the units. A sharp reduction in the number of emergency shut-downs was revealed in the first three years examined, but this trend did not continue into 1982. The average number of emergency shut-downs per unit per year recorded in 1981 and 1982 on units in operation for more than six months after initial criticality was about 8.5. Problems with the steam generator feed were responsible for more than a quarter of the emergency shut-downs recorded in these two years. Emergency shut-downs resulting from turbine trips play an im portant role for the six units not equipped with a system whereby a turbine trip can occur without an emergency shut-down ensuing. Finally, testing was responsible for one-fifth of the emergency shut-downs in 1982. Human factors were the cause of one-third of all emergency shut-downs in 1981 and 1982. Various measures of a specific or general nature have been implemented to reduce the frequency of emergency shut-downs, and these take into account the results of the analysis carried out.

ARRETS D’URGENCE SURVENUS SUR LES TRANCHES REP 900 DU PARC EDF DE 1979 A 1982.

L’action «d’arrêt d’urgence» (AU), qui résulte d’une sollicitation du système de protection du réacteur constitue, sur le plan de la sûreté, un transitoire sur le combustible et le circuit primaire et, par sa fréquence, un indicateur parmi d’autres du niveau de mise au point de la tranche et de la qualité de son exploitation. A partir des éléments collectés sur les centrales du parc d’Electricité de France (EDF) entre 1979 et 1982 sur une population totale de 55 années- réacteur, constituée par des unités peu anciennes, une étude a été effectuée et a permis de

227

228 \ CASSETTE et al.

définir l’évolution du nombre moyen d’arrêt d’urgence par tranche en tenant compte de l’âge des tranches. Une importante réduction du nombre d’AU a pu ainsi être mise en évidence au cours des trois premières années considérées. Cette réduction ne s’est pas poursuivie en 1982.La valeur moyenne du nombre d’AU par tranche et par an, observée en 1981 et 1982 sur les tranches ayant plus de six mois de fonctionnement, après première divergence, est de 8,5 environ. Les problèmes liés à l’alimentation des générateurs de vapeur sont à l’origine de plus du quart des AU observés ces deux dernières années. Les AU faisant suite aux déclenchements turbine jouent un rôle im portant pour les six tranches non munies d’une logique de déclenchement turbine sans arrêt d’urgence. Enfin, les essais sont à l’origine du cinquième des AU survenus en 1982. Au niveau des causes, les facteurs humains sont à l’origine du tiers de la totalité des AU survenus en 1981 et 1982. Différentes actions spécifiques ou d’ordre général ont été entreprises qui prennent en compte les résultats de l’analyse effectuée en vue de réduire la fréquence des arrêts d’urgence.

1. IN T R O D U C T IO N

L’a rrê t d ’u rg en ce (A U ) d ’u n ré a c te u r n u c léa ire , q u i ré su lte d ’u n e so llic ita tio n d u sy s tèm e de p ro te c tio n , se p ré sen te sous tro is aspects:— il c o n s titu e to u t d ’ab o rd u n e p e r te de d isp o n ib ilité de la tra n c h e ; l’in d isp o n ib ilité

fo r tu ite ré s u lta n t des a rrê ts d ’u rgence observés su r les tran ch es en e x p lo ita tio n en F ra n c e e s t en m o y e n n e de 5 h eu res ;

— il c o n d u it à u n tra n s ito ire , en règle généra le p eu sévère, su r le co m b u s tib le e tle c irc u it p rim a ire , tra n s ito ire d o n t il co n v ien t de lim ite r le n o m b re à u n e va leu r in fé rie u re à celle p rise en c o m p te p o u r la c o n c e p tio n de la ch au d iè re n uc léa ire (4 0 0 év én em en ts);

— en fin , le n o m b re d ’a rrê ts d ’u rgence su rvenus su r u n e tra n c h e p e u t ê tre considéré co m m e u n in d ic a te u r , p a rm i d’au tre s , de la f iab ilité au sens large de celle ci e td u n iveau de m ise au p o in t de ses co m p o san ts ou de la q u a lité de son e x p lo ita tio n .

Ces d if fé re n ts asp ec ts de l’év én em en t a rrê t d ’u rg en ce c o n d u ise n t l ’e x p lo ita n t, co m m e l’a u to r ité de sû re té , à e ffe c tu e r des analyses de n a tu re s ta tis tiq u e p o r ta n t su r la fréq u en ce des A U , leu rs causes p rin c ip a les e t, le cas é ch é a n t, à d é fin ir des m esu res co rrec tiv es v isan t à réd u ire l’o ccu ren ce de ce t év én em en t.

2. M E T H O D E D E T R A V A IL U T IL IS E E P O U R L ’A N A L Y S E

2.1 . C o llec te des a rrê ts d ’u rg en ce

P o u r les années 1981 e t 1982 , les d o n n ées cen tra lisées dans u n fich ie r in fo r­m atisé en co u rs de c o n s t i tu tio n dans c e tte p é rio d e , e t a c tu e lle m e n t to ta le m e n t o p é ra tio n n e l, o n t p u ê tre u tilisées. E lles o n t é té c o m p lé tée s en ta n t q u e de b eso in p a r l’ana ly se des d if fé re n ts d o c u m e n ts occasionne ls ém is p a r les cen tra le s p o u r

IAEA-SM-268/42 ^

T A B L E A U I. B IL A N D E S A R R E T S D ’U R G E N C E

229

Annéecalendaire

Tranche en service

Tranchesdemarrées au cours de l’année

Total en années-réacteur

1979 4 2 5,25

1980 6 5 9,8

1981 13 8 18,4

1982 21 2 21,5

to u s les passages à charge n u lle e t les in c id e n ts q u a lifiés de s ign ifica tifs (les A U , h o rm is ceux p ro v o q u é s p a r u n d é c le n c h e m e n t de la tu rb in e , so n t décla rés aux a u to r ité s de sû re té en ta n t q u ’in c id e n ts s ign ifica tifs e t fo n t a insi l’o b je t d ’u n ra p p o r t c irc o n s ta n c ié é tab li p a r la cen tra le ) .

P o u r les an n ées a n té r ieu re s , les d o n n ées re la tives aux A U o n t é té co llec tées à l’a ide d ’u n q u e s tio n n a ire tran sm is au x cen tra les .

Les essais d ’a rrê t d ’u rgence n ’o n t n a tu re lle m e n t pas é té com p tab ilisés .La co lle c te a p o r té su r u n en sem b le de 55 a n n ées-réac teu r q u i se d éc o m p o se n t

co m m e in d iq u é au ta b le a u I.

Il fa u t aussi n o te r q u e les d e u x p rem iè res tra n c h e s R E P 9 0 0 d u p arc (F essen h e im 1-2) o n t d ivergé en 1977.

D ans l’en sem b le , le p a rc frança is se p ré se n te co m m e u n g ro u p e de tra n c h e s p eu an c iennes e t trè s sem b lab les su r le p la n de la co n c e p tio n .

2 .1 . T ra ite m e n t des in fo rm a tio n s

Les ré su lta ts o b te n u s o n t fa it l’o b je t d ’u n tra ite m e n t m an u e l (u n o u til in fo rm a tisé d ’ana ly se s ta tis tiq u e e s t en co u rs de d é fin itio n ).

Ce tr a ite m e n t a u tilisé les n o tio n s su ivan tes:1) D é te rm in a tio n d u n o m b re d ’A U p a r tra n c h e p o u r u n e an n ée ca len d a ire , en te n a n t c o m p te , le cas é c h é a n t, d u te m p s de fo n c t io n n e m e n t ré a c te u r c ritiq u e .D ans ce d e rn ie r cas, la n o tio n d ’A U p a r m illie r d ’h eu res de fo n c tio n n e m e n t de ré a c te u r c r i tiq u e a é té u tilisée . C e tte n o tio n p e rm e t de co m p a re r des tran ch es , ou g ro u p es de tra n c h e s , e n tre eu x d ’u n e an n ée su r l’au tre en in té g ra n t des tem p s d ’a rrê ts so u v en t trè s variables.

230 CASSETTE et al.

2 ) D é fin itio n de p o s te s d ’A U re g ro u p a n t des sy s tèm es, o u sous-systèm es, où le d é fa u t in i t ia te u r de l ’A U s’es t p ro d u it que lles q u e so ie n t la o u les causes du d é fa u t. Ces p o s te s d ’A U o n t é té m is en év idence ; ce so n t:

— a lim e n ta tio n s é lec triq u es ,— c o n trô le co m m an d e des grappes,— tu rb o -p o m p e s a lim en ta ires ,— a lim e n ta tio n des g én é ra teu rs de vapeur,— d é c le n c h e m e n t tu rb in e ,— divers.

3 ) Les A U se p ro d u ise n t lo rs d ’essais q u i o n t é té m is en év idence d an s u n p o s te séparé.

4 ) Les causes o rig ines o n t é té reg ro u p ées se lon les ca tégo ries su ivan tes:— avarie d e m atérie ls ,— d é fa u t de p e rfo rm a n c e re g ro u p a n t les p h é n o m è n e s ex té r ieu rs à la tra n c h e e t

les d é fa u ts de fo n c t io n n e m e n t de systèm es,— fa c te u rs h um ains.

2 .3 . R em arq u e s généra les c o n c e rn a n t l ’éch an tillo n n ag e

Le n o m b re to ta l d ’év én em en ts co llec té s a é té d ’en v iro n 7 2 0 A U p o r ta n t su r 55 an n ées-réac teu r. Il n ’e s t c e p e n d a n t pas p o ss ib le de ti re r de ces d eu x ch iffres u n e v a leu r m o y e n n e e x p rim é e en A U p a r an n é e -ré a c te u r en ra ison de la fo r te in h o m o g é n é ité d u n o m b re d ’A U p a r ré a c te u r observée au co u rs des années 1979 à 1981 .

P a r a illeurs, l’in c id en ce de l’âge des tra n c h e s su r le n o m b re d ’A U p a r an e t p a r tra n c h e n ’a p u ê tre m ise en év idence en ra ison d ’u n e p a r t d u tro p fa ib le é ca rt e x is ta n t d an s les m ises en service des tran ch es e t, d ’a u tre p a r t , d u fa it q u e les six tra n c h e s les p lu s an c ie n n es n e so n t pas éq u ip ée s d ’u n e lo g iq u e p e rm e tta n t d ’év ite r l’a rrê t d ’u rg en ce en cas de d é c le n c h e m e n t tu rb in e .

3. R E S U L T A T S O B S E R V E S

3.1 . E v o lu tio n g loba le

A u co u rs des an n ées 1979 à 1981 , o n a p u c o n s ta te r u n e ré d u c tio n sensib le d u n o m b re m o y e n d ’a rrê ts d ’u rg en ce p a r an e t p a r tra n c h e o u p a r m illie r d ’heu res de fo n c t io n n e m e n t ré a c te u r c r itiq u e su rvenus su r les tran ch es d u p a rc R EP. C e tte ré d u c tio n co rre sp o n d à l’é lim in a tio n progressive e t généra lisée p o u r les nouvelles tra n c h e s des d é fa u ts de jeu n esse de to u te s so rtes.

C e tte ré d u c tio n ne s’es t pas p o u rsu iv ie en 1982 , m algré la m ise en oeuvre de

m esu res co rrec tiv es v isan t à ré d u ire ce rta in e s causes d ’A U (m o d if ic a tio n des

IAEA-SM-268/42 231

AU/1000 h

FIG. 1. Nombre d'arrêts d'urgence (A U) pour 1 ООО h de réacteur critique. Trait plein: ensemble du parc. Pointillé: tranches de moins d’un an. O: nombre de tranches en service.

log iques de p ro te c tio n des tu rb o -p o m p e s a lim en ta ire s , p a r ex em p le ) e t la m ise en service d ’u n n o m b re lim ité de n ouve lles u n ité s .q u ’elle n ’e s t pas trè s sign ifica tive su r le p la n s ta tis tiq u e , p ro v ie n t e ssen tie llem en t des d if fé re n ts p ro b lèm es re n c o n tré s su r p lu s ieu rs tra n c h e s e t q u i o n t c o n d u it à des in d isp o n ib ilité s p a rtie lle s o u to ta le s im p o rta n te s . P a r ailleurs, de n o m b reu se s tran ch es d ém arrée s en 1980 e t 1981 o n t su b i des a rrê ts p ro g ram m és im p o rta n ts co rre sp o n d a n t à la p rem iè re v is ite co m p lè te d u c irc u it p rim aire .

D e fa it, u n a rrê t de trè s lo n g u e d u rée e n tra în e u n e a u g m e n ta tio n très sensib le d u n o m b re d ’A U observé su r u n e tran ch e .

Les figures 1 e t 2 re p ré se n te n t l’év o lu tio n c o n s ta té e de 1979 à 1982 d u n o m b re d ’A U p a r m illie r d ’h eu re s de fo n c t io n n e m e n t c r itiq u e ou p a r a n n ée -réac teu r ta n t p o u r l’en sem b le d u p a rc q u e p o u r les tra n c h e s a y a n t p lu s d ’u n an de fo n c t io n ­n e m e n t à la fin d e l’an n ée considérée .

232 CASSETTE et al.

AU/tr. an

30

25

20

15

10

i I © ®

1979 1980 1981 1982 Année

FIG.2. Nombre d’arrêts d’urgence (AU) par tranche par an. Trait plein: ensemble du parc. Pointillé: tranches de moins d’un an. O: nombre de tranches affectées par an.

L a d if fé ren ce e n tre les d eu x co u rb es f ig u ran t sur ch aq u e figu re illu s tre le fa it q u e , ap rès q u e lq u e s m o is d e fo n c t io n n e m e n t ap rès p re m iè re d ivergence , o n p e u t c o n s ta te r , su r u n e tra n c h e , u n e n e t te ré d u c tio n de la fréq u en ce des a rrê ts d ’u rgence .

La figure 3 rap p e lle l’év o lu tio n du n o m b re d ’A U p a r m illie r d ’h eu re s de fo n c t io n n e m e n t ré a c te u r c r i tiq u e p o u r les tra n c h e s a y a n t p lu s d ’u n an d ’âge dans l’an n ée co n sid é rée en in d iq u a n t les valeurs ex trê m e s observées. C e tte figure d o n n e u n e in d ic a tio n de la d isp e rs io n des résu lta ts .

Le n o m b re d ’A U observé p a r an e t p a r tra n c h e en 1981 e t 1982 , de l’o rd re de 8 ,5 p o u r les tra n c h e s a y a n t passé le cap de la p rem iè re année , a p p a ra î t com m e su p é r ie u r à ce lu i observé su r u n éch an tillo n n ag e co m p arab le en âge de R E P W estinghouse au x E ta ts-U n is en 1 9 8 0 —81 (6 ,2 A U /a n n é e -ré a c te u r) m ais in fé rie u re à ce lu i de la p é rio d e 1 9 7 5 —77 (1 2 A U p a r an e t p a r tra n c h e en v iron ).

IAEA-SM-268/42 233

AU/1000 h

1979 1980 1981 1982 Année

FIG.3. Nombre d’arrêts d’urgence (A U) pour 1000 h de réacteur critique pour les tranches de moins d’un an. Trait plein: moyenne. Traits pointillés: valeurs extrêmes observées.

3 .2 . P rin c ip au x p o ste s d ’A U e t causes

3.2.1. Postes d ’AU

A fin de p o u v o ir d é fin ir la nécess ité e t la n a tu re des ac tio n s co rrec tiv es à e n tre p re n d re , les A U recensés o n t é té déco m p o sés en d if fé re n ts p o s te s reg ro u p a n t les sy s tèm es ou sous-sy stèm es o ù s’e s t p ro d u ite la d éfa illan ce à l’o rig ine de l’AU.

Les figures 4 à 9 in d iq u e n t les év o lu tio n s d u p o u rc e n ta g e de ch acu n de ces p o s te s vis-à-vis d u n o m b re to ta l d ’A U observés ainsi que le n o m b re d ’A U p a r tr a n c h e e t p a r an re la ti f au p o s te considéré .

234 CASSETTE et al.

AU/tr. an

FIG.4. Alimentations électriques.

AU/tr. an

FIG.5. Contrôle commande des grappes.

AU/tr. an

FIG. 6. Turbo-pompes alimentaires.

%IAEA-SM-268/42

FIG. 7. Alimentation des générateurs de vapeur.

FIG.8. Déclenchement turbine (ensemble du parc).

236 CASSETTE et al.

% AU/tr. an

1979 1980 1981 1982 Année

FIG.9. Déclenchement turbine selon le type de tranches.- CP1-CP2 (déclenchement sans arrêt d’urgence:

O: % par rapport au nombre total d’AU +: nombre d’A U par tranche par an

— Fessenheim et Bugey•: % par rapport au nombre total d'AU ,X: nombre d’A U par tranche par an.

1) A lim e n ta tio n s é le c triq u es (fíg .4 ):

S o n t co m p tab ilisé s d an s ce p o ste les d é fau ts de to u te n a tu re su rvenus su r des sy s tèm es d ’a lim e n ta tio n é lec triq u e c o u ra n t c o n tin u ou a lte rn a tif . D ’une faço n généra le , ce p o s te jo u e u n rô le fa ib le su r le n o m b re to ta l des a rrê ts d ’u rgence e t a u c u n e a c tio n co rrec tiv e n ’est a u jo u rd ’h u i envisagée.

2) S y stèm e de c o n trô le co m m an d e des g rappes (fig .5 ):

Les d é fa u ts à l’o rig ine de ces A U p ro v ie n n e n t e ssen tie llem en t des m o d u les é le c tro n iq u e s u tilisés p o u r le sy s tèm e de rég u la tio n . Ces d é fa u ts e n tr a în e n t des in tro d u c tio n s in tem p es tiv e s de g ro u p es de b a rres e t p a r ta n t l’a rrê t d ’u rg en ce p a r d fl/d t.

IAEA-SM-268/42 237

Ce p o s te a p p a ra î t su r les tra n c h e s françaises n e t te m e n t p lu s im p o r ta n t q u e son éq u iv a len t p o u r les tra n c h e s R E P W estinghouse au x E ta ts-U nis.

Des a c tio n s co rrec tiv es s o n t p rogram m ées.

3) T u rb o -p o m p e s a lim en ta ire s (f ig .6 ):

T o u s les A U de ce p o ste , engend rés p a r le signal « très bas n iveau G V », so n t liés au d é c le n c h e m e n t d ’u n e o u des d eu x tu rb o -p o m p e s a lim en ta ire s (T PA ).

D eux cas so n t possib les:— u n e seu l T P A e s t en service d o n t le d é c le n c h e m e n t e n tra în e Г A U ;— les d eu x T P A so n t en service e t le d éc le n ch em en t de l’u n e e n tra în e la m o n té e en v itesse de l’a u tre e t so n d é c le n c h e m e n t (su rd é b it o u N PSH ).

Le d e u x iè m e cas é ta i t à l’o rig ine d ’env iron la m o itié des A U de ce p o s te re­censés su r l’en sem b le d u p a rc en 1981.

Des ac tio n s co rrec tives , m ises en oeuvre à p a r t ir de la fin 1981 e t généralisées à l’en sem b le d u p a rc vers la m i-82 , o n t e n tra în é u n e trè s n e t te ré d u c tio n de ce p o s te p o u r la d e rn iè re année prise en co m p te .

4 ) A lim e n ta tio n des g én é ra teu rs de v a p e u r (fig .7 ):

Les A U générés p a r u n n iveau G V , n o n co rré lés avec u n d é fa u t p ro v e n a n t des T P A o u u n e a u tre cause e x té r ie u re au sy s tèm e d ’a lim e n ta tio n des G V , ap p ara issen t dans c e tte ca tégorie .

Les causes fo n d âm en ta le s des A U ainsi recensés p ro v ie n n e n t de:— d é fa u ts su r les vannes d ’eau a lim en ta ire ;— d ifficu lté s , liées o u n o n à l’o p é ra te u r , re n c o n tré e s lo rs d u passage « p e tit d é b it — gros d éb it» ;— d ifficu lté s id e n tiq u e s lo rs d u passage a lim e n ta tio n n o rm a le -a lim e n ta tio n de secou rs des GV.

Ce p o s te est a c tu e lle m e n t le p lu s lo u rd dans le b ilan des A U e t u n e ac tio n co rrec tiv e e s t en co u rs d ’é tu d e .

5) D éc len ch em en t tu rb in e (fig. 8 e t 9):

T ous les A U a y a n t é té p ro v o q u és p a r le signal « d éc le n ch em en t tu rb in e» , que lle q u ’en so it la cause , so n t c o m p tab ilisé s d an s ce p o ste .

Il fa u t c e p e n d a n t n o te r q u e les tra n c h e s coup lées au réseau à p a r t ir de l’an n ée 1980 so n t d o té e s d ’u n e log ique p e rm e tta n t, q u a n d le c o n d e n se u r e s t d isp o n ib le , d ’év ite r Г A U en cas de d é c le n c h e m e n t tu rb in e . P o u r ces tra n c h e s (1 7 en 1982), les A U p a r d é c le n c h e m e n t tu rb in e n e c o n s t i tu e n t en 1981 e t 1982 q u e 15% en v iro n du n o m b re to ta l des A U observés au lieu de 40% su r les tran ch es n o n d o té e s de c e tte lo g iq u e (v o ir fig.9).

238 CASSETTE et al.

AU/tr. an

_1_________ I_________ __________I_________________ ,1979 1980 1981 1982 Année

FIG. 10. Essais.

3.2.2. Essais

T o u s les A U su rvenus, que ls q u e so ie n t la cause ou le p o s te a ffec té a lo rs q u ’u n essai é ta i t en co u rs su r u n e tra n c h e , so n t co m p tab ilisé s dans ce p o s te (fig. 10).Les valeu rs in d iq u ées p o u r les années 1979 e t 1980 s o n t c e r ta in e m e n t sous- estim ées.

3 .3 . R é p a r ti tio n p a r causes

U ne ré p a r ti t io n p a r causes a é té e f fe c tu é e p o u r les A U recensés en 1981 e t1982.

3.3.1. Facteurs humains

U ne e rre u r h u m a in e e s t à l’o rig ine de 38% de la to ta li té des A U observés; c ep e n d a n t, la q u a s i- to ta lité (8 su r 9 ) des A U su rv en an t lo rs d ’essais est d u e à u n e cause de ce ty p e .

Les fac teu rs h u m a in s en ra p p o r t avec le re sp e c t des règles de l’o rg an isa tio n de la q u a li té dans la c e n tra le , te ls q u ’e rre u r d an s la ré d a c tio n d ’u n d o c u m e n t de c o n d u ite , a c tio n de c o n trô le n o n e ffe c tu é e , cu m u l d ’ac tio n s in co m p a tib le s , c o n s t i tu e n t m o in s de la m o itié des causes d ’A U p a r e rre u r h u m ain e .

IAEA-SM-268/42 239

3.3.2. Avaries de matériels

Les avaries o u défa illan ces d e m a té rie ls s o n t à l’o rig ine de 37% des A U observés. E lles jo u e n t u n rô le p ré p o n d é ra n t p o u r les A U récap itu lé s dans le p o s te c o n trô le c o m m a n d e des grappes.

3.3.3. Défauts de performance

Les d é fa u ts de fo n c t io n n e m e n t so n t à l’o rig ine d u q u a r t des A U observés.

4. A C T IO N S C O R R E C T IV E S E N C O U R S O U P R E V U E S

Des a c tio n s sp éc ifiq u es so n t a c tu e lle m e n t engagées q u i v isen t à réd u ire le n o m b re d ’AU.1 ) M ise en p lace , s u r les tra n c h e s n o n équ ipées, d ’u n e lo g iq u e de d é c le n c h e m e n t tu rb in e sans A U p e rm e tta n t d ’év ite r l’A U en cas de d é c le n c h e m e n t tu rb in e si la p u issan ce e s t in fé rie u re à 30%.2) L ’é tu d e dé ta illée des causes des A U p a r a lim e n ta tio n des G V . C e tte é tu d e a fa it a p p a ra î tr e q u ’à l’o rig ine de ces évén em en ts , q u i se p ro d u ise n t lo rs des m o n té e s en p u issan ce à basse charge (0 à 20% PN ), on tro u v e u n e ce rta in e in su f­fisance des c h a în e s de rég u la tio n (im p réc is io n des m esu res e t rép o n se le n te ) co m b in ée avec des ré a c tio n s m al a d ap té e s des o p é ra teu rs . D e fa it, la s i tu a tio n a c tu e lle n écess ite u n e tro p g ran d e h a b ile té de la p a r t des o p é ra teu rs . Les ac tio n s co rrec tiv es p révues p o r te n t en c o n séq u en ce su r u n e a c tio n de sen s ib ilisa tio n des o p é ra te u rs ( fo rm a tio n péd ag o g iq u e e t en se ig n em en t assisté p a r o rd in a te u r ) e t l ’u ti lis a tio n p o u r les ch a în e s de rég u la tio n d ’u n e te ch n o lo g ie p lu s avancée.3 ) A naly se d é ta illé e des d é fa u ts observés su r les m o d u le s é le c tro n iq u es u tilisés p o u r le c o n trô le co m m an d e des b a rre s de co m m an d e .

S ur u n a u tre p lan , des a c tio n s générales o n t é té engagées p a r E D F q u i v isen t à ré d u ire l’in f lu en ce des fa c te u rs h u m a in s su r les in c id e n ts e t, p a r ta n t, les a rrê ts d ’u rgence.

C es a c tio n s so n t p ré se n té e s d an s les m ém o ires IA E A -S M -268 /58 e t SM -268/61 (p ré se n ts c o m p te s ren d u s , v o l.I).

5. C O N C L U SIO N

L ’é tu d e des a rrê ts d ’u rg en ce su rv en u s su r les tran ch es R E P de 9 0 0 MWe d u p a rc E D F e n tre 1979 e t 1982 m o n tre q u e la fréq u en ce an n u e lle des a rrê ts d ’u rg en ce e s t a c tu e lle m e n t in fé rie u re à 10 p a r an p o u r les tra n c h e s a y a n t u n tem p s

240 CASSETTE et al.

de fo n c t io n n e m e n t su p é r ie u r à six m ois. C e tte v a leu r e s t a c tu e lle m e n t enve loppée p a r le n o m b re de tra n s ito ire s de ce ty p e pris en c o m p te à la c o n c e p tio n de la cen tra le e t re s te c o h é re n te avec la fréq u en ce des a rrê ts d ’u rg en ce co n sid érés dans le ca lcu l de p ro b a b ili té d ’o ccu rren ce des ATW S.

C e tte é tu d e m e t en év idence les causes p rin c ip a le s a y a n t c o n d u it à la so llic ita ­tio n de la p ro te c tio n « a rrê t d ’urgence» e t p e rm e t de d é fin ir les m esures co rrec tives de n a tu re à en d im in u e r la fréq u en ce .

La fré q u e n c e des a rrê ts d ’u rg en ce e s t u n in d ic a te u r , p a rm i d ’au tre s , p e rm e tta n t de ju g e r d u n iveau de m ise au p o in t des c o m p o sa n ts des cen tra le s e t de la q u a lité de le u r e x p lo ita tio n . A ce t i tr e , c’e s t u n fa c te u r q u i est suivi avec a t te n t io n p a r l’e x p lo i ta n t e t l’a u to r ité de sû re té .

IAEA-SM-268/90

S E G U I M I E N T O , E N U N P A I S I M P O R T A D O R ,

D E L A E X P L O T A C I O N D E U N A C E N T R A L N U C L E A R

C O N P R O B L E M A S D E D I S E Ñ O :

C E N T R A L N U C L E A R D E A L M A R A Z

J. R E IGC onse jo d e S egu ridad N u clear,M adrid , E spaña

A b strac t-R esu m en

MONITORING OF THE OPERATION OF A NUCLEAR POWER STATION WITH DESIGN PROBLEMS IN AN IMPORTING COUNTRY THE ALMARAZ POWER STATION.

The purpose of this paper is to describe the regulatory activities carried out in Spain as a result of the design problem occurring in the steam generators during operation of Unit I of the Almaraz nuclear power station. First, a brief introduction is given to the operating history and characteristics of Unit I of Almaraz. Particular attention is paid to the specific licences issued subsequent to commercial operation which place limitations on the operation of the station and to the operational incidents of which the Nuclear Safety Council (CSN) has been notified. Next, a description is provided of the safety evaluation carried out by the CSN. Three aspects merit particular attention: methodology, evaluation and conclusions. The methodology applied by an importing country is normally based on that of the country of origin of the design, so that the overall evaluation by the NRC has been considered sufficiently representative of aspects specific to the Almaraz power station. In this regard the importance of international collaboration is clearly seen as a principal instrument for performing the evaluation. In the evaluation a distinction is made between general and specific aspects and between inspection programmes and quality assurance requirements. In addition, the conclusions leading to the requirement of the imposition of additional limitations on the operating licence are stated.Apart from the safety evaluation carried out by the CSN, other regulatory activities have been performed over this two-year period. These activities, which include site inspections, audits of the principal supplier company, other independent calculations and so on, are described.Lastly, the paper refers to the lessons learned from the operation of the above-mentioned unit, which are immediately applicable to other Spanish nuclear power stations.

SEGUIMIENTO, EN UN PAIS IMPORTADOR, DE LA EXPLOTACION DE UNA CENTRAL NUCLEAR CON PROBLEMAS DE DISEÑO: CENTRAL NUCLEAR DE ALMARAZ.

El objeto de este trabajo es exponer las actividades de reglamentación realizadas en España a raíz del problema de diseño surgido en los generadores de vapor durante la operación de la Unidad I de la central nuclear de Almaraz. Para comenzar, se hace una breve introducción sobre el historial de explotación y características de la Unidad I de Almaraz. Se aborda con especial atención el tema de los permisos específicos concedidos después de la explotación comercial imponiendo limitaciones a la operación de la central, y los incidentes operacionales notificados al Consejo de Seguridad Nuclear (CSN). Seguidamente se describe la evaluación de seguridad realizada por el CSN. Tres aspectos merecen especial atención: metodología,

241

242 REIG

evaluación y conclusiones. La metodología utilizada por un país importador se ajusta normal­mente a la del país de origen del proyecto, por lo que la evaluación global de la NRC ha sido considerada adecuadamente junto con los aspectos específicos de la central nuclear de Almaraz.A este respecto, se resalta la importancia de la colaboración internacional como instrumento principal para llevar a cabo la evaluación. En ésta se distingue entre aspectos generales y aspectos específicos, como los programas de inspección y los requisitos de garantía de calidad. Por último, se señalan las conclusiones que exigen imponer limitaciones adicionales al permiso de explotación. Además de la evaluación de seguridad realizada por el CSN, se han llevado a cabo, durante este período de dos años, otras actividades reguladoras. Se describen aquí estas actividades, que incluyen las inspecciones del emplazamiento, las auditorías de la principal empresa suminis­tradora, otros cálculos independientes, etc. Para finalizar, este trabajo trata de las enseñanzas extraídas de la explotación de esta Unidad, que son inmediatamente aplicables a otras centrales nucleares españolas.

1. IN T R O D U C C IO N

El o b je to de e s te tra b a jo es e x p o n e r las ac tiv idades llevadas a cab o p o r el o rg an ism o re g u la d o r en E spaña , co m o co n secu en c ia del p ro b lem a de d iseño su rg ido en los g en e rad o res de v a p o r d u ra n te la o p e rac ió n de la U n id ad I de la c en tra l n u c le a r (C N ) de A lm araz .

A d ife ren c ia de los p ro b lem as p ro p ia m e n te o p e rac io n a les d eb id o s a fac to res h u m a n o s , p ro c e d im ie n to s de o p e rac ió n , g a ra n t ía de ca lidad en e x p lo ta c ió n , e tc ., el in c id e n te de los g en erad o res de v ap o r ex ig ió u n p la n te a m ie n to d ife re n te p o r p a rte del C o nse jo de S egu ridad N u c lea r (C SN ), y a que se tra ta b a de un p ro b lem a g enérico de u n d iseñ o n o d e sa rro llad o en n u e s tro p a ís . L a cap ac id ad del o rgan ism o re g u la d o r de u n p a ís im p o r ta d o r está m u ch as veces co n d ic io n ad a p o r las d ificu ltad es q u e e n tra ñ a el seg u im ien to de u n a m o d ific ac ió n de d iseñ o fu e ra de sus fro n te ra s .P o r o tro lad o , en el caso de E sp añ a , el h ech o de q u e n in g u n a ce n tra l de E E U U se e n c o n tra ra en e x p lo ta c ió n c o n el m ism o p ro b lem a su p u so u n a d ificu ltad ad ic io n a l, p u e s to q u e en n u e s tro p a ís , co n recu rso s h u m a n o s lim itad o s en el c am p o reg u lad o r, se tie n e n m u y en c u e n ta las a c tu a c io n es del c u e rp o reg u lad o r d e l p a ís de o rigen del p ro y e c to , en este caso la N R C .

El a su n to a d q u ir ió g ran im p o rta n c ia en E spaña , y a q u e a fec tab a a seis u n id ad es q u e in c o rp o ra b a n el m ism o m o d e lo de g en e rad o r de vap o r: A lm araz I у II, A seó I у II y L em ó n iz I у II. E stas c o n s titu y e n la segunda gen erac ió n de cen tra le s , p rev istas p a ra e n tra r en e x p lo ta c ió n co m erc ia l en el p e r ío d o de 1980 s a 1984 .

IAEA-SM-268/90 243

C U A D R O I. C A R A C T E R IS T IC A S T E C N IC A S D E LA C E N T R A L N U C L E A R D E A L M A R A Z

Concepto Característica

Tipo de reactor PWR, diseño Westinghouse

Potencia térmica 2696 MW(t)

Potencia eléctrica neta 930 MW(e)

Número de lazos 3

Combustible UO2 enriquecido

Número de elementos combustibles 157

Número de barras de control 48

Generador de vapor Westinghouse modelo D3

Temperatura RCS

entrada a la vasija 288°Csalida de la vasija 328°C

Presión RCS 156kg/cm2

Caudal RCS 47 X 106 kg/h

Tipo contención Cilindro de hormigón con cúpula semiesférica

Refrigeracióir Circuito abierto al embalse de Arrocampo(rio Tajo)

2. C E N T R A L N U C L E A R D E A L M A R A Z . C A R A C T E R IS T IC A S T EC N IC A SE H IS T O R IA L D E E X P L O T A C IO N

L a c e n tra l n u c lea r de A lm araz (C N A ) c o n s ta d e d o s u n id a d e s gem elas del tip o de agua ligera a p res ió n (PW R ) de d iseño W estinghouse , co n u n a p o te n c ia e léc trica n e ta de 9 3 0 M W (e) cada u na . El C u ad ro I recoge las p rin c ip a les c a ra c te r ís tic a s té cn ica s de la U n id ad I de la CNA.

P o r lo q u e re sp e c ta a la licencia , la a u to r iz a c ió n prev ia fue c o n ced id a en o c tu b re de 1971 y el p e rm iso de c o n s tru c c ió n en ju l io de 1973 . La CN A o b tu v o el p e rm iso de e x p lo ta c ió n p ro v is iona l (PE P) el 13 de o c tu b re de 1 980 ; c o n éste se a u to r iz a en n u e s tro p a ís a ca rg a r el n ú c leo y rea liza r las p ru eb as nuc lea res . E n el C u ad ro II se reco g en los p rin c ip a les h ito s , desde la co n ces ió n del P E P h a s ta la e x p lo ta c ió n co m erc ia l en ju lio de 1981 , así co m o el fa c to r de carga y la en e rg ía e léc trica gen erad a h a s ta feb re ro del 83.

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C U A D R O II. H IT O S P R IN C IP A L E S E N LA F A S E D E A R R A N Q U E D E LA C E N T R A L N U C L E A R D E A L M A R A Z

Hitos Fechas

Concesión del permiso de explotación provisional 13.10.80

Carga del núcleo 24.10.80 al 29.10.80

Pruebas parada fría 3.11.80 al 19.1.81

Pruebas parada caliente 24.1.81 al 5.4.81

Criticidad inicial 5.4.81

Pruebas a cero potencia 5.4.81 al 30.4.81

Pruebas hasta el 30% de potencia 1.5.81 al 23.5.81

Pruebas al 50% de potencia 28.5.81 al 7.6.81

Pruebas al 75% de potencia 29.6.81 al 8.7.81

Pruebas al 90% de potencia 8.7.81 al 10.7.81

Pruebas al 100% de potencia 10.7.81 (sin finalizar)

Energía generada hasta el 28.2.83 5133 GW h

Factor de carga 35,96

El 21 de o c tu b re de 1981 se d e te c tó u n a fuga en u n o de los g en erad o res de v ap o r de la U n id ad 3 de la CN de R inghals en Suecia . La in specc ión de los tu b o s de los g en erad o res de v a p o r reveló la ex is ten c ia de u n desgaste s ign ifica tivo de a lgunos tu b o s en la z o n a f re n te a la to b e ra de agua de a lim en tac ió n p rin c ip a l, ap rec ián d o se en u n o de ellos u n a ro tu ra de 4 m m de d iám e tro .

A p ro p u e s ta de W estinghouse , el d ía 2 de n o v iem b re se e fe c tu ó u n a p a rad a fr ía en la U n id a d I d e la C N A . L a in sp ecc ió n de los tu b o s de los gen erad o res de v ap o r re fle jó la ex is ten c ia d e l m ism o p ro b lem a d e te c ta d o en R inghals-3 .

L os re su lta d o s o b te n id o s en las in sp ecc io n es e fec tu ad as en las cen tra le s de R inghals-3 y A lm araz I c o n d u je ro n a la co n c lu s ió n de que se tr a ta b a d e u n d e fe c to gen érico del p ro y e c to de lo s g en e rad o res de v ap o r W estinghouse , m o d e lo D. El d e fe c to c o n s is tía en la v ib rac ió n de los tu b o s p ró x im o s a las p lacas d e ch o q u e , d e b id o a la d is tr ib u c ió n in c o r re c ta del caudal de agua de a lim e n ta c ió n (FW ) en la z o n a del p re c a le n ta d o r . La v ib rac ió n de los tu b o s c o n tra sus p lacas so p o rte o casio n ab a , en c ie rta s co n d ic io n es d e o p e rac ió n , el ad e lg a zam ien to de la p a red de d ichos tu b o s .

IAEA-SM-268/90 245

C U A D R O III. M E D ID A S D E L IC E N C IA T O M A D A S E N R E L A C IO N C O N LO S G E N E R A D O R E S D E V A PO R D E LA C E N T R A L N U C L E A R D E A L M A R A Z - U N ID A D I

Fecha Medida

3.11.81 ParadaMétodo diferencial de corrientes inducidas (ECT) 39 tubos taponados 2 tubos extraídos

20.12.81 Permiso de operación al 30% de potencia (tobera agua alimentación auxiliar (AFW))

7.1.82 Permiso de 1500 h al 50% caudal y pico de 40 h al 100% caudal (tobera agua alimentación principal (MFW))

11.3.82 ParadaMétodo diferencial y absoluto de ECT 2 tubos extraídos

31.3.82 Autorización modificación para alimentar toberas MFW y AFW

20.4.82 Permiso de 1500 h al 50% caudal (tobera MFW)

7.7.82 Prórroga del permiso hasta 2000 h

24.7.82 ParadaMétodo diferencial y absoluto de ECT

18.8.82 Permiso de 4000 h al 50% caudal (tobera MFW) y pico de 75 h al 63% (50/13) (Toberas MFW/AFW)

3.3.83 Prórroga de 840 h al 50% caudal

8.3.83 Solicitud de modificación de los generadores de vapor

E ste h e c h o ex ig ió , e n tre o tr a s ac tu a c io n es , la de im p o n e r lim itac io n es a la e x p lo ta c ió n de la c en tra l. A p a r t ir de en to n ce s se su ced en p a ra la U n idad I de la C N A u n a serie d e permisos específicos de explotación q u e tien en p o r o b je to re d u c ir las v ib rac io n es d e los tu b o s h a s ta u n nivel q u e p e rm ita g a ran tiz a r la in teg rid ad de lo s m ism os. L as co n d ic io n es inc lu idas en los m en c io n ad o s perm isos h an id o ev o lu c io n an d o a m ed id a q u e se ha ido co n o c ie n d o co n m a y o r p ro fu n d id a d el fe n ó m e n o , a través de los análisis y m ed ic io n es rea lizad o s en la CN A I y o tra s cen tra le s a fe c ta d a s en el ex tra n je ro .

A c o n tin u a c ió n se re su m en las m ed id as m ás sign ificativas to m a d a s p o r el CSN y la C N A h as ta la fech a , in c lu y e n d o to d o s los p e rm iso s e sp ec ífico s d e o p e rac ió n co n ced id o s . E l C u ad ro II I recoge u n a s ín te s is de ta les m ed idas.

246 REIG

— P rim era p a rad a . A la v is ta de lo o c u rr id o en R inghals-3 el 2 .1 1 .8 1 , se to m ó la d ec is ió n de p a ra r la C N A I e in sp ecc io n a r los tu b o s de los g en e rad o res de v ap o r (G V ). Se in sp ecc io n a ro n , u ti liz a n d o el m é to d o de co rr ien te s in d u c id as (E C T ), m ás de 1400 tu b o s en los tres g en e rad o res (4 5 5 en G V -1, 49 3 en G V -2 y 4 6 0 en G V -3), d e te c tá n d o se u n ad e lg a zam ien to de la p a red en97 tu b o s (5 3 en G V -1, 13 en G V -2 y 31 en G V -3), sin ap rec ia rse ro tu ra en n in g u n o de ellos. A ra íz de la in sp ecc ió n se ta p o n a ro n 39 tu b o s (2 3 en G V -1 , 4 en G V -2 y 12 en G V -3) y se e x tra je ro n 2 tu b o s del GV-1 para en sayos d e s tru c tiv o s y m e ta lo g rá fico s , a s í co m o p ara c o m p a ra r los desgastes reales con las m ed idas o b te n id a s p o r E C T .

— El 21 de d ic iem b re de 1981 , el CSN a u to r iz ó a la C N A , con c a rá c te r p rov isiona l, a o p e ra r a la p o te n c ia q u e p e rm itie ra la a lim e n ta c ió n de los g en e rad o res de v ap o r a través de la to b e ra de agua de a lim en tac ió n au x ilia r (a p ro x im a d a m e n te u n 30% ). E s te p erm iso p rov isiona l p ro h ib ía a lim e n ta r p o r la to b e ra de a lim en tac ió n p rin c ip a l, p o r e n te n d e rse que e ra la causa del suceso .

— El 7 d e e n e ro de 1 982 , y co m o co n secu en c ia de los e s tu d io s e fe c tu a d o s y de los análisis de los tu b o s e x tra íd o s ta n to en la C NA -I co m o en R inghals-3 ,el CSN a u to r iz ó u n p e r ío d o de o p e rac ió n de 1500 h , p e rm itie n d o p o r la to b e ra de a lim e n ta c ió n p rin c ip a l h a s ta u n m áx im o del 50% del cauda l n o m in a l

(ap ro x . u n 54% de p o ten c ia ). A sim ism o , a u to r iz ó un p ico de 4 0 h al 100% de p o te n c ia p a ra e fe c tu a r m ed idas. E l CSN e n te n d ió q u e d ism in u y en d o la a lim en tac ió n al 50% se red u c ía la a m p litu d de las v ib rac io n es de los tu b o s , con lo q u e se ev itab a el ch o q u e con las p lacas so p o r te y el ad e lg a zam ien to consigu ien te .Se ex ig ió al t i tu la r q u e p re se n ta ra dos in fo rm es a las 500 h y 1000 h de fu n c io n a m ie n to , re f le jan d o las m ed idas y p ru eb as e fec tu ad as , así com o cu a lq u ie r in fo rm a c ió n ad ic io n a l re sp ec to al m ecan ism o de desgaste o re su ltad o s en o tra s cen tra le s e x tran je ra s a fec tad as.

— 2a p a rad a . F in a lizad as las 1500 h , la c en tra l p a ró el 10 de m arzo de 1981 p ara e fe c tu a r u n a nueva in sp ecc ió n de tu b o s y c o m p ro b a r a s í la efec tiv idad de la lim itac ió n del caudal de a lim en tac ió n . Se vo lv ieron a ex am in a r un o s 1400 tu b o s , m ás o tro s 4 tu b o s tap o n a d o s . Ig u a lm en te , se e x tra je ro n p ara en say o s 2 tu b o s del G V -3. A l o bservar en los re su ltad o s o b te n id o s p o r el m é to d o d ife ren c ia l q u e se h a b ía n p ro d u c id o ad e lg a zam ien to s en 35 tu b o s , se d ec id ió u ti liz a r el m é to d o a b so lu to de ECT, q u e es m ás p rec iso p e ro m en o s co n se rv ad o r, c o m p ro b á n d o se que las m ed id as o b te n id a s co n el m é to d o d ife ren c ia l e ran m u y conservado ras . La Fig. 1 m u e s tra la co m p arac ió n e n tre los re su ltad o s o b te n id o s p o r E C T , co n los dos m é to d o s , y lo s consegu idos p o r en say o s m e ta lo g rá fico s de los tu b o s e x tra íd o s .

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— El 31 de m arzo , el C SN a u to r iz ó la m o d ific ac ió n del sis tem a de agua de a lim e n ta c ió n p a ra u n a po sib le u tiliz ac ió n s im u ltán ea de las to b e ra s de ali­m e n ta c ió n p rin c ip a l y aux ilia r . D icha a u to r iz a c ió n p e rm itía ú n ic a m e n te re a liza r la m o d ific ac ió n , n o p u d ie n d o o p e ra r co n ella sin la ap rec iac ió n favo rab le del CSN.

— T ras la p a rad a y rea lizad o s los c o rre sp o n d ie n te s análisis y e s tu d io s , el CSN a u to r iz ó el 2 0 de ab ril u n n u ev o p e r ío d o de o p e rac ió n de 1500 h al 50% del caudal de a lim e n ta c ió n p o r la to b e ra p rin c ip a l, p ro rro g á n d o se p o s te r io rm e n te h as ta las 2 0 0 0 h.

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— 3 a p a rad a . El 19 de ju lio y después de fina lizadas las 2 0 0 0 h se rea liza ron nuevas m ed id as p o r E C T de los tu b o s m ás a fec tad o s . Se em p lea ro n am bos m é to d o s , d ife renc ia l y ab so lu to , re f le jan d o los re su ltad o s o b te n id o s p o r este ú lt im o q u e n o se h a b ía p ro d u c id o u n a deg rad ac ió n ap rec iab le de los tu b o s .El C u a d ro IV m u e s tra la co m p a rac ió n de las m ed id as o b te n id a s con el m é to d o a b so lu to en las p a rad as de m arzo y ju lio . E l C u ad ro V recoge la m ism a co m p arac ió n , p e ro e n tre los re su ltad o s o b te n id o s con el m é to d o d ife renc ia l en las p a rad as de n o v iem b re , m arzo y ju lio . C o m o se p u ed e c o m p ro b a r en la c o lu m n a de d ife ren c ia de m ed id a ex is ten g ran d es variaciones.

— El 18 de ag o sto se a u to r iz ó u n p e río d o de o p e rac ió n de 4 0 0 0 h , d iv id ido en dos su b p e r ío d o s de 2 0 0 0 h. D u ran te el p r im e ro se p e rm it ía o p e ra r al 50% del cauda l de a lim e n ta c ió n p o r la to b e ra p rin c ip a l, m ás u n p ico de 75 h al 63% de l cauda l a lim e n ta n d o s im u ltá n e a m e n te p o r las to b e ra s p rin c ip a l y aux ilia r . A la v is ta de lo s re su ltad o s o b te n id o s con e s ta p ru e b a se a u to r iz a r ía el fu n c io n a m ie n to al 63% d u ra n te el segundo su b p e r ío d o de 2 0 0 0 h.El p e r ío d o de 4 0 0 0 h h a sido p ro rro g a d o re c ie n te m e n te o tra s 8 4 0 h m ás al 50% del cauda l n o m in a l, después de las cuales el ti tu la r d eb e rá rea liza r u n a nueva in sp ecc ió n de tu b o s an te s de in c o rp o ra r la m o d ific ac ió n de los g en erad o res de v ap o r. L a p ró rro g a fina liza el 23 d e ab ril, y se h a p ro g ram ad o el co m ien zo de la m o d ific ac ió n p a ra el 10 de m ay o .

Es in te re sa n te h ace r, p a ra c o m p le ta r el h is to ria l de e x p lo ta c ió n de la CN A I, u n b reve re su m en de la experiencia de explotación, a p a r te del in c id e n te genérico de los g en erad o res de vapor.

L a C N A I h a te n id o u n to ta l de 29 d isp a ro s y 6 p a rad as n o p ro g ram ad as desde el in ic io de la c ritic id ad in icial, es dec ir casi dos añ o s . L os d isparo s se h a n d e b id o p rin c ip a lm e n te a fa llo s de eq u ip o , a e rro res de o p e rac ió n y a n o h a b e r seguido los p ro c e d im ie n to s e s tab lec idos.

E n el m ism o p e r ío d o de tie m p o , la C N A I ha re m itid o al CSN , de a c u e rd o a la n o rm a tiv a v igen te , 134 in fo rm es de sucesos n o tif ic ab le s en 1 981 , 131 en 1982 y 4 0 en lo s tre s p rim e ro s m eses de 1983. De e s to s sucesos se p u e d e n e x tra e r las sigu ien tes co n c lu s io n es:

— C ie rto s sistem as tie n e n u n a frecu en c ia de in o p e ra b ilid a d su p e rio r a lo deseab le . Se e n c u e n tra n e n tre e llos el s is tem a de agua de a lim en tac ió n au x ilia r , el s is tem a de p ro te c c ió n c o n tra in cen d io s, el sistem a de v igilancia de la rad iac ió n y el sistem a de a spersión de la co n te n c ió n . La causa p rin c ip a l es el fa llo de b o m b as , válvulas o in s tru m e n ta c ió n asociada .

— L os sucesos o b je to de in fo rm e al CSN d eb erán ser rev isados, ya que casi el 50% de lo s n o tif ic a d o s c o rre sp o n d en a s itu ac io n es de in o p e rab ilid ad en s istem as p a ra re a liz a r o rd e n e s de tra b a jo co rrec tiv o . E s in te n c ió n del CSN a p ro v e c h a r e s ta rev isión p a ra ad ap ta rse lo m ás posib le a la g u ía del O IE A

IAEA-SM-268/90 251

“ N a tio n a l S ystem fo r C o llec ting . A ssessing a n d D issem ina ting In fo rm a tio n o n S a fe ty -R e la te d E v en ts in N u c lea r P o w er P la n ts” , en fase de p ru e b a p o r do s años.

C o m o re su m en de este p u n to , el h is to g ram a de la Fig. 2 m u e s tra el h is to ria l de e x p lo ta c ió n de la C N A h a s ta el 1 de ab ril de 1983.

3. A C T IV ID A D E S D E L C O N S E JO D E S E G U R ID A D N U C L E A R

El C o n se jo de S egu ridad N u c lea r h a p ro g ram ad o sus ac tiv id ad es de su p er­v isión y c o n tro l re la tivas al p ro b le m a gen érico de los g en e rad o res de v ap o r co n d o s o b je tivos :

(a) E fe c tu a r el seg u im ien to de la e x p lo ta c ió n de la C N A I g a ran tiz an d o q u e su o p e rac ió n n o im p liq u e u n a d eg rad ac ió n d e los m árgenes de seguridad .

(b ) E fe c tu a r el seg u im ien to de las ac tiv id ad es rea lizadas p o r W estinghouse p ara llegar al d iseñ o fina l de la m o d ific ac ió n d e los g en e rad o res de vapor.

R ec o n o c ie n d o la im p o rta n c ia de u n a re lac ió n e s trech a con los o rgan ism os reg u lad o res de los pa íses co n cen tra le s a fe c ta d a s p o r el m ism o p ro b lem a genérico , el C SN ha m a n te n id o c o n ta c to s fre c u e n te s ta n to co n la N R C de E E U U co m o co n el In sp e c to ra d o sueco (S K I). U na vez m ás, la co o p e ra c ió n in te rn a c io n a l ha p ro b a d o ser in d isp en sab le , e sp ec ia lm en te en el caso de n u e s tro p a ís , q u e cu e n ta c o n recu rso s h u m a n o s lim itad o s en el cam p o re g u la d o r de la segu ridad nuc lea r.

R e la tiv o al seguimiento de la explotación, el C SN , p o r m ed io de los perm iso s e sp ec ífico s de o p e ra c ió n y a co m e n ta d o s , ha lim ita d o las co n d ic io n es de o p e rac ió n de fo rm a q u e el desgaste de los tu b o s n o se in c re m e n te ap rec iab lem en te . Las lim ita c io n e s im p u e s ta s se h an b asad o en lo s e s tu d io s rea lizad o s ta n to p o r la em presa su m in is tra d o ra co m o p o r el CSN y en lo s re su lta d o s de las in specc iones de lo s tu b o s .

El c u m p lim ie n to de las lim itac io n es d e o p e rac ió n ha sido verific ad o p o r el C onsejo p o r m e d io de in sp ecc io n es de seg u im ien to de ex p lo ta c ió n . Ig u a lm en te , el CSN h a e s tad o p re se n te en la rea lizac ió n d e las in sp ecc io n es p o r E C T de los tu b o s de los g en e rad o re s de v ap o r. P o r ú ltim o , y a través de u n m iem b ro del C onse jo d e s ta c a d o en la sede de la N R C , el C SN h a te n id o acceso d ire c to a la in fo rm a c ió n so b re la e x p lo ta c ió n p rov is iona l d e M cG uire-1 , q u e in c o rp o ra un m o d e lo sim ilar de g e n e ra d o r de vapor.

C on re sp e c to a la modificación p ro p u e s ta p o r W estinghouse p ara ev ita r el desgaste de tu b o s , el C onse jo , a través de su re p re se n ta n te en la N R C , h a segu ido la ev o lu c ió n de su d e sa rro llo a s í co m o las re u n io n e s m a n te n id a s p o r la N R C co n em p resas e léc tricas y W estinghouse co n o b je to de d is c u tir la a c e p ta c ió n de la m o d ific ac ió n . E l CSN ha m a n te n id o reu n io n es co n la N R C y W estinghouse en

252 REIG

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E stad o s U n id o s y co n el SK I en E s to c o lm o . A sim ism o, lo s tre s o rgan ism os reg u lad o res h a n ce le b rad o re u n io n e s en P a rís , W ash ing ton y E s to co lm o . F in a l­m e n te , u n a re p re se n ta c ió n esp añ o la asis tió a la p re se n ta c ió n del in fo rm e rea lizado p o r el p an e l de rev is ió n de d iseñ o , c read o a in s tan c ia s de la N R C , y q u e tu v o lugar en en e ro d e 1983 en E E UU.

T o d as las m en c io n ad as a c tu a c io n es de l CSN te n ía n c o m o o b je to d isp o n e r de la m áx im a in fo rm a c ió n p ara re a liza r la ev a lu ac ió n y , en su caso , a u to r iz a r la m o d ific a c ió n de d iseñ o de los g en e rad o res d e vapor.

4 . E V A L U A C IO N D E L A M O D IF IC A C IO N D E D ISE Ñ O D E LOS G E N E R A D O R E S D E V A PO R

Se resu m e a q u í la ev a lu ac ió n de seguridad rea lizad a p o r el C o nse jo de S eguridad N uclear. C abe d e s taca r tre s a sp ec to s de in te ré s p ara e s te tra b a jo :

(1 ) La m e to d o lo g ía(2 ) La evaluac ión(3 ) L as co n c lu s io n es

4 .1 . M eto d o lo g ía

La m e to d o lo g ía de ev a luac ión em p lead a p o r u n p a ís im p o r ta d o r se a ju s ta n o rm a lm e n te a la d e l c u e rp o reg u lad o r del p a ís de o rig en del p ro y e c to . E n este caso , se h a te n id o m u y en c u e n ta la evaluac ión genérica rea lizada p o r la N RC . C o m o y a se h a m e n c io n a d o , u n m ie m b ro del C SN tu v o acceso d ire c to a d ich o tra b a jo desde sus in icios.

P o r o tra p a rte , se h an e fe c tu a d o vario viajes a S uecia co n o b je to de v is ita r R inghals-3 y c o n o c e r las p ru eb as rea lizadas c o n u n m o d e lo a escala u n id a d . Se m a n tu v ie ro n d iscu sio n es co n el In s p e c to ra d o sueco (S K I) y co n las em presas e léc tricas (SSPB ). E sta co la b o ra c ió n f lu y ó en a m b o s sen tid o s , ya q u e tam b ién e x p e rto s su eco s v ia ja ron a E sp añ a co n el fin de v is ita r la c e n tra l n u c lea r de A lm araz .

F in a lm e n te , se h a n e fe c tu a d o reu n io n es de tra b a jo c o n W estinghouse , ta n to en Е Е U U co m o en E sp añ a , p ara d is c u tir d e ta lla d a m e n te so b re la m o d ificac ió n .

C om o se p u e d e ver, la co o p e ra c ió n in te rn a c io n a l ha su p u e s to u n a a y u d a im p o rta n te p a ra n u e s tro p a ís . D icha co la b o ra c ió n se ha m a n te n id o a to d o s los niveles de tra b a jo , y el h e c h o de que n o ex is tie ra u n a c u e rd o fo rm a l de co ­o p e rac ió n co n S uecia , co m o ex is te co n Е Е U U , n o ha su p u e s to n in g u n a b a rre ra p a ra el in te rc a m b io de in fo rm ac ió n .

D ád o q u e en E sp añ a se ib an a seguir lo s c rite r io s de la N R C , el CSN d ec id ió q u e n o a u to r iz a r ía la in s ta lac ió n de la m o d ific ac ió n h a s ta q u e la N R C la h u b ie ra a p ro b a d o g en é ricam en te .

254 REIG

El C SN co n sid e ra que ex is ten dos a sp ec to s b ien d ife ren c iad o s en la evaluación de la m o d ific ac ió n :

(a ) A sp ec to s genéricos: A q u ello s q u e p u e d e n ser re su e lto s d e fo rm a c o n ju n ta p a ra to d a s las cen tra le s co n m odelo s D 2 y D3 de g en erad o res de vapor.

(b ) A sp ec to s e sp ec ífico s: A q u ello s q u e son de ap lic ac ió n a cada ce n tra l en p a rtic u la r , d e b id o a p ecu lia rid ad es d e l p ro y e c to , o a ser o n o la p rim era en o p e ra r co n la m o d ific ac ió n in sta lada .

L os aspectos genéricos h an sido evaluados p o r la N R C am erican a y el SKI sueco . D ada la re c o n o c id a co m p e te n c ia técn ica de estas o rgan izac iones , el CSN co n sid e ró q u e n o e ra necesaria u n a evaluación e n p ro fu n d id a d , lim itán d o se a v erific a r q u e las co n d ic io n es esp ec íficas de la C N A estab an d e n tro las co n d ic io n es co n sid e rad as en el e s tu d io genérico .

D ada la ex is ten c ia en E E U U de varias cen tra le s co n m o d e lo s D 2 y D3 de g en e rad o res de v ap o r, la N R C , en v ista de la m ag n itu d del p ro b lem a , re c o m e n d ó a las c o m p a ñ ía s p ro p ie ta r ia s q u e fo rm aran u n p an e l de rev isión de d iseñ o (D R P ) para evaluar la p ro p u e s ta de m o d ificac ió n a e lab o ra r p o r W estinghouse. E l D R P se e s tab lec ió en m ay o de 1982 y re m itió a la N R C su in fo rm e final en en e ro de1983.

P o r o tr a p a rte , en S uecia , el e x p lo ta d o r d e R inghals (SSPB ) p ro c e d ió a evaluar varios de lo s a sp ec to s de la m o d ificac ió n , p a rt ic ip a n d o ac tiv am en te en las ta reas de id e n tif ic a c ió n de las causas del p ro b lem a y en las p ru eb as a escala u n id ad de la m o d ific ac ió n p ro p u e s ta p o r W estinghouse.

Las co n c lu s io n es d e esto s trab a jo s en a m b o s p aíses, q u e h an a c e p ta d o la m o d ific ac ió n g enérica , son las sigu ien tes:

— La m o d ific ac ió n p e rm ite u n a red u cc ió n sign ifica tiva de las v ib rac iones.— L a m o d ific a c ió n es a cep tab le desde el p u n to d e v is ta e s tru c tu ra l y capaz de

so p o r ta r lo s tra n s ito r io s aplicab les.— L os p ro c e d im ie n to s de in s ta lac ió n son ad ecu ad o s , a s í co m o los c rite r io s p ara

la re d u c c ió n de dosis a lo s tra b a ja d o re s d u ra n te el m o n ta je e in specc ión .— L os req u is ito s de p ru e b a e in sp ecc ió n en servicio de la m o d ificac ió n

p ro v ee rán ev idenc ia su fic ien te de su id o n e id ad .— L os g en e rad o res de v ap o r m o d e lo D 2 y D3 p u e d e n ser o p e ra d o s de fo rm a

segura al 100% de su cap ac id ad de d iseño u n a vez in s ta lad a la m o d ificac ió n .

E n re u n ió n ce leb rad a en E sto co lm o en fe b re ro de 1983 , los tre s o rgan ism os reg u lad o res N R C -SK I-C SN llegaron al a cu e rd o de a c e p ta r la m o d ificac ió n . P o r o tro lad o , el C o nse jo co m p ro b ó q u e los e s tu d io s genéricos e ran to ta lm e n te ap licab les al caso de A lm araz , ya q u e se h a b ía h e c h o u n a u tiliz ac ió n ex haustiva de in fo rm a c ió n p ro v in ie n te de la o p e rac ió n de d ich a cen tra l.

4.2. Evaluación

IAEA-SM-268/90 255

U na vez a c e p ta d a g en é ricam en te la m o d ificac ió n , se id e n tif ic a ro n aq u e llo s aspectos específicos que h a b r ía n de evaluarse p a ra cada c e n tra l en p a rticu la r.Para C N A se e s tab lec ie ro n los s igu ien tes tem as:

— M edida d e o sc ilac iones de p res ió n en la tu b e r ía de agua de a lim en tac ió n .— E lim in ac ió n del tra n s ito r io de in y ecc ió n de agua fr ía .— C apac idad y o p e r^b ilid ad del sistem a de v ib f tc io n e s y de d e te c c ió n de p a rte s

sueltas.— M éto d o de in sp ecc ió n visual de la m o d ificac ió n .— C o n tro l de la q u ím ic a del secu n d ario .— A nálisis de d a to s d e los ace le ró m e tro s .— P ru eb as in iciales de verificac ión .— P rog ram a de in sp ecc ió n en servicio.— D u rac ió n del p r im e r p e r ío d o de ex p lo tac ió n .

4 .3 . C onclu siones

4.3.1. Aspectos genéricos

La m o d ific ac ió n p ro p u e s ta re d u c e s ig n ifica tivam en te la v ib rac ió n d e tu b o s .La ve loc idad de desgaste es su f ic ie n te m e n te p eq u eñ a , p e rm itie n d o la id en tif ic ac ió n de los tu b o s desgastados m e d ia n te in sp ecc ió n p a ra p ro c e d e r a su ta p o n a m ie n to .El D R P rea lizó u n a e s tim ac ió n co n se rv ad o ra del desgaste en el p e o r tu b o , q u e a lca n za ría u n 40% de re d u c c ió n de espeso r de p a re d en 5 ,33 años.

L a C N A d e b e rá rea liza r u n a in sp ecc ió n p o s te r io r a la in s ta la c ió n de la m o d ific a ­c ión y a n te s de o p e ra r co n ella, q u e sirva de “ base lin e” p a ra la fu tu ra co m p a rac ió n de las in sp ecc io n es de v igilancia. E n base al c o m p o r ta m ie n to de la m o d ificac ió n se d eb erá c o n s id e ra r u n a p o sib le rev isión de los lím ite s de ta p o n a d o de tu b o s .

4.3.2. Aspectos es pe с i f icos

El p e rm iso de o p e rac ió n con la m o d ific ac ió n de los g en e rad o res de v apo r c o n te n d rá las s igu ien tes co nd ic iones:

— F recu en c ia y niveles de p o te n c ia p a ra la rea lizac ió n de las m ed id as de o sc ilac ión de p res ió n en la tu b e r ía de agua de a lim en tac ió n .

La C N A y a d isp o n e de senso res de p res ió n s itu ad o s en d ichas tu b e r ía s .

— R e q u is ito s o p e rac io n a les p ara ev ita r la in y ecc ió n de agua f r ía al g en e rad o r de vapor.

La C N A h a in c o rp o ra d o u n a tu b e r ía p ara p u rg a r el agua co n te m p e ra tu ra in fe rio r a 2 0 0 ° C, llevándo la al c o n d en sad o r. La C N A rea liza rá u n análisis de ro tu ra p a ra e s ta nu ev a tu b e r ía .

PREVISTO

256 REIG

FIG.

3. Pr

ogram

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las mo

difica

cione

s de

los ge

nera

dores

de

vapo

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las ce

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clear

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IAEA-SM-268/90 257

— R eq u is ito s o p e rac io n a le s m ás e s tr ic to s p ara el s is tem a de v ib rac io n es y v ig ilancia de p a rte s su e ltas (V L PM S ), p a ra d e te c ta r c u a lq u ie r ro tu ra en la m o d ific a c ió n o en tu b o s tap o n ad o s .

— F recu en c ia de la in sp ecc ió n v isual de la m o d ific ac ió n . D ep en d e rá de si es o n o la p rim e ra en o p e ra r co n la m o d ific ac ió n en lo s g en e rad o res de vapor.

— F recu en c ia de las m ed id as rea lizadas co n los a c e le ró m e tro s , in c lu y e n d o el p e r ío d o de su b id a de p o ten c ia .

— R ea lizac ió n d e u n a p ru e b a h id ro s tá tic a de las tu b e r ía s de agua de a lim en tac ió n .— F ijac ió n del n ú m e ro de tu b o s q u e inc lu irá el p ro g ram a de in sp ecc ió n en

servicio , a s í c o m o su rea lizac ión .— F ijac ió n d e u n p e r ío d o in ic ia l de o p e rac ió n co n la m o d ific ac ió n . E l C onsejo ,

co n c a rá c te r p re lim in a r, h a e s tab lec id o un p e r ío d o de seis m eses eq u iv a len tes a p le n a p o te n c ia . A l fija r la d u ra c ió n del p e r ío d o h ay q u e so p esa r la co n fian za en la cap ac id ad de la m o d ific ac ió n p a ra re d u c ir v ib rac io n es y el p e r ío d o m ín im o , p a ra q u e las m ed id as p o r E C T e in sp ecc ió n visual sean significativas.

5. E S T A D O A C T U A L D E L A S C E N T R A L E S N U C L E A R E S E SPA Ñ O L A SA F E C T A D A S

A u n q u e el p ro b lem a g enérico de los desgastes de tu b o s só lo h a a fe c ta d o a la U n id ad I de A lm araz , ha sido la U n id ad II la p rim era en re c ib ir a u to r iz a c ió n del CSN p a ra in c o rp o ra r la m o d ific ac ió n . L a m en c io n ad a evaluac ión se rea lizó p ara d ich a in c o rp o ra c ió n , y será to ta lm e n te ap licab le a las d em ás u n id ad es españo las con la v a rian te de in c lu ir lo s c rite r io s d e re d u c c ió n d e dosis a los trab a ja d o re s p a ra la in c o rp o ra c ió n en la U n idad I d e la CNA .

La F ig . 3 m u e s tra el c a len d ario p rev isto de in c o rp o ra c ió n de la m o d ific ac ió n a las d is tin ta s c e n tra le s esp añ o las a fec tad as , así co m o las fases sigu ien tes de ex p lo ta c ió n .

B IB L IO G R A F IA

CONSEJO DE SEGURIDAD NUCLEAR, Informe al Congreso de los Diputados y al Senado, CSN/IS/2/82 y CSN/IS/3/82 (1982).

CONSEJO DE SEGURIDAD NUCLEAR, Informe Público sobre la Central Nuclear de Almaraz, CSN/IP/1/82 (1982).

NUCLEAR REGULATORY COMMISSION, SER related to the D2/D3 Steam Generator Design Modification, NUREG-0966, 1983.

258 REIG

O R G A N I S M O I N T E R N A C I O N A L D E E N E R G I A ATOMICA, Guide on a National System for

Collecting, Assessing and Disseminating Information on Safety-Related Events in Nuclear Power

Plants, A Pre-Publication Working Document, Colección de Informes Técnicos 278, OIEA,

Viena (1983).

UTILITY DESIGN R E V I E W PANEL, Evaluation Report D2/D3 Steam Generator Design

Modification, 1983.

VILLADONIGA, J.I., Informe de Evaluación para la Autorización de Instalación de la

Modificación de Proyecto de Westinghouse de los Generadores de Vapor de la Unidad I de la

Central Nuclear de Almaraz, CSN/SANYC/ALI/05/83 (1983).

W E S T I N G H O U S E ELECTRIC CO., Westinghouse Preheat Steam Generator D2/D3 Design

Modification, Evaluation Package, 1982.

IAE A-SM-268/91

A N T I C I P A T E D T R A N S I E N T W I T H O U T S C R A M

E V E N T S A T S A L E M - A N O T H E R

L E S S O N I N O P E R A T I N G E X P E R I E N C E *

W A Y N E D. L A N N IN G O ffice o f A nalysis an d E v a lu a tio n

o f O p e ra tio n a l D ata ,U n ited S ta te s N u c lea r R eg u la to ry C om m iss ion ,W ash ing ton , DC,U n ited S ta te s o f A m erica

A bstract

ANTICIPATED TRANSIENT WITHOUT SCRAM EVENTS AT SALEM - ANOTHER LESSON IN OPERATING EXPERIENCE.

The two anticipated transient without scram (ATWS) events at the Salem nuclear power plant have been called the most significant operating events in terms of reactor safety since the accident at Three Mile Island. Simultaneous equipment failures at Salem in February 1983 resulted in the first time a U.S. commercial nuclear power plant failed to scram automatically on a valid reactor protection signal. The plant was operating at low power levels on both occasions and was promptly scrammed manually so there was no plant damage and no direct danger to public health and safety. However, the implications of the Salem events are of wide significance in terms of reactor trip system reliability in particular and utility management controls in general. The Salem events were only days apart and the first occurred without the operators recognizing that the automatic reactor trip system had failed. An assessment of this event by the Salem management wrongly concluded that manual actions to trip the plant by the operator had been taken before the automatic system responded although operational data were available which, if properly analysed, would have prevented the second ATWS event. The plant management’s failure to understand properly the nature of their operating experience and, thus, to identify the failure of the automatic safety system prior to restarting the reactor highlights the value and importance of operating experience to plant safety. Moreover, its value resides in the degree to which that experience is thoroughly understood and properly acted upon. The Salem event, by itself, was a mild transient, but the potential existed for a much more serious event. Together, the two Salem events provide a number of specific lessons for improving and assuring the safety, reliability and economics of commercial nuclear power plants. The paper gives the details of the ATWS events. The reactor trip system is described with emphasis on the reasons why the trip breakers failed to open on demand. The operating history of the circuit breakers used in the reactor trip system at Salem and other PWRs is analysed and evaluated. The implications of the Salem events were assessed by the United States Nuclear Regulatory Commission (NRC) and a number of proposed actions have been identified to ensure proper operation of all

* This paper is a summary of a USNRC Report entitled “Generic Implications of ATWS Events at the Salem Nuclear Power Plant” , NUREG-1000, Vol.l (April 1983).

259

260 LANNING

reactor trip breakers in the future. Further, as the result of the Salem events, the NRC continued to study the proposed ATWS regulation with regard to additional requirements such as whether a diverse scram system for Westinghouse-designed plants is necessary.

1. IN T R O D U C T IO N

A fte r a d ecad e o f d iscussions o n a n tic ip a te d tra n s ie n ts w ith o u t scram (A T W S), th e f irs t ATW S ev en t a t a licensed PW R in th e U SA w en t to ta lly u n n o tic e d a t U n it 1 o f th e Salem n u c lea r p o w er p la n t o n 22 F e b ru a ry 1983 (T ab le I).

A t a few m in u te s p a s t m id n ig h t o n 25 F e b ru a ry 1 983 , S alem U n it 1 e x p e rie n c e d th e seco n d to ta l fa ilu re o f an y U .S. re a c to r to sc ra m 1 au to m a tic a lly (T ab le II).

T h e re la tiv e ly m ild c o n d itio n s lead ing to th e d e m a n d fo r b o th o f th ese sc ram s an d th e rap id m an u a l sh u td o w n o f th e r e a c to r b y th e o p e ra to rs tu rn e d th ese ev en ts in to li t t le m o re th a n ro u tin e r e a c to r sh u td o w n s . H ow ever, th e im p lic a tio n s o f th ese even ts , in te rm s o f re a c to r t r ip sy s tem re lia b ility in p a rtic u la r , a n d o f m an ag e m en t c o n tro ls in g en era l, a re b o th s ign ifican t a n d fa r reach ing .

T h e U n ited S ta te s N u c lea r R eg u la to ry C om m ission (N R C ) req u ire s th a t th e r e a c to r tr ip sy s tem s o n all p o w e r re a c to rs be sing le-failu re p ro o f a n d h igh ly re liab le . A s fa r b ack as th e la te 19 6 0 ’s th e r e a c to r t r ip sy s tem w as reco g n ized to be so im p o r ta n t th a t se rious c o n s id e ra tio n w as g iven to th e n eed fo r a d d itio n a l re d u n d a n c y , d iv e rs ity a n d m itig a tio n sy s tem s to o ffse t sy s tem fa ilu res. T hese ac tiv itie s have co m e to be k n o w n as ATW S ana ly ses an d have led to th e still c o n tin u in g fo rm u la t io n o f a n ew reg u la tio n k n o w n as th e ATW S ru le .

In v iew o f th e h igh sa fe ty sign ificance o f th e S alem even ts , o n 28 F e b ru a ry 1 9 8 3 , th e N R C E x ecu tiv e D ire c to r o f O p e ra tio n s d ire c te d th e s ta f f to u n d e r ta k e th re e re la te d ac tiv ities : (1 ) an ev a lu a tio n o f w h en a n d u n d e r w h a t c o n d itio n s th e S alem p la n ts w ou ld b e a llo w ed to re s ta r t (S a lem U n it 2 w as sh u t d o w n d u rin g th e se ev en ts ); (2 ) p re p a ra tio n o f a fa c t-fin d in g re p o r t o f th e ev en ts a t S alem U n it 1 a n d th e c ircu m stan ces lead ing to th e m ; and(3 ) p ro d u c t io n o f a r e p o r t o n th e g eneric im p lica tio n s o f th e se even ts .

1 The terms trip and scram are used interchangeably to refer to a sudden shutting down of a reactor, usually by rapid insertion of control rods.

IAE A-SM-268/91 261

TABLE I. ATWS EVENT AT SALEM 1 O N 22 F E B R U A R Y 1983

Time (min.sec) Event

0 Plant stable at 20% full power

Main feedwater in automatic

Of Bus de-energized

Loss of reactor coolant pump and main feedwater pump

1.54 Low low steam generator level

Auto reactor trip signal

Auxiliary feedwater system auto start

1.58 Manual reactor trip

9.00 Safety injection

11.00 Second reactor coolant pump lost

Two Porvs3 open

16.00 Safety injection terminated

Porvs® closed

Plant stable

a Porv — power-operated relief valve.

T A B L E II. ATW S E V E N T A T SA LE M 1 O N 25 F E B R U A R Y 1983

Time (min.sec) Event

0 Plant stable at 12% full power

Main feedwater in manual

Steam generator level unstable

0+ Low low steam generator level

Auto reactor trip signal

Auxiliary feedwater system auto start

Possible false alarm

No scram indicated

0.25 Manual reactor trip

Plant stable

3 0 -6 0 Reactor trip system and instrumentation checks

Both breakers fail repeated test

ATWS identified

262 LANNING

CQ CDm ш P

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IAEA-SM-268/91 263

T he W estinghouse re a c to r tr ip sy s tem (R T S ) co n sis ts o f p la n t p ro cess in s tru m e n ta t io n (senso rs , tra n sm itte rs , b is tab le s an d fie ld c o n ta c ts ) th a t m o n ito rs v a rio u s p la n t p a ram e te rs . T y p ica lly , th e re a re fo u r re d u n d a n t in s tru m e n t ch an n e ls p e r p a ra m e te r . (T h is varies w ith th e p a r tic u la r p la n t an d th e p a rtic u la r p a ra m e te r . In so m e cases, o n ly th re e o r even tw o re d u n d a n t ch an n e ls a re u sed .) T he o u tp u ts o f th e se in s tru m e n t ch an n e ls a re u sed as in p u ts to each o f tw o re d u n d a n t tra in s o f logic c irc u itry (so lid s ta te p ro te c t io n sy s tem (SSPS) tra in s ‘A ’ an d ‘B ’). T h e o u tp u t o f e ach SSPS tr a in p ro v id es p o w e r fo r tw o u n d e r ­v o ltage (U V ) tr ip a tta c h m e n ts , o n e fo r its asso c ia ted re a c to r tr ip b re a k e r and o n e fo r th e by p ass b re a k e r (w h en in serv ice) in para lle l w ith th e o th e r re a c to r t r ip b re a k e r (see Fig. 1 ). T h e b y p ass b reak e rs are u sed o n ly d u rin g tes tin g .W hen tw o o u t o f th e fo u r in s tru m e n t chan n e ls fo r a g iven p a ra m e te r are in th e tr ip p e d s ta te (i.e . th e p a ra m e te r h as ex ceed ed its s e tp o in t) , th e logic o f each SSPS tr a in is sa tisfied , an d p o w e r is in te r ru p te d to th e tw o U V tr ip a tta c h m e n ts asso c ia ted w ith each tra in . T h is loss o f p o w e r a u to m a tic a lly o p e n s th e asso c ia ted c irc u it b reak e rs . W hen e ith e r o f th e tw o series r e a c to r tr ip b reak e rs o p en s , p o w e r p ro v id ed fro m th e m o to r-g e n e ra to r (M G ) se ts to th e c o n tro l ro d drive la tch in g m ech an ism s is in te r ru p te d , th u s a llow ing all c o n tro l ro d s to d ro p in to th e co re .

M anual r e a c to r t r ip c a p a b ility is p ro v id ed b y tw o sw itch es o n th e m a in c o n tro l b o a rd in th e c o n tro l ro o m . A c tu a tio n o f e ith e r sw itch in te r ru p ts p o w e r to all U V tr ip a tta c h m e n ts ( fo r b o th re a c to r t r ip b reak e rs a n d th e ir asso c ia ted b y p ass b reak e rs ) a n d s im u ltan eo u s ly energ izes all sh u n t tr ip a tta c h m e n ts fo r th e se b reak e rs . T h u s , d iverse m ean s (U V tr ip a tta c h m e n ts an d sh u n t tr ip a tta c h m e n ts ) a re u sed to o p e n th e re a c to r tr ip b reak e rs o n a m an u a l re a c to r tr ip signal, w hereas o n ly th e U V tr ip a tta c h m e n ts are a c tu a te d o n an a u to m a tic r e a c to r t r ip signal f ro m th e SSPS.

In te r lo c k s a re p ro v id ed to p re v e n t th e c losing o f b o th b y p ass b reak e rs a t th e sam e tim e . A n n u n c ia tio n is p ro v id ed in th e c o n tro l ro o m w h en ev er a b y p ass b re a k e r is p laced in th e closed p o s itio n . O p e ra tio n o f th e by p ass b reak e rs is ad m in is tra tiv e ly co n tro lle d .

O ld e r W estinghouse p la n ts use re lay s an d c o n ta c ts to p e rfo rm th e logic fu n c tio n s . N ew er p la n ts use so lid s ta te d ig ita l logic c ircu its . T h e overa ll re a c to r tr ip sy s tem designs, in c lu d in g th e tr ip b re a k e r a rra n g e m e n t (w ith th e a ssoc ia ted U V a n d s h u n t t r ip a tta c h m e n ts ) , a re essen tia lly id en tic a l. C e rta in o ld e r W esting­h o u se p la n ts , h o w ev er, d o n o t have b y p ass b reak e rs in c lu d ed in th e i r design.F o r th e se p la n ts , th e r e a c to r tr ip b reak e rs a re te s te d a t each re fu e llin g , as o p p o se d to ev ery o th e r m o n th . O n e p la n t , Y an k ee R o w e , d o es n o t have UV tr ip a t ta c h m e n ts ; o n ly th e s h u n t tr ip a t ta c h m e n t is p ro v id ed an d i t is p a r t o f th e re a c to r tr ip sy s tem .

2. WESTINGHOUSE R E A C T O R TRIP SYSTEM (RTS) DESIGN

264 LANN1NG

A ty p ic a l W estinghouse re a c to r co re c o n ta in s a p p ro x im a te ly 50 c o n tro l ro d s (a lso ca lled ro d c lu s te r c o n tro l assem blies), h a lf o f w h ich are u sed o n ly to sh u t d o w n th e re a c to r an d th e o th e r h a lf to c o n tro l th e re a c to r p o w e r level as w ell as sh u t d o w n th e re a c to r . T he c o n tro l ro d drive m ech an ism s ta tio n a ry g rip p e r co ils m u s t re m a in energ ized to m a in ta in th e i r a ssoc ia ted c o n tro l ro d s in th e w ith d ra w n p o s itio n . S ince th e m in im u m degree o f re d u n d a n c y in th e r e a c to r tr ip sy s tem is tw o , a t lea s t tw o fa ilu re s a re re q u ire d to p re v e n t a re a c to r t r ip w h en a m o n ito re d p a ra m e te r exceeds its s e tp o in t . S u ch m u ltip le fa ilu res th a t p re v e n t p o w e r f ro m be in g rem o v ed fro m th e c o n tro l ro d m ech an ism s can cause a fa ilu re to scram . N u m ero u s m ech an ica l fa ilu re s w ith in th e c o n tro l ro d s them selves co u ld also re s u lt in a sim ilar fa ilu re . F a ilu res to tr ip th e re a c to r due to m u ltip le fa ilu re s w ith in th e p rocess in s tru m e n ta t io n o r th e c o n tro l ro d s them selves a re co n sid e red u n lik e ly ow ing to th e d iv e rsity o f sensed p a ram e te rs a n d th e large n u m b e r o f fa ilu re s req u ired . F a ilu re s w h ich co u ld p rev en t a r e a c to r tr ip a re m o re lik e ly to o c c u r w ith in th e logic c irc u itry o r th e re a c to r tr ip b reak e rs a n d th e i r a c tu a tin g devices (e.g . U V tr ip a tta c h m e n ts ) .

F a ilu res to t r ip W estinghouse re a c to rs re su lt in all ro d s being m a in ta in ed in th e i r w ith d ra w n p o s itio n since th e sam e p a th is u sed to p rov ide p o w e r to all c o n tro l ro d drive m echan ism s. We shall n o w d iscuss th e su scep tib ility o f th e W estinghouse design to m u ltip le fa ilu res w h ich w o u ld p rev en t a r e a c to r tr ip .T he fa ilu res co n sid e red are as fo llow s:

(a ) S o lid s ta te p ro te c tio n sy s tem (SSPS) o u tp u t fa ilu res. E ach SSPS tra in n o rm a lly p ro v id es 4 8 V dc to its a sso c ia te d U V tr ip a tta c h m e n ts and in te r ru p ts th is vo ltage (0 V dc) w hen a c o n d itio n req u irin g a re a c to r tr ip is sensed . F a ilu re o f th e SSPS tra in to de-energ ize its U V tr ip a tta c h m e n ts (i.e . in te r ru p t th e 4 8 V dc) p rev en ts th e re a c to r tr ip b re a k e r (an d bypass b re a k e r i f in u se ) a ssoc ia ted w ith th e fa iled SSPS tra in fro m o p en in g in re sp o n se to an a u to m a tic re a c to r t r ip signal. T hese b reak e rs a re still cap ab le o f re sp o n d in g to a m an u a l t r ip signal via b o th th e U V an d s h u n t tr ip a tta c h m e n ts , how ever.

(b ) U nd erv o ltag e t r ip a t ta c h m e n t o r dev ice fa ilu res. T h e U V tr ip a tta c h m e n ts ( th e re is o n e fo r e ach re a c to r tr ip an d bypass b reak e r , a n d i t consis ts o f a U V co il an d asso c ia ted m ech an ica l linkage) a re n o rm a lly en erg ized . W hen th e U V co il is de-energ ized , th e m ech an ica l linkage is re leased , causing th e c irc u it b re a k e r to o p en . A n U V tr ip a tta c h m e n t fa ilu re w ill p rev en t its asso c ia ted b re a k e r fro m o p en in g in re sp o n se to an a u to m a tic r e a c to r tr ip signal. T h e b re a k e r can still be o p en ed b y a m an u a l tr ip signal, b u t o n ly v ia th e sh u n t tr ip a tta c h m e n t . T he m a jo rity o f fa ilu res o f re a c to r tr ip b reak e rs to o p e n have b een a t t r ib u te d to fa ilu res w ith in U V tr ip a tta c h m e n ts .

(c ) S h u n t t r ip a t ta c h m e n t o r dev ice fa ilu res. T he s h u n t t r ip a tta c h m e n ts ( th e re is o n e fo r each b re a k e r) are n o rm a lly de-energ ized . W hen th e tr ip

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coil o f th e s h u n t tr ip dev ice is ene rg ized , a m ech an ica l linkage o p e ra te s to o p e n th e b reak er . We have b een to ld b y b re a k e r m a n u fa c tu re rs - and th e o p e ra tin g d a ta ap p e a r to b ea r th is o u t — th a t s h u n t tr ip a tta c h m e n t fa ilu res a re less lik e ly th a n U V tr ip a t ta c h m e n t fa ilu res. In th e p re sen t W estinghouse design th e y are a n y w ay o f l i tt le c o n seq u en ce since th e b re a k e r can still re sp o n d to b o th a u to m a tic an d m an u a l r e a c to r tr ip signals.A sh u n t tr ip a t ta c h m e n t fa ilu re in c o n ju n c tio n w ith a U V tr ip a tta c h m e n t fa ilu re o n th e sam e b re a k e r w ill re s u lt in th e loss o f c ap ab ility o f th a t b re a k e r to re sp o n d to e ith e r a u to m a tic o r m an u a l re a c to r tr ip signals. I t m a y still b e p o ss ib le to o p en th e b re a k e r loca lly , h ow ever. In g en era l, th e sh u n t tr ip a tta c h m e n ts in R T S b reak e rs are n o t co n sid e red by W estinghouse an d its c u s to m e rs to be sa fe ty re la ted .

(d ) B reak e r fa ilu re s in d e p e n d e n t o f th e U V a n d sh u n t tr ip a tta c h m e n ts .P hysica l b in d in g o f th e b re a k e r i ts e lf w ill p re v e n t i t fro m re sp o n d in g to re a c to r t r ip signals, even th o u g h th e U V a n d /o r sh u n t tr ip a tta c h m e n ts have fu n c tio n e d p ro p e r ly . In th is case, th e b re a k e r w o u ld have to be o p e n e d lo ca lly (o u ts id e th e c o n tro l ro o m ). F a ilu re s o f th is ty p e are a p p a re n tly less lik e ly th a n U V tr ip a t ta c h m e n t fa ilu res.

O n th e basis o f th e fa ilu re m ech an ism s ju s t ite m iz e d , th e fo llo w in g m u ltip le fa ilu res o f r e d u n d a n t re a c to r tr ip sy s tem c o m p o n e n ts w h ich re su lt in fa ilu re to tr ip th e re a c to r (e i th e r a u to m a tic a lly o r b o th a u to m a tic a lly an d m an u a lly ) have b een id e n tif ie d . In each case, th e m in im u m n u m b e r o f r e d u n d a n t c o m p o n e n t fa ilu re s w as co n sid e red .

(a ) F a ilu re o f o u tp u t fro m b o th SSPS tra in s ‘A ’ a n d ‘B \ T h is re su lts in loss o f a u to m a tic r e a c to r tr ip fu n c tio n re q u ire d b y G D C 2 20 . M anual scram c a p a b ility fro m th e c o n tro l ro o m still ex is ts in th is in s tan ce (via b o thth e U V a n d sh u n t tr ip co ils) since th is c a p a b ility is p ro v id ed ‘d o w n s tre a m ’ o f th e SSPS o u tp u ts . S im ilar fa ilu res can be p o s tu la te d in th e re la y -c o n ta c t logic sy s tem designs fo r th e o ld e r W estinghouse p lan ts .

(b ) F a ilu re o f th e U V tr ip a t ta c h m e n t in b o th th e ‘A ’ and ‘B ’ re a c to r tr ip b reakers . T h is fa ilu re re su lts in th e loss o f b o th a u to m a tic re a c to r tr ip fu n c t io n an d m an u a l re a c to r tr ip cap ab ility via th e U V tr ip a tta c h m e n ts .T he re a c to r c an still be tr ip p e d m an u a lly fro m th e c o n tro l ro o m via th e s h u n t tr ip a tta c h m e n ts . T h is ap p ea rs to be th e fa ilu re m o d e w h ich caused th e ATW S ev en ts a t Salem o n 22 a n d 25 F e b ru a ry 1983 .

2 GDC — General design criterion.

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(c ) F a ilu re o f b o th th e ‘A ’ a n d ‘B ’ re a c to r tr ip b reak e rs in d e p e n d e n tly o f th eU V a n d s h u n t tr ip a tta c h m e n ts . T h is p rev en ts a re a c to r tr ip via all a u to m a tic an d m an u a l signals. A n a lte rn a tiv e m eans o f tr ip p in g th e re a c to r w ou ld th e n be re q u ire d (e.g. fo rc in g o n e o f th e b reak e rs o p e n loca lly o r tr ip p in g th e MG sets).

In a d d it io n to th e se fa ilu res , th e re a re c e rta in c o m b in a tio n s o f fa ilu res (a lth o u g h n o t w ith in re d u n d a n t devices) w h ich can p re v e n t a re a c to r tr ip . F o r e x am p le , fa ilu re o f th e SSPS tr a in ‘A ’ o u tp u t in c o n ju n c tio n w ith a U V tr ip a t ta c h m e n t fa ilu re a t th e ‘B ’ r e a c to r tr ip b re a k e r w ill p re v e n t an a u to m a tic scram . T he fa ilu re o f b o th th e U V and s h u n t tr ip a tta c h m e n ts fo r a given b re a k e r w ill p re v e n t th a t b re a k e r fro m re sp o n d in g to all re a c to r tr ip signals (b o th a u to m a tic a n d m an u a l). T o p re v e n t a re a c to r t r ip w ou ld req u ire th a t b o th tr ip dev ices fo r each o f th e tw o re a c to r tr ip b reak e rs fail. T he s im u ltan eo u s fa ilu re o f tw o se ts o f d iverse tr ip devices is co n sid e red u n lik e ly .

T he above d iscussion assum es th a t b o th bypass b reak e rs are o p e n (i.e . th e sy s tem is n o t be ing te s te d ) . W hen th e re a c to r tr ip sy s tem is te s te d w ith th e r e a c to r a t p o w e r, b o th th e t r ip b re a k e r rem ain in g in serv ice an d th e bypass b re a k e r a ro u n d th e b re a k e r be ing te s te d receive t r ip signals fro m th e sam e tra in . T hus, d u rin g th is tim e , th e re a c to r tr ip sy s tem is su scep tib le to single fa ilu res (e.g. SSPS o u tp u t fa ilu re ) w h ich co u ld p re v e n t re a c to r tr ip .

3. P O S T -T R IP R E V IE W A N D R E S T A R T R E Q U IR E M E N T S

3.1 . P ro b lem a t Salem

A th o ro u g h e x a m in a tio n o f th e p la n t c o m p u te r sequence-o f-even ts p r in to u t fo r th e 22 F e b ru a ry 1983 ev en t w ou ld have en ab le d th e o p e ra tin g s ta f f o r th e S h if t T ech n ica l A dv iso r to reco g n ize th a t a fa ilu re to scram h ad o ccu rred . A t th e tim e o f th is e v en t, P SE & G 3 d id n o t have a re q u ire m e n t w h ich w o u ld ensu re a th o ro u g h an d sy s tem a tic ev a lu a tio n o f re a c to r t r ip even ts . A lth o u g h th e re w as a w rit te n p ro c e d u re , i t re q u ire d o n ly th a t th e cause o f a re a c to r tr ip be d e te rm in e d b e fo re re s ta r t an d id e n tif ie d th e p e rso n n e l w ho co u ld a u th o r iz e p la n t re s ta r t a f te r a tr ip . T he p ro c e d u re s ta te d th a t i f th e cause o f th e re a c to r tr ip h a d b e e n id e n tif ie d a n d c o rre c te d , th e o p e ra tin g en g in ee r co u ld m ak e th e d ec is ion fo r re s ta r t , b u t i f th e cause co u ld n o t be id e n tif ie d , h ig h e r m an ag e m en t h a d to a u th o r iz e re s ta r t . T h e re w as n o re q u ire m e n t fo r a d d it io n a l review o f p la n t tr ip s by o th e r p e rso n n e l, e.g. th e S ite O p e ra tio n s R eview C o m m itte e . T he S h ift T ech n ica l A dv iso r w as d ire c te d to c o n d u c t an in v es tig a tio n o f all in c id en ts ,

3 PSE&G — Public Service Electric and Gas Corporation.

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c o m p le te th e in itia tio n se c tio n o f th e in c id e n t re p o r t , an d d e te rm in e th e re p o r tin g re q u ire m e n ts o f th e ev en t.

N R C w as in fo rm e d b y te le p h o n e o f th e u t i l i ty ’s d ec is io n to re s ta r t a f te r th e 22 F e b ru a ry ev en t an d th e N R C R e sid en t In s p e c to r rev iew ed th e licen see ’s scram su m m ary re p o r t , t r e n d re c o rd e rs a n d o p e ra to r a c tio n s . H e d e te rm in e d th a t th e licensee fa iled to n o tify N R C w ith in o n e h o u r a f te r th e tr ip ; th e licensee was a b o u t 3 0 m in u te s la te . T h e n N R C w as n o tif ie d o f th e 25 F e b ru a ry even t. A fte r c o n su lta tio n w ith th e N R C , th e licensee agreed to d e fe r p la n t s ta r tu p p en d in g th e o u tc o m e o f fu r th e r review s.

3 .2 . C ause o f fa ilu re

T he basic cause o f th e licensee fa iling to id e n tify th a t an ATW S ev en t h ad o ccu rred o n 2 2 F e b ru a ry 1983 w as th e lack o f th o ro u g h an d sy s tem a tic rev iew n ecessary to ach ieve a co m p le te u n d e rs ta n d in g o f th e ev en t. T h ere w as a q u e s tio n w h e th e r th e o p e ra to r h a d tr ip p e d th e p la n t o r w h e th e r th e p la n t tr ip p e d a u to m a tic a lly . T he o p e ra to r a p p a re n tly believed th a t h e h a d m an u a lly tr ip p e d th e re a c to r , an d y e t th e o p e ra tin g en g in ee r p rep a rin g th e p o s t- tr ip re p o r t c o n c lu d e d th a t th e p la n t tr ip p e d a u to m a tic a lly . T h is q u e s tio n o f m an u a l versus a u to m a tic sc ram co u ld have b een sp ec ific a lly reso lved b y th e sequence-o f-even ts p r in to u t . I t co u ld also have b een reso lved by th e o p e ra to rs a t th e tim e o f th e ev en t i f th e y h ad p ro p e r ly co n sid e red th e f irs t-o u t a n n u n c ia to r p an e l. T he o p e ra tin g o rg a n iz a tio n d id n o t a d e q u a te ly use o r u n d e rs ta n d th e in fo rm a tio n available.

3 .3 . O p e ra tin g ex p e rien ce

T he o p e ra tin g h is to ry o f th e c irc u it b reak e rs u sed in th e re a c to r tr ip sy s tem (R T S ) a t S alem an d o th e r o p e ra tin g n u c lea r p o w er p la n ts is rev iew ed in th is sec tio n . T he fa ilu re o f b reak e rs in o p e ra tin g p la n ts designed b y W esting­h o u se , B abcock and W ilson, an d C o m b u stio n E ng ineering w as rev iew ed to d e te rm in e th e re lia b ility an d to e s tab lish w h e th e r a fo re c a s t o f th e co m m o n m o d e fa ilu res ex p e rien ced a t S alem co u ld have b een m ad e o n th e basis o f an analysis o f o p e ra tin g ex p e rien ce . S ince th e R T S b re a k e r is o n e c o m p o n e n t in a co m p lex , m u ltip le -c o m p o n e n t e le c tro m ech an ica l sy s tem , o th e r re p o r te d fa ilu res in th e R T S w ere also rev iew ed to d e te rm in e w h e th e r overa ll o p e ra tio n a l ex p e rien ce s u p p o r te d th e n eed fo r a m o re d iversified re a c to r t r ip sy s tem design.

T h e fa ilu re s o f th e b reak e rs a t S alem have b een a t t r ib u te d to p ro b le m s in th e U V tr ip a tta c h m e n ts . T hese a tta c h m e n ts have also b een id e n tif ie d as th e cause o f b re a k e r fa ilu re s a t o th e r o p e ra tin g p la n ts b o th b e fo re an d a f te r th e Salem events. A n in v es tig a tio n by th e N R C c o n tra c to r , th e F ra n k lin R esearch C en te r, to d e te rm in e th e fa ilu re m o d e fo r th ese U V tr ip a tta c h m e n ts w as ca rried o u t.

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TABLE III. B R E A K E R OPERATING EXPERIENCE BEFORE SALEM EVENTS

Vendor Failures Estimated breaker demands

Breaker failures (probability/demand)

Westinghouse 26 6000 0.004

Combustion 6a 5000 0.001aEngineering

Babcock & Wilcox 21 5000 0.004

All plants 53 16000 0.003

a These values are questionable since the UV and shunt trip attachments may not have been tested independently in the CE design.

3.3.1. Circuit breaker failures in the R TS

A ll o p e ra tin g W estinghouse p lan ts , e x c e p t M cG uire U n its 1 an d 2,F a rley U n its 1 an d 2, an d V .C. S u m m er U n it 1, em p lo y W estinghouse D B -50 c ircu it b reak e rs in th e R TS. T he e x c e p tio n s e m p lo y W estinghouse D S-416 c irc u it b reak e rs . T h e B ab co ck an d W ilcox (B&W ) an d C o m b u stio n E ng ineering (C E ) p la n ts (a p a r t f ro m Palisades an d F t. C a lh o u n )4 use th e G en era l E lec tric ty p e A K -2 c irc u it b reak e rs . G enera l E lec tric p la n ts do n o t e m p lo y b reak e rs in th e r e a c to r t r ip sy s te m ; n e i th e r do Palisades o r F t . C a lhoun .

P rio r to th e S alem A TW S ev en ts in F e b ru a ry 1 9 8 3 , th e re p o r te d R T S b re a k e r fa ilu re s invo lved e ith e r th e W estinghouse D B -50 o r th e G en era l E lec tric ty p e A K-2 b reak e rs . F if ty - th re e R T S b re a k e r fa ilu re s a re n o w k n o w n to have o c c u rre d u p to 1 982 , a t 2 0 d if fe re n t p la n ts (T ab le III).

T h e W estinghouse D B -50 b re a k e r w as designed in th e 1 9 4 0 ’s an d u sed in n o n -n u c le a r a p p lic a tio n s b e fo re it b ecam e p a r t o f n u c le a r p la n t R T S designs in th e 1 9 6 0 ’s. Y an k ee R ow e began co m m erc ia l o p e ra t io n w ith th e D B -50 in 1961 . F a ilu re s o f th e D B -50 w ere firs t re p o r te d a t H .B . R o b in so n and H addam N eck in 1 9 71 . T h ese ev en ts w ere o f p a rt ic u la r c o n c e rn because H ad d am N eck e x p e rien ced s im u lta n e o u s fa ilu re s o f th e U V tr ip a tta c h m e n t in tw o R T S b reak e rs w h en th e tr ip signal w as in itia te d d u rin g a surveillance te s t. S ince th e s h u n t a tta c h m e n ts o n b o th b reak e rs w ere d e te rm in e d to be o p e ra b le , th is even t d id n o t c o n s t i tu te a c o m p le te fa ilu re o f th e t r ip sy s tem . As a re s u lt th e A to m ic E n erg y C o m m iss io n issued th e firs t o f 34 B u lle tin s an d o th e r n o tic e s co n ce rn in g various ty p e s o f c irc u it b reak e rs an d re lay fa ilu re s in re a c to r sa fe ty system s.Som e o f th e se d o c u m e n ts re la te to fa ilu res in th e re a c to r t r ip sy s tem .

4 These plants do not have the UV trip attachment in the RTS and are not subject to the same failure as other plants which use the AK-2.

IAE A-SM-268/91 269

T A B L E IV . C A U SE S O F U N D E R V O L T A G E

T R IP D E V IC E F A IL U R E S

Westinghouse DB-50

Dust

Wear

Lack of lubrication

Too frequent operation

General Electric AK-2

Manufacturing tolerances

Adjustments

Lack of lubrication

In B u lle tin 71-2 , th e causes o f a series o f D B -50 fa ilu res w ere a t t r ib u te d to d ir t , b ro k e n p a r ts , a n d m ech a n ica l b in d in g o f th e U V tr ip a tta c h m e n t . W ith few e x c e p tio n s since 1 971 , th e 26 re p o r te d fa ilu res o f th e W estinghouse D B -50 b reak e rs invo lved th e U V tr ip a tta c h m e n t . T he causes a re h a rd to d e te rm in e f ro m th e d a ta availab le , b u t m o s t a p p e a r to be fa ilu re s o f th e m ech an ica l p o r t io n o f th e U V tr ip a t ta c h m e n t cau sed by d ir t , w ear, lack o f lu b r ic a tio n an d c o m p o n e n t fa ilu re s (see T ab le IV ). A few w ere fa ilu re s o f th e e le c tric a l coils.O ne fa ilu re w as a t t r ib u te d to th e U V tr ip a tta c h m e n t n o t e x e rtin g e n o u g h fo rce .

T he firs t o f 27 re p o r te d fa ilu re s (u p to an d in c lu d in g 1982 ) o f th e G enera l E lec tric ty p e A K -2 c ircu it b re a k e r in re a c to r tr ip sy s tem s o c c u rre d in a B ab co ck an d W ilcox p la n t in 1972 . S ince th e n , fa ilu re s have o cc u rre d in A K-2 b reak e rs in b o th B&W an d C E re a c to r t r ip sys tem s. L ike th e W estinghouse b reak e r , th e A K -2 b re a k e r w as designed a b o u t 25 y ea rs e a rlie r fo r n o n -n u c lea r ap p lica tio n s . F ro m 1975 to 1979 th e re w ere 12 re p o r te d fa ilu res o f th e A K-2 design in sa fe ty -re la te d sy s tem s in c lu d in g th e R T S . As a re s u lt o f th ese fa ilu res , th e N R C issued B u lle tin 79 -0 9 re p o r tin g th a t th e causes w ere e ith e r b in d in g w ith in th e linkage m ech a n ism o f th e U V tr ip a tta c h m e n t a n d tr ip sh a ft, o r o u t-o f-a d ju s tm e n t c o n d itio n s in th e linkage m echan ism . T h e B u lle tin a t t r ib u te d th e fa ilu re s to in a d e q u a te p rev en tiv e m a in ten an ce p ro g ram m es. T h ere have b een o th e r fa ilu re s o f th e A K -2 re p o r te d since th e 19 7 9 B u lle tin . O f th e 21 R T S b re a k e r fa ilu res re p o r te d b e tw e e n 1972 a n d 1982 a t B&W p lan ts , 18 id e n tif ie d th e U V tr ip a tta c h m e n t as th e cause.

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C o m b u stio n E ng ineering p la n ts also use th e G en era l E lec tric ty p e A K-2 b reak e rs in th e R T S (e x c e p t a t Palisades an d F t. C a lh o u n ). A to ta l o f six fa ilu re s o f th is b re a k e r o ccu rred a t th re e su ch p la n ts , i.e . C alvert C liffs U n its 1 an d 2 an d S t. L ucie U n it 1 p r io r to th e Salem ATW S events. T h is sm all n u m b e r o f re p o r te d fa ilu res c o m p a red to th e n u m b e r o f fa ilu re s a t B&W p lan ts is p ro b a b ly d u e to th e diverse b reak e r-tr ip p in g m ech an ism s em p lo y ed in th e ty p e A K -2 b reak e rs a t C E p lan ts . B o th a s h u n t t r ip an d an U V tr ip a tta c h m e n t o p e ra te s im u ltan eo u s ly to o p en th e b reak e r an d a fa ilu re o f e ith e r device

w ou ld n o t be reco g n ized d u rin g a scram . In a d d it io n , b o th tr ip a tta c h m e n ts have o f te n b een te s te d to g e th e r . T h u s a fa ilu re o f th e U V tr ip a tta c h m e n t w ou ld n o t n ecessarily be d e te c te d i f th e sh u n t tr ip a t ta c h m e n t o p e ra te d p ro p e rly .

In 1980 an ev en t invo lv ing u n u su a l R T S b re a k e r fa ilu res o cc u rre d a t S t. L ucie U n it 1, a C E designed p lan t. A n analysis o f th is ev en t b y th e N R C O ffice fo r A nalysis an d E v a lu a tio n o f O p e ra tio n a l D a ta re s u lte d in th e issuance o f C ircu lar 81 -12 p o in tin g o u t th a t th e p e rio d ic te s ts u sed a t C E p la n ts sh o u ld verify th e tr ip fu n c t io n o f th e U V tr ip a t ta c h m e n t in d e p e n d e n tly o f th e sh u n t tr ip a tta c h m e n t.

A s a re su lt o f an A K -2 b re a k e r fa ilu re o f R an ch o Seco in 1 982 , generic p ro b lem s w ith th e A K -2 ‘o p en in g sp rings’ an d ‘p o s itio n in g o f th e tr ip p a d d le ’ w ere id e n tif ie d in an 4 O c to b e r 1982 le t te r f ro m J .L . C rew s, N R C R eg ion V.A fte r th e Salem even ts , B u lle tin 83-01 was issued . I t re q u ire d te s tin g o f D B-50 ty p e b reak e rs u sed in th e R T S o f W estinghouse p lan ts . N o fa ilu res w ere re p o r te d . S h o rtly th e re a f te r d u rin g te s tin g o f th e A K -2 b reak e rs in th e R T S a t San O n o fre U n its 2 a n d 3 , fo u r fa ilu res o f U V a tta c h m e n ts w ere o b se rv ed ; th re e re a c to r tr ip b reak e rs o n U n it 2 an d o n e o n U n it 3 fa iled to o p e n o n ac tiv a tio n o f o n ly th e U V tr ip a tta c h m e n t . B u lle tin 83-04 w as th e n issued req u irin g U V tr ip fu n c t io n te s tin g fo r all PW R licensees w ith o th e r th a n D B -50 b reak e rs in th e R TS. F a ilu res o f A K -2 b reak ers o ccu rred d u rin g su b se q u e n t te s tin g a t C alvert C liffs U n its 1 and 2 a n d a t M aine Y ankee.

In a d d itio n to re c e n t fa ilu res a t CE p la n ts , M cG uire U n its 1 and 2 and F a rley U n it 1 have re p o r te d fa ilu re s o f th e W estinghouse D S-416 b reak ers used in th e ir R TSs. T ab le III show s th e R TS b re a k e r fa ilu re s re p o r te d a t th e o p e ra tin g p la n ts since th e Salem ev en ts a n d m a lfu n c tio n s re p o r te d as th e re su lt o f IE B u lle tin 8 3 -04 , w h ich re q u ire d n o tif ic a tio n o f m a lfu n c tio n s n o t p rev iously re p o r te d . F o r th e se la t te r uses, T ab le III also id e n tif ie s th e basis fo r th e licensee ju d g e m e n t th a t th e o bserved m a lfu n c tio n s w ere n o t re p o r ta b le as a L icence E v en t R e p o r t (L E R ).

T he listing in T ab le III show s ap p ro x im a te fa ilu re ra te s fo r e ach v en d o r design based o n an e s tim a te d n u m b e r o f d em an d s , w h ich w as co n firm e d to th e T ask F o rc e b y th e R e g u la to ry R esponse G ro u p s . T he n u m b e r o f d em an d s w ere e s tim a te s o f ro u t in e surveillance te s t fre q u e n c y an d w ere n o t based o n p lan t-sp ec ific analysis.

IAEA-SM-268/91 271

20

x

Q

ш Q сс шCL СС LUЦ. 10 < ш сс со сс шCLш

< 5 сс ш сс 3<U.

о70 71 72 73 74 75 76 77 78 79 80 81 82 83

CALENDAR YEAR

FIG.2. Reactor trip breaker failure rate.

T h e c o m p ariso n show s th a t th e p e rfo rm a n c e o f th e R T S b reak e rs ap p ears c o m p a rab le w ith th e ra te c o m p u te d in th e ‘R e a c to r S a fe ty S tu d y ’ (W A SH 1400 ) co n sid e rin g th e u n c e r ta in tie s in th e analyses. (W A SH 1400 u sed a b e s t-e s tim a te va lue o f 0 .001 an d a range o f 0 .0 0 0 3 to 0 .0 0 3 .) T h is ty p e o f analysis, b y itse lf, w ou ld n o t g e n e ra te c o n c e rn fo r R T S b re a k e r re lia b ility o n th e basis o f o p e ra tin g ex p erien ce .

Salem U n it 1 h ad n o t re p o r te d a n y b re a k e r fa ilu re s p r io r to th e ATW S ev en ts in F e b ru a ry 1983 . H ow ever, Salem U n it 2 h a d ex p e rien ced fa ilu res o n 6 F e b ru a ry 1 979 , 20 A u g u st 1982 an d 6 Ja n u a ry 1983 . T he fa ilu re o f th e by p ass b re a k e r o n 6 F e b ru a ry 1979 o cc u rre d d u rin g p re -o p e ra tio n a l te s tin g an d was, th e re fo re , n o t re q u ire d to b e re p o r te d in an L E R . T he L E R re p o r tin g th e fa ilu re o n 2 0 A u g u st 1982 d id n o t id e n tify th e cause o f th e U V tr ip a tta c h m e n t fa ilu re . A n L E R d a te d 27 J a n u a ry 1983 re p o r te d th e b re a k e r fa ilu re on6 J a n u a ry 1983 an d id e n tif ie d d ir t o r c o rro s io n as th e cause fo r th e U V tr ip a tta c h m e n t fa ilu re . T h e U n it 2 b re a k e r th a t fa iled in Ja n u a ry was su b se q u e n tly re p a ire d an d in s ta lled in U n it 1 an d fa iled again d u rin g th e ev en ts o n 22 and 25 F e b ru a ry 1983.

R o u tin e s ta tis tic a l analysis o f single fa ilu re s an d fa ilu re ra te d a ta w o u ld p ro b a b ly n o t have suggested a h ig h p o te n t ia l fo r co m m o n cause fa ilu re

272 LANNING

re su ltin g in m u ltip le , s im u lta n e o u s b reak e r fa ilu res. H ow ever, w ith h in d s ig h t i t ap p ea rs th a t p ro p e r id e n tif ic a tio n o f ro o t causes w ith co m m o n m o d e fa ilu re p o te n t ia l c o u p le d w ith a d e ta iled eng inee ring u n d e rs ta n d in g an d care fu l review o f L E R s m ig h t have g iven an advance w arn ing o f th e S alem failu res. C o m p le te n a rra tiv e d e sc r ip tio n s re p o r tin g th e fa ilu res an d an in -d e p th en g inee ring review w ou ld be n ecessa ry to id e n tify p o te n tia l co m m o n cause failu res. F u tu re re q u ire m e n ts asso c ia ted w ith th e p ro p o se d L E R R u le sh o u ld re su lt in im p ro v ed re p o r tin g o f sig n ifican t ev en ts so th a t eng inee ring ana ly ses can address th e generic im p lic a tio n o f fa ilu res. C o m p o n e n t fa ilu res m u s t be b e t te r re p o r te d u n d e r an im p ro v ed N u c lea r P lan t R e liab ility D a ta S y stem (N P R D S ).

T he tr e n d o f R T S b re a k e r fa ilu res versus tim e is sh o w n in F ig .2. C au tio n m u s t be u sed in in te rp re tin g th is tre n d because o f th e sm all n u m b e r o f b reak e r fa ilu res an d th e asso c ia ted large u n c e rta in tie s . T h e h is to g ram show s an u p w ard tr e n d in 1978 . A b o u t th is tim e , th e increasing n u m b e r o f fa ilu res w as id e n tif ie d by th e N R C , an d a B u lle tin 79 -09 was issued req u es tin g licensee a c tio n . T he decreasing tr e n d o f fa ilu res a f te r 1979 can p ro b a b ly be a tt r ib u te d to licensee ac tio n s in re sp o n se to th e B u lle tin . T he n u m b e r o f R T S b re a k e r fa ilu res in r e c e n t y ea rs w o u ld n o t have p ro m p te d a c o n c e rn regard ing re liab ility because th e fa ilu re s w ere o ccu rr in g ra n d o m ly a t a few p la n ts w h ich w ere ex p erien c in g a p p a re n tly u n iq u e d ifficu ltie s , e.g. re p e a te d fa ilu res o f th e sam e b reak er. T he m u ltip le fa ilu res a t S t. L ucie in 1980 , w here o n e b re a k e r fa iled an d tw o o th e rs a c te d sluggishly , m ay have b een in d ica tive o f co m m o n cause fa ilu res. N ow here p r io r to Salem , h o w ev er, d id a n y o f th e o p e ra tin g ex p erien ce rev iew s reveal th e lack o f a su ff ic ie n t design m arg in in th e U V tr ip a tta c h m e n ts fo r e i th e r th e D B -50 o r th e A K -2 b reakers.

3.3.2. Other failures in the RTS

R eview o f o p e ra tin g ex p erien ce w ith th e R T S has id e n tif ie d n u m e ro u s re lay , logic and o th e r e lec trica l fa ilu res. In fa c t , a p p ro x im a te ly 2 5 0 0 fa ilu res have b een re p o r te d in L E R s p e rta in in g to th e R T S since a b o u t 1972 . R elay fa ilu re s m ake up a large p o r t io n o f th e 2 5 0 0 fa ilu res. C o m m o n cause fa ilu res o f re lay s have o cc u rre d in th e R T Ss a t K ah l (F ed e ra l R ep u b lic o f G erm an y ) an d M on tice llo (U S A ) an d in th e R TS logic a t A ngra (B razil). S im ilarly , th e 14 sc ram -p ilo t valve fa ilu re s a t G ran d G u lf re p re se n t a p o te n t ia l co m m o n cause fa ilu re in th e BW R R TS. T h is ev idence o f co m m o n cause fa ilu res co n firm s th e n eed fo r d iv e rs ity in th e R TS.

T he tw o ev en ts a t Salem , fa ilu res o f b reak e rs to tr ip a t o th e r p lan ts fo llow ing de-energ iz ing o f th e U V tr ip a tta c h m e n ts , th e in ves tiga tions by th e F ra n k lin R esea rch C en te r, and d iscussions w ith c irc u it b reak e r v en d o rs have in d ic a te d a g enera l p ro b le m w ith th e q u a li ty assu rance re q u ire d b y n u c lea r s team su p p ly sy s tem (N SS S) v en d o rs w h en specify ing an d p ro cu r in g re a c to r tr ip

IAE A-SM-268/91 273

T ABLE V. ATWS RULEMA K I N G

Previously proposed

Auto (auxiliary feedwater system ) initiation and turbine trip (PWR)

Diverse scram system (GE and B&W)

Alternate rod injection (BWR)

Augmentation of standby liquid control system (BWR)

Auto trip of recirculation pumps (BWR)

Implementation of mitigation procedures and training

Additions proposed

Diverse scram system for Westinghouse design

Reliability assurance programme for RTS (PWR and BRW)

c irc u it b reak e rs . T hese ven d o rs have a p p a re n tly n o t re q u ire d su ffic ien t c irc u it b re a k e r design v e rif ic a tio n te s tin g to en su re th a t th e b reak e rs w ill have h igh re lia b ility th ro u g h o u t th e ir o p e ra tin g life. T h ere has a lso a p p a re n tly n o t b een en o u g h em p h as is o n estab lish in g an d c o n tro llin g m an u fa c tu r in g to le ra n c e s on th e c irc u it b reakers .

4 . G E N E R IC IM P L IC A T IO N S O F T H E SA LE M E V E N T S O N R E A C T O RT R IP SY STE M D E SIG N

E x p erie n ce w ith c ircu it b re a k e r fa ilu res in re a c to r tr ip sy s tem s in d ica te s th e n eed to in c rease th e assu ran ce th a t p o w e r to th e c o n tro l ro d s o n PW Rs will be re liab ly in te r ru p te d fo llo w in g a re a c to r t r ip signal. T he U V tr ip a tta c h m e n ts c u rre n tly u sed have sh o w n m a lfu n c tio n s o f th e ty p e s genera lly c o n sid e red to be can d id a te s fo r causing co m m o n m o d e fa ilu res. T hese U V tr ip a tta c h m e n ts are c o m p lic a te d , a re su b jec t to m a n u fa c tu r in g v a ria tio n s , a n d re q u ire ca re fu l m a in te n a n c e , lu b r ic a tio n an d a d ju s tm e n t. T h ey a re , h o w ev er, k ey c o m p o n e n ts in PW R re a c to r tr ip sy s tem designs.

T he Salem ev en ts also re -em p h asize th e genera l n eed to co n sid e r co m m o n m o d e fa ilu res w h ich co u ld p re v e n t re a c to r tr ip w hen req u ired . T h is is p a rt ic u la r ly th e case w hen th e h is to ry o f fa ilu res in re a c to r tr ip sy s tem c o m p o n e n ts is co n sid e red . T h ere is a p o te n t ia l w ith in all r e a c to r t r ip sy s tem designs fo r

274 LANNING

c o m m o n cause fa ilu re s o f id e n tic a l o r sim ilar c o m p o n e n ts to re su lt in a fa ilu re to tr ip . T he w eaknesses fo u n d in th e re a c to r tr ip sy s tem in te rm s o f u n re lia b ility a n d th e p o te n t ia l fo r c o m m o n cause fa ilu re s n eed to b e inves tig a ted . P ro p o sed ATW S ru le s have in th e p a s t in c lu d ed a re q u ire m e n t fo r d iv e rsity in acco m plish ing re a c to r t r ip fo r all b u t th e W estinghouse designed p lan ts .

D ivers ity o f re a c to r tr ip in th e W estinghouse-designed p la n ts w as n o t to be re q u ire d b y N R C s ta f f an d in d u s try a lte rn a tiv e s becau se th e tra n s ie n t fo llow ing an ATW S is less severe o n W estinghouse p la n ts th a n fo r th e o th e r v en d o r designs. H ow ever, th e re liab ility assu rance p ro g ram m e in th e so-called H en d rie a lte rn a tiv e ru le p ro p o se d b y N R C m ig h t have led to su ch d iv ersity be ing ad d ed to th e W estinghouse design.

In th e W estinghouse-designed sy s tem a t S alem , a co m m o n m o d e fa ilu re o f tw o id e n tic a l c irc u it b re a k e r tr ip devices p re v e n te d th e a u to m a tic sy s tem o p e ra tin g .

H aving o n ly tw o re d u n d a n t logic tra in s , th e re are o th e r p o in ts w ith in th e W estinghouse sy s tem w here c o m m o n m o d e fa ilu re s o f tw o sim ilar c o m p o n e n ts can p re v e n t a r e a c to r tr ip . F u r th e rm o re , d u rin g p e rio d ic te s tin g o f a logic tra in in th e W estinghouse-designed sy s tem , a single fa ilu re can p re v e n t tr ip . T h e final ATW S ru le (see T ab le V ) sh o u ld co n sid e r th e S alem even ts , th e ex p e rien ce w ith r e a c to r tr ip sy s tem c o m p o n e n t fa ilu res in g en era l, th e v u ln e rab ility o f each re a c to r tr ip sy s tem to co m m o n m o d e fa ilu res an d th e fu n d a m e n ta l im p o rta n c e o f re a c to r tr ip to sa fe ty .

S U M M A R Y O F S E S S I O N V

Chairmen: F.Ya. Ovchinnikov and T.P. Haire

In this session, one paper was given on a system developed to utilize operating experience while other papers described actual operating experience, the lessons learned from this experience and systems developed for the determination of component and system reliability.

The task of collecting, screening, analysing and distributing relevant experience of abnormal incidents was considered to be very difficult. For a country like Italy, which receives a lot of information on incidents from the USA, the difficulties are increased as a result of language difference, lack of knowledge of overseas plant designs and their behaviour under degraded conditions, and deficiencies in component lists.

Among the incidents reported from the Federal Republic of Germany, the one most likely to have the widest interest was related to loss of off-site power.This resulted in the formation of a steam bubble in the primary pressure vessel because the vessel head was not cooled sufficiently under natural circulation.It was deduced that these conditions would arise as a result of any rapid cool down. Procedures are needed to avoid sudden condensation of the bubble.

From a number of incidents evaluated over several years in France, one conclusion that may be of general interest is that an analysis of many incidents with potentially serious consequences from the safety point of view showed that no clear distinction should be made between items important to safety and other items. This implies that some reconsideration should be given to the use made of the safety classification system. For example, failure of items not classified as important to safety may have some considerable safety importance (e.g. pressure relief valve at Unit 2 of Three Mile Island and the loss of instrument supplies at Unit 3, Crystal River). The design organization in France has also analysed operational incidents and this work included, in appropriate cases, investigations carried out into the effects of any additional failures which could have occurred during the incident in order to identify weak points in the lines of defence built into the design.

Of the two incidents reported from Brazil, one was a failure of a switch in the control rod supply circuit to open. Since two switches are supplied in series and the second switch operated correctly there was no failure to trip. It was, however, a first step towards an anticipated transient without scram, and thus had some affinities to the Salem incident discussed below.

275

276 SUMMARY OF SESSION V

The experience reported on the operation of fast reactor plants highlighted the problems of sodium contamination for maintenance personnel, since the sodium emits a high level of gamma radiation. The lifetime of cold traps was determined by the limit on the surface gamma dose. From the point of view of control and the consequences of incidents, however, fast reactors seem to be proving simpler than thermal reactor plants.

Speakers from two countries reported on the development of reliability data collection systems. The objective of the Japanese system is to determine system and component reliability, but one difficulty is to obtain availability figures or operating times for redundant systems and components. The Hungarian system appears to have broad objectives, since it is to be used additionally for probabilistic risk assessments and the establishment of operating and maintenance strategies.

Incident reporting systems to collect, screen and analyse incidents require considerable effort and organization, but these activities are making a valuable contribution to the safety of nuclear power plants.

The operating experience of gas-cooled ‘magnox’ reactors in the United Kingdom, all of which have now had long operating lives, does not reveal any trend attributable to ageing. Indeed, generally speaking there has been an improvement in reliability with time. The conclusion that the predominant causes of reactor trips and of the majority of spurious trips are faults in the reactivity control equipment seems an interesting one. Another interesting con­clusion is that failure rates in analogous systems and components in PWRs showed similarities with the G C R experience.

Experience with PWRs in France shows that the rate of trips decreased from 1979 to 1982 but thereafter it has been increasing. Many trips are due to feed­water faults, testing and human errors. A serious problem in Spain was generic to the steam generator design and is now well known. This problem arose from vibrations in the tubes close to the feedwater inlet duct. It is of interest here to see the methods adopted by an importer of nuclear technology.

Very interesting information was given about two anticipated transient without scram (ATWS) incidents which occurred at the Salem (USA) nuclear power plant in February 1983. On both occasions the plant was operating at low level and was scrammed manually, so there were no significant consequences. Subsequent investigations, however, showed that the plant had failed to scram automatically from a valid reactor protection signal. The incidents were not correctly assessed by the plant personnel although the necessary operational data were available. The main reason for the failure to scram was that the circuit breakers in the control rod system did not open, and it was subsequently found that a number of similar failures had occurred in other plants.

The main conclusions are that ATWS needs to be seriously considered, and management must ensure that a proper systematic review of the causes of a scram is undertaken before restarting the reactor.

SUMMARY OF SESSION V 277

In the USA, a requirement to provide diversity of scram systems is under consideration. This would affect only Westinghouse plants. Also, changes to procedures may be required to delineate the steps the operator should take. This may require the operator always to manually scram after each automatic scram event. For some plants this may require a response in less than two minutes.

The IAEA paper looked at the response of a number of countries to the lessons learned from the TMI incident of March 1979. One of these lessons was that a safe plant was an economic necessity, so that there should be an economic incentive in providing greater safety margins than those obtained merely by simple compliance with regulatory requirements. With this in mind it is interesting to examine the ‘lessons learned’ given in the paper and to consider whether they really do represent lessons that need to be learned.

It may be concluded from the papers and discussions in this session that a properly structured approach to comprehensive safety evaluation is important as a basis for the efforts expended in the analysis of incidents of safety significance. International co-operation in this field is also important, particularly for countries which are importers of nuclear technology.

I N T E R N A T I O N A L A C T I V I T I E S T O I M P R O V E S A F E T Y

( S e s s i o n V I )

ChairmanH. F U K U M O T O

Japan

IAEA-SM-268/39

L E S A C T I O N S D E S A U T O R I T E S D E S U R E T E

F R A N Ç A I S E S E N M A T I E R E D E C O O P E R A T I O N

I N T E R N A T I O N A L E S U R L A S U R E T E

D ’E X P L O I T A T I O N D E S C E N T R A L E S N U C L E A I R E S

M. LAVERIEService central de sûreté des installations nucléaires,Ministère de l’Industrie et de la recherche,Paris, France

Abstract-Résumé

A C TIV ITIE S O F THE FREN CH S A F E T Y AU TH O RITIES R E L A T E D TO IN T E R N A TIO N A L

CO -O PER ATIO N ON N U C L E A R POWER P L A N T O PER A TIN G S A F E T Y .The French safety authorities are keen to develop a num ber o f international co-operation

initiatives which can be split into four main groups: (1) exchanges o f operating experience which provide the safety authorities o f each country w ith ‘operating feedback’ on as large a num ber o f facilities as possible; (2) exchanges o f regulatory texts from different authorities, either through bilateral arrangements which seem particularly appropriate for collecting reference texts and comparing regulatory positions, or within the fram ework o f international organizations which, at the multilateral level, perform a useful function in preparing such reference texts; (3) special exchanges for pow er plants sites close to frontiers which provide the authorities o f the neighbouring country with a flow o f basic inform ation on the plant’s safety characteristics, events affecting plant safety and, more generally, any event which might give rise to concern or debate among the local population; and (4) activities relating to the exports o f the French nuclear industry, since the French safety authorities consider it their responsibility to provide the authorities o f client countries with full inform ation on regulatory texts and to examine, if requested, any form o f support that could be given to the client countries.

LES A C TIO N S DES A U TO R IT E S DE SU R ETE F R A N Ç A ISE S EN M ATIER E DE CO O PER A TIO N IN T E R N A TIO N A L E SUR L A SU R ETE D’EX PLO ITA TIO N DES

C E N TR A LE S N U CLEA IR ES.Les autorités de sûreté françaises portent un intérêt particulier au développement des

actions de coopération internationale, parmi lesquelles on peut distinguer schématiquement quatre principaux domaines: 1) les échanges d’expérience d’exploitation, qui perm ettent aux autorités de sûreté de chaque pays de disposer d ’un «retour d’expérience» portant sur un parc d’installations aussi étendu que possible; 2) les échanges de références réglementaires provenant des diverses autorités à l ’occasion, notam m ent, d’accords bilatéraux qui paraissent particulièrement bien adaptés pour la collecte de ces références et pour la confrontation des points de vue réglementaires, et dans le cadre des organismes internationaux qui établissent

utilem ent, au plan multilatéral, de tels états de références; 3) les échanges particuliers relatifs aux centrales frontalières, qui perm ettent aux autorités du pays frontalier de disposer d’un flux d’inform ations de base leur faisant connaître les caractéristiques de sûreté de la centrale, les événements affectant la sûreté de l’installation, et, plus généralement, tout événement qui pourrait susciter des inquiétudes ou des interrogations dans la population; 4) les actions liées

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282 j I LAVERIEi

aux exportations de l ’industrie nucléaire française, car, vis-à-vis des responsables des pays «clients» les autorités de sûreté françaises considèrent qu’il leur appartient d’assurer une inform ation com plète du point de vue des références réglementaires et d’examiner, à la demande, toute form e d’appui pouvant être apportée aux pays clients.

Les autorités de sûreté françaises portent un intérêt tout particulier aux actions de coopération internationale, notamment dans le domaine de la sûreté de fonctionnement des centrales nucléaires. Les unités d'oeuvre consacrées à cette tache par le service central de sûreté des installations nucléaires et ses appuis techniques ont crû rapidement dans les dernières années.

La diversification, l'élargissement et l'approfondisse­ment de ces collaborations me semblent avoir considérablement enrichi les réflexions internes des autorités de sûreté françai­ses en permettant notamment de mieux apprécier l'importance relative des divers problèmes de sûreté et de les aborder dans un cadre plus cohérent.

Au delà de cette constatation très égoïste, j'espère que nos partenairës ont trouvé dans ces collaborations la même valeur ajoutée.

Il n'est pas aisé de présenter clairement ces diffé­rents échanges, compte tenu de leur diversité : diversité dessujets techniques, diversité des niveaux de détail ou de généralité, diversité des motivations engendrant ces échanges, diversité des partenaires. C'est pourquoi, pour la commodité de mon propos, je classerai ces échanges par "motivation", même si les domaines techniques traités dans chaque rubrique se révèlent le plus souvent étroitement imbriqués :

- les échanges ayant pour but l'acquisition d'une expérience d'exploitation aussi vaste que possible,

- les échanges relatifs aux textes et références réglementaires élaborés et utilisés par les autorités de sûreté.

J'évoquerai également deux types d'échanges plus spécifiques, auxquels il convient d'apporter une attention toute particulière :

- les échanges relatifs aux centrales frontalières,

- les actions liées aux exportations de l'industrie nucléaire française.

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Dans chaque domaine, je m'efforcerai de décrire ce que je crois être les modalités de collaboration les plus efficaces et, en particulier, les rôles respectifs des travaux bi-latéraux et des travaux multilatéraux à travers divers organismes internationaux dont, bien entendu, l'Agence Internationale de l'Energie Atomique.

Je précise enfin que mon exposé ne traduira qu'unevision partielle : celle d'une personne travaillant au sein desautorités de sûreté ; il ne décrira pas toutes les autres formes de collaborations internationales relatives à la sûreté d'exploi­tation des centrales nucléaires : celles entre exploitants,constructeurs, organismes de recherche et de développement,...

1 - Les échanges ayant pour but 1 1 acquisition d 1une expérience d'exploitation aussi vaste que possible

Il convient de distinguer deux préoccupations succes­sives :

- l'accès à un champ d'information aussi vaste quepossible, avec une transmission rapide, fiable,adaptée et homogène de l'information.

Le rôle des organismes internationaux concernés par la sûreté nucléaire est essentiel. Nous portons un intérêt particu­lier à 1'"incident reporting system" de l'O.C.D.E. Les possibili­tés offertes par l'AIEA sont également évidentes, compte tenu en particulier du champ extrêmement vaste que constituent les pays membres.

Il convient dans ce domaine de veiller à la parfaite coordination des différentes initiatives internationales. Il serait regrettable de voir se développer des "banques d'informa­tions" parallèles, même si chacune pouvait avoir certaines qualités spécifiques (champs, présentation, niveau de détail de l'information, analyse accompagnant l'information).

Les accords bilatéraux permettent d'ajouter au "tableau général" ainsi constitué des éclairages complémentaires, en particulier entre pays exploitant des réacteurs très similaires.

- l'analyse approfondie de certains événements sélec­tionnés en petit nombre

Le système (ou les systèmes) d'acquisition précité peut certes procéder à une analyse de certains des événements

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collectés. Ceci peut permettre une exploitation rapide du fichier par certains utilisateurs.

Mais je ne pense pas que l'organisme collecteur doive aller trop loin dans cette voie. Il doit appeler l'attention, plutôt que de traiter à fond le problème technique. Les enseignements à tirer sont fonction du contexte du pays qui les tire et ce n'est que par leurs propres travaux que les responsables de chaque pays se convaincront de l'importance des leçons à tirer.

Les travaux menés dans le cadre d'accord bilatéraux sont mieux adaptés à des réflexions approfondies. A titre d'exemple, plutôt que de rechercher au plan international les enseignements de TMI, ne vaut-il mieux pas, après une phase de réflexions internes à chaque pays, comparer bilatéralement et périodiquement les conclusions de chacun. Une telle méthode me paraît susceptible de conduire plus rapidement à des conclusions utilisables par les différents responsables.

Conformément à cette analyse, le service central de sûreté des installations nucléaires constate que de tels échanges constituent une partie notable et particulièrement intéressante des travaux menés dans divers accords bilatéraux qu'il a conclus (par exemple avec les Etats-Unis, la République Fédérale d'Allemagne, le Japon, l'Espagne...).

2 - Les échanges relatifs aux textes et références réglementai­res élaborées et utilisées par les autorités de sûreté

Je traiterai très brièvement ce point, qui relève de l'évidence : les autorités de sûreté ont besoin en permanence de pouvoir "recaler" leurs décisions réglementaires par rapport à celles de leurs homologues.

Ces échanges se font soit de façon bilatérale, soit de façon multilatérale, dans un cadre informel ou institutionnel (c'est, par exemple, le cas de la Communauté Economique Européenne).

Toute action d'échange, de collecte, de synthèse ou de comparaison des dispositions réglementaires est donc la bienve­nue .

Par contre, se pose à ce sujet une question fondamen­tale : faut-il aller plus loin ? Dans le domaine de la sûreté,convient-il, au-delà des échanges d'informations sur les posi­tions réglementaires respectives, d'élaborer au plan internatio­nal des recommandations, des références, voire des directives

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(lorsque la nature de l'organisme le rend juridiquement possible) qui aillent plus loin que les dispositions réglementaires préexistantes dans les principaux pays concernés.

J'aurai tendance pour ma part, (mais ce n'est qu'une opinion personnelle) à répondre par la négative. Chaque pays doit rester pleinement responsable de ses orientations réglementaires et, dès lors qu'il connaît les positions prises dans les autres pays, il dispose de tous les éléments d'appréciations. Vouloir coordonner, normaliser, uniformiser les dispositions réglementai­res de différents pays représente-t-il réellement une "valeur ajoutée", non seulement pour l'organisme promoteur, mais aussi pour chacun des pays concernés ? Le constat des traditions techniques différentes des divers pays, de la lourdeur et du délai inhérents à de tels travaux, de la diversité des voies techniques permettant d'assurer la sûreté, me conduit en effet à douter de l'existence d'une telle valeur ajoutée.

3 - Les échanges spécifiques relatifs aux centrales frontalières

Pour ce domaine de collaboration, il convient de rechercher, dans chaque cas et de façon bilatérale les modalités de nature à répondre aux préoccupations des deux pays concernés. Je ne vois pas, pour ma part, de raison conduisant à vouloir uniformiser ces pratiques, même sur les diverses frontières d'un même pays.

La France a, bien entendu, de par l'ampleur de son programme électronucléaire et sa configuration géographique, une expérience particulière des dialogues liés aux centrales fronta­lières. Pour ce qui concerne les autorités de sûreté, je formulerai les constatations suivantes :

3.1. Il est indispensable que les autorités qui ont un pouvoir réglementaire sur la centrale frontalière mettent à disposition de leurs homologues du pays voisin concerné un ensemble d'infor­mations techniques permettant à ces derniers d'apprécier la sûreté de l'installation et, en conséquence, la nature et le niveau des risques induits.

Cette mise à disposition ne peut se limiter à de simples transmissions de documents. Il est très souhaitable que soit choisie dans chaque pays une centrale de référence et qu'un travail approfondi et commun permette d'effectuer une analyse comparative des principaux aspects de ces installations. Il faut se garder de considérer à priori que "sûreté équivalente" signifie "dispositions identiques" : il y a très souvent des

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voies techniques fort différentes permettant d'atteindre des niveaux de sûreté équivalents.

Compte tenu de ces travaux, il importe que lesautorités de sûreté du pays "voisin" de la centrale soient aptes à répondre, dans leur propre pays aux questions (voire auxinquiétudes) relatives à la sûreté de la centrale frontalière.

3.2. Outre cette réflexion technique générale, il y a lieu de définir avec précision certaines modalités pratiques :

. il convient tout d'abord d'établir des procédures efficaces d'information en cas d'accident, même hautement improbable, susceptible d'affecter le pays voisin. Les interlocu­teurs et les liaisons doivent être parfaitement définis.

. il convient en outre qu'une collaboration s 'instaure pour la mise en oeuvre, dans un tel cas, des plans d'urgence des pouvoirs publics. Ceci ne signifie nullement qu'il faille normaliser les caractéristiques de ces plans dans les deux pays : chacun peut agir selon ses propres pratiques, l'autre pays luiapportant tout le concours possible.

enfin, il convient d'étendre l'information aux événements de la "vie quotidienne" de l'installation : tout fait, même mineur, doit être porté à la connaissance des autorités du pays voisin dans un délai approprié s'il est susceptible de susciter des inquiétudes ou des questions dans ce pays.

3.3. Pour illustrer les considérations précédentes, je citerai maintenant deux exemples pratiques d'échanges spécifiques rela­tifs aux centrales frontalières.

. Entre la République Fédérale d'Allemagne et la France

Je crois que mes collègues allemands ne me démentiront pas si j'affirme que cette collaboration peut être considérée comme exemplaire. La "Commission franco-allemande de sûreté des installations nucléaires" constitue, à travers une dizaine.de groupes de travail, le cadre d'échanges techniques intensifs qui dépassent d'ailleurs largement les questions relatives aux centrales frontalières. Cette commission (créé en 1976 par un accord conclu entre le ministère fédéral de l'intérieur de la République Fédérale d'Allemagne et le ministère de l'industrie de la République française, prenant la suite de contacts informels existant depuis 1972) a consacré ses premiers travaux à une comparaison de la sûreté de la centrale nucléaire française de

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Fessenheim et de la centrale nucléaire allemande de Neckarwei- steim. Avec le projet de création de la centrale française deCattenom, les travaux se sont portés sur cette centrale et sur la centrale allemande de Philippsburg 2, dans le but de fournir très tôt une information mutuelle sur les équipements de sûreté et l'influence sur l'environnement des deux centrales. A cette fin, un questionnaire comparatif fut établi conjointement. Les réponses ont été examinées en 1981 et 1982 au sein des groupes spécialisés. En fin 1982, la commission a émis un rapport de synthèse formulant la conclusion suivante :

"Sur la base de ces informations, la commission arrive à la conclusion que les mesures de sûreté, de radioprotection et de protection de l'environnement ainsi que les plans d'urgence déjà mis en place ou prévus pour les centrales nucléaires de Cattenom et de Philippsburg 2 sont comparables, notamment pour les conséquences au-delà des frontières, et que la population frontalière bénéficiera dans chaque cas par rapport à la centrale étrangère d'une protection analogue à celle prévue dans levoisinage des centrales nationales.

Dans les deux pays existent des objectifs de protection comparables. Pour les atteindre on utilise parfois des solutions techniques et des méthodes différentes afin d'apporter la preuve de leur efficacité (base de calcul, modèles...). La commission et ses groupes de travail suivront le déroulement des procédures d'autorisation en cours, discuteront des informations et docu­ments échangés au fur et à mesure de l'avance des travaux de construction des centrales de Cattenom et Philippsburg 2."

. Entre la Belgique et la France

Dans le même esprit, ont été mis en place fin 1982(avec la coordination, côté français, du secrétariat général ducomité interministériel de la sécurité nucléaire) trois groupes de travail relatif à la sûreté, à la protection du milieu et à celle des personnes. Le service central de sûreté des installa­tions nucléaires contribue principalement aux travaux du groupe "sûreté", qui a adopté les centrales de référence de Chooz B1 en France et de Tihange 2 en Belgique. Bien que ces travaux en soient seulement à leur début, il convient d'ores et déjà d'en souligner l'intérêt technique. Je suis persuadé qu'ils permet­tront de traiter de façon approfondie et constructive les questions relatives à la centrale frontalière de Chooz Bl.

4 - Les actions liées aux exportations de 1 1 industrie nucléaire française

4.1. Il convient tout d'abord de souligner l'importance et laqualité des actions menées par l'AIEA, visant à mettre à

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disposition de pays entamant un programme électronucléaire des références techniques, ainsi qu'un appui pour la mise en pratique de ces références. Le service central de sûreté des installations nucléaires participe avec intérêt à ces programmes.

Il est évident qu'au-delà de principes et de disposi­tions générales dont l'application peut être considérée comme universelle, l'élaboration des références précitées et l'organi­sation des cours correspondant doit veiller à rendre compte des pratiques alternatives existant dans les pays engagés dans les principaux programmes nucléaires, et non pas présenter comme une référence universelle la pratique particulière de tel ou tel pays. Ce souci d'objectivité est pris en compte par l'AIEA.

4.2. Il faut insister maintenant sur le rôle et la responsabili­té des pays "fournisseur" de produits relatifs aux installations nucléaires (installations clés en main, services technologiques, matériels,...). Une installation nucléaire est un mécanisme trop délicat, dont les risques potentiels sont trop important pour qu'un pays "fournisseur" (je dis bien un "pays" et non pas seulement un "prestataire") ne veille pas soigneusement à une mise en oeuvre satisfaisante au plan de la sûreté de ses prestations, quelle que soit la forme juridique des liens qui en résultent.

Pour leur part, les autorités de sûreté françaises considèrent qu'il leur appartient, vis à vis des responsables (exploitants et autorités de sûreté) des pays "clients" effectifs ou potentiels de l'industrie nucléaire française :

- de mettre à disposition et d'expliciter en tant que de besoin. Les diverses références réglementaires existant en France ainsi que le détail de leurs modalités pratiques d'application.

- d'exprimer officiellement leur position sur les codes et normes élaborés par l'industrie nucléaire fran­çaise, et qui sont utilisés tant en France qu'à 1 'exportation.Je fais ici référence, en particulier, aux "règles de conception et de construction" (R.C.C.) publiées et mises en oeuvre (volumes : procédés, matériaux, génie civil, matériels électriques, combustible, incendie). Ces documents, par leur niveau et détail et par leur mise en oeuvre systématique permettent d'apporter au plan international la référence du programme nucléai­re français et des dispositions de sûreté adoptées dans ce programme.

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- de mettre en place, avec les autorités de sûreté du pays "client" un flux d'échanges réglementaires et techniques. Les prises de positions des autorités de sûreté française dans le cadre du retour d'expérience à travers le fonctionnement des unités françaises doivent en particulier être ainsi explicitées.

- d'engager les collaborations qui apparaîtraient souhaitables à l'occasion de ces échanges (approfon­dissements techniques ou administratifs, formation du personnel de l'autorité de sûreté,...).

- d'examiner au cas par cas, si cela leur est demandé,la possibilité d'exercer certaines parties des analyses et contrôles de sûreté qui seraient effec­tués sur une installation similaire en France. Il s'agit là de proposer un acquis technique et une organisation disponible, et non bien évidemment de l'imposer sous quelque forme que ce soit : il estlégitime qu'un pays client ait le souci de diversi­fier les appuis dont il s'entoure pour juger, au plan de la sûreté, de prestations fournies par l'industrie française.

- d'étudier de façon bilatérale l'appui qui peut être apporté aux autorités du pays client, tout au long de la vie de l'installation.

- d'examiner et de préparer de façon bilatérale l'appuiqui pourrait, en cas d'accident, être apporté aux autorités du pays client dans l'exercice de ses responsabilités, tant en ce qui concerne l'analyse technique de l'événement que la mise en oeuvre du plan d'urgence des pouvoirs publics. Une telle action dépasse bien entendu le cadre de la "sûreté" et implique, sous la coordination du secrétariat généraldu comité interministériel de la sécurité nucléaire,l'ensemble des organismes français concernés par la préparation et la mise en oeuvre des plans particu­liers d'intervention.

4.3. A titre d'exemple et d'illustration des considérations qui précèdent, je citerai les actions menées dans le cadre de l'accord de coopération entre la République de Corée et la France. Outre les contrats et accords existant au niveau des constructeurs et exploitants, outre l'accord de collaboration relatif aux technologies de sûreté entre le Korean Atomic EnergyInstitute et l'Institut de Protection et de Sûreté Nucléaire duCommissariat à l'Energie Atomique, le Nuclear Regulatory Bureau

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du ministère coréen de la science et de la technologie et le service central de sûreté des installations nucléaires collabo­rent activement. Cette collaboration a bien sûr été axée tout d'abord vers les questions relatives à la conception et la construction des centrales. Mais d'ores et déjà, le centre d'intérêt se déplace vers le domaine qui sera sans nul doute le plus important : la collaboration relative à la sûreté d'exploi­tation.

Conclusion

En conclusion d'une présentation qui ressemble peut être à un long inventaire, j'espère avoir illustré tout l'intérêt que portent les autorités de sûreté françaises à la collaboration internationale en matière de sûreté nucléaire, et tout particu­lièrement dans le domaine de l'expérience d'exploitation des centrales nucléaires.

Quant à la question de savoir quels sont les meilleurs canaux pour assurer cette collaboration, dans chacun des multiples domaines évoqués, je vous ai fait part de mes convic­tions et aussi de quelques hésitations, en ce qui concerne en particulier les vocations et les spécificités des différents organismes internationaux. Je pense que l'Agence Internationale de l'Energie Atomique, compte tenu du rôle éminent et incontesté qu'elle joue dans le domaine des collaborations multilatérales, peut fournir le cadre d'une intéressante réflexion sur ce sujet.

IAEA-SM-268/71

N E A I N C I D E N T R E P O R T I N G S Y S T E M :

T H R E E Y E A R S ’ E X P E R I E N C E

Y. OTSUKA, W. H À U S S E R M A N N Nuclear Safety Division,OECD Nuclear Energy Agency,Paris

Abstract

N E A INCIDENT REPO RTIN G SYSTEM : TH REE Y E A R S ’ EXPERIENCE.The paper presents an overview o f the N E A Incident Reporting System (1RS) which was

set up to collect, assess and disseminate inform ation on safety-related incidents in nuclear pow er plants. The 1RS inform ation exchange is significant in tw o senses. First, it enables regulatory authorities and utilities in participating countries to take appropriate action to prevent the reported mishaps occurring again elsewhere. Secondly, the continuous collection and system atic analysis o f such inform ation allows identification o f areas o f concern where safety research should be strengthened. There are tw o stages in the 1RS inform ation exchange. First, the national 1RS Co-ordinator selects inform ation on significant incidents, in accordance with a com m on reporting threshold, from the abnormal occurrences reported to the regulatory body, to be distributed through the N E A Secretariat. This screening is intended to exclude minor events, so that on ly significant inform ation is sent to participating countries. Secondly, a group o f experts periodically reviews the incidents reported during the preceding twelve months to identify major areas o f concern. To assist this process, a computer-based data retrieval system is being developed for 1RS incident reports. The paper gives some details o f the 1RS mechanism and discusses reporting criteria and the inform ation included in a report. Areas o f concern derived from reported incidents, an outline o f the data retrieval system, and examples o f feedback o f lessons learned and possibilities for international co-operation are also discussed.

1. INTRODUCTION

Efforts to enhance the safe operation of nuclear power plants include theoretical studies as well as experiments. Yet nothing can replace actual experi­ence gained in day-to-day plant operation, especially as regards equipment failures or other safety-related incidents. In this respect, the increasing number of nuclear power plants in operation in the world today, some 295 as compared to 109 in 1972 and 26 in 1962, provide nuclear safety engineers with an important source of information on technical experience. This very growth of nuclear capacity has generated a parallel need to feed back the lessons learned from operating experi­ence, not only at the national but also at the international level, and this is

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especially true for countries with relatively modest nuclear programmes. Such information should be exchanged on as wide a scale as possible, so as to optimize the benefits of this experience.

The international exchange of information on operating experience in nuclear power plants is significant in two senses. First, it enables the regulatory authorities and utilities in participating countries to take immediate action to prevent the reported mishaps occurring again elsewhere. Secondly, the continuous collection and systematic analysis of such information allows identification of areas of concern where safety research should be strengthened or system design improved; in this way operating experience is fed back, not only to the operators, but also to those deciding safety research policy and the constructors.

With this in mind, the Committee on the Safety of Nuclear Installations (CSNI) of the OECD Nuclear Energy Agency (NEA) started the Incident Reporting System (1RS) in January 1980 to exchange information on operating experience gained in the thermal nuclear power plants of the N E A member countries and to facilitate proper feedback of this experience. The system was operated initially for a two-year period on a trial basis, at the end of which the participating countries agreed on formal guidelines stipulating detailed procedures for information exchange and thresholds for incidents to be reported. These guidelines were made the subject of an OECD Council Recommendation in February 1983 in order to place the system on a more formal basis.

The 1RS system experienced a number of teething troubles during its intro­ductory period, but became fully operational in 1982. It must be pointed out that since 1965, long before the 1RS existed, N E A member countries had regularly exchanged information on significant operating experience from the standpoint of safety during the annual meetings of the CREST (Committee on Reactor Safety Technology) and of its successor CSNI. Moreover, the CSNI has a standing agree­ment to convene a special meeting of the full Committee in the event of any nuclear accident; the first meeting of this kind was held in June 1980 following the Three Mile Island accident. Mutual understanding and trust built up during this period contributed to a relatively rapid development of the 1RS.

2. PARTICULAR OBJECTIVES

There are four essential rules which characterize the 1RS:(a) The information exchanged through the system is first screened in the country

where the incident occurred, in order to avoid reporting abnormal occurrences with relatively minor or no safety significance. The occurrences reported to national regulatory authorities in member countries total several thousand per year: sending all these to the 1RS would overload the mechanism;

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moreover it would be difficult for recipients to discover important lessons from such a mass of information.

(b) The information is restricted to the nuclear community represented by the regulatory authority and is not released to the general public so as to avoid misinterpretation.

(c) An 1RS report is expected to provide consistent, technically accurate and adequate information on the incident in question so that recipients may judge whether any lessons from the incident could be applied to their own nuclear power plants.

(d) The information should be provided as soon as possible after the occurrence of the incident so that participating countries can take corrective action immediately if appropriate. This requirement may contradict the call for complete information and then a suitable balance between the two require­ments must be struck.

3. 1RS MECHANISM

To satisfy the requirements set out above, the following mechanism has been established.

A. Participants

Participants in the 1RS system undertake to report operating experience in their own nuclear power plants according to the common reporting procedures and criteria given in the 1RS guidelines. All the 13 N E A countries having commercial nuclear power plants in service participate in the 1RS, and thus a total of 230.reactors (approximately 80% of the world’s operating reactors) are covered by the NEA-IRS.

An N E A country with no nuclear power plant of its own may participate in the system as an observer and receive the reported information, providing it agrees to enter into the reporting commitment should it possess a nuclear reactor in the future.

B. Co-ordinators

All communications between participating countries and the N E A Secretariat are handled by the ‘1RS Co-ordinators’ designated by their competent authorities. A Co-ordinator:(a) Screens the events which have occurred in his country, and selects incidents

to be reported through the 1RS;

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(b) Disseminates the 1RS reports received from the N E A Secretariat to the proper organizations, such as utilities and research institutes, in his country.

C. Reporting criteria

The agreed reporting criteria constitute a key factor in the system since they define the level of reportable events. To begin with, the threshold was considered to lie somewhat above the level of the Licensing Event Reports of the US Nuclear Regulatory Commission (about 50 events/reactor year in 1981) but significantly below that of the accident at Three Mile Island. Initial criteria were agreed upon and tested during the trial operation of the 1RS. They were found to have been subject to wide differences in interpretation, some countries reporting every unplanned shutdown, others reporting no events at all. It was clearly necessary to arrive at a more detailed definition of reporting criteria so that participants would have a coherent understanding of what should be reported. To give further assistance, examples of typical occurrences were added under each criterion. For example, under criterion 2.2 ‘Degradation of the primary coolant pressure boundary, main steam line or feedwater line’, the following examples were added:(a) Through-wall failures of the piping or of significant components of the

primary coolant circuit;(b) Welding defects or material defects in the primary coolant circuit;(c) Rapid temperature or pressure transient exceeding the authorized limits;(d) Loss of relief and/or safety valve functions during tests or operation.

The reporting criteria developed in this way, and still in use, are given in the Appendix (the examples themselves are omitted owing to limited space).

D. Nature and timing of reports

(a) ‘Ordinary Reports’ are sent by mail to the N E A Secretariat as a rule withinthree months after the incident occurred or was recognized. Usually, onlyone ‘Ordinary Report’ is sent in respect of each incident.

(b) An ‘Immediate Notification’ is sent within one month of the incident. For incidents which may attract great interest from other participating countries owing to their safety significance, this report is often sent by telex; it may be distributed by the Secretariat in this way. For example, the anticipated transient without scram (ATWS) at the Salem 1 plant in February 1983 was notified as an ‘Immediate Notification’.

(c) ‘Follow-up Reports’ are provided when additional information is requested on an incident reported in an ‘Ordinary Report’ or when a detailed study of the incident is prepared.

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(d) ‘Generic Reports’ provide information on a generic issue, covering a series ofincidents where each incident alone may not be significant.All reports are in either English or French. Upon request by a Co-ordinator,

the N E A arranges translation between these two languages.

E. Information included in reports

Every 1RS report carries a cover sheet giving its title, country, plant name, unit number, authorized power, date of incident, reactor type, licensee, constructor, date of first commercial operation, systems or components affected, initial plant condition, how the incident was detected, and any radiation exposure or release.

The report itself gives a narrative description of the incident, its possible causes, any lessons learned and actions taken. Also ‘Reasons for Reporting’ are included, to indicate why the Co-ordinator regarded the incident as significant enough to be reported. This item has proved very useful to readers considering the significance of the incident.

4. ASSESSMENT O F REPORTED INCIDENTS

1RS information is assessed in the first instance by each participating country, since the applicability of lessons learned from an incident usually depends on factors specific to each country or even to each plant. For example, if an incident reveals an error in the design of a safety/relief valve, the lessons learned from the incident will be applicable only to the plants where the same or a similar type of valve is used.

In the longer term, however, the international assessment of reported incidents is useful so that areas of concern or generic safety issues may be identified from a study of trends and patterns. To this end, the CSNI Incident Analysis Group was established to select safety issues with major safety interest for thorough discussion by the CSNI. This Group has met twice, in 1981 and 1982, to assess the incidents reported during the preceding year. The criteria selected by the Incident Analysis Group include the potential safety significance of the issue, the reported frequency of incidents, the applicability to other types of reactor, and the relevance to current international safety concerns.

A particular advantage in these Group meetings was found to be the prompt and easy access to full information about an incident being assessed; participants could obtain detailed background information by directly questioning the reporter of the incident. This helped considerably in assessing operating experience in different countries by overcoming the lack of technical data on different system designs. *

296 OTSUKA and HÀUSSERMANN

The following brief outlines describe certain safety issues selected bythe Group:(a) Degradation o f the primary coolant pressure boundary due to through-wall

failures

A large number of reported incidents can be classed under this heading.Major weaknesses recognized in the primary circuit are coolant pump seals and steam generator (SG) tubes. When all pump seals fail during power operation, rapid release of coolant into the containment sump causes a transient and subsequent initiation of the Safety Injection System. Causes of SG tube degradation are varied (such as corrosion, vibration, mechanical wear or impact). An incident at Ginna in the United States of America demonstrated that SG tubes can rupture suddenly and without any prior indication of leakage.

(b) Procedural deficiencies during maintenance or testing

A number of incidents have been caused by inadvertent actions or procedural deficiencies during maintenance or tests. The consequences and significance of these incidents vary widely, e.g. temporary loss of residual heat removal (RHR) capability, reduction in the negative reactivity margin, inadvertent initiation of containment spray or inadvertent isolation of safety injection signals. The importance of consistent operating procedures and proper training of operators are highlighted by these incidents.

(c) Loss o f emergency power

Loss of emergency power is important to safety because it could interrupt the functioning of engineered safety features, or prevent correct recovery action by operators through supply of erroneous data on the plant status, when off-site supplies are lost. Various types of potential loss of supplies have been reported concerning dieáel generator (DG) systems (e.g. a broken connecting rod in a diesel generator, loss of D G cooling water due to a check valve failure or a fire in a diesel generator). Another cause of loss of emergency power is thb failure of breakers connecting the emergency D G or generating system to the emergency bus.

(d) Loss o f residual heat removal (RHR) capability

The causes of a temporary or potential loss of R H R capability include the loss of power supplies to R H R pumps, inadvertent operation of an R H R isolation valve, or a blockage in R H R heat exchangers. Any loss of R H R function is significant, as it can result in a core temperature increase and subsequent core boiling under shutdown conditions.

IAEA-SM-268/71 297

(e) Auxiliary system failures

It has been noted that a single failure of non-redundant auxiliary systems can cause a loss of significant safety functions. For example, a degradation of containment integrity caused by a valve failure in an air supply system has been reported in a PWR. Loss of R H R capability due to a valve failure in the component cooling system has also been reported.

( f) Other safety issues

Other selected safety issues include:— Corrosion of components or parts inside the reactor vessel— Corrosion of bolts— Loose or missing thermal sleeves— Valve failures (safety/relief valve, main steam isolation valve,

check valve, etc)— Pressurized thermal shock.

5. D A T A RETRIEVAL

By the end of 1982, a total of 310 reports covering 263 incidents had been exchanged through the NEA-IRS. At present, most countries have this information filed in the form of hard copy, except those which have set up their own computer files for 1RS information. Retrieval of reports will become increasingly difficult in the future, as more than 150 incidents are likely to be reported every year from 1983 onwards.

A computerized data retrieval system is now being developed with the co­operation of the Ispra Joint Research Centre of the Commission of the European Communities (CEC) in order to:(a) Facilitate the search for incidents already reported, for 1RS participants and

the N E A Secretariat;(b) Provide necessary information for assessing incidents.

All 1RS incidents have been coded using the format prepared for the CEC Abnormal Occurrences Reporting System, which provides a function of key-word searching. Where an incident consists of more than one step in its sequence, it is coded step-by-step. Trial operation of the data retrieval system is planned for mid-1983 and it is expected to become a powerful tool for incident assessment.Any information derived from this data base will be treated in the same way as other 1RS reports and restricted to participating countries.

298 OTSUKA and HÀUSSERMANN

6. FEEDBACK OF OPERATING EXPERIENCE

The international feedback of operating lessons learned takes two forms: one is intended to improve a particular component, system or plant, the other is to enrich international safety research activities.

In the first case, the recipients of the 1RS information:(a) Check whether their plant is fitted with the same or a similar component

(or system);(b) Investigate whether the reported failure has been observed in their plant;(c) Take corrective action such as replacing or repairing the defective component,

or even installing a new system when necessary.In most circumstances, feedback results in the first of the above steps and

proceeds no further. It is rare that the third step is taken. The following are some examples:(a) In February 1980 in a Japanese PWR, cracks were found in some of the

support pins on control rod guide tubes. The pins were designed to align the guide tube to the upper core plate. All the support pins were replaced by pins of improved design. When similar failures were found in French PWRs in 1982, the information on the corrective action taken in Japan was invaluable to the French utility in deciding what remedial action to take.This type of support-pin failure was also found in the United States of America and relevant investigations are under way in another country.

(b) In September 1981 in a Japanese PWR, two thermal sleeves welded to the charging lines of the chemical volume control system were found to be missing. The cause was thermal fatigue of the weld combined with vibration from the coolant pump. Investigation of the same part of the system in PWRs in another country also revealed loose or missing thermal sleeves. Investigations are now in hand in at least two other countries.

(c) In January 1981 in a US PWR, the station batteries were found to have been inadvertently disconnected from the emergency bus, a fact unknown in the control room. As a corrective measure, an instrument to give warning of battery disconnection was installed in the control room. Investigations were carried out in at least two other countries, and similar instrumentation was installed in one B W R plant to prevent the same incident.

(d) A connecting rod broke in a diesel generator (DG) in a P W R plant. In two other countries, the utilities which have DGs manufactured by the same maker examined them and found no defects.

(e) Partial failure to scram at Browns Ferry 3 in June 1980 resulted in some instrument and procedural modifications in other BWRs.

IAEA-SM-268/71 299

(f) SG tube ruptures at the Ginna station in January 1983 are also likely to cause modifications in operating procedures in other countries. Investigations are under way.As regards the second form of feedback (to benefit international safety

research activities) it is too early to expect any quick response, as this is a long­term process. There is however a tendency to take account of operating experience in other CSNI activities.

Following the recognition that procedural deficiencies can become a generic safety issue, continued efforts are being made to use the 1RS reports for studying the influence of human factors on power plant operation. A classification system developed for the analysis of operators’ actions in emergency conditions has been applied to several incidents on an experimental basis. National approaches to emergency operating procedures are also reviewed in this context. Very recently, a CSNI Specialist Meeting on decay heat removal (DHR) systems was held in Switzerland, where an important item discussed was operating experience with such systems. In the field of probabilistic risk assessment, it is also planned to use 1RS reports for developing hypothetical severe accident scenarios. In future, closer contact with and feedback to other CSNI activities is planned, e.g. in the field of thermal-hydraulic studies.

7. INTERNATIONAL CO-OPERATION

The NEA-IRS has objectives and mechanisms similar to those of the Incident Reporting System recently developed by the International Atomic Energy Agency (IAEA). The CEC Abnormal Occurrences Reporting System also deals with operating experience, although its reporting threshold is lower. Since the participants in these three systems overlap to some degree, there is a strong desire in N E A member countries for these three activities to be co-ordinated to avoid unnecessary duplication. In this context, the N E A and IAEA are planning a joint meeting for the assessment of incidents, from 12th to 14th September 1983 in Paris. This joint assessment meeting should provide a good start to co-ordination between the two systems.

8. CONCLUDING R E M A R K S

The N E A Incident Reporting System is now fully operational, three years after its initiation. It has gradually fulfilled its objective, namely to further improve the safe operation of nuclear power plants through a world-wide exchange of information on reactor incidents. It also facilitates the analysis of general safety

300 OTSUKA and HAUSSERMANN

issues and assists the international nuclear community in the development of a comprehensive data bank on safety-related incidents. It contributes to the better regulation of the utilization of nuclear power plants and last but not least provides additional guidance for international safety research programmes.

Finally, it must be stressed that the remarkable success of the system is due mainly to the willingness of the thirteen participating countries to share their operating experience without undue restrictions. ‘Reciprocity’, i.e. a mutual ‘give and take’, is the secret of the success of this international co-operative venture.

Appendix

REPORTING CRITERIA F O R THE N E A INCIDENT REPORTING SYSTEM

1. Significant release of, or exposure to, radioactive material.2. Significant degradation of safety-related systems

2.1. Fuel cladding failure2.2. Degradation of the primary coolant pressure boundary, main steam

line or feedwater line2.3. Loss of containment function or integrity2.4. Degradation of systems required to control criticality2.5. Degradation of systems required to control the system pressure or

temperature2.6. Loss of essential support system.

3. Significant deficiencies in design, construction, operation or safety evaluation.4. Significant generic problems.5. Significant consequential actions.

Significant consequential actions resulting from reported events occurring in another country, taken by the competent safety authority on licensing, design or operation.

6. Incidents of potential safety significance.Events which have no significant consequence but may be considered as approaching ‘near misses’, i.e. events which could have resulted in serious consequences under other plant conditions.

7. Effects of unusual external events either of man-made or natural origin.8. Events which attract significant public interest (optional).

IAEA-SM-268/72

I A E A A C T I V I T I E S A I M E D A T

I M P R O V I N G T H E F E E D B A C K O F

E X P E R I E N C E I N O P E R A T I O N A L

S A F E T Y O F N U C L E A R P O W E R P L A N T S

H. WRIGHT, V.S. OSMACHKIN International Atomic Energy Agency,Vienna

Abstract

IA E A A C T IV IT IE S AIM ED A T IM PROVING TH E FE E D B A C K O F EX PERIEN CE IN O P E R A T IO N A L S A F E T Y O F N U C L E A R POW ER PLA N TS.

This paper describes IA E A activities being taken and planned to improve the feedback o f experience derived from the maloperation o f nuclear pow er plants. It discusses mainly the IA E A Incident Reporting System that has been established for the collection, evaluation and dissemination o f operating experience on an international basis. This Incident Reporting System is considered to be com plem entary to the national incident reporting systems which were the subject o f a recently published IA E A guide. The IA E A activities concerned with periodic meetings to review incidents o f significance to safety and o f possible interest to the world com m unity are also discussed. The first such meeting, at which descriptions o f incidents were presented and the lessons learned from them were identified, has already been held.This meeting indicates the pattern to be follow ed for the future.

INTRODUCTION

A large e f fo rt i s expended and a variety of measures are taken by the many organizations involved in nuclear power programmes throughout the world in order to ensure sa fety of nuclear power plants. These e f f o r t s and

measures are continually being improved, with the resu lt that the world has now about 2800 reactor-years of power operation with few Incidents of s ig n if ica n t importance to sa fe ty and no large-sca le acc idents . One of the measures taken to maintain th is favourable p osit ion i s the use of the experience that can be derived from unusual events occurring during the operation of d if feren t p lants . Such unplanned events can highlight the

corrective actions that are needed to prevent a recurrence of the event and

to m itigate i t s consequences and the other actions that should be taken as a result of the lessons learned. The operation of nuclear power plants has of course provided a great deal of information that i s p o te n t ia l ly useful as feedback to people engaged in nuclear safety a c t i v i t i e s .

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302 WRIGHT and OSMACHKIN

The incident which occurred at TMI-2 in March 1979 highlighted the need to make more use of information being co l lec ted on sa fety s ig n if ica n t

unusual events (or incidents) by Increasing the e f fo r t s spent on analysing

the causes and disseminating the lessons learned. This incident a lso showed that a l l countries with nuclear power plants can ben ef it from an in ternational exchange of information. Countries with large nuclear programmes w i l l learn lessons which may be applicable to a number of

plants . On the other hand countries with only one or two nuclear power plants benefit because they are l e s s l ik e ly to have accumulated so much

technical operating experience. The IAEA b el ieves i t could help i t s Member States '■o improve nuclear sa fety by the establishment of an international system to provide a means of exchanging information on incidents of particu lar in te re st to the world community.

The or ig in a l IAEA programme, recommended in 1979, therefore included proposals for a c t i v i t i e s related to the c o l le c t io n and an a lys is of abnormal

occurrence reports from operating nuclear power plants . Steps were then

taken to e s ta b l ish a reporting system based to some extent on the Licensee Event Reports (LERs) used in the USA by the u t i l i t i e s for reporting to the regulatory body, but the IAEA received in s u f f ic ie n t support to proceed further along these l in e s . It was then decided to in v ite Member States to p artic ipate in a system for exchange of information about se lected s ig n if ica n t sa fe ty -re la ted events reported to regulatory bodies within the framework of the national systems.

Although i t has been general practice to require operating organizations to report sa fe ty -re la ted events to the national regulatory body or other responsible organizations, there have been wide variations in the degree of s ign if ican ce of the events. It was therefore considered by the IAEA that a guide for a national incident reporting system would be welcomed by Member S ta tes . Such a document could a lso help to es ta b lish systems with c loser s im i la r i t i e s and thereby promote the successfu l development of an international incident reporting system.

These ideas were discussed at an Advisory Group Meeting in November

1981, which recommended the following important measures:

1. Development of a guide to a s s i s t Member States in estab lish in g

the ir own national systems for the c o l le c t io n , dissemination and review of information on sa fety -re la ted unusual events.

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2. In te n s i f ica t io n of IAEA e f fo r t s to e s ta b l ish an international incident reporting system (IAEA-1RS). The objective of the system would be to achieve an e f f e c t iv e world-wide reporting system. Appropriate steps would have to be taken to achieve harmonization between the system to be developed by the IAEA

and in tern ationa lly developed systems.3. Establishment of arrangements for the se le c t io n and periodic

review of those events which are of in te r e s t to the in ternational nuclear community.

Accordingly, in 1982 a draft of the guide on national systems was produced and the f in a l document was agreed by a Technical Committee. This guide has now been published as a working document [1].

The Technical Committee a lso reviewed arrangements for the incident reporting system proposed by the S ecretariat. The document that described these arrangements was circu lated to Member States for comments. In April 1983 o f f i c i a l in v ita t io n s were sent to appropriate Member States to make formal requests to part ic ipate in the system.

In these a c t i v i t i e s , the IAEA received ass is tan ce from the Nuclear Energy Agency of the OECD, which had launched the ir own incident reporting

system (NEA-IRS) in 1979. A description of the operation of the NEA-1RS i s

given in R e f . [2 ] . The IAEA has taken steps to e s ta b l ish a Technical Committee dealing with the assessment of incidents: the f i r s t meeting washeld in Madrid in 1982. Information on incidents was presented and the lessons learned were discussed.

PRINCIPAL COALS AND FEATURES OF THE IAEA-IRS

In the national incident reporting system, the operator has the

r e sp o n s ib i l i ty of reporting unusual events to the appropriate management le v e l s in the operating organization. The analyses and correct ive actions are performed by the operating organizations. Those unusual events that are safety related have to be reported to a safety co-ordinating body (usually the regulatory body). This body screens the information to id en ti fy the

most s a fe ty -s ig n i f ic a n t events (Inc id en ts) . In the IAEA-IRS these incidents are expected to be reported to the IAEA, and the reports w i l l then be distributed by the IAEA to the p artic ipants . 'The basic reporting scheme i s shown in Fig 1. <-

304 WRIGHT and OSMACHKIN

FIG.l. Reporting scheme.

The IAEA considers i t important that the IAEA-IRS should provide assurance to participants that a fa ir exchange of information w i l l take place. As a consequence the IAEA-IRS has the following ch arac ter is t ics :

1. Countries commit themselves to send information to the IAEA in accordance with the procedures la id down. This information co n s is ts primarily of reports on unusual events with safety s ign if ican ce ( in c id en ts ) . Reports may be written in a free

s t y le form although a sp e c i f i c format has been recommended.

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2. The number of events most s ig n if ica n t to sa fety reported to theIAEA per year by a participant i s expected to be between 0.5 to

1.0 times the number of operating u n its .3. Only p artic ipating countries receive the information sent to

the IAEA. All partic ipants are expected to designate aco-ordinator who w i l l be responsible for sending and receivinginformation d irect to or from the IAEA.

The co-ordinator rece ives reports from the operating organization as

recommended in the guide on the national reporting system. The incidents reported are to be id e n t i f ie d in accordance with the recommended categories and category numbers (see Annex I) which give the areas of safety in te r e s t .From these reports the co-ordinator s e le c ts those that are concerned withevents most s ig n if ic a n t to sa fe ty and of in te re s t to the in ternational community, and sends them to the IAEA. The le v e l o f s ign if ican ce of the events to be reported has of course to be determined by national au th or it ie s and may change in the future.

Co-ordinators are most l ik e ly to be senior members of the regulatory body, i . e . government employees. They w i l l ensure that a l l bodies that receive information through them w i l l observe the requirements of the system and w i l l use the information for o f f i c i a l purposes only.

The duty of the IAEA in the 1RS i s in the f i r s t place to act as a central clear ing house. To increase the speed of dissemination, an abstract

of each report should be supplied in English. This abstract i s immediately sent to a l l other participants to enable countries to be a lerted to the

possib le ex istence of a problem. The reports w i l l be d istr ibuted as soon as

possib le a f te r certa in processing (such as translat ion) has been undertaken.

After an i n i t i a l period, the Information from participants w i l l provide a pool of experience which participants or the IAEA may wish to

consult and analyse. The IAEA w i l l therefore store the information in such a way that particular aspects can be retrieved.

306 WRIGHT and OSMACHKIN

FIG

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hand

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It i s envisaged that the IAEA Incident Reporting System w i l l provide

the following functions:

rece ip t and transfer of incident reports- processing of reports for storage

c o l le c t io n of relevant reactor data for an a lys is of events

storage of information so that i t can be retrieved for

Investigation .

Reports may need to be processed: th is w i l l include any necessarytran sla t ion , ed it in g , screening and c la s s i f i c a t io n , and, when warranted,

preparation for computer storage.

Any proper an a lys is and evaluation of events requires the sa fe ty -re la ted information to be stored. Such data as reactor type, design, plant layout and s i t e features need to be c o l le c te d . For th is purpose the IAEA Power Reactor Information System (PRIS) [3] might be used, but th is system i s mainly concerned with plant a v a i la b i l i t y , production and outage data. Additional information on the safety features of plants has therefore to be c o l le c te d . The search for such data from s c i e n t i f i c l i t e r a tu r e or the International Nuclear Information System (INIS) [4] has been arranged. In th is connection, INIS practice provides useful ideas about p ossib le ways of interrogating and assessing the data c o l le c t io n .

The storage of f i lm s , video-tapes and supplementary event descrip tions i s a lso envisaged for the purposes of d eta iled an a lys is and evaluation. Figure 2 shows the general scheme of communications within the IAEA-IRS.

The main ch a ra c ter is t ic s planned for the computer storage system can be summarized as:

Similar to INIS arrangements and compatible with PRIS [3, 4] Arranged to maintain c o n f id e n t ia l i ty requirements

Containing the p o s s ib i l i t y for lin k s to be opened with other computers in p artic ipating countr ies , part icu lar ly for access

to basic information on plant d e ta i l s- Containing reference to a l l availab le translat ions of IAEA-IRS

reports produced by any participants in the system.

INFORMATION STORAGE AND RETRIEVAL

308 WRIGHT and OSMACHKIN

COMPATIBILITY WITH THE NEA INCIDENT REPORTING SYSTEM (NEA-1RS)

The NEA Incident Reporting System has been in operation for the la s t three years. The IAEA had the advantage of a NEA representative on the Technical Committee providing advice on how to harmonize the IAEA-IRS with

the NEA-1RS. Consequently, incidents reported in the IAEA-IRS are expected to be categorized in the same way as that used in the NEA-IRS. It was even considered advantageous to adopt a s im ilar t i t l e for the IAEA system and to use the same term "co-ordinator".

The IAEA recognizes that some countries are already partic ipating in the NEA Incident Reporting System. It i s e s s e n t ia l that d i f f i c u l t i e s are

not put in the way of these countries p artic ipating in a second system, i . e .

the IAEA-IRS, the advantages of which l i e in the future. With th is in mind, the IAEA-IRS i s designed so as not to involve such countries in any

additional e f f o r t .

ANALYSIS OF EVENTS

As mentioned above, an Advisory Group recommended the holding of periodic meetings to review incidents of in te re s t to the international

community. The f i r s t of these meetings was held in Madrid in 1982. The main ob ject ives of the meeting were to provide an opportunity for the exchange of experience with national reporting systems, the performance of in-depth assessments of Incidents, and the d is tr ib u t io n of the lessons learned to those concerned. I t was a f i r s t informal exchange of information on recent unusual events in nuclear power plants with relevant reports from NEA, CMEA and developing countries. Suggestions for the Agency's future work in th is f i e ld were a lso presented.

The advantage of reviews of Incidents undertaken at an Internationally convened meeting i s that they would enable lessons to be learned by sa fety personnel from d ifferen t parts of the world and would highlight lessons that are applicable to many d ifferen t countries and organizations.

Any d eta iled analysis of an incident must be carried out In the country where the incident occurred since an in tern ationa lly convened

IAEA-SM-268/72 309

meeting i s not a su itable forum for performing th is task. I t i s important

for the members of such a meeting to be given s u f f ic ie n t information to enable them to understand the reasons for the conclusions reached and to derive lessons that may be applicable in their own countries .

The relevant circumstances that ex isted just prior to the in i t ia t in g

events usually need to be described in d e t a i l . It i s a lso usually important

to s ta te p rec ise ly the cause of any malfunction and i f p ossib le the indicat ions ava ilab le to the operator, and whether they were true or f a l s e ,

so that i t i s p ossib le to deduce what the operator thought was happening at

the time. It i s quite p ossib le for the operator to do the right thing for the wrong reason or the wrong thing for the right reason.

The type of recommendations that can be envisaged from these periodic sa fe ty review meetings would be those having general a p p l ic a b i l i ty to many nuclear power plants and many operating and regulatory organizations. I t

was deemed usefu l to examine the report of a particu lar incident and draw up p ossib le recommendations. The report, chosen at random, was that which

dealt with an incident in the Crystal River Plant in the USA [5]. This report had been prepared by the Nuclear Safety Analysis Center (NSAC) and

the I n s t i tu te of Nuclear Power Operations. The recommendations drawn up by the present authors are given in Annex I I . Although opinions may d i f f e r

over the v a l id i t y of these proposals, they nevertheless show the types of

recommendations that an in ternational meeting might provide from i t s review of a number of incident reports. In particu lar , such recommendations

— could apply to types or designs of plant d if feren t from the one in which the incident occurred;

— could be d irected to senior management of the operating organization, the regulatory body, plant designers and o n -s i te

plant management;— could cover both administrative as w ell as technical aspects.

One important problem that may be d i f f i c u l t to overcome i s the

id e n t i f ic a t io n of those events that indiv idu ally are not s ig n if ic a n t but taken together indicate that a problem of sa fety s ign if ican ce e x i s t s .

Reliance w i l l i n i t i a l l y be placed on partic ipants to id en ti fy such events in accordance with the ir national system and to a le r t the IAEA so that other countries can be informed.

310 WRIGHT and OSMACHKIN

It i s considered that the dissemination of information on incidents requires carefu l consideration, and perhaps Increased a ttent ion should be given to th is process. The aim of dissemination can be summarized as

"putting an old head on young shoulders".

An individual w i l l not perceptibly increase h is experience simply by being informed of lessons learned by others: some rationale for acceptingth is experience i s needed. The rationale i s obtained from learning the d e t a i l s of actual incidents and the conclusions derived from them.

It i s therefore usefu l to compile f i l e s of case h is to r ie s in the manner that records of court decis ions are kept. I t should then be possib le

to add continually to the lessons learned and to re trieve information

according to the sp ecia l in te re s t of the individual concerned.

An additional aid to the retention of the experience of others i s the development for each plant of fau lt trees which are modified whenever incidents occur in which the in i t ia t in g event or sequence of events were not previously postulated.

Other aids to gaining experience and retaining i t include reviews to incorporate lessons learned from post in c id en ts . Such reviews might involve

safety assessment reports, Including the sp ec if ica t io n of the

contentsdesigns for new plant

- operational a c t i v i t i e s , including procedures and equipment for operation, maintenance and Inspection, commissioning, rad io log ica l protection, emergency preparedness, core management and fu e l handling, waste management, quality assurance, f i r e protection, and management practices

- training programmes regulatory pract ices .

CONCLUSIONS

It i s believed that world-wide p art ic ipation in the exchange of information on unusual events with safety s ign if ican ce would make a valuable

DISSEMINATION

IAEA-SM-268/72 311

contribution to sa fety provided that the causes are analysed and the lessons

learned are adequately disseminated. The IAEA-IRS i s envisaged as an

e s s e n t ia l aid to the accomplishment of th is ob ject ive .

For the su ccessfu l operation of the IAEA-IRS, the partic ipating

countries need to be w il l in g to send information on incidents to the IAEA on the basis of fa ir exchange and on the understanding that the information

w i l l be used for o f f i c i a l purposes only.

A useful a c t iv i t y for the IAEA i s to hold meetings to review incidents sent to them in accordance with the arrangements se t out in the IAEA-IRS. This i s expected to be a valuable contribution to the dissemination of the lessons learned from operating experience.

It i s believed that more a ttention should be given to the process of dissemination of the lessons learned from experience, and i t i s hoped that the IAEA w i l l be able to a s s i s t Member States In th is process.

ANNEX I

Categories for a Reporting System on Safety-re lated Events

(1) Exposure to radiation or release of radioactive material

(2) Degradation of items important to sa fety (s tructu res , systems, components)

(3) D efic ien cies in design, construction, operation and quality assurance

(A) Generic problems (recurring events which, taken together, have im plications for other s im ilar plants)

(5) S ignificant consequential actions (act ions taken by the regulatory body as a resu lt of reported events)

312 WRIGHT and OSMACHKIN

(6) Events of p oten t ia l s ign if ican ce to sa fety (those during which a protection system operates unnecessarily , or f a i l s to actuate when required)

(7) Unusual events, e ith er of man-made or natural or ig in , that d ir e c t ly or in d irec t ly threaten the a b i l i t y of the plant to operate sa fe ly

(8) Events which, although they have no sa fety s ign if ican ce , a ttract s ig n if ic a n t public Interest

ANNEX II

Example of Recommendations that Could Be Made as a Result of the Review of the Crystal River - Unit 3 Incident [5]

1. The fa u lt trees for plants should be reviewed to ascerta in whether the sequence of events in incident reports have been taken into account.

2. Consideration should be given to methods for continual monitoring ofinstruments and protective equipment, so that the operator knows when indications become fa u lty .

3. Selected plant data, including the p os it ions of switches and valves,should be recorded continuously and automatically in a s im ilar manner to theblack box provided in aeroplanes.

A. The permit-to-work procedures should prevent or minimize thep o s s ib i l i t y of personnel causing a fau lt highly s ig n if ic a n t to sa fety on a control or instrument panel.

5. The operator should have operating procedures for sp ec if ied plantconditions. The operator however must take a l l actions he or she considers necessary for sa fe ty and so should be fam iliar with these procedures but

they should not be mandatory.

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6. Instrument power supplies sh a l l be availab le from a ltern at ive busbars with automatic change-over switch f a c i l i t i e s . Non-nuclear control room

instruments should be given the same importance as nuclear instrumentation

in th is respect.

7. The sa fety analysis report should include an a lys is of the e f f e c t s of

power supply fa i lu r e s to instrumentation and protective equipment.

8. The safety analysis report should include the e f f e c t s of accident conditions on the information supplied to the operator.

9. Reviews should be undertaken to consider the a d v isa b i l i ty of making design modifications to prevent i s o la t io n of the steam generators for events which do not involve ruptures in the steam generator system.

10. Consideration should be given to the provision of an automatic

reactor tr ip when instrument supplies are l o s t .

11. The coupling of indications should be id en t i f ie d and avoided whenever

p ossib le to minimize lo s s of information to the operator.

12. The design should prevent pin misalignment.

13. Computer printouts should be able to cope with a l l postulated plantfa u l t s . For events which require the computer to g ive a large amount of data, consideration should be given to printing out summaries with a reduction in the frequency of printout of the more d eta iled information. Inaddition, parameter values which are excess ive ly high should be distinguished from those which are excess ive ly low.

14. Copies of a l l instru ct ions and temporary instru ct ions issued by authorized personnel sh a ll be sent to a records department at the time of issue and retained for a minimum of one year a f te r they cease to be va lid .

f i]

[2J

[3]

m

314

[5]

REFERENCES

International Atomic Energy Agency, Guide on a National System for C ollecting , Assessing and Disseminating Information on Safety-related

Events in Nuclear Power Plants, IAEA-TECDOC-278, Vienna (1983).

Hausserman, W., Otsuka, Y. "The NEA Incident Reporting System:Three year's experience”, paper IAEA-SM-268/71, these Proceedings.

Laue, H .J ., Qureshi, A., Sk joldebrand, R. , White, D. "The IAEA Power

Reactor Information System - PRIS", paper IAEA-SM-269/118, IAEA International Symposium on R e l ia b i l i ty of Reactor Pressure Components

(S tu ttgart , Federal Republic of Germany, 21-25 March 1983).

International Atomic Energy Agency, INIS Today, An introduction to the International Nuclear Information System, Vienna (1982).

Analysis and Evaluation of Crystal River - Unit 3 Incident, Rep. NSAC-3, E lec tr ic Power Research I n s t i tu te , Palo Alto, INPO-1 (March

1980).

WRIGHT and OSMACHKIN

IAEA-SM-268/33

I N T E R N A T I O N A L G U I D A N C E O N T H E

Q U A L I F I C A T I O N S O F N U C L E A R

P O W E R P L A N T O P E R A T I O N S P E R S O N N E L

B.J. CSIKInternational Atomic Energy Agency,Vienna

AbstractIN T E R N A T IO N A L G U ID A N CE ON THE Q U A LIF IC A T IO N S O F N U C L E A R POWER P L A N T O PER A TIO N S PERSONN EL.

Nuclear pow er plant operation and maintenance as w ell as training o f operations personnel are activities where a large amount o f experience is available. Though it would seem that the status o f a well-established practice, requiring constant attention but no major efforts directed towards improvem ents, should have been reached, this is not the case. Currently, upgrading o f the qualification requirements and training procedures o f nuclear power plant operations personnel is a major issue and substantial efforts are being expended to this effect. The availability o f international guidance in this field is perceived to be o f benefit to all; therefore the A gency has undertaken to develop such guidance. In addition to earlier publications, a guidebook on this subject area is being prepared. Important problems and current issues have been identified and these are comm ented upon in the present paper. The specific topics referred to include: the role o f the operating organization and the regulatory body; organi­zational aspects; staffing requirements; com petence requirements for personnel; establishment and verification o f competence; and personnel management. It is recognized that developing

international guidance is a difficult and delicate task, especially when it is intended to go beyond stating the obvious and expressing generalities which are certain to meet a general consensus.

1. C U R R E N T STATUS

Throughout the world, the total number of operations personnel (including direct operation, maintenance and technical support functions) of the 294 operating nuclear power plants (as of December 1982) can be estimated at about 60 000. When the 215 nuclear power plants under construction become operational, which is expected to occur before the year 1990, the number of technical operations personnel will pass the 100 000 level. It can also be estimated that currently some 20 000 people are undergoing training. By the end of 1982, about 2800 power reactor-years of operating experience had been accumulated; there are 25 countries with operating nuclear power plants and 6 more are constructing their first units.

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With this background, it would seem that the qualification of nuclear power plant operations personnel should have reached the status of a well-established practice requiring constant attention but no major efforts directed towards improvements. This, however, is not the case. Currently, upgrading of the qualification requirements and training procedures of nuclear power plant operations personnel is a major issue and substantial efforts are being expended in this direction. The reasons for this derive from the worldwide interest in improving even further the safety and reliability of nuclear power plants and these goals depend very much on the competence of operations personnel. It has been perceived that assurance of safety and reliability vitally affects the future development of the nuclear industry, and therefore efforts directed towards achieving this objective are eminently justified.

Prevailing national requirements and utility practices have been undergoing reassessment during the last few years, in particular since the TMI accident.Most of the improvements proposed have been or are being implemented, while some measures remain as controversial issues. Requirements and practices in different countries show many similarities, but there are also substantial differences in some aspects. Drawing on each other’s experience is clearly of benefit to all, and so is the availability of international guidance.

2. D E V ELOPMENT OF IAEA INTERNATIONAL GUIDANCE

As part of the Agency’s objectives, a series of publications are prepared to provide international guidance on various subjects. Concerning the qualification of nuclear power plant operations personnel, two recent publications are particularly relevant. One of them is the IAEA Safety Guide 50-SG-01 “Staffing of Nuclear Power Plants and the Recruitment, Training and Authorization of Operating Personnel”, published in 1979. The other is the Guidebook on “Manpower Development for Nuclear Power: A Guidebook” (Technical Reports Series No.200), published in 1980. Both publications contain information, advice and recommendations.

The Safety Guide is one of the publications produced within the NUSS (Nuclear Safety Standards) programme, and as such it is primarily intended to provide recommendations for use by Member States in the context of their own' nuclear safety requirements. The NUSS documents constitute an internationally agreed frame of reference for dealing with the essential safety and regulatory issues involved in the planning and implementation of a nuclear power programme.

The Guidebook on manpower development is one of a series of technical guidebooks prepared by the Division of Nuclear Power which are applicable to any country but are intended to be especially relevant for developing Member States. These technical guidebooks should not be considered in any way as

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regulatory guides. The manpower development Guidebook, which has been extensively used by the Member States and the Agency since it was published, presents and discusses the manpower requirements associated with all major activities of a nuclear power programme, the technical qualifications of this man­power, and the manpower development corresponding to these requirements and qualifications.

Though both publications refer to the qualification of nuclear power plant operations personnel, it was judged that the development of a technical guide­book covering this important subject area specifically and in depth is necessary, convenient and feasible. Consequently, work on a guidebook “Qualification of Nuclear Power Plant Operations Personnel” was initiated and is presently being carried out with the intent of publishing in 1984. It has been recognized from the start that the development of such a guidebook is a difficult and delicate task.

The new publication is intended to be directed primarily towards the needs of the plant operating organization, but it should be relevant also to regulatory authorities. It is intended to include both reliability and nuclear safety aspects, and to present desirable goals over and above minimum standards. Any inter­national guidance in this field must evidently be based on available experience and must take into account the approaches taken in different countries.

To take into account the different national and utility approaches and practices, available published information has been consulted, and the direct advice of leading experts in the field has been obtained through Advisory Group and Technical Committee meetings. In addition, the Agency has directed to its Member States with nuclear power plants in operation or under construction an enquiry consisting of two questionnaires.

The first questionnaire concerns the competence of personnel employed in nuclear power plant operations and the manning of nuclear power plants.This is intended for operating organizations. The second questionnaire con­cerns the regulations and guidance affecting the competence of nuclear power plant operations personnel and the manning of nuclear power plants. This is intended for the national regulatory authority. By March 1983, sixteen Member States had answered the enquiry, fifteen of these having nuclear power operating experience, thus providing a fairly good overview of the situation.

Important problem areas and issues have been identified. Some of these, as well as possible measures and improvements, will be commented on in the following sections.

3. THE ROLE OF THE OPERATING ORGANIZATION A N D THER E G U L A T O R Y B O D Y

In principle, there are no conflicting views regarding the assignment of the respective functions and responsibilities. It is clear that the operating organization

318 CSIK

has full responsibility for the safe and reliable operation of its nuclear power plants. The regulatory body’s functions consist of establishing rules and regulations and of surveillance and control with regard to all aspects relevant to safety and environ­mental protection; it has the primary responsibility of ensuring the health and safety of the public.

Where national practices differ is in the ways the regulatory functions and responsibilities are effectively implemented. And this in turn affects the ways the operating organization carries out its own functions and responsibilities. Just as there are different answers to the question ‘how safe is safe enough?’, there are also different answers to the question ‘how much regulation is enough?’. Some countries, in particular the USA and those which follow the USA example in this field, tend to implement the regulatory functions through a detailed and in-depth coverage of every aspect that can be conceived to have a safety significance. The approach of other countries, such as France or the United Kingdom, consists more of the issuance of general broad directives and of the overall surveillance of their implementation.

In the qualification of nuclear power plant operations personnel, neither over-regulation nor the lack of regulation are appropriate. Regulations always refer to minimum acceptable standards. In an over-regulated situation, the operating organization tends to acquire the feeling that its responsibilities regarding nuclear safety are fulfilled if it complies with regulations, while in the other extreme, the operating organization might become complacent and increase the safety risk by assigning priority to economic aspects. It is clear that both extremes have to be avoided and that the optimal solution lies somewhere in between. This optimal solution differs from country to country, because it depends on the traditions and methods normally used for regulating other activities and on the prevailing situation (such as whether there is just one strong utility or many utilities with a wide spectrum of experience and practices).

In general, it does not seem advisable to adopt and apply in one country the approach developed in another, without a thorough previous analysis. Also, the approach to regulatory implementation should remain under constant critical review within each country in order to introduce correcting measures whenever symptoms showing trends towards over-regulation or lack of regulation are perceived.

4. ORGANIZATIONAL ASPECTS

The organizational structures adopted for the operation and maintenance of nuclear power plants are fundamentally similar all over the world. They differ in detail only and there are no major problems. The utility practices regarding the shift system, however, differ widely in some aspects, and this seems to constitute a problem area.

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As a general rule, there are 3 shifts per working day, normally 8 hours each. The number of shift teams varies. The current preferred trend is to have 6 teams, but some organizations operate with 5 or even 4, while others have as many as 7. Regarding the rotational system, there seems to be no rule at all: the number of consecutive days on the same shift varies between 1 and 7; some utilities apply phase advance and others phase delay. There are many reports of difficulties in recruiting and keeping people, especially qualified engineers, for shift work.

Shift work is certainly nothing new in industry in general and in the electrical industry in particular. It is also well known that shift work affects job performance and error rate. Many studies have been made on the effects of shift work and on optimizing adjustment to it. Nevertheless, in practice, the usual method followed in adopting a certain shift system is based more on tradition and custom than on the results of studies. It seems reasonable to recommend that a more scientific approach should be applied to the choice of the shift system, and also that instruction should be provided to the shift personnel on how to mitigate the negative effects of shift work.

5. STAFFING REQUIREMENTS

Regarding the number of technical operations personnel (professionals, technicians and craftsmen), the requirements are in general similar for each specific function and task to be performed at any unit (except for maintenance, where differences appear). In utilities that have several nuclear power plants and centralized maintenance services, or in countries with a strong industrial infra­structure well qualified for nuclear power plant maintenance work, the mainte­nance staff at individual units corresponds to the minimum needed for routine operations. Other utilities require a larger maintenance staff in order to minimize down-time of their plants.

The overall number of technical operations personnel of a single-unit station is usually around 200 to 250 persons, but owing to the maintenance aspect and also to differences in national labour practices and policy there are examples of units with staff amounting to twice as many or even more. Operating shifts have 10 to 14 persons.

The main general problem is understaffing, which results in the application of overtime working conditions with increased fatigue and a higher risk of mis­takes, and also a lowering of the qualification level of personnel through the need to assign responsibilities to staff with less than adequate training and experience.A policy of moderate overstaffing is advisable, especially for countries starting on their nuclear power programme and for those functions that require relatively long periods of training. The higher personnel costs of overstaffing are more than compensated by increased plant reliability and safety.

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It is widely recognized and accepted that the key to safe and reliable operation of a nuclear power plant is the presence of operations personnel who are highly qualified and dedicated.

The competence required is basically similar among countries and utilities for the upper level management and also for the lower level craftsmen and auxiliary technician personnel. Differences appear in the middle level direct operating staff, up to and including the shift supervisory function, and in some supporting supervisory functions. Here, the level of competence requirements constitutes a major problem as well as an important and contraversial current issue, especially with regard to educational qualifications and previous experience.

It is generally accepted that full responsibility for direct operation of the plant requires a level of knowledge and intellectual skill corresponding to a professional engineer’s educational qualification. This responsibility is normally fulfilled by the shift supervisors of the plant. Some countries require professional engineers for the shift supervisor, but others do not. In the USA, for example, the engineering knowledge and skills are provided by having a ‘Shift Technical Advisor’ present on the shift, while in Switzerland there is always a ‘Picket Engineer’ in the plant who can reach the control room if needed within a few minutes of being called.

Such compromise solutions have their merits and may work in their respective specific environments. It seems, however, that the approach to be preferred is to have professional engineers directly in charge of operating nuclear power plants in the shift supervisory functions, even if this implies the need for upgrading the status of the shift supervisor and of other direct operating functions within the corresponding career-path to a level that will attract and retain professional engineers.

Many measures have been proposed during the last few years to improve the competence of operations personnel. The practical implementation of such measures, however, involves a long-term process and there is also strong resistance to modify established practices.

It is not possible to give firm recommendations equally applicable to any country and situation; it is also difficult to define clear competence requirements, which are composed of educational, training and experience qualifications, physical and mental capabilities, and social skills.

It is advisable, however, to promote the general approach of setting high targets for competence requirements, which should certainly be over and above the usual practices followed in fossil-fuelled power plants. For those countries that are starting their nuclear power programmes and have no staff experienced in the operation of nuclear power plants, high educational and training qualifi­cation requirements are especially important. In countries and utilities with a

6. COM PETENCE REQUIREM ENTS

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long nuclear power tradition, excessive reliance on experience and training only, without an adequate educational background, should be avoided.

7. ESTABLISHING COMPETENCE

Education provides the basis of general knowledge as well as intellectual skills. Training adds the specific knowledge and skills needed for performing the particular tasks of a position. Experience confirms and develops what has been learned and contributes forms of knowledge and skills which cannot be acquired by education and training alone. All three components are needed to establish competence.

The general structures of the technical educational systems of practically all countries are similar, but the level and content differ widely from country to country and even within a particular country. The technical educational systems share the common characteristic of reflecting the national industrial needs, though usually with some delay. Improving educational systems or adjusting them to the particular needs of the nuclear power industry is a slow and difficult process, so in practice the utilities have to recruit their personnel with whatever eductional background they have acquired at the level corresponding to the qualification requirements, and then provide training and experience. It is possible through training to correct some educational deficiencies or supplement omissions, but normally a utility’s role is not to serve as an educational institute.

Experience has shown that systems and methods for training operations personnel are fundamentally similar everywhere, notwithstanding the differences in previous educational qualification requirements. There is an extensive choice of measures that have been proposed and that are being adopted to improve practices. Possibly the most important recent developments are the general up­grading of training curricula and the increased use of simulators as training tools.

Operating organizations with long nuclear power traditions usually assign a very important role to the acquisition of experience through the establishment of career-paths and relatively long length-of-service requirements in successive posts at increasing levels of responsibility. This method is not available to utilities just starting their nuclear power programmes, so they have to rely more on experience acquired in fossil-fuelled plants, on-the-job training, and participation in the commissioning of the nuclear plants, unless they have access to a national labour market of experienced nuclear power reactor operations personnel.

There are several areas where further improvements could and should be introduced. Systematic training of maintenance personnel is usually not given the attention it deserves. On-the-job training opportunities are few, difficult to get access to, and even when obtained are often not used in a sufficiently efficient or effective way. Training conducted in a foreign language is frequently unduly

322 CSIK

prolonged because of the language barrier or because of insufficient efforts invested in the development of adequate training material in the local language. Qualification requirements of trainers and instructors are often either inadequate or if adequate, not fully complied with. The need for and importance of intellectual capabilities and basic scientific and technical knowledge is often under­estimated, especially by those who are themselves deficient in these aspects but who have nevertheless reached supervisory positions in their careers. Once policy decisions are taken, remedies to these problems can usually be applied without major difficulties.

8. VERIFICATION OF COMPETENCE

There are many different ways and means available to verify the initial competence, as well as the preservation of the competence, of a person. These include: written and oral tests of knowledge, educational certificates, previous employment records, technical and non-technical interviews, personality and aptitude tests, physical and psychological medical examinations, performance tests during and after training, licensing examinations, and assessment by super­visors during the performance of duties.

The verification methods that are used vary according to the level of the position and the prevailing practices and tradition. Relatively simple methods are normally used for lower-level technician and craftsmen posts, such as reviewing educational certificates and previous employment records and per­forming technical interviews and physical medical examinations. For higher responsibility posts, especially those in direct operation, the complexity of the verification methods is increased. Usually, oral and written tests of knowledge, non-technical interviews, personality tests, and licensing examinations are added. Sometimes, psychological aptitude tests and psychological medical examinations are also included. Except in countries where the role of the regulatory body is limited to general surveillance, it is common practice for the licensing examinations to be performed with the participation of or directly by the regulatory body. Formal verification methods, such as tests or examinations, are very rarely applied for management level personnel.

For verifying the preservation of competence, the direct supervisor’s assess­ment is normally the decisive factor. For personnel licensed by regulatory bodies, periodic requalification tests are usually added.

The verification of competence itself is a problem area, because objective judging of human competence is extremely difficult. Each method has its merits and disadvantages, and universally valid optimal solutions are not available. It seems generally advisable to assign primary importance to the selection of the verifiers, to the definition of their qualification requirements, and to compliance with these requirements.

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It is well known that operations personnel not only have to be well trained, but have also to be retrained and motivated, and that good and efficient working conditions must prevail.

The need for sound personnel management is not unique to nuclear power; however, it does acquire particular importance here because the operation and maintenance personnel of nuclear power plants do present some special features. The technical staff has to be highly competent in their particular disciplines, and require specific knowledge of the plant they are to operate; training, especially of the direct operations personnel, is of a relatively long duration and high cost, and experience is also required; working conditions involve occasional stress situations and require exceptionally high levels of responsibility, work discipline, safety consciousness and quality of work.

Some problems which frequently cause difficulties are: whether a special status should be assigned to the operations personnel of nuclear power plants in comparison with fossil-fuelled plants; the possible constraints in the career develop­ment prospects of the operations staff; and the salary systems and scales applied.

Some utilities maintain the attitude in their personnel management policy that a nuclear power plant is just another electric generation plant, even though they are fully aware of the differences between nuclear and fossil-fuelled units for all other purposes. This attitude is difficult to reconcile with their high expectations regarding the knowledge, skills and attitudes of their nuclear power plant personnel, and may lead to a general lowering of the standards to the level equivalent to fossil-fuelled plants, which would be inadequate for nuclear power.

The higher the quality of an individual, the greater his expectations that his aspirations will be met within the organization. Should there be important constraints limiting the possiblity of career development, such as for example the requirement for an extra educational qualification at a certain stage of the expected career-path, it would not be reasonable to hope for high-quality candidates nor to expect a person to remain motivated at a post above which he cannot aspire to be promoted.

State-owned utilities frequently apply salary systems for nuclear plant personnel which correspond to the civil service in general and may be far below the prevalent salary levels in private industry. This will inevitably lead to unacceptably high rates of attrition, especially among the most experienced and competent people, and to a general lowering of standards and moral of those who remain.

Available measures towards solving these problems are usually the results of compromises within the national and utility environment. It seems advisable to adopt personnel management policies consistent with the desire of complying with the high-quality requirements accepted as necessary for nuclear power plant operations personnel.

9. PER SO N N EL MANAGEM ENT

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International guidance, like other guidance, is usually welcomed by all those who have a coincident opinion, or who have no position at all. It is, however, frequently resisted and may even be resented by those who have a contrary opinion or who follow a different approach. It is fully recognized that inter­national guidance can never be compulsory; nevertheless it may be difficult to maintain opposing views and approaches, especially when controversial issues are involved.

International guidance developed by the Agency, except in a few instances, cannot be too specific and detailed. Agency guidance consists mostly of indicating possible solutions to identified problems, and of providing advice on how these solutions can be applied in practice. Care must be taken, however, not to limit international guidance to the statement of the obvious and the expression of generalities which are certain to meet a general consensus. It is therefore the Agency’s intention to develop and provide meaningful technical guidance for the qualifications of nuclear power plant operations personnel, beyond what is currently available and directed primarily towards the needs of the plant operating organization.

10. CO N STRAIN TS TO INTERN A TIO N A L GUIDANCE

IAEA-SM-268/77

A S S U R I N G N U C L E A R S A F E T Y

F R O M T H E P O I N T O F V I E W

O F S T A N D A R D I Z A T I O N

V. KRETT, L. JANÍK Nuclear Research Institute,vRez, Czechoslovakia

F.Ya. OVCHINNIKOV, V.CHEBOTAREV IEA Interatomenergo,Moscow

AbstractASSU RIN G N U C L E A R S A F E T Y FROM THE POINT O F VIEW O F STA N D A R D IZA T IO N .

The paper presents the principles adopted in Czechoslovakia for the preparation o f technical regulatory documents dealing with nuclear pow er plant safety assurance at the design, construction and operation stages. Czechoslovak technical regulatory documents are pre­pared in co-operation w ith the member states o f the International Econom ic Association Interatomenergo. The main aspects o f the preparation o f the regulatory documents and Czechoslovak participation in the process are described.

1. INTRODUCTION

Nuclear energy in Czechoslovakia is expected to provide the main part of the growing demands for electricity and heat.

This point is well illustrated by the fact that the last power plant burning fossil fuel was built in 1982. So, thë further increase in supplied power will be a task for nuclear plants. According to the energy development programme, power stations with a total capacity of 9300 M W should be put into operation in the CSSR before 1995.

The fast rate of nuclear plant construction, and especially the enhanced demands for their safe and reliable operation, have necessitated the preparation of technical regulatory documents corresponding to up-to-date industrial levels. The demands for nuclear power plant safety assurance in Czechoslovakia are incorporated into legal regulations.

The technical regulatory documents concerning nuclear energy in the CSSR have been developed on the basis of corresponding documents valid in the USSR, in accordance with the national rules and regulations, as well as recom­mendations issued by the IAEA, ISO and other international organizations.

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326 KRETT et al.

According to the Treaty for Specialization and Co-operation, Czechoslovak industry, using these documents, manufactures equipment for nuclear power plants with WWER-type reactors which are being built in Czechoslovakia and other countries. Czechoslovak industry is able to deliver complete power plants.

2. N U C L E A R P O W E R PLANT SAFETY ASSURANCE IN CZECHOSLOVAKIA

The construction of reliable and operationally safe nuclear power plants is in Czechoslovakia based on the strict implementation of appropriate national regulations. The technical regulatory documents, dealing with nuclear power plant safety in the CSSR, can be divided into five groups, according to their importance (Fig. 1 ):(1) Laws: these form the legal basis for nuclear power plant safety assurance

and establish the main requirements and safety aims.(2) Decrees: these incorporate the permission to construct nuclear power plants

and establish the principles of nuclear safety, radiological protection, radioactive materials handling, etc.

(3) The main regulatory documents covering safety: this group includes all documents which in accordance with the first and the second groups establish basic aspects and technical demands for nuclear power plant safety assurance during siting, construction (including manufacturing and component safety assurance) and operation.

(4) The specific regulatory documents: these establish requirements for speci­fic equipment, e.g. design and stress analysis of a core pressure vessel, etc.

(5) Other technical regulatory documents.At present in Czechoslovakia a number of general decrees of the

Czechoslovak Atomic Commission are in force for nuclear power plant safety assurance, namely:

— nuclear safety assurance in design, licensing application for construction and nuclear power plant construction [ 1 ]

— general criteria for safety assurance in nuclear power plant siting [2]— quality assurance of selected components for safety in nuclear power

plants [3]— safety assurance during startup and operation [4].

Governmental legislative documents dealing with nuclear power plant construction are produced on the basis of the above-mentioned decrees. Nuclear power plant construction is at present carried out according to the Soviet technical and regulatory documentation, altered, if necessary, to correspond to the

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Issued Situation in CSSR

By legislative and governmental bodies

By international organizations {ISO , IA E A ) and national organizations for standardization

Competent law for nuclear safety

Decrees Nos 2 ,3 ,6 and 5of CzechoslovakAtom ic Energy Commission

Documents of IE A Inter- atomenergo

F IG .L H ierarchy o f nuclear energy regulatory documents.

Czechoslovak standards [5]. These documents include the main principles and safety criteria and also contain administrative and technical demands whose ful­filment is a necessary condition for nuclear power plant safety assurance.

The implementation of these demands is provided by:— selection of the appropriate site— selection of the necessary health protection zone— inclusion of the necessary control and protection systems— quality assurance in manufacturing, assembly, repair and reconstruction of

the equipment and piping systems— quality assurance in construction and assembly work— maintenance of safety system reliability through permanent observation and

periodic tests of the in-service performance— observance during operation of the requirements included in the technical

regulatory documentation— appropriate personnel qualification in manufacturing, assembly and operation.

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The maximum permissible dose to the personnel and public as well as the level of environmental contamination during normal operation and in anticipated operational occurences are established for all the enumerated cases by the ‘Health-related regulations for design and operation of nuclear power plants’ and by other regulatory documents related to nuclear safety. Subsequently, personnel and public protection during accident conditions is anticipated in the plan of the appropriate measures for the site and its surrounding area.

The safe operation of a reactor is secured by the safety systems which ensure:— shutdown of a reactor and subcriticality maintenance— emergency core cooling— emergency cooling of a reactor and residual heat removal— protection of primary circuit from overpressure— retention of radioactive release within a hermetic primary circuit.

All anticipated safety systems must meet the demands of ‘Design and operation safety rules for equipment and piping of nuclear power plants’. These include instructions for periodic testing of the functioning of systems as well as surveillance requirements for in-service inspection of the welds in equipment and piping. In addition, measures for preventing incorrect actions by personnel are implemented.

3. QUALITY ASSURANCE F O R N U C L E A R P O W E R PLANT EQUIPMENT

Nuclear power plant safety is greatly dependent on the quality in manu­facturing, assembly and operation of equipment.

In Czechoslovakia, the implementation of these requirements is met through the establishment of quality assurance programmes, which include both organi­zational and all inspection activities necessary to ensure the quality assurance of given items. The scope and methods of inspection are laid down in the corresponding technical regulatory documents.

At present, quality assurance programmes are an integral part of the design of each constructed nuclear power plant as dictated by the increasing importance of plant quality. The programmes are consistent with the demands of national and international technical regulatory documents.

Quality control and equipment inspection during operation are provided for at the design stage and are included in the appropriate technical regulatory documents. The requirements for equipment and material inspection are being met on the basis of overall safety-related activities.

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As has been mentioned, nuclear power plants are largely constructed in accordance with Soviet technical and standard documentation because the USSR has greater experience in this field. This activity is outlined in the ‘Treaty for Multilateral International Specialization and Co-operation in the Manufacture and Supply of Equipment for Nuclear Power Plants’.

However, the direct application of technical regulatory documents in force within the USSR is difficult and sometimes even impossible for other countries.

Moreover, each country participating in the Treaty has its own, sufficiently well developed, industrial and regulatory base with its own specific national practice.

This fact has necessitated the modification of the USSR technical regulatory documents, with due regard being given to current world experience in the nuclear energy field, the requirements laid down in the appropriate standards and recommendations of the IAEA, the ISO and other international organizations, and the specific nature of each country’s manufacturing industry.

This being the case, the International Economic Association (IEA) Inter- atomenergo has developed and now implements a programme of activities for the creation of unified regulations and standards in the manufacturing and operation of equipment for nuclear power plants. These include unified require­ments for reliability and quality.

This programme aims to develop, and to gain agreement from the member states on 85 technical regulatory documents dealing with the following topics (see Fig.2):

— general safety considerations in nuclear power plants— reliability of the nuclear power plant and its equipment— rules for safe design and operation of power plant equipment and piping— standards for equipment and piping stress analysis— materials for equipment and piping— general rules for welding— inspection procedure for seam welds and weld deposits, including welder

qualification examination— metrological assurance of nuclear power plant operation.

The main technical regulatory documents represent general safety con­siderations and requirements which have a universal validity (Fig.3). They con­tain safety criteria and organizational as well as technical demands which should be complied with. These documents establish a basis for the implementation of

4. IN TERN A TIO N A L CO-OPERATION

330 KRETT et al.

General regulations for nuclear power plant safety (decrees)

Nuclear power plant equipment, piping, accessories and instruments {technical requirements)

Metrological assurance for nuclear power plant

Materials for nuclear power plant equipment and piping

Inspection rules for welds and weld deposits

r - — ,I Basic technical |I regulatory documents |I (C M EA , national) |

I----------------------------------- 1

F IG .2 . Scheme o f nuclear technical regulatory documents.

IAEA-SM-268/77 331

F IG .3 . Technical regulatory documents fo r nuclear power plant safety assurance.

technical procedures in nuclear power plant safety assurance from design to operation. They also permit the establishment of detailed special technical regulatory documents which cover technical requirements and procedures or appropriate technical solutions.

Within the scope of this programme, technical regulatory documents are drawn up by organizations and corporations in the member states of the IEA Interatomenergo on the basis of the documents valid in the USSR. The co­ordination of this work in Czechoslovakia is carried out by the Nuclear Research

v

Institute, Rez.Under the plans for the year 1984, it is proposed to submit all contemplated

technical regulatory documents for member states’ approval. These documents will then be transmitted to design organizations and manufacturers and will be used for the preparation of the common quality assurance programme in the manufacture of items for nuclear power plants.

332 KRETT et al.

Subsequently, Interatomenergo intends to prepare a programme of work which should establish the system of international technical regulatory documents for the design, construction, assembly and operation of nuclear power plants.The implementation of this programme will help to establish a common technical regulatory base in member states, provide them with the documentation necessary for construction and operation, and thus increase the quality and safety of nuclear power plants.

5. CONCLUSION

The development and the improvement of regulatory documents is a matter of co-operation between member states of IEA Interatomenergo and is based on experience acquired during research, design, manufacture, construction and operation of nuclear power plants. At the same time, valid legislative, technical and other documents in the field of nuclear power plant safety assurance are being observed. The experience and achievements of other countries, and the recommendations and standards of the IAEA and other international organi­zations, are taken into account.

The development of international technical regulatory documents makes it possible to provide a common guidance for the manufacture and operation of equipment, to enhance its quality and to assure the safe operation of nuclear power plants.

REFERENCES

[1] C ZE C H O SL O V A K ATOM IC E N E R G Y COM M ISSION, Decree No.2 (27 O ctober 1978).

[2] C ZE C H O SL O V A K ATOM IC E N E R G Y COM M ISSION, Decree N o.3 (31 March 1979).

[3] C ZE C H O SL O V A K ATOM IC E N E R G Y COM M ISSION, Decree No.5 (14 November 1979).

[4] C ZE C H O SL O V A K A TO M IC E N E R G Y COM M ISSION, Decree No.6 (23 November 1980).

[5] C ZE C H O SL O V A K M IN ISTR Y O F M E T A L L U R G Y AN D H E A V Y EN GINEERING,

Regulations on the Use o f Rules and Standards in the Design o f Czechoslovak Nuclear

Power Plants with WWER-440 T ype and B -213 Type Reactors (19 8 1).

IAEA-SM-268/68

I A E A - A S S I S T E D R E S E A R C H W O R K I N T H E

F I E L D O F O P E R A T I O N A L S A F E T Y F O R

H U N G A R Y ’S F I R S T N U C L E A R P O W E R P L A N T

I. TÓTH, L. SZABADOSCentral Research Institute for Physics,Budapest, Hungary

AbstractIA E A -A SSISTED RE SE A R CH W ORK IN THE FIELD O F O P E R A T IO N A L S A F E T Y FO R H U N G A R Y ’S F IR ST N U C L E A R POWER PLA N T.

Hungary’s first nuclear pow er plant (NPP) consisting o f 440 MW WWER-type PWRs is under construction at Paks. F or countries just taking their first steps in nuclear energy produc­tion it is o f vital importance to have a good understanding o f NPP behaviour, especially in off- normal conditions. In Hungary a Government-sponsored research programme has been initiated for nuclear reactor safety analysis. The therm ohydraulic part o f the programme aims at establish­ing a set o f carefully selected com puter codes, sufficiently tested by experim ent, to allow ana­lyses to be perform ed under different accident conditions for the Paks NPP. In support o f these goals an experim ental facility will be constructed to investigate single- and two-phase natural circulation phenomena. A short description o f the main characteristics and the experim ental programme is given. The paper discusses the way in which the IA E A programme o f assistance in the uses o f com puter codes for safety analysis is supporting the calculational activities. Results o f calculations for small-break processes are presented, including the effect o f safety injection tank set-point pressure and that o f secondary side cool-down. The way the research activities support the training o f plant personnel is also considered.

1. INTRODUCTION

Nuclear energy production is very new to Hungary — the first unit of the Paks nuclear power plant (NPP) is currently being commissioned; its electric output at present is 50% of the nominal power. Four units are under construction on the same site, all being equipped with a WWER-type 440 M W pressurized water reactor. Such reactors are slightly different to PWRs of the usual design: a 6-loop primary circuit, horizontal steam generators, loop seals in hot and cold legs, and safety injection tank (SIT) set-point pressure higher than secondary pressure.

In a country just entering the ‘era of nuclear energy’ it is of vital importance for plant personnel, licensing authorities and research engineers in the safety field to have a thorough understanding of NPP behaviour, especially in off-normal conditions. Although plant operators participate in special courses, it is necessary to ensure continuous training so that they may efficiently face possible accident

333

334 TÓTH and SZABADOS

conditions. One method of training is to use a plant simulator; an alternative possibility is the application of experimental and calculational results.

A Government-sponsored programme was initiated in 1981 for reactor safety analysis. The thermohydraulic part of the programme comprises both experimental investigations and computation and its main aims are to assess the transient behaviour of the Paks NPP, including large- and small-break LOCAs.The P M K 1 test facility is due to be constructed at the Central Research Institute for Physics (CRIP) in the near future to analyse primary circuit dynamics in small- break LOCAs and disturbances originating from the secondary circuit. The compu­tational part of the programme comprises the adaptation of different computer codes. Priority is given to codes that permit supplier-independent calculations. These codes will be checked against experimental results obtained, for example, by the P M K facility and data directly from the plant, and the necessary modifica­tions will be carried out. In this field we are being greatly helped by the IAEA.

2. IAEA ASSISTANCE

At the beginning of 1982 the IAEA programme of assistance in the use of computer codes for safety analysis was initiated with the idea of helping Member States with limited access to codes and/or computers in the field of nuclear reactor safety. In the framework of this programme, the IAEA puts at the participants’ disposal its IBM 3081 computer to run a number of selected safety codes. At the moment, one code represents each of the following subjects: thermohydraulic analysis (RELAP4/mod6), containment response (CONTEMPT-LT-026), and fuel behaviour (SSYST-2).

First results, problems and future directions within the programme were discussed at a Technical Committee/Workshop in Budapest [1], where 16 coun­tries and international organizations were represented. The workshop part of the meeting permitted participants to exchange information on the applicability of RELAP4/mod6 for different types of transients as well as on difficulties encountered in running the code. The Technical Committee put forward several recommendations:

(a) Code-oriented training courses should be organized for inexperienced investigators;

(b) Problem-oriented workshops should regularly be held for experienced investigators to review the state of knowledge on particular problems:

(c) The proposed list of computer codes should be implemented by the IAEA Computer Centre.

1 PMK: Primerkori M odell Kisérlet (Primary Circuit Model Experiment).

IAEA-SM-268/68 335

Hungary was among the first countries to participate in this programme: on the basis of their experience with different members of the RELAP4 family, research engineers from CRIP performed numerous calculations with the RELAP4/mod6 code. The use of a high-speed computer, the availability of a more advanced code version and, last but not least, the very effective organization of the assistance programme ensured a much higher efficiency in carrying out the safety analyses.

3. C O M P U T E R ANALYSIS

In the Government-sponsored safety analysis programme, the RELAP4 code family was chosen for the thermohydraulic assessment of the primary circuit during accidents. This choice was motivated by the fact that the RELAP4 family is the most widely used code for safety analysis throughout the world and that CRIP had already acquired experience in running the RELAP4/mod3 and mod6 versions.

Work at CRIP started by using RELAP4/mod3 but it was much impeded by the fact that this code version is somewhat out-dated as to its models and capa­bilities. In addition, the low speed and the 1 Mbyte core capacity of CRIP’s ES 1040 computer impose serious limitations especially with calculations involving considerable process time — this being a further reason why the IAEA assistance was most welcome.

The main aims of computer analysis are:

(a) To widen the basis of Safety Analysis Reports (SARs) for the Paks NPP.(b) To gain additional information about NPP behaviour in accident conditions.

Cases generally discussed in SARs — although sufficient to prove plant safety — do not cover a wide enough spectrum of occurrences to allow their use for the training of operators: calculations can be performed to fill in such gaps in understanding. It is of great importance that operators be familiar with accident scenarios of various kinds and that they shouldalso be able to identify the type of transient in order to act correctly. One way to achieve this goal is to use calculational results of these processes for the training of plant operators. Such calculations can be helpful in fixing time delays so that operators can perform a given action during a recognized transient. Furthermore, the effectiveness of different operator actions can be judged by calculation.

(c) In accident conditions there are alternative ways of operator intervention that are not (or not yet) allowed at the NPP. Calculations and experiments should then be performed to broaden our knowledge of such processes and to assess their feasibility. Feed and bleed of the primary circuit or a rela­tively fast cooling down of the steam generator secondary side in order to reduce system pressure may serve as examples for interventions of this kind.

336 TÓTH and SZABADOS

(d) The P M K test facility (described in the next section) requires a large number of pre-test calculations. First code runs have already been performed in the planning stage of the loop in order to check whether P M K adequately models the primary circuit of the W W E R NPP. Pre-test calculations of transients to be run on the test facility are a very useful means of obtaining information on the sequence and duration of the thermohydraulic processes. This informa­tion is necessary for choosing the proper type and position of the instruments as well as for planning the most effective method of data acquisition.

(e) Results of calculations are useful also for the activities connected with the NPP simulator. In order to choose the pertinent accident conditions the simulator will be able to handle, it is necessary to have a broad knowledge of the possible transients and their thermohydraulic characteristics: these latter characteristics are particularly important when defining the relatively simple models that describe plant behaviour in the simulator.

At present, RELAP4/mod6 is the only code available through the IAEA assistance programme that calculates primary circuit thermohydraulics during transients. RELAP was, of course, originally developed for LOCA analysis; thus its ability to calculate processes where disturbances originating from the secondary circuit would be handled are rather restricted, especially if the reactor control system plays an important role. The IAEA intends to increase the number of safety codes available through its assistance programme. In view of the activities described above CRIP would be very much in favour of a computer code for cal­culating primary circuit dynamics without depressurization including reactor control effects.

Two examples of RELAP4/mod6 calculations are presented to show the effects of SIT set-point pressure and secondary side cool-down, respectively.

3.1. Cold-leg break of 1 per cent

Calculations were performed for both the Paks plant and the P M K test facility. First results and a comparison of the two calculations were presented in Refs [2] and [3]. The P M K results are discussed here because of the longer process time calculated. It was ensured that no SIT injection takes place and that two of the three high-pressure safety injection (HPSI) pumps are working. Functioning of SITs was not considered in the assessment of plant behaviour for the case of a hypothetical lowering of SIT set-point pressure (originally 6 MPa). Two cases were run: one with constant secondary pressure, the other with the secondary side cooled down at a rate of 100 K/h.

The thermohydraulic phenomena can be explained with the aid of the pressure-time diagram (Fig. 1 ). After the reactor is scrammed at 40 s the depres­surization rate increases. The pressurizer empties at 120 s and this continues to

RELflP4-M0D6 PMK MODEL Г/. LOCR «83.02.02.«

IAEA-SM-268/68 337

FIG.l. Calculated variation of system pressure following a 1% cold-leg break with and withoutsecondary side cool-down.

enhance depressurization until, after 140 s, steam generated in the core begins to accumulate in the upper plenum thereby resulting in a slight increase of system pressure. At about 400-500 s the mixture level in the upper plenum drops to the hot-leg elevation and the steam in the hot leg forces down the liquid level on the reactor side of the loop seal; this leads to increased repressurization of the primary circuit. The loop seal is finally cleared at about 700 s, in the case when steam generator (SG) secondary pressure is kept constant throughout the transient, and steam passing through the loop seal is condensed in the SG. This involves an increased mass flow rate in the loop and the core and system pressure stabilizes slightly above the secondary pressure level.

This situation lasts until the mixture level in the system decreases sufficiently to influence the break flow rate. At 1550 s, the mixture quality increases at the break level and this involves faster depressurization; at 1600 s the break is uncovered. This means a radical reduction in the break flow rate; in fact, the break flow falls below that delivered by the HPSI pumps and the system level begins to rise. At about 2000 s the break is covered again with a subsequent rise in system pressure. However, this process is limited in time by the fact that

3 3 8 TÓTH and SZABADOS

RELflP4-M0D6 S440 7.4V. SBIOCR *82. 11.22. RLP4CT/006 02/23/7

TIME W

FIG.2. Calculated variation of system pressure, core inlet and outlet temperatures following a 1% cold-leg break without SIT injection.

the mixture level drops again because of the increased break flow rate; the whole process is repeated again and again, thereby producing a sawtooth-like behaviour in the system pressure.

The lower curve in Fig.l shows the pressure evolution when the secondary side is cooled down at a rate of 100 K/h. The initial behaviour of the system is similar to the case with constant secondary pressure: after 800 s the primary pressure closely follows the secondary one, underlining the importance of secondary cooling. The main effect is that — assuming that the SIT initial pressure is lowered somewhat below the secondary pressure — SIT injection would start much earlier than in the case without cool-down.

The results have indicated some phenomena of interest to plant operators:

(a) Loop seal may cause considerable pressure increase.(b) If HPSI pumps deliver a flow rate just in between steam and water critical

break flow rate, a sawtooth-like periodic pressure variation can be expected after the break is first uncovered.

(c) Secondary pressure strongly influences primary pressure even after break uncovering.

IAEA-SM-268/68 3 39

FIG.3. Calculated variation of system pressure following a 7% cold-leg break with SIT injection.

3.2. Cold-leg break of 7 per cent

T w o types of calculations have been performed for the Paks NPP, with and without SIT in function. Code input was based on data taken from Refs [4] and [5]. The secondary side pressure was kept constant in both calculations.Figure 2 shows the system pressure and temperature variation without SIT injection. Initial depressurization is fast and the primary circuit mixture level drops accordingly: at about 70 s it decreases to the elevation of the hot legs. Pressure then stabilizes somewhat above S G secondary pressure level indicating that the break flow alone cannot remove sufficient energy to depressurize the system. From 220 s the break is fed by two-phase flow, which leads to renewed depressurization, but it is not before 400 s - when the break is fully uncovered - that the primary system pressure becomes independent of secondary pressure. In this period there is reverse heat flow in the SGs.

If SITs start to inject at 6 MPa, the whole process in changed drastically (Fig.3). The large amount of cold water injected from the SITs condenses steam in the upper plenum; consequently the depressurization rate is increased. Pressure thus drops below the secondary pressure and the heat flow is reversed in the SGs.

3 4 0 TÓTH and SZABADOS

The amount of heat transferred to the primary circuit in this way is so important that it produces steam in the SG exit chamber: it is this steam production that stops further depressurization. In the meantime, the mixture level in the pressurizer is rising since the SIT flow exceeds break flow. At about 75 s the pressurizer gets completely filled, primary and SIT pressures equalize and consequently the SIT flow drops to zero. The system pressure is maintained by the steam production in the SGs. Because of the reverse heat flow in the SGs, loop and core flows begin to stagnate thereby causing some steam production in the core as well.

Further system behaviour depends on how long the steam produced in the primary circuit will be able to maintain the system pressure and this, in turn, depends mainly on the heat capacity of the SG secondary side and on the possible intervention on this side.

Phenomena of interest to plant personnel can be summarized as follows:

(a) Reverse SG heat flow plays an important role in maintaining primary system pressure with both high and low SIT set-point pressure.

(b) With an SIT set-point pressure of 6 MPa, injection is soon arrested becauseof pressure equalization, and core flow stagnation leads to some steam produc­tion in the core.

4. E X P E R I M E N T S

In the framework of the Government-sponsored safety analysis programme the experimental activities are based on the P M K loop [3]. The loop is designed mainly to investigate processes (both steady- and non-steady-state) following a small break in the primary circuit, but it was conceived in a way that allows simulation of a variety of plant dynamical processes.

The first aim is felt to be very important since relatively few results have been published on small-break behaviour of WWER-type plants. Finland has already expressed interest in participating in the project and the possibility exists of widening the circle of countries concerned with the experimental activities. It can be envisaged that the facility and/or the experimental results could be made available for international co-operation (e.g. within the framework of the IAEA Technical Committee on Thermal Reactor Safety Research), although a broadening of the experimental programme would make some support — perhaps from the IA E A — necessary.

The P M K test facility in its present design is a model of the primary circuit with a W W E R - 4 4 0 reactor of the Paks NPP. The operating pressure and tempera­ture of the model are 16 M P a and 623 K, respectively. It was conceived for the investigation of single- and two-phase natural circulation processes that are gravity dominated, therefore the elevations are the same as in the plant, with the

IAEA-SM-268/68

TABLE I. SCOPE O F INV ESTIG A TIO N S ON TH E PMK TEST FACILITY

''Ч Types

Effects 'v

Natural circulation ( 1 - and 2-phase)

Primarycircuitdynamics

ECCsystemeffects

Thermal,acousticnoise

Waterchemistry

Remarks

Core оIо _ 0 1 о 0-1.0 Fraction ofpower nominal power

</}UJH Primary a - - + + From normalUJ level to partiallyH< covered coreHCO>• Secon­ 0-0.1 _ - - - Fraction ofQ< dary level nominal levelШHCO Non- b - - + + Effect in SG,

conden- upper plenumsibles and core

Break 1-20% HL, CL + _ HL - hot legsize + HL, CL, CL - cold leglocation SG.l'R PR - pressurizer

No. of 0-3 0 1 Ы _ + _HPSIpumps

No. of 3—4C _ 3—4C + - cConnected toSIT upper plenum

and downcomer

SIT d _ + _ ^NominalV)b- set-point and reducedСЛUJ pressureHHШ SG + + + + -

So cool-downz<OÍ Feed + - _ + -

and bleed

No. of _ _ 0-3 + _LPSIpumps

Secondary + + + + -perturba­tions

+ tests planned.— no tests planned.

3 4 2 TÓTH and SZABADOS

exception of the lower plenum and the pressurizer. The scaling ratio of volumes and power is 1:2070. A core model of 19 rods is used. The six loops of the NPP are modelled by a single loop, the broken loop is modelled by hydraulic resistances. Instead of the cross-section ratio of the loops, the pressure drop ratio is 1:1.Access or missing volumes are lumped into the volumes of the lower plenum, the SG collectors and the upper plenum. O n the S G secondary side the steam volume ratio is kept.

The main objective of the experiments is to investigate primary circuit behaviour in single- and two-phase natural circulation. Both steady-state and transient tests are planned: the former will assess parametric effects like primary circuit mixture level, the latter will model entire small-break processes. The test facility will also be used to simulate different plant transients without loss of coolant (e.g. turbine trip, steam line break, etc.), although some limitations are imposed in these cases by the fact that the secondary side and its control system could not be fully modelled. The P M K may be used in a later stage to study system effects in E C C processes; it is not possible to define this activity until after the results of separate effects of E C C tests on the N V H 2 loop become available. Instru­mentation and design of the P M K will also permit acoustic and temperature noise measurements as well as studies on water chemistry.

The scope of investigations to be performed on the P M K loop is presented in Table I.

5. DISCUSSION

W e believe that in a country just starting on nuclear energy production, nuclear safety research must serve as a basis for, and have a great impact on, power plant operation. In Hungary, CRIP realizes its responsibility in this field and this paper reflects our activities in support of this goal.

Let us n o w summarize in what manner these activities may assist safe NPP operation. Calculations and experiments can be used first of all in the training of plant operators, but are important for other reasons as well:

(a) Results can be obtained on the timing of different transient processes and accident scenarios. These may be classified so that they can be used by operators in recognizing the type of accident they are facing.

(b) Time delays available for operators to perform corrective actions can be fixed.

(c) Alternative corrective actions can be assessed and such actions that are not yet allowed at the N P P can be tried.

NVH: Nagynyomású Vizhütésü Hurok (High-Pressure Water Loop).2

IAEA-SM-268/68 3 4 3

(d) A large amount of experience is acquired that may serve as background information for the safe operation of the NPP. A relevant example of the use of this information is its application in building a plant simulator; this is the case in Hungary.

In addition, a test facility modelling the NPP is useful for operator training, as a substitute for a plant simulator. Operator actions in response to different plant processes can be exercised, to assess instrumentation behaviour during accident conditions. Experimental evidence may result in propositions for additional plant instrumentation ensuring safer plant operation.

With regard to calculations, the results obtained up to now would not have been possible without the I A E A aid within its assistance programme on the uses of computer codes for safety analysis. It is the intention of CRIP to make further use of the possibilities within this programme. It is also realized that international co-operation in safety research could benefit the safe operation of NPPs, especially in countries just beginning to utilize nuclear energy. It is for this reason that Hungary firmly supports the I A E A initiatives within the Technical Committee on Thermal Reactor Safety Research.

A C K N O W L E D G E M E N T S

W e wish to thank Mr. L. Epel and Mr. V. Osmachkin of the I A E A for their efforts in bringing about the assistance in the uses of computer codes for safety analysis. Our thanks are also due to Mrs. K. Lewis-Goettler and Mr. J. Barton of the I A E A Computer Section for their constant and efficient help in performing the calculations.

Finally we acknowledge the valuable participation of Dr. L. Perneczky in the computer analysis.

R E F E R E N C E S

[1] Technical Committee/Workshop on IAEA Assistance in Uses of Computer Codes for Safety Analysis, Budapest (1982).

[2] TÓTH, I., et al., Results of SB LOCA Calculations for the Paks NPS, Technical Communi­cation, Budapest (1982).

[3] SZABADOS, L., et al., Calculations for the PMK-NVH Test Facility, Technical Communica­tion, Budapest (1982).

[4] SIDORENKO, V.A., Operational Safety of WWER Reactors (in Russian), Atomizdat, Moscow (1977),

[5] Thermohydraulic Safety of WWER Reactors (in Russian) (Proc. Teplofizika 82,Prague, 1982).

P oster Presentations

IAEA-SM-268/10P

C O M P U T E R I Z E D P E R S O N N E L D O S I M E T R Y M O N I T O R I N G A N D M A N A G E M E N T S Y S T E M

A. Y A N A G I S A W A , M. T A K A Y A M A Fuchu Works, Toshiba Corporation,Fuchu-shi, Tokyo

Y. K I M U R A , A. K A W A M U R A Nuclear Energy Group,Toshiba Corporation,Tokyo

Japan

Radiological management work in nuclear power plants consists of: personnel dosimetry monitoring and management; work environment control; process radiation control; and peripheral environmental control. Radiological data cover both the area inside and outside the nuclear power plant and consist of complex data concerning the environment, weather, processes, etc. The collection of enormous amounts of data from various kinds of radiation monitors and dosimeters, and their monitoring, analysis and evaluation require considerable manpower and the participation of advanced specialists. Process computer systems are being applied to management work with the aim of achieving decreased exposure through a reduction of labour, an improvement in data control efficiency, the enforcement of accurate and strict dosimetry monitoring, and the proper evaluation of dose data. The paper deals with the functions, composition and features of a computerized radiological management system, and in particular a computerized personnel dosimetry monitoring and management system.

1. I N T R O D U C T I O N

Nuclear power plants have been growing in scale year after year, and the number of units installed at individual sites has also increased. This necessitates increased management work, and the efficient and accurate control of this work becomes an urgent requirement. A m o n g the various types of management work at nuclear power plants, the greatest emphasis should be placed on radiological

3 4 5

3 4 6 POSTER PRESENTATIONS

management because of the enormous amount of data involved and the regulation requirements. Efficient radiological management is essential for overall plant safety.

In studying the application of computer systems, special attention must be given to ensuring that the design will meet the needs of the overall operation of the nuclear power plant.

2. BASIC S Y S T E M D E S I G N POLICY

The radiological control system should be designed in accordance with the following policy:

(a) Efficiency: efficient man-machine system with suitable peripheral devices, and high-speed data search and reference and editing of the accumulated data;

(b) Reliability: highly reliable operation, round-the-clock on-line data acquisition;

(c) Flexibility: provision for linkage to various devices or additional systems for further expansion of the system.

3. R A D I O L O G I C A L M A N A G E M E N T

Examples of the useful functions which it would be desirable to incorporate in the radiological control system in a nuclear power plant are:

(a) Personnel dosimetry monitoring and management ; dosimetry control of workers who enter controlled areas;

(b) Work environment control: radiation monitoring with area and dust monitors in controlled areas;

(c) Process radiation control: monitoring of process radiation data and their management;

(d) Peripheral environment control: control of data concerning weather, emission, radioactive waste, peripheral environment monitoring, etc.

4. P E R S O N N E L D O S I M E T R Y M O N I T O R I N G A N D M A N A G E M E N T S Y S T E M

Personnel dosimetry monitoring and management is one of the most important, complex, and large-scale systems in radiological control, involving on-line data acquisition, a huge data base, and a distributed computer network.Its main functions are as follows:

POSTER PRESENTATIONS 3 4 7

(a) Registration control: data registration control for entrants to the controlled area.

(b) Entry and exit control: monitoring of workers at check-point to the controlled area;

(c) Dose control: calculation, editing and documentation of dose data by person;

(d) Work control: calculation, editing and documentation of dose data by work and period.

This system consists of a computer and the following terminal controllers connected by communication lines:

(a) Information display terminal;(b) R W P (Radiation Work Permit) data entry terminal;(c) Personnel data entry terminal;(d) Radiation monitoring terminal;(e) Gate monitors (surface dosimetry measurement devices);(f) Automatic T L D (thermoluminescence dosimeter) readers and controller.

The system configuration features a large data base and a network architecture to enforce simultaneous centralized control of personnel data and on-line data acquisition. To meet the need for high reliability, the host c o m ­puter system is redundant.

5. C O N C L U S I O N

The computerized radiological management system, which constitutes a subsystem of the total nuclear power plant data management system, can perform accurate and strict dosimetry monitoring and proper evaluation of data with reduced manpower and time. The application of such systems, e.g. personnel dosimetry monitoring and management, to several power plants has given very satisfactory results.

3 4 8 POSTER PRESENTATIONS

E F F E C T O F E X T E R N A L D E C O N T A M I N A T I O N O F P E R S O N S C O N T A M I N A T E D W I T H R A D I O N U C L I D E S A T A N O P E R A T I N G N U C L E A R P O W E R P L A N T

D. STOJANOVlC, Z. DJUKlC, M. TRAJKOVlC,Dragana VELJKOVIC, Katarina MILIVOJEVIC,BosiUjka A L EKSICMedical Protection Laboratory,‘Boris Kindric’ Institute of Nuclear Sciences,Vinca, Belgrade, Yugoslavia

In the paper, the results are presented of external decontamination over a period of twenty years in 34 cases of accidental contamination of persons occupationally employed at the R A reactor in Vinfca (nominal power of 6.5 MW). The radioactive contamination occurred as a result of the performance of repair and regular maintenance operations: fuel rod extraction, mounting and demounting of the heavy water pump; changing the cable for can transport; changing of fuel under distilled water shield; cleaning of technological channels; manipulation of valves during installation of graphite gasket on the body of the heavy-water pump; evacuation of the hot cell and transportation of waste materials; dispersion of graphite from lye; handling of irradiated samples, etc.

The radiocontaminants were in different states of aggregation (dust, gas, liquid). They appeared as isolated radionuclides (60Co, 3H, 24Na,27Al,109 Ag,1311) or as a mixture of fission products. Very often the composition was unknown, especially when the contaminant was in the form of dust.

The effect of external decontamination has been analysed as a function of certain physiological, radiological, physical and chemical characteristics, including: state of the skin and visible mucous membrane; anatomical region involved; duration of contact of the radionuclide with the barrier; levels of initial activity; chemical form of contaminant; state of aggregation; adequacy of the primary treatment on arrival at the decontamination centre; duration of treatment for different cases; means and procedures for decontamination.

The different means used for decontamination (of national and foreign production) with their various mechanisms of action were ranked according to their efficiency of decontamination and their different frequencies of application. A special analysis was made of surface-active substances as an effective means for decontamination. The paper also describes the approaches and procedures used in radiotoxicological and other diagnostic methods for supervision of contaminated persons.

The data obtained at the R A reactor are applicable also to operational safety in other nuclear power plants.

IAEA-SM-268/27P

SU M M A RY O F SESSIO N VI

Chairman: H. Fukumoto

The main interest in this session was in the activities of the O E C D / N E A and the I A E A in developing international incident reporting systems. The O E C D / N E A system has been in operation since 1980, whereas the I A E A had asked Member States with operating plants to participate in the system in 1983. Both organizations arrange periodic meetings to examine incidents which are considered to be of major interest and both are developing the necessary co-ordination.

Another field in which the I A E A is involved is the development of guidance on qualifications for nuclear power plant operations personnel. O n the question of the provision of technical support to operating shift teams, the preferred approach that was stated is to have professional engineers directly in charge of the plant in the shift supervisory positions, even if this implies the need for upgrading the status of the shift supervisor and other direct operating functions to a level that will attract and retain professional engineers.

A French speaker mentioned the need for international co-operation in the exchange of operating experience, but stated that bilateral arrangements are preferable for questions concerning nuclear plants sited near borders. Inter­national co-operation has been of particular use to Hungary as the I A E A has made one of its computers available for investigations into nuclear power plant behaviour under abnormal conditions. Progress is also being made in the develop­ment of technical regulations and safety standards among the Member States of the International Economic Association Interatomenergo. The documents will provide c o m m o n guidance for the manufacturing and operation of equipment for nuclear power plants.

349

EM ERG ENCY PR EPA R ED N E SS

(Session VII)

Chairman

J. R A S M U S S E NDenmark

IAEA-SM-268/63

O R G A N ISA T IO N D E S PLANS D ’U R G EN C E EN CAS D’A C CID ENT D A N S U N E C E N T R A LE N U C L E A IR E A E A U SO US PR ESSIO ND i s p o s i t i o n s p r i s e s p a r l ’e x p l o i t a n t

e t l e s p o u v o i r s p u b l i c s

M. L A V E R I EService central de sûreté des installations nucléaires,Ministère de l’Industrie et de la recherche,Paris

L. B E R T R O NService de la production thermique,Electricité de France,Paris,

France

Abstract-Résu mé

ORGANIZATION OF EMERGENCY PLANS FOR A PWR PLANT ACCIDENT: ARRANGEMENTS MADE BY THE OPERATOR AND PUBLIC AUTHORITIES.

A nuclear accident would be the result of a situation which was mishandled by the operator arising either because of an incorrect analysis made by him of the event or, more probably, of his being unable to apply the instructions available in the event of a multiple failure of safety equipment. To be able to analyse a situation which, by definition, has gone beyond the scope of plant personnel, it is necessary for Electricité de France (EDF) and the Central Service for the Safety of Nuclear Facilities (SCSIN) to have teams which can make available in the shortest possible time the highest expertise in respect of such events. To do so, the SCSIN and EDF have set up, at different analytical and decision-making levels, coherent and co­ordinated organizational arrangements which, while respecting the responsibilities of each person, would enable a common evaluation to be obtained as quickly as possible of the situation, its possible evolution and the best measures to take to limit the consequences of the accident.Such a level or intervention is necessary to complement the preventive and protective measures taken during the design, construction and operation of nuclear power plants in order to ensure that workers, the public and their environment are fully protected under any circumstances.

ORGANISATION DES PLANS D’URGENCE EN CAS D’ACCIDENT DANS UNE CENTRALE NUCLEAIRE A EAU SOUS PRESSION: DISPOSITIONS PRISES PAR L’EXPLOITANT ET LES POUVOIRS PUBLICS.

Un accident nucléaire serait l’aboutissement d’une situation mal maîtrisée par l’exploitant résultant soit d’une analyse incorrecte qu’il aurait faite de l’événement, soit plus vraisemblablement de l’impossibilité où il se trouverait d’appliquer les consignes mises à sa disposition si des défaillances multiples du matériel de sauvegarde survenaient. Pour analyser une situation qui, par définition, est sortie du domaine d’action du personnel des centrales, il est nécessaire, pour

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Electricité de France comme pour le Service central de sûreté des installations nucléaires, de disposer d’équipes réunissant, dans les meilleurs délais, les plus grandes compétences dans la connaissance de tels événements. Pour ce faire, le Service central de sûreté des installations nucléaires et Electricité de France ont mis en place, à différents niveaux d’analyse et de décision, des organisations cohérentes et coordonnées qui permettraient, dans le respect des responsabilités de chacun, d’obtenir, dans les meilleurs délais, une appréciation partagée de la situation, de son évolution possible et des meilleures dispositions à prendre pour limiter les conséquences de l’accident. Un tel niveau d’intervention est le complément nécessaire des mesures de prévention et de parade qui sont prises lors de la conception, de la construction et de l’exploitation des centrales nucléaires, afin d’assurer pleinement et en toute circonstance la protection des travailleurs, des populations et de leur environnement.

U n accident nucléaire susceptible d’avoir des conséquences radiologiques pour l’environnement est un événement dont la probabilité d’occurrence est très faible, mais que tout exploitant de centrale nucléaire responsable doit prendre en considération de deux façons.

Tout d’abord, il doit faire en sorte que soient réunies toutes les conditions pour que l’accident ne se produise pas.

Pour cela, il doit disposer, d’une part, d’une installation dont les caracté­ristiques physiques sont adéquates au plan de la sûreté (dispositions constructives initiales, modifications liées au retour d’expérience, qualité de la maintenance, etc.) et, d’autre part, d’une organisation permettant aux équipes de conduite d’être à tout moment en mesure de maîtriser un incident se produisant en exploitation avant qu’il ne dégénère en accident grave.

Les mesures qui ont été prises en France, et qui ont fait l’objet d’autres publications, reposent sur les principes suivants:1) Formation du personnel à la connaissance et à l’identification d’accidents de très faible probabilité d’occurrence. Un simulateur d’accident est en cours d’étude pour donner au personnel de conduite une représentation des divers paramètres caractérisant l’état de l’installation.2) Redondance dans l’analyse des événements au niveau des équipes qui en sont chargées et au niveau de la méthodologie. Un accident est analysé simul­tanément par l’équipe de quart selon une méthode séquentielle et par l’ingénieur de permanence sûreté par une méthode globale d’analyse des états de refroidis­sement du réacteur.3) Aide au diagnostic par un prétraitement des informations logiques et analogiques caractéristiques de la situation, regroupées sur un panneau de sûreté. Ce système prévoit en particulier une remise en cause périodique du diagnostic permettant à l’exploitant de ne pas persister dans l’erreur s’il s’était engagé sur une mauvaise voie.

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4) Consigne claire et précise basée sur les critères de conduite représentés sur le panneau de sûreté.5) Retour d’expérience permettant à chacun de bénéficier de l’expérience de tous.

L ’exploitant doit ensuite reconnaître que toute organisation, aussi parfaite soit-elle, est susceptible de défaillance et que l’accident, aussi improbable soit-il, peut se produire; il doit donc disposer d’une organisation lui permettant de gérer au mieux l’accident sur le plan local et d’informer toutes les instances qui ont à connaître de l’événement ou qui ont des responsabilités à assumer.

De son côté, au sein de l’organisation générale des pouvoirs publics, le Service centrale de sûreté des installations nucléaires (SCSIN) doit en particulier:— veiller à ce que l’exploitant exerce pleinement les responsabilités énumérées ci-dessus, tant au stade de la prévention qu’au cours du déroulement d’un éventuel accident;— assurer l’information technique des différentes autorités concernées;— conseiller le commissaire de la République, responsable de la mise en oeuvre éventuelle des plans d’urgence des pouvoirs publics.

Ce mémoire décrit l’organisation commune mise en place par le SCSIN et Electricité de France (EDF), à laquelle est associé très largement le constructeur de la chaudière nucléaire, Framatome, pour gérer l’aspect technique d’un accident nucléaire. Il ne décrit pas, par contre, l’organisation générale des pouvoirs publics en matière de sécurité nucléaire faisant intervenir en particulier, dans un ensemble coordonné par le Secrétariat général du Comité interministériel de la sécurité nucléaire, le SCSIN et la Direction de la Sécurité civile.

1. L A G E S T I O N D ’U N A C C I D E N T N U C L E A I R E : LES C O N C E P T S D E B A S E

L ’organisation qui a été mise en place en France repose sur les cinq concepts détaillés ci-après:

1.1. Premier concept

U n accident nucléaire serait l’aboutissement d’une situation que l’exploitant aurait mal maîtrisée, soit parce qu’il aurait fait une analyse incorrecte de l’évé­nement, soit plus vraisemblablement parce que les consignes qu’il aurait dû appliquer ne seraient pas applicables à la suite de défaillances multiples du matériel de sauvegarde. L’exploitant aurait fait vainement usage de toutes les consignes mises à sa disposition:— consigne d’accident;— consigne applicable pour les événements non pris en compte dans le dimen- sionnement (défaillances multiples du matériel de sauvegarde);

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— consigne d’urgence, donnant, en dernière limite, à l’exploitant la conduite à tenir pour assurer coûte que coûte la protection du coeur du réacteur.

Pour analyser une situation qui, par définition, est sortie du domaine d’action du personnel des centrales, il est nécessaire pour E D F c o m m e pour le SCSIN de disposer d’équipes réunissant, dans les meilleurs délais, les plus grandes compé­tences dans les domaines suivants:— connaissance de la sûreté des régimes accidentels;— connaissance des répercussions possibles de certaines manoeuvres sur l’état de contrainte du circuit (risque de choc froid sur la cuve);— connaissance des conséquences potentielles sur l’environnement (terme source, transferts, etc.).

1.2. Deuxième concept

Compte tenu de leurs responsabilités respectives, tant l’exploitant que le SCSIN doivent disposer d’un système d’information d’une très grande fiabilité permettant, en particulier, d’entrer en communication entre eux, ainsi qu’avec le commissaire de la République responsable de la protection des populations et de l’information du public.

1.3. Troisième concept

Les organisations mises en place par le SCSIN et par l’exploitant doivent être cohérentes et coordonnées et doivent permettre, dans le respect des responsa­bilités de chacun, d’obtenir, dans les meilleurs délais, par un échange réciproque d’informations, une appréciation partagée de la situation, de son évolution possible et des meilleures dispositions à prendre pour limiter les conséquences de l’accident.

1.4. Quatrième concept

Les responsabilités et les domaines d’intervention des divers organismes impliqués en cas d’accident nucléaire doivent être parfaitement définis et connus de tous. Afin qu’aucune ambiguïté ne subsiste, il est souhaitable que les pro­tocoles concrétisent ce partage de responsabilités.

1.5. Cinquième concept

Dès l’instant que la connaissance d’un événement affectant une centrale nucléaire franchit les limites du site, la centrale risque d’être submergée de demandes d’informations.

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L’organisation mise en place doit être capable d’apporter des réponses à ces demandes tout en assurant la protection des équipes chargées de réfléchir et de décider, qui doivent pouvoir continuer à travailler dans la plus grande sérénité.

2. D E S C R I P T I O N D U S C H E M A D ’O R G A N I S A T I O N

L’organisation mise en place par le SCSIN et par E D F repose sur divers échelons de décision (PC) et sur des équipes de crise chargées d’analyser la situation mais ne disposant pas de pouvoir de décision. Les échelons de direction d’une part, et les équipes de crise d’autre part, travaillent en étroite concertation. Chaque équipe de crise rapporte à l’échelon de direction dont elle dépend.

2.1. Organisation mise en place par Electricité de France

En cas d’accident, E D F met en place une organisation locale au niveau de la centrale concernée et une organisation centrale au niveau de la direction du Service de la production thermique (SPT).

2.1.1. L’organisation mise en place au niveau local est celle définie dans le plan d’urgence interne et comprend:

2.1.1.1. Quatre PC opérationnels

1 ) Un PC direction tenu par le chef de centrale ou son représentant, seul responsable des décisions à prendre pour assurer la sûreté des installations, la pro­tection du personnel et la sauvegarde des matériels.

Le responsable de ce PC assure les liaisons officielles de la centrale avec les pouvoirs publics au niveau local. Il informe en particulier le commissaire de la République concerné de l’état de l’installation, des prévisions d’évolutions envisageables et des possibilités, associées à ces évolutions, de rejets éventuels de radioactivité dans l’environnement.

Le responsable de ce PC assure également les liaisons officielles de la centrale avec les PC direction du SCSIN et du Service central de la production thermique, ainsi qu’avec le Service central de protection contre les rayonnements ionisants.(b) Un PC local chargé d’assurer les fonctions conduite et sauvegarde à la tranche affectée.(c) Un PC contrôle chargé de la centralisation et de l’interprétation des mesures radiologiques et météorologiques et de l’évaluation des conséquences radiologiques de l’incident ou de l’accident.(d) U n PC mouvement chargé de contrôler les mouvements de personnel, de coordonner l’utilisation des véhicules et, d’une manière générale, d’assurer le service logistique interne.

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2.1.1.2. Une équipe locale de crise

Elle est formée d’ingénieurs de la centrale et d’ingénieurs mandatés par divers organismes (dont le SCSIN, le Service central de la production thermique et Framatome). Ces ingénieurs possèdent une bonne connaissance des questions de sûreté et de radioprotection en situation accidentelle.

Le rôle de cette équipe est double:— analyser et évaluer la situation et son évolution prévisible, afin d’émettre périodiquement des avis et recommandations vers le PC direction (chef de centrale) sur la conduite à tenir à court et moyen terme;— assurer l’information nécessaire à leur travail des équipes de crise de l’échelon central (SCSIN et SPT).

La décision de mise en place de cette équipe est prise par le chef de centrale dès qu’il juge que ceci est souhaitable ou si le chef du SCSIN décide de mettre en place sa propre organisation. Dès la décision de mise en place prise, le Chef de centrale désigne le responsable de l’équipe qui est obligatoirement un ingénieur de la centrale.

Ce responsable ou son représentant anime le travail de l’équipe, coordonne les demandes d’informations, rassemble ces informations en prenant contact avec les responsables de la centrale, transmet les avis et recommandations au PC direction.

L ’équipe se réunit dans un local technique de crise où sont retransmises des informations provenant de la tranche concernée et où se trouvent les moyens de télécommunication et les documents techniques nécessaires.

L’équipe de crise, pour son travail, bénéficie du soutien logistique de la centrale.

2.1.2. L’organisation mise en place au niveau central comporte:

2.1.2.1. U n PC direction tenu par le chef du SPT ou son représentant, qui constitue un échelon de décision central en relation permanente avec le chef de centrale. Il assure les liaisons avec les pouvoir publics au niveau national etles liaisons avec la direction générale d’EDF.

2.1.2.2. Une équipe de crise nationale chargée de compléter l’information du PC direction et de lui communiquer, le cas échéant, des avis et recommandations. Elle est en contact étroit avec l’équipe de crise locale qui lui fournit des informa­tions et ses analyses. Elle est également en contact avec l’équipe de crise du SCSIN.

Elle sollicite et suit le travail d’équipes spécialisées appartenant à d’autres services d’E D F ou aux constructeurs (Framatome). Elle effectue les recherches documentaires éventuellement nécessaires, à son initiative ou à la demande de l’équipe de crise locale.

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Le responsable de cette équipe est désigné par le chef du PC direction. Elle comprend les ingénieurs mandatés par le SCSIN, des ingénieurs de la Direction de l’équipement d’EDF, des ingénieurs de Framatome. L ’équipe nationale se réunit dans un local technique de crise situé dans les locaux d’E D F (Paris).

En outre, le SPT peut envoyer un ou plusieurs ingénieurs pour participer aux travaux de l’équipe de crise et du PC direction mis en place par le SCSIN.

2.2. Organisation mise en place par le SCSIN

En cas d’accident, le SCSIN met en place l’organisation suivante:a) U n PC direction situé au centre de crise du Ministère de l’Industrie et de la recherche, dirigé par le chef du SCSIN ou son représentant.b) Une équipe de crise située au centre technique de sûreté du Centre d’études nucléaires de Fontenay-aux-Roses, placée sous l’autorité du chef du Département de sûreté nucléaire1 ou de son représentant.c) Une mission locale répartie entre le site (équipe locale de crise) et la préfecture concernée, composée d’inspecteurs des installations nucléaires de base et d’ingénieurs de la Direction interdépartementale de l’industrie, du SCSIN et du Département de sûreté nucléaire.

Les membres de cette mission placés auprès du commissaire de la République ont pour tâche d’apporter à ce dernier leur concours technique et de faciliter l’exercice de la mission de conseil du SCSIN à l’intention du commissaire de la République.

Ceux faisant partie de l’équipe locale de crise ont notamment pour rôle de faciliter la bonne information de l’équipe de crise du SCSIN.

A partir des informations sur la situation de l’installation et de l’analyse qui en est faite par son équipe de crise, le chef du SCSIN s’assure du bien-fondé des dispositions prises par l’exploitant; il établit des prévisions d’évolutions envi­sageables et les possibilités, associées à ces évolutions, de rejets de radioactivité à l’extérieur de l’installation (pronostic) et il précise les transferts éventuels correspondants de radioactivité dans l’environnement, compte tenu des prévisions météorologiques disponibles. Ces prévisions, c o m m e celles fournies par l’exploitant, doivent permettre au commissaire de la République, après avis du Service central de protection contre les rayonnements ionisants, de prendre les mesures nécessaires de protection des populations.

1 Rappelons que, d’une façon générale, le Département de sûreté nucléaire de l’Institut de protection et de sûreté nucléaire du Commissariat à l’énergie atomique apporte son appui technique au SCSIN.

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Le chef du SCSIN rend compte de son action au Directeur général de l’industrie.

Le PC direction du SCSIN assure les liaisons avec les autres organismes centraux concernés des pouvoirs publics.

3. LIAISONS E N T R E LES O R G A N I S A T I O N S MISES E N P L A C E P A R L E SPT E T L E SCSIN

Les liaisons entre les organisations mises en place par le SPT et par le SCSIN se font dans le respect des principes rappelés ci-après.

3.1. La mise en place par le SCSIN, à la suite d’un accident sur une centrale, de son centre de crise a pour conséquence la mise en place sans délai de l’organisation prévue par EDF, au moins dans une configuration réduite.

Inversement, toute mise en oeuvre par E D F de cette organisation a pour conséquence la mise en place sans délais de l’organisation prévue par le SCSIN.

3.2. Tous les avis, ainsi que les informations importantes de synthèse, échangés entre les organisations d’E D F et du SCSIN, ne peuvent être considérés c o m m e officiels que s’ils émanent d’un échelon de décision. Ces échelons de décision sont reliés par des lignes directes.

3.3. Les inspecteurs des installations nucléaires de base et les ingénieurs envoyés sur le site concerné par le SCSIN sont intégrés dans l’équipe de crise locale. Le chef de centrale prend toutes les dispositions nécessaires pour faciliter l’accomplis­sement de la mission de ces représentants.

Les inspecteurs des installations nucléaires de base peuvent procéder à des visites de surveillance. Ces visites ont lieu sur instruction du chef du SCSIN qui prend au préalable l’attache du SPT pour s’assurer que le bon déroulement de ces visites est compatible avec l’état de l’installation et les mesures de sauvegarde en cours ou prévues.

Le chef de centrale prend toutes dispositions pour organiser la visite et assurer la protection du personnel y participant.

3.4. Les ingénieurs envoyés par le SPT au PC direction du SCSIN et au Centre technique de Fontenay-aux-Roses sont intégrés respectivement dans ce PC direction et dans l’équipe de crise du SCSIN.

3.5. Les ingénieurs envoyés parle SCSIN au local technique de crise du SPT sont intégrés dans l’équipe de crise du SPT.

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3.6. De façon à obtenir une appréciation cohérente rapidement partagée de la situation et de son évolution, des échanges directs d’informations s’établissent entre l’équipe de crise locale, l’équipe de crise du SPT et l’équipe de crise du SCSIN. En particulier, les chefs des équipes de crise procèdent à un point périodique de leurs analyses.

Le responsable de l’équipe de crise de la centrale fournit aux responsables des deux autres équipes les informations techniques qui lui parviennent.

En outre, les informations particulièrement caractéristiques de l’état de la tranche concernée sont transmises par des moyens automatiques aux trois équipes de crise. En attendant la mise à disposition de matériels plus performants (panneaux vidéo, audioconférence, etc.), ces informations seront transmises, selon une présentation standardisée, par télécopieur (sur lignes directes) à l’équipe de crise du SPT et à celle du SCSIN par l’équipe locale de crise.

3.7. Sans préjudice des échanges décrits sous 3.6, le chef du PC direction et le chef de l’équipe de crise du SCSIN ou leurs représentants peuvent en outre obtenir, à tout moment, les informations complémentaires qui leur paraissent nécessaires auprès de la mission du SCSIN sur le site, à laquelle ils sont liés en permanence par un moyen de télécommunication utilisable à cet effet.

3.8. Les responsables des équipes de crise ne rendent compte qu’au chef du PC direction dont ils dépendent (chef de centrale, chef du SPT, chef du SCSIN) ou à son représentant, auxquels ils sont reliés par des lignes directes.

3.9. Les moyens de télécommunication, mis à la disposition des équipes de crise, sont gérés par les responsables de l’équipe selon des ordres de priorité définis à l’avance.

3.10. L’appel aux moyens d’études d’autres services d’E D F ou à ceux de Framatome est à la charge du responsable de l’équipe de crise du SPT, sur demande, le cas échéant, du responsable de l’équipe de crise du SCSIN.

4. D E T A I L P R A T I Q U E D E L ’O R G A N I S A T I O N

4.1. Appel des équipes de crise

L ’alerte déclenchée par le chef de centrale aboutit à un dispositif automatique permettant d’atteindre toutes les personnes concernées par l’organisation et équipées dans ce but d’un système de réception «Eurosignal». Chaque participant connaît par une consigne individuelle la conduite qu’il a à tenir: rejoindre le lieu

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d’embarquement pour un acheminement vers la centrale ou rejoindre l’équipe de crise nationale.

Le SCSIN dispose d’un moyen d’appel équivalent pour ses propres équipes.

4.2. Acheminement vers la centrale du personnel affecté à l’équipe de crise locale

En fonction de la situation de la centrale, cet acheminement peut se faire:— en voiture;— par hélicoptère pendant les heures du jour et avec visibilité correcte;— par avion: un contrat a été passé avec une compagnie garantissant de pouvoir disposer à tout moment et dans un délai de deux heures d’un moyen de transport.

4.3. Transmission des informations caractéristiques de l’état de l’installation vers les différentes équipes de crise

Les informations transmises permettent de contrôler l’évolution des cinq grandes fonctions de sûreté:— réactivité (flux);— évacuation de la chaleur du coeur (niveau pressuriseur, fonctionnement pompe primaire, température, ДТ);— évacuation de la chaleur par le secondaire (niveau et pression générateur de vapeur, débit d’eau d’alimentation);— masse du réfrigérant primaire;— intégrité enceinte (pression, température, activité, rejets cheminée).

Celles-ci sont complétées par:— la marche-arrêt pompes primaires;— l’ouverture-fermeture décharge et aspersion pressuriseur.

Ces données, transmises provisoirement sous forme écrite (via télécopieur), se feront ultérieurement sous forme de présentations analogiques de courbes d’évolution sur écran.

En outre, toutes les images d’aide à la conduite ou d’aide à la surveillance seront accessibles.

4.4. Moyens de télécommunication

Les moyens de télécommunication en cas de crise permettent la mise en oeuvre d’applications de:— téléphonie;— télégraphie;— télécopie;— audioconférence;— transmission de données.

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Ils relèvent, dans le respect de la réglementation PTT, de:a) réseaux publics:— téléphonie réseau commuté;— télex;— téléphonie réseau Caducée.b) réseaux privés:— liaisons téléphoniques point à point;— réseau téléphonique de sécurité de l’exploitant;— réseau téléphonique du Ministère de l’Intérieur (Régis);— réseau télégraphique de l’exploitant (Comète);— réseau télégraphique du Ministère de l’Intérieur (Diadème).

Les matériels mis en place ou en cours de mise en place sont:— des équipements termineurs pour utilisation mixte «phonie-signaux» ;— des pupitres téléphoniques avec leur dispositif d’exploitation (aiguillage de circuits, signalisation, etc.) ou des postes téléphoniques;— des télécopieurs;— des téléimprimeurs;— des terminaux d’audioconférence;— des équipements de transmission de données.

Les réseaux ainsi constitués permettent de mettre en relation la centrale concernée par la crise avec:— le service central de la production thermique (PC direction et équipe de crise);— le SCSIN;— le Service central de protection contre les rayonnements ionisants;— l’équipe de crise du SCSIN;— le PC opérationnel et la Préfecture de la région où se trouve la centrale;— la gendarmerie et le centre de sécurité civile les plus proches.

C O N C L U S I O N

Une organisation destinée à gérer un accident nucléaire implique forcément un nombre important de participants qui, tous, à des titres divers, doivent être informés afin qu’ils prennent en temps voulu, et dans la plus grande cohérence, les décisions qui leur incombent. Une organisation aussi complexe ne peut fonctionner que si les divers domaines de responsabilité sont parfaitement définis et coordonnés et si l’intendance suit. Cela suppose que l’organisation soit validée par des exercices progressifs impliquant de plus en plus complètement l’ensemble de la structure. Ces exercices doivent être réalisés avec un grand souci du détail, le manque de rigueur dans le détail étant de nature à faire échouer toute organi­sation d’une certaine complexité, aussi bien pensée fût-elle.

3 6 4 LAVERIE et BERTRON

Des exercices impliquant partiellement ou totalement l’organisation doivent être réalisés périodiquement afin d’entraîner le personnel et de maintenir les dispositifs matériels en parfait état de fonctionner.

Ces exercices devront avoir une fréquence suffisante pour maintenir les équipes en situation d’intervenir efficacement et suffisamment faible pour ne pas porter atteinte à leur crédit.

U n exercice annuel mettant en jeu l’ensemble de l’organisation et un exercice partiel annuel par centrale constituent une périodicité qui paraît raisonnable.

C ’est à ce prix que l’on sera en mesure de maîtriser un événement, certes hautement improbable, mais auquel l’exploitant c o m m e les pouvoirs publics doivent cependant se préparer à faire face. U n tel niveau d’intervention est le complément nécessaire des mesures de prévention et de parade normalement prises lors de la conception, de la construction et de l’exploitation des centrales nucléaires, afin d’assurer pleinement la protection des travailleurs, des populations et de leur environnement.

IAEA-SM-268/37

PLAN D ’U R G EN C E ET EX PER IEN C E D’EX PLO ITA TIO N

O. H A L P E R N , J. B R E N I E R E Secrétariat général,Comité interministériel de la sécurité nucléaire, Paris, France

Abstract-Résumé

EMERGENCY PLANNING AND OPERATING EXPERIENCE.The purpose of this paper is to derive lessons from operating experience for the planning

of emergency measures. This operating experience has two facets: it is obtained not only from the various incidents and accidents which have occurred in countries with nuclear power programmes and from the resulting application of emergency plans but also from the different exercises and simulations carried out in France and in other countries. Experience generally confirms the main approaches selected for emergency plans. The lessons to be derived are of three types: first, it appears necessary to set forth precisely the responsibilities of each person involved in order to prevent a watering-down of decisions in the event of an accident; secondly, considerable improvements need to be made in the different communication networks to be used; and thirdly, small accidents with minor radiological consequences deserve as systematic and thorough an approach as large and more improbable accidents.

PLAN D’URGENCE ET EXPERIENCE D’EXPLOITATION.Le but de ce mémoire est de tirer les leçons de l’expérience d’exploitation du point de vue

de la planification des mesures d’urgence. Cette expérience d’exploitation a un double aspect: elle résulte soit des différents incidents et accidents survenus dans les pays nucléaires et des mises en oeuvre des plans d’urgence qui en ont résultés, mais aussi des différents exercices et simulations conduits en France ou dans les autres pays. L’expérience conforte de façon générale les grandes options de la planification. Les enseignements à tirer sont de trois ordres: premièrement, il apparaît nécessaire de préciser de façon claire les responsabilités de chaque intervenant de façon à éviter la dilution des décisions en cas d’accident; deuxièmement, il convient d’améliorer de façon notable les différents réseaux de communication à utiliser; troisièmement, les petits accidents aux conséquences radiologiques mineures sont justiciables d’une approche aussi systématique et aussi approfondie que les grand accidents plus improbables.

I N T R O D U C T I O N

L ’expérience d’exploitation des plans d’urgence a trois volets: les mises en oeuvre réelles à l’occasion d’incidents ou d’accidents, les simulations visant à vérifier la possibilité des différentes actions des services concernés et les services sur le terrain, généralement limités à l’entraînement des personnels impliqués.

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3 6 6 HALPERN et BRENIERE

En ce qui concerne les mises en oeuvre réelles, l’expérience de la France après environ 40 ans de développement de l’énergie nucléaire civile est restée très heureusement limitée. Si quelques incidents donnent lieu, à intervalles réguliers, au déclenchement des plans d’urgence internes (on-site response plan), un seul ces dernières années a conduit à prendre des mesures à l’extérieur du site et de façon d’ailleurs informelle: il s’agit de l’incendie survenu dans un site de stockage de chemises de graphite au Cap de la Hague en janvier 1981.

Il est clair que, dans le domaine des plans d’urgence c o m m e dans celui de la sûreté, l’accident de TMI constitue l’expérience irremplaçable qui permet d’apporter aux mesures définies dans les plans d’urgence une occasion de vérification inégalable.

Pour ce qui est des simulations, la France a conduit, jusqu’à ce jour séparément, celles qui visent à vérifier les mesures des plans d’urgence internes et celles qui visent l’organisation des pouvoir publics dans le cadre des plans d’urgence à l’extérieur du site.

A l’évidence, ces deux types de simulation mettent en oeuvre des relations différentes: les premières conduisent essentiellement à un dialogue technique entre cadres de la centrale nucléaire, équipes d’assistance issues de la compagnie d’électricité ou du fournisseur et autorités de sûreté. Les secondes pour leur part sont plus directement consacrées à l’instauration du dialogue entre techniciens et responsables administratifs et politiques et concernent davantage les décisions à prendre face aux éléments techniques disponibles plutôt que la vérification de ces éléments techniques.

Enfin, ces simulations sont complétées par des entraînements sur le terrain, menés régulièrement et visant l’action des agents de la centrale (mise en oeuvre des postes centraux en cas d’accident, mesures de radioactivité), des services de secours (mesures de radioactivité dans l’environnement, activation des PC, mise en oeuvre des schémas de transmission) et des forces de l’ordre (exercices de bouclage, exercices d’alerte).

L ’ensemble des éléments de jugement ainsi mis à disposition des pouvoirs publics conduit ceux-ci à confirmer l’adéquation du dispositif actuellement arrêté en France pour faire face aux événements d’urgence nucléaire, dispositif que nous allons décrire ici brièvement.

Le dispositif français est fondé sur une double responsabilité, celle du directeur de centrale pour tout ce qui concerne les mesures à prendre à l’intérieur de la centrale, celle du commissaire de la République du département concerné pour ce qui touche à l’extérieur. Les actions à mener par ces deux responsables sont organisées dans des plans selon plusieurs niveaux, le directeur de la centrale fixant les niveaux de réponse de son propre plan et donnant au commissaire de la République un avis sur les niveaux du plan à l’extérieur.

A chaque niveau correspondent, bien évidemment, un catalogue de mesures à prendre. Par exemple, pour le niveau de gravité le plus élevé du plan d’urgence

IAEA-SM-268/37 3 6 7

extérieur, le commissaire de la République choisit classiquement entre mesures de confinement, mesures sanitaires individuelles et mesures d’évacuation, ces dernières mesures étant considérées c o m m e exceptionnelles. Il les applique dans des zones définies à l’avance (rayons de 5 et 10 k m et dans le secteur du vent).

S’il est une spécificité des plans français, assez comparables, en général, aux dispositifs arrêtés dans les autres pays, et aux recommandations des guides de sûreté de l’AIEA, c’est l’accent mis sur les dispositions à prendre dans les premières heures. Dans la conception française, les mesures prévues dans les plans n’ont leur plein intérêt que dans les premières heures après le début de l’accident. A u terme de ce délai, le directeur de la centrale d’une part, le commissaire de la République d’autre part, disposent de moyens d’expertise suffisamment importants pour pouvoir procéder à des analyses fines et des mesures ponctuelles. Dans cet esprit l’accent est mis essentiellement sur la voie atmosphérique c o m m e voie de transfert la plus rapide; la voie aquatique, par exemple, sans être exclue reste considérée c o m m e relevant moins d’une planification d’urgence. D ’une façon générale, dans le cadre du vocabulaire retenu par l’AIEA, la planification ne couvre explicitement que la première phase et partiellement la phase intermédiaire.

Au-delà, les mesures à prendre paraissent aux autorités françaises relever davantage d’une planification indicative visant à la mobilisation de compétences pour déterminer les actions que d’une planification vraie qui définit ces actions. C ’est dans cet esprit qu’un guide de mesures post-accidentelles est en cours de préparation.

De façon générale, la volonté de privilégier l’action par rapport à l’analyse au niveau des plans pourrait conduire à enchaîner les décisions à prendre de façon automatique par rapport à un certain nombre d’indicateurs. O n peut noter, à cet égard, des tentatives visant à relier, de manière plus ou moins stricte, des mesures à prendre au niveau des populations à des indicateurs d’exposition observés sur le terrain ou anticipés. Des travaux ont été menés, à ce sujet, à l’AIEA, à l’O C D E ou dans le cadre de la Communauté européenne de l’énergie atomique. La France considère avec intérêt ces tentatives mais garde quelques doutes sur leur efficacité opérationnelle.

Pour en revenir à Inexpérience d’exploitation» des plans d’urgence, les axes de réflexion qu’elle inspire peuvent être regroupés en trois domaines:— l’exercice des responsabilités et l’aide à la décision,— la circulation de l’information,— le problème des petits incidents ou accidents.

1. L ’E X E R C I C E D E S R E S P O N S ABILITES E T L ’A I D E A L A DECISION

Le schéma des responsabilités telles que définies plus haut est, dans un pays c o m m e la France, compliqué par de nombreuses interventions. Il nous faut

3 6 8 HALPERN et BRENIERE

notamment prendre en compte celles du gouvernement, dont le commissaire de la République est le représentant au plan local, et celles des services de sûreté et de santé qui exercent une tutelle sur l’exploitant nucléaire.

Aussi, dans un accident, le commissaire de la République va-t-il rendre compte de ses actions au Ministère de l’Intérieur, le directeur de la centrale des siennes au Service central de sûreté des installations nucléaires et au Service central de protection contre les rayonnements ionisants.

De plus, il est explicitement prévu par la réglementation que ces deux derniers services doivent fournir au commaissaire de la République un avis sur le déroulement de l’accident et sur ses conséquences sur la santé des populations. Le directeur de la centrale bénéficiera lui des conseils des équipes de crise mises en place par la compagnie d’électricité et le constructeur.

Il importe de veiller à ce que ces interventions complémentaires ne viennent pas perturber l’exercice des responsabilités initiales. Ce n’est que de façon absolument exceptionnelle que le Gouvernement ou les services de sûreté pourraient être amenés à se substituer au commissaire de la République ou à l’exploitant; dans le schéma général, leurs interventions doivent être strictement limitées à une aide à la décision.

De plus, beaucoup d’installations nucléaires sont situées en France à la frontière de plusieurs départements, les fleuves ayant été en général pris c o m m e limites. Dans ces conditions le principe de la responsabilité unique des mesures externes doit être aménagé mais préservé en nommant un commissaire de la République coordonnateur et en organisant une hiérarchie des responsabilités.

Enfin, dans un pays c o m m e la France qui recèle de nombreuses compétences techniques dans le domaine nucléaire, l’exploitant c o m m e le commissaire de la République peuvent faire appel à des équipes, soit venant d’autres centrales soit provenant du Commissariat à l’énergie atomique. Cette richesse en compétences de toutes natures doit être utilisée dans le respect des responsabilités et du principe du «commandement unique» à l’intérieur c o m m e à l’extérieur. Ceci est particulièrement important dans le domaine des mesures de radioactivité, dont le commissaire de la République est seul habilité à inférer des mesures à prendre vis-à-vis des populations; il est notamment nécessaire de prévoir une centralisation des différentes mesures.

A ce problème se rattache celui de la définition du seuil de radioactivité correspondant aux mesures à prendre. Le Comité national des experts médicaux, chargé en France d’élaborer la doctrine sanitaire pour ce qui concerne les mesures en cas d’accident, n’a pas jusqu’à présent adopté ce type d’approche. D u point de vue des pouvoirs publics, à l’aide de la décision importante que constitueraient pour le commissaire de la République de pareils seuils, s’opposent quelques problèmes d’utilisation que mettent en lumière aussi bien les accidents observés que les simulations effectuées.

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On peut notamment citer, à cet égard, les points suivants:— Les seuils ainsi définis s’appliquent-ils aux doses anticipées ou aux doses mesurées sur le terrain. S’il s’agit de doses anticipées, quel niveau de conservatisme faut-il adopter pour l’évaluation?— Dès l’instant où les mesures à prendre ne peuvent s’appliquer qu’à des groupes et non à des individus, est-ce que les valeurs à prendre en compte sont les valeurs moyennes des doses auxquelles le groupe est exposé ou les valeurs extrêmes?— Ne peut-on craindre que, malgré la flexibilité recommandée dans l’utilisation des seuils, ils ne puissent servir de base à des recours contre les autorités.

Ces différentes difficultés, encore largement non résolues, laissent penser que l’utilisation de seuils relève plus de l’activité d’experts chargés de conseil que de celle du décideur. Ils doivent dès Ion conserver une valeur inidicative et exploratoire et ne peuvent servir de base à la planification.

2. L A C I R C U L A T I O N D E L ’I N F O R M A T I O N

Un accident ou incident nucléaire met en oeuvre pour le moins deux circuits d’information.1) Un circuit d’information permettant la prise de décision des deux responsables, le directeur de la centrale et le commissaire de la République.2) Un circuit d’information visant la presse, les élus et la population et ayant pour objet soit d’éviter les paniques en expliquant la situation et le sens des mesures déjà prises, soit de diffuser des consignes, soit simplement de répondre aux sollicitations des médias.

Le fonctionnement de ces circuits pose des problèmes spécifiques qu’il convient d’expliciter.

Pour ce qui touche tout d’abord le circuit de prise de décision, il faut noter que c’est le personnel de la centrale qui est le plus sollicité pour l’alimenter. Il lui faut constituer une interface importante pour:— dialoguer avec les équipes de crise extérieure,— répondre aux demandes des autorités de sûreté et de santé,— tenir le commissaire de la République informé de l’évolution de la situation.

Cette interface doit disposer de moyens de liaison extérieure nombreux, diversifiés et performants. Mais le problème essentiel réside dans sa capacité de mener simultanément le recueil et la transmission des informations. Pour résoudre ce problème extrêmement difficile, l’exploitant français a choisi de télétransmettre automatiquement certaines données sur l’état du coeur à ses conseils et aux autorités ce qui facilite le dialogue. Reste à résoudre le problème de l’information du commissaire de la République qui lui n’a que faire de données techniques brutes mais entend disposer à tout instant de pronostics sur l’évolution de la situation et les rejets à l’extérieur. Une solution, partiellement adoptée en

3 7 0 HALPERN et BRENIERE

France, vise à charger les services centraux d’alimenter le commissaire de la République, mais cela pose évidemment des problèmes de délais supplémentaires d’analyse et de transmission. Il vaut mieux au fond reconnaître que le personnel de la centrale aura à mener de front deux tâches presque incompatibles: décider et réfléchir, agir et conseiller et, dans ces conditions, mettre au point des méthodes pour l’y préparer au mieux. U n des modes de préparation vise à imposer à la direction de la centrale un effort de traduction en termes clairs des données techniques qu’il manipule. L ’expérience prouve en effet que lorsque, dans une crise, gestionnaires et techniciens se rencontrent, ils ont une peine infinie à trouver un langage commun. L’emploi de sigles est particulièrement à proscrire à cet égard.

En ce qui concerne le circuit d’information du public, l’accident de TMI a apporté beaucoup d’enseignements sur les mesures à prendre vis-à-vis de la presse. A u niveau français, on a retenu essentiellement de pouvoir mettre en place tant à la centrale qu’à la préfecture des salles de presse bien équipées dans des délais brefs, de tenir à la disposition de la presse dès le début de l’accident des brochures décrivant l’installation et des glossaires réunissant les termes techniques employés, de charger un proche collaborateur du directeur de la centrale des relations avec la presse, relations qu’il doit entretenir dès le fonc­tionnement normal. Le choix de ce responsable est d’ailleurs particulièrement délicat: trop près du directeur, il peut avoir des tâches urgentes à effectuer, trop loin il risque d’être coupé de la véritable information: là encore, il s’agit d’un h o m m e qui doit effectuer des tâches presque incompatibles et donc être formé de façon approfondie.

A ces relations avec la presse s’ajoutent les actions visant à répondre aux questions du public directement (mise en place d’un système de réponse téléphonique) ou indirectement (information de relais privilégiés: médecins, pharmaciens, vétérinaires et, surtout, information précise des employés de la centrale). De plus, il faut également informer de façon précise et constante les élus locaux et notamment les maires qui, en plus de leur rôle d’information, ont un rôle d’organisation des secours au niveau de leur commune. Afin de préparer les relations en cas de crise avec ces élus locaux, il est dès lors nécessaire de les associer aux simulations et de les convier à des exercices sur le terrain.

De façon générale le fonctionnement de ce double réseau d’information en cas de crise nécessite la mise en oeuvre de très importants moyens de télé­communication (lignes réservées, fac-similés, réseaux de téléconférence, réseaux hertziens, standards complémentaires, centre de réponse téléphonique) qu’il convient de définir et de mettre au point au niveau local mais aussi pour certains d’entre eux au niveau national.

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Les différentes simulations effectuées mettent généralement en lumière une tentation des autorités visant à supprimer des plans un niveau d’intervention correspondant à un accident sans conséquence extérieure au site; en effet, ce niveau apparaît c o m m e un intermédaire sans utilité réelle. S’il est clair qu’un tel niveau d’intervention n’a pas de caractère opérationnel dans un accident conduisant à des rejets extérieurs importants, il ne faut pas oublier que, dans la pratique, ce sont les petits accidents sans conséquence notable à l’extérieur qui constituent le véritable champ d’action des responsables, comme, par exemple, un dégagement d’iode lors du déchargement d’éléments combustibles ou un déversement d’une quantité limitée de liquides faiblement radioactifs. En pareil cas, l’autorité responsable des mesures à l’extérieur n’a pas de véritable tâche opérationnelle et son rôle vise à vérifier l’inexistence ou l’innocuité des relâchements et à rassurer les populations, et ce dans les plus bref délais, afin d’empêcher les rumeurs alarmistes. Donc, m ê m e en pareil cas, le commissaire de la République doit disposer d’une expertise rapide et indépendante, d’un avis d’expert de la santé publique afin de donner, notamment par voie de presse, une image rapide et responsable de la situation ou d’en charger selon les cas le directeur de la centrale. Donc, m ê m e dans une situation qui ne contient pas des rejets extérieurs significatifs, la double responsabilité et le double circuit d’information doivent être mis en oeuvre de façon efficace.

C O N C L U S I O N

L ’expérience d’exploitation des plans d’urgence se limite en France, pratiquement, à des simulations et à des exercices sur le terrain. Cette expérience, jointe à celle dont on dispose à l’étranger, conduit à valider les schémas actuel­lement retenus tant en France qu’à l’étranger ou au niveau international.

Il faut néanmoins prendre en compte la difficulté pratique qu’il y a à main­tenir opérationnel le principe de double responsabilité dans un pays où les com­pétences ne manquent pas. U n effort constant de classification doit permettre tant au commissaire de la République qu’au directeur de la centrale d’exercer leurs responsabilités respectives qui ne doivent pas se partager. Les autres intervenants doivent prendre la mesure de leur rôle de conseils et des conditions de leur efficacité.

Une crise nucléaire, par ailleurs, met en oeuvre de nombreux réseaux d’infor­mation dont l’animation pèse de façon parfois critique sur les responsables. Des mesures techniques peuvent être prises pour faciliter la diffusion de l’information, mais elles ne peuvent permettre de faire disparaître complètement la difficulté que constitue pour chaque responsable le fait d’avoir simultanément à agir et à

3. LE PROBLEM E DES PETITS ACCIDENTS

3 7 2 HALPERN et BRENIERE

informer. Il lui faut dès lors s’y préparer en mettant un accent particulier sur les problèmes de langage.

Il faut enfin noter qu’un accident nucléaire sans conséquence extérieure nécessite des actions qui, au niveau de l’information, sont largement comparables à ce qui se passe en cas d’accident plus grave.

IAEA-SM-268/85

EM ERG ENCY PLA N S FO R CIVIL N U C L E A R IN ST A L L A T IO N S IN TH E U N IT E D KINGDOM

W.S. G R O N O WHer Majesty’s Nuclear Installations

Inspectorate,Health and Safety Executive,London, United Kingdom

AbstractEMERGENCY PLANS FOR CIVIL NUCLEAR INSTALLATIONS IN THE UNITED KINGDOM.

The operators of nuclear installations in the United Kingdom have plans to deal with accidents or emergencies at their nuclear sites. These plans provide for any necessary action, both on and off the nuclear site, to protect members of the public and are regularly exercised.The off-site actions involve the emergency services and other authorities which may be called upon to implement measures to protect the public in any civil emergency. In a recent review of these plans by Government Departments and agencies and the nuclear site operators, a number of possible improvements were identified. These improvements are concerned mainly with the provisions made for liaison with local and national authorities and for public information and have been incorporated into existing plans. An outline is given of the most likely conse­quences of an accidental release of radioactive material and the scope of emergency plans.Details are also provided on the responsibilities and functions of the operator and other organiza­tions with duties under the plans and the arrangements made for public information.

I N T R O D U C T I O N

The safety precautions taken in the design and construction of nuclear installations, and the safety standards used in operating them, reduce the chance of accidents which might affect the public to an extremely low level. But however remote the risks, as a matter of prudence, provision should be made for dealing with an accidental release of radioactivity. For this reason every nuclear plant has a site emergency plan which details the action to be taken by the management and staff and other responsible authorities to protect the public in the vicinity of the site should this ever become necessary. Nuclear accidents could involve nuclear power reactors or other nuclear installations concerned with the handling, treatment and storage of spent fuel or nuclear waste, but the type of emergency planning necessary to deal with the consequences outside the site would be broadly similar.

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Under the site emergency plan, the police and emergency services, local, health and water authorities, Government agencies and other organizations which may be called upon to take actions to protect the public would be immediately informed should an emergency be declared. Detailed responsibilities are set out in the various emergency plans of the organizations involved. These organizations have plans to cope with many different kinds of civil emergencies — floods, explosions, chemical accidents and serious fires and crashes. An accident at a nuclear plant could present a different type of hazard, but is highly unlikely to pose a significant threat to public safety or require actions to protect the public which are different from those required for other civil emergencies.

In this paper an outline is given of the precautions taken to prevent accidents at nuclear plants and the scope of emergency plans. It describes the likely conse­quences of an accidental release of radioactivity and the actions that may be required to protect members of the public. Details are given of the responsibilities and functions of the operators and other organizations with duties under the plans and the arrangements made for public information.

T H E C O N S E Q U E N C E S O F A N U C L E A R A C C I D E N T

The main potential hazard from operating nuclear plants lies in the radio­active fission products which accumulate in the nuclear fuel while the reactor is operating. In the event of failure of the safety systems and devices incorporated in nuclear plants some small fraction of these products might be released into the environment. The designs of the gas cooled reactors developed in the United Kingdom incorporate a series of safety barriers against a release of radioactivity which constitutes a defence-in-depth against potential faults and failures. The greater the potential hazard, the more stringent become the safety precautions and the risk of exposure of members of the public to a radiation hazard is thus made extremely small.

The most likely outcome of any accident at a nuclear plant is that no-one would be hurt at all because at least one of the safety barriers would prevent the accident from developing to the stage where a significant release of radioactivity could take place. It is a requirement of the Nuclear Installations Inspectorate of the Health and Safety Executive that a detailed safety analysis is carried out for each nuclear plant before construction to ensure that the appropriate protection is provided by the design. This analysis identifies potential accidents or accident sequences in which failure or partial failure of the safety barriers could occur, some of which might lead to a release of radioactivity and consequently to a risk of members of the public being exposed. Although such accident sequences are

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highly improbable they are used to determine the adequacy of the safety and protection systems built into the nuclear plants and are sometimes described as ‘design bases accidents’ (dba). The dba which leads to the largest off-site release is called the ‘reference accident’. It is for these potential accidents that detailed emergency plans are prepared, but even if the postulated release is very small, every nuclear site is required to have an emergency plan. It is possible however to postulate even more improbable events resulting in larger releases of radioactivity. The likelihood of such releases is so remote that further design safety measures to reduce their chance of occurrence or more extensive emergency plans are unlikely to be justified. Nevertheless the emergency plans drawn up for reference accidents provide a basic response to any emergency at a nuclear plant and are capable of extension should the need ever arise.

An accident at a nuclear plant could lead to a release of radioactivity to the atmosphere; some of the gaseous and volatile radioactive isotopes, such as krypton, xenon, iodine and caesium, would be transported by the wind from the site. The release could take place over a relatively short timescale but could be spread over a few hours or even longer depending on the type of operations at the plant and the mechanism of the release. Estimates of the source terms associated with reference accidents for gas cooled reactors are given in Table I. The radioactive material would disperse into the atmosphere and deposit some of its contents on the ground. The concentration of radioactivity in the plume rapidly decreases with distance from the site but some traces of the material might be found at large distances.

The radioactivity in the plume presents a risk of radiation exposure in three different ways. First, from external exposure to radiation emitted by the material in the plume as it passes downwind and from material deposited on the ground and possibly on people in the path of the plume; second, from internal radiation exposure by inhalation of material in the plume; and third, on a longer timescale, from the possible consumption of contaminated foodstuffs and drinking water.

The scale of release of radioactivity in reference accidents is such that it would not cause any immediate harm to people. Direct radiation from the passing plume or from deposited material should not present a significant hazard but it may be necessary to require people in the vicinity of the site to shelter, or take potassium iodate tablets, or possibly temporarily evacuate their homes to limit radiation exposure. The potassium iodate tablets would inhibit the uptake of radioactive iodine which when inhaled or ingested concentrates in the thyroid gland. It may also be necessary to introduce restrictions on the distribution of locally produced milk or other foodstuffs out to perhaps 20 kilometres from the site to prevent exposure from these sources. These actions should ensure that no member of the public is exposed to a significant risk to health. However, in the course of the passage of the dispersing plume, large numbers of people at long distances from the site might be exposed to very small doses of radiation. O n the

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assumption that even the smallest exposure to radiation may carry with it some risk to health, there is a statistical possibility of a few additional deaths from cancer in the whole of the exposed population over the course of the following 20 to 30 years.

If the scale of the accidental release were to exceed that for reference accidents, the hazard from the plume could extend over a greater range and require more extensive action to protect the public. Exposure to radiation from the plume or from material deposited on the ground would have greater significance and evacuation plans might have to be extended and remain in force over a longer timescale. Restrictions on the distribution of milk and foodstuffs would also have to be introduced over a larger area. In the event that this should happen, the existing emergency plans will provide the necessary immediate response in the vicinity of the site and will form the basis for action on a wider scale.

The emergency plans for nuclear installations define the circumstances under which they would be put into operation and provide for a range of actions to be taken to protect the public in the vicinity of the site. They cover emergency procedures both on and off site and the arrangements for alerting emergency services (police, fire and ambulance), local, health and water authorities, Govern­ment Departments and agencies (Nuclear Installations Inspectorate) and other nuclear establishments. The emergency arrangements are fully rehearsed once a year at each establishment and staff training and exercising goes on routinely. Copies of the plans are held by the emergency services and local, health and water authorities in the areas where nuclear plants are located, and are usually incorporated in their own plans for dealing with civil contingencies such as fires, floods and serious accidents. Copies are also held by Government Departments and the Nuclear Installations Inspectorate. A description of the basic emergency plan for each nuclear site is available in local libraries for public information and at the headquarters of the nuclear site operators.

The declaration of a site emergency is a formal decision to alert all those on site, the operator’s headquarters, and relevant outside organizations that there is a possibility that an accident on the plant may lead to a release of radioactivity.In the event of such a release an assessment would be made by the Site Emergency Controller — a senior manager of the nuclear plant — of the extent of any radio­activity released and the level of any radioactivity off the site. The emergency plans provide for radioactivity monitoring up to a distance of 40 kilometres from the site. The monitoring equipment on the site would provide information on the amount of radioactive material released to the environment and mobile teams in direct radio contact with the site would measure the radioactivity in the plume as it travelled downwind from the site and the level of radioactive material deposited on the ground. Assessments of this information would determine the advice to be given on measures to protect the public.

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If the assessments indicated that the public in the vicinity of the site were at risk, one or more of the following actions would be taken in potentially affected areas'.

(a) Sheltering — the public are advised to stay indoors and close doors and windows.

(b) Issue of potassium iodate tablets to those who might be exposed during the passage of the plume to minimize the effects of any uptake of radioactive iodine.

(c) Evacuation of the public from a downwind sector up to a distance of2— 3 kilometres from the site to reduce the risk of exposure to radioactivity in the plume.

(d) Control of potentially contaminated food and water supplies.

Any of the actions listed above could be taken as a precautionary measure but detailed guidance is provided in each emergency plan of the levels of radiation dose at which the Emergency Controller would recommend sheltering, the issue of potassium iodate tablets and temporary evacuation of the public (see below). Potential radiation exposure from contaminated foodstuffs and milk would not present an immediate hazard and there would be time for appropriate restrictions to be introduced in affected areas.

The duration of an emergency will depend on the scale and nature of the radioactive release. Once the release has been terminated and the radioactive plume has been diluted and dispersed into the atmosphere, people who might have been sheltering will be advised that the emergency has ended. Anyone who has been evacuated will be advised when they can return home. The restrictions on milk and foodstuffs may need to be continued for a further period in the areas most affected. Monitoring for radioactivity in the area will continue until it is confirmed that the situation has returned to normal.

For the case of an accident where members of the public might be exposed to radiation the National Radiological Protection Board (NRPB) has issued guidance on the criteria to be used in assessing the need for emergency counter­measures. These levels of exposure, called ‘emergency reference levels’, are those which would be used as the basis of advice to the police to carry out predetermined actions to protect the public. In assessing the need for countermeasures the Emergency Controller will take into account relevant circumstances at the time of the accident. These may include weather conditions and the number, location and mobility of persons in potentially affected areas, as well as the situation at the nuclear plant. Whilst exposure at the emergency reference level of dose implies a small increased risk to health, the harmful effects which might occur in the longer term would be very small and could not subsequently be distinguished from the normal incidence of such effects in the exposed population.

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It is particularly important in a nuclear emergency that responsibilities for making assessments, giving advice, taking decisions and implementing decisions should be absolutely clear. These responsibilities have been recently reviewed by the U K Government with the organizations concerned and are set out below.

Responsibilities of the management

In a nuclear emergency the management of the nuclear installation (known as ‘the operator’) remains fully responsible for the nuclear site. The operator may receive advice, depending on the type of emergency, from the Nuclear Installations Inspectorate, the fire services, or other nuclear establishments, but the responsi­bility for ensuring the restoration of safe conditions remains with him.

The manager of the site or his nominated substitute would act as the Emergency Controller. He would be in command of the emergency organization at the site and would set up the Site Emergency Control Centre. He will have responsibility for initiating emergency action, including the monitoring of radio­activity on and off the site, and for advising the police and local authorities on any immediate action necessary to protect the public.

Within a few hours of an emergency being declared at a nuclear power station an Operational Support Centre (OSC) would be set up. These OSCs are located within 10— 30 kilometres of each power station and are fully equipped with communications and facilities designed for use in an emergency. Details are given in each site emergency plan. The main purpose of the O S C is to relieve the Emergency Controller at the power station of the responsibility for advising on emergency action outside the site and to provide any necessary support to the site. The Emergency Controller would retain responsibility for control of on-site activities and for restoring the plant to a safe condition, but liaison with all other organizations with duties under the emergency plan would pass to the O S C as soon as it became functional.

The O S C and not the nuclear site would then become the focal point for all liaison activities and the co-ordination of advice to all outside organizations.It would be under the control of a senior manager of the operating organization and staffed by this organization. The OSCs have been planned to accommodate also representatives of the police, local and health authorities, Government Departments, the Nuclear Installations Inspectorate, the N R P B and the Government Technical Adviser (see below). Similar arrangements are provided by the operators of nuclear fuel reprocessing and research facilities at or adjacent to these sites but because of the scale of operations and the size of the sites the Emergency Control Centre under the Emergency Controller will continue to act as the focal point for advice on off-site actions.

TH E RESPONSE TO A NUCLEAR EM ERGENCY

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The O S C Controller would be responsible for the co-ordination of assessments of the monitoring of any radioactivity released from the site. He would also be responsible for assessing the course of the accident based on information from the Emergency Controller and his headquarters. These assessments will continue throughout the emergency, and enable authoritative advice to be given to the police and the local, health and water authorities on measures needed to protect the public.

It is essential that it should be clearly understood who is responsible for giving this advice during the course of an emergency. In the first few hours of the emergency the Site Emergency Controller would provide it. Once the O S C had been activated the O S C Controller would assume this responsibility and would inform the police and all the other authorities that he had taken over.If, however, the emergency was particularly severe or likely to be prolonged beyond 24 hours or so, a Government representative would take over the specific responsibility of giving this advice. This step would become necessary if the Government decided it should be directly involved in making decisions affecting public safety.

The Government representative would go to the O S C as quickly as possible after the emergency was declared. He would have the title of ‘Government Technical Adviser’ (GTA) once he had assumed his responsibilities. These would include briefing Government officials on the course of the accident. He would also be the principal Government spokesman to brief the media. The decision to appoint the Government Technical Adviser would be taken at the Department of Energy in London for an accident in England or Wales and by the Scottish Economic Planning Department in Scotland. His appointment would be formally notified by the Department to the O S C Controller, the police and the local, health and water authorities. The Government Adviser would be professionally qualified and one of the Deputy Chief Inspectors of Nuclear Installations would undertake this role.

Responsibilities of the police

The responsibility for taking action to protect the public following a nuclear accident in the United Kingdom lies with the police, as in any other type of civil emergency. The leading role of the police in this respect, and their experience in dealing with many other types of emergency, cannot be too strongly emphasized. Police forces in areas that could be affected by a nuclear accident have their own standing instructions on the actions to be taken in a nuclear emergency. These are within the framework of general plans to respond to any type of major accident or emergency in their area. The police would thus be responsible for telling people to stay indoors, to take potassium iodate tablets, or evacuate, and for carrying out any consequence actions.

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All county authorities in England and Wales have ‘County Disaster Plans’ or ‘Co-ordination Plans for Major Incidents’. These are designed to cope with a wide range of emergencies, such as floods, major fires and crashes. Most nuclear installations are so situated that only one county is likely to be involved, and these counties have in their plans a section on emergencies at nuclear sites located within their boundaries. In a nuclear emergency, the plan would be activated (as in other emergencies) by the police notifying designated representatives of the county and district authorities. These authorities would have a major role to play in any evacuation measures including responsibilities for such matters as emergency housing, feeding and transport and provision of social services. The responsibility of each county department is laid down in the County Emergency Plans. For example, the County Engineer or Surveyor would normally be responsible for emergency transport, the Chief Education Officer for emergency feeding, and the Housing Authority for emergency accommodation. County Emergency Planning Officers are, in most counties, responsible to their Chief Executive for contingency planning, and for the co-ordination of their services in an actual emergency. Information will be provided by the Operational Support Centre to the County Emergency Planning Officer (or deputy) in order that the authority may be kept fully informed on the course and consequences. In Scotland the responsibility for preparing emergency plans for civil contingencies rests with the Regional and Island’s Area Councils. Actions by local authority departments are laid down in these plans.

Health authorities

A nuclear accident could result in demands being made on hospitals and the Health Service generally. These demands would fall into two categories: an immediate need for treatment of casualties, and a possible demand for medical advice for people who had been exposed (or thought they had been exposed) to radioactivity. Casualties, i.e. cases of physical injury resulting from the accident, would almost certainly be limited to personnel on the site. Operators are responsible for ensuring, in consultation with Health Authorities, that arrangements exist with particular hospitals for emergency treatment of personnel injured on a nuclear site. Health authorities would be notified of a nuclear site emergency.

Medication and medical advice to people living or working in the vicinity of the site may be needed depending on the scale of the accident. The Emergency Controller or O S C Controller will advise the police on the issuing of potassium iodate tablets. Stocks are held as appropriate at nuclear sites, police stations, hospitals or other suitable points. Arrangements for the issue of tablets, including the place at which they are held, are laid down in site emergency plans.

RO LE O F LOCAL, HEALTH AND W ATER A U TH O RITIES

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Following a ‘reference accident’ the levels of radiation dose or contamination of people outside the site would be very unlikely to cause harm to health and would require little action by the Health Service apart from reassurance. This reassurance might involve monitoring of members of the public who may have been contaminated during the release. This would be done at local centres with the assistance of nuclear plant operators.

Water authorities

The water authorities are responsible for deciding what action, if any, is necessary to restrict water supplies as a result of a nuclear incident. In practice, it is most unlikely that the level of contamination of water following an accidental release of radioactivity from a nuclear site would necessitate the restriction of water supplies. Water authorities would, however, be informed promptly by the operator of any nuclear emergency and the possibility of substituting alternative supplies would be examined, even at very low levels of contamination of a particular source.

R O L E O F G O V E R N M E N T D E P A R T M E N T S A N D A G E N C I E S

It is Government policy that civil emergencies shall be managed by the police and local authorities. The main responsibility for action in responding to the possible off-site effects of an emergency would therefore rest at county levels.All off-site operations would be controlled locally by the organizations concerned — the site operator at the site or the Operational Support Centre, the police at their operations room and the local, health and water authorities through their own emergency planning arrangements. Given the scale of the emergencies envisaged there would be no need for regional or national co-ordination of the emergency measures. The Nuclear Installations Inspectorate and some central Government Departments would, however, be actively involved in a nuclear emergency, and have their own emergency plans for this purpose.

The Department of Energy

The Secretary of State for Energy would have ministerial responsibility for co-ordinating the Government response to a nuclear emergency for installations in England and Wales.

The Department of Energy would be responsible for setting up a Nuclear Emergency Briefing R o o m in London (NEBR). The Briefing R o o m would be opened soon after the emergency had been declared by the operator. It would not be an operations room or control room, but would be the focal point for all

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the information and briefing of Government Ministers and Departments on the emergency. The Department would be in close touch with the operator and the Nuclear Installations Inspectorate and other Government Departments and agencies. It would be responsible for the formal appointment of the Government Technical Adviser if the emergency was considered to be serious or likely to be prolonged much beyond 24 hours. The Department would also provide a central press briefing centre where Government statements on the emergency would be issued.

Her Majesty’s Nuclear Installations Inspectorate (HMNII)

The N11 on behalf of the Health and Safety Executive requires operators of nuclear plants to prepare and regularly exercise emergency plans at licensed nuclear sites. Similar arrangements exist for sites operated by the U K A E A . On notification of an emergency, the N11 would send one or more inspectors to the site to assess the situation and the actions taken to restore control. It would set up its own emergency centre at headquarters and from the information provided by the operator and inspectors on the site make independent assessments of the likely course of the accident and its consequences. Advice based on these assess­ments would be given to the Health and Safety Executive/Health and Safety Commission, Government Departments and the operator as appropriate.

Ministry of Agriculture, Fisheries and Food (MAFF)

A release of radioactivity following an accident would contaminate grass, crops and produce. Milk of grazing animals could also be contaminated. There is a comprehensive M A F F Memorandum of Procedures setting out the Depart­ment’s policy and contingency planning for all types of nuclear emergency in England and Wales. Each region also has a nuclear contingency plan which provides for farmers or producers whose land is affected to be notified quickly by the police or M A F F officials. The M A F F Chief Regional Officer or his nominee is responsible for deciding what countermeasures are required, such as restricting movement of produce and milk. The monitoring distance for milk control is identified in the site emergency plan and can extend up to 40 kilometres. In deciding what range of restrictions to impose, Chief Regional Officers would be advised by the Atomic Energy Unit of M A F F ’s Food and Science Division. This advice would be based on the results of monitoring co-ordinated at the Emergency Control Centre or the O S C and in consultation with the Controller or Government Technical Adviser. M A F F would set up its own control centre for the implementation of any necessary measures. The Department Memorandum advises Chief Regional Officers to be cautious by initially setting wide boundaries to the milk restriction area.

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Key: NEBR :

SOER:

Nuclear Emergency Briefing RoomScottish Office Emergencies Room

MAFF: Ministry of Agriculture,Fisheries and Food

DAFS: Department of Agricultureand Fisheries for Scotland

F IG .l. Nuclear installations emergency arrangements.

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The Radiochemical Inspectorate (RCI)

The RCI is responsible for giving advice to water authorities on the risks of contamination of water supplies from any radioactive source in England and Wales. The RCI and water authorities would be informed promptly by the operator of any nuclear emergency. Water supplies would be monitored by the RCI, and samples assessed at the operator’s laboratories and by the Laboratory of the Government Chemist. This monitoring would be important, whether or not significant contamination was suspected, in order to reassure the public about the safety of the water supply.

National Radiological Protection Board (NRPB)

The N R P B is responsible for advising Government Departments and other bodies on radiological protection matters. In an emergency it would undertake the co-ordination of monitoring for radioactivity outside the area covered by the site emergency plan and would make assessments of the radiological hazards within the emergency plan area. It would liaise with the Nil, Government Depart­ments and operators, and provide advice, as necessary, on the radiological hazards.

Scottish Office

In Scotland the arrangements are broadly similar with some differences of responsibility as set out below.

(a) The Secretary of State for Scotland will have Ministerial responsibility for co-ordinating the Government response to an emergency at nuclear installations in Scotland.

(b) The Scottish Economic Planning Department (SEPD) would set up the Scottish Office Emergencies R o o m (SOER) in Edinburgh and provide a central briefing point for Government Departments and Ministers.

(c) The Department of Agriculture and Fisheries for Scotland (DAFS) would be responsible for the control of foodstuffs.

(d) Her Majesty’s Industrial Pollution Inspectorate (HMIPI) would be responsible for advice on the control of water supplies and for monitoring these supplies as necessary.

I M P O R T A N C E O F T H E M E D I A

In a nuclear emergency, the media would have an important and responsible role to play in informing the public of the facts and of the assessments being

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made on the course of the accident. Careful arrangements have been made by operators in their contingency plans to provide full briefing to the media. They will make a formal announcement as soon as possible after the emergency has been declared, and set up a press, radio and television briefing centre near the nuclear site. All media briefing by the operator will then be done at that centre, not at the nuclear site itself.

The operator would provide the principal spokesman to brief the media both on the course of the accident and on the off-site consequences. However, once the G T A h a d been appointed he will, as chief Government spokesman take over the lead in briefing the media. The assessments given at the Media Briefing Centre will provide the most authoritative and up-to-date information. Any statements by the police, local authority or other Government agencies will be based on those given at the Briefing Centre. These organizations may also brief the media on their particular activities, e.g. in arranging evacuation or controlling milk supplies.

The press briefing centres in London or in Edinburgh will be the focal point for handling requests for information from Government Departments.

C O N C L U S I O N

The nuclear industry has an excellent safety record and in over 20 years experience with a substantial programme of nuclear power in the United Kingdom there has never been a nuclear emergency. The very high standards of safety used in the design and construction of nuclear plants and the strict control of operations provide a very high degree of confidence that accidents which might affect the public will not happen. Emergency planning (Fig. 1 ) provides an additional assurance that even if an accidental release of radioactive material were to occur arrangements exist for prompt action to protect the public.

IAEA-SM-268/31

EM ERG ENC Y PR E PA R E D N E SS IN TH E CEGBD e v e l o p m e n t o f e m e r g e n c y a r r a n g e m e n t s

f o l l o w i n g t h e T h r e e M i l e I s l a n d a c c i d e n t

T.P. H A I R ECentral Electricity Generating Board,London, United Kingdom

Abstract

EMERGENCY PREPAREDNESS IN THE CEGB: DEVELOPMENT OF EMERGENCY ARRANGEMENTS FOLLOWING THE THREE MILE ISLAND ACCIDENT.

The Central Electricity Generating Board (CEGB) has had comprehensive emergency arrangements for each of its nuclear power stations for the past 20 years. These arrangements provide for any necessary action on and off the nuclear site to protect the public. They are regularly exercised and involve emergency services and Government Departments. The TMI incident led to a reappraisal within the United Kingdom of the adequacy of emergency procedures to cope with longer-term accident scenarios: some possible improvements were identified and are being implemented. The paper considers the lessons learnt from the accident, the way in which the CEGB is developing its long-standing emergency arrangements to meet the extended scenario, and the way in which it is co-operating with Central Government to support the United Kingdom arrangements for a more co-ordinated response. The paper describes the extended CEGB arrangements for providing additional support, in the event of an extended emergency, to each of its 12 nuclear power stations through strategically placed operational support centres, and the part these centres play in producing a co-ordinated source of information and advice to the station emergency controller and Government Departments. The paper also refers to the additional arrangements to improve communications and to provide suitable facilities for the news media. It describes the means of briefing large numbers of media personnel and the facilities for them to transmit information and reports to their home base. Reference is made to the exercises carried out both by the CEGB and Government Departments to test communications, and to ensure that the new procedures can be effectively implemented.

1. I N T R O D U C T I O N

Since the start of its nuclear power programme, the Central Electricity Generating Board (CEGB) has given the highest priority to ensuring that its nuclear power stations are built to meet high standards of safety. The effectiveness of this policy is endorsed by the fact that during the past 22 years of reactor operation there has not been a nuclear accident or incident resulting in injury to personnel or a significant release of activity off site. This policy is supported by comprehensive emergency arrangements which are regularly reviewed and rehearsed to ensure they remain effective. As part of this review, following the

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ï S *

F IG .l. Location o f nuclear pow er stations.

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accident at Three Mile Island a group from the United Kingdom, consisting of engineers, scientists and a trade union official, led by the C E G B ’s Director of Health and Safety, visited the site and the area in order to determine what lessons might be learned. This paper outlines the basic emergency arrangements for the nuclear sites and the lessons learned from the Three Mile Island accident and describes the subsequent developments applied to the C E G B emergency arrange­ments. Reference is also made to the full-scale rehearsal of such developments.

2. E M E R G E N C Y A R R A N G E M E N T S A T T H E N U C L E A R P O W E R S T A T I O N S

The attainment of high standards of design, construction, commissioning and operation has formed the primary and major contribution to nuclear safety for the C E G B since the beginning of its nuclear power programme in 1956. These standards have culminated in the formation of design criteria which n o w form the basis for developing the safety requirements for new nuclear stations [ 1 ]. A secondary contribution is the application of a national siting policy [2, 3] which ensures that in the remote event of an accidental release of radioactivity off site, the population at risk would be limited and effective remedial measures could be put in action. This siting policy is supported by a system of development control which ensures that possible changes in population or demography do not affect the emergency measures. Figure 1 shows nuclear stations in the United Kingdom.

Such measures are rigorously applied to nuclear plants in order to ensure an extremely low level of risk. However, where nuclear safety is concerned the C E G B takes nothing for granted and for protection purposes assumes the most unlikely combination of events can occur at a given time, or in a particular sequence, to create a dangerous situation, and if necessary additional equipment and/or controls will then be installed to ensure the necessary safety level.

As an additional and prudent measure, the C E G B has from the beginning of its nuclear programme made comprehensive arrangements at each of its nuclear sites for dealing with any conceivable accident or emergency. These arrangements which subsequently became a formal requirement under the nuclear site licence, and require formal approval, include such matters as:

(a) The measures to be taken in the event of a nuclear incident or emergency on site;

(b) The reporting of any such accident or emergency to any person or to any local authority or public authority considered appropriate or as specified by the Health and Safety Executive;

(c) The supply and maintenance of adequate protective clothing and equipment for use in any emergency; and

(d) The supply of instruments and equipment for testing levels of ionizing radiation or contamination as may be required.

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When making the arrangements the licensee is required to consult those authorities or other bodies w h o m a y provide assistance and services. The arrange­ments as approved shall be rehearsed to such an extent and at such times as the Health and Safety Executive m a y direct. In practice however, and in order to ensure adequate training of all site personnel, five full exercises are held each year, with one being used for formal demonstration purposes. The experience gained in implementing these arrangements is covered in detail elsewhere [4].

3. R E V I E W O F E M E R G E N C Y A R R A N G E M E N T S F O L L O W I N G T H E T H R E E M I L E I S L A N D INCIDENT

The comprehensive review of the existing emergency arrangements within the C E G B confirmed that they were adequate for the protection of the public.It did identify, however, that where a nuclear incident, or its effects, lasted for a period of days, possibly extending into weeks, there was a need to take special measures to provide public information and support to the incident site. The review identified five specific areas requiring revision. These are as follows:

(a) Managerial responsibilities during an emergency;(b) Public relations and the news media;(c) Telecommunications;(d) Liaison with external organizations; and(e) Population dose assessment.

Each area together with the relevant development of its emergency arrange­ments is outlined in the following sections.

4. M A N A G E R I A L RESPONSIBILITIES D U R I N G A N E M E R G E N C Y

The review confirmed the need for clearly identifying, establishing and maintaining managerial control both during and following a nuclear incident.It identified the need for clear definition of the role and responsibilities of the personnel and organizations involved, and also the importance of limiting the numbers involved to those with a specific task to perform.

One of the most important findings of the review was recognition of the breadth of impact a nuclear incident would have. The existing emergency arrangements involved various centres of activity, including regional and national emergency information rooms [4] and it was clear that additionally a large number of outside bodies would also become involved, with a broad spectrum of support, needs and requirements. This would include, in addition to the Nuclear Installations Inspectorate (N11), the Department of Energy, the Department of

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Environment and the Ministry of Agriculture, Fisheries and Food (see Appendix I for a list of organizations which might be involved). The Emergency Controller would be responsible for directing both on-site and off-site recovery operations and at the same time providing a focal point for the activities of the relevant external bodies.

Whilst the existing emergency arrangements were considered satisfactory for an incident lasting no more than a few hours, it was clear that the overall responsi­bility of the Emergency Controller would be too great if the emergency were to be prolonged, beyond say eight hours, and that it would be necessary to arrange additional support for off-site activities following the early stages.

5. O P E R A T I O N A L S U P P O R T C E N T R E S

In developing the emergency arrangements to meet this requirement, the responsibility of the Emergency Controller for the direction of on-site activities at all times remains unchanged. The short-term responsibility for off-site activities will also remain with the Emergency Controller, but arrangements are made for a senior management team to give additional support to the site and to take over responsibility for liaison with Government organizations, county authorities, police and other off-site organizations. Responsibility for the co-ordination of off-site health physics activities, in particular population dose assessment, will be assumed by specialist Operational Support Centre (OSC) staff at an early stage, and any requirements by the Emergency Controller for external assistance or extra resources will be channelled solely through this Centre. This team will be located at an O S C situated at a distance of between 5 to 20 miles from the power station. The OSCs which are not necessarily purpose-built or permanently staffed utilize existing facilities such as police stations, town halls or fossil-fired power station buildings where accommodation can be quickly made available as required. The O S C must also be capable of housing C E G B support staff and representatives of the relevant authorities. (See Appendix 2 for the general criteria for OSCs.)

The O S C will be headed by a senior C E G B manager of Director General or Director level and supported by appropriate regional staff. The Director of Health and Safety, or his senior representative will also be present.

The detailed staffing of the O S C is determined by the Director General of the region concerned and will depend on various considerations including the geographical location of the site but will in general cover senior operational, engineering, health physics, medical, public relations and administrative support. With this support the O S C Controller will be able to meet the wide range of responsibilities which are summarized in Appendix 3.

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The accident at Three Mile Island emphasized the need for the rapid, clear, reliable and authoritative issue of information to the public. It also illustrated the deficiencies in the provision and dissemination of such information and it was clear that the existing C E G B arrangements (which, in general, were fairly limited) would be inadequate to meet the demands of the media for news in the event of a nuclear incident continuing for a longer term. It is accepted that the initial generation of information is primarily a matter for the operator, who should prepare an assessment of the accident and issue the necessary informative and authoritative statements based on a full knowledge of the plant and its operation. Such statements will need to be issued by a suitably senior officer in the C E G B and it was decided that separate press briefing centres (PBCs) should be installed for each station with adequate facilities for briefing a large number (up to 250) of media representatives. Whilst it was decided that the PBC should be sited some­where in the vicinity of the power station, its precise location is not critical, although there are a number of factors in c o m m o n with the OSC, including high-level staffing and a requirement for adequate communications which will make it an advantage to have a c o m m o n centre. The media representatives will of course wish to be near the scene of the incident but this has to be weighed against the possibility of creating road congestion near to the station and possible communi­cations difficulties. Consideration of the relevant factors indicated that there would be advantage in accommodating the O S C and the PBC in one combined unit. Whilst there may be a problem of ensuring the necessary privacy of the O S C and the suitable separation of the P B C from the OSC, this was not thought insuperable, and was considered to be outweighed by the increased advantage of having senior staff immediately available for authoritative statements.

It was decided that PBCs should be installed for each nuclear power station and that where practical these should be sited adjacent to the O S C in order to form a combined unit and should be established in accordance with the criteria set out in Appendix 4.

6. PUBLIC RELA TIO N S AND TH E NEWS M EDIA

7. PRESS BRIE F I N G C E N T R E S

Press Briefing Centres have now been set up for all C E G B nuclear power stations and with certain exceptions they are sited adjacent to the OSC. As with the OSC, they are not purpose-built and utilize accommodation available at a number of locations, with additional equipment being installed as necessary.This includes a large number of telephone lines specially’allocated for the media

IAEA-SM-268/31 393

representatives. The PBC provides the interface between the O S C and the media and will be staffed by the regional Public Relations Officer and suitable support staff to ensure effective management of the relations and communications with the media. This will include, subject to authorization by the O S C Controller, issuing press briefing material and press statements, arranging press conferences and personal interviews with senior staff on radio and television, and liaison with the local media to keep the public informed. It will also be necessary to main­tain communications with the Press and Publicity Office at C E G B Headquarters.

8. T E L E C O M M U N I C A T I O N S

The availability of a good communication system is an obvious requirement for the proper management of any emergency arrangements. The TMI incident revealed the problems which can arise if telecommunications are weak, resulting in the local system being overwhelmed with calls from the public and employees’ relatives in the short term, and with calls from outside the local area adding to the congestion in the longer term.

The importance of adequate telecommunications was recognized in the development of the C E G B emergency arrangements and the existing system, which on average consists of some eight telephone lines for each station, is basically divided into two systems: the C E G B privately owned systems, and those systems operating on the public network. The main demand on these systems will be for operational and general communication by the CEGB, inquiries by the public, and the requirements of the media for communication with their various agencies. The C E G B telephone system which is primarily provided for operational communication between the Grid Control Centres and the power stations is considered adequate for this purpose. However the links provided are not particularly substantial and might show deficiencies if long technical discussions had to take place. It was considered therefore that some internal reinforcement of the system was necessary and that this should take the form of strengthened links between the Power Stations and Regional Headquarters and between Regional Headquarters and Board Headquarters.

The power stations’ connections to the public telephone network was con­sidered to need considerable reinforcement, including the provision of ‘outgoing only’ exchange lines from power stations to both local and ‘out-of-area’ telephone exchanges. It was considered that, subject to the individual requirements of each site, two independent routes should be used wherever practicable for all essential communication, taking into account the need for both geographical and equipment diversity.

394 HAIRE

The station telecommunications are being strengthened by an additional ex-directory line connected to an ‘out-of-area’ telephone exchange. Three private lines are provided connecting the power station to the O S C and the O S C to the Headquarters Nuclear Emergency Information Room. The O S C will also have lines to the local telephone exchange and private lines to the local police and Government offices. In addition to this, the telephone facilities for the media mentioned in Section 6 will be provided. Recording equipment, teleprinter lines and facsimile machines will also be installed for communications between the O S C and other centres.

9. A D DITIO N A L COMMUNICATIONS SERVICES

10. LIAISON W I T H E X T E R N A L O R G A N I Z A T I O N S

The C E G B consults with the local authorities and the emergency services during the preparation of the emergency plan and its subsequent demonstration. County and district emergency plans, which set out the individual responsibilities of their officials and the emergency services, also include specific references to the nuclear power station(s) in their area. In these arrangements the police exercise short-term and local control, with the County Chief Executive or his nominee (sometimes the County Emergency Officer) taking responsibility for the longer-term co-ordination of services. The emergency services (police, fire and ambulance) form an integral part of the C E G B nuclear emergency arrange­ments, with the police providing a channel of emergency communications to the county services, setting up traffic controls and, if advised by the Emergency Controller, issuing potassium iodate tablets and evacuating the general public.

The police and local authorities will play an essential part in the management of action to protect the public. They are fully experienced in arranging evacuation, sheltering and other remedial actions which are required for emergencies (e.g. each county authority in England and Wales has its o w n county emergency plan for disasters or major incidents), in general, but will be totally reliant in making their decisions on the expert advice given to them by the CEGB, i.e. the Station Emergency Controller or the O S C Controller when he activates the OSC. In the event that the emergency was particularly serious, or prolonged beyond 24 hours, the Government would appoint a Government Technical Adviser to take over this responsibility. The functions of this official are covered more fully in Ref.[5] but his appointment will not reduce the C E G B ’s responsibility for controlling the incident or affect the line of command to the station.

The review of the liaison arrangements with external organizations during an emergency showed that these were generally adequate, but could be improved by more definition and formality. The OSCs and PBCs will clearly have an

IAEA-SM-268/31 395

important part to play in the co-ordination and control of external relations, and the provision of suitable accommodation at the centre should encourage the development of close and effective liaison between the C E G B and the relevant authorities. This will have the great potential benefit of ensuring that in the event of a nuclear incident requiring resources beyond the large capability of the CEGB, additional assistance can be centrally co-ordinated through the appropriate Government Department.

11. P O P U L A T I O N D O S E A S S E S S M E N T

The T M I accident emphasized the importance of accurate determination of the radiation dose received by members of the public. The widespread public concern and the demand for information on the level of dose received showed that it would be necessary to have precise figures available with the necessary assurance on the small effect of low doses in order to recover and retain public confidence. In the C E G B emergency planning, action is based on the E R L (Emergency Reference Level) concept in order to determine the level of radiation or contamination at which remedial action to protect the public becomes necessary; the standing emergency arrangements referred to previously ensure that each station has sufficient resources in the form of local survey facilities and laboratory support to assess the radiological hazard of any off-site release and to advise on methods of safeguarding the public during the early stages of an incident. Arrangements are also made for back-up support from other nuclear stations and the nuclear establishments of U K A E A and BNFL. Whilst such measures will determine airborne activity and ground deposition for the necessary advice on remedial action for public safety, they will not necessarily give the detailed information on a possible radioactive release that will be necessary to assess population dose at low levels in order to allay public anxiety. The C E G B accepts that in the event of an incident leading to a release of radioactivity it has the responsibility of producing the best estimates of both individual and collective effective dose equivalent at dose levels well below an ERL.

The revised monitoring arrangements to determine the external and internal doses of radioactivity are more fully described elsewhere [6]: they include measures for assessing individual effective dose equivalent at a minimum level of 50 millirem (0.5 mSv), i.e. one tenth of the annual dose limit for the public, the measurement of external doses by thermoluminescent dosimeters (TLDs) situated at verying distances from the station and the installation of fence radiation monitors to give a time profile of any release for help in interpolating and extrapolating the release measurements. The C E G B ’s Berkeley Nuclear Laboratories will assess the effective dose equivalent from all sources based on data received by telephone, teleprinter, and the facsimile transmission of survey

396 HAIRE

■ » ■■ D ire ctio n of m ain in fo rm a tio n flow s

--------------- No active p articipatio nOp eratio nal Supp o rt System

Press B riefing Centre

FIG.2. N etw ork o f communications.

IAEA-SM-268/31 397

forms. By these measures it is hoped to provide the authoritative and detailed assurance that will be required following a nuclear incident.

12. I M P L E M E N T A T I O N O F D E V E L O P E D E M E R G E N C Y A R R A N G E M E N T S

The paper has outlined the developments to the emergency arrangements which were produced by a working party chaired by the Director of Health and Safety. These developments have been fully implemented in each of the C E G B ’s four nuclear regions, with the OSCs and PBCs selected and the necessary arrange­ments for equipment, telecommunications and so on having been made.Emergency plans for these centres have been written and rehearsals have been carried out.

A national exercise based on the Sizewell ‘A ’ magnox station and the associated OSC/PBC based at the Suffolk County Police Headquarters was held in November 1982. The exercise, which lasted 36 hours, was based on the formal annual demonstration of the Sizewell ‘A ’ emergency plan and involved a wide range of Government Departments, police and local authorities, the Nuclear Installations Inspectorate and the National Radiological Protection Board.(Figure 2 shows the lines of communication which are necessary.) The O S C was fully staffed with a Director of Production as O S C Controller. Almost 24 hours into the exercise, the Government Technical Adviser was appointed and assumed his duties. Realism was introduced by a flood of external telephone enquiries from the local population and the media, by simulated labour trouble at the station and by a group of retired employees who were suitably briefed as a knowledgeable, probing group of media representatives for the press conferences held by the O S C Controller and Government Technical Adviser.

It was considered that the exercise demonstrated that the developments of the C E G B ’s emergency arrangements provided a satisfactory and effective means of support to the power stations and, whilst a number of lessons were learned for future improvements, it fully endorsed the C E G B policy of providing such arrange­ments. The exercise also allowed the Health and Safety Executive and Govern­ment Departments to test their part of the national arrangements.

13. C O N C L U S I O N S

The accident at Three Mile Island revealed areas where improvements in the long-term management of a nuclear incident were necessary. Following a review of this situation, the C E G B considered that existing emergency arrangements were satisfactory in the short term but decided to implement the arrangements

398 HAIRE

described in this paper to provide additional support to the incident site manage­ment, to improve public communication, and to obtain more detailed assessment of possible radiation doses to the public for the necessary assurance.

These developments are now functional throughout the C E G B and, whilst they are at an early stage, rehearsals indicate that the revised emergency arrange­ments will fully meet their purpose.

Appendix 1

E X T E R N A L O R G A N I Z A T I O N S W I T H W H I C H LIAISON M I G H T BE N E C E S S A R Y IN T H E E V E N T O F A N U C L E A R INCIDENT A T A

C E G B N U C L E A R P O W E R S T A T I O N

O R G A N I Z A T I O N

Police

Fire Service

Ambulance Service

Local Government Authorities

Ministry of Agriculture,Fisheries and Food

Nuclear Installations Inspectorate

United Kingdom Atomic Energy Authority

Department of Energy

Electricity Council

F U N C T I O N

Restriction of access to area surrounding power stationEvacuation of local population if required

Fire fighting/rescue

Transport of casualties to hospital

Co-ordination of local activities

Control of distribution of milk and other agricultural products, and restrictions on fishing

Advice and assistance at the station and communication with Secretary of State for Energy

Technical advice and resources Advice to H M Government

Provision and co-ordination of technical assistance

Co-ordination of assistance from parts of the Electricity Supply Industry

IAEA-SM-268/31 399

R o y a l N a t i o n a l L i f e b o a t

I n s t i t u t e

B r i t i s h T e l e c o m m u n i c a t i o n s

A r e a H e a l t h A u t h o r i t y

C o m m u n i t y P h y s i c i a n

L o c a l W a t e r A u t h o r i t y

W o m e n ’s R o y a l V o l u n t a r y

S e r v i c e , R e d C r o s s a n d o t h e r

v o l u n t a r y s e r v i c e s

L o c a l m e d i c a l p r a c t i t i o n e r s

A d v i c e t o l o c a l s h i p p i n g , c o n t r o l o f

s m a l l b o a t s i n v i c i n i t y o f s t a t i o n

T e l e c o m m u n i c a t i o n s t o a n d f r o m t h e

p o w e r s t a t i o n , t h e O S C a n d t h e P B C

C o - o r d i n a t i o n o f m e d i c a l a s s i s t a n c e i f

r e q u i r e d

C o - o r d i n a t i o n o f m e d i c a l a s s i s t a n c e i f

r e q u i r e d

C o - o r d i n a t i o n o f a n y a c t i o n s i n v o l v i n g

w a t e r s u p p l i e s , r i v e r s , e t c .

W e l f a r e s e r v i c e s i n t h e e v e n t o f

e v a c u a t i o n

M e d i c a l a s s i s t a n c e a s r e q u i r e d

A p p e n d i x 2

S U G G E S T E D C R I T E R I A F O R O P E R A T I O N A L S U P P O R T C E N T R E S

1 . L o c a t i o n

T h e C e n t r e s h o u l d :

( a ) B e l o c a t e d o u t s i d e a n y p r o j e c t e d e v a c u a t i o n z o n e f o r t h e s t a t i o n c o n c e r n e d ;

( b ) B e c l o s e e n o u g h t o t h e p o w e r s t a t i o n t o e n a b l e e a s y t r a n s f e r o f C E G B

p e r s o n n e l f r o m o n e l o c a t i o n t o t h e o t h e r i f s o r e q u i r e d ;

( c ) B e f a r e n o u g h a w a y t o a v o i d c o n g e s t i o n i n t h e i m m e d i a t e v i c i n i t y o f t h e

p o w e r s t a t i o n s i t e ;

( d ) T a k e i n t o a c c o u n t t h e l o c a t i o n o f t h e h e a d q u a r t e r s o f t h e l o c a l p o l i c e , t h e

D i s t r i c t a n d C o u n t y A u t h o r i t i e s a n d a n y o t h e r l o c a l o r g a n i z a t i o n s w i t h w h o m

c l o s e c o - o p e r a t i o n i s e n v i s a g e d ;

( e ) B e l o c a t e d i n , o r r e a s o n a b l y n e a r t o , c e n t r e s o f p o p u l a t i o n h a v i n g h o t e l

a n d r e s t a u r a n t f a c i l i t i e s ;

( f ) H a v e g o o d r o a d a c c e s s .

2 . A c c o m m o d a t i o n

T h e C e n t r e s h o u l d :

( a ) C o n t a i n a n u m b e r o f p r i v a t e o f f i c e s f o r s e n i o r C E G B p e r s o n n e l a n d

r e p r e s e n t a t i v e s f r o m o t h e r o r g a n i z a t i o n s i n c l u d i n g t h e p o l i c e a n d c e r t a i n

G o v e r n m e n t D e p a r t m e n t s ;

( b ) B e a b l e t o a c c o m m o d a t e a m u l t i - d i s c i p l i n e d t e a m i n c o n d i t i o n s c o n d u c i v e

t o t h e s o l u t i o n o f t e c h n i c a l a n d a d m i n i s t r a t i v e p r o b l e m s .

3 . C o m m u n i c a t i o n s

T h e C e n t r e s h o u l d :

( a ) H a v e r e l i a b l e o p e r a t i o n a l t e l e p h o n e l i n k s w i t h :

( i ) T h e n u c l e a r p o w e r s t a t i o n c o n c e r n e d ;

( i i ) T h e C E G B H e a d q u a r t e r s N u c l e a r E m e r g e n c y I n f o r m a t i o n R o o m ;

( b ) H a v e r e l i a b l e l i n k s w i t h t h e p u b l i c t e l e p h o n e s y s t e m ;

( c ) H a v e f a c i l i t i e s f o r r e c o r d i n g a l l o p e r a t i o n a l t e l e p h o n e c o n v e r s a t i o n s i f r e q u i r e d ;

( d ) H a v e , o r b e c a p a b l e o f h a v i n g q u i c k l y i n s t a l l e d , t e l e x a n d f a c s i m i l e t r a n s ­

m i s s i o n e q u i p m e n t .

4 . F a c i l i t i e s

T h e C e n t r e s h o u l d h a v e :

( a ) A d e q u a t e o f f i c e f a c i l i t i e s , e . g . s e c r e t a r i a l , t y p i n g a n d p h o t o c o p y i n g , e t c . ,

f o r t h e m a n a g e r i a l s t a f f ;

( b ) F a c i l i t i e s f o r t h e c o - o r d i n a t i o n o f o f f - s i t e h e a l t h p h y s i c s s u r v e y s a n d

m o n i t o r i n g , e . g . V H F r a d i o , p l o t t i n g m a p s , e t c . ;

( c ) F a c i l i t i e s f o r h e l i c o p t e r s .

4 0 0 H A IR E

A p p e n d i x 3

O S C C O N T R O L L E R ’S R E S P O N S I B I L I T I E S

( D i r e c t o r - G e n e r a l o r N o m i n e e )

I n g e n e r a l t h e r e s p o n s i b i l i t i e s o f t h e O S C C o n t r o l l e r a r e :

( a ) M a n a g e m e n t o f a l l t h e a c t i v i t i e s o f t h e O p e r a t i o n a l S u p p o r t C e n t r e . I n t h i s

t h e C o n t r o l l e r w i l l b e s u p p o r t e d b y t h e D i r e c t o r s o f P r o d u c t i o n a n d

E n g i n e e r i n g t o g e t h e r w i t h t h e G r o u p M a n a g e r .

IAEA-SM-268/31 401

( b ) L i a i s o n w i t h t h e D e p a r t m e n t o f E n e r g y N u c l e a r E m e r g e n c y B r i e f i n g R o o m

l o c a t e d a t W h i t e h a l l .

( c ) L i a i s o n w i t h t h e p o l i c e , a d v i s i n g t h e m o n t h e n e c e s s i t y t o i s s u e i o d a t e t a b l e t s

o r e v a c u a t e m e m b e r s o f t h e p u b l i c . T h i s f u n c t i o n w i l l p a s s f r o m t h e p o w e r

s t a t i o n E m e r g e n c y C o n t r o l l e r a s d i r e c t e d b y t h e O S C C o n t r o l l e r w h e n h e i s

s a t i s f i e d t h a t h i s c e n t r e i s f u l l y o p e r a t i o n a l .

( d ) T h e l o n g - t e r m a s s e s s m e n t o f p u b l i c e x p o s u r e t o r a d i a t i o n ;

( e ) L i a i s o n w i t h G o v e r n m e n t b o d i e s r e g a r d i n g t h e r e s t r i c t i o n o n m o v e m e n t o f

c a t t l e , c r o p s , e t c . , o r t h e b a n n i n g o f m i l k s u p p l i e s a n d t h e c o n t r o l o f

d r i n k i n g w a t e r a n d f o o d s t u f f s .

( f ) L o n g e r - t e r m a d v i c e t o L o c a l A u t h o r i t i e s a n d t o G o v e r n m e n t D e p a r t m e n t s .

( g ) D i s s e m i n a t i n g a n y i n f o r m a t i o n o n t h e i n c i d e n t t o t h e m e d i a t h r o u g h t h e P B C .

( h ) L i a i s o n b e t w e e n t h e E m e r g e n c y C o n t r o l l e r a n d o u t s i d e b o d i e s c o n c e r n i n g

a n y r e q u e s t s f o r a s s i s t a n c e o r p r o v i s i o n o f e x t r a r e s o u r c e s .

( i ) L i a i s o n w i t h r e g i o n a l a n d o t h e r p a r t s o f t h e C E G B o r g a n i z a t i o n a n d a l l o t h e r

b o d i e s .

A p p e n d i x 4

S U G G E S T E D C R I T E R I A F O R P R E S S B R I E F I N G C E N T R E S

1 . L o c a t i o n

T h e C e n t r e s h o u l d :

( a ) B e l o c a t e d o u t s i d e a n y p r o j e c t e d e v a c u a t i o n z o n e f o r t h e s t a t i o n c o n c e r n e d ;

( b ) B e c l o s e e n o u g h t o t h e p o w e r s t a t i o n c o n c e r n e d t o b e s e e n t o b e “ i n t h e a r e a ” ,

b u t f a r e n o u g h a w a y t o a v o i d c o n g e s t i o n i n t h e i m m e d i a t e v i c i n i t y o f t h e

s t a t i o n s i t e ;

( c ) H a v e g o o d r o a d l i n k s w i t h m a j o r c e n t r e s ;

( d ) B e l o c a t e d i n , o r r e a s o n a b l y n e a r t o , c e n t r e s o f p o p u l a t i o n h a v i n g h o t e l a n d

r e s t a u r a n t f a c i l i t i e s .

2 . A c c o m m o d a t i o n

T h e C e n t r e s h o u l d :

( a ) P r o v i d e a d e q u a t e f a c i l i t i e s f o r t h e s i m u l t a n e o u s b r i e f i n g o f u p t o 2 5 0 r e p r e s e n ­

t a t i v e s o f t h e n e w s m e d i a ;

( b ) H a v e p r i v a t e o f f i c e a c c o m m o d a t i o n f o r t h e p r e p a r a t i o n o f b r i e f i n g s t a t e m e n t s .

3 . C o m m u n i c a t i o n s

T h e C e n t r e s h o u l d :

( a ) H a v e r e l i a b l e o p e r a t i o n a l t e l e p h o n e l i n k s w i t h :

( i ) T h e n u c l e a r p o w e r s t a t i o n c o n c e r n e d ;

( i i ) T h e H e a d q u a r t e r s N u c l e a r E m e r g e n c y I n f o r m a t i o n R o o m ;

( b ) H a v e r e l i a b l e l i n k s w i t h t h e p u b l i c t e l e p h o n e n e t w o r k ;

( c ) H a v e , o r b e c a p a b l e o f h a v i n g q u i c k l y i n s t a l l e d , t e l e x a n d f a c s i m i l e t r a n s ­

m i s s i o n e q u i p m e n t ;

( d ) H a v e , o r b e c a p a b l e o f h a v i n g q u i c k l y i n s t a l l e d , t e l e p h o n e f a c i l i t i e s f o r

n e w s m e d i a r e p r e s e n t a t i v e s .

4 . F a c i l i t i e s

T h e C e n t r e s h o u l d h a v e :

( a ) A d e q u a t e o f f i c e f a c i l i t i e s , e . g . t y p e w r i t i n g s e r v i c e s , p h o t o c o p y i n g , e t c . ;

( b ) R e a s o n a b l e d o m e s t i c f a c i l i t i e s f o r t h e n u m b e r s o f p e o p l e e x p e c t e d t o b e

p r e s e n t ;

( c ) F a c i l i t i e s f o r d e a l i n g w i t h e n q u i r i e s f r o m m e m b e r s o f t h e p u b l i c , e i t h e r

d i r e c t l y , o r b y t e l e p h o n e ;

( d ) F a c i l i t i e s f o r h e l i c o p t e r s .

4 0 2 H A IR E

R E F E R E N C E S

[ 1 ] HEALTH AND SAFETY DEPARTMENT, Design Safety Criteria for CEGB Nuclear Power Stations, Rep. HS/R167/81 (Revised) (1982).

[2] GRONOW, W.S., “Application of safety and siting policy to nuclear plants in the United Kingdom”, Environmental Contamination by Radioactive Materials (Proc. Sem. Vienna, 1969), IAEA, Vienna (1969) 549.

[3] HAIRE, T.P., SHAW, J., Nuclear power plant licensing procedures in the United Kingdom, Prog. Nucl. Energy 4 (1979) 161-182.

[4] ORCHARD, H.C., WALKER, C.W., “Experience in the provision and exercising of emergency arrangements at CEGB nuclear power stations”, Handling of Radiation Accidents 1977 (Proc. Symp. Vienna, 1977), IAEA, Vienna (1977) 371.

[5] GRONOW, W.S., paper IAEA-SM-268/85, these Proceedings.[6] GOLDFINCH, E.P., ORCHARD, H.C., “A review of the emergency arrangements for

CEGB nuclear power stations following the accident at Three Mile Island” (Société française de radioprotection and Fachverband für Strahlenschutz e.V. - Joint Radiation Protection Meeting on Radiological Impact of Nuclear Power Plants and other Nuclear Installations on Man and his Environment), Lausanne ( 1981).

IAÈA-SM-268/28

I M P O R T A N C E O F T H E C O N T R O L

R O O M D U R I N G A N U C L E A R

E M E R G E N C Y S I T U A T I O N

K . N O W A K , H . S C H N A D T

I n s t i t u t e f o r A c c i d e n t R e s e a r c h ,

T Ü V R h e i n l a n d ,

C o l o g n e ,

F e d e r a l R e p u b l i c o f G e r m a n y

A b s t r a c t

IMPORTANCE OF THE CONTROL ROOM DURING A NUCLEAR EMERGENCY SITUATION.

The emergency preparedness in nuclear power plants is briefly described in terms of: the design requirements for the control room and the emergency control room within the scope of the Federal German licensing procedure; regulations for the emergency protection of nuclear power plants, addressing public authorities as well as licensees; and the possibilities of obtaining further information during an emergency from the installed remote monitoring system and incident instrumentation. It is shown that safety features and displays provided for design incidents have to be used in an emergency situation. From a review of the protective actions which are possible in an emergency situation, it is evident that detailed information is required on emission and the plant status, and that a reliable prognosis of the further develop­ment is necessary if the appropriate actions are to be chosen. The accuracy of prognosis is extremely important when precautionary measures are taken. The paper describes the type and extent of the information and the actual difficulties in making a correct diagnosis, especially in emergency situations. When the required information is compared to the possible ways of obtaining it, it is clear that the requirements are met for many but not all conceiveable nuclear accidents. In particular, the fact that it may become necessary to abandon the control room diminishes the chances of making a correct diagnosis or giving reliable prognoses. The possibilities of taking measures in the station itself are also reduced. From the point of view of emergency preparedness, control room protection should be improved by shielding and ventilation measures. This is judged to be more effective and less expensive than the improvement of other systems.

1 . S I T U A T I O N I N T H E F E D E R A L R E P U B L I C O F G E R M A N Y ( F R G )

1 . 1 . C o n t r o l r o o m a n d e m e r g e n c y c o n t r o l r o o m

T h e c o n t r o l r o o m o f a n u c l e a r p o w e r p l a n t i s d e s i g n e d t o c o p e w i t h t h e

m o s t u n f a v o u r a b l e t a s k s a n d c o n d i t i o n s w h i c h c a n o c c u r w i t h i n t h e s c o p e o f

t h e o v e r a l l d e s i g n o f t h e p l a n t . T h e d e s i g n c o v e r s a l l r e q u i r e m e n t s f r o m n o r m a l

o p e r a t i o n ( s t a r t u p , p o w e r o p e r a t i o n , s h u t d o w n , f u e l e l e m e n t c h a n g e a n d m a i n t e ­

n a n c e ) , t o a b n o r m a l o p e r a t i o n ( d e v i a t i o n s f r o m t h e o p e r a t i o n a l r a n g e w i t h o u t

4 0 3

4 0 4 NOWAK and SCHNADT

s a f e t y - r e l a t e d c o n s e q u e n c e s ) a n d t h e o c c u r r e n c e o f i n c i d e n t s a g a i n s t w h i c h t h e

p l a n t i s d e s i g n e d .

T h e l a t t e r p o i n t c o v e r s a l l t a s k s w h i c h a r e n e c e s s a r y t o c o n t r o l t h e i n c i d e n t s

a n d r e t u r n t h e p l a n t t o a s a f e c o n d i t i o n .

A n e m e r g e n c y c o n t r o l r o o m i s l o c a t e d b e s i d e t h e c o n t r o l r o o m t o c o p e

w i t h i n c i d e n t s c a u s e d b y e x t e r n a l i m p a c t s , e . g . p l a n e c r a s h , a n d w i t h t h e o c c u r r e n c e

o f a l a r g e - s c a l e f i r e . T h e n u c l e a r s t e a m g e n e r a t i o n s y s t e m , w h i c h i n t h i s c a s e i s

a s s u m e d t o b e c o m p l e t e l y i n t a c t i n a c c o r d a n c e w i t h t h e d e s i g n , c a n b e k e p t i n

a s a f e c o n d i t i o n f r o m t h i s e m e r g e n c y c o n t r o l r o o m . S i m i l a r l y , t h e r e a c t o r s h u t ­

d o w n a n d r e s i d u a l h e a t r e m o v a l c a n b e c o n t r o l l e d f r o m * t h i s p o i n t . O f c o u r s e

i t i s p e r m i s s i b l e t o d e s i g n t h e c o n t r o l r o o m i t s e l f a g a i n s t s u c h e x t e r n a l i m p a c t s , b u t

t h i s a l t e r n a t i v e h a s n o t y e t b e e n r e a l i z e d .

T h e r e f o r e i n p r e s e n t - d a y p o w e r p l a n t s t h e c o n t r o l r o o m i s d e s i g n e d t o w i t h ­

s t a n d t h e c o n s e q u e n c e s r e s u l t i n g f r o m i n c i d e n t s o c c u r r i n g i n s i d e t h e p l a n t b u t

n o t a g a i n s t e x t e r n a l i m p a c t s . B y c o n t r a s t , t h e e m e r g e n c y c o n t r o l r o o m , w h i c h

o n l y a c c o m m o d a t e s p a r t o f t h e c o n t r o l r o o m i n s t r u m e n t a t i o n , i s p r o t e c t e d a g a i n s t

e x t e r n a l i m p a c t s b y m e a n s o f a b u n k e r c o n s t r u c t i o n , a n i s o l a t e d v e n t i l a t i o n s y s t e m

a n d a n i n d e p e n d e n t e m e r g e n c y p o w e r s u p p l y . A d e q u a t e s t o c k p i l i n g o f f u e l , f o o d

a n d d r i n k i n g w a t e r s u p p l i e s c o m p l e t e s t h e p r o t e c t i v e m e a s u r e s .

1 . 2 . E m e r g e n c y p r o t e c t i o n

F r o m a n e m e r g e n c y p r e p a r e d n e s s p o i n t o f v i e w , i t i s a s s u m e d t h a t s e q u e n c e s

o f e v e n t s l e a d i n g t o a c o n s i d e r a b l e r e l e a s e o f r a d i o a c t i v e m a t e r i a l s t o t h e e n v i r o n ­

m e n t a r e p h y s i c a l l y p o s s i b l e i n t h e n u c l e a r p o w e r p l a n t a n d t h e r e f o r e c a n n o t

b e c o m p l e t e l y e x c l u d e d w i t h a b s o l u t e c e r t a i n t y . S u c h s e q u e n c e s o f e v e n t s , w h i c h

e x c e e d t h e d e s i g n s c o p e o f t h e p o w e r p l a n t , a r e c a l l e d ‘a c c i d e n t s ’ ( U n f á l l e ) in

G e r m a n t e r m i n o l o g y [ 1 ] . I t h a s b e e n d e m o n s t r a t e d t h a t s u c h a c c i d e n t s a r e

e x t r e m e l y i m p r o b a b l e [ 2 , 3 ] b u t t h a t i f t h e y d i d o c c u r , t h e y c o u l d c a u s e c a t a s ­

t r o p h i c d a m a g e t o t h e e n v i r o n m e n t o f a n u c l e a r p o w e r p l a n t a n d t o t h e p e o p l e

l i v i n g t h e r e i n t h e e x t r e m e c a s e . T h e a i m a n d t a s k o f e m e r g e n c y m e a s u r e s i s t o

k e e p t h e c o n s e q u e n c e s o f s u c h a c c i d e n t s a s l o w a s p o s s i b l e .

T h e F e d e r a l G e r m a n B a s i c R e c o m m e n d a t i o n s f o r E m e r g e n c y P l a n n i n g [ 4 ]

a r e r e g u l a t i o n s w h i c h a r e d i r e c t e d t o w a r d s t h e a u t h o r i t i e s r e s p o n s i b l e f o r e m e r g e n c y

p r e p a r e d n e s s . T h e y s t i p u l a t e t h e s c o p e a n d t y p e o f p l a n n i n g a s w e l l a s t h e m e a s u r e s

t o b e t a k e n i n a n e m e r g e n c y . I n g e n e r a l , t h i s i s w i t h i n t h e r e s p o n s i b i l i t y o f t h e

p u b l i c s a f e t y a u t h o r i t i e s o f t h e G e r m a n F e d e r a l S t a t e s .

B y c o n t r a s t , t h e R e c o m m e n d a t i o n s f o r t h e P l a n n i n g o f E m e r g e n c y P r o t e c t i o n

M e a s u r e s b y t h e l i c e n s e e [ 5 ] m u s t b e t a k e n i n t o a c c o u n t f o r t h e l i c e n s i n g o f

n u c l e a r p o w e r p l a n t s . T h e y e s s e n t i a l l y s t i p u l a t e o r g a n i z a t i o n a l a n d a d m i n i s t r a t i v e

m e a s u r e s a n d p r e c a u t i o n s t o b e e f f e c t e d b y t h e l i c e n s e e . A s w e l l a s t h e i m m e d i a t e

a l e r t i n g o f t h e E m e r g e n c y P r o t e c t i o n A u t h o r i t i e s a n d t h e c a r r y i n g o u t o f a l l f e a s i b l e

IAEA-SM-268/28 405

m e a s u r e s t o l i m i t a r a d i o a c t i v e r e l e a s e r e s u l t i n g f r o m a n a c c i d e n t , p a r t i c u l a r

e m p h a s i s m u s t b e p l a c e d o n t h e f a c t t h a t t h e l i c e n s e e i s o b l i g e d t o g i v e t h e

E m e r g e n c y P r o t e c t i o n A u t h o r i t i e s a l l n e c e s s a r y i n f o r m a t i o n o n t h e s t a t e o f t h e

p l a n t , t h e s c o p e a n d t y p e o f r e l e a s e a n d t h e m e t e o r o l o g i c a l c o n d i t i o n s g o v e r n i n g

a t m o s p h e r i c d i s p e r s i o n .

N o m a t e r i a l d e s i g n r e q u i r e m e n t s f o r a p o w e r p l a n t r e s u l t s o l e l y f r o m t h e

f a c t t h a t t h e l i c e n s e e i s o b l i g e d t o p r e p a r e f o r e m e r g e n c i e s i n a c c o r d a n c e w i t h

F e d e r a l G e r m a n l a w s a n d r u l e s [ 1 , 6 ] . O n t h e c o n t r a r y , i t i s p l a n n e d t o u t i l i z e

t h e n u m e r o u s s a f e t y f e a t u r e s a n d d i s p l a y s p r o v i d e f o r c o n t r o l l i n g d e s i g n i n c i d e n t s

i n a c c i d e n t s i t u a t i o n s a s w e l l . I n t h e f a c e o f t h e f u n d a m e n t a l l y u n l i m i t e d s c o p e o f

p o s s i b l e a c c i d e n t s e q u e n c e s , t h i s i s a p e r f e c t l y j u s t i f i a b l e c o n c e p t . T h i s p a p e r

c o n s i d e r s t o w h a t e x t e n t t h i s c o n c e p t i s a d e q u a t e f o r c o n t r o l r o o m d e s i g n .

1 . 3 . R e m o t e m o n i t o r i n g a n d i n c i d e n t i n s t r u m e n t a t i o n

R e m o t e m o n i t o r i n g o f n u c l e a r p o w e r p l a n t s i s n o w b e i n g i n t r o d u c e d i n t o

t h e F e d e r a l R e p u b l i c o f G e r m a n y ( F R G ) [ 7 ] . I t i s p l a n n e d a n d i m p l e m e n t e d

b y t h e S u p e r v i s o r y A u t h o r i t i e s o f t h e G e r m a n F e d e r a l S t a t e s u s i n g u n i f o r m

p r i n c i p l e s [ 8 ] . T h e k e y p o i n t s a r e t h e m o n i t o r i n g o f t h e e m m i s s i o n a n d i m m i s s i o n

o f r a d i o a c t i v e m a t e r i a l s , t h e l o g g i n g o f m e t e o r o l o g i c a l c o n d i t i o n s f o r d i s p e r s i o n

a n d t h e m o n i t o r i n g o f t h o s e o p e r a t i o n a l p a r a m e t e r s w h i c h i n d i c a t e t h e o p e r a t i o n a l

s t a t u s o f t h e p o w e r p l a n t .

T h e m o n i t o r i n g i s c o m p u t e r i z e d a n d f u l l y a u t o m a t i c . I t s p r i m a r y t a s k i s t o

p e r m i t m o n i t o r i n g o f t h e a d m i s s i b l e o p e r a t i o n o f t h e p o w e r p l a n t b y t h e S u p e r ­

v i s o r y A u t h o r i t i e s . A t t h e s a m e t i m e , r e m o t e m o n i t o r i n g a l s o h a s a n ‘a la r m

f u n c t i o n ’ a s i t a u t o m a t i c a l l y a n d p r o m p t l y i n f o r m s t h e S u p e r v i s o r y A u t h o r i t y

i f t h e m o n i t o r e d p a r a m e t e r s d e p a r t f r o m t h e o p e r a t i o n a l l y a d m i s s i b l e r a n g e . I n

t h e e v e n t o f a n a c c i d e n t , t h e m e t e o r o l o g i c a l c o n d i t i o n s a t t h e s i t e a n d t h e d o s e

r a t e i n t h e s t a c k c a n b e d e t e r m i n e d b y m e a n s o f r e m o t e m o n i t o r i n g .

I n a d d i t i o n , c o n s i d e r a t i o n i s a l r e a d y b e i n g g i v e n t o i m p r o v i n g r e m o t e

m o n i t o r i n g w i t h r e f e r e n c e t o r e l e a s e s e x c e e d i n g t h e o p e r a t i o n a l a d m i s s i b l e l i m i t [ 9 ] .

F o r t h i s p u r p o s e , r e s e a r c h p r o j e c t s h a v e b e e n s t a r t e d o r a r e i n p r e p a r a t i o n i n t h e

F R G . T h e i r a i m i s t h e s p e c i f i c a t i o n o f t h e p a r a m e t e r s t o b e l o g g e d , t h e d e v e l o p ­

m e n t o f m e a s u r i n g i n s t r u m e n t s , t h e t r a n s m i s s i o n o f t h e p a r a m e t e r s a n d t h e

d e v e l o p m e n t o f s u i t a b l e c o m p u t e r c o d e s . A s s u m i n g t h a t t h e p a r a m e t e r s a r e

s u i t a b l y c h o s e n , s u c h a n i m p r o v e d r e m o t e m o n i t o r i n g s y s t e m c o u l d a l s o s u p p l y

i m p o r t a n t d a t a f o r a s s e s s i n g t h e p l a n t s t a t u s a n d i t s f u r t h e r d e v e l o p m e n t i n t h e

e v e n t o f a n a c c i d e n t .

F u r t h e r m o r e , i n c i d e n t i n s t r u m e n t a t i o n i s s p e c i f i e d f o r F e d e r a l G e r m a n n u c l e a r

p o w e r p l a n t s [ 1 0 ] . I n t h e c a s e o f a n i n c i d e n t , i . e . s t i l l w i t h i n t h e d e s i g n s c o p e

o f t h e p l a n t , t h e p u r p o s e o f t h e i n s t r u m e n t a t i o n i s t o e n s u r e t h a t t h e p l a n t s t a t u s

c a n b e r e c o g n i z e d , t h a t t h e n e c e s s a r y m e a s u r e s c a n b e t a k e n f o r t h e p r o t e c t i o n

T A B L E I . O V E R A L L I N C I D E N T D I S P L A Y F O R P W R [ 1 0 ]

4 0 6 NOWAK and SCHNADT

Measured variable RangeDisplaycontrolroom

Located in emergency control room

Neutron flux 1(T6 ... 10‘3full power X X

Boron concentration of reactor building sump water

50 ... 2600 ppm xc -

Reactor coolant temperature hot and cold leg

50 ... 400°C X X

Core exit temperature 100 ...1000°C X -

Pressurizer level 10% a.d.v.3 X X

Steam generator level 10% a.d.v.a X X

Sump water temperature 10 ... 150°C X -

Sump water level 10% a.d.v.3 X -

Departure from saturation 50 ...O K X -

Fuel storage water temperature 10 ... 150°C X X

Reactor coolant pressure 1 ...250 bar X X

Steam pressure, each steam generator

1 ... 150 bar X X

Containment pressure -0 .5 ... 5.5 bar X X

Reactor building pressure hintsb X X

Containment hydrogen concentration

hintsb X —

Containment temperature (upper region)

20 ... 160°C Xd

Containment radiation monitoring 1 0 '1 ... 10+6 R/h Xd

Gaseous effluent monitoring (stack)

hints b Xd

Liquid effluent monitoring

Meteorological data (wind

hintsb Xd

direction and speed, turbulence type)

hints*5 Xd

a at least 10% above design value b special hints are given within the text of the rule c sampling allowed d or other accessible location

IAEA-SM-268/28 407

F IG .l. Incident instrumentation terms.

o f t h e p l a n t a n d t h e e n v i r o n m e n t , a n d t h a t t h e r a d i o l o g i c a l e f f e c t s o f t h e i n c i d e n t

c a n b e e s t i m a t e d . T h e s i g n a l s f r o m t h e i n c i d e n t i n s t r u m e n t a t i o n a r e d i s p l a y e d

i n t h e c o n t r o l r o o m o f t h e n u c l e a r p o w e r p l a n t a n d i n t h e e m e r g e n c y c o n t r o l

r o o m .

T h e i n s t r u m e n t a t i o n c o m p r i s e s t h e d e t a i l e d i n c i d e n t d i s p l a y , t h e o v e r a l l

i n c i d e n t d i s p l a y , t h e w i d e r a n g e d i s p l a y a n d t h e i n c i d e n t r e c o r d i n g ( F i g . 1 ) .

T h e o p e r a t i o n a l i n s t r u m e n t a t i o n i s u s e d f o r t h e d e t a i l e d i n c i d e n t d i s p l a y . I t

s e r v e s t o m o n i t o r t h e i n d i v i d u a l s a f e t y f e a t u r e s a n d t h e i r s u b o r d i n a t e a u x i l i a r y

s y s t e m s . T h e m e a s u r e d v a l u e s o n t h e o v e r a l l i n c i d e n t d i s p l a y p e r m i t a n e v a l u a t i o n

o f t h e p l a n t s t a t u s : e f f e c t i v e n e s s o f s h u t d o w n , r e s i d u a l h e a t r e m o v a l a n d a c t i v i t y

e n c l o s u r e , c o n d i t i o n s i n t h e c o n t a i n m e n t a n d e m i s s i o n w i t h w a s t e w a t e r a n d

e x h a u s t a i r ( T a b l e I ) .

T h e w i d e r a n g e d i s p l a y h a s o n l y a f e w m e a s u r e d v a l u e s , t h e m e a s u r i n g r a n g e s

o f w h i c h , h o w e v e r , e x c e e d t h e d e s i g n v a l u e s o f t h e p l a n t . I t i s u s e d t o r e c o r d

w h e n i m p o r t a n t d e s i g n l i m i t v a l u e s a r e a p p r o a c h e d o r e x c e e d e d d u r i n g s e q u e n c e s

o f e v e n t s w h i c h w e r e n o t c o n s i d e r e d i n t h e d e s i g n o f t h e n u c l e a r p o w e r p l a n t .

T h e w i d e r a n g e d i s p l a y t h e r e f o r e a l s o s u p p l i e s i m p o r t a n t d a t a i n a c c i d e n t

s i t u a t i o n s ( T a b l e I I ) .

2 . E M E R G E N C Y M E A S U R E S

2 . 1 . P o s s i b l e m e a s u r e s a n d d e c i s i o n - m a k i n g

T h e p r e s e n t a t i o n i s l i m i t e d t o t h e s h o r t - t e r m m e a s u r e s , i . e . t h o s e w h i c h h a v e

t o b e i m p l e m e n t e d d u r i n g t h e f i r s t t w o d a y s o f a n a c c i d e n t . I n t h i s c a s e , t h e

4 0 8 NOWAK and SCHNADT

T A B L E I I . W ID E R A N G E D IS P L A Y F O R P W R [1 0 ]

Measured variable Range

Core exit temperature

Reactor coolant pressure

Containment pressure

Fuel storage water level

Sump water level

Containment hydrogen concentration

Gaseous effluent monitoring

Containment radiation monitoring

100 ... 1000°C

1 ... 400 bar

— 1 ... 15 bar

0 .. . 100%

depending on type of plant

special hints given in the rule

special hints given in the rule

10_I ... 10+7R/h

a u t h o r i t i e s c a n c h o o s e b e t w e e n t h r e e b a s i c p o s s i b i l i t i e s , w h i c h m a y b e c o m b i n e d

i f n e c e s s a r y :

— p o p u l a t i o n r e m a i n s i n d o o r s ( i n c r e a s e d s h i e l d i n g )

— d i s t r i b u t i o n o f i o d i n e t a b l e t s ( r e d u c t i o n o f t h e t h y r o i d d o s e )

— e v a c u a t i o n .

I f a n a c c i d e n t o c c u r s , a d e c i s i o n m u s t b e t a k e n a s t o w h i c h m e a s u r e i s t o b e

i n i t i a t e d i n w h i c h a r e a a n d a t w h a t t i m e . T h e f o l l o w i n g a i d s c a n a s s i s t d e c i s i o n ­

m a k i n g :

— e m i s s i o n v a l u e s , m e a s u r e d i n t h e n u c l e a r p o w e r p l a n t

— i m m i s s i o n v a l u e s m e a s u r e d i n t h e e n v i r o n m e n t

— d a t a c o n c e r n i n g t h e a c u t e s t a t u s o f t h e n u c l e a r p o w e r p l a n t

— p o s s i b l e m e a n s f o r r e d u c i n g e m i s s i o n s ( p l a n t - i n t e r n a l m e a s u r e s )

— p r o g n o s e s o n t h e f u t u r e d e v e l o p m e n t w i t h i n t h e p l a n t a n d t h e e x p e c t e d

d e v e l o p m e n t o f t h e r a d i o a c t i v e r e l e a s e

— e m e r g e n c y p r o t e c t i o n l e v e l s , i . e . d o s e l i m i t v a l u e s f o r w h i c h c e r t a i n p r o t e c t i v e

m e a s u r e s a r e n e c e s s a r y o r r e c o m m e n d e d [ 4 ] .

I n a d d i t i o n t o t h i s i n f o r m a t i o n , w h i c h c a n p o i n t t o t h e a p p r o p r i a t e m e a s u r e ,

o t h e r a s p e c t s , w h i c h i n d i c a t e t h e d i s a d v a n t a g e s o f t h e m e a s u r e s , m u s t b e t a k e n

i n t o a c c o u n t . T h e s e a r e :

— r i s k s c o n n e c t e d w i t h t h e e x e c u t i o n o f t h e p r o t e c t i v e m e a s u r e

— t e c h n i c a l f e a s i b i l i t y

— u n f a v o u r a b l e w e a t h e r c o n d i t i o n s a n d t i m e o f d a y

— c o s t - b e n e f i t r a t i o .

IAEA-SM-268/28 4 0 9

T h e m a i n p o i n t i s t h a t i n f o r m a t i o n a n d m e a s u r e s i n t h e n u c l e a r p o w e r p l a n t

a r e e x t r e m e l y i m p o r t a n t i n f i n d i n g t h e c o r r e c t a n s w e r t o t h e q u e s t i o n s : ‘W h a t ? ’ ,

‘W h e n ? ’ a n d ‘W h e r e ? ’ . I n t h i s r e s p e c t n o t o n l y t h e a c c u r a c y o f t h e s t a t u s s i g n a l ,

b u t a l s o t h e r e l i a b i l i t y o f t h e p r o g n o s e s o f f u r t h e r d e v e l o p m e n t i s o f g r e a t

i m p o r t a n c e .

T h i s r e s u l t s f r o m t h e f a c t t h a t t h e a u t h o r i t i e s h a v e o n l y a v e r y l i m i t e d

s c o p e f o r d e c i s i o n - m a k i n g . T h i s a p p l i e s t o b o t h t h e d o s e l i m i t v a l u e s — t h e

r a n g e o f t h e t o t a l b o d y d o s e w i t h i n w h i c h a d e c i s i o n m u s t b e m a d e b e t w e e n

d i f f e r e n t p r o t e c t i v e m e a s u r e s i s l e s s t h a n o n e o r d e r o f m a g n i t u d e — a n d t o t h e

t i m e f a c t o r . A l l e m e r g e n c y m e a s u r e s r e q u i r e a t i m e r a n g e o f 3 t o 1 5 h o u r s f r o m

d e c i s i o n - m a k i n g t o t h e c o n c l u s i o n o f t h e i r e x e c u t i o n .

T h e r e s u l t s o f r i s k s t u d i e s h a v e l a r g e l y l e d t o t h e c o n c l u s i o n t h a t p r e c a u ­

t i o n a r y p r o t e c t i v e m e a s u r e s s h o u l d b e t a k e n i f c e r t a i n s e q u e n c e s o f e v e n t s o c c u r .

T h i s w a s o b v i o u s i n t h e d e c i s i o n s m a d e b y t h e a u t h o r i t i e s d u r i n g t h e T M I - i n c i d e n t

o r t h e r a i l a c c i d e n t i n M i s s i s s a u g a [ 1 1 ] . S i m i l a r l y , t h e e x e r c i s e s c r i p t s f o r e m e r g e n c y

e x e r c i s e s i n t h e F R G i n c r e a s i n g l y a s s u m e t h a t , f o r e x a m p l e , a n e v a c u a t i o n s h o u l d

b e i n i t i a t e d a s a p r e c a u t i o n a r y m e a s u r e [ 1 2 ] . T h e a c c u r a c y o f t h e p r o g n o s i s

f o r t h e f u r t h e r d e v e l o p m e n t o f a n a c c i d e n t g a i n s d e c i s i v e i m p o r t a n c e a s t h e b a s i s

f o r a d e c i s i o n c o n c e r n i n g p r e c a u t i o n a r y e m e r g e n c y m e a s u r e s .

2 . 2 . R e q u i r e m e n t s i m p o s e d o n t h e n u c l e a r p o w e r p l a n t

T h e n e e d f o r c o m p r e h e n s i v e a n d e x a c t i n f o r m a t i o n o n t h e s t a t u s o f t h e

n u c l e a r p o w e r p l a n t a f f e c t e d b y t h e a c c i d e n t a n d f o r r e l i a b l e p r o g n o s e s c o n c e r n i n g

t h e f u r t h e r d e v e l o p m e n t r e s u l t s i n c l e a r d e m a n d s o n t h e n u c l e a r p o w e r p l a n t f r o m

a n e m e r g e n c y p r e p a r e d n e s s p o i n t o f v i e w . T h e s e a r e i n i t i a l l y f o r m u l a t e d a s t a s k s ,

i n d e p e n d e n t o f t h e i r t e c h n i c a l r e a l i z a t i o n .

I n t h e e v e n t o f a n u c l e a r a c c i d e n t , i t i s a b s o l u t e l y e s s e n t i a l t o g i v e t h e

f o l l o w i n g i n f o r m a t i o n t o t h e e m e r g e n c y c o m m a n d c e n t r e :

( a ) P r i o r t o a r e l e a s e , t o a l l o w a d e c i s i o n t o b e t a k e n o n t h e p r e c a u t i o n a r y

e m e r g e n c y m e a s u r e s :

( i ) A n t i c i p a t e d t i m e o f r e l e a s e ( i n t e r i m t i m e )

( i i ) E x p e c t e d t e m p o r a l c o u r s e o f t h e r e l e a s e

( i i i ) E x p e c t e d s c o p e o f t h e r e l e a s e a n d t h e p o s s i b l e n u c l i d e c o m p o s i t i o n

o f t h e e m i s s i o n ( n o b l e g a s e s / i o d i n e / a e r o s o l s )

( i v ) I n f o r m a t i o n o n t h e p o s s i b l e p o i n t o f r e l e a s e ( r e l e a s e v i a s t a c k o r g r o u n d

r e l e a s e )

( v ) M e t e o r o l o g i c a l d a t a a t t h e s i t e

( b ) A f t e r c o m m e n c e m e n t o f t h e r a d i o a c t i v e e m i s s i o n , t o s u p p o r t t h e d e c i s i o n ­

m a k i n g o f t h e e m e r g e n c y p r o t e c t i o n a u t h o r i t i e s :

4 1 0 NOWAK and SCHNADT

( i ) I n f o r m a t i o n o n t h e s o u r c e s t r e n g t h a n d t h e n u c l i d e c o m p o s i t i o n o f t h e

e m i s s i o n ( n o b l e g a s e s / i o d i n e / a e r o s o l s )

( i i ) I n f o r m a t i o n o n t h e p o i n t o f r e l e a s e ( r e l e a s e v i a s t a c k o r g r o u n d r e l e a s e )

( i i i ) M e t e o r o l o g i c a l d a t a a t t h e s i t e

( i v ) R e s u l t s o f e m i s s i o n m e a s u r e m e n t s p e r f o r m e d b y t h e l i c e n s e e ’s

m e a s u r i n g g r o u p s .

A l l i n f o r m a t i o n m u s t b e u p d a t e d a t r e g u l a r i n t e r v a l s .

T h e d e m a n d f o r r e l i a b l e p r o g n o s e s m e a n s t h a t t h e p l a n t s t a t u s m u s t b e

c l e a r l y i d e n t i f i e d . T h e i n c i d e n t i n t h e n u c l e a r p o w e r p l a n t T M I - 2 i l l u s t r a t e d

h o w d i f f i c u l t i t c a n b e t o i d e n t i f y t h e a c c i d e n t e x a c t l y a n d t o a n a l y s e t h e p l a n t

s t a t u s . A p o s s i b l e a i d f o r d e t e r m i n i n g t h e a c t u a l s i t u a t i o n c a n , f o r e x a m p l e , b e

t h e i n p u t o f d e f i n e d d i s t u r b a n c e s i g n a l s i n t o t h e n u c l e a r p o w e r p l a n t a n d t h e

a n a l y s i s o f t h e r e s u l t i n g r e a c t i o n ( e x a m p l e T M I - 2 : p u m p s o f f , p u m p s o n ) .

A l o t o f a t t e n t i o n h a s b e e n p a i d t o t h e e x a m i n a t i o n o f t h e d i a g n o s i s p r o c e s s e s

t h e m s e l v e s a n d t o t h e d i s c u s s i o n o f s u i t a b l e d i a g n o s i s s t r a t e g i e s a n d a i d s s i n c e T M I

[ 1 3 ] . H i n t s f o r t h e i d e n t i f i c a t i o n o f a c o n c r e t e a c c i d e n t , w h i c h m a y p r e s e n t a

d i f f u s e p i c t u r e , a r e p r e s e n t e d i n R e f s [ 1 4 , 1 5 ] . E m p i r i c a l e x a m i n a t i o n s o f t h e

d i a g n o s i s s t r a t e g i e s a s a c t u a l l y u s e d b y t h e c o n t r o l r o o m p e r s o n n e l o f a n u c l e a r

p o w e r p l a n t a n d o f t h e c o n c e p t u a l m o d e l s o n w h i c h t h e s e a r e b a s e d a r e b e i n g

c a r r i e d o u t a t p r e s e n t [ 1 6 ] . I t i s e v i d e n t t h a t t h e n o n - a v a i l a b i l i t y o f t h e c o n t r o l

r o o m d u r i n g a n e m e r g e n c y s i t u a t i o n w o u l d l i m i t t h e d i a g n o s t i c p o s s i b i l i t i e s .

T h e d e m a n d f o r a c c u r a t e k n o w l e d g e o f t h e p l a n t s t a t u s — t h e p l a n t a s a

w h o l e a n d s u b - s y s t e m s — a l s o r e s u l t s f r o m a n o t h e r f a c t . T h e l i c e n s e e m u s t

a l w a y s m i t i g a t e t h e d a n g e r t o t h e h e a l t h a n d l i v e s o f p e r s o n s a n d t o m a t e r i a l g o o d s ,

a n d , i n a d d i t i o n , h e m u s t m i n i m i z e t h e r a d i a t i o n e x p o s u r e . E v e n i n t h e e v e n t

o f a n a c c i d e n t i t i s t h e l e g a l o b l i g a t i o n o f t h e l i c e n s e e [ 1 ] t o t a k e a l l p o s s i b l e

m e a s u r e s — p r e p l a n n e d o r a d h o c — t o i n f l u e n c e t h e a c c i d e n t t o w a r d s a m o r e

f a v o u r a b l e c o u r s e . T h e e x e c u t i o n o f s u c h p l a n t m e a s u r e s t o r e d u c e d a m a g e

p r e s u m e s a n e x a c t k n o w l e d g e o f t h e p l a n t s t a t u s a n d t h e e x i s t e n c e o f m e a s u r i n g

a n d s w i t c h i n g p o s s i b i l i t i e s .

3 . S U I T A B I L I T Y O F I N F O R M A T I O N S O U R C E S F O R A C C I D E N T

C O N D I T I O N S

T h e e x i s t i n g t e c h n i c a l p o s s i b i l i t i e s f o r i n f o r m i n g t h e a u t h o r i t i e s i n t h e e v e n t

o f a n a c c i d e n t a r e d e s c r i b e d i n t h e f i r s t p a r t o f t h i s p a p e r .

T h e i m p o r t a n c e a t t r i b u t e d t o i n f o r m a t i o n a n d p r o g n o s i s h a s b e e n p r e s e n t e d

a b o v e . W e w i l l n o w e x a m i n e w h e t h e r t h e a c t u a l p o s s i b i l i t i e s f u l f i l t h e s e r e q u i r e ­

m e n t s .

T h e c o n t r o l r o o m o f a p o w e r p l a n t i s t h e p r i m a r y i n f o r m a t i o n s o u r c e . I t i s

g e n e r a l l y a v a i l a b l e d u r i n g t h e i n t e r i m p e r i o d o f a n u c l e a r a c c i d e n t ; t h e r e b y o n e

IAEA-SM-268/28 411

c a n j u s t i f i a b l y a s s u m e t h a t i n m o s t c a s e s t h i s i n t e r i m p h a s e w i l l b e o f l o n g e r d u r a t i o n .

I t i s , h o w e v e r , i m p o s s i b l e t o e x c l u d e t h e p o s s i b i l i t y o f a n a c c i d e n t c o u r s e w i t h

s h o r t i n t e r i m p h a s e s . R e c e n t i n v e s t i g a t i o n s i n d i c a t e t h a t t h e c o n t r o l r o o m o f a n u c l e a r

p o w e r p l a n t c a n b e s u b j e c t e d t o a h i g h r a d i a t i o n i n t e n s i t y ( p a r t i c u l a r l y d u e t o f a l l o u t )

a f t e r t h e o c c u r r e n c e o f a r a d i o a c t i v e r e l e a s e [ 1 7 ] . C o n s e q u e n t l y t h e c o n t r o l

r o o m w o u l d h a v e t o b e a b a n d o n e d a t a n e a r l y p o i n t i n c a s e s o f e a r l y r a d i o a c t i v e

r e l e a s e b e c a u s e o f i t s i n a d e q u a t e p r o t e c t i o n .

O w i n g t o i t s e x t e n s i v e i n s t r u m e n t a t i o n , i n p a r t i c u l a r a s r e g a r d s t h e o p e r a t i o n a l

i n s t r u m e n t a t i o n , t h e c o n t r o l r o o m w o u l d b e t h e m o s t s u i t a b l e p l a c e f o r d e t e r m i n i n g

t h e p l a n t s t a t u s a n d t h e t y p e o f a c c i d e n t , i n p a r t i c u l a r d u r i n g s u c h a c c i d e n t s e ­

q u e n c e s . D u r i n g a n . a c c i d e n t , o n e m u s t a s s u m e f a i l u r e o f t h e i n s t r u m e n t a t i o n

t o a g r e a t e r o r l e s s e r e x t e n t . T h e la r g e n u m b e r a n d t h e r e d u n d a n c y o f

d i s p l a y s i n t h e c o n t r o l r o o m m e a n t h a t f a i l u r e s a n d m a l f u n c t i o n s c o u l d m o s t

e a s i l y b e c o m p e n s a t e d t h e r e u s i n g i n t a c t d i s p l a y s .

A b a n d o n i n g t h e c o n t r o l r o o m i n t h e c a s e o f a c c i d e n t s w i t h e a r l y r e l e a s e w o u l d

i m p l y t h a t n o c o u n t e r m e a s u r e c a n b e i n i t i a t e d f r o m t h e r e . I f a t a l l p o s s i b l e

t h e n , t h e g r e a t e s t c h a n c e o f i n f l u e n c i n g t h e f u r t h e r c o u r s e i n a f a v o u r a b l e m a n n e r

i s p r o v i d e d b y t h e c o n t r o l r o o m w i t h i t s v a r i e t y o f c o n t r o l p o s s i b i l i t i e s . E v e n a

d e f i n e d d e l a y i n t h e i n c r e a s e o f t h e r e l e a s e r a t e r a i s e s t h e e f f e c t i v e n e s s o f t h e

p r o t e c t i v e m e a s u r e s t a k e n b y t h e a u t h o r i t i e s .

I f t h e c o n t r o l r o o m h a s t o b e a b a n d o n e d d u r i n g t h e i n t e r i m p h a s e o f a n

a c c i d e n t b e c a u s e o f o t h e r r e a s o n s , e . g . f i r e , t h e p o s s i b i l i t i e s f o r l i m i t i n g t h e d a m a g e

a r e r e d u c e d a n d t h e p r o b a b i l i t y o f a m o r e u n f a v o u r a b l e a c c i d e n t c o u r s e i s i n c r e a s e d .

O f c o u r s e o n e c a n a r g u e t h a t o n e c a n f a l l b a c k o n t h e e m e r g e n c y c o n t r o l

r o o m w i t h o u t g r e a t l y l i m i t i n g t h e p o s s i b i l i t i e s f o r v e r i f y i n g t h e p l a n t s t a t u s a n d

i n f l u e n c i n g t h e c o u r s e o f t h e a c c i d e n t . T h i s e m e r g e n c y c o n t r o l r o o m i s w e l l

p r o t e c t e d a g a i n s t t h e m e c h a n i c a l a n d r a d i o l o g i c a l c o n s e q u e n c e s o f a n a c c i d e n t .

A s a l r e a d y m e n t i o n e d , t h e i n s t r u m e n t a t i o n o f t h e e m e r g e n c y c o n t r o l r o o m

i s d e s i g n e d t o c o n t r o l i n c i d e n t s w i t h a n i n t a c t p r i m a r y c o o l i n g l o o p . I n c i d e n t s

h a v i n g a m a s s i v e i m p a c t o n t h e e n v i r o n m e n t a r e e v e n t s i n w h i c h t h e p r i m a r y l o o p

i s n o l o n g e r i n t a c t . O n e c a n t h e r e f o r e r a i s e t h e q u e s t i o n w h e t h e r t h e d i s p l a y s

a n d c o n t r o l s i n t h e e m e r g e n c y c o n t r o l r o o m c a n a c t i n a n e f f e c t i v e a n d l i m i t i n g

w a y i n t h e e v e n t o f a n a c c i d e n t w h i c h o n t h e o n e h a n d i s e x t r e m e l y u n l i k e l y a n d

o n t h e o t h e r h a s a w i d e r a n g e o f p o s s i b i l i t i e s .

T h e i n c i d e n t i n s t r u m e n t a t i o n d e s c r i b e d a b o v e , w h i c h i s a l s o a v a i l a b l e i n t h e

e m e r g e n c y c o n t r o l r o o m , c e r t a i n l y i m p r o v e s t h e l i m i t e d a n a l y t i c a l p o s s i b i l i t i e s .

I n o u r o p i n i o n , t h e f a c t t h a t p a r t o f t h e i n c i d e n t i n s t r u m e n t a t i o n e v e n e x p l i c i t l y

e x c e e d s t h e d e s i g n l i m i t s o f t h e n u c l e a r p o w e r p l a n t i n d i c a t e s t h a t t h e l i c e n s i n g

a u t h o r i t i e s m u s t h a v e f e l t t h a t t h e r e w a s a l a c k o f i n f o r m a t i o n i n a c c i d e n t

s i t u a t i o n s . C o n s i d e r a t i o n s o n t h e i m p r o v e m e n t o f r e m o t e m o n i t o r i n g o f n u c l e a r

p o w e r p l a n t s t e n d i n t h e s a m e d i r e c t i o n .

4 1 2 NOWAK and SCHNADT

4 . 1 . Q u a l i t y o f t h e a v a i l a b l e i n f o r m a t i o n

A s s h o w n a b o v e , t h e q u a l i t y o f t h e p l a n n e d i n f o r m a t i o n c a n v a r y .

A l l d a t a r e f e r r i n g t o t h e e v a l u a t i o n o f a r e l e a s e w h i c h h a s a l r e a d y o c c u r r e d

a r e r e l a t i v e l y a c c u r a t e a n d r e l i a b l e , i . e . m e t e o r o l o g i c a l c o n d i t i o n s , s o u r c e t e r m

f o r s t a c k r e l e a s e . I f , h o w e v e r , t h e r e l e a s e d o e s n o t o c c u r v i a t h e s t a c k , w e a r e

a l r e a d y m i s s i n g a c c u r a t e i n f o r m a t i o n f o r t h e s o u r c e t e r m a n d t h e p o i n t o f

r e l e a s e .

T h e r e l i a b i l i t y o f d a t a w h i c h p e r m i t a p r o g n o s i s o f t h e s u b s e q u e n t c o u r s e

o f e v e n t s i s b a s i c a l l y p o o r e r . A s l o n g a s t h e c o n t r o l r o o m c a n b e s t a f f e d d u r i n g

a n i n c i d e n t , i t i s c e r t a i n l y p o s s i b l e t o m a k e a p r o g n o s i s . T h e c u r r e n t p l a n t

s t a t u s c a n b e d e t e r m i n e d f r o m t h e c o n t r o l r o o m , i n p a r t i c u l a r b y m e a n s o f

s p e c i f i e d s w i t c h i n g o p e r a t i o n s ( t e s t s i g n a l s ) .

I f , h o w e v e r , t h e c o n t r o l r o o m h a s t o b e a b a n d o n e d d u r i n g t h e i n t e r i m p h a s e

o f a n a c c i d e n t o w i n g t o u n f o r e s e e n r e a s o n s o r t o r a d i a t i o n e x p o s u r e a f t e r c o m m e n ­

c e m e n t o f a r e l e a s e , o n l y t h e d i s p l a y s i n t h e e m e r g e n c y c o n t r o l r o o m a r e a v a i l a b l e

f o r m a k i n g a p r o g n o s i s o f t h e s u b s e q u e n t c o u r s e . T h e i r s c o p e w a s n o t i n t e n d e d

t o c o v e r a l l e v e n t u a l i t i e s o c c u r i n g d u r i n g a n i n c i d e n t / a c c i d e n t .

4 . 2 . R e q u i r e m e n t s f r o m a n e m e r g e n c y p l a n n e r ’s p o i n t o f v i e w

T h e n e e d t o g i v e a c c u r a t e a n d r e l i a b l e i n f o r m a t i o n t o t h e a u t h o r i t i e s a n d t h e

s c o p e o f t h e n e c e s s a r y i n f o r m a t i o n h a v e b e e n i n d i c a t e d a n d t h e a v a i l a b l e m e a n s

p r e s e n t e d a n d q u a l i f i e d .

F r o m t h e e m e r g e n c y p l a n n e r ’s p o i n t o f v i e w , t h e c o m p a r i s o n o f m e a n s a n d

r e q u i r e m e n t s l e a d s t o t h e c o n c l u s i o n t h a t t h e o p t i m u m s o l u t i o n w o u l d b e

t h e a v a i l a b i l i t y o f t h e c o n t r o l r o o m o f a n u c l e a r p o w e r p l a n t d u r i n g a n e m e r g e n c y .

T h e c o n t r o l r o o m o f f e r s t h e m o s t e x t e n s i v e a n d r e l i a b l e m e a n s f o r i d e n t i f y i n g

t h e p l a n t s t a t u s a n d f o r e c a s t i n g t h e f u r t h e r d e v e l o p m e n t . T h e c o u r s e o f e v e n t s

c a n b e s t b e c o n t r o l l e d f r o m t h e c o n t r o l r o o m i n o r d e r t o p r e v e n t , m i n i m i z e o r

a t l e a s t d e l a y t h e r e l e a s e o f r a d i o a c t i v e m a t e r i a l s .

T h e u n l i m i t e d n u m b e r o f e x e p t i o n a l l y i m p r o b a b l e b u t , n o n e t h e l e s s , c o n c e i v ­

a b l e a c c i d e n t s m a k e s i t i m p o s s i b l e t o p o s i t i v e l y p r o v e t h a t t h e c o n t r o l r o o m o f

a n u c l e a r p o w e r p l a n t m u s t a l w a y s b e a v a i l a b l e . O n t h e o t h e r h a n d , i t s h o u l d h a v e

b e c o m e c l e a r t h a t t h e a v a i l a b i l i t y o f t h e c o n t r o l r o o m d u r i n g a n a c c i d e n t i s

o b v i o u s l y o f v a l u e .

T h e d e m a n d f o r c o n t r o l r o o m a v a i l a b i l i t y d u r i n g a n a c c i d e n t d o e s , h o w e v e r ,

n e c e s s i t a t e p r o t e c t i o n a g a i n s t t h e m e c h a n i c a l a n d r a d i o l o g i c a l i m p a c t s o f a n

a c c i d e n t b y m e a n s o f b u n k e r c o n s t r u c t i o n a n d i n d e p e n d e n t v e n t i l a t i o n . ( I t w o u l d

b e p s y c h o l o g i c a l l y a d v a n t a g e o u s , i f t h e c o n t r o l r o o m p e r s o n n e l i s n o t d i s t r a c t e d b y

w o r r y i n g a b o u t i t s o w n s a f e t y . )

4 . C O N C L U S IO N S

IAEA-SM-268/28 4 1 3

T h e e m e r g e n c y c o n t r o l r o o m , i n c i d e n t i n s t r u m e n t a t i o n a n d r e m o t e

m o n i t o r i n g a r e f e a t u r e s w h i c h h a v e a l r e a d y b e e n i n t r o d u c e d w i t h i n t h e s c o p e

o f g e n e r a l n u c l e a r p o w e r p l a n t d e s i g n . T h e y a r e a i d s w h i c h a l r e a d y f u l f i l t h e

r e q u i r e m e n t s o f e m e r g e n c y p r o t e c t i o n i n a n u m b e r o f w a y s . I n o u r o p i n i o n , h o w ­

e v e r , f u r t h e r i m p r o v e m e n t o f t h e s e f e a t u r e s w o u l d b e l e s s e f f e c t i v e a n d m o r e

e x p e n s i v e t h a n a w e l l - p r o t e c t e d c o n t r o l r o o m .

R E F E R E N C E S

[ 1] FEDERAL GERMAN GOVERNMENT, Verordnung iiber den Schütz vor Scháden durch ionisierende Strahlen (Strahlenschutzverordnung — StrlSchV), 13.10. 1976,BGB1. I, Bonn (1976) 2905.

[2] RASMUSSEN, N.C., Reactor Safety Study, Rep. WASH-1400 (NUREG-75/014),United States Atomic Energy Commission, Washington D.C. (October 1975).

[3] GESELLSCHAFT FÜR REAKTORSICHERHEIT, Deutsche Risikostudie Kernkraftwerke (BMFT, Ed), Verlag TÜV Rheinland, Kôln (1979).

[4] FEDERAL GERMAN GOVERNMENT, Rahmenempfehlungen fiir den Katastrophen- schutz in der Umgebung kerntechnischer Anlagen, 15. 12. 1977, GmBl. 28 31, Bonn (1977).

[5] FEDERAL GERMAN GOVERNMENT, Empfehlungen zur Planung von Notfallschutz- mafinahmen durch Betreiber von Kernkraftwerken, 04. 02. 1977, GMB1. 28 4, Bonn (1977).

[6] FEDERAL GERMAN GOVERNMENT, Gesetz über die friedliche Verwendung der Kernenergie und Schütz gegen ihre Gefahren (Atomgesetz-AtG), 31. 10. 1976, BGB1.1, Bonn (1976) 3053.

[7] POHL, W.K., “Off-site assessment of nuclear power plant information”, Current Nuclear Power Plant Safety Issues (Proc. Conf. Stockholm, 1980) Vol. 1, IAEA, Vienna (1981) 185.

[8] FEDERAL GERMAN GOVERNMENT, Rahmenempfehlungen fiir die Fernüberwachung von Kernkraftwerken, 30. 10. 1980, GMB1. 31 30, Bonn (1980).

[9] BUNDESMINISTER DES INNEREN (FRG), Schreiben vom 06. 08. 1982 an den Innen- ausschufi des Deutschen Bundestages, Umwelt Nr. 92, 09. 11. 1982, Bonn.

[10] KERNTECHNISCHER AUSSCHUSS (KTA), Stôrfallinstrumentierung, Rep. KTA-3502, 30. 11. 1982, Carl Heymanns Verlag KG, Kôln (1983).

[11] HESEL, D., SCHNADT, H., Die Evakuierung von Mississauga (St. Sch. 776), TÜV Rheinland, Institut fiir Unfallforschung, Kôln (1981).

[12] REGIERUNG VON UNTERFRANKEN, Katastrophenschutzübung KKG 82, Übungsbestimmungen, Akt. Z. 201-48a 14/82, Würzburg (1982).

[13] RASMUSSEN, J., “Models of mental strategies in process plant diagnosis”, Human Detection and Diagnosis of System Failures (RASMUSSEN, J., and ROUSE, W.B., Eds), Plenum Press, New York (1981) 241.

[14] BECKER, G., PREUSS, W., TIETZE, A., Hypothetische Stôrfalle bei leichtwasser- moderierten Kernenergieanlagen im Rahmen der Notfallschutzplanung (St. Sch. 624), TÜV Rheinland, Institut fiir Unfallforschung, Kôln (1979).

4 1 4 NOWAK and SCHNADT

[15] TIETZE, A., Die Unfallanalyse im Rahmen der Notfallschutzplanung, Habilitations- schrift, Universitat-Gesamthochschule Wuppertal, Wuppertal (1981).

[16] PAGE, S., HEYDEN, W., LIERE, B., Verhalten des Kernkraftwerk-Wartenpersonals (im Auftrag des BMFT), TÜV Rheinland, Institut für Unfallforschung in Zusammen- arbeit mit Kraftwerk Union AG, Kôln (in press).

[17] TÜV Rheinland: Strahlenschutz des Wartenpersonals, Kôln (1983) (in press).

IAEA-SM-268/20

D E V E L O P M E N T O F B W R C O M P U T E R I Z E D

O P E R A T O R S U P P O R T S Y S T E M F O R

E M E R G E N C Y C O N D IT IO N S

F . M U R A T A

N u c l e a r P o w e r G e n e r a t i o n D i v i s i o n ,

H i t a c h i W o r k s , H i t a c h i L t d ,

I b a r a k i

К . K A T O

E n e r g y R e s e a r c h L a b o r a t o r y ,

H i t a c h i W o r k s , H i t a c h i L t d ,

I b a r a k i

S . H A S H I M O T O

O m i k a W o r k s , H i t a c h i L t d ,

I b a r a k i

J a p a n

A b s t r a c t

DEVELOPMENT OF BWR COMPUTERIZED OPERATOR SUPPORT SYSTEM FOR EMERGENCY CONDITIONS.

A BWR computerized operator support system (COSS) for emergency conditions has been under development for three years. The conceptual design of the system has been settled and some of the subsystems are in the detailed design or manufacturing stage. The principal functions are technical specification monitoring, diagnosis, guidance during emergency conditions, predictive simulation and safety monitoring. Before a reactor trip, alternative operational guidance for anomalous events is provided by utilization of the CCT (cause consequence tree) and FPS (failure propagation simulator). After the trip, operational guidance is based on event-oriented and symptom-oriented methods in association with the safety function monitor. The technical specification monitor controls the readiness monitor and performs surveillance tests of safety systems to maintain plant operational reliability and to ensure correct performance when initiated. The predictive simulator gives the future trends of significant plant parameters. These subsystems are expected to assist the operational personnel. The feasibility of the COSS functions is confirmed separately by off-line simulation. The paper considers the conceptual design, the functions of the subsystems and the off-line simulation results. Each subsystem has shown that useful information to operational personnel is provided. Henceforth these functions will be integrated into a single system and the feasibility will be thoroughly evaluated using a plant simulator which is being separately developed to verify the COSS.

415

4 1 6 M U RATA et al.

A B W R c o m p u t e r i z e d o p e r a t o r s u p p o r t s y s t e m f o r e m e r g e n c y c o n d i t i o n s i s

u n d e r d e v e l o p m e n t a s a f i v e y e a r s p r o j e c t ( 1 9 8 0 - 8 4 ) f i n a n c i a l l y a i d e d b y t h e

J a p a n e s e M i n i s t r y o f I n t e r n a t i o n a l T r a d e a n d I n d u s t r y ( M I T I ) .

A f t e r t h e a c c i d e n t a t T h r e e M i le I s l a n d , v a r i o u s p r o j e c t s [ 1 , 2 ] w e r e s t a r t e d

t o i m p l e m e n t t h e l e s s o n s l e a r n e d f r o m t h e a c c i d e n t . T h e p r e s e n t d e v e l o p m e n t ,

c o n s i d e r e d a s o n e o f t h e p r o j e c t s , i s t o i n c r e a s e o p e r a t i o n a l r e l i a b i l i t y a n d p l a n t

a v a i l a b i l i t y b y h e l p i n g t h e o p e r a t i n g p e r s o n n e l t o r e c o g n i z e t h e p r i m a r y c a u s e o f

a f a i l u r e a n d p r o v i d e o p e r a t i o n a l g u i d a n c e a s w e l l a s d i s p l a y i n g p r e s e n t s t a t u s

a n d e x p e c t e d c o n s e q u e n c e s .

B e f o r e t h i s , H i t a c h i h a d b e e n d e v e l o p i n g p l a n t d i a g n o s i s m e t h o d s s u c h a s a

m o d e l c o m p a r i s o n m e t h o d [ 3 ] a n d a t i m e s e r i e s a n a l y s i s m e t h o d [ 4 ] .

M o r e o v e r , w e d e v e l o p e d a n a d v a n c e d c o n t r o l c o m p l e x n a m e d N U C A M M - 8 0

[ 5 , 6 ] w h i c h i s e q u i p p e d w i t h a s u p e r v i s o r y m o n i t o r i n g f u n c t i o n a n d a n a u t o m a t i c

m a n o e v e r i n g f u n c t i o n t o s t a r t u p a n d s h u t d o w n t h e p l a n t . T h e s y s t e m w i l l b e

i n c o m m e r c i a l o p e r a t i o n i n t h e n e a r f u t u r e . O n t h e b a s i s o f t h i s e x p e r i e n c e , w e

h a v e b e e n d e v e l o p i n g a B W R c o m p u t e r i z e d o p e r a t o r s u p p o r t s y s t e m ( C O S S )

f o r e m e r g e n c y c o n d i t i o n s . T h e C O S S i s c o m p o s e d o f s e v e r a l s u b s y s t e m s w h i c h

c o v e r t h e r o l e s f o r w h i c h t h e o p e r a t i o n a l p e r s o n n e l a r e r e s p o n s i b l e .

T h e d o m i n a n t s u b s y s t e m s a r e a s f o l l o w s :

( 1 ) D e t e c t i o n a n d d i a g n o s i s o f a d i s t u r b a n c e

( 2 ) O p e r a t i o n a l g u i d a n c e b a s e d o n t h e d i a g n o s i s

( 3 ) S u b s y s t e m s t o s u p p o r t o p e r a t i o n a l g u i d a n c e .

T h i s p a p e r f i r s t a d d r e s s e s t h e s t r u c t u r e o f t h e C O S S . I t t h e n d e s c r i b e s t h e

f u n c t i o n s o f t h e s u b s y s t e m s , p r e s e n t s t h e s i m u l a t i o n r e s u l t s t o v e r i f y f e a s i b i l i t y o f

t h e s u b s y s t e m a n d f i n a l l y d e s c r i b e s t h e m e t h o d o f p r e s e n t i n g i n f o r m a t i o n .

W e h a v e n o w c o n f i r m e d t h a t t h e s u b s y s t e m s w i l l s u p p o r t o p e r a t i o n a l

p e r s o n n e l e f f e c t i v e l y . W e a r e p r o c e e d i n g w i t h t h e d e v e l o p m e n t o f t h e s u b ­

s y s t e m s a n d w i l l v e r i f y t h e i r f u n c t i o n s u s i n g a p l a n t - w i d e s i m u l a t o r .

1. IN T R O D U C T IO N

2 . S T R U C T U R E O F B W R C O M P U T E R I Z E D O P E R A T O R

S U P P O R T S Y S T E M

T h e C O S S i s c o m p o s e d o f s e v e r a l s u b s y s t e m s w h i c h c o i n c i d e w i t h t h e

r o l e s o f o p e r a t i o n a l p e r s o n n e l a s s h o w n i n F i g . l . T h e d y n a m i c r e l a t i o n s h i p

b e t w e e n t h e s u b s y s t e m s o f t h e C O S S i s i l l u t r a t e d i n F i g . 2 . T h e s t r u c t u r e i s

d e s c r i b e d i n a c c o r d a n c e w i t h t h i s f i g u r e .

IAEA-SM-268/20 4 1 7

B e f o r e p l a n t t r i p , t h e p l a n t s y s t e m s s h o u l d b e s e t u p t o m a i n t a i n h i g h

o p e r a t i o n a l r e l i a b i l i t y c o n f o r m i n g t o t h e t e c h n i c a l s p e c i f i c a t i o n s . I n t h e C O S S ,

t h e t e c h n i c a l s p e c i f i c a t i o n m o n i t o r s u r v e y s w h e t h e r t h e p l a n t s y s t e m s , s u c h a s t h e

s a f e t y s y s t e m s , a r e r e a d y t o s t a r t a n d c a r r i e s o u t t h e n e c e s s a r y s u r v e i l l a n c e t e s t s

t o e n s u r e t h e y o p e r a t e c o r r e c t l y w h e n n e e d e d .

O n c e a f a i l u r e o c c u r s i n t h e p l a n t s y s t e m s , t h e C O S S s u p p o r t s t h e o p e r a t i o n a l

p e r s o n n e l w i t h i n f o r m a t i o n o n t h e e x i s t i n g s t a t u s a n d g u i d a n c e o n r e s t o r a t i o n

w i t h d e t a i l s o n t h e p r i m a r y c a u s e a n d t h e e x p e c t e d c o n s e q u e n c e s o f t h e f a i l u r e .

E v e n i f t h e p l a n t i s o p e r a t e d a c c o r d i n g t o t h e g u i d a n c e g i v e n b y t h i s m e t h o d ,

t h e p l a n t m a y t r i p w h e n m o r e s e r i o u s f a i l u r e s o c c u r . I n s u c h a c a s e , t h e C O S S

f u r n i s h e s g u i d a n c e o n s h u t t i n g t h e p l a n t d o w n i n a s a f e m a n n e r . W h e n t h e

p l a n t s t a t u s ( i . e . w h i c h p l a n t s y s t e m s a r e u n a v a i l a b l e a n d w h a t k i n d o f e v e n t h a s

o c c u r r e d ) i s d e t e r m i n e d , t h e C O S S p r o v i d e s e v e n t - o r i e n t e d g u i d a n c e o n s h u t t i n g

t h e p l a n t d o w n i n a p r o p e r a n d e f f i c i e n t w a y . W h e n t h e p l a n t s t a t u s i s n o t

i d e n t i f i e d c l e a r l y o r t h e p l a n t s t a t u s g o e s n e a r s a f e t y l i m i t s , t h e C O S S p r o v i d e s

s y m p t o m - o r i e n t e d o p e r a t i o n a l g u i d a n c e o n h o w n o t t o e x c e e d t h e l i m i t s .

I n o r d e r t o p r o v i d e r e l i a b l e a n d a p p r o p r i a t e g u i d a n c e b a s e d o n b o t h t h e

e v e n t a n d s y m p t o m - o r i e n t e d m e t h o d s , t h e s a f e t y f u n c t i o n m o n i t o r o f t h e C O S S

e v a l u a t e s w h e t h e r t h e p l a n t s y s t e m s a r e c a r r y i n g o u t t h e i r e x p e c t e d r o l e s .

M o r e o v e r , t h e f u t u r e t r e n d s o f s o m e s i g n i f i c a n t p a r a m e t e r s s u c h a s t h e r e a c t o r

w a t e r l e v e l a n d t h e r e a c t o r p r e s s u r e c a n b e o b t a i n e d f r o m t h e p r e d i c t i v e s i m u l a t o r .

T h e s e s u b s y s t e m s c o m p o s e t h e C O S S a n d t h e i r f u n c t i o n s c o m p l e m e n t

o n e a n o t h e r d u r i n g e m e r g e n c y p l a n t c o n d i t i o n s .

3 . F U N C T I O N O F T H E S U B S Y S T E M S

3 . 1 . T e c h n i c a l s p e c i f i c a t i o n m o n i t o r

T h e p u r p o s e o f t h i s s u b s y s t e m i s t o k e e p p l a n t r e l i a b i l i t y h i g h b y c o n t r o l l i n g

t h e r e a d i n e s s m o n i t o r a n d p e r f o r m i n g t h e s u r v e i l l a n c e t e s t s i n a c c o r d a n c e w i t h

t h e p l a n t s t a t u s . I f t h e r e a d i n e s s m o n i t o r d e t e c t s t h a t a s a f e t y s y s t e m i s i n o p e r a b l e ,

a p a r t i c u l a r s u r v e i l l a n c e t e s t i s r e c o m m e n d e d b y t h e t e c h n i c a l s p e c i f i c a t i o n

m o n i t o r . O t h e r w i s e , o r d i n a r y p e r i o d i c s u r v e i l l a n c e t e s t s a r e c a r r i e d o u t b y t h e

m o n i t o r o n t h o s e s y s t e m s w h i c h a r e e s t a b l i s h e d t o b e o p e r a b l e .

T h i s m o n i t o r h e l p s t o e n s u r e t h a t t h e s a f e t y s y s t e m s w i l l s t a r t r e l i a b l y

w h e n e v e r t h e s i g n a l s t o i n i t i a t e t h e m a r e r e c e i v e d .

3 . 2 . D e t e c t i o n a n d d i a g n o s i s

D i s t u r b a n c e s a r e d e t e c t e d b y l i m i t c h e c k i n g o f t h e a p p r o p r i a t e s i g n a l s

u n d e r p l a n t o p e r a t i o n . W h e n a d i s t u r b a n c e h a s b e e n d e t e c t e d , t h e d i a g n o s i s

4 1 8 M U RATA et al.

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IAEA-SM -268/20 419

FIG. 2. Operator support system configuration.

s u b s y s t e m w i l l c o m e i n t o o p e r a t i o n u s i n g c a u s e c o n s e q u e n c e t r e e ( C C T ) [ 7 ] ,

f a i l u r e p r o p a g a t i o n s i m u l a t o r ( F P S ) [ 8 ] a n d l o g i c a l m e t h o d s .

( i ) D i a g n o s i s b y C C T

T h e C C T m e t h o d h a s a l r e a d y b e e n d e s c r i b e d i n m a n y p a p e r s a n d t h e r e a d e r

i s r e f e r r e d t o t h e l i t e r a t u r e [ 7 ] . O n e n e w d e v e l o p m e n t i s t h e a u t o m a t i c g r a p h i c

d i s p l a y o f t h e C C T . U s u a l l y , t h e C C T i s c o m p o s e d o f h u n d r e d s o f n o d e s a n d

h a s m u l t i p l e c a u s e a n d c o n s e q u e n c e s t e p s . I t i s d i f f i c u l t t o d i s p l a y i t o n a C R T

a l l a t o n c e a n d t h e r e f o r e o p e r a t i o n s h a v e t o s e l e c t a p a r t o f t h e C C T o f i n t e r e s t .

B y i n t r o d u c i n g a n a u t o m a t i c g r a p h i c d i s p l a y , t h e m o s t s i g n i f i c a n t e v e n t i s a l w a y s

f o l l o w e d a n d d i s p l a y e d a u t o m a t i c a l l y o n t h e C R T w i t h o u t o p e r a t o r i n t e r v e n t i o n .

( i i ) D i a g n o s i s b y F P S

A f a i l u r e p r o p a g a t i o n s i m u l a t o r i s u s e d t o d e t e r m i n e t h e p r i m a r y c a u s e a n d

e s t i m a t e t h e p r o p a g a t i o n o f t h e f a i l u r e . T h i s m e t h o d i s a s f o l l o w s . F i r s t , a

4 2 0 M U RATA et al.

d i a g r a p h w h i c h s h o w s t h e f a i l u r e p r o p a g a t i o n n e t w o r k o f t h e p l a n t i s c o n ­

s t r u c t e d f r o m p l a n t d e v i c e s o r d e v i c e f a i l u r e m o d e s ( n o d e s ) a n d t h e r e l a t i o n

b e t w e e n f a i l u r e p r o p a g a t i o n a n d n o d e s ( b r a n c h e s ) . C a n d i d a t e s f o r t h e f a i l u r e

c a u s e a r e t h e n s e l e c t e d i n t h e d i a g r a p h b y b a c k - t r a c k i n g o n b r a n c h e s s t a r t i n g

f r o m t h e f a i l u r e p r o p a g a t e d n o d e s . T h e s e c a n d i d a t e s a r e s c r e e n e d b y b a c k ­

t r a c k i n g , s t a r t i n g f r o m n o r m a l s t a t e n o d e s , f a i l u r e p r o p a g a t i o n p r o b a b i l i t i e s a n d

f a i l u r e p r o p a g a t i o n t i m e s b e t w e e n a d j a c e n t n o d e s . F i n a l l y , t h e f a i l u r e p r o ­

p a g a t i o n p r o b a b i l i t i e s a n d t h e f a i l u r e r a t e s o f t h e d e v i c e s a r e u s e d t o e v a l u a t e

t h e p r i o r i t y r a n k i n g a m o n g t h e s c r e e n e d c a n d i d a t e s .

T h e m e t h o d m a k e s i t e a s y t o f i n d t h e f a i l u r e c a u s e a n d t o t a k e p r o p e r

c o u n t e r m e a s u r e s w h e n e v e r t h e d e t e c t o r i n f o r m s t h e o p e r a t o r s o f s o m e t h i n g w r o n g .

( i i i ) L o g i c a l m e t h o d

T h i s m e t h o d i s a p p l i e d t o p h e n o m e n a i n w h i c h t h e c a u s e s a n d c o n s e q u e n c e s

c a n b e e a s i l y c o n n e c t e d . W h e n s i g n a l c h a n g e s r e s u l t i n g f r o m f a i l u r e s a r e d e t e c t e d ,

t h e c a u s e i s e a s i l y i d e n t i f i e d a n d c o u n t e r m e a s u r e s t o b e t a k e n a r e e a s i l y p r o v i d e d .

3 . 3 . G u i d a n c e s u b s y s t e m

T h e g u i d a n c e i s g i v e n i n t w o d i f f e r e n t w a y s . O n e i s t o p r o v i d e g u i d a n c e

f r o m t h e s t a n d p o i n t o f s h u t t i n g t h e p l a n t d o w n b y e f f i c i e n t a n d p r o p e r m e a n s .

T h e o t h e r i s t o p r o v i d e g u i d a n c e o n s a f e t y a s p e c t s .

( i ) E v e n t - o r i e n t e d g u i d a n c e

E v e n t - o r i e n t e d g u i d a n c e p r o v i d e s o p e r a t i o n a l g u i d a n c e o n t h e b a s i s n o t o f

t h e i n i t i a l e v e n t o r p r i m a r y c a u s e o f t h e f a i l u r e b u t o f a c o m b i n a t i o n o f f o u r

e v e n t s ( a n o m a l y g r o u p s ) s u c h a s ‘m a i n s t e a m i s o l a t i o n v a l v e c l o s u r e ’ , ‘l o s s o f

f e e d w a t e r ’ , ‘s m a l l L O C A ’ a n d ‘n o t s m a l l L O C A ’. T h e s e e v e n t s a r e s e l e c t e d f r o m

t w o c o n s i d e r a t i o n s . O n e i s t o d e t e r m i n e w h i c h s y s t e m i s a v a i l a b l e t o m i t i g a t e t h e

a n o m a l o u s s t a t u s . T h e o t h e r i s t o d e t e r m i n e i f c o o l i n g w a t e r i s n e e d e d . F o r

e a c h a n o m a l y g r o u p , t h e m o s t e f f e c t i v e a n d p r o p e r m i t i g a t i o n s y s t e m i s s e l e c t e d

a n d i t s i n i t i a t i o n s e q u e n c e i s e s t a b l i s h e d b y n u m e r i c a l a n a l y s i s i n a d v a n c e .

O n - l i n e , t h i s g u i d a n c e i s e s t a b l i s h e d a c c o r d i n g t o t h e f o l l o w i n g p r o c e d u r e

( w h i c h i s a l s o i l l u s t r a t e d i n F i g . 3 ) .

F i r s t , t h e p l a n t c o n d i t i o n i s i d e n t i f i e d w i t h o n e o f t h e a n o m a l y g r o u p s

j u s t a f t e r f a i l u r e d e t e c t i o n . T h i s g r o u p i n g i s c a r r i e d o u t b y t h e d i a g n o s i s m e n t i o n e d

i n S e c t i o n 3 . 2 . S e c o n d , t h e m o s t e f f e c t i v e p l a n t s y s t e m i s s e l e c t e d d e p e n d i n g o n

t h e a n o m a l y g r o u p . T h i r d , t h e o p e r a t i o n a l g u i d a n c e i s d i s p l a y e d o n a C R T i f

t h e p l a n t c o n d i t i o n g o e s o v e r t o a s t a t e i n w h i c h a m i t i g a t i o n s y s t e m n e e d s t o b e

s t a r t e d . A f t e r t h e o p e r a t i o n i s c a r r i e d o u t a c c o r d i n g t o t h e g u i d a n c e , t h e p l a n t

IAEA-SM-268/20 421

FIG.3. Block diagram o f guidance system.

c o n d i t i o n i s a u t o m a t i c a l l y e v a l u a t e d . I f i t i s n o t a s e x p e c t e d , f u r t h e r g u i d a n c e

w i l l b e f u r n i s h e d .

( i i ) S y m p t o m - o r i e n t e d g u i d a n c e

E v e n t - o r i e n t e d g u i d a n c e t a k e s i n t o c o n s i d e r a t i o n t h e e v e n t a n d t h e s t a t u s

o f t h e p l a n t s y s t e m s . O n t h e o t h e r h a n d , s y m p t o m - o r i e n t e d g u i d a n c e i s d i r e c t e d

m a i n l y t o s y m p t o m s d e r i v e d f r o m t h e c r i t i c a l r e a c t o r s a f e t y p a r a m e t e r s .

T h i s g u i d a n c e i s u s e d w h e n t h e p l a n t s t a t u s i s n o t c l e a r l y d e t e r m i n e d b y

t h e e v e n t - o r i e n t e d g u i d a n c e o r t h e p l a n t c o n d i t i o n g o e s n e a r t h e s a f e t y l i m i t e v e n

a f t e r e x e c u t i o n o f e v e n t - o r i e n t e d o p e r a t i o n a l g u i d a n c e .

I n t h e s y m p t o m - o r i e n t e d g u i d a n c e p h a s e , a l l t h e m i t i g a t i n g a c t i o n s w h i c h

c a n b e t a k e n f o r a p a r t i c u l a r s a f e t y p u r p o s e s u c h a s t o m a i n t a i n t h e r e a c t o r

w a t e r l e v e l , d e p r e s s u r i z e t h e r e a c t o r p r e s s u r e s y s t e m i n t h e p r o p e r m a n n e r , e t c . ,

a r e l i s t e d . T h e o p e r a t i o n a l g u i d a n c e f o r t h e s e s y s t e m s i s t h e n g i v e n s e q u e n t i a l l y

4 2 2 M U RATA et al.

a c c o r d i n g t o t h e s y m p t o m s s h o w n b y t h e p l a n t s a f e t y p a r a m e t e r s , i n a s s o c i a t i o n

w i t h a n e v a l u a t i o n o f t h e r e s p o n s e a f t e r e v e r y s y s t e m t o m i t i g a t e t h e c o n d i t i o n s

h a s b e e n i n i t i a t e d . -

3 . 4 . S u p p o r t i n g s u b s y s t e m s

( i ) S a f e t y f u n c t i o n m o n i t o r

T h e c o n d i t i o n s o f t h e s a f e t y s y s t e m s a r e d i v i d e d r o u g h l y i n t o a s t a n d - b y

p h a s e , a m i n i m u m - f l o w o p e r a t i o n p h a s e a n d a n i n j e c t i o n p h a s e . T h e s a f e t y

f u n c t i o n m o n i t o r e v a l u a t e s w h e t h e r e v e r y s a f e t y s y s t e m p e r f o r m s i t s r o l e s a t

e a c h p h a s e a s r e q u i r e d b y t h e p l a n t c o n d i t i o n . T h e r e s u l t s o f t h e e v a l u a t i o n

a r e a p p l i e d t o s e l e c t t h e m o s t e f f e c t i v e p l a n t s y s t e m i n b o t h e v e n t - o r i e n t e d

a n d s y m p t o m - o r i e n t e d g u i d a n c e .

( i i ) P r e d i c t i v e s i m u l a t o r

T h e f u t u r e t r e n d s o f s i g n i f i c a n t p a r a m e t e r s , s u c h a s t h e r e a c t o r w a t e r

l e v e l a n d r e a c t o r v e s s e l p r e s s u r e , a r e p r e d i c t e d b y a c c e l e r a t e d n u m e r i c a l s i m u l a t i o n .

T h e i n i t i a l c o n d i t i o n s a r e g i v e n b y a u t o m a t i c c a l c u l a t i o n o r b y t h e o p e r a t i o n a l

p e r s o n n e l a n d t h e s a f e t y s y s t e m s a r e a s s u m e d t o p e r f o r m t h e i r r o l e s a s e x p e c t e d

f r o m t h e d e s i g n .

O n t h e b a s i s o f t h e s e a s s u m p t i o n s , t h e f u t u r e t r e n d j u s t a f t e r t h e f a i l u r e

o c c u r s c a n b e o b t a i n e d . T h e o p e r a t i o n a l p e r s o n n e l c a n c o m p a r e t h e a c t u a l p l a n t

r e s p o n s e w i t h t h e p r e d i c t e d r e s p o n s e .

4 . O F F - L I N E S I M U L A T I O N R E S U L T S

A l l t h e s u b s y s t e m s h a v e b e e n s e p a r a t e l y v e r i f i e d b y o f f - l i n e s i m u l a t i o n .

I n t h i s S e c t i o n , t w o t y p i c a l r e s u l t s ( F P S a n d e v e n t - o r i e n t e d g u i d a n c e s i m u l a t i o n )

a r e r e p o r t e d .

4 . 1 . F P S r e s u l t s

T h e F P S i s a p p l i e d t o t h e p r i m a r y l o o p r e c i r c u l a t i o n s y s t e m o f t h e B W R .

T h i s s y s t e m i s u s e d t o r e c i r c u l a t e t h e r e a c t o r c o o l a n t t o c h a n g e t h e r e a c t o r

p o w e r a n d i s c o m p o s e d o f m o t o r g e n e r a t o r s , p u m p s , a c o n t r o l s y s t e m , w a t e r

c o o l e r s u b s y s t e m a n d o i l c o o l e r s u b s y s t e m . A s a n e x a m p l e , t h e c a s e i n w h i c h

s e v e r a l t e m p e r a t u r e s e n s o r s i n d i c a t e h i g h t e m p e r a t u r e i s c o n s i d e r e d . F i r s t , t h e

p r i m a r y c a u s e i s l o o k e d f o r a n d f o u n d t o a r i s e i n t h e o i l c o o l e r s u b s y s t e m . T h e n

t h e p r o p a g a t i o n o f t h e f a i l u r e i s p r e d i c t e d a s s h o w n i n F i g . 4 .

IAEA-SM-268/20 4 2 3

O S E N S O R © A N O M A L O U S V A L U E

---------- F A I L U R E C A U S E ( E S T I M A T E D )

FIG. 4. Off-line simulation o f FPS.

4 . 2 . E v e n t - o r i e n t e d g u i d a n c e s i m u l a t i o n r e s u l t s

T h e e v e n t - o r i e n t e d g u i d a n c e i s a p p l i e d t o a m a i n s t e a m l i n e b r e a k a c c i d e n t

t o e v a l u a t e w h e t h e r t h e s y s t e m p r o v i d e s t i m e l y g u i d a n c e a b o u t t h e p l a n t s t a t u s

c h a n g e .

T h e r e s u l t s a r e s h o w n i n F i g . 5 . F i r s t , t h e h i g h p r e s s u r e c o r e c o o l i n g s y s t e m

( H P C S ) a n d t h e r e a c t o r c o r e i s o l a t i o n c o o l i n g s y s t e m ( R C I C ) a r e a u t o m a t i c a l l y

i n i t i a t e d i n r e s p o n s e t o t h e l o w r e a c t o r w a t e r l e v e l . A f t e r t h e r e a c t o r w a t e r l e v e l

i s b r o u g h t u n d e r c o n t r o l , i t i s r e c o m m e n d e d t h a t t h e s t e a m c o n d e n s i n g m o d e

b e u s e d t o d e c r e a s e t h e r e a c t o r p r e s s u r e . T h e m o d e , h o w e v e r , i s f o u n d t o

f a i l t o s t a r t . T h e n d e p r e s s u r i z a t i o n b y t h e s a f e t y - r e l i e f ( S / R ) v a l v e i s r e c o m ­

m e n d e d b y t h e g u i d a n c e s y s t e m . B y m e a n s o f t h e S / R v a l v e s t h e o p e r a t o r c a n

d e c r e a s e t h e r e a c t o r p r e s s u r e a n d b r i n g t h e p l a n t t o s a f e s h u t d o w n s t a t u s . I t i s

c l e a r l y s e e n t h a t t h e s y s t e m p r o v i d e s t i m e l y g u i d a n c e a b o u t t h e p l a n t s t a t u s c h a n g e .

5 . M A N - M A C H I N E S Y S T E M

T h i s p a p e r h a s s t r e s s e d t h e m e t h o d o l o g y . H o w e v e r , i t i s i m p o r t a n t t o

p r e s e n t t h e C O S S i n f o r m a t i o n s m o o t h l y t o t h e o p e r a t i o n a l p e r s o n n e l . T h e

i n f o r m a t i o n s h o u l d b e c l a s s i f i e d a n d a r r a n g e d a n d t h e n p r o v i d e d t o t h e p e r s o n n e l .

4 2 4 M U RATA et al.

Eo\ШJÉ

Шcc=>to(/)ШccQ.

trOh-O<lüСГ

T IME (h)

Э< G U 1 D E L I N E S E L E C T I O N S T A R T S >

A N O M A L Y G R O U P C L A S S I F I C A T I O N [ L O S S O F F W . M S I V C L O S U R E H A P P E N E D ]

c = J > G U I D A N C E F O R R E A C T O R L E V E L C O N T R O L S T A R T S ( R C I C , C R D )

ЭG U I D A N C E F O R D E P R E S S U R I Z A T I O N S T A R T S

( S T E A M C O N D E N S I N G M O D E O F R H R - S / R V )

dG U I D A N C E F O R R E S I D U A L H E A T R E M O V A L S T A R T S

( S H U T D O W N C O O L I N G M O D E O F R H R )

FIG.5. Guideline selection procedure fo r event-oriented guidance.

I n a c c o r d a n c e w i t h t h e f u n c t i o n s o f t h e C O S S , t h e i n f o r m a t i o n c a n b e c a t e g o r i z e d

i n t o t w o g r o u p s . O n e g r o u p s u p p o r t s k n o w l e d g e - b a s e d o p e r a t i o n s , a n d t h e o t h e r

g r o u p s u p p o r t s s k i l l - b a s e d o p e r a t i o n s .

T h e f o r m e r i n f o r m a t i o n , s u c h a s t h e o u t p u t s o f t h e F P S a n d t h e p r e d i c t i v e

s i m u l a t o r , h a s t o b e a c c e s s e d b y a d i a l o g u e m e t h o d , a n d t h e r e f o r e s h o u l d b e

d i s p l a y e d o n t h e s u p e r v i s o r y c o n s o l e . T h e l a t t e r , s u c h a s t h e o u t p u t s o f C C T

a n d t h e e v e n t - o r i e n t e d g u i d a n c e , s h o u l d b e o b t a i n e d w i t h o u t i n t e r v e n t i o n b y

t h e o p e r a t i o n a l p e r s o n n e l . T h e r e f o r e , i t s h o u l d b e p r e s e n t e d t h r o u g h t h e m a i n

IAEA-SM-268/20 425

FIG. 6. Provision o f information.

c o n t r o l c o n s o l e a s a u t o m a t i c a l l y a s p o s s i b l e . T h e f u n c t i o n s o f t h e C O S S a r e

c l a s s i f i e d a n d p r e s e n t e d a s i l l u s t r a t e d i n F i g . 6 . E a c h c o n s o l e i s e q u i p p e d w i t h

t h e n e c e s s a r y m a n - m a c h i n e i n t e r f a c e s t o a c c e s s t h e C O S S i n f o r m a t i o n .

B y m e a n s o f t h i s a r r a n g e m e n t , t h e i n f o r m a t i o n f r o m t h e C O S S i s r e c o g n i z e d

a n d r e a d i l y i n t e r p r e t e d i n t o p l a n t o p e r a t i o n b y t h e o p e r a t i o n a l p e r s o n n e l .

6 . C O N C L U D I N G R E M A R K S

( a ) T h e C C T a n d F P S d i a g n o s i s m e t h o d s p r o v i d e u s e f u l i n f o r m a t i o n t o t h e

o p e r a t i o n a l p e r s o n n e l .

( b ) T h e e v e n t - o r i e n t e d a n d s y m p t o m - o r i e n t e d g u i d a n c e s y s t e m s f u n c t i o n i n a

c o m p l e m e n t a r y m a n n e r a n d g i v e g u i d a n c e o n s h u t t i n g t h e p l a n t d o w n i n a

s a f e a n d r e l i a b l e w a y .

( c ) T h e i n f o r m a t i o n f r o m t h e C O S S i s c a t e g o r i z e d i n t o t w o g r o u p s . O n e i s f o r

k n o w l e d g e - b a s e d o p e r a t i o n a n d t h e o t h e r d i r e c t l y r e f l e c t s p l a n t o p e r a t i o n .

T h e s e r e s u l t s a r e n o t f i n a l b e c a u s e t h e C O S S i s s t i l l u n d e r d e v e l o p m e n t .

W e a r e n o w a t t e m p t i n g t o g e t m o r e f r u i t f u l r e s u l t s t h r o u g h v e r i f i c a t i o n t e s t s

u s i n g a n o n - l i n e p l a n t s i m u l a t o r .

4 2 6 M U RATA et al.

A C K N O W L E D G E M E N T S

T h e a u t h o r s w i s h t o e x p r e s s t h e i r g r a t i t u d e t o t h e s t a f f o f t h e C O S S

d e v e l o p m e n t p r o j e c t f o r t h e i r e n c o u r a g e m e n t a n d f o r f r u i t f u l d i s c u s s i o n s .

R E F E R E N C E S

[1] ELECTRIC POWER RESEARCH INSTITUTE, Computerized Operator Support System (Proc. Conf. Tampa), EPRI (Dec. 1980).

[2] YOSHITOSHI, H., NOH, K., HIRAKOCHI, Y., OKAMOTO, Y., ITOH, M., MONTA, К., “ Development of a computerized operator support system”, Nuclear Power Plant Control and Instrumentation 1982 (Proc. Symp. Munich, 1982), IAEA, Vienna (1983) 235.

[3] MURATA, F., et al., Development of a diagnosis system for a boiling water reactor, Nucl. Technol. 44(1979) 104.

[4] FUKUNISHI, K., Noise sources estimation of boiling water reactor power fluctuation by autoregression, Nucl. Sci. Eng. 67 (1978) 296.

[5] YANAI, K., NISHIZAWA, K., IIDA, H., NAKAMURA, H., JOGE, T., KIGUCHI, T., ITO, T., “Development of new plant monitoring and control systems with advanced man/machine interfaces” , Current Nuclear Power Plant Safety Issues (Proc. Conf. Stockholm, 1980), IAEA, Vienna (1981) 453.

[6] JOHGE, T., WAKABAYASHI, Y., MIYAKE, М., NIGAWARA, S., “Development of automatic plant start-up and shut-down system for BWR power plants” , Nuclear Power Plant Control and Instrumentation 1982 (Proc. Symp. Munich, 1982), IAEA, Vienna (1983) 475.

[7] MEIJER, C.H., FROGNER, B., On-Line Power Plant Alarm and Disturbance Analysis System, Rep. EPRI-NP-1379, Electric Power Research Inst., Palo Alto, CA (April 1980).

[8] KOKAWA, М., et al., Automática 18 3 (1982).

S U M M A R Y O F S E S S I O N V I I

C h a i r m a n : J . R a s m u s s e n

T h e p r e p a r a t i o n s m a d e i n F r a n c e a n d t h e U n i t e d K i n g d o m f o r a n e m e r g e n c y

a r i s i n g f r o m a c c i d e n t s i n n u c l e a r p o w e r p l a n t s s h o w s i m i l a r a p p r o a c h e s . A l l

s p e a k e r s e m p h a s i z e d t h e n e e d f o r a r r a n g e m e n t s t o b e m a d e f o r c o n s e q u e n c e s s o m e ­

w h a t w o r s e t h a n t h e d e s i g n b a s i s a c c i d e n t . T o a c h i e v e s u c c e s s i n t h e i m p l e m e n t a ­

t i o n o f e m e r g e n c y p l a n s , c o m m u n i c a t i o n f a c i l i t i e s h a v e t o b e e x t e n s i v e a n d

r e l i a b l e , t h e r e s p o n s i b i l i t i e s o f a l l o r g a n i z a t i o n s i n v o l v e d h a v e t o b e c l e a r l y d e f i n e d ,

t h e p u b l i c ( a n d p r e s s ) h a v e t o b e w e l l i n f o r m e d a n d a l l e m e r g e n c y a r r a n g e m e n t s

m u s t b e p e r i o d i c a l l y r e h e a r s e d . D e t a i l e d p l a n n i n g i s n e c e s s a r y f o r t h e i n i t i a l s t a g e s ,

b u t l a t e r s t a g e s r e q u i r e o n l y o u t l i n e a r r a n g e m e n t s w h i c h a r e c a p a b l e o f e x t e n s i o n

t o f i t m o r e s e r i o u s s i t u a t i o n s .

T h e o t h e r p a p e r s i n t h i s s e s s i o n c o v e r e d t h r e e d i f f e r e n t a s p e c t s o f e m e r g e n c y

p r e p a r e d n e s s . O n e c o n s i d e r e d t h e m e r i t s o f p r o v i d i n g a n e m e r g e n c y c o n t r o l r o o m

w h i c h i s p r o t e c t e d a g a i n s t e x t e r n a l i m p a c t s b y m e a n s o f a b u n k e r c o n s t r u c t i o n

b u t d u p l i c a t e s o n l y p a r t o f t h e m a i n c o n t r o l r o o m i n s t r u m e n t a t i o n . T h e r e a r e ,

h o w e v e r , g r e a t e r a d v a n t a g e s i n d e s i g n i n g t h e m a i n c o n t r o l r o o m t o b e h a b i t a b l e

f o r b o t h i n t e r n a l a n d e x t e r n a l e v e n t s . F r o m t h i s p o i n t o f v i e w a c o n s i d e r a b l e

i m p r o v e m e n t w a s c l a i m e d t o b e a c h i e v e d s i m p l y b y s i t i n g t h e m a i n c o n t r o l r o o m

a t g r o u n d l e v e l .

T h e s e c o n d a s p e c t w a s t h e p r o v i s i o n o f r e m o t e m o n i t o r i n g s o t h a t a p p r o p r i a t e

a u t h o r i t i e s c o u l d r e c e i v e i n f o r m a t i o n o n r a d i o a c t i v e r e l e a s e s t o e n a b l e t h e m t o

m a k e d e c i s i o n s i n a c c o r d a n c e w i t h t h e i r r e s p o n s i b i l i t i e s f o r t h e s a f e t y o f t h e

p u b l i c .

A t h i r d q u e s t i o n w a s t h e p r o v i s i o n o f a n o p e r a t o r s u p p o r t s y s t e m t o a s s e s s

p l a n t s t a t u s a n d p r o v i d e g u i d a n c e t o t h e o p e r a t o r w h e n a b n o r m a l e v e n t s o c c u r

o r e v e n w h e n l i m i t s d e f i n e d b y t e c h n i c a l s p e c i f i c a t i o n s a r e l i k e l y t o b e e x c e e d e d .

427

P an e l

F U T U R E A C T I V I T I E S T O I M P R O V E S A F E T Y O F O P E R A T I O N S

C h a i r m a n : F . K o s c i u s k o - M o r i z e t ( F r a n c e )

M e m b e r s : L . B e r t r o n ( F r a n c e )

T . H a g a ( J a p a n )

W .D . b a n n i n g ( U S A )

V . O s m a c h k i n ( I A E A )

G . A . V e r e t e n n i k o v ( U S S R )

R . D . W e n d l i n g ( F e d e r a l R e p u b l i c o f G e r m a n y )

S U M M A R Y O F D I S C U S S I O N

F o u r s u b j e c t s w e r e p r o p o s e d f o r d i s c u s s i o n :

( a ) M a n a g e m e n t o f n u c l e a r p o w e r p l a n t s

( b ) S a f e t y r e s e a r c h

( c ) F e e d b a c k o f o p e r a t i n g e x p e r i e n c e

( d ) I n t e r n a t i o n a l c o - o p e r a t i o n

M a n a g e m e n t o f n u c l e a r p o w e r p l a n t s

M r . B e r t r o n i n t r o d u c e d t h e f i r s t s u b j e c t b y r e c a l l i n g t h a t t h e t h r e e o b j e c t i v e s

— s a f e a n d e c o n o m i c o p e r a t i o n a n d h i g h p l a n t a v a i l a b i l i t y — a r e p e r f e c t l y

c o m p a t i b l e .

T h e m e m b e r s o f t h e p a n e l p r o p o s e d t h e f o l l o w i n g r e q u i r e m e n t s a s a i d s t o t h e

a c h i e v e m e n t o f t h e s e o b j e c t i v e s :

( a ) R e s p o n s i b i l i t i e s o f p l a n t p e r s o n n e l u n d e r n o r m a l a n d a c c i d e n t c o n d i t i o n s

s h o u l d b e a b s o l u t e l y c l e a r ;

( b ) O p e r a t o r s s h o u l d b e c o m p e t e n t t o c o p e w i t h a c c i d e n t c o n d i t i o n s , i n c l u d i n g

t h o s e w i t h l o w p r o b a b i l i t i e s ;

( c ) I n f o r m a t i o n a v a i l a b l e t o t h e o p e r a t o r a n d o p e r a t i n g i n s t r u c t i o n s s h o u l d

b e c l e a r ;

( d ) T h e o p e r a t o r s s h o u l d b e o r g a n i z e d i n t o w e l l - m o t i v a t e d t e a m s t o m a i n t a i n

s a f e t y n e e d s ;

( e ) T h e q u a l i t y a s s u r a n c e o r g a n i z a t i o n s h o u l d a s s i s t i n r e d u c i n g e r r o r s ;

( f ) I n c i d e n t s s h o u l d b e a n a l y s e d a n d p r e c u r s o r e v e n t s o f s i g n i f i c a n c e s h o u l d b e

i d e n t i f i e d .

4 2 9

4 3 0 P A N EL

A d i f f i c u l t p r o b l e m i s t h a t o f e n s u r i n g t h a t t h e a b o v e r e q u i r e m e n t s a r e

i m p l e m e n t e d . T w o s t e p s t h a t a r e n e e d e d a r e t o e n c o u r a g e s a f e t y c o n s c i o u s n e s s

a m o n g p e r s o n n e l a n d t o p r e v e n t c o m p l a c e n c y c a u s e d b y t h e l a c k o f s e r i o u s

i n c i d e n t s .

S a f e t y r e s e a r c h

M r . H a g a p r o p o s e d t h a t t w o s u b j e c t s n e e d e d t o b e i n c l u d e d i n s a f e t y r e s e a r c h .

T h e f i r s t i s t h e d e v e l o p m e n t o f s t a n d a r d p r o c e d u r e s f o r e m e r g e n c y c o n d i t i o n s ,

u s i n g f o r i n s t a n c e s t a n d a r d s c e n a r i o s s o t h a t t h e a u t h o r i t i e s i n a n y c o u n t r y c o u l d

a r r iv e a t t h e s a m e c o n c l u s i o n s f o r i d e n t i c a l s c e n a r i o s . T h e s e c o n d i s t h e d e v e l o p ­

m e n t o f c o m p u t e r a n a l y s e s f o r c o m p a r i s o n w i t h d y n a m i c t e s t s , s o t h a t t h e

c o m p u t e r p r o g r a m s c a n b e v a l i d a t e d .

T h e p a n e l m e m b e r s n o t e d t h a t s t a n d a r d s c e n a r i o s a r e l i k e l y t o b e l i m i t e d t o

s i m i l a r p l a n t s . S e v e r a l a l s o m e n t i o n e d t h e e f f o r t s b e i n g m a d e t o c o r r e l a t e

t h e o r e t i c a l s t u d i e s w i t h p l a n t b e h a v i o u r a c t u a l l y e x p e r i e n c e d .

F e e d b a c k o f o p e r a t i n g e x p e r i e n c e

M r . W e n d l i n g c o n s i d e r e d t h e r e w a s a p r o b l e m i n m a k i n g e f f e c t i v e u s e o f

o p e r a t i n g e x p e r i e n c e . T h e O E C D / N E A a n d I A E A e f f o r t s i n t h i s f i e l d c a n b e n e f i t

t h e n u c l e a r c o m m u n i t y , b u t e a c h c o u n t r y w o u l d n e e d t o e v a l u a t e t h e i n f o r m a t i o n

i t r e c e i v e s i n o r d e r t o d r a w i t s o w n c o n c l u s i o n s .

M r . b a n n i n g e m p h a s i z e d t h e n e e d f o r i n c i d e n t r e p o r t s t o b e a c c u r a t e a n d

d e t a i l e d e n o u g h t o e n a b l e c o r r e c t a n d c o m p l e t e e v a l u a t i o n s t o b e m a d e .

T h e p a n e l m e m b e r s u n d e r l i n e d t h e i m p o r t a n t p a r t p l a y e d b y t h e o p e r a t o r

a n d t h e n e e d f o r a g o o d u n d e r s t a n d i n g o f t h e i n c i d e n t s t o b e r e p o r t e d . E x p e r i e n c e

f r o m c o n v e n t i o n a l p l a n t s i s a l s o u s e f u l .

I n t e r n a t i o n a l c o - o p e r a t i o n

M r . O s m a c h k i n c o n s i d e r e d i n t e r n a t i o n a l c o - o p e r a t i o n t o b e e s s e n t i a l i n t h e

s a f e t y f i e l d , s i n c e a n a c c i d e n t i n a n u c l e a r p o w e r p l a n t i n o n e c o u n t r y h a s

i m p l i c a t i o n s i n o t h e r c o u n t r i e s . T h e I A E A m a y b e a b l e t o s u p p o r t o p e r a t o r s i n

M e m b e r S t a t e s b y p r o v i d i n g c o m p u t e r f a c i l i t i e s d u r i n g a c c i d e n t c o n d i t i o n s , w i t h

e x p e r t s t o u n d e r t a k e c a l c u l a t i o n s , a n d a l s o b y m a k i n g a v a i l a b l e s i m u l a t o r

f a c i l i t i e s t o t r a i n o p e r a t o r s f o r n o r m a l a n d a c c i d e n t c o n d i t i o n s o n a n i n t e r n a t i o n a l

b a s i s .

T h e p a n e l m e m b e r s g e n e r a l l y e x p r e s s e d s u p p o r t f o r i n t e r n a t i o n a l c o - o p e r a t i o n

i n s a f e t y r e s e a r c h a n d f o r t h e i n t e r n a t i o n a l e f f o r t s i n t h e u t i l i z a t i o n o f o p e r a t i n g

e x p e r i e n c e , a l t h o u g h b i l a t e r a l c o - o p e r a t i o n i n t h i s l a t t e r f i e l d , p a r t i c u l a r l y b e t w e e n

o p e r a t i n g o r g a n i z a t i o n s , i s a l s o c o n s i d e r e d t o b e v e r y v a l u a b l e .

P A N EL 431

I n h i s s u m m i n g u p , t h e C h a i r m a n n o t e d t h a t t h e r e w a s a c o n s e n s u s o f

o p i n i o n a m o n g p e o p l e f r o m m a n y d i f f e r e n t c o u n t r i e s , a s a r e s u l t o f w h i c h :

— a c o n t i n u o u s e f f o r t w a s b e i n g m a d e t o i m p r o v e s a f e t y b y u t i l i z i n g o p e r a t i o n a l

e x p e r i e n c e ;

- p r i o r i t y w a s b e i n g g i v e n t o u n d e r s t a n d i n g t h e h u m a n f a c t o r s , a n d p a r t i c u l a r l y

t o i m p r o v i n g t h e m a n - m a c h i n e i n t e r f a c e a n d t h e a r r a n g e m e n t o f t h e o p e r a t o r

t e a m s .

T h e C h a i r m a n u n d e r l i n e d t h e n e e d t o c o n v i n c e t h e p u b l i c o f t h e h i g h l e v e l s

o f s a f e t y a c h i e v e d i n n u c l e a r p o w e r p l a n t s .

S e s s i o n I V

S e s s i o n V

S e s s i o n V I

S e s s i o n V I I

P a n e l

S c i e n t i f i c

S e c r e t a r y :

S p e c i a l

A s s i s t a n t

A d m i n i s t r a t i v e

S e c r e t a r y :

E d i t o r s :

C H A I R M E N O F S E S S IO N S

W . R O E H N S C H G e r m a n D e m o c r a t i c R e p u b l i c

F . Y a . O V C H I N N I K O V U S S R

T . P . H A I R E U n i t e d K i n g d o m

H . F U K U M O T O J a p a n

J . R A S M U S S E N D e n m a r k

F . K O S C I U S K O - M O R I Z E T F r a n c e

S E C R E T A R I A T

V . O S M A C H K I N D i v i s i o n o f N u c l e a r S a f e t y ,

I A E A , V i e n n a

H . W R I G H T D i v i s i o n o f N u c l e a r S a f e t y ,

I A E A , V i e n n a

C . D E M O L

V A N O T T E R L O O

D i v i s i o n o f E x t e r n a l R e l a t i o n s ,

I A E A , V i e n n a

J . - N . A Q U I S T A P A C E

R . F . K E L L E H E R

D i v i s i o n o f P u b l i c a t i o n s ,

I A E A , V i e n n a

4 3 3

L I S T O F P A R T I C I P A N T S

A N D D E S I G N A T I N G M E M B E R S T A T E S

A N D O R G A N I Z A T I O N S

A R G E N T I N A

Perl, H.

A U S T R A L I A

Wilson, A.R.W.

B E L G I U M

Contratto, R.J.

Deckers, B.

De Clercq-Versele, H.M.H.

Decreton, M.

Dozinel, P.A.

Renard, A.F.

Staellaert, P.

Comisión Nacional de Energía Atómica,Avenida del Libertador 8250, 1429-Buenos Aires

Australian Atomic Energy Commission, Regulatory Bureau,549 Gardiners Road, Mascot, NSW 2020

Westinghouse Nuclear International-Europe, Rue de Stalle 73, В-1180 Bruxelles

Association Vinçotte,Chaussée de Waterloo 935, B-l 180 Bruxelles

Institut d’hygiène et d’épidémiologie,Rue J. Wytsman 14, B -l050 Bruxelles

Centre d’étude de l’énergie nucléaire, Boeretang 200, B-2400 Mol

Tractionel,Rue de la Science 31, B -l040 Bruxelles

Belgonucléaire SA,Rue du Champ de Mars 25, B -l050 Bruxelles

Ministère de la Santé publique,Quartier Vésale, B -l000 Bruxelles

4 35

4 3 6 L IS T O F PA RT IC IPA N TS

B R A Z I L

Almeida, C.U.C.De Lima, J.M.

C A N A D A

Black, D.W.

Comeau, J.G.

Natalizio, A.

C Z E C H O S L O V A K I A

Beránek, J.

Havlicek, J.

Kiett, V.

Ziman, V.

D E N M A R K

Hansen, J.L.

Hoejgaard, K.E.

Jensen,A.

Comissáo Nacional de Energía Nuclear, Rua General Severiano, 90, Botafogo, 22.294 Rio de Janeiro, RJ

Atomic Energy of Canada Ltd, Engineering Company, Sheridan Park Research Community,Mississauga, Ontario L5K 1B2

New Brunswick Electric Power Commission,Point Lepreau Generating Station,Lepreau, New Brunswick EOG 2H0

Atomic Energy of Canada Ltd, Engineering Company, Sheridan Park Research Community,Mississauga, Ontario L5K 1B2

Czechoslovak Atomic Energy Commission, Slezská 9, Praha 2

Skoda - ZVE,Spálená 17, CS-110 00 Praha 1

Nuclear Research Institute,CS-250 68 Reü (Praha)

Nuclear Power Station,CS-919 31 Jaslovské Bohunice

Inspectorate of Nuclear Installations,Ris0 Huse, P.O. Box 217, DK-4000 Roskilde

Elsam,DK-7000 Fredericia

Danatom,Allégade 2, DK-4000 Elsinere

L IS T OF PA RT IC IPA N TS 4 37

Rasmussen, J.

Zakora, M.

Ris0 National Laboratory,P.O. Box 49, DK-4000 Roskilde

Inspectorate of Nuclear Installations,Risф Huse, P.O. Box 217, DK-4000 Roskilde

F I N L A N D

Âkesson, T.E.

Junttila, J.J.

Karling, K.J. Komsi, M.J.

Rannila, P.

Rinttilá, E.

Sjôblom, K.Â.H.

Wahlstrôm, B.

Institute of Radiation Protection,P.O. Box 268, SF-00101 Helsinki 10

Electronics Division, Nokia Electronics, P.O. Box 780, SF-00101 Helsinki 10

Imatran Voima Power Company,P.O. Box 138, SF-00101 Helsinki 10

Institute of Radiation Protection,P.O. Box 268, SF-00101 Helsinki 10

Imatran Voima Power Company,P.O. Box 138, SF-00101 Helsinki 10

Imatran Voima Power Company, Loviisan voimalaitos, SF-07900 Loviisa

Electrical Engineering Laboratory, Technical Research Centre of Finland, Vuorimiehentie 5, SF-02150 Espoo 15

F R A N C E

Amiel, A.

Ancelin, C.

Argillier, B.

Sintra — Alcatel,76, avenue Gabriel Péri, F-92730 Gennevilliers

Département Physique des réacteurs,Direction des études et recherches,Electricité de France (EDF),1, avenue du Général de Gaulle,F-92141 Clamart Cedex

EDF, Direction des études et recherches,6, quai Watier, B.P. 49, F-78400 Chatou

Augustin, B. Secrétariat général du Comité interministériel de la sécurité nucléaire,

54, rue de Varenne, F-75007 Paris

4 3 8 L IS T OF PA RT IC IPA N TS

Auvergnon, F.

Avenas, M.

Barbet, J.F.

Bergeret, J.-P.

Bernard, A.

Bertagnolio, D.

Bertron, L.

Bessou, F.

Blot, F.

Bluet, J.-C.

Bonnemay, A.

Bordignon, S.

Botte, D.

F R A N C E (c o n t .)

Cabannes, J.-L.

Sofinel,Tour Fiat, Cedex 16, F-92084 Paris La Défense

Service central de sûreté des installations nucléaires, Ministère de l’Industrie et de la recherche,99, rue de Grenelle, F-75700 Paris Cedex

EDF, Département Physique des réacteurs,Direction des études et recherches,1, avenue du Général de Gaulle,F-92141 Clamart Cedex

Sofratome,Tour Horizon,52, quai de Dion Bouton,F-92806 Puteaux

CEA, Centre d’études de Valduc,B.P. 14, F-21120 Is-sur-Tille

EDF, Région Equipement,Parc de Grandmont, B.P. 1808, F-37018 Tours

EDF, Service de la production thermique,3, rue de Messine, F-75384 Paris Cedex 08

EDF,140, avenue Viton, B.P. 560, F-13401 Marseille Cedex 9

Cerci Grenoble,Zirst 4, Chemin du Vieux-Chêne, F-38240 Meylan

CEA, Centre d’études nucléaires (CEN) de Cadarache, B.P. 1, F-13115 Saint-Paul-lez-Durance

CEA, CEN de Saclay,B.P. 2, F-91191 Gif-sur-Yvette Cedex

EDF, Région d’équipement Alpes-Lyon,35—37, rue Louis Guérin, F-69100 Villeurbanne

EDF, Région d’équipement Tours,Aménagement de Dampierre,B.P. 5, F-45570 Ouzouer-sur-Loire

EDF, Région d’équipement Alpes-Marseille,140, avenue Viton, F-13401 Marseille Cedex 9

L IS T OF PA RT IC IPA N TS 4 3 9

Cahuzac, A.

Calamand, A.

Candiotti, C. Cassette, P.

Cayol, A.

Chiron, A.

Comillon, J.R.

d’Argentre, E. de Braquilanges, B.

de Lapparent, D.

de Mazancourt, R.

Derive, C.

Destot, M.

de Tonnac, A.

Dredemis, G.

Dupraz, R.

EDF, Direction des études et recherches,1, avenue du Général de Gaulle,F-92141 Clamart Cedex

Framatome,Tour Fiat, Cedex 16, F-92084 Paris La Défense

Commissariat à l’énergie atomique,31—33, rue de la Fédération, B.P. 510,F-75752 Paris Cedex 15

EDF, Service de la production thermique,3, rue de Messine, F-75384 Paris Cedex 08

Société Bertin,B.P. 3, F-78373 Plaisir

CGEE Alsthom,13, rue Antonin-Raynaud,F-92309 Levallois-Perret Cedex

Novatome,20, avenue Edouard-Herriot,F-92350 Le Plessis-Robinson

CEA, CEN de Cadarache,B.P. 1, F-13115 Saint-Paul-lez-Durance

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

EDF, Direction des études et recherches,6, quai Watier, B.P. 49, F-78400 Chatou

CEA,31—33, rue de la Fédération, B.P. 510,F-75752 Paris Cedex 15

Framatome,Tour Fiat, Cedex 16, F-92084 Paris La Défense

CEA,31—33, rue de la Fédération, B.P. 510,F-75752 Paris Cedex 15

Novatome,20, avenue Edouard-Herriot,F-92350 Le Plessis-Robinson

4 4 0 L IS T OF PA RT IC IPA N TS

F R A N C E ( c o n t . )

Eschbach, C.

Fabre, C.Favez,B.

Feger, M.Felgines, R.

Feltin, C.

Feraud, R.

Fourest, B.

Fournier, C.

Francillard, D.

Gachot, B.Garcin, G.

Gauvenet, A.

Giroux, C. Gomolinski, M. Gouffon, A.

Griffon-Fouco, M.

Gros, G.

Gutner, G.

Halpem, О.

EDF,3, rue de Messine, F-75384 Paris Cedex 8

EDF, Région d’équipement Alpes-Marseille,140, avenue Viton, F - l3401 Marseille Cedex 9

EDF, Mission d’assistance aux centrales étrangères (MACE),

11 — 13, avenue de Friedland, F-75008 Paris

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

EDF, Région d’équipement Alpes-Marseille,140, avenue Viton, F-13401 Marseille Cedex 9

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

CEA, Centre d’études de Valduc,B.P. 14, F-21120 Is-sur-Tille

Sofratome,Tour Horizon, 52, quai de Dion Bouton,F-92806 Puteaux

EDF, Région d’équipement Alpes-Marseille,140, avenue Viton, F-13401 Marseille Cedex 9

EDF,32, rue de Monceau, F-75384 Paris Cedex 8

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

EDF, Service de la production thermique,3, rue de Messine, F-75384 Paris Cedex 08

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

EDF,6, quai Watier, B.P. 49, F-78400 Chatou

Secrétariat général du Comité interministériel de la sécurité nucléaire,

54, rue de Varenne, F-75007 Paris

L IS T OF PA RT IC IPA N TS 441

Hillairet, J.

Jacquot, J.P.

Jeandidier, C. Kechavarzi, C.

Knockaert, T.

Kosciusko-Morizet, F.

Lancereau, P.

Laurent, R.

Lavérie, M.

Lebouleux, Ph.

Magnon, B.

Malherbe, J.-F.

Manin, P.

Marcille, R.Mercier, J.-P.

Mira, J. J.

Moriette, P.

EDF, Région d’équipement Alpes-Marseille,140, avenue Viton, F-13401 Marseille Cedex 9

EDF, Direction des études et recherches,6, quai Watier, B.P. 49, F-78400 Chatou

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

EDF,11-13, avenue de Friedland, F-75008 Paris

Ministère de l’Industrie et de la recherche,99, rue de Grenelle, F-75007 Paris

Service des piles, Groupe physique,CEA, CEN de Grenoble,Avenue des Martyrs, 85 X, F-38041 Grenoble Cedex

EDF, Direction des études et recherches,6, quai Watier, B.P. 49, F-78400 Chatou

Service central de sûreté des installations nucléaires, Ministère de l’Industrie et de la recherche,99, rue de Grenelle, F-75700 Paris Cedex

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

EDF, Région d’équipement Alpes-Lyon,2, rue Curtelin, F-69006 Lyon

Secrétariat général du Comité interministériel de la sécurité nucléaire,

54, rue de Varenne, F-75007 Paris

Cerci Grenoble,Zirst 4, Chemin du Vieux-Chêne, F-38240 Meylan

EDF, Service de la production thermique,3, rue de Messine, F-75384 Paris Cedex 08

EDF, Service de la production thermique,3, rue de Messine, F-75384 Paris Cedex 08 (See also under World Energy Conference)

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

Morlat, G.

Nicolet, J.-L.

Oliot, A.

Olivry, J.L.

Ortal, C.

Pelloux, J.C.

Pelouzet, J.

Poujol, A.

Procaccia, H.

Puyal, C.

Quenon, J.

Quinton, J.C.

Reneaud, J.-M.

Roche, J.P.

4 4 2

F R A N C E (c o n t .)

L IS T O F PA RT IC IPA N TS

EDF, Direction des études et recherches,1, avenue du Général de Gaulle,F-92141 Clamart Cedex

Euréquip,19, rue Yves Dumanoir, F-92420 Vaucresson

Framatome,Tour Fiat, Cedex 16, F-92084 Paris La Défense

EDF, Studio Audio visuel,6, rue Ampère, F-93200 Saint-Denis

EDF, Groupe régional de production thermique,Allée des Fenaisons, B.P. 664, F-84032 Avignon Cedex

EDF, Région d’équipement Alpes-Marseille,140, avenue Viton, F-13401 Marseille Cedex 9

CEA, Centre d’études scientifiques et techniques d’Aquitaine,

B.P. 2, F-33114 Le Barp (Belin Beliet)

CEA, CEN de Saclay,F-91191 Gif-sur-Yvette Cedex

EDF, Direction des études et recherches,25, allée Privée, Carrefour Pleyel,F-93206 Saint-Denis Cedex 1

EDF, Division surveillance et diagnostic,Direction des études et recherches,6, quai Watier, B.P. 49, F-78400 Chatou

G/C Engineers & Consultants, Berkeley Building, 19/29, rue du Capitaine Guynemer, Cedex 19 F-92081 Paris La Défense

CEA, CEN de Cadarache,F-13115 Saint-Paul-lez-Durance

Eurodif production,B.P. 175, F-26702 Pierrelatte Cedex

EDF, Région d’équipement Alpes-Marseille,140, avenue Viton, F-13401 Marseille Cedex 9

L IS T O F PA RT IC IPA N TS 4 4 3

Rodriguez, A.

Rolland, P.

Schwartz, A.

Sicard, Y.

Sureau,H.

Tabouret, Y.

Tournier, B.

Vaissiere, M.

Villemeur, A.

Vittet, J. Zermizoglou, R.

Zwingelstein, G.

EDF, Région d’équipement Paris,22/30, avenue de Wagram, F-75008 Paris

EDF, Service de la production thermique,3, rue de Messine, F-75384 Paris Cedex 08

EDF, Région d’équipement Alpes-Marseille,140, avenue Viton, F-13401 Marseille Cedex 9

Labsys, Cermo,B.P. 53, F-38000 Grenoble

EDF-Septen,Tour EDF-GDF, Cedex 8, F-92080 Paris La Défense

D 11 PACAC,37, boulevard Périer, F-13285 Marseille Cedex 02

CEA, Centre d’études de Valduc,B.P. 14, F-21120 Is-sur-Tille

EDF, Région d’équipement Paris,30, avenue de Wagram, F-75008 Paris

EDF, Département physique des réacteurs,Division des études et recherches,1, avenue du Général de Gaulle,F-92141 Clamart Cedex

CEA, CEN de Fontenay-aux-Roses,B.P. 6, F-92260 Fontenay-aux-Roses

EDF, Direction des études et recherches,6, quai Watier, B.P. 49, F-78400 Chatou

G E R M A N D E M O C R A T I C R E P U B L I C

Brune, W. Staatliches Amt für Atomsicherheit undRoehnsch, W. Strahlenschutz,

Waldowallee 117, DDR-1157 Berlin

G E R M A N Y , F E D E R A L R E P U B L I C O F

Bohr, E. Technischer Uberwachungs-Verein (TUV) Rheinland, Postfach 10 17 50, D-5000 Kôln 1

4 4 4 L IS T OF PA RT IC IPA N TS

G E R M A N Y , F E D E R A L R E P U B L IC O F (c o n t .)

Brust, E.P.

Dietlmeier, W.

Girke, H.

Hartfiel, H.-D.

Krings, T.

Maier, E.

Nowak, K.

Rheinisch-Westfâlischer TUV eV,Richard Wagner-Strasse 5, D-4300 Essen 1

Industrieanlagen-Betriebsgesellschaft mbH, Einsteinstrasse 20, D-8012 Ottobrunn

TÜV Norddeutschland eV,Grosse Bahnstrasse 31, D-2000 Hamburg 54

Kraftwerk Union AG,Hammerbacherstrasse 12—14, Postfach 3220, D-8520 Erlangen

TÜV Bayern eV,Westendstrasse 199, D-8000 München 21

Gesellschaft für Reaktorsicherheit, Schwertnergasse 1, D-5000 Kôln 1

TÜV Rheinland, Institut für Unfallforschung, Postfach 10 17 50, D-5000 Kôln 1

Richter, H.

Sartori, R.

Schnadt, H.

Schüler, R.

Simon, M.

Sunder, R.

Gesellschaft für Reaktorsicherheit,Schwertnergasse 1, D-5000 Kôln 1

Rheinisch-Westfâlischer TUV eV,Steubenstrasse 53, D-4300 Essen 1

TÜV Rheinland, Institut für Unfallforschung, Postfach 10 17 50, D-5000 Kôln 1

Rheinisch-Westfâlischer TÜV eV,Langemarckstrasse 20, D-4300 Essen 13

Gesellschaft für Reaktorsicherheit (GRS) mbH, Schwertnergasse 1, Postfach 10 16 50, D-5000 Kôln 1

Gesellschaft für Reaktorsicherheit mbH, Forschungsgelànde, D-8046 Garching

Wendling, R.D. Bundesministerium des Innem, Graurheindorferstrasse, D-5300 Bonn

Wildberg, D.W. TÜV Baden,Dudenstrasse 28, Postfach 2420, D-6800 Mannheim 1

L IS T OF PA RTIC IPA N TS 445

Czoch, I.

Tóth, I.

Vamos, G.

H U N G A R Y

National Atomic Energy Commission, P.O. Box 565, H-1374 Budapest

Central Research Institute for Physics, P.O. Box 49, H-1525 Budapest

Paks Nuclear Power Plant,P.O. Box 71, H-7031 Paks

I N D I A

Bhasin, B.K. Tarapur Atomic Power Station, Department of Atomic Energy, District Thana, Maharastra 401 504

Murthy, L.G.K. Reactor Analysis and Studies Section, Bhabha Atomic Research Centre, Trombay, Bombay 400 085

I T A L Y

Basso, G.

Bertini, A.

de Luccia, R. Eletti, G.

Fusari, W.

Giordano, P.

Giulianelli, S.

Nobile, M.

Comitato nazionale per la ricerca e per lo sviluppo dell’ energía nucleare (ENEA),

Viale Regina Margherita 125,1-00198 Roma

Ente Nazionale per l’Energia Elettrica (ENEL), Via G.B. Martini 3,1-00198 Roma

ENEA,Viale Regina Margherita 125,1-00198 Roma

ENEL,Viale Regina Margherita 137,1-00198 Roma

Nucleare Italiana Reattori Avanzati (NIRA) SpA, Via dei Pescatori 35, Genova

ENEA,Viale Regina Margherita 125, 1-00198 Roma

ENEL,Via G.B. Martini 3,1-00198 Roma

Rogani, A. Laboratorio di Fisica, Istituto Superiore di Sanità, Viale Regina Elena 299,1-00161 Roma

4 4 6 L IS T O F PA RT IC IPA N TS

I T A L Y ( c o n t . )

Tabellini, G.

Tabet, E.

Tripputi, I.

ENEA,Via dell’Arcoveggio 5 6 /2 3 ,1-40129 Bologna

Laboratorio di Fisica, Istituto Superiore di Sanità, Viale Regina Elena 299,1-00161 Roma

ENEL,Via G.B. Martini 3,1-00198 Roma

J A P A N

Fukumoto, H.

Haga, T.

Monta, К.

Murata, F.

Neda, T.

Ogino, T.

Taniguchi, K.

Tomizawa, T.

Energy and Environment Laboratory,Central Research Institute of Electric Power Industries,2—11 — 1, Iwato-Kita, Komae-shi, Tokyo 201

Institute of Nuclear Safety,Mita Kokusai Building,1—4—28,Mita, Minato-ku, Tokyo 108

Nippon Atomic Industry Group Co. Ltd,4-l,U kishim a-cho, Kuwasaki-ku, Kawasaki-shi

Nuclear Power Generation Division,Hitachi Works, Hitachi Ltd,3—1 —l,Saiwaicho, Hitachi-shi, Ibaraki-ken

Power Generation Control Systems Department,Fuchu Works, Toshiba Corporation,1, Toshiba-cho, Fuchu-shi, Tokyo 183

Nuclear Technology Group, Central Research Laboratory, Mitsubishi Electric Corporation,

8 -1 - 1 , Tsukaguchi Honmachi, Amagasaki, Hyogo 661

Hitachi Energy Research Laboratory,1168 Moriyama, Hitachi-shi, Ibaraki-ken

Control and Electrical Engineering Dept,Nuclear Energy Group, Toshiba Corporation, 3 -1 3 -1 2 , Mita, Minato-ku, Tokyo 108

Tsuyuki, T. Tokyo Electric Power Company, London Office, 30 Charles II Street, London, United Kingdom

L IS T O F PA RTIC IPA N TS 447

N E T H E R L A N D S

Montizaan, J.

Van Daatselaar, J.

N O R W A Y

Ф fjord, K.

Sekkesaeter, H.

P O L A N D

Byszewski, W.

Nycz, C.

P O R T U G A L

Assunçâo, J. Henrique da Silva, M.

Santos Bento, J.

S O U T H A F R I C A

Els, J.S.

Hellstrôm, G.F.

Netherlands Energy Research Foundation (ECN), P.O. Box 1, NL-1755 ZG Petten

Nuclear Department, Ministry of Social Affairs, B. van Anderplein 2, P.O. Box 69, Voorburg

Norwegian Nuclear Energy Safety Authority, Statens Atomtilsyn, P.O. Box 2495 Solli, Oslo 2

Institute for Energy Technology,P.O. Box 40, N-2007 Kjeller

Institute of Nuclear Research, PL-05-400 Otwock

Department of Technical Progress, Ministry of Mining and Power, ul. Krucza 36, PL-00-921 Warszawa

Gabinete de Protecçio e Segurança Nuclear, Av. da República, 4 5 -6 ° , P-1000 Lisboa

Electricidade de Portugal,Rua Conde Redondo, 145—3°, P-l 100 Lisboa

Electricity Supply Commission (ESCOM), P.O. Box 1091, Johannesburg 2000

ESCOM,P.O. Box 6117, Roggebaai 8012

Jones, I.O. Pabot, J.L.

ESCOM,P.O. Box 1091, Johannesburg 2000

4 4 8 L IS T O F PA RT IC IPA N TS

S O U T H A F R I C A ( c o n t . )

Semark, P.M.

Walmsley, J.W.

S P A I N

Castellón Leal, J.M.

Reig, J.

Sustacha, A.

S W E D E N

Hellstrand, E.Johansson, G.Nilson, R.M.

Persson, P.I.

S W I T Z E R L A N D

Ammon, H.

Buclin, J.-P.

Dinkelacker, H.

Hürlimann, T.G.

Robert, A.

ESCOM, Koeberg Power Station, Private Bag X10, Melkbosstrand, Cape

ESCOM,P.O. Box 1091, Johannesburg 2000

Hidroeléctrica Española, S.A., Hermosilla 3, Madrid

Consejo de Seguridad Nuclear,Cáseo de la Castelliano 135, Madrid-16

Ente Vasco de la Energía,Edificio Albia H-8, Bilbao-1

Reactor Technology Department,Studsvik Energiteknik AB,S-611 82 Nykoping

Nuclear Safety Board of the Swedish Utilities, P.O. Box 5864, S-10248 Stockholm

Centre nucléaire Gosgen-Dâniken,B.P. 55, CH-4858 Daniken

Division principale pour la sécurité des installations nucléaires,

Office fédéral de l’énergie,CH-3003 Bern

Hauptabteilung fiir die Sicherheit von Kemanlagen, CH-5303 Wiirenlingen

Eidgenôssisches Institut fiir Reaktorforschung, CH-5300 Wiirenlingen

Electrowatt,P.O. Box 8022, Zürich

L IS T O F PA RT IC IPA N TS 4 4 9

T U R K E Y

Ozdemir, A. Reactor Safety and Licensing Division,Turkish Atomic Energy Authority,Karantil Sokak No.67, Bakanliklar, Ankara

U N I O N O F S O V I E T S O C I A L I S T R E P U B L I C S

Bagdasarov, Yu.E.

Cherkashov, Yu.M.

Ovchinnikov, F.Ya.

Poletaev, G.N.

Veretennikov, G.A.

Institute for Physics and Power Engineering, Obninsk

Scientific Research and Design Institute of Power Technology,

Moscow

International Economic Association (IEA), Interatomenergo,Moscow

I.V. Kurchatov Institute of Atomic Energy, Moscow

USSR Ministry of Energetics and Electrification, Moscow

U N I T E D K I N G D O M

Cave, L.

Davidson, P.H.

Goodison, D. Gronow, W.S.

Haire, T.P.

Hancock,W.

Risk Assessment Ltd,Crown House, Eridge, Tunbridge Wells, Kent

NNL Ltd,Booths Hall, Knutsford, Cheshire

Health and Safety Executive,Nuclear Installations Inspectorate,Thames House North, Millbank, London SW1P 4QJ

Nuclear Safety Branch, Health and Safety Department, Central Electricity Generating Board (CEGB),Sudbury House, 15 Newgate Street, London EC1A 7AU

United Kingdom Atomic Energy Authority (UKAEA), Wigshaw Lane, Culcheth, Warrington, Cheshire WA3 4NE

Henry, K .J . UKAEA, Atomic Energy Research Establishment (AERE), Harwell, Didcot, Oxon 0X11 ORA

4 5 0 L IS T OF PA RT IC IPA N TS

U N I T E D K I N G D O M ( c o n t . )

Jeffery, J.

Johnstone, I.

Márchese, C.J.

Redpath, W.

Sell, J.E.

Tildsley, F.C.J.

Watson, I.A.

Wyse, W.H.

Yeomans, R.

Nuclear Installations Inspectorate,Thames House North, Millbank, London SW1 4QJ

UKAEA, Safety and Reliability Directorate,Wigshaw Lane, Culcheth, Warrington, Cheshire WA3 4NE

CEGB,Sudbury House, 15 Newgate Street, London EC1A 7AU

UKAEA, Safety and Reliability Directorate,Wigshaw Lane, Culcheth, Warrington, Cheshire WA3 4NE

National Nuclear Corporation Ltd,Cambridge Road, Whetstone, Leicester LE8 3LH

Nuclear Installations Inspectorate,Thames House North, Millbank, London SW1P 4QJ

UKAEA, Systems Reliability Service,Wigshaw Lane, Culcheth, Warrington, Cheshire WA3 4NE

Rolls-Royce & Associates Ltd,Raynesway, P.O. Box 31, Derby DE2 8BJ

South of Scotland Electricity Board,Cathcart House, Spean Street, Cathcart, Glasgow G44 4BE

U N I T E D S T A T E S O F A M E R I C A

Joosten, J.

Kelly, R.T.

Lafleur, J.D., Jr.

Lanning, Wayne D.

United States Nuclear Regulatory Commission (NRC), 1717 H Street NW, Washington, DC 20555

Institute for Nuclear Power Operations,1100 Circle 75 Parkway, Suite 1500,Atlanta, Georgia 30339

U.S. NRC, Office of International Programmes, Washington, DC 20555

U.S. NRC, Office of Analysis and Evaluation of Operational Data,

Washington, DC 20555

Pate, Z.T. Institute of Nuclear Power Operations, 1100 Circle 75 Parkway, Suite 1500, Atlanta, Georgia 30339

L IS T OF PA RTIC IPA N TS 451

Y U G O S L A V I A

“ Energoinvest” ,Institute for Control and Computer Sciences, YU-71000 Sarajevo

Institute for Thermal Engineering and Energy Research,

Boris Kidric Institute of Nuclear Sciences-Vinca, P.O. Box 522, YU-11001 Beograd

Medical Protection Laboratory,Boris Kidric Institute of Nuclear Sciences-Vinca, P.O. Box 522, YU-11001 Beograd

O R G A N I Z A T I O N S

C O M M I S S I O N O F T H E E U R O P E A N C O M M U N I T I E S ( C E C )

Bastianini, P. Joint Research Centre,Caruso, S. 1-21020 Ispra, ItalyMancini, G.

Tolley, B. 200, rue de la Loi, B-1049 Bruxelles, Belgium

I N T E R N A T I O N A L A T O M I C E N E R G Y A G E N C Y ( I A E A )

Csik, B.J. Division of Nuclear Power,Wagramerstrasse 5, P.O. Box 100, A-1400 Wien, Austria

Rosen, M. Division of Nuclear Safety,Wright, H. Wagramerstrasse 5, P.O. Box 100, A-1400 Wien, Austria

N U C L E A R E N E R G Y A G E N C Y O F T H E O E C D

Otsuka, Y. Nuclear Safety Division,38, boulevard Suchet, F-75016 Paris, France

W O R L D E N E R G Y C O N F E R E N C E ( W E C )

Mira, J. J. Service de la production thermique,Direction Production et transport,Electricité de France,3, rue de Messine, F-75384 Paris Cedex 08, France (See also under France)

Brasnic, J.

Jovié, V. Spasojevic, D.

Stojanovió, D.

A U T H O R I N D E X

Roman numerals refer to the volume number and arabic numerals to the first page of a paper

by the author concerned.

A b a g y a n , A . A . s ( I ) 4 3

A l e k s i é , B . s ( I I ) 3 4 8

A n c e l i n , C . s ( I I ) 9 4

A v e n a s , М . : ( I ) 2 7

B a g d a s a r o v , Y u . E . s ( I I ) 1 8 3

B a l o g i , J . s ( I ) 3 7 2

B a n d y o p a d h y a y , S . K . s ( I I ) 5 1

B a r b e t , J . F . s ( I I ) 9 4

B e r â n e k , J . s ( I ) 4 9

B e r t i n i , A . s ( I ) 7 5

B e r t r o n , L . s ( I I ) 3 5 3

B h a s i n , B . K . s ( I I ) 9 3

B l a c k , D . W . : ( I I ) 6 1

B o h r , E . s ( I ) 2 2 1

B r e n i è r e , J . : ( I I ) 3 6 5

C a b a n n e s , J . - L . : ( I I ) 1 5

C a h u z a c , A . : ( I ) 1 3 9

C a l a m a n d , A . s ( I I ) 1 3 5

C a s s e t t e , P . : ( I I ) 2 2 7

C a v e , L . s ( I I ) 1 9 7

C a y o l , A . s ( I I ) 2 2 7

C h e b o t a r e v , V . s ( I I ) 3 2 5

C h e r k a s h o v , Y u . М . : ( I ) 5 9

C l a r k e , A . W . s ( I I ) 1 9 7

C o m e a u , J . G . s ( I I ) 6 1

C o n t r a t o , R . J . s ( I ) 3 1 3

C s i k , B . J . s ( I I ) 3 1 5

C z o c h , I . s ( I I ) 1 6 3

D e L i m a , J . M . s ( I I ) 1 7 3

D e p o n d , G . s ( I I ) 7 9

D j u k i é , Z . s ( I I ) 3 4 8

D r o u l e r s , Y . s ( I I ) 1 2 1

D u n a j e v , V . G . s ( I I ) 3

E f i m o v , I . A . s ( I I ) 1 8 3

F e l g i n e s , R . s ( I ) 6 7

F e l t i n , C . s ( I I ) 1 2 1

F é r a u d , R . s ( I ) 2 4 3

F i l ' , N . S . s ( I I ) 3 3

F i l i p c h u k , E . V . s ( I I ) 3

F o u r e s t , B . s ( I I ) 1 2 1

F u j i i , M . s ( I ) 2 6 7

F u k u m o t o , A . s ( I ) 3 3 3 , 3 4 9

F u k u m o t o , H . s ( I I ) 1 5 1

G a r c i n , G . s ( I ) 2 4 3

G h e r t m a n , F . s ( I ) 1 5 7

G h o s h , A . K . s ( I I ) 5 1

G o r o k h o v , A . K . s ( I I ) 3 3

G r i f f o n - F o u c o , M . s ( I ) 1 5 7

G r o n o w , W . S . s ( I I ) 3 7 3

H a i r e , T . P . s ( I I ) 3 8 7

H a l p e r n , O . s ( I I ) 3 6 5

H a r t f i e l , H . - D . s ( I ) 2 3 1

H a s h i m o t o , S . s ( I I ) 4 1 5

H a u n h o r s t , H . : ( I I ) 1 1 3

H a u s s e r m a n n , W . s ( I I ) 2 9 1

H e l l s t r a n d , E . s ( I ) 3 0 1

I v a n e n k o , V . N . s ( I I ) 1 8 3

J a c q u o t , J . P . s ( I ) 3 7 1

J a n í k , L . s ( I I ) 3 2 5

J o h a n s s o n , G . s ( I ) 1 2 3

K a t o , K . s ( I I ) 4 1 5

K a w a m u r a , A . s ( I I ) 3 4 5

K i m u r a , Y . s ( I I ) 3 4 5

K m o s h e n a , Y u . s ( I ) 1 7 3

K o t t h o f f , K . s ( I I ) 1 1 3

K o v á r , P . s ( I ) 4 9

K r e t t , V . s ( I I ) 3 2 5

K r í z , Z . s ( I ) 4 9

K u z n e t s o v , I . A . s ( I I ) 1 8 3

L a n n i n g , W . D . s ( I I ) 2 5 9

L a v e r i e , M . s ( I I ) 2 8 1 , 3 5 3

L e b o u l e u x , P h . s ( I ) 1 1 1

L e s n o j , S . A . s ( I ) 4 3

L u k y a n e t s , I . A . s ( I I ) 3

453

4 5 4 AU TH O R IN D EX

L u k y a n o v , M . A . s ( I I ) 3 3

M a c o u n , J . : ( I ) 4 9

M a r c i l l e , G . : ( I ) 2 4 3

M e r c i e r , J . - P . : ( I ) 8 7

M i l i v o j e v i c , К . : ( I I ) 3 4 8

M i n e o , Y . ; ( I ) 2 6 7

M i r a , J . J . : ( I ) 1 4 5

M i y a o k a , S . : ( I I ) 1 5 1

M o n t a , К . : ( I ) 3 3 3

M o r i , N . : ( I ) 3 3 3

M o r l a t , G . : ( I ) 1 3 9

M u r a t a , F . s ( I I ) 4 1 5

M u r t h y , L . G . K . s ( I I ) 5 1

N a i t o , N . : ( I ) 3 3 3

N a t a l i z i o , A . : ( I I ) 6 1

N e d a , T . s ( I ) 3 4 9

N i c o l e t , J . - L . : ( I ) 1 1 1

N o b i l e , М . : ( I I ) 1 0 3

N o w a k , К . : ( I I ) 4 0 3

O g i n o , T . s ( I ) 2 6 7

O l i o t , A . : ( I I ) 7 9 , 1 3 5

O l i v o n , М . : ( I I ) 1 5

O l i v r y , J . L . s ( I ) 6 7

O s m a c h k i n , V . S . s ( I I ) 3 0 1

O t s u k a , Y . : ( I I ) 2 9 1

O v c h i n n i k o v , F . Y a . : ( I I ) 3 2 5

P a l a b r i c a , R . J . : ( I I ) 2 1 5

P a r k , К . : ( I I ) 2 2 7

P a t e , Z . T . : ( I ) 1 9

P e d e r s e n , O . M . г ( I ) 1 8 1

P e r e l l o , М . : ( I ) 9 7

P e t i t , R . s ( I I ) 1 5

P i e r a r d , A . : ( I ) 3 1 3

P o t a p e n k o , P . T . : ( I I ) 3

P o u j o l , A . : ( I ) 3 7 1

P r o k o p o v i c h , S . R . : ( I ) 3 1 3

P u y a l , C . s ( I I ) 9 6

R a m a m o o r t h y , N . г ( I I ) 5 1

R a s m u s s e n , J . : ( I ) 1 8 1

R e i g , J . : ( I I ) 2 4 1

R é s c h , P . : ( I I ) 1 6 3

R i c h t e r , H . : ( I ) 6 9

R i n t t i l a , E . : ( I ) 2 5 5

R o l l a n d , P . : ( I I ) 9 8

R o l l e t , P . ; ( I ) H i

R o s e n , M . s ( I ) 3

S a s a k i , S . s ( I I ) 1 5 1

S a t o , N . : ( I ) 3 3 3

S c h l e i f e r , F . : ( I I ) 1 1 3

S c h n a d t , H . : ( I I ) 4 0 3

S h a s h a r i n , G . A . ; ( I ) 4 3

S i m o n , М.: ( I I ) 1 1 3

S j ô s t r a n d , К . : ( I ) 1 2 3

S m i d t O l s e n , H . s ( I ) 2 5 5

S p a s s k o v , V . P . : ( I I ) 3 3

S t o j a n o v i c , D . s ( I I ) 3 4 8

S u g a w a r a , М.; ( I ) 3 3 3

S u n d e r , R . s ( I ) 2 8 1

S u r e a u , H . : ( I I ) 7 9

S v a n s s o n , L . s ( I ) 3 0 1

S z a b a d o s , L . s ( I I ) 3 3 3

T a i , I . : ( I ) 3 3 3

T a k a y a m a , М.: ( I I ) 3 4 5

T a k i z a w a , Y . s ( I ) 3 4 9

T a l l ó s y , J . s ( I I ) 1 6 3

T i m o k h i n , E . S . : ( I I ) 3

T o d a , Y . î ( I ) 3 4 9

T o l l e y , B . s ( I ) 1 9 5

T o m i z a w a , T . s ( I ) 3 4 9

T ó t h , I*. * ( I I ) 3 3 3

T r a j k o v i d , М . : ( I I ) 3 4 8

T r i p p u t i , I . s ( I I ) 1 0 3

T s u c h i d a , M . s ( I ) 3 3 3

V a l k ó , J . s ( I I ) 1 6 3

V a m o s , G . : ( I ) 3 7 2

V a n R e i j e n , G . : ( I ) 1 9 5

V e l j k o v i c , D . : ( I I ) 3 4 8

V e r e t e n n i k o v , G . A . : ( I ) 4 3

V i l l e m e u r , A . s ( I I ) 9 4

V i t e t , J . s ( I ) 1 3 7

V ô r ô s s , L . s ( I I ) 1 6 3

V o z n e s e n s k i j , V . A . s ( I I ) 3 ,

W a c h , D . ; ( I ) 2 8 1

W a h l s t r o m , B . s ( I ) 2 5 5

W a t s o n , I . A . : ( I ) 1 9 5

W r i g h t , H . s ( I I ) 3 0 1

Y a n a g i s a w a , A . : ( I I ) 3 4 5

Y o k o y a m a , T . s ( I ) 2 6 7

Z i m a n , V . s ( I ) 1 7 3

I N D E X O F P A P E R S B Y N U M B E R

2

5

7

1 0 P

1 1

1 3

1 5

1 7

2 0

2 I P

2 2

2 3

2 4

2 5

2 6 P

2 7 P

2 8

2 9

3 0

3 1

3 2

3 3

3 5

3 6

3 7

3 8

3 9

4 I P

4 2

4 3

4 4

4 5 P

4 7

4 9

5 1 P

5 2 P

5 3

5 4 P

5 5

IAEA-SM-268/ V o l u m e P a g e

I 1 8 1

I 2 5 5

I I 1 7 3

I I 3 4 5

I 3 3 3

I I 1 5 1

I 2 6 7

I 3 4 9

I I 4 1 5

I I 9 3

I I 5 1

I I 1 0 3

I 1 9 5

I I 1 6 3

I 3 7 2

I I 3 4 8

I I 4 0 3

I 2 2 1

I I 1 9 7

I I 3 8 7

I I 6 1I I 3 1 5

I 1 2 3

I 3 0 1

I I 3 6 5

I 2 7

I I 2 8 1

I 1 3 7

I I 2 2 7

I I 1 2 1

I 1 1 1

I 3 7 1

I I 1 3 5

I I 2 1 5

I I 9 4

I I 9 6

I I 7 9

I 6 7

I 8 7

455

4 5 6 IN D EX O F PAPERS B Y N UM BER

I A E A - S M - 2 6 8 / — V o l u m e P a g e

5 6 I 2 4 3

5 7 P I I 9 8

5 8 I 1 5 7

6 1 I 1 4 5

6 2 I I 1 5

6 3 I I 3 5 3

6 4 P I 1 3 96 5 I 1 96 6 I 9 7

6 7 I 3 1 3

6 8 I I 3 3 3

7 0 I 3

7 1 I I 2 9 17 2 I I 3 0 17 3 I 7 5

7 4 I I 1 8 3

7 5 I I 3

7 6 I I 3 3

7 7 I I 3 2 57 8 I 1 7 3

7 9 I 4 9

8 0 P I 6 9

8 1 I I 1 1 3

8 2 I 2 8 1

8 3 I 4 3

8 4 I 5 9

8 5 I I 3 7 3

8 7 I 2 3 1

9 0 I I 2 4 1

9 1 I I 2 5 9

FACTORS FOR CONVERTING SOME OF THE MORE COMMON UNITS TO INTERNATIONAL SYSTEM OF UNITS (SI) EQUIVALENTS

NOTES:(1) SI base units are the metre (m), kilogram (kg), second (s), ampere (A), kelvin (К), candela <cd) and mole (mol).(2) ► indicates SI derived units and those accepted for use with SI;

^ indicates additional units accepted for use with SI for a limited time.[For further in form ation see the curren t ed ition o f The In ternational S ystem o f Units (SI), pub lished in English b y HMSO, London, and N ational Bureau o f Standards, W ashington, DC, and International Standards ISO -1000 a nd the several parts o f ISO-31, pub lished b y ISO, Geneva. ]

(3) The correct symbol for the unit in column 1 is given in column 2.(4) * indicates conversion factors given exactly; other factors are given rounded, mostly to 4 significant figures:

= indicates a definition of an SI derived unit: [ ] in columns 3+4 enclose factors given for the sake of completeness.

The following conversion table is provided for the convenience of readers

Column 1M u l t ip ly d a ta g iv e n in :

Column 2 Column 3b y :

Column 4to o b ta in d a ta in :

R a d ia t io n u n its

^ b e c q u e r e l

d is in t e g r a t io n s p e r s e c o n d (= d is /s )

1 B q

1 s ' 1

(h a s d im e n s io n s o f s " 1 ) 1 .0 0 X 1 0 ° B q *

> c u r ie 1 C i = 3 . 7 0 X 1 0 10 B q *

> r o e n tg e n 1 R [= 2 . 5 8 X 1 0 '4 C / k g ] *► g r a y 1 G y И 1 .0 0 X 1 0 ° J / k g ] *> r a d 1 ra d = 1 .0 0 X 1 0 ~ 2 G y *► s ie v e r t ( r a d ia t io n p r o te c t io n o n ly ) 1 S v 1 1 .0 0 X 1 0 ° J / k g ] *

> r e m ( r a d ia t io n p r o te c t io n o n ly ) 1 r e m = 1 .0 0 X 1 0 -2 S v *

M ass

► u n i f i e d a t o m ic m a s s u n i t ( ï i o f t h e m a s s o f 12C ) 1 u 1 = 1 .6 6 0 5 7 X 1 0 ~ 27 k g , a p p r o x . ]

^ t o n n e (= m e t r i c t o n ) 1 t 1 = 1 .0 0 X 1 0 3 k g ] *

p o u n d m a s s ( a v o i r d u p o is ) 1 Ib m = 4 . 5 3 6 X 1 0 ' 1 k9o u n c e m a s s ( a v o i r d u p o is ) 1 o z m = 2 . 8 3 5 X 1 0 1 9

t o n ( lo n g ) ( = 2 2 4 0 tb m ) 1 t o n = 1 .0 1 6 X 1 0 3 k g

t o n ( s h o r t ) (= 2 0 0 0 Ib m ) 1 s h o r t t o n 9 . 0 7 2 X 1 0 2 k g

L e n g th

s t a t u t e m i le 1 m i le = 1 .6 0 9 X 1 0 ° k m

> n a u t ic a l m i le ( i n t e r n a t io n a l ) 1 n m i le = 1 .8 5 2 X 1 0 ° k m *

y a r d 1 y d = 9 . 1 4 4 X 1 0 ' 1 m ■*

f o o t 1 ft = 3 . 0 4 8 X 1 0 ' 1 m *

in c h 1 in = 2 . 5 4 X 1 0 1 m m *

m i l (= 1 0 “ 3 in ) 1 m i l = 2 . 5 4 X 1 0 ' 2 m m *

A re a

^ h e c ta r e 1 h a [ « 1 .0 0 X 1 0 “ m 2 ] *

> b a r n (e f fe c t iv e c ro s s -s e c t io n , n u c le a r p h y s ic s ) 1 b I - 1 .0 0 X 1 0 ' 28 m 2 ] *

s q u a re m i le , ( s t a t u t e m i l e ) 2 1 m i l e 2 = 2 . 5 9 0 X 1 0 ° k m 2

a c re 1 a c re 4 . 0 4 7 X 1 0 3 m 2

s q u a re y a r d 1 y d 2 = 8 .3 6 1 X 1 0 _1 m 2

s q u a re f o o t 1 ft2 = 9 . 2 9 0 X 1 0 -2 m 2

s q u a re in c h 1 i n 2 = 6 . 4 5 2 X 1 0 2 m m 2

V o lu m e

► l i t r e 1 I o r 1 L [ = 1 .0 0 X 1 0 -3 m 3 ] *

c u b ic y a r d 1 y d 3 = 7 .6 4 6 X 1 0 ’ 1 m 3

c u b ic f o o t 1 ft3 = 2 . 8 3 2 X 1 0 -2 m 3

c u b ic in c h 1 i n 3 1 .6 3 9 X 1 0 4 m m 3

g a l lo n ( im p e r ia l ) 1 g a l ( U K ) = 4 . 5 4 6 X 1 0 ~ 3 m 3

g a l lo n (U S l i q u id ) 1 g a l ( U S ) = 3 . 7 8 5 X 1 0 ‘ 3 m 3

This table has been prepared by E.R.A. Beck for use by the Division of Publications of the IAEA, While every effort has been made to ensure accuracy, the Agency cannot be held responsible for errors arising from the use of this table.

Column 1 Column 2 Column 3 Column 4M u l t ip ly d a ta g iv e n in : b y : to o b ta in d a ta in :

V e lo c ity , a c c e le ra t io n

f o o t p e r s e c o n d (= fp s ) 1 f t / s = 3 . 0 4 8 X 1 0 " ' m /s *

f o o t p e r m in u t e 1 f t / m i n = 5 . 0 8 X 1 0 " 3 m /s *

( 4 .4 7 0 X 1 0 " ' m /sm i le p e r h o u r (= m p h ) 1 m i le / h

[1 .6 0 9 X 1 0 ° k m / h

|> k n o t ( i n t e r n a t io n a l ) 1 k n o t = 1 .8 5 2 X 1 0 ° k m / h *

f r e e f a l l , s ta n d a r d , g = 9 .8 0 7 X 1 0 ° m /s 2

f o o t p e r s e c o n d s q u a re d 1 f t / s 2 = 3 . 0 4 8 X 1 0 " 1 m /s 2 *

D e n s ity , v o lu m e tr ic ra te

p o u n d m a s s p e r c u b ic in c h 1 I b m / i n 3 = 2 . 7 6 8 X 1 0 4 k g / m 3

p o u n d m a s s p e r c u b ic f o o t 1 lbm/ft3 = 1 .6 0 2 X 1 0 ' k g / m 3

c u b ic f e e t p e r s e c o n d 1 f t 3 /s = 2 . 8 3 2 X 1 0 ' 2 m 3 /s

c u b ic f e e t p e r m in u t e 1 f t 3 / m in = 4 . 7 1 9 X 1 0 ~ “ m 3 /s

F o rc e

► n e w t o n 1 N [ = 1 .0 0 X 1 0 ° m - k g - s - 2 ] *

d y n e 1 d y n = 1 .0 0 X 1 0 “ s N *

k i lo g r a m f o r c e (= k i lo p o n d ( k p ) ) 1 kgf = 9 . 8 0 7 X 1 0 ° N

p o u n d a l 1 p d l = 1 .3 8 3 X 1 0 ~ ‘ N

p o u n d f o r c e ( a v o i r d u p o is ) 1 I b f = 4 . 4 4 8 X 1 0 ° N

o u n c e f o r c e ( a v o i r d u p o is ) 1 o z f = 2 . 7 8 0 X 1 0 ~ ‘ ,N

P ressure, s tress

^ p a s c a l3 1 Pa [ = 1 .0 0 X 1 0 ° N / m 2 ] *

a tm o s p h e r e ^ , s ta n d a r d 1 a tm = 1 .0 1 3 2 5 X 1 0 s Pa *

> b a r 1 b a r

ОXооII P a *

c e n t im e t r e s o f m e r c u r y ( 0 ° C ) 1 c m H g = 1 .3 3 3 X 1 0 3 Pa

d y n e p e r s q u a re c e n t im e t r e 1 d y n / c m 2 = 1 .0 0 X Ю " 1 Pa *

fe e t o f w a t e r ( 4 ° C ) 1 f t H j O = 2 . 9 8 9 X 1 0 3 Pa

in c h e s o f m e r c u r y ( 0 ° C ) 1 in H g = 3 . 3 8 6 X 1 0 3 Pa

in c h e s o f w a t e r ( 4 ° C ) 1 inHjO = 2 .4 9 1 X 1 0 2 Pa

k i lo g r a m fo r c e p e r s q u a re c e n t im e t r e 1 k g f / c m 2 = 9 . 8 0 7 X 1 0 4 Pa

p o u n d f o r c e p e r s q u a re f o o t 1 I b f / f t 2 = 4 . 7 8 8 X 1 0 ' Pa

p o u n d f o r c e p e r s q u a re in c h (= p s i ) c 1 I b f / i n 2 = 6 . 8 9 5 X 1 0 3 Pa

t o r r (0°C} ( - m m H g ) 1 t o r r = 1 .3 3 3 X 1 0 2 Pa

E n e rg y , w o rk , q u a n t i t y o f h e a t

^ jo u le W s ) 1 J [ = 1 .0 0 X 1 0 ° N m ] *

► e le c t r o n v o l t 1 eV [ = 1 .6 0 2 1 9 X 1 0 “ 1! J , a p p r o x . ]

B r i t i s h t h e r m a l u n i t ( I n t e r n a t i o n a l T a b le ) 1 B tu = 1 .0 5 5 X 1 0 3 J

c a lo r ie ( t h e r m o c h e m ic a l ) 1 c a l = 4 . 1 8 4 X 1 0 ° J *

c a lo r ie ( I n t e r n a t i o n a l T a b le ) 1 саЦт = 4 . 1 8 7 X 1 0 ° J

e rg 1 e rg = 1 .0 0 X 1 0 " 7 J *

f o o t - p o u n d f o r c e 1 f t - I b f = 1 .3 5 6 X 1 0 ° J

k i l o w a t t - h o u r 1 k W h = 3 . 6 0 X 1 0 6 J *

k i l o t o n e x p lo s iv e y ie l d ( P N E ) ( = 1 0 l 2 g -c a l) 1 k t y ie ld =“ 4 . 2 X 1 0 '2 J

a P a (g ) : p a s c a ls g a u g e ^ a t m (g ) (= a t ü ) : a tm o s p h e r e s g a u g e c l b f / i n 2 (g ) (= p s ig ) g a u g e p re s s u re

P a a b s : p a s c a ls a b s o lu te a t m a b s (= a ta ) : a tm o s p h e r e s a b s o lu te l b f / i n 2 a b s (= p s ia ) a b s o lu te p re s s u re

Column 1M u l t ip ly d a ta g iv e n in :

Column 2 Column 3b y :

Column 4to o b ta in d a ta in :

P o w e r, r a d ia n t f lu x

> w a t t 1 W [ h 1 .0 0 X 1 0 ° J /s )

B r i t i s h t h e r m a l u n i t ( I n t e r n a t i o n a l T a b le ) p e r s e c o n d 1 B t u / s = 1 .0 5 5 X 1 0 3 W

c a lo r ie ( I n t e r n a t i o n a l T a b le ) p e r s e c o n d 1 c a l i f / s = 4 . 1 8 7 X 1 0 ° W

f o o t - p o u n d fo r c e / s e c o n d 1 f t - I b f / s = 1 .3 5 6 X 1 0 ° wh o r s e p o w e r ( e le c t r ic ) 1 h p = 7 . 4 6 X 1 0 2 wh o r s e p o w e r ( m e t r i c ) (= ps) 1 p s = 7 . 3 5 5 X 1 0 2 wh o r s e p o w e r ( 5 5 0 f t * I b f / s ) 1 h p = 7 .4 5 7 X 1 0 2 w

T e m p e ra tu re

► k e lv in

► d e g re e s C e ls iu sgrees ueisius, tw h e r e T is t h e t h e r m o d y n a m ic t e m p e r a t u r e in k e lv in

a n d T 0 is d e f in e d as 2 7 3 . 1 5 К

d e g re e F a h r e n h e i t

d e g re e R a n k in e

t e m p e r a t u r e d i f f e r e n c e ^

_ K ________

t = T - T 0"

t o c - 3 2

A T Or <= ú t . F )

X | ~ l g iv e s

t ( in deg rees C e ls iu s )

T ( in k e lv in )

Д Т (= A t )

T h e rm a l c o n d u c t iv i t y ^

1 B t u * i n / ( f t 2 - s - ° F ) ( In te rn a t io n a l T a b le B tu ) = 5 . 1 9 2 X 1 0 2 W - r r T ' - K '

1 B t u / ( f t * s , 0 F ) ( In te r n a t io n a l T a b le B tu ) ~ 6 .2 3 1 X 1 0 3 W t t T ' - K -

1 c a l |T / ( c m - s - ° C ) = 4 . 1 8 7 X 1 0 2 W - m _ 1 - K “

M is c e lla n e o u s q u a n t it ie s

l i t r e p e r m o le p e r c e n t im e t r e (1 M/cm =) 1 L -m o f1 cm’ 1 = 1 .0 0 X 1 0 ' 1 m 2 / m o l *(molar e x tin c tio n co e ffic ien t o r m olar absorption co e ffic ien t)

G - v a lu e , t r a d i t i o n a l l y q u o t e d p e r 1 0 0 e V

o f e n e r g y a b s o r b e d 1 X 1 0 “ 2 e V " 1 = 6 . 2 4 X 1 0 16 J ' 1

(radiation y ie ld o f a chem ical substance)m a s s p e r u n i t a re a 1 g / c m 2 [= 1 .0 0 X 1 0 1 k g / m 2 1 *(absorber thickness a n d m ean mass range)

^ A t e m p e r a t u r e in t e r v a l o r a C e ls iu s t e m p e r a t u r e d i f f e r e n c e c a n b e e x p re s s e d in d e g re e s C e ls iu s as w e l l as in k e lv in s .

* *

*

H O W T O O R D E R I A E A P U B L I C A T I O N S

■ A n e x c l u s i v e s a l e s a g e n t f o r I A E A p u b l i c a t i o n s , t o w h o m a l l o r d e r s

a n d i n q u i r i e s s h o u l d b e a d d r e s s e d , h a s b e e n a p p o i n t e d

in t h e f o l l o w i n g c o u n t r y :

U N I T E D S T A T E S O F A M E R I C A U N I P U B , P .O . B o x 4 3 3 , M u r r a y H i l l S t a t io n , N e w Y o r k , N Y 1 0 1 5 7

In t h e f o l l o w i n g c o u n t r i e s I A E A p u b l i c a t i o n s m a y b e p u r c h a s e d f r o m t h e

s a l e s a g e n t s o r b o o k s e l l e r s l i s t e d o r t h r o u g h y o u r

m a j o r l o c a l b o o k s e l l e r s . P a y m e n t c a n b e m a d e in l o c a l

c u r r e n c y o r w i t h U N E S C O c o u p o n s .

A R G E N T I N A

A U S T R A L I A

B E L G I U M

C Z E C H O S L O V A K I A

F R A N C E

H U N G A R Y

I N D I A

IS R A E L

I T A L Y

J A P A N

N E T H E R L A N D S

P A K I S T A N

P O L A N D

R O M A N I A

S O U T H A F R I C A

S P A IN

S W E D E N

U N I T E D K I N G D O M

U .S .S .R .

Y U G O S L A V I A

C o m is ió n N a c io n a l d e E n e r g ía A t ó m ic a , A v e n id a ‘ d e l L i b e r t a d o r 8 2 5 0 ,

R A - 1 4 2 9 B u e n o s A i r e s

H u n t e r P u b l ic a t io n s , 5 8 A G ip p s S t r e e t , C o l l i n g w o o d , V i c t o r i a 3 0 6 6

S e r v ic e C o u r r ie r U N E S C O , 2 0 2 , A v e n u e d u R o i , В - 1 0 6 0 B ru s s e ls

S . N . T . L . , S p á le n á 5 1 , C S - 1 1 3 0 2 P ra g u e 1

A l f a , P u b l is h e r s , H u r b a n o v o n á m e s t ie 6 , C S - 8 9 3 3 1 B r a t is la v a

O f f i c e I n t e r n a t i o n a l d e D o c u m e n t a t io n e t L ib r a i r i e , 4 8 , r u e G a y -L u s s a c ,

F - 7 5 2 4 0 P a r is C e d e x 0 5K u l t u r a , H u n g a r ia n F o r e ig n T r a d in g C o m p a n y

P .O . B o x 1 4 9 , H - 1 3 8 9 B u d a p e s t 6 2

O x f o r d B o o k a n d S t a t io n e r y C o . , 1 7 , P a r k S t r e e t , C a lc u t t a - 7 0 0 0 1 6

O x f o r d B o o k a n d S t a t io n e r y C o . , S c in d ia H o u s e , N e w D e lh i - 1 1 0 0 0 1

H e i l ig e r a n d C o . , L t d . , S c ie n t i f i c a n d M e d ic a l B o o k s , 3 , N a th a n S tra u s s S t r e e t , J e ru s a le m 9 4 2 2 7

L ib r e r í a S c ie n t i f i c a , D o t t . L u c io d e B ia s io " a e i o u " .

V ia M e ra v ig M 1 6 , I - 2 0 1 2 3 M i la n

M a r u z e n C o m p a n y , L t d . , P .O . B o x 5 0 5 0 , 1 0 0 - 3 1 T o k y o I n t e r n a t io n a l

M a r t in u s N i j h o f f B . V . , B o o k s e l le r s , L a n g e V o o r h o u t 9 - 1 1 , P .O . B o x 2 6 9 ,

N L - 2 5 0 1 T h e H a g u e

M ir z a B o o k A g e n c y , 6 5 , S h a h r a h Q u a id - e - A z a m , P .O . B o x 7 2 9 , L a h o r e 3

A r s P o lo n a - R u c h , C é n t r a la H a n d lu Z a g r a n ic z n e g o ,

K r a k o w s k ie P r z e d m ie s c ie 7 , P L - 0 0 - 0 6 8 W a rs a w

l l e x im , P .O . B o x 1 3 6 - 1 3 7 , B u c a r e s t

V a n S c h a ik 's B o o k s t o r e ( P t y ) L t d . , L i b r i B u i ld in g , C h u r c h S t r e e t ,

P .O . B o x 7 2 4 , P r e t o r ia 0 0 0 1

D ia z d e S a n to s , L a g a s c a 9 5 , M a d r id - 6

D ia z d e S a n to s , B a lm e s 4 1 7 , B a r c e lo n a - 6A B C .E . F r i t z e s K u n g l . H o v b o k h a n d e l , F re d s g a ta n 2 , P .O . B o x 1 6 3 5 6 ,

S - 1 0 3 2 7 S t o c k h o lm

H e r M a je s t y 's S t a t io n e r y O f f i c e , P u b l ic a t io n s C e n t r e

P .O . B o x 2 7 6 , L o n d o n S W 8 5 D R

M e z h d u n a r o d n a y a K n ig a , S m o le n s k a y a - S e n n a y a 3 2 - 3 4 , M o s c o w G - 2 0 0

J u g o s lo v e n s k a K n j ig a , T e r a z i je 2 7 , P .O . B o x 3 6 , Y U - 1 1 0 0 1 B e lg ra d e

O r d e r s f r o m c o u n t r i e s w h e r e s a l e s a g e n t s h a v e n o t y e t b e e n a p p o i n t e d a n d

r e q u e s t s f o r i n f o r m a t i o n s h o u l d b e a d d r e s s e d d i r e c t l y t o :

^ D i v i s i o n o f P u b l i c a t i o n s

^ i W $ I n t e r n a t i o n a l A t o m i c E n e r g y A g e n c y

W a g r a m e r s t r a s s e 5 , P .O . B o x 1 0 0 , A - 1 4 0 0 V i e n n a , A u s t r i a

i

I N T E R N A T I O N A L S U B J E C T G R O U P : 11

A T O M I C E N E R G Y A G E N C Y N u c l e a r S a f e t y a n d E n v i r o n m e n t a l P r o t e c t i o n / N u c l e a r S a f e t y

V I E N N A , 1 9 8 4 P R I C E : A u s t r i a n S c h i l l i n g s 9 0 0 , —