THE IMPACT OF ORGANIC COMPOUNDS ON IODINE

BEHAVIOUR UNDER CONDITIONS RELATING TO

NUCLEAR REACTOR ACCIDENTS

Fariborz Taghipour

A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy

Graduate Department of Chemical Engineering and Applied Chemistry University of Toronto

O Copyright by Fanborz Taghipour 1999

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The Impact of Organic Compounds on Iodine Behaviour under Conditions Relating to Nuclear Reactor Accidents

Fariborz Taghipour PhD, 1999

Department of Chernical Engineering and Applied Chemistry University of Toronto

ABSTRACT

The impact of organic compounds on iodine behaviour was investigated under a range of

post-accident chernical conditions expected in a reactor contairunent structure. A bench scale

apparatus installed in the irradiation chamber of a G a m a c e I l was used to provide

continuous measurement of iodine volatilization rates from 10" to 1 O-' M Cs1 solutions with

pH values from 5 to 9. The rate of production of volatile iodine was evaluated in the

presence of IO-' M concentrations of various alkyl halides, carbonyls. and aromatics; the

three classes of organic compounds most likely present in containment. lodo-organics and

molecular iodine in the gas and liquid phases of the irradiated samples were analyzed using

gas chrornatography, mass spectrometry, and UV spectrophotometry. A mode1 was

developed that simulates the radiation chemistry of iodine in the presence of organic

compounds and evaluated against the experimental results.

The results indicated that organic compounds can be classified into groups, based on their

distinct effects on iodine behaviour. Iodine volatilization increased significantly? up to two

orders of magnitude, in the presence of carbonyls and alkyl chlorides, while it decreased in

the presence of aromatics. Gas and liquid phase anaiysis indicated that chloro-iodo organics

and alkyl iodides are the major types of volatile iodo-organics formed in the presence of alkyl

chlorides and carbonyls, respectively, while no volatile iodo-organics are fonned in the

presence of aromatics. Molecular iodine measurements in the systems showed that I2

concentration increases in the presence of dkyl chlorides and decreases in the presence of

carbonyls and aromatics.

The kinetic-based model. containing a mechanistic description of iodine chemistry and

generic semi-mechanistic reactions for various classes of organics, provided a reasonable

prediction of the experimental results. The majority of the model and experimental results

were in agreement tvithin an order of magnitude.

The results of this research will assist in predicting and reducing the radiological

consequences of reactor accidents. In particular. the results indicate the advantage of

maintaining basic pH and avoiding aikyl halide or ketone based solutions in post-accident

reactor containment- in order to reduce radioactive iodine volatility. and hence. improve

reactor safety -

I would like t express my d

Acknowledgments

eep gratitude and appreciation to:

Professor Greg J. Evans for his excellent supervision. advice. and encouragement

throughout this work. He is a great fnend to al1 his students. and I am tmly gratehl to be

his student and his friend.

Professors M. Kawaji and C.A. Mims, members of the advisory cornmittee. for their

valuable cornments which contributed to the successfùl completion of this work.

My Iab colleagues who have assisted in making my graduate studies much more

meaningfiil and mernorable. especially Christine, Evon, Jim, Juliette. Kai, Nawal. Phil.

Sandu, Sophe, Tinku, and Tutun. Also. a special gratitude to Anandhi, Ed, and Mark for

their invaluable help.

h i r , Madjid. Kamran. and Thuy for fostering such a pleasant environment of fiendship

and camaraderie. They are truly great friends.

- Finally, my deepest appreciate goes to my farnily whose love. inspiration, and support

through al1 my life enabIed me to reach this milestone. 1 would like to dedicate this work

to them.

Table of Contents

-4bstrac t

Ackoocviedgments

Tale of Contents

List of Tables

List of Figures

List of Appendices

1 Introduction

2 Literature Review

2.1 Reactor Accident and Radioactivity Releases

2.2 Iodine Behaviour Under Reactor Accident Conditions

2.3- 1 Radiation

2.2.2 Iodine Concentration

2-22 Solution pH

2.2.4 Dissolved Oxygen Concentration

3 -33 Temperature

2.2.6 Inorganic Irnpurities

2.2.7 Organic lodide Formation

2.3 Modeling of Fission Product Behaviour Followîng Reactor Accident

2.3.1 Iodine Behaviour Models

3.3 -2 Organic Iodide Models

xiv

1

7

7

9

1 O

12

12

13

14

14

15

18

19

21

3 Theoretical Principles

3 - 1 Radiation Chemistry of Aqueous Solutions

3 2 Radiation Chemistry of Iodine Solutions

3 -3 Radiation Chemistry of Organic Solutions

3 -3.1 Alkyl Haiides

3 -3 -2 Carbonyls

3 -3 -3 Aromatics

3 -4 Organic Iodide Formation and Destruction

4 Experirnental Methods

4.1 Iodine Volatilization Rate

4- 1.1 Experimental Apparatus

4.1.2 Experirnental Conditions

4-13 Experirnental Procedure

4- 1-4 Analytical Procedure

4- 1 -5 Mass Transfer Parameters

4- 1.6 Commissioning Experiments

3.2 Identification and Quantification of Iodine Species

4.2.1 Sarnple Preparation

4.2.2 Identification of the Types of Organic Iodides Formed in the System

4.2.3 Measurement of Organic Iodide Formation

4.2.4 Measurement of Molecular Iodine Formation

4.3 Quality Assurance

42.1 Iodine Volatilization Rate 43

4.3 2 Gas and Aqueous Phase Analysis 41

5 Resdts And Discussion

5 1 Iodine Volatility in the Absence of Organics

5.1.1 Radiation

5.1.3 Iodine Concentration

5.1 -3 Solution pH 53

5.1 -4 Solution Buffer and pH Adjusters 54

5.2 Iodine Volatility in the Presence of Various Organics 55

5.2.1 The Impact of Organics on Sorution pH 55

5 - 2 2 The Impact of Various Carbonyls. Aromatics, and Alkyl Halides on Iodine Volatility 58

5.3 iodine Volatility in the Presence of Organics at Various pH and iodine Concentrations 60

5.3.1 The Effect of Carbonyls 6 1

5.3 -2 The Effect of Alkyl Haiides 64

5.3 -3 The Effect of Aromatics 66

5.3-4 Cornparison of the Impact of Organics on Iodine Volatility 69

5.3.5 The Impact of Organics on Iodine Volatility in The Presence of Other Organics 72

5.4 Gas and Liquid Phase Analysis 80

5.4.1 Identification of the Types of Organic lodides Fonned in the Systerns 80

5 -4-1.1 Alkyl Halides 8 1

vii

5 - 4 1 2 Carbonyls

5 -4.1 -3 Aromatics

5.4.2 ~Measurement of Organic Iodide Formation

5.4.3 Measurement of Moiecular lodine Formation

5.5 Cornparison of the Experimental Results With Other Related Works

5.6 Modeling of lodine Radiation Chemistry

5.6.1 Water Radiolysis Reactions

5.62 Iodine Reactions

5.6.3 Organic Compound Reactions

5 -6.3.1 Alkyl Haiides

5.6.3 -1 Carbonyls

5.6.3 -3 Arornatics

5.6.3 -4 Organic Iodides

5.7 Mode1 Evaluation

5.7.1 Mass Transfer Parameters

5 -7.2 Water Radiolysis Reactions

5-73 Iodine Volatilization

5.7.4 Iodine Volatilization in the Presence of Organics

5.7.4-1 Alkyl Haiides

5.7.4.2 Carbonyls

5.7.4.3 Aromatics

5.7.4.4 Mixture of Various Organics

viii

57-43 Summary of the Results

5.8 Application of the Results in ReaI Reactor Accidents

6 Conclusions and Recomrnendations

Nomenclature

References

Appendices

List of Tables

Table 5.1 Reduction in pH for unbuffered solutions with added organics

Table 5.2 Liquid speciation in the presence of 10" M MEK

Table 5.3 Gas speciation in the presence of 10' M MEK

Table 5.4 Gas and liquid phase speciation in the presence of 1 O-' M TCA

Table 5.5 Iodine volatilization rates (l7 10" M' pH 5 ) in the presence of MEK (105 M) after addition of various concentrations of benzene.

Table 5.6 The impact of diethyl ketone and styrene on iodine volatilization rates in the presence of dichloromethane 78

Table 5.7 Organic iodide formation in the presence of alkyl hdides 83

Table 5.8 Organic iodide formation in the presence of carbonyls 86

Table 5.9 Iodornethane and iodoethane concentrations in the gas phase. in the presence of various organics (organic concentration 1 o5 M, iodine concentration 1 O-' M, pH 5)

Table 5.10 Iodine concentration in the liquid and gas phase, in the presence of various organics (organic concentration 1 O' iM. iodine concentration IO-' M, PH 5 )

List of Figures

Figure 4.1 Experimental apparatus for measuring iodine volatilization rates 34

Figure 5.1 Iodine volatility in non-irradiated system (iodine concentration 1 O-' M- PH 7 ) 48

Figure 5.2 Increase in iodine volatility &er tramferring the system to the irradiation site

Figure 5.3 Cornparison of iodine volatilization rate and hydrogen peroside concentration at the begiming of irradiation

Figure 5.4 Volatilized iodine at various Cs1 concentrations (pH 5)

Figure 5.5 The impact of pH on iodine volatilization rate

Figure56 Theimpactofme~hyl ethyl ketone(MEK)andtrichloroethane (TCA) on solution pH and iodine volatility (iodine concentration IO-' M. unbuffered solution)

Figure 5.7 The impact of radiation on solution pH and iodine volatiliry (iodine concentration 1 O-' M_ unbuffered solution)

Figure 5.8 Iodine voIatilization rates in the presence of various organics (iodine concentration 10" MI organic concentrations 1 o - ~ M)

Figure 5.9 The impact of MEK on iodine volatilization rate at various iodine and MEK concentrations (pH 5) 6 1

Figure 5.10 The impact of MEK on iodine volatilization rate at various pH and iodine concentrations 62

Figure 5.1 1 The impact of TCA on iodine volatilization rate at various iodine and TCA concentrations (pH 5) 65

Figure 5.12 The impact of TCA on iodine volatilization rate at various pH and iodine concentrations 65

Figure 5-13 The impact of toluene on iodine volatilization rate at various iodine and totuene concentrations (pH 5) 67

Figure 5.14 The impact of toluene on iodine volatilization rate at various pH and iodine concentrations 68

Figure 5-15 Increase in iodine volatility afier addition of 1 O-' M MEK and TCA (iodine concentration 1 O-' M. pH 5)

Figure 5.16 Increase in iodine volatility after addition of 10" M TCA at various pH values (iodine concentration 1 O" M)

Figure 5.17 Increase in iodine volatility after addition of 10" M TCA and DCM (iodine concentration 1 O-' My pH 5)

Figure 5.18 Decrease in iodine volatility afier addition of 10' M toluene and benzene (iodine concentration 1 O-' M' pH 5)

Figure 5.19 [odine volatility- afier addition of MEK and TCA in the presence of benzene 73

Figure 5.20 Comparison of iodine volatility d e r addition of MEK. in the presence and absence of benzene 74

Figue 5.21 Comparison of iodine volatility d e r addition of IMEK and K A T in the presence and absence of benzene 74

Fisure 5.22 Decrease in iodine volatility in the presence of trichloroethylene f i e r addition of benzene

Figure 5-23 Decrease in iodine volatility in the presence of MEK (IO-' M) afrer addition of various concentrations of benzene 76

Fi=gre 5.24 Iodine volatility afier addition styrene in the presence of benzene 77

Figure 5.25 Cornparison ofreplicate results for iodine volatilization rates at various iodine concentrations (pH 5) 79

Figure 5.26 Comparison of replicate results for iodine volatilization rates at various iodine and organics concentrations (pH 5 ) 80

Figure 5.27 Comparison of the modeling and experimental results of hydrogen peroxide concentration (iodine concentration 1 O-' MI pH 5)

Figure 5.25 Comparison of the rnodeling and experimental results of total voIatilized iodine (modeling iodine concentration 0.6 x 10" M. experirnental iodine concentration 1 x 10-5 MI pH 5 ) 1 07

xii

Figure 5.29 Comparison of the modeling and experimental results of iodine volatilization rate at different I- concentrations (pH 7) 1 08

Figure 5.30 Comparison of the modeling and experimental results of iodine volatiliration rate at different pH values (iodine concentration IO-' M) 1 09

Figure 5.3 1

Figure 5.32

Figure 5.33

Figure 5.34

Figure 5.35

Figure 5.36

Comparison o f the modeling and experimental results of iodine volatilization rate in the presence of organics (iodine concentration 1 O-' M, pH 5 ) I l 1

Comparison of the modeling and experimental results of iodine volatilization rate in the presence of dkyl haiides (iodine concentration IO-5 M)

Comparison of the modeling and experimental results of iodine volatiIization rate in the presence of carbonyls (iodine concentration 1 O-' Mj 113

Comparison of the modeling and experirnental results of iodine volatilization rate in the presence of aromatics (iodine concentration 10-5 hl) 115

Comparison of the modeling and experimental results of iodine volatilization rats in the presence of organics (iodine concentration IO-' M. pH 5) 116

Comparison of the modeling and experimental results of iodine volatilization rate (rn~Vrnin)~ for a wide range of iodine concentration (1 O-'. 1 O-'. 10" M) and pH (5.7.9): in the absence and presence of organics ( 1 O" M)

List of Appendices

Appendix A: Caiculation of Mass Transfer Coefficients

Appendix B: Calibration Data and Graphs

Appendix C: Iodine Volatilization Rates

Appendix D: StatisticaI Analysis o f Data

Appendix E: Identification of the Types oCOrganic Iodides in the Solutions Containing A k y l Halides

Appendis F: Model of Iodine Radiation Chemistry in the Presence of Organics

Appendix G: Relationships Between the Governing Equations in the Model

Appendix H: Rate Constants of Organic Reactions

Appendix 1: Cornparison of Modeling and Experimental Results

xiv

1 INTRODUCTION

The safety philosophy and technology of nuclear generating stations have evolved

continuously over the course of their development. Every effort has been made to make

appropriate provisions for the nuclear plant to survive accidents IL-ithorit causing h m to the

public. The operation of nuclear stations is for the most part environmentally benign.

However. a serious accident at a nuclear generating station could cause a substantial social

and environmenta1 impact.

During the normal operation of a nuclear reactor. radioactive fission producrs are

produced and accumulate in the fuel elernents. These fission products. which represent over

99% of the radioactivity in a nuclear pouver plant. nomally remain in the reactor f i i d

Hocc-ever, in the ment of a serious accident. these hazardous radionuclides could bs reIsased.

Some of the radioactivity may become airborne in the reactor containment atmosphere and a

portion of this activity could be released to the environment through dsliberate \-enling or

penetration through any impairment in the containment envelope. Since it is the airborne

radionuclides that can potentially escape to the outside atmosphere. a knowledge of their

behaviour in the containment atmosphere is critical for reactor saf'ety .

Al1 fission product releases from a nuclear reactor contribute to the radiological dose.

However. the most potentially significant releases are the radioisotopes of iodine due to their

biosensitivity and volatility. The impact of radioiodine rslease can be controlkd and

minimized by understanding its behaviour under reactor accident conditions. From the

perspective of reactor safety. it is therefore important that iodine behaviour be understood

and predicted.

Organic compounds can have a substantial impact on iodine volatility. yet this aspect

of post-accident iodine behaviow is still not adequatety understood. in containment, organic

irnpurities will arise in the aqueous phase fiom sources such as paints. oils. and insulation

material. These organic compounds react with molecular iodine. in the presence of radiation,

to forrn a variety of volatile organic iodides. Organic iodides pose a signiticant safety

probiem. Volatile low molecular weight organic iodides are not easily removed by

engineered safety systems. such as sprays, and they are not significantly depleted through

deposition processes. They are. therefore persistent and remain available to leak to the

environment. In past reactor accidents. organic iodides dominated the p e o u s iodine

spwiation.

Despite some studies on the impact of organics on iodine volatility to date. there has

been no single self-consistent set of separate-eftècts esperiments, covering the wide range of

conditions related to reactor accidents. As well. no mode1 esists that provides an adequate

quantifkation of the impact of organics on iodine volatility.

The overall scope of the curent research therefore involved investigatiny the impact

of organic compounds on iodine behaviour. For a range of conditions espected post-accident

in a reactor containment structure. This goal was divided into several specific objectives.

The main objectives of this research were to:

1. evaluate the impact of organic compounds on iodine chemistry in irradiated systems for a

range of conditions likelely to arise in a reactor containment stmcrure followine a sevrre

accident.

2. develop a model that sirnulates the radiation chemistry of iodine in the presence of organic

compounds and evaluate its strengths and weaknesses.

Four sub-objectives were required to support the main objectives- These were to:

1. quantify the role of parameters affecting iodine vohtirity in the absence of organic

compounds. including radiation. iodine concentration. and solution pH.

2. refine and evaluate a mechanistic kinetic-based model for the inorganic radiation che rn i s t~

of iodine.

3. identify the types of organic iodides formed above irradiated iodine solurions containing

various organic compounds.

4. msasure the quantity of molecular iodine and organic iodides present in systems

containing organic compounds.

The first sub-objective provided a

of added organics. Not only did

new set of measurements of iodine volatility in the absence

these results serve as controls for assessing the impact of

organics. they also provided a basis for the modeling evaluation performed to meet the

second objective. The last two sub-objectives sen-ed to increase the fiindamental

understanding of the impact oforganics on iodine radiation c h e m i s t ~ .

The release of iodine from an irradiated aqueous pool in reactor containment depends

upon the fraction of the iodine within the pool that is in volatile forms. This fiaction is

determined by the balance betcveen the rates of production and elimination ot' the volatils

species, such as molecuiar iodine and organic iodides. through radiolytic processes. Givrn

the rapid kinetics associated with the reactions of the Free radicals produced by the irradiation

of water, the concentrations of the volatile iodine species quickly achieve a steady state.

These concentrations depend upon the prevailing chernical conditions as these conditions

detemine the rates o f and relative importance of the numerous reactions involved. Hence.

prediction of the release of iodine from irradiated solutions requires an understanding of how

the c hemical conditions govern the concentrations of volatile iodine species in solutions-

Direct measurement of the concentrations of \.olatils iodine species in irradiated

solutions is very difflcult since, under the dilute concentrations of interest, the concentrations

involved are usually ~indetectable. A more effective approach. the one selected for use in this

research, is to measure the rats ofrelease of iodine From irradiated solutions under conditions

of constant mass transfer. Using this approach. the volatilization rates measured under

different chernical conditions can be directly compared. providing insight into the underlying

chemistry within the aqueous solution.

A bench scale apparatus that allows continuous measurement of iodine volatiIization

rate was used to perform the esperiments. The esperiments were carried out in the

irradiation chamber of a Garnrnacell in order to sirnulate the strong radiation field present in

reactor containment following an accident. The influence of parameters that affect iodine

volatility in the absence of organics was initially studied. including radiation. iodine

concentration and solution pH. The rate of production of volatile iodine in irradiated systems

was then evaluated in the presence of various aikyl halides. carbonyls. and aromatics. the

three classes of organic compounds rnost likely present in containment. Iodo-organics and

molecular iodine in the gas and liquid phase of the irradiated samples were malyzed using

gas chromatography. mass spectrometry. and UV spectrophotometry.

The concentration of volatile iodine species in irradiated systems is detemined by

reaction kinetics. Therefore. any model for simulating the chemistry in irradiated systems

must be based on the rates of the major reactions that occur. The model h r simulating iodine

chrmistp under reactor accident conditions \vas based on a set ot' the most important

radiol!.tic and thermal reactions of iodine aIong with those representing the radiolysis of

water. A semi-mechanistic mode1 for organic iodide reactions inchding the major reactions

of organic iodide formation and destruction u-as incorporated into the inorganic reaction set-

-4 generic approach was used in which the main reactions representative of given classes of

organic compounds were considered. The required rate constants cvere estimated based on

representative compounds. -4 simple representation OF mass transfer betn,ern the liquid and

cas phases \vas also incorporated into the reaction set. The model was evatuated and refined L

by cornparison with the esperimental results.

The thesis consists of 6 sections. The literature review in Section 2 includes an

esplmation of some general aspects of a reactor accident- a detaiIed discussion on iodine

behaviour under post-accident reactor conditions. and a review of existing iodine behaviour

models. The theoretical pnnciples governing radiation chemistry of aqurous iodine solutions

in the presence of organic compounds are provided in Section 3. The esperimental procedure

is presented in Section 4. Section 5 includes the presentation and discussion of the results

obtained from the volatilization rate and gadliquid phase analysis rsperiments. This section

also covers the explanation and evaluation of the iodine behaviour model. Finally. Section 6

summarizes the work by providing conclusions and recommendations for tùture research.

2 LITERATURE: REVIEW

Radionuclide behaviour under reactor accident conditions has been investigated f%r many

years. Radioiodine has received the most attention- due to its importance among radioactive

fission products. Most of the rnechanisms involved in the inorganic radiation chernistry of

iodine have been elucidated and mechanistic models are in an advanced state of development.

The ef-fect of organic material on iodine radiation chemistry. however. is not cvell understood.

The following describes the current understanding of radioiodne behaviour under post-

accident reactor conditions.

2.1 Reactor Accident and Radioactivity Reiease [l-81

A nuc1ea.r reactor accident couId result in the release of considerable radioactivity to the

environment. Although such an accident is very unIikely. an understanding O t- the associated

consequences is required in order to evaluate the sakty of nuclear generating stations. One

of the more probable and fiequently considered types of accidents are the loss-of-coolant

accidents (LOCAs) which involve failures in the cooling systems used to transfer heat fiom

the reactor hel.

A break in the reactor coolant system will result in the release of prima? coolant into

the containrnent structure. Containment is designed to prevent any released activity trom

escaping to the environrnent. Depending on the size and location of the break. containrnent

safety systems such as emergency core coo1ing and dousing water flow will be initiated.

Primary circuit coolant and emergency core cooling water are discharged through the break

and collected as a water pool in the reactor containment. If the break is large enough to

initiate dousing, this water also collects in the water pool.

Radioactive fission products are present in the fuel lattice. They c m gradually

migrate from the lattice and accumulate in grain boundaries or gaps. as a result of thermal

motion, Failed fuel elements release their gap radionuclide inventory and, if the temperatures

are high enough. part of the bound inventory into the coolant. Radionuclides are circulated in

the primary circuit and eventualIy discharged into the reactor containment.

Iodine, cesium. and tellunum are considered to be the most important fission products

released in the early stages of a severe accident. Other important tïssion products are

unlikely to be released in any quantitics until core rnelting occurs [9] .

I f radionuclides are released into the reactor building as a result of an accident, a

portion of the radionuclides can escape into the environment leaking through the containment

envelop. Releases may also take place from penetrations in the containment building if there

is a containment boundary failure or if the operator perfoms a controIIed vent under

favorable weather conditions. As it is primarily the airborne radionuclides that can escape to

the outside atrnosphere, the ability of radionuclides to become airborne in the containnîent

atmosphere directly deterrnines the magnitude of any radioactivity releases.

Arnong al1 the radioactive fission products, iodine is the most important with regards

to its release to the environment following reactor accidents. Its high radioactivity and

potentiaI volatility motivates a continued investigation of iodine behaviour in der reactor

accident conditions, for the purpose of assessing and improving reactor safety.

2.2 Iodine Behaviour Under R~lactor Accident Conditions

In most of the nuclear reactor accidents. the short terrn radiological consequences are

espected to be dominated by the radioisotopes of iodine. Radioiodine causes great concern

due to its high fission yield. its potential volatility. and its radiobiological hazard.

Radioiodine is highly concentrated in the human thyroid gland and can lead to cancer of the

thyroid.

Due to its importance. iodine behaviour has been subject to bench scale. intemediate

scale, and farge scde e'cperimemts~ Bench scde separate-effect experiments have been

performed to identiQ the parameters that a e c t iodine volatility. Previous anal>-sis of iodine

volatility has involved studying the iodine partition coefficient ( IPC) ' [ 10- 141. However. the

need for greater versatility and serisitivity ofdynamic rneasures of iodine volatility has Isd to

the exploration of iodine volatilization rates [15-171-

To study the behaviour crf iodine species within containment under severe reactor

accident conditions. some multi-effects esperiments have been conducted. Canadian

research in this area is mainly conductsd in the Radioiodine Test Facility (RTF). The RTF is

an intemediate scale facility in which iodine behaviour under simulated containment

accident conditions c m be studied [18-311.

Large scale experiments have also been conducted in order to more closely simulate

the release of iodine into a reactor containment during a severe accident. ln much of the

earlier work the emphasis was on the behaviour of iodine vapor species and aerosol

formation and deposition [22]. Mare recently. a series of tests has been initiated in the large

t IPC is the ratio ofthe total aqueous to tatal airborne iodine concentrations. When the volatiiity increasss. the IPC decreases.

scaIe PHEBUS facility. PHEBUS-FP is an international prograrn invoIving benchmark

esercises to study iodine behaviour under prototypical L WR severe accident conditions [23 1.

These tests allow an integrated investigation of the release of fission products from in-core

irradiated firel, their transport and deposition within piping, and their interfacial transfer and

chemistry within a containment vessel. The Grst ttvo of these tests have already been

perforrned, although only a smail part of the results is openly available.

Only airborne iodine has the potential for release dong bvith the containinent

atmosphere to the enviromient, Therefore. from the perspective of reactor sakty,

identification of parameters that affect iodine volatility is important. Under many reactor

accident conditions. iodine' is espected to be released from fuel as Cs[. which will dissolve

to form the aqueous non-volatile iodide ion (1-). Some of the iodine hobvever. can

subsequently be converted to volatile molecular iodine (12) and volatile organic iodides (RI).

The volatility of radioiodine following a reactor accident depends. to a large estent. on its

aqueous chemistry. Parameters such as radiation. iodine concentration. pH. temperature. and

the presence of inorganic and organic imp~irities have been found to be important factors

influencing iodine volatility in irradiated systems. These parameters will be discussed here.

2.2.1 Radiation

The radiation field in post-accident reactor containment results from fission product decay

and hence would primarily consist of beta and gamma radiation. The dose rate depends on

parameters such as the quantity of fuel present in the core and its bumup. the radionuclide

activity released from the fuel. and core geometry. Dose rate has been estimated to be on the

' todine in this document represents the element iodine in iü al1 chernical foms. The species II is referred to as molecular iodine.

order of 2 4 k G y h during a typical reactor accident [24]. although this \vil1 depend on the

scenario and wîll Vary greatly over time.

The impact of radiation on iodine volatility has been investigated in bench scale and

intemediate scale esperiments. The esperimental investigations have primarily usrd gamma

radiation. which does not represent the cornples energ- spectrum found in containment.

Honever. the resulting radiolysis mechanisms are not espected to differ significantly. Bench

scale experiments have employed a range of dose rates v q i n g from 0.3 to 10 kGy/hr. \vhiIe

intermediate scale esperirnents such as RTF have used an average dose rate of 2 kGy/hr.

Radiation has been found to be a v e q important factor influencing iodine t.olatilit>- in

aqueous solütions. This influence can be attributed primarily to aqueous phase radiolysis

reactions. The radiation energy is absorbed by water molecules to produce radiolysis

products. LVater radiolysis products c m osidize non-\,olatils iodids to 1-olatile molscular

iodine.

RTF experiments have showin that interconversion of 1-. t7- and organic iodides is

very slow. in the absence of radiation [19]. In bench-scale esperiments it has been found that

irradiation causes the iodine partition coefficient to decrease by one to tuo ordsrs of

magnitude [ X I . In another study- the rate of evolution of t2 increased in proportion to dose

rate at pH 1.6. whereas at pH 6 and 7 this was not the case [16]. For the relatively rapid

interfacial transfer of this system increasing the dose rate by a factor of 9 led to an increase in

iodine evolution by a factor of 5 at pH 6 falling to 3.8 at pH 7 [16]. One c m h>-pothesize chat

for slow mass transfer conditions the dependence of volatilization rate on dose rate would be

much weaker,

2.2.2 Iodine Concentration

The total iodine concentration in reactor containment following an accident wouId depend on

the extent of fùel failure and the m o u n t of mater released. it has bren sstimated that

releasing al1 the iodine in the reactor fuel into containment ~t-outd produce a total iodine

concentration on the order of 1 O-' M [9]. Considering that under realistic conditions only a

small portion of this iodine would be released. the aqueous concentration in a reactor

containment would likely be about 10" to 1 O-' M [ l O]. Iodine concentration is espected to

affect its volatilization rate. as the reactions of iodine with water radiolysis products are

concentration dependent for low concentrations of iodine.

A range o f concentrations spanning 1 O-' to 1 O" M is commonl y investigated in bench

scale ssperirnents. Evaluation of iodine volatilization rats has shon-n that the rate of'

molecular iodine production falls by a facior of 10 on reducing the 1- concentration from IO-'

to IO-' M. indicating that the fiactionai volatilization rate is independent of concentration

otrer this range [16]. However this ma. not be the case for lon-er concentrations. For

ssarnple. the iodine partition coefficient has besn found to depend on the total iodine

concentration for concentrations below 10" M [14].

2.2.3 Solution pH

The pH of the water in containment rnay van; substantialIy between accident scenarios or

even over the course of a given scenario. Factors such as the initial pH. the presence of

buffers. radiolytic nitric acid formation. the radiolytic degradation of organics. and the

effectiveness of any deliberately added matenal such as NaOH may al1 contribute to such

variation. The pH of the solution can have a significant effect on iodine behaviour mainly

because some of the reduction reactions of I2 to non-volatile 1- are pH dependent.

One study of the impact of pH on iodine partition coeffkient indicated that the LPC

varies substantially with changing solution pH. For IO-' and IO-' M iodine solutions. the pH

dependence occurred primarily in the range of' pH 5 to 8. with the LPC rising from below 1 O'

at pH < 5 to above 10' at pH > 8 [14]. In another study. IPC shon-ed a strong dependence on

pH- particularly in the pH range of 5 to 7 [XI . An evaluation of iodine volatilization rate

showed a considerable pH dependence on the rate of evolution of I2 with an increase in pH,

and a small. but not insignificant production of 1, at the highest pH (pH 9) [17. 251. The

strong dependence of iodine volatilization on solution pH has also been esamined in

intermediate scale experiments where iodine volatility increased significantly with decreasing

pH po] .

2.2.4 Dissolved Oxygen Concentration

Dissolved oxygen concentration can be affected by some reactions such as the reactions of

organic impurities. Dissolved osygen affects iodine volatiIity through its reaction uith the

hydrated electron (a water radiolysis product). to form O?- urhich is a strong reductant that

converts LI to a non-volatile r and 1:- form.

An investigation of the effects of nitrogen and osygen on the radiolysis of iodine

solutions indicated that the presence of oxygen in solution reduces the arnount of oxidation of

r to I2 [27]. A similar observation suggested that a decrease in oxygen concentration at pH 7

leads to an significant increase in the iodine volatilization rate [16]. In another study.

however. lowering the dissolved oxygen concentration under different pH and mass transfer

conditions resulted in a reduction in the iodine volatilization rate [15]. Measuring the yield

of iodine production showed that at low doses the yirld is greater in the deoxygenated

solutions but at high doses therr does not appear to be any difference [25] .

2-25 Temperature

The arnbient ternperature in a breached reactor depends on reactor core design. in multi-unit

CANDU stations for e'tarnple. the arnbient temperature and pressure may increase up to 90

"C and 1-3 atm follow-ing an accident. Ho~vever. the!. attain stable conditions shortly ahsr

initiation of the ernergency systems giving temperatures in the range of 25 to -50" C and

pressures in the range of 0.7 to 0.9 atm [l].

A study of the effect of temperature in the range of 35 to 70" C on iodine volatilit>-

indicated that the volatilization rate Falls with increasing temperature [Io]. On esarnining the

effect of temperature in the range of 40 to 130" C it was shown that the radio1 ytic production

of 1- in solution decreases at higher temperatures [29]. A study on iodine partition coefficient

at 25 and 80" C also shocved an increase in IPC with increasing temperature. particulark

irnder acidic conditions [ X I .

2.2.6 Inorganic lmpurities

Inorganic impurities including trace rnetals rnay be present in the reactor's aqueous phase

following an accident. For example. silver. one of the control rod-s constituents. is vaporized

at the core melt ternperature and may reach the containment sump. Sillrer can react \\mith

iodine to form solid precipitates. silver iodide (A@).

A study on the effect of metal impurities such as ~ n " . ~e" . and Mo. indicated that

these metals do not affect the iodine voIatilization rate [16]. The results were assumed to be

attributed to the formation of insoluble hydroxides that makes the species unreactive. On the

other nand silver. added as a powder. reduced the iodine volatilization rate [16]. Particles of

silver metals or oside in the aqueous phase should react with molecular iodine and iodide

ions to form non-volatile silver iodide.

2.2.7 Organic Iodide Formation

Organic impurities will arise in the aqueous phase from various sources such as paints. oils.

and greases. These organic compounds significantly affect iodine volatility. by undergoing

radioi'ic decomposition to form organic acids that reduce the solution pH. Organic

compounds also react with molecular iodine. forming a vanzty of organic iodidrs.

The possible sources of organic materials in containment after a reactor accident are

numerous. Their type. concentration, and location determine their impact on iodine

behaviour. Materials such as paints- insulations. seals. and oils in containment could be

sources of many different types of organics. Although there are a number of potentia1 types

of organic compounds in containment. w-ater-soluble compounds present in containment

paints. have been identified as having the greatest impact on iodine bçhaviour [30]. Thrir

pronounced impact is due to the aqueous phase reactions play-ing a dominant role in organic

iodide formation.

Chemical analyses of the aqueous phase in intermediate scale tests have contimed

that a variety of organic compounds c m be released from containment paints in contact \vit11

the aqueous solutions [2 1_ 3 11. Although the quantities and type of organic compounds \ .an

somewhat for different paint types. certain compound classes are ubiquitous. Carbonyl

compounds (methyl ethyl ketone and methyl isobutyl ketone) are commonly used in the

application of paints. whereas methylated aromatics (xylene and toluene) are present in

thinners. Alcohols and halogenated hydrocarbons (trichloroethane) are also common

additives [3 11. Al1 of these species could be released into the aqueous pool in considerable

quantities after an accident.

The actual concentration of organic compounds in the reactor pool follocving an

accident is difficult to predict. An estimation of the likely aqueotis concentration of organics

c m be obtained from studies addressing the release oforganic materia1 from païnts [3 11. For

exarnple. in the absence of radiation. concentration of ketones in the 1 O-' to 1 O-' iL1 range

have been observed [31]. In addition, sylene and toluene were released in significant

quantities [3 11- Hotvever. the actual concentration in containment cvould be determined

through a balance betcveen the rate of release of the compound. fiom paints. plastics.

lubricants. etc.. and the rate of destruction through radiolytic processes.

A review of the eicisting Iiterature regarding organic iodide formation in nvo phase

irradiated systems concludes that aqueous phase processes are the dominant pathway for

organic iodide formation [32 ] . Following a reactor accident. the majority of the iodine

inventory in containment will initially reside in the aqueous phase and large quantities of

organics may be present in the aqueous phase as the result of dissolution of organic solvents

from containrnent paints. These facts provide suppon for the importance of aqueous

processes. However. a large proportion of the organic iodide compounds forrned in the

aqueous phase may be relatively non-volatile in nature. It is still unclear to what extent other

pathways. such as surface mechanisms or perhaps even gas phase radiolysis. contribute to the

formation of airborne organic iodides in containment.

Organic compounds play an important role in determining iodine behaviour by virtue

of their ability to undergo radiolysis in the aqueous phase. Under radiolytic conditions

organic compounds may undergo radiolytic oxidation to organic acids thereby decreasing

solution pH and O? concentrations. conditions which favor higher I2 production. They may

also react with OH radical- thereby competing with the oxidation of 1- to [?. Organic

cornpounds may form organic iodides by radiolytic or thermal reactions. The impact of these

organic iodides on iodine volatility will be dependent on whether the species are more or less

volatile than Iz [32]-

The effects of organic compounds on the production O E volatile species of iodine have

been investigated in bench scale [12. 13. 30. 33. 341 and intermediate scale [18, 3 l. 35. 361

esperiments. The measurement of IPC and solution pH in the presence of various organics

indicated that many of these compounds enhance iodine volatihty and that the degree of

volatility is relâted to system pH [12. 133, A study of the impact of different types of

organics on IPC showed that some types of organics. such as aromatic and phenolic

compounds. suppress overall iodine volatility with little impact on airborne organic iodide

concentrations while others. such as alkyl halides and carbonyl compounds. enhance organic

iodide formation with Little impact on overall iodine volatility [XI. In an investigation of the

types of organic iodides forrned in the presence of organics. methyI iodide kvas the only

compound detected in measurable quantities [30].

The effects of containment swface coatings on iodine behaviour have besn

investigated in intermediate scale tests. The esperiments with zinc-primer-coated surfaces

showed remarkably low iodine volatility [35]. However, in the presence of a vinyl surface.

iodine volatilization rate increased significantly and this may be attributed to organics

released fiom the paint [36]. In another intemediate scale test. the addition of rnethyl ethyl

ketone (MEK) to irradiated Cs1 solutions resulted in a decrease in pH and dissolved osygen

concentration as well as a reduce IPC 118 3.

2.3 iModeling of Fission Product Behaviour FoIIowing Reactor Accident

The physical and chernical conditions in containment afier an accident are beyond those

encountered in normal plant conditions and are correspondingly difficult to reproduce and

study. Because of the nurnber and range of parameters to be encompassed. it is not practical

to experimentally reproduce al1 the possible accident sequences. Such esperiments are

espensive and extremely time-consuming to set up and interpret. The only practical way to

deal with this problem is a combined strategy of studying separate efkcts and developing, in

paraIlel. sophisticated models that enable accident progression to bs calculated taking into

account the interdependence of the relevant phenomena, These separate sffects studies

produce data and confirm the fundamental scientific modeling. whilst the codes enabls that

scientific modeling to be applied to specific plants and accidents [9 ] .

Using computer codes to predict the radioactivity released foliowing reactor accidents

is common. As an example, the behaviour of radionuclides in postulated CANDU reactor

accidents are currently predicted using FISSCON [37] and SMART [38] codes. These codes

account for the radiological and some of the physical aspects of fission product behaviour

including: the production and decay of radionuclide isotopes, their adsorption and desorption

by various sinks. the retention and desorption of fission products by any ernergency filters

and the dispersion of radioactive material in the environment. However. these codes do not

simulate the complex radiation chemistry of fission products such as radioiodine.

2.3.1 lodine Behaviour NIodels

A number of empirical and mechanistic models for the simulation of iodine behaviour in

irradiated systems esist. The most propounded of' these models are LIMC (Canada) [39]

TRENDS (US) [4O], ihrSPECT (UK) [41]. IMPAIR (Germany) [42]. and IODE (France)

1431- LIRIC is a kinetic database of iodine reactions being developed at Whitrshell

Laboratories. LIRIC consists of approsimately 150 reactions and the rate constants are

derived primarily From literature. LIRiC is a valuabIe tool for understanding iodine

chemistry under reactor accident conditions. However. physical phenomena, such as

transport between compartrnents. are not included and the representation of mass transïer

phenomena is incomplete- TRENDS models both chernical and physical katures sucb as

radiolysis effects. hydrolysis. and deposition/revaporization on aerosols and structural

surfaces. TRENDS also includes a calculation of the radiation dose rate based on the fission

product inventory. iNSPECT sirnulates iodine behaviour by considering thermal and

radiolytic reactions for reactor accidents where the aqueous medium exists in the forms of

aerosol spray. sump and reactor water. mixed and contacted with the large ~rolurne of

containment air. The IMPAIR code considers 6 iodine species in 2 1 differential equations

containing relevant physico-chemical behaviour such as transfer from containment. droplet

carry-over. liquid and gas phase deposition. aerosol phase transfer. and droplet precipi~ation.

IODE considers empirical forms of the thermal and radiolytic reactions of iodine in the

aqueous (12 reactions) and gas (2 reactions) phases. as well as physical phenomena such as

mass transfer. iodine dragging by steam condensation. and iodine deposi tion on surfaces.

m i l e al1 thsse codes consider iodine chemistry. the chemical reaction mechanisrns in LIRiC

and INSPECT are more detailed.

Five iodine codes (LIRiC. TRENDS, INSPECT. IMPAiR. and IODE) participated in

the Advanced Containment Esperïments (ACE) code comparikon esercise EL541 which

involvsd prediction of iodine behaviour in a number of the ACE-RTF esperirnents. The

predicted iodine partition coefficient differed bj- several orders of magnitude amon_ost the

codes. While ail the codes consistently predicted a lotv airborne iodine fraction, the codes

often predicted less than the measured airborne concentration. The results of PE-IEBLIS-FP

esercise have been compared cvith the iodine code predictions [45]. It \\-as concluded that

mechanistic codes (INSPECT and LIRIC) show considerable agreement for molecular iodine

concentration in the gaseous phase. whereas empirical codes (IODE and IMPAIR-2) are in

disagreement because they mode1 the HO1 disproportionation differentIy and u s e different

radiolytic rate constant values. Iodine behaviour codes continue to be moditïed. Simulation

of the experimental results using the new versions of LIRiC [46], nrSPECT [47]. IMPAIR

[48. 491. and IODE [50] presented reasonable results.

In general the esisting iodine models c m provide reasonable predictionç of iodine

volatility under some conditions. based on cornparison with intermediate scale e.~periments.

However. for other conditions the mode1 predictions are inconsistent. both among themszl\.es

and with experiments.

2.3.2 Organic Iodide Models

A study of the esisting organic iodide modeis indicates that [ 32 ] : a) there are no

available mechanistic models for organic iodide reactions, b) semi-mechanistic models for a

k w individual organic compounds which are presented in sorne models. such as LIRiC [46].

are questionable, c) the existing empirical modeis such as Deane-s model and Postma's

model are inadequate due to a former lack of understanding of the relationship between

organic radiolysis. iodine kinetics. and organic iodide formation. More importantly. although

some modeling predictions have been compared with intermediate scale esperimental results.

no self-consistent set of experiments has previously existed for evaluating the modeling of

iodine chemistry in the presence oforganic compounds.

3 THEORETICAL PRINCIPLES

The volatilization of dissoIved iodine following a reactor accident depends upon its aqueous

chernistry. which in turn is Iargely iduenced by the high radiation tïeld present in post-

accident reactor containment. Theoretical principles governing the radiation chemistry of

aqueous-iodine solutions in the presence of organic compounds are described in this section.

3.1 Radiation Chemistry of Aqueous Solutions

Radiation is energy that travels through space in the form of high-eners!. particles or

elecuomagnetic waves. Ionizing radiation is radiation that lias sufficient energy to remove

bound electrons fiom the atoms in the matter through which it passes. When ionizing

radiation interacts with matter. photons or charged particles in the incident raj- collide ii-irh

atoms or molecules in the matter and ionize or excite them. Depending on the mean ionizing

energy of atoms and the initial energy of the incident particle: the incident panicle can ionize

thousands of atoms before it cornes ta rest- The process by which radiation interacts with a

soIution resulting in the formation of ionized atoms is called radiobsis.

In the radiolysis of relatively dilute aqueous solutions. almost al1 the absorbed energy

is deposited into water molecules. This leads to the production of several very reactive

primary species (OH: e-,,? H) and molecular products (Hl. HzOt). In oxygenated water

hydrogen atoms (H) and the hydrated electrons (e,). are converted into perhydrosyl radicals

(HOz) and superoxide ions (O2-). The primary water radiolysis products and their yield or

G-value (the number of moIecules formed per 100 eV absorbed radiation snergy) are as

Water radiolysis reactions have been investigated estensivsly [cg. 5 1-55]. The

major reactions taking place in irradiated water are as fo llows:

2 e-,- H 2 + 2 OH-

e;, + H- HZ *OH-

e,, + OH- OH-

Ca, + H'- Hi H,O

2H-Hz

E-r+OH---+HzO

2 OH - Hz02

OH t H702- H 2 0 + HOî

2 HOZ - K 2 0 2 + 0:

In the presence of oxygen:

3.2 Radiation Chemistry of Iodine Solutions

The Ilndamental radiation chemistry of iodine solutions has been unaerstood and the main

reactions have been identified [e-g. 141. The radiation chernistry OF iodine in dilute aqueous

solutions is initially governed by the reaction of water radiolysis products with iodine. Some

of these reactions oxidize non-volatile r to volatile 12. while others reduce I7 to 1-- Iodine

volatility in the system is the result of a balance between these oxidations and reductions.

There are a k w iodine reactions. illustrated below. that are key in determining iodine

voIatility :

The oxidation of T by OH to fonn 1?

I-tOH-I+-OH-

E+[-12

The reduction of 1, to i- through reaction with some water radiolysis productsi

12+H20,+- 21 -+2H-+0->

I7 f 0,- - 17- + O2

17- f 12- [ j- + I-

I?- -i 0,- - 2 I- 4- O,

1;- 4- 0:- - 1- + 1,- + o1

The hydrolysis of molecular iodine

I, + HZO - HO1 +- 1- + H-

HO1 e E i t + 01-

The formation of organic iodides

R + OH (or e,) - - R' + products

R' + 4 - - RI + prodricts

I Double arrows represent several reaction steps.

The reduction of iodine by H202 has been studied and the following rnechanism has been

proposed [46. 561:

11 t HzO - 120H- + Hy (3-23)

[?OH- + H102 1- + [OZH + H1O ( 3 -34)

IOlH +OH-- I- +O1 + H20 ( 3 -35)

Rsaction 3.12 is main117 responsible for the significant increases in iodine volatility observed

as a result of radiation. Reactions 3. lrC - 3.19 explain the effect of pH and dissolved osygen

on iodine volatility.

3.3 Radiation Chemistry of Organic Solutions

Radiation chemistry of aqueous systems containing organic compounds invollies the reaction

of mater radiolysis products with the organic solutes. The organic radicals produced by these

reactions can react further before being converted to chemically stable products. which may

lead to complex radiolysis mechanisrns.

Three groups of organic compounds are more likely present in containment: alkyl

halides. carbonyls, and aromatics (see Section 2.2.6). The radiation chemistry of aqueous

solutions containing these groups of organics. therefore is briefly discussed here.

3.3.1 Alkyl halides

The reaction mechanisms of alkyl halide solutions have been investigatsd for some alkyl

chlorides [57]. Based on these studies a general mechanism can be considered for alkyl

halides. Alkyl chlorides are rapidly dechlorinated throrcgh reaction u-ith the hydrated

electron. They can also react with OH or 0, (being derived from r-, +- O2 ---+ O-?)

resulting in hydrogen abstraction.

RCI, + e- ., - R'Cl(,-, , + CI-

RC1, + OH - KCI, + H-O

RCI, + - KCl, + HO-?

It is generally assurned that the transients produced by either pathway are unstable. and they

decompose by hydrolysis and/or are scavenged by O,. forming the corresponding perosy

radicals.

R'CI, +- H,O - R'OHCI(,-, , + Cl- + H-

R'Cl, - O-, - RCln02' (peroxy radical)

The chloro-orpanic radicals. produced by the reactions of RCI with water radiolysis

products. should be able to react with I2 and i to form volatile chloro-iodo organics or organic

iodides.

For mono-chlorinated alkyl chlorides. a reaction with the li).drated electron \id1 produce

aky l radicals which should also react with 1, and I to form organic iodides.

3.3.2 Carbonyls

Carbonyl compounds react predominantly in air-saturated solutions to form carbosylic acids

[58].

RCHO + OH - RC'O + H20 (3 -3 3)

RC'O + 0, - R(02')C0 (3 -3 4)

R(O<)CO ---+ -t RCOzH + products (3.35)

n e dominant organic radicals involveci in this mechanism contain oxygen. dius. there is no

obvious source of aikyl radicals.

A number of possible pathways for alkyl radicai formation tiom the radiolysis of

aqueous carbonyls esists [32. 341. For esample. foilowing hydrogrn abstraction. aldchyde

radicals may decompose to give an aLkyI radical

RC'O- R ' + C O (3 -36)

However. the rate of this decomposition process is likely far slower than the reaction with

dissolved oqrgen

RC'O + O2 - R(0,')CO

The organic peroxide could combine to form organic radicals

2 R(02*)C0 v 3 R' + 2 CO2 + 0- (3 -3 7 )

The production of alkyl radicals from similar reactions as those of photolq-sis of aldehpdes

c m also bs considered as another root [34]- The process involves abstraction of hydrogen by

OH followed by addition of O? to fomi an organic perosy radical

RHCO + OH - RC'O + H 2 0 (3-33)

RC'O + 0 2 - R(O<)CO ( 3 . 3 )

An oxygen atom is then transkrred foIlowed by scission of the carbon-carbon bond to give

CO2 and an alkyl radical

R(0,')CO + NO - R(0')CO + NOî

R(O0)CO - R' + CO2

It is not clear what molecule could play the role of the oxygen atom acceptor (Le. NO) in

irradiated solutions but othenvise this mechanism for the formation of alkyI radicals fi-om

aldehydes is quite feasible. It appears that the mechanistic details for the radiolytic

decomposition of the carbonyl radicds to give alkyl radicals are not known.

Any a k y l radicds produced from the radiolysis of carbonyls cvould react with 1, and

1, leading to the formation oEvoIatile alkyl iodides.

RCHO+OK--R'+H70+C0 (3 -40)

K+12-RI+I (3 -4 1 )

K+I-RI (3 -42)

Alky 1 iodides may aIso be produced through the reaction of R'CO cvith 1-. as this mechanism

has been srrggested for aldehydes [32].

R'CO + IZ---+ RCOI + 1

RCOI + OH - KCO1 +- H70

R'COI - KI + CO

KI -i RCHO ---+ RI + RC'O

3.3.3 Aromatics

The radiolysis of aqueous aromatic solutions such as benzene [59] and toluene [60] has been

studied to some exrent. Arornatic compounds react with OH to t o m the hydrosy-

cycIo hesadienyl radical.

C6H6 + OH 0 C6H60H (3 -47)

In the presence of oxygen. this radical reacts with O? through a complex process. which

usually leads to the formation of hydrosylated species.

C,H,OH + O? - C6H,0H +- HO- (3 -48 j

There is no literary documentation of the reaction of Oz- with aromatics. However. relatively

high rates of this reaction with phenolic compounds have been reported [6 11.

I t is evident that the reaction of aromatics with OH occurs primarily through an

addition of OH to the ring. Therefore, organic radicals are not created and thus there should

not be a signiiïcant formation of organic iodides- The production of phenolic compounds,

hotvever. can lead to the formation of iodophenol (an essentially non-volatile organic iodide)

through tlieir reactions with HO1 (621.

C,H,OH +- HO1 - C,H,IOH + H,O

3.1 Organic Iodide Formation and Destruction

Based on the production of methyl iodide in two-phase waterhir espenments [30]. it is

believed that generally aqueous phase processes dominate organic iodide formation. The

formation of rnethyl iodide from methane is through the reaction of methyi radicals with

iodine [JO]. In a similar manner. it is reasonable to assume that organic iodides are formed

from radical-molecular iodine reactions for more comples compounds. Houlever. there is

very little mechanistic data available for the radiolytic formation of organic iodides.

Difficulty in obtaining mechanistic details arises because many of the major products from

the radiolysis of organics can also react to produce organic iodides [J2]. Thermal process

may also play a role in organic iodide formation particularly from solutions containing

aldehydes and ketones [32] .

The initial reactions leading to the formation o f methyl iodide c m be descnbed as

fiollows 1301:

CH4 + OH CH; + H20 (3 -50)

In the absence o f other reactants. methyl radicals can abstract a hydrogen atom from other

organic compounds or react to form ethane. although these reactions are generally slow.

CH3+R-CH,+R' (3.5 1 )

CH; + CH; CIH6 (3 -52)

In the presence o f O-, or 1,. the follow-ing rapid reactions occur:

CH, + O-, ---+ CH,O-, (3 -53)

CH; + 17----+ CHji + 1 (3 54)

The rate of the reaction of 1, ~ 6 t h a methyl radical is very rapid in the aqueous solutions

phase. being limited only by difiùsion [30].

Organic iodides decompose through reactions with water radiolysis products. The

radiolytic decomposition of some alkyl iodides in aqueous soIutions has been studied and the

reaction rate constants have been identified 163. 641. The reactions for rnethyl iodide are as

fiollows:

CH,[ -+ e-,, - CHj + 1- (3 -55)

CH$ +- H+ CH3 -+ 1- + HT (336)

The reaction with OH is less characterîzed. but the overall reaction is thought to be [3 21:

CH3[ + OH - CH;IOH ( 3 3 7 )

The adduct can then oxidize 1-. although the overall rnechanism is in doubt.

CH310H + I- - CH31 + I O K (3 -58)

Ln the presence o f osygen? O is produced through the reaction of hydrated electrons with

oxygen. O may abstract H Fiom CH31 but it will not remove iodine. allorving a possible

significant decomposition route to be eliminated [32]. Thermal reactions. such as the

hydrolysis reactions could be important in decomposition (Equation 3-39). However. the rate

constants of these reactions are significantly lower than those of ndiolytic elimination

reactions.

CH3[ t H 2 0 - CH30H + 1- + H- (3 -59)

Hydrolysis of alkyl iodides is a facile process under certain conditions. and p l a y a role in

determining their steady state concentrations in the aqueous phase. However. this reaction

for aromatic iodides is generally slow [3Z].

4 EXPERIMENTAL WORK

The experiments were performed in order to examine the impact of organic compounds on

iodine behaviour over a range of possible post-accident reactor conditions. The esperimsnts

can be cIassified into two main sets. In the first set ofexperiments. the impact oforganics on

the rate of volatile iodine production kvas investigated. The second set of experiments

focused on identieing, and when possible quantiQing. organic iodide formation through the

analysis of the gas and aqueous phases of irradiated iodine solutions. The follo~ving is a

description of the experiments.

1 lodine VolatiIüation Rate

The objective of this set of experiments \vas to study the impact of organic compounds on

iodine volatility in irradiated systems over a range of possible conditions prevailing in a

reactor containment following an accident. A bsnch scale apparatus that allows continuous

measurement of the rate of iodine volatilization \vas used to perforrn these experiments. The

gas and aqueous phase speciation. as well as the hydrogen peroside concentration were

assessed for some tests.

4.1.1 Esperimental Apparatus

The apparatus was designed to allow the manipulation of individual parameters in order to

investigate iodine volatility in an irradiated s ystem under various conditions. The

esperiments kvere psrtomed in the irradiation chamber of a Gammace11 to simulatr the

radiation field in the reactor containment following an accident.

The constructed apparatus (Figure 4.1) c m be described as follows Ils]. The

centsrpisce of the apparatus was a 0 3 5 L stainless steel irradiation ~.esseI. This \.essel and a

custom built magnetic stir plate tvere pIacsd in the irradiation charnber of a Gamacel l 230,

~vhich had an a\-erage dose rate of 0.15 kGy/hr. The stir pIats itself \vas connected to a miser

capable of k-aqing the stir speeds (10-500 rpm) and consequent1)- the interfacia1 mass

transkr conditions insids the \-essel. A stir bar. inside a glass sleeve \\-as ~rsed to mis the

solution. Four gas-tight. stainless steel- needle \-alves connecte8 the irradiation vesse1 to gas

and liquid phase recirculation loops made of a combination of 1/8" and 1!16" stainless steel

tribirg.

Using a tubing pump (Mac;tdïes. model 7530-60 and a PTFE pump head). the liquid

Ioop transported the aqueous material inside the irradiation [.essel to a 50 mL Plexiglas

monitoring charnber outside the Gammacell at a rats of 0.15 mL.'s. This custom buiIt

charnber housed a water analyzer (ICM. model 5 160 1 ). consisting of pH. dissol\-ed os)-gcn

and temperature sensors. Each value was recorded at set timc intends (ranging betn-een 2-

30 minutes) as dictated by the test conditions.

Gas phase loop circulation was controlled with the use of a diaphragm pump (GAST

rnodel DOA-P104-AA) possessing a tïxed flow rate of 70 mL/sec. This allow-ed the \-olatiIe

material produced in the vesse1 to be transferred to a monitoring assembly. The monitoring

assembly consisted of species selective adsorbents - Cdl, and triethylenediamine (TEDA)

impregnated charcoal - housed in Tygon tubing to trap the gaseous iodine species. and 2

2x2 Nd detector (Aptec, mode1 DB-I O 1)-

13 1 Radioactive i was introduced Ui the system as a tracer in order to obtain the

necessary rneasurements. The detector continuously rnonitored the activity in the adsorbent

(TEDA Charcoal). which was proportional to accurnulated volatile iodine. The signals from

the detector were sent to a cornputer (IBM 386) equipped wirh a multichannel analyzer -

MCArd - (Aptec PCMCNWin. version 5.3). A data acquisition and control program

(Aptec. Supervisor) kvas used to collect the data. Thé program \vas set to record a

measurement every 300 S.

NaI Detector with Collimator

&&se r to Computer Wate r -A.nalper

Adsorbent

Irradiation Vesse1

Stir-plate

Figure 4.1 Experimental apparatus for measuring iodine volatilization rates

4.1 -2 Experirnental Conditions

The esperimental conditions were based primarily on their espected values in a post-accident

reactor containment. The temperature and pressure of the system w-ere not controlled, but the

temperature remained stable at 28-30 OC and the pressure stayed near atmospheric. In heavy

tvater reactors the arnbient temperature and pressure may increase follow-ing an accident.

However, they stabilize to their pre-accident conditions shortly afier initiation of the

ernergency systems. A 0.15 k G y h Co-60 source was used as the radiation source.

Although the radiation dose rate \vas at the low end of that estimated for containment

structure folIowing a - p i c d accident. it was quite adequate to study the radiolytic chemistry

of iodine. A low radiation dose was in one way advantageous çince the radiolytic

accumulation and decomposition of products was sIowed d o m facilitating their

investigation.

The impact of organics on iodine volatility was evaluated for a range of possible post-

accident reactor conditions. The esperimental matris included the organic type. organic

concentration. iodine concentration. and solution pH. Threc organic types (alkyl halides.

carbonyls. and aromatics), three iodine concentrations ( IO-'. 10~'. and 1 o - ~ M). three pH

levels (5 . 7. and 9): and four organic concentrations (IO-'. IO-'. IO-'. and 1 o - ~ M) were

evaluated.

4.1.3 Experirnental Procedure

De-ionized water. used to make al1 the solutions. was prepared through a water purification

system (Bamstead Nanopure). The system consisted of two beds of ion-eschange resins to

remove inorganic impunties, and a charcoal bed to reduce the organic substances to 10 ppm.

The water was first passed through a reverse osmosis system (Culligan). before entering the

purification system. Iodine solutions were prepared using cesiurn iodide. Csl. (Aldrich 'Gold

Label'): iodine is expected to be released in form of Cs1 from breached fuel. Radioactive '"1

(Mandle Scientitïc) was introduced into the system as the tracer. Given the detection

efficiency of the N d detector. it was determined that a maximum of O. L mCi of '"1 \ a s

needed to detect volatilization rates as low as 1 0 - ' ~ mol/min. To prepare dilute organic

solutions, laboratory grade chernicals were used without q additional purification. For

buffered solutions, a combination of 0.1 M potassium phosphate monobasic (KH2P0,) and

0.05 M sodium tetra borate 0\la2B407.10H20) was used. This solution \vas effective for

buffet-& pH levels spanning the range of 5.8 to 9. The actual pH of the system was adjusted

using LiOH and H2S04.

An esperirnental run involved the following procedrire. A measursd amount of

watedbuffered-water. typically 250 mi,. was added to the vessel. ~vhich then was sealed and

connected to the recirculation loops- The gas and aqueous phase purnps were then activated

and the system pH kvas adjusted to the required level. The vessel \vas Iowered into the

irradiation site and the stir plate motor was initiated (at 110 rpm) to establish the desired

mass transfer conditions. A mixture of iodine (Cd) and tracer (radioactive "Il) was then

added to the system through an injection port in the aqueous phase line to produce the desired

iodine concentration in the vessel. Depending on the test conditions. a known amount of

organic compound was also added at this time. The rate of volatile iodine production as welI

as the gas and liquid phase speciation were assessed during the esperiments (see Section

1.1.4). At the end of each test- the apparatus was cleaned by rinsing a11 its interior surfaces.

hcluding those in the vesse1 and the aqueous loop. with a 5% nitric acid solution followed by

a nnse with purified water.

4.1.1 Analytical Procedure

Many of the measurements were achieved using radiochemical methods. which are quite

suitable for studying the behaviotir of iodine under the dilute conditions of interest. The rate

of volatile iodine production in the system was evaluated by continuousIy measuring the

activity of '"1 in air passing over well-rnixed irradiated Cs1 solutions. The arnount of

activity in the adsorbent, which was proportional to the mass of accumulated volatile iodine,

n-as monitored continuously by the detector. Iodine volatilization rate \vas calculated from

the slope of the accurnulated volatile iodine vs. time.

The gas and liquid phase iodine speciation in the presence ot'organics was evaluated

using radiochemical rnethods. Organic iodide and iodine in the gas phase were determined

using species selective adsorbents: CdI, on chromosorb-p and TEDA charcoal [65]- Cd[?

adsorbs molecular iodine while the charcoal adsorbs organic iodides and other volatile iodine

forms. The gas flow rate was reduced to 7 mL/s to provide an adequate residence time within

the adsorbents. The aqueous phase speciation was evaluated using a moditied version of the

procedure described by Evans et. al. [65]. 1 mL saniples of the aqueous phase werr estracted

into 2 rnL of chloroform. The iodine concentrations in the aqueous and organic phases were

determined by measurïng the iodine activity in the hvo phases. Determining the arnount of

activity in chloroform portion of the original sample indicated the relative moun t of organic

iodides and molecular iodine in solution.

Hydrogen peroxide measurements were performed using the Ghormley technique

[66] . A UV spectrophotometer (CARY 3Bio) was used to measure the triiodide

concentration, which was then related to a hydrogen peroxide concentration.

4.1.5 Mass Transfer Parameters

The liquid side mass transfer coefficient (k,) was determined by esarnining the mass transfer

of osygen from the gas to the liquid phase. using a dissolved osygen concentration probe

(ICM, mode1 51601). A dissolved oxygen level of near O pprn was obtained by bubbling

nitrogen through the liquid, after which air was added to the vesse1 gas phase. The liquid

side rnass transfer coefficient was determined to bc 1 -5x lo4 and 4.5, IO-' d d s for stir

speeds of 1 10 and 380 rpm, respectively (see Appendix A).

The gas side mass transfer coeficient (kg) - was determined by measuring the change

in the relative humidity of the air passing through the vessel, using a relative humidity and

temperature probe (Barnant Co.. mode1 637-0050). More specitically- the rate ofevaporation

of water, which is directly proportional to the gas side mass transfer coefficient. could be

calculated based on the change in the relative humidity and the kno~vn flow rate of the air.

The gas side mass transfer coefficient was found to be 1 x IO-' dm/s and was not significantly

affected by the stir speed (see Appendix A). Based on the partition coefficients (H) of the

volatile iodine species' the liquid side mass transfer was espected to dominate the overall

mass transfer rate.

The above results were confirmed by measuring the rate of iodine volatilization in an

irradiated system at two different stir rates (1 10 and 380 rpm). The ratio of the volatilization

rates was 2.3, which is in good agreement with the corresponding ratio of the total mass

transfer coeff~cients which was 2-5 (from I/KoL = l/k, + H/k& -

The fact that for this apparatus the iodine volatilization rate \vas nearly proportional to

the mass transfer coefficient in the system indicates that the steady state volatile iodine

concentration in the aqueous phase was not changed significantiy by aitering mass transfer

conditions- The proportionality c ~ ~ r r n e d that the release of iodine from the solution,

required in these tests in order to obtain the desired measurements. did not interkre cvith the

radiation chemistry witl-iin the solutions. It can be inferred that the rates of the formation and

destruction reactions responsible for determining the volatile iodine concentration were rnuch

faster than that of mass transfer under the given conditions. The esperiments for determining

iodine volatilization rates were conducted using constant mass transfer conditions (stir rate of

110 rpm). Therefore, the changes in the volatifization rates observed under various

conditions could be used as a measure of the changes in the aqueous phase iodine chemistry.

4.1.6 Commissioning Experiments

In order to evaluate the reliability of the apparatus. a set of experiments was performed to

examine the gas phase iodine measurement system. the adsorbent efficiency. and the

potential for iodine capture by the interior surfaces of the system.

The efficiency of the Na1 detector \vas evaluated. rising a 3x3 well type N d gamma

counter ( L m 1282 Cornpugamma). The results indicated that the N d detector. with an

average efficiency of 2%' was suitable for measuring the gas phase activity. The TEDA

charcoal retention efficiency for adsorption of volatile iodine species was more than 97%.

The activity measured in the line samples indicated that the iodine remaining on the entire

gas and liquid loops was less than 2% of the total iodine in the system. An activity balance

perfomed at the end of various tests showed that the retention of iodine on surfaces within

the apparatus represented a negligible portion of the total iodine in the system. The addition

of 105 M ~ e " to a pH 5. 10-' M Cs1 solution did not have any significant impact on iodine

volatility. indicating that any corrosion in the system should not have affected the results.

This experiment was performed to evaluate the potential impact of corrosion even though

there \vas no visual evidence of corrosion in the vessei.

Due to the highly reactive nature of the iodine. the possibility of interaction with the

surface of the apparatus \vas esarnined. Molec ular iodine concentrations in a soIution

irradiated in the stainless steel apparatus were compared to those observed in a similar

solution irradiated to various doses in a glass container. The 1, concentrations were identical,

indicating that reduction of 12(aq) due to interaction with the stainless steel surface did not

have any significant impact on the results.

4.2 Identification and Quantification of Iodine Specics

The objective of this set of experiments was to identify. and when possible quantify. organic

iodide and molecular iodine formation through the analysis of the gas and aqueous phases of

irradiated iodine solutions. Gas chromatograp hy. mass spectrometry. and UV

spectrophotometry were used to analyze the gas and liquid phases of irradiated iodine

solutions containing added organics.

4.2.1 Sample Preparation

Cesium iodide. (Aldrich 'Gold Label') and laboratory grade organic compounds were

usrd to make the test solutions. The sarnples had an iodine concentration of IO-' M and an

organic concentration of 10" M. For mass spectrometry experiments some solutions with

higher iodinr concentrations (1 O-' and 10" M) were also sxarnined. The solution pH was 5.

~ki th a buffer consisting of 0.1 M potassium phosphate and 0.05 M sodium borate.

The sarnples. 20 mL in volume. were placed in 40 mL glass scintillation vials capped

with a septa and cvere irradiated in a Co-60 Gammacell 220 with an average dose rate of 5

kGy/h, This dose rate, whïch represents the expected dose rate in a post-accident reactor

containment. \vas about 40 times higher than the one used in iodine volatilization tests. The

dose rate will affect the total molecular iodine concentration under some conditions.

However, the types of organic iodides Formed should be relatively independent of the dose

rate. Sarnples were irradiated for a dose of 2.5 kGy to establish a steady state concentration

of hydrogen peroside. afier which organics werr added to the solutions and the smples cvsre

re-irradiated with an additionai dose of 2.5 kGy.

42.2 Identification of the Types of Organic todides Formed in the Systern

A gas chromatograph (HP 5890 11) with a mass selective detector (HP 5971A) was used to

identi- organic iodides in the gas and liquid phases of the samples containing various

organics. The gas chromatograph had a capillaq- column (HP-5. 30 m x 0.25 mm) suitable

for detecting halogenated compounds. The gas phase anaiysis of the sarnples was perfbrmed

by injecting up to 500pl of the gas above the solutions into the gas chromatograph. The

carrier gas was helium with a flow rate of 30 mL/min. The initial column temperature \vas

70°C. which was held for 10 minutes, and then raised at a rate of 50 "C/min to a finai

temperature of 120 OC. which was held for 3 minutes. The injector and detector temperatures

were 100 OC and 380 OC, respectively.

The liquid phase analysis of the samples cvas carried out by extracting organics tiom

20 mL sarnple solutions into 2 rnL of isooctane. 10 pL of the isooctane was injected to the

gas chromatograph. The carrier flow rate was 20 d / m i n . The initial c o l u m temperature

\vas 90°C- which cvas held for 5 minutes, and then raised at a rate of 50 "C/min to a final

temperature of 170 OC. which was held for 3 minutes. The injector and detsctor temperatures

were 150 OC and 280 OC- respectiveiy.

4.2.3 Measurement of Organic lodide Formation

A gas chromatograph (PEFKN-ELMER Auto System XL) with an electron capture detector

(Pm N610-0063) was used for determining iodo-organic concentrations in the gas phase.

The _sas chromatograph had a c a p i l l q colurnn (Simplicity 5, 30 m x 0.32 mm) suitable ['or

detecting halogenated compounds. The gas phase analysis of the samples was p e r h e d by

injecting 5OpL of the gas above the soIutions to the gas chromatograph. The carrier tlow rate

\vas 30 mL/min. The initial column temperature cvas 40°C. which \vas heId for 10 minutes.

and then raised at a rate of 40 "C/min to a final temperature of 120 OC. which was held for 3

minutes. The injector and detector temperatures were 100 OC and 200 OC. respectively. A

four point standard solution with

employed to create the calibration

B.

known iodomethane and iodoethane concentrations was

curves. The calibration curves are providrd in Appendis

4.2.4 Measurement of Molecular Iodine Formation

A W spectrophotometer (CARY 3Bio) was used to measure the molecular iodine

concentration in the presence of organics. The liquid phase i, concentration was evaluated

using the Leuco Crystal Violet method [67]. A six point standard solution cvith known I2

concentrations aras employed to create the caIibration cume. The calibration c w e is

provided in Appendis B

1.3 Quality Assurance

Procedues were implemented to ensurc the continued accuracy of the msasuremsnts

performed in the expenments.

43.1 Iodine Volatilization Rate

The majority o f the rneasurernents obtained for this set of esperiments involved a direct

reading fi-orn various probes and detectors. Accurate gas phase iodine volatilization rates

were dependent on several parameters such as the detection process. The efficient- of the

N d detector used to monitor the gas phase was evaluated by measuring the activity of the

charcoal traps collected in each test and comparing the Nd detector measurements with those

obtained by a gamma counter (LKB 1282 Cornpugamma). The ongoing performance of this

Na1 detector was monitored by verifying its efficiency at the end of each test.

The total activity in the solution was established by measuring the activity of 1 mL

Iiquid samples at the beginning of each test. The total initial iodine (as 12 concentration in

some of the solutions was checked using a UV spectrophotometer.

Flow meters used for the gas phase loops were calibrated and used to ensure that the

flow rate did not Vary appreciabky bettveen tests.

Two probes were used to ensure the accuracy of the pH measurements during the

tests- One probe was used on line as it was incorporated in the water analyzer. while the

other kvas an extemal pH probe (Orion. mode1 410A). Comparative probe readings were

found to vrvy by Iess than + 0.07. The dissoIved oxy-gen probe kvas calibrated at the start of

each of the tests in which it was iised. However. unlike the pH measurements, it was not

possible to confirm the values obtained using an estemal probe.

The pipettes used to rneasure the volumes of the tracer and aqueous saniples were

calibrated in regular bases by an electric balance (Ohasu. modei TS 120).

4.3.2 Gas and Aqueous Phase Analysis

The analytical equipment was tested in order to ensure the accuracy of the measurements.

The UV spectrophotometer was calibrated for I1 concentrations between 10-' and 1 0 - ~ M

and for H202 concentration between 2 x 10-' and 5 x 10-' M. Statistical analysis of the

results showed that the absorbance readinzs obtained €rom the UV were linrarly correlated

tvith the concentrations and that the intercept \vas not significantly different fiom zero at the

95% confidence level (Appendix B). The gas chromatograph was calibrated for iodoethane

and iodomethane concentrations between 1 0 - ~ and IO-' M. Statistical analysis of the results

showed that the pick areas. obtained from the GC. were linearly correlated with the

concentrations and that the intercepts were not significantly different from zero at the 95%

confidence level (Appendix B). The continued analytical performance of bot11 the W

spectrophotometer and the gas chromatograph \vas monitored by the analysis OF standard

sarnp les.

5 FWSULTS AND DISCUSSION

The impact of organic compounds on iodine behaviour in irradiated systems was studied.

The rate of voIatile iodine production was evaluated for a range of- post-accident containment

conditions in the presence and absence of organics. The results obtained could. for the most

part, be interpreted based on the existing theories. Gas and liquid phase analysis enabled the

identification of the types of organic iodides Eormed with different organics present in the

irradiated systems. A kinetic-based mode1 was developed to simulate iodine radiation

chemistry in the presence of organics. The mode1 was evaiuated through a cornparison of its

results with those of the experiments. The following. is a description and discussion of the

esperimental results, as well as an explmation and evaluation of the model. A detailed

compilation of the experimental results is provided in Appendix C.

5.1 Iodine Volatility in the Absence of Organic Compounds

In order to study iodine volatilization in the absence of organic compounds. a set of control

experiments were performed. Key parameters that affect iodine volatilization. such as

radiation, iodine concentration_ and solution pH were esamined. The impacts of the solution

buffer and pH adjusters were also investigated.

5.1.1 Radiation

The radiation field in a post-accident reactor containment would Vary with the amount of

radionuclides released fiom the core. Radiation significantly affects iodine volatility by

inducing chemicai changes in irradiated solutions. throush the production of reactive free

radicals.

In order to evaluate the importance of radiation on iodine volatility and organic iodide

formation. the iodine volatilization rate in non-irradiated systems was evaluated in the

absence and presence of organics. No appreciable arnount of iodine was transferred to the

sas phase in the absence of radiation. The iodine volatilization rate for a non-irradiated IO-'

M iodine solution at pH 7 \vas about 3 x 10-l3 rnol/rnin. This rate is two orders of magnitude

lower than that under similar conditions in the presence of radiation (see Section 5.1 -3).

Neither the addition of IO-' M organics such as rnethyl ethyl ketone (MEK). toluene. and

trichloroethane (TCA) to the system nor the change in the solution pH to 5. had any

significant impact on iodine volatility (Figure 5.1). When the system kvas transferred to the

irradiation site. however. the volatility increased significantly (Figure 5.2). This test

indicated radiolytic iodine reactions are responsible for iodine volatility in irradiated systems.

both in the absence and presence oforganics.

0 100 200 300 JOO 500 600 700 a00 900 1000

Time (min)

Figure 5.1 Iodine volatility in non-irradiated system (iodine concentration 1 O-' M. pH 7): organic addition: MEK at t = 500. toluene at t = 650. TCA at t = 800. changing solution pH to 5 at t = 900 min

200 400 600 800 1000 1200 1400 1600 1800 2000

Titne (min)

Figure 5.2 Increase in iodine volatility after transferring the system to the irradiation site at t = LOO0 min

The results are as expected since aqueous chernistry is Iargely influenced by

- radiation. Water radiolysis products (e, . H. OH. H202). which are formed through the

interaction of radiation vclth water molecules. arc highly reactive species that can react with

each other and with any other chernicals that esist in the solution such as iodine and organics.

Iodine volatility increases considerably with irradiation, due to the osidation of non-volatile

1- to volatile 1, by the primary cvater radiolysis product- OH (Equations S. 1 and 5.2)-

F + O H - I + O H (5.1)

I d - - + ( 5 2 )

Since these reactions do not occur in the absence of radiation. any signiiicant volatilization of

iodine is not expected. The lotv volatilization rate observed in the absence of radiation

(Figure 5.1) is probably due to the thennai osidation of iodide.

Liquid phase speciation of non-irradiated systems in the presence of various organics

(MEK. toluene, and TCA) at different pH values (5 . 7. and 9) did not shou- any significant

increase in organic iodides formation. The percentage of total estracted iodine to the organic

phase was less than 0.5% under al1 the above conditions. Hotvever. when esposed to

radiation the organic iodide formation increased in the system. Liquid phase speciation

showed that more than 4% of the aqueous phase iodine was in a form that was estracted into

chloroform, and hence presurnably in the form of I2 or organic iodide. Thus it appears that

organic iodide formation mainly occurs through radiolytic reactions.

The formation of organic iodides is believed to occur mainly through the reaction of

organic radicds with molecular iodine (Equation 5.3).

K+12-M+I

Radiation is essential to the production of the reactants. R' and i2. in this reaction (see

Sections 5.4.1.1 and 5-4-12). Hence. without radiation no significant organic iodide

formation occurred in the system.

The eEect of radiation dose rate on iodine volatilization rate was not studied due to

experimental limitations. The radiation dose rate will affect the rate of formation of çvater

radiolysis products and hence, rnay influence the aqueous phase molecular iodine

concentration and the volatilization rate. However. the underlyuig mechanism associated

with the aqueous phase radiation chemistry will not be affected by the radiation dose rate.

Therefore, the trends associated with various parameters. including the presence of organic

cornpounds, on iodine radiation chemistry discussed in the foIlowing sections will not be

expected to Vary substantially at different dose rates.

The effect of water radiolysis product concentration was studied in a solution without

organics. The iodine volatilization rate. under acidic conditions slowIy increased at the

beginning of radiation reaching a constant value in about 500 min. This corresponds to the

time required for H202 to accumulate in the solution. The accumulation of H202 will affect

the concentration of other water radiolysis products that also play an important role in

determining iodine volatilization rate. Figure 5.3 shows the concentration of H,O,. measured

by a UV spectrophotometer, and the iodine volatilization rate.

At the beginning of irradiation, a low production of I2 results because the yield of e',,

and H is higher than that of OH and so little oxidation of 1- occurs through the following

reaction:

1- + OH --+ --+ 1, +- products

Once a sufficient concentration of H202 has built up in the systern. its reaction with e-,, to

form OH (Equation 5.5) can cornpete to a significant estent with the reactions of O2 cmd H

with e, (Equations 5.6 and 5.7). Therefore. the system becomes more oxidizing and the

concentration of I2 increases. AS a result of this increase in I2 concentration. the

volatilization rate also increases until it approaches a constant value. The iodine

volatilization rates reported

O btained.

here are based on measurements made once constant values

HZO1 + e-aq ---+ OH +- OH-

O? - e-,, - O?-

Hie-,--+H2+OK

Time (min) 1 e H202 o lodine 1

Fioure 5.3 Cornparison of iodine volatilization rate and hydrogen peroside concentration at the beginning of irradiation (iodine concentration 10-> M. pH 5 )

5.1.2 Iodine Concentration

The total iodine concentration in reactor contaiment following an accident would depend on

the e?crent of fuel fàilure. In a severe accident. the aqueous phase iodine concentration has

bern estimated to be in the order of 10" M. HLowever. due to many uncertainties associated

with the possible extent of the accident and containment geometry, a wide range of

concentrations are possible. In this stridy. iodine solutions (as Csl) ranging from 1 O-' to 1 oV6

M were exarnined.

Over the range of study. the results (Figure 5.4) indicated that iodine volatilization is

strongly dependent on the initial iodine concentaation. For instance. at pH 5 the volatilization

rate increased 10 times when the iodine concentration was raised from 1 oV6 to IO-' M. The

results were as expected since iodine volatility depends greatiy on the osidation of non-

volatile r by OH to the volatile I2 form. At l o w 1- concentrations. cornpetition between 1-

and other molecules and radicals for OH inhibwits the production of 12. For esample. H202

can compete with r for OH. Therefore. for hipher r concentrations. the opponunity for its

reaction with OH is greater. thereby producing more volatile 1,. At lower I- concentrations

other less volatile iodine species. such as HOI. become more important [16].

i O 1 00 200 300 400 sa0 600 700 aoo guo rooo Time (min)

1 ~ ( C S I 1E-4 M) E6 9 (Cs1 1E-5 M) €7 2 (Cs1 1E-6 M j E8 1

Figure 5.4 Volatilized volatilized iodine for Cs1 and 10'. rcspectively.

iodine at various Cs1 concentrations (pH 5 ) . In this figure. the concentrations of 1 O? 1 O-'. and 10-~ M are rnultiplied by 106. 10'

5.1.3 Solution pH

The pH of the water in containment rnay vary substantially between accident scrnarios

depending on factors such as the initial pH, the presence of buffers and the éffectivençss of

any deliberately added material. Thus a range of possible pH in containment water is

expected. In this study the effect of pH. between 5 and 9. on iodine volatility was sxarnined.

The pH \vas found to be a very importani factor influencing iodine volatility for al1

the 1- concentrations exaniined. The trend of increasing volatility rates with decreasing pH is

provided in Figure 5.5. As an example? for a 10-' M 1- solution. the volarilization rate

decreased from 1.2 x 1 O-" rnol/min at pH 5 to 5 x 10-%ol/rnin at pH 9. The. effect of pH

on iodine volatility can Iargely be attributed to the pH dependency of the reduction of 1, bj-

HzO, (Equation 5.8) and the hydrolysis of IZ (Equation 5.9). Under acidic conditions, the rate

of Iz reduction decreases Ieading to an increase in volatile species.

Figure 5.5 The impact of pH on iodine volatilization rate

5.1.4 Solution Buffer and pH Adjusters

A combination of 0.1 M potassium phosphate and 0-05 M sodium borate \vas used as the

bufter. This combination. which is used in some reactor containments to control the pH

following an accident, is effective for a range of acidic and alkaline conditions. The impact

of the buffer was investigated by initiating a test (Cs1 IO-' Mt pH 7) in the absence of the

buffer and consequentiy injecting a concentrated buffer into the system. The iodine

volatilization rate decreased by about 40% in the presence of the buKer. This is likely due to

the cornpetition between phosphate and H202 for e-,,, (Eqiiations 5.10 and 5.5). Therefore.

the effect of the phosphate is to reduce the oxidation of iodine by inhibiting the formation of

OH from eA,,.

- e , + H2P0,-- HPO/- + H (5.1 O)

e;, + H202- OH + O H (5.5)

The rate constant for reaction S. 10 is about 3 orders of magnitude lower than that of reaction

5.3 [16]. but the concentration of phosphate at pH 7 is several orders of magnitude higher

than that of

3-

LiOH and H2S04 were used as the pH adjusters. The impacts of Li7 and SO,- were

examined by adding 1 O-' M Li2S0, to the systern. LilSO, did not show any impact on iodine

volatiIity. indicating that these pH adjusters do not &kt the results.

5.2 Iodine Volatility in the Presence of Various Organics

Three groups of organic compounds are likely to be tound i n containment: carbonyls.

aromatics. and alkyl halides (see Section 32.7). Carbonyl compounds rnay be released in

signifiant amounts from the paints used in the containment. h o m a t i c compounds rnay be

released by the paints; they rnay also be representative of the oïl and Iubricants present in

containment. Alkyl halides rnay be present in containment due to the degradation of plastics

or paints containing vinyl chloride. The effects of these organics on iodine volatility were

investigated in irradiated systerns.

5.2.1 The Impact of Organics on Solution pH

Figure 5.6 shows the typical results on the addition of orpnic impwities in an irradiated

system. Solution pH decreased and iodine volatilization rate increased following addition of

organic compounds. The decrease in the solution pH is due to the radiolytic oxidation of

organics to organic acids. The impact of organics therefore rnay be partially indirect due to

induced changes in pH and partially direct, due to scavenging of radicals or formation of

organic iodides. To investigate this phenomenon. the experiments were performed in pH

controlled solutions.

O IO0 200 300 400 SOC 600

Time (min)

f 0 PH ovolatilized lodine

Figure 5.6 The impact of methyl ethyl ketone (MEK) and trichloroethane (TCA) on solution pH and iodine volatility (iodine concentration IO-' M. unbuffered solution)

In irradiated systems. even in the absence of organics. the solution pH decreased due

to the formation of water radiolysis products (Figure 5.7). However, a decrease in solution

pH. resulting in an increase in iodine volatility. was much more pronounced in the presence

of organics (cornparison of Figures 5.6 and 5.7).

300

Time (min)

Figure 5.7 The impact of radiation on soIution pH and iodine volatility (iodine concentration 10" M. unbuffered solution)

A cornparison of the change in solution pH in the absence and presence of various

organics after receiving a total dose of 5 kGy, (TabIe 5.1) showed that the amount of

reduction in pH is dependent upon the organic type.

Table 5.1 Reduction in pH for unbuffered solutions with added organics (1- concentration 1 O-' M, organic concentration 10" My total dose 5 kGy. dose rate. 5 kGy/h)

1 I

1 trichloroethylene 6-1 3.3 1 Organic Type initial pH

methyl ethyl ketone

toluene

no organics

pH afier 5 kGy 1 6.1

6.1

6.1

4.7

5 .O

5.8

5.2.2 The Impact of Various Carbonyls, Aromatics, and Alhyl Halides on Iodine

Volatility

A set of experiments was performed to study the impact of various types of carbonyls.

aromatics. and alkyl halides on iodine volatility. The principal objective \vas to evaluate the

feasibility of classiQing organic compounds into groups, based on their distinct impacts on

iodine volatilization. I f such a classification is possible. one organic in each group can be

considered for detaiied study to represent the behaviour of other organics in its group.

Besidss, such a classification is essential in developing a generic mode1 of organic iodide

formation for di fferent types of organics.

The primary water radiolysis products tend to react cvith the functional group present

in an organic molecule rather than the molecule as a whole. Hence. each organic cornpound

should be reasonably representative of other simple organic compounds containing the same

f~inctional groups [68]. In such a manner. a theoretical basis esists for chssi@ing organic

cornpounds into groups. based on their molecular structures- Hon-e\-er, esperimental

evidence is needed to evaluate the strengths and limitations of such a classification.

Iodine volatilization rates were evaluated in the presence of various alkyI halides

(dichloromethane. 1.1.1-trichloroethane. trichloroethylene). carbonyls (methy 1 ethyl ketone.

methyl isobutyl ketone. diethyl ketone). and aromatics (benzene. toluene. styrene). The

experiments were performed under the fo llowing conditions: iodine concentration 1 O-' M.

organic concentration 10" M. and pH 5. Al1 the experiments were started without any added

organics. Organics were then injected into the system (after 1000 to 2000 min).

The rate of iodine volatilization in the absence of organics was (1.5 * 0.3) x IO-"

movmin. This small variation indicated that the reproducibility of chis type of esperirnent

\vas typically within 25%-

The rates of iodine volatilization in the presence of various organics are provided in

Figure 5.8. The results indicated that organics with simiIar rnolecular structures have a

similar impact on iodine volatility- The iodine volatilization rate increased 50-1 00 times in

the presence of alkyl halides. and 3 4 times in the presence of carbonyls. The volatilization

rate decreased to 25-5096 of its original value in the presence of aromatics. Liquid phase

speciation showed an increase in organic iodide formation for solutions containing carbonyls

and alkyl halides. The results of the impact of various organics on iodine behaviour are

discussed in Section 5.3.

halides

Figure 5.8 Iodine volatilization rates in the presence of various organics (A: trichloroethane, B: trichloroethylene. C: dichloromethane. D: methyl ethyl ketone. E: methyl isobutyl ketone, F: diethyl ketone, G: styrene, H: toluene, 1: benzene) (1- IO-^ M. pH 5 )

5.3 Iodine Volatility in the Presence of Organics at Various pH and Iodine

Concentrations

The effect of organics on iodine volatility for a range of iodine concentrations and solution

pH \vas snidied. Previous experiments indicated that various organics that belong to an

organic type have similar impacts on iodine volatility (see Section 5.2). Therefore. one

chemical in each of the carbonil. alkyl halide. and aromatic group was chosen for detailed

study: methyl ethyl ketone (MEK). toluene- and 1.1.1 -trichloroethane (TCA).

Selection of the sarnple chemicals was based pnmanly on the composition of the

largsst potential source of organics in the containment. which are surface paints. MEK and

toluene are the main constituents of vuiyl paint and the thinner used with this paint,

respectively. while TCA is the main component of polyurethane paint and its thimer [3 11.

The actual concentration of organic compounds in the reactor pool following an

accident is difficult to predict. An estimation of the iikely aqueous concentration of organics

in the 1 O-' to 1 O-' M range was obtained from the release of ketones from paints [3 11.

However. the actual concentration in containment would be detennined through a balance

between the rate of release of thz compound, from paints. plastics. lubricants. etc., and the

rate of destruction through radio lytic processes. In this study, organic concentrations in the

range of 10-~ to 10-' M were esarnined. The upper lirnit was based pnmanly on solubility

considerations while the lower value was based on the cornpetition for radiolytic radicals.

The matrix for these experiments involved organic type. organic concentration. iodine

concentration, and pH. The experiments for each organic compound involved t h e e iodine

concentrations (10"' 10-j, and IO-' M) and three pH values (5. 7. and 9). For pH 5. four

organic concentrations (10"- 10-~; IO-'. and 10" M) were examined while for pH 7 and pH

9 only an organic concentration of 10" M was studied. The organics at concentrations of

less than IO-' M did not have any significant impact on iodine volatility. Gas and liquid

phase speciation in the presence of organics were perfomed using radiochernical methods.

5.3.1 The Effect of Carbonyls

The presence of MEK significantly increased iodine volatilization rates (Figures 5.9 and

5.10)- in some cases. by more than an order of magnitude. The impact of MEK was more

pronounced for lower iodine concentration (Figure 5.9). For example. at pH 5 the

volatilization rates increased 10' 4, and 2 times for the r concentrations of IO". 10-'. and

1 O-' M. respectively.

Figure 5.9 The impact of MEK on iodine volatilization rate at vanoris iodine concentrations (PH 5 )

L O .- Ii' 2 IE- I I

Figure 5.10 The impact of MEK on iodine volatilization rate (bvo adjacent coturnns represent the results for solutions with the same iodine concentrations and pH values. MEK concentration is 1V3 M in the right side and O M in the left side colurnn)

Liquid speciation in the absence of organic compounds indicated that under al1 the

examined conditions less than 1% of the total iodine was in an organic form. Table 5.2

shows Iiquid speciation for various iodine concentrations and pH in the presence of MEK.

Organic iodide in the liquid phase increased signiticantly under acidic conditions and for Iow

iodine concentrations,

Table 5.2 Liquid speciation in the presence of 10" M MEK: the percentage of total iodine extracted to the organic phase

Gas phase speciation in the presence o f MEK at various pH and iodine concentrations

is provided in Table 5.3. It is evident that the majority of volatile iodine particularly at low

iodine concentration and under acidic conditions were in non molecular iodine forms. In the

absence of organics in the solutions, about 50% of the volatile iodine was absorbed in the

charcoal.

Table 5.3 Gas speciation in the presence of 10-' M MEK: the percentage of iodine adsorbed in the CdIl (assumed to be 12) and TEDA charcoal (organic iodides and other volatile iodine forms)

pH 5 (% in CdIz & % in Charcoal)

pH 7 (% in CdIz & % in Charcoal)

The overafl increase in votatitization rates and the formation of organic iodides in the

presence of MEK may be descnbed as follows. Alkyl radicals- produced through the

radiolysis ofdilute carbonyl solutions. react with I2 and 1 to produce volatile organic iodides.

A more detailed mechanistic interpretation is provided in Section 5.4.1.2. The organic

iodides formed. in many cases. are more volatile than molecular iodine? resulting in an

increase in the volatilization rates. The rates of destruction of some organic iodides are

slower than those of I2 and 1. This can also contribute to an increase in the volatiIization rate.

A higher organic iodide formation at lower pH (Tables 5.2 and 5.3) is partLy due to the

increase in molecular iodine formation under these conditions. Obviously with an increase in

molecular iodine concentration_ there is more I2 available to react with organic radicals to

12% & 88%

7% & 93%

pH 9 (% in CdIz & % in C harcoal) 18% 6C 82%

9%&91% 2% & 98%

form organic iodides. An increase in the percentage of organic iodides formed at lower

iodine concentrations (Tables 5.2 and 5.3) may have resulted from the cornpetition of r and

organics for OH. At loi\-er iodine concentrations the ratio of r to organic molecuIes is lower

and hence. more of the OH reacts with organics than T. This results in a higher ratio of

organic radicals to Iz, which in tum results in the conversion of higher tiaction of I2 to

organic iodides.

5.3.2 The Effect of Alkyl Halides

Iodine volatilization rates increased greatly. in some cases by more than two orders of

magnitude, in the presence of TCA (Figures 5.1 1 and 5.12). As in the case of MEK. the

impact of TCA was more pronounced at lower iodine concentrations. with the exception of

the pH 5. Cs1 1 0 - ~ M solution. For esample. at pH 7 the volatilization rate increased by 55.

15. and 4 tirnes for r concentrations of 10". 1 O-'. and 104 MI respectively. Therefore. with

higher TCA concentrations (e-g. 10" M). iodine volatilization rates were l e s concentration

dependent (Figure 5.12). The impact of pH on iodine volatilization rates for TCA systems

was aiso addressed. For the IO-' and IO-' M Cs1 addition of TCA had a greater impact on

volatility at lower pH values (Figure 5.12). For esample. at 1 O-' M iodine concentration. the

votatilization rates increased by 100. 15. and 9 tinles for pH 5. 7- and 9. respectively,

Figure 5.1 1 The impact of TCA on iodine volatilization rate at various iodine concentrations (PH 5 )

Figure 5.12 The impact of TCA on iodine volatilization rate (two adjacent colurnns represent the results for solutions with the sarne iodine concentrations and pH values. TCA concentration is IO-' M in the right side and O M in the lefi side column)

The gas and the liquid phase speciation in the presence of TCA is provided in Table

5 4 The gas phase speciation indicated that. unlike in the case of MEK. approvimately half

of the airborne iodine adsorbs in cdlll. assurned to be 1?.

Table 5.4 Gas and liquid phase speciation in the presence of IO-' M trichloroethane (pH 5 )

1 liquid speciation (% extracted to chloroform) 1 I I

2.5 % 8% 1

The increased rate of iodine volatilization in the presence of TCA ma), be desct-ibed

as foilows. Organic radicals produced through the dechlorination of alkyl halides in

irradiated solutions react with I2 and I to produce volatile chloro-iodo organics and organic

iodides. The increase in II concentration in the presence of alkyl harides likely resulted tiom

the scavenging of by RCl that leads to less conversion of I? to 1-. A more detailed

mechanistic interpretation is provided in Sections 5.4.1.1 and 5-43. The larger increases in

the volatilization rates at lower iodine concentration and lower solution pH observed for TCA

systerns share a similar esplmation as that for MEK systems (Section 4.3. I ).

5.3.3 The Effect of Aromatics

Toluene affected iodine volatility in a manner different to that of MEK and TCA. Under

acidic conditions. at al1 iodine concentrations the volatilization rates were reduced in the

Cs1 IO-" M

47% & 53%

L

gas speciation (% in CdI, & % in charcoal)

presence of toluene (IO-' M) to as low as 30% of its original values (Figure 5.13). Under

Cs1 IO-' LM

45% & 55%

basic conditions, however, the iodine volatilization rate increased at lower iodine

1 The iodine adsorbed on the CdI, is comrnonly believed to be in the form of 1:- However. iodofonn is also absorbed hence it is possible that chloro-iodo organics were also retaiiied.

concentrations (Figure 5. f 4). Toluene was more effective in reducing the iodine

volatilization rates at higher iodine concentrations and lower pH values. Similady, it was

more effective in increasing the volatilization rates at Lower iodine concentrations and higher

pH values. For example. the volatilization rates decreased to 30% of its original value at 1-

104 M and pH 5. while it increased to 5 times its original value at 1 0 - ~ M and pH 9. Since

toluene was more effective in reducing volatility at higher iodine concentrations. the

volatilization rates in the presence of toluene were less concentration dependent. Liquid

speciation at various iodine concentrations did not show any significant change in organic

iodide formation in the presence of toluene.

Figure 5.13 The impact of toluene on iodine volatilization rate at various iodine concentrations (pH 5 )

Fipure 5.14 The impact of toluene on iodine volatilization rate (two adjacent colurnns represent the results for solutions with the sarne iodine concentrations and pH values. toluene concentration is IO-' M in the right side and O M in the left side column)

The reduction of the iodine volatilization rates and lack of organic iodide formation in

the presence of toIuene c m be descnbed as follocvs. The apparent decrease of the overaI1

volatilization rate is likely due to the competition of aromatics with 1- for the OH r a d i d .

thereby decreasing the radiolytic osidation of T. The phenolic compounds fomed fiom the

radiolysis of aromatics tvould also decrease the volatility by scavenging OH radicals. The

decrease in the volatilization rate was more pronounced at higher iodine concentration and

locver pH conditions in which more r reacts with OH. Therefore, introducing aromatics that

scavenge the OH radicals makes a greater diffèrence in reducing the volatilization rates under

these conditions. The lack of organic iodide formation is due to the absence of organic

radicals in the systems. The reaction of aromatics with OH is primarily through ring

addition. Therefore. organic radicals are not created and there should not be significant

formation of organic iodides.

The increase in iodine volatility under basic conditions and Iow iodine concentrations

is Iess clear. A possible explanation is that under these conditions in the absence of organics.

the overall volatilization rate is relatively low. Therefore, formation of even low quantities of

aromatic iodides may affect total volatilization rate. In a study of LPC in the presence of

aromatics- it was suggested that these compounds do not appear to enhance organic iodide

formation. other than perhaps under basic conditions. but reduce the concentration of I2 1341.

5.3.4 Cornparison of the Impact of Organics on Iodine Volatility

Tne increase in volatile iodine formation, afier an addition of IO-' M MEK and TCA are

cornpared in Figure 5.15. When MEK \vas added, the volatilization rate increased and

remained constant (for more than 500 min.) afier which it slowly decreased to its original

value. With TCA, however, the volatilization rate sharply increased and afier a shorter time

period (about 50 min.) decreased rapidly. This quick change is most likely the resuit of a

decrease in TC A concentration through evaporation and/or destruction. When TCA and

MEK concentrations were decreased by a factor of 10; iodine volatilization rates dropped by

a factor of 100 and 2.5_ respectively (see Sections 53.1 and 5 - 3 2 } . CIearly the effect of the

elimination of TCA can cause a considerable change in the volatilization rate.

Time (min)

1 a TCA : ivlEK 1

Fisure 3.15 Increase in iodine volatility after addition of 10' M MEK and TCA (iodine concentration IO-' M' pH 5 )

A cornparison to assess the increase in iodine volatilization rates in the presence of

1 O-' M TCA at various pH values (Figure 5.16) indicated a similar behaviour. However. the

dope of change in the volatilization rate of a pH 5 solution was steeper. A rapid change in

iodine volatilization was also observed for solutions containing DCM (Figure 5.17)

Time (min)

Figure 5-16 Increase in iodine volatility d e r addition of IO-' M TCA at various pH values ( iodinr concentration 1 O-' M)

Time (min)

Figure 5.17 Increase in iodine volatility afier addition of 10" M TCA and DCM (iodine concentration 10-j M1 pH 5 )

Unlike the alkyl halides? the aromatics had a lasting effect on the iodine volatilization

rate. As it is seen fiom Figure 5.18 with the addition of toluene and benzene, the iodine

volatilization rate decreased. but remained at a constant value sven afier 600 minutes,

1 o Toluene -2 Benzene 1

Fioure 5.1 8 Drcrease in iodine volatility afier addition of 1 O-' M toluene and benzene at t =

50 min (iodine concentration IO-' MI pH 5 )

5.3.5 The Impact of Organics on Iodine Volatility in the Presence of Other Organics

Since the different types of organics had unique effects on iodine volatility. the impact of

some oryanics in the presence of others was studied. The p r i m q objective of these

experiments was to investigate whether the addition of aromatics to a system containing

carbonyls and alkyl halides woufd decrease the iodine volatilization rate. I f this \vas the case,

the release of aromatics from paint to the post-accident reactor poo1 could negate much of the

impact of the volatility erihancing solvents. Alternatively, pnmarily aromatic based paints

might be developed for use as a passive safety feature.

Benzene. MEKI and TCA (10" M) were added to the system (r IO-' M. pH 5 ) each

at various time intervals (Figure 5.19). The iodine volatilization rate decreased tvhen

benzene was added to the systern (fiorn 1.2 x !O-'* to 3.0 x 10-" rnoihin). Conversely. an

increase was observed following the addition of MEK and TCA (4 x 1 O-'' and 1.5 x 1 O-''

moVmin for MEK and TCA. respectively). However. the volatilization rates were

significantly lower than those observed in the absence of benzene. more specifically. the

addition of MEK and TCA to a benzene free system under similar conditions produced iodine

volatilization rates that were one to two orders of magnitude higher (3 -7 x 1 O-'' and 1 x 1 O-"

moumin for MEK and TCA. respectively) (Figures 5.20 and 5.3 1).

oO Aoooo V

@O0 oOo

&'" o0

. I 1

O 50 100 130 200 250 300 350

Tirne (min)

Figure 5.19 Iodine volatility after addition of MEK (at t = 150 min) and TCA (at t = 250 min) in the presence of benzene (added at t = 70 min)

Time (min)

oBenzene at t=70 MEK at t=150 3 MEK in the absehce of other araanics

Figure 5-30 Cornparison of iodine volatility afier addition of iLIEK- in the presence and absence of benzene

Time (min)

o Benzene at t=7O MEK at t=150 TCA at 1=250 c MEC.: in the absence of other org'anics ù TCA in the absence of other organics

Figure 5.21 Cornparison of iodine volatility afier addition of MEK and TCA. in the presence and absence of benzene

In another test. benzene was added to a system (1- IO-' M- pH 5 ) containing

trichloroethylene. Trichloroethylene alone in the systern, caused the iodine volatilization rate

7 5

to increase from 1.2 x 1 O-'' to 7.0 x 1 o - ~ mol/min. With the introduction of benzene to this

system the volatilization rate was significantly reduced to 2.0 x 10-'O rnol/rnin (Figure 5.22).

These experiments shocved that the iodine volatilization rate in the presence of carbonyls and

alkyl halides can be controlled by introducing aromatics to the system. either prior to or after

addition of other organics.

O O

O OOEiDO -r000000-CLO~3"00° I I I

O 50 100 1 50 200 250

Time (min]

Figure 5.22 Decrease in iodine volatility in the presence of trïchloroethylene (added at t 50) after addition of benzene (at t = 150)

Figure 5-23 illustrates the results on the addition of various concentrations of benzene

to an iodine solution (1- 1 M, pH 5 ) containing MEK ( 1 O-' M). I t is seen that introducing

any arnount more than IO-' M benzene decreases iodine volatility. The volatilization rate

decreases as benzene concentration increases from lo4 to 5 x IO-' M. However. at higher

concentrations of benzene (10" and 5 x 10" M)_ the volatilization rate does not significantly

decrease with an increase in the benzene concentration (Table 5.5).

100 150 200 250 300 350 400 450 500 Tirne (min)

Ficure 5-23 Decrease in iodine volatility in the presence of MEK (IO-' M) after addition of various concentrations of benzene ( total benzene concentrations in the system: IO-' at t = 65. 104a t t= 115_7.5x 104at t= 1 9 0 . 5 ~ 1o4att=280. 1 0 " a t t = 3 8 5 . 5 ~ 10"att=435)

Table 5.5 Iodine volatilization rates (r IO-' M. pH 5 ) in the presence of MEK (10" M) afier addition of various concentrations of benzene.

In order to study the effect of aromatics in the presence of other aromatics styrene was

Total Concentration of Benzene (M)

O

I E-5

1 E-4

2.5 E-4

5 E-4

1 E-3

5 E-3

added to an iodine solution containing benzene. Addition of IO-' M styrene to the solution

Iodine Volatilization Rate (mollmin)

4.5 E-10

3.4 E-IO

3.2 E-10

2.1 E-10

1.5 E-10

1.3 E-10

1.2 E-IO

containing 1 O-' M benzene did not affect iodine volatility significantl y (Figure 5.24).

O 50 100 150 200 250 300 350 400 430 50U Time (min)

Figure 5.24 Iodine volatility after addition of styrene (added at t = 3 10 min) in the presence of benzene (added at t = 50 min)

The rate constants for the reactions of benzene and I- with hydrosyl radicals are

simiiar:

C6H6 - OF[ v hq-drosy-cyclohexadienyi k = 7.8 x l o9 dm3 mol-' s-' (5.1 1)

t--oH----,~+oH- k = 7.7 1 0 h d m 3 nlo~-L S-' (5.1)

If the benzene concentration is significantly higher than that of iodine. it can effectively

compete with 1- for the OH radical. Therefore. less 1 and 1, are available in the solution to

react w-ith carbonyl and alkyl halide radicals and produce volatile organic iodides. Benzene

c m also effectively compete with other organics for the OH radical. leading to the less

organic radicals and, consequently. a lower rate of organic iodide formation. Many other

reactions will also take pIace in irradiated solutions containing aromatics. Therefore the

resuits of iodine volatilization rate c m not be interpreted quantitatively based on Equations

5.1 1 and 5.1 alone.

In general, the chanse in the volatilization rate as a result of introducing an organic

compound into a solution is affected by the presence of other organic irnpurities in the

system. A cornparison of iodine volatilization rates in solutions containing dichloromethane

in the absence and presence of other types of organics is provided in Table 5.6. This

illustrates ano ther exarnple of aîTecting iodine vo latilization rates when alky 1 halides are

introduced to the sjrstem containing aromatics and carbonyls.

Table 5.6 The impact of diethyl ketone and styrene on iodine voIatilization rates in the presence of dichlo romethane

1

1 dichloromethane 5.5 E-9

Organics lodine Volatilization Rate (moumin)

diethy 1 ketone + dichloromethane

5.3.6 Reproducibi l i~

Esecution of the volatilization esperiments was quite dernanding- with each test requiring a

cveek or two to complete. Hence, it was not possible to perforrn replicate tests in general. In

order to evaluate the reproducibility al1 the experiments were started without organics.

Organics were introduced to the systerns after 1000-2000 min. The rate of iodine

volatilization in the absence of organics, therefore, couid be used as an indicator to assess the

reproducibility of the results. For esperiments conducted in the presence of organics. a few

tests at various organic and iodine concentrations were also duplicated. A cornparison of the

replicate test results (Figures 5.25 and 5.26) indicated that the agreement was typically within

L-IE-9

styrene + dichloromethane 3.3E-10

25% and hence that the impact of parameters such as pH. iodine concentration, and organics

could be clearly distinguished. The average standard deviation for the volatilization rates in

the absence of organics was about 15%. Statisticd analyses of the resdts are provided in

Appendis D. A regression analysis of .-volatilized iodine vs. rime" yielded an value of

0.99 for most of the conditions (Table C-8)- indicating a very good correlation between the

variables. This shows that the dope of the line (volatilized iodine / time = iodine

volatilization rate) is constant for given conditions.

Figure 5-35 Cornparison of replicate results for iodine volatilization rates at various iodine concentrations (pH 5 )

IE-II L-

-4 M I MEK 1 E-3 M

1 E-3 M

Figure 5.26 Cornparison of replicate results for iodine volatilization rates at various iodine and organics concentrations (pH 5 )

5.4 Gas and Liquid Phase Analyses

Gas and liquid phases of irradiated iodide solutions in the presence of organics were analyzed

qualitatively and quantitatively. Any organic iodides and moIecuIar iodine formed in the

systems were identified and measured.

5.4.1 Identification of the Types of Organic Iodides Formed in the Systerns

Identification of the types of organic iodides formed in the presence of various organics

provides useful insight into understanding the process of organic iodide formation. It can

also be a valuable aid for modeling the system. Gas chromatography dong with mass

spectrornetry was used in order to identify the types of organic iodides formed in the gas and

liquid phases. in irradiated Cs1 (104 M? pH 5) solutions containing organics (10" M). The

reproducibility of the results was determined by perforrning andysis of the replicate sarnples.

Mass spectrornetry results are provided in Appendix E.

5.4.1.1 AIhyl Hatides

Different types of alkyl halides were added to Csi solutions during irradiation. Mass

spectrometry of the gas phase indicated that chloro-iodo organics are the major type of

volatile organic iodides formed in these systerns. Chloro-iodomethane was forrned in the

presence of dichloromethane. Dichloro-iodoethane and dichloro-iodoethylene were formed

in the presence of trichloroethane and trichloroethylene, respectively. A detectable amount

of rnolecular iodine was also identified in the gas phase.

Very few mass spectra for chloro-iodo organics are included in mass spectroscopy

libraries. Hence. these libraries could not be used as the basis for identieins the chloro-iodo

organics fomed in the presence of trichloroethane and trichloroethylene- These chernicals

were identified through interpretation of their mass spectrums (Appendis E).

Mass spectrometry is an excellent tool for identifiing unknown organics. with the

limitation that. it is more suitable for qualitative use and is not particularly sensitive to

organohalides. Therefore. iodo-organics at relatively Iow quantities may not be detected by a

mass spectrometer. Electron capture detection. which is well suited for deterrnining

organohalides. was therefore used to determine any other type of organic iodides formed in

the gas phase. Electron capture detectors are sensitive to even very low quantities of

organohalides. The results revealed that in addition to the chloro-iodo organics. iodomethane

is present.

Mass Spectrometry of the liquid phase was performed in order to determine the

presence of any significant quantity of non-volatile organic iodides in the liquid phase. Only

the same iodo-organics as those observsd in the gas phase of the solutions were detected in

the liquid phase.

It was suspected that other types of iodo-organics may have esisted in relatively low

quantities in the bas and Iiquid phases. Attempts were made to improve the detection by

mass spectrometry. by increasing iodide concentration of the solutions. When the iodide

concentration \vas increased to IO-' M and 10-' MI there \vas still no other detectable iodo-

organics in the gas and the liquid phases.

The results obtained from the mass spectrometry of the alkyl halides rnight be

interpreted as follows. The types of chloro-iodo organics formed in the irradiated systems

depend on the form of the radicals produced in the dechlorination processes which. in tum.

shodd depend on the mo1ecula.r structure of the original alkyl halide. Dichloromethane is

dechlorinated forming a chloromethane radical, which then reacts with iodine to create

cliloro-iodomethane. Trichiomethane is dechlorinated to forrn dichloroethane radical, which

reacts with iodine to produce dichloro-iodoethane. Tt-ïchloroethyIene is dechlorinated to

form dichloroethylene radical' which reacts with iodine to produce dichloro-iodoethylene.

The results of these experirnents might be extended to predict the types of iodo-organics that

c m be formed in the presence of other low molecular weight alkyl chlorides in irradiated

systems. Tt appears that the organic iodides have a sirnilar molecular structure as that of the

original alkyl chioride, with the exception of the replacement of a chlorine by an iodine

(Table 5.7). The presence of iodomethane in the systems is probably due to fùrther

dechiorination of the dkyl chlorides producing alkyl radicds. The alkyl radicals can then

react with iodine to form alkyl iodides.

Table 5.7 Organic iodide formation in the presence of dky l halides

Iodo-organic Formula Organic

dichlo romethane

The formation of dichloro-iodoethane in the presence of trichloroethane can be

described as follows. Water radiolysis products react with TCA to form chloro-organic

radicals. TCA dechlorination through its reaction with the hydrated electron (Equation 5.12)

is the dominant reaction in deoxygenated water.

C2H3Cl; + e-, ---+ C2H3C12 + CI- k = 2.5 x 10" dm3 mol-' s-' [69] (5.12)

CzHjClj + H- C2H;Clr + Cl- + HT (5.13)

C1H3Cls + OH - C2H2C1; i- HzO k = 1 x 10' dm3 mol-' s" 1691 (5.14)

In oxygenated water (O2 concentration: 2.5 x IO-' M) a portion of the eV, and H are

scavenged by oxygen. This amount depends upon the rate constants for the reaction of RCl

Mith the primary products of water radiolysis and the concentration of RC1.

e-,, + O?- 02- k = 1.9 x 10'' dm3 mol-'s-' [jj] (5.15)

H + 02- HO2 k = 2.0 x 10" dm3 mol-' s-' [ S I (5.16)

Organic Formula

trichloroethane

trichloroethylene

alky 1 halides

CHZCl2 CHICII

C2H3C13

C2HC13

RC 1,

C,H3C 12i

C2HC171

wn-~J

84

HO1 c-t H' + O-? pK, = 4.8 (5.17)

Hence. if the concentration of alkylchloride is low compared to that of dissolved oxygen- and

no other radical scavengers are present in the system. alkylchloride compounds. in most

cases. will primarily be attacked b y OH (Equation 5-14) and possibly O-? (or HO2) (Equation

5-18). However. since in the case of this study the TCA concentration and its rate constant

with the e-,, are relatively hi& the majority of the e, will react with TCA.

C2H3CI; + O-? - CZH2C1; + HO2- ( 5 - 18)

In the absence of other chemicals, the transients forrned from the above reactions (Equations

5.12-5.14 and 5.18) are scavenged by oxygen to form corresponding peroxy radicals which

undergo further reactions to form stable products such as aldehydes.

C2H;CII + 01- CzH;CI3O2 (5.19)

C2H2C13 + O7 - C2H2C1302 (5 -30)

2 C7H3C1102 / 2 C2H2C1307 +---+ tetraoxides --+ --, products (5.21)

With iodine in the solution- chloro-organic radicals react tviîh the iodine to form chloro-iodo

organics. The rate constant for the reaction of TCA with the e , is much higher than for the

reaction with OH. Therefore, C7H3C12 - is the major radical attacking 1, and I to f o m

In a similar manner, dichlaroethane and uichloroethylene can be dechlorinated to

produce corresponding chloro-organic radicals:

CHICi2 + eVa, - CHzCl + CI- k = 6 x lo9 dm3 mol-' s-' [70]

C2HC13 + e- ,, - C2HC12 + CL- k = 8.5 x 10' dm3 mol-' s-' [70] (5 -25)

The very generd description of the Formation of chloro-iodo organics may be given

as follows. Alkyl halides are rapidly dechlorinated through their reaction with e,_ or lose a

hydrogen by reactîng with OH and 07.

RCI, + e,, - R'CI~,.,, + CI- (5.26)

RCl, + OH - R'C1, + H1O (5.27)

RCl, +- O - R'Cl, + HO-: (5.28)

The radicals produced by these reactions are able to react with I2 and I to form volatile

chloro-iodo organics or organic iodides.

R'Cl~,-Il + l2 --> RCI(,I,I + 1 ( 5 -29)

rCI,n-l , + 1 - RCI,n-,$ (5.30)

Some of these reactions are likely more important than others under specific conditions.

5.4.1.2 Carbonyls

Mass spectrometry did not detect any iodo-organic in the gas phase above the IO-' M Cs1

solutions. in the presence of carbonyls. However. when the iodide concentration was

increased to IO-' M. trace amounts of iodomethane. iodoethane. and C,H,I were detected.

Electron capture detection was used to detect organic iodides above the IO-' M Cs1 solution.

in the presence of carbonyls. lodomethane and iodoethane were detected in the presence of

methyl ethyl ketone (MEK). while only iodoethane was detected in the presence of diethyl

ketone (DEK). Iodomethane and another organic halide, assumed to be C,H,I. were detected

in the presence of methyl isobutyl ketone (MIBK). Mass spectrometry of the liquid phase.

even at relatively high iodide concentrations

organic iodide in the system.

(10" and 10-' M) did not reveal any other

The results suggested that the types of iodo-organics that are formed depend on the

molecular structures of the carbonyls. Both iodomethane and iodoethane wsre formed in

solutions with MEK. most likely because the MEK molecule contains both methyl and ethyl

groups. Iodornethane and C4H91 were formed in the presence of MIBK. which contains

methyl and C4H9 fùnctional groups in its molecule. Finally, iodoethane was forrnsd in

solutions containing DEK. which only contains ethyl groups in its molecule. These results

might be extended to predict the types of organic iodides formed in the presence of other low

molecular weight carbonyls in irradiated systems. it appears that organic iodides formed in

the system are alkyl iodides with the same alkyl groups in their molecuIes as those in the

original carbonyl molecules (Table 5 -8).

Table 5.8 Organic iodide formation in the presence of'carbonyls

Organic

methyl ethyl ketone

Organic Formula

methyl iso butyl ketone

Iodo-organic Formuia

CH3-CO-C2HS

I I

1

The formation of alkyl iodides in the presence of carbonyls may be described in a

general manner as foIlows. Carbonyl compounds react with OH to form carbonyl radicals

CH31 & CIHSI

C H3-CO-C4H9

diethyl ketone

carbonyls

CH31 & C,H,I

I CIFI,-CO-C2H

R-CO-R'

C,H51

R I & R ' I

that can undergo further reactions to form a variety of alkyl radicais (Equation 5.3 1). These

organic radicds react with Iz and 1. Ieading to the formation of volatile dkyl iodides

(Equations 5-33 and 5.33)- T h e mechanistic details for the radiolytic decomposition of the

carbonyl radicais to give alkyl radicds are not known. Howeve. a nurnber of pathways for

the formation of aikyl radicals esist. as described earlier in Section 3 -3 -2.

R C H O + O H ~ R C O ' + H,O---+- R ' + H 2 0 + C 0 (5.3 1 )

R'+12-R[+l (5.32)

R'+I----+RZ (5.33)

5.4.1.3 Aromatics

Mass spectrometry of the gas phase above IO-'. IO-'. and 10-' M Cs1 solutions. in the

presence ofaromatics. did not show any detectable iodo-organics in the gas phase. Electron

capture detection kvas also not able to detect any significant quantities of iodo-organics above

the irradiated IO-' M Cs1 solution in the presence of benzene. toluene. and styrene. Mass

spectrometry of the liquid phase for IO-' and IO-' M Cs1 solutions contaking aromatics did

not show any evidence of iodo-organic formation.

Clearly the presence of aromatics does not Iead to the production of significant

quantities of organic iodides. The reaction of aromatics with OH occurs primarily rhrough its

addition to the ring. Therefore. organic radicals are not created and there should not be

significant formation of organic iodides. The reactions of benzene and toluene with the OH

radical are as follows.

C6H6 + OH - C6H60H

C6HjCHj f OH HOC6HjCH3

5.4.2 Measurement of Organic Iodide Formation

Quantitative rneasurernents of the concentration of organic iodides formed in the presence of

organics were performed using gas c hromatograp hy with an electron capture detector. The

concentrations of iodomethane and iodoethane were evaluated in the presence of- various

organics. The reproducibility of the results was detennined by measurement of replicate

sarnples. The average standard deviation for the iodomethane and iodoethane concentrations

was about 25% (Appendix D). The concentrations of iodo-chloro organics could not be

quantified since iodo-chloro organics are not commercially available and therefore. the

required standard solutions could not be prepared.

The results (Table 5.9) indicated that iodomethane. in the concentration range of IO-'

M forms when alkyl chlorides are present in the system. However. iodo-chloro organics

were the dominant organic iodide forrns in the gas phase based on the large amounts detected

by mass spectrometry. The resuits also suggested that iodomethane and iodoethane in the

concentration range of IO-' M, exist in the gas phase in the presence of carbonyls. No

measurable amount of iodomethane and iodoethane was formed in the presence of aromatics.

Table 5.9 Iodomethane and iodoethane concentrations in the gas phase, in the presence of various organics (organic concentration IO-' M. iodine concentration 1 O-' M. pH 5 )

Iodoethane (M)

< I E-8

trichloroethane

dichloromethane

lodomethane (Ml

< 1E-8

Organic Type

No Organics

tric hloroethy Iene

methyl ethyl ketone

Organic

-------------

4E-7

I

1 E-7 I

I < 1 E-8

< 1 E-8

Carbonyls

diethyl ketone

Aromatics

methyI isobutyl ketone

benzene

< 1 E-8

I

.CE-7

< 1 E-8

toluene

- -- --

5.4.3 Measurement of Molecular Iodine Formation

3E-7

< 1 E-8

styrene

The concentration of molecuiar iodine for systerns containing organics was measured using a

UV spectrophotometer. The I1 concentration was measured in the liquid phase and its gas

phase concentration was estimated by assurning a liquid-gas iodine partition coefficient of

80. The reproducibility of the results was determined by measurement of replicate samples.

The average standard deviation for the molecuIar iodine concentrations was about 3%

(Appendix D).

< l E-8

< 1 E-8 < 1 E-8

< 1 E-8 < 1 E-8

The results (Table 5.10) show that the concentration of molecular iodine decreased

with carbonyk and increased with alkyl halides in the solution. The presence of aromatics

reduced the molecular iodine concentration by 2-4 times. Comparison OF Tables 5.9 and

5.10 indicates that the majority of the airborne iodine in the presence of alkyl halides and

carbonyls was in an organic form.

Table 5.10 Iodine concentration in the iiquid and gas phase. in the presence of various organics (organic concentration 10-' MI iodine concentration 1 O-' M. pH 5 )

The apparent decrease in 1, concentrations when carbonyls and aromatics are in the

Organic Type

No Organics

Alkyl Halides

Carbony 1s

Aromatics

system, is likely due to the cornpetition between these compounds and 1- for the OH radical

(Equations 5.36 and 5.37) which decreases the radiolytic oxidation of 1- (Equations 5.1 and

a) estimated by dividing the aqueous phase I2 concentration by 80.

IZ in the Gas Phase (M)"

7E-8

1 E-7

1.7E-7

1 .SE-8

3 E-8

3 E-8

1 .SE-8

3 E-8

2E-8

Organic

-------------

trichloroethane

dichlorornethane

methyl ethyl ketone

methyl Esobutyl ketone

diethyl ketone

benzene

toluene

styrene

1, in the Liquid Phase (M)

5 -9 E-6

8.5E-6

1.4E-5

1 -2E-6

2.3E-7

2.6E-7

I.3E-6

2 -4 E-6

1.7E-6

RCHOsOH---+- R'+HzO +CO (5.36)

Aromatic -1- OH w Product (5 -3 7)

I - i O H - - - - - + t + O H (5.1)

I+ I - IZ (5.2)

The increase in I2 concentration in the presence of alkyl halides likely resulted from the

scavenging of ei , by RCI (Equation 5.26) thereby decreasing the formation of O?- (Equation

5.38)- Oz- is a reductant species that converts 1, to ï (Equations 5.39 and 5-40).

RCl, +- e, ---es R'CI(,.,, + Cl-

- e ,+02-02-

Il + O-?+ r7 + O2

I-1 + O-: - 2 r + O?

5.5 Cornparison of the Experimental Results With Other Related Work

The majority of the expenmentai results obtained from this work are new and hence no

results of other studies are available for cornparison. However, for some of the esperiments.

the control tests in particuIarT similar measurements have been previously reported. In order

to further examine the reliability of the current results, the results for these esperiments were

compared with those reported in previous studiss. The following is a review of these

comparisons.

In this study. radiation was found to be a very important factor influencing iodine

volatility and organic iodide formation. lodine volatiIization rates increased by two orders of

magnitude in the presence of radiation (Section 5.1.1). Sirnilar results were observed in other

bench scale [35] and interrnediate scde studies [19]. A bench scale study of iodine partition

coeficient indicated that IPC? the inverse of volatility, decreased by one to two orders of

magnitude in the presence of radiation [ E l . The current study did not show any organic

iodide formation in the absence of radiation (Section 5.1.1). Similar conclusions were

obtained by Lutz et. ai. as they reported that the presence of methane in the absence of

radiation has no effect on the I f C values [33]. When radiation was present. the formation of

methyl iodide. and therefore a decrease in the IPC was observed [33]. Similady. in tests in

the Radioiodine Test Faciiity (RTF)? the inter conversion of I-. II, and organic iodides was

found to be veq- slow in the absence of radiation [19]. The slow increase in iodine

volatilization at the beginning of irradiation, rmder acidic conditions. observed in this study

(Section 5.1. l), was similarly observed by Ashrnore et. al. 1161.

In this study, the iodine volatilization rates were proportional to the Csl concentration

(Section 5.1 -3). In a similar study. Ashrnore et. al. observed a 10 foId increase in the

volatilization rate. when r concentration increased frorn IO-' to IO-' M [16]. In another

study. conducted by Evans to measure LPC at various iodine concentrations. the IPC in

alkaline solution did not depend on the 1- concentration that agrees with these results. For

acidic systerns the LPC did not depend on the 1- concentration for IO-' and 10-' M solutions.

but showed dependency for 1 O-' to 1 M solutions [14].

The impact of the solution pH on iodine volatility in the current study \vas found to be

very significant, increasing with a decrease in pH (Section 5-13). This is in agreement with

the strong dependence of IPC on pH, observed in other studies [14.25. 281. In this study. for

IO-' M Cs1 solutions the volatilization rate increased by a factor of 5. when pH was changed

from 7 to 5. Similar experirnents were conducted by Ashrnore et. al. for a IO-' M Cs1

solution using different mass transfer conditions and a slightly higher dose rate [26]- In their

study the volatilization rate increased by a factor of 16. as a result of changing pH fiom 5 to

7. The reason for this discrepancy is not cIear- however differences in apparatus design m a i

have contributed to the difference. In general. the trend obtained in this work at various pH

values agreed with the trend found in the previous works [14. 15. 16.361.

There is much less experïmental data available for iodine behaviour in the presence of

organics than in their absence. The following is a cornparison of the results obtained from

this work with the few existing relevant resuits.

In this study, organic compounds were cIassified in groups based on their impact on

iodine volatility (Section 5.2). Evans suggested that such a classification is possible afier

reviewing the criteria required to establish a basis for the classification [34]-

This study revealed an increase in iodine volatilization rate, moIecular iodine

concentration. and organic iodide fornation for systems containing alkyl halides (Sections

5-32? 5-42: and 5.4.3)- Carbonyls caused an increase in the volatilization rate and organic

iodide formation. but caused a reduction in the rnolecular iodine concentration (Sections

5.3-1. 5-42, and 5.4.3). Aromatics caused a decrease in the votatilization rate and molecuIar

iodine concentration, wïth no sign of organic iodide formation (Sections 5.3.3. 5.4.2. md

5.4.3). The overaIl trends of these results are in agreement with that of other studies

performed to identie [PC in the presence of organics. Evans reported that alkyl halides and

carbonyl compounds enhance organic iodide formation and increase the overa11 iodine

volatility; while aromatic compounds suppress the overall iodine volatility with linle impact

on airbome organic iodide formation [ X I . In their study for measuring IPC in the presence

of organics, Qum et. al. found organics have a dif-ferent impact on the iodine partition

coefficient [ l j ] . Some organics containing MEK and dichloroethane tend to produce low

IPC and Iotver the pH- some others containing benzene and toluene produce high IPC and do

not significantly alter the solution's pH. The results of intermediate scale experirnents

performed at RTF were also in agreement with this current work, since the addition of MEK

to the solution at RTF experiments greatly enhanced iodine volatility [18].

In this study. the iodine volatilization rate in the presence of toluene decreased under

acidic conditions and increased under basic conditions (Section 5 - 3 3 ) . A similar behaviour

kvas obsened by Evans in studying IPC in the presence of aromatics [34]. From this work it

\vas observed that for an MEE; system. the majority of airbome iûdine was found to be in

org"c form (Section 5 - 4 3 . RTF results also suggested that volatile Iow molecular weizht

organic iodides contribute a significant fraction of the airbome iodine in the presence of

MEK [3 11.

Gas and liquid phase analyses perfomed in this m-ork w-ere compared with the

esisting data. In the current work. iodomethane was the main form of airborne organic

iodides detected in the presence of MEK (Section 5.4.2). Sirnilar results were observed when

analyzing the gas phase afier the addition of MEK in RTF esperiments [3 I l . In this work.

5.9 x 1oW6 M molecular iodine Lias found in a IO-' M Cs1 solution at pH 5. afieter receiving a

total dose of 5 kGy (Section 5 - 4 3 . This value is in a reasonable agreement with the value of

3.9 x 10" M obtained by B m s et. al. under similar conditions at p H 5 -6 [?SI.

In general. the experimental results obtained through this study agree with relevant

results from other studies. However. it shouId be emphasized that most of the results of the

current study represent new rneasurements as little work in the past has focused on the impact

of organics on iodine behaviow,

5.6 Modeling of Iodine Radiation Chemistry

One of the objectives of uiis project was to develop a kinetic-based model that simulates the

radiolytic chernistry of iodine. This model was to provide a mechanistic description of iodine

chemistry. in the presence of organic compounds, for conditions relevant to reactor accident.

Such a model was created and found to give a reasonable representation of the experimental

results.

In irradiated systems the species concentrations are the result of a balance between the

rates of the relevant chemical reactions. Therefore, a kinetic approach is required for

modeling the system in order to consider the relationships between the chernicaI conditions

and steady state concentrations. In addition, the model may be either mechanistic, based on

the representation of the underlying reactions. or empirical. based on assumed relationships

that are fitted to the observed trends. An empirïcal approach for modeling the system based

on the experimental results has some merits: simplicity is one of the greatest advantages.

However, this approach only provides a description of the experimental trends rather than

demonstrating the fundamental understanding of the relationships between chernical

conditions and volatile iodine concentrations. Furthemore. empirical models may not be

estendible outside the experirnental conditions. whereas a mechanistic mode]. the approach

used here. may be applied outside this range with much greater confidence.

The model (Appendix F) used as a starting point a set of the most important radiolytic

and thermal reactions of iodine along with those representing the radiolysis of water. A

semi-mechanistic model for organic iodide reactions including the major reactions of organic

iodide formation and destruction was incorporated into this inorganic reaction set. A generic

approach was used in which the main reactions representative of given types of organic

compounds (dkyl halides, ketones, and arornatics) were considered. The required rate

constants were estimated based on representative compounds. Partitioning of volatile species

and a simple repressntation of rnass transfer between the liquid and tas phases were also

incorporated into the reaction set. The model was evaluated and r e h e d by comparison with

the experimental results.

The mode1 can be considered to be the input data set for the FACSIMILE [73]

computer package. FACSIMILE converts chemical reactions into a set of di fferential

squations and solves them by numerical integration methods. The FACSIMILE prograrn is

well suited to such a simulation as it is designed for modeling of complex chemical reactions

processes.

A simple representation of the relationships between the governing equations in the

mode1 is provided in Appendix G. The mass transfer parameters in the mode1 were

determined experimentally (see Appendis A). The chemical reactions in the model can be

classified as water radiolysis reactions. iodine reactions. and organic iodide reactions. The

following is a description of these reactions,

5.6.1 Water Radiolysis Reactions

Following a reactor accident, iodine exists in dilute solution, and therefore, radiation energy

is deposited into water molecules. The set o f reactions for the radiolysis of water and the G-

value of the products are well established. A comparison of a number of reaction sets and G-

values indicated that they are almost equivalent 1551. In this model. the water radiolysis

98

reaction set suggested by B u t o n and EIIiot [55] was used. The major water radiolysis

reactions incorporated in the mode1 and their rate constants (k) are as follows:

H- + OH- A HZO k = 1.1 x 10" dm' mol-' s-'

- 1 - 1 2 r-,,- Hz i 2 OH- k = 5 . 2 x 10'dm3rnol s

-1 - 1 e-,+ H d H2+OH- k = 2.5 x 10" dm' mol s

Y,, -7- OH --f OH- k=3.O x I O ' ~ dm3 mol-' ç-'

e-,,+H-- H + H1O -1 - i k=2.3 x 10'"dm3moI s

ZH-H2 k = 5 3 x 10' dm3 mol-' s-'

H t OH --+ H,O k = 2.5 x 10" dm3 mol-' s-'

H + OH- - Caq k = 1.5 x lo7 dm3 mol-' s-'

2 OH ---+ FI-0-7 - - k = 5.5 x 1 0' dm' mol-i s-'

OH t H,OT - H 2 0 i- HO2 - 1 _ - l k = 9.0 x 107 dm3 mol

2 HO7 - H-0, + 0: - 1 - 1 k = 7 . 6 x 10'drn3mol s

OHt-- ,HT+O- pK = 11.9

HzOz c-, H+ + HO2- pK = 11.65

In the presence of oxygen:

H + O2 --+ HO2 k = 2.0 x 1 0[Qdm3 mol-' ç-'

eu, + O2 ---+ 02- k = 1.9 x 10" dm3 molAi s-'

5.6.2 Iodine Reactions

Most of the processes involving iodine reactions in irradiated aqueous

(5.41 )

(5.42)

(5.43)

(5.44)

( 5 -45)

( 5 -46)

(5.47)

(5.48)

( 5 -49)

(5.50)

(5.5 1 )

(5.52)

(5.53 )

(5.54)

(5.55)

solutions are

understood and the intermediates have been determined. The rate constants for the majority

of these reactions are also fairly well established. The effect of radiation on iodine chernistry

is through the reactions of water radiolysis products with varîous iodine species. The most

imporrant iodine reactions relevant to calculating iodine concentrations in the gas and liquid

phases were incorporated into the mode1 [13.46.47, 561.

Non-volatile iodide 1- is oxidized by the hydroxyl radical to produce atomic iodine

(1). cvhich is typicaIly in equilibrium with 12-:

I-+OH-1+OH k = 7.7 x 1 0' dm3 mo1-' s-' (5.56)

I + 1- - 17- kr= 1 . 2 ~ l ~ ~ ~ d m ~ r n o l - ' s - ' k ,= 1.1 x 10's-' (5.57)

Atomic iodine and 12- can react to forrn Ii:

I+t--+ll k = 1 x 10" dm3 mol-' s-' (5.58)

I ~ - + I?- - I j- t I- k = 4.5 x 109 dm3 mo~-l S-l (5.59)

I -t- 12- ----+ 1;- k = 4-5 x 1 0' dm3 mol-' s-' (5.60)

13- * 1? +- 1- -1 -1 kt- = 7.5 x 1 o6 s-' k, = 5-6 x 1 O' dm3 mol s (5.6 1)

- The 1,. - 1, - - and 1;- are reduced through their reaction with superoxide (O7-):

Il i- Oz- p Il- 4- O2 k = 6 x lo9 dm3 mol-' s-' (5.62)

12- + O?- - 21- + O2 k = 5 x 10' dm3 mol-' s-' (5.63)

Ij- +O2-----+ 1- + II- + O2 k = 2.5 x 10"rn3 mol-' s? (3-64)

The I2 disproportionates through thermal reactions to produce hypoiodus acid (HOI). cvhich

dissociates to hypoiodite (013:

I2 + HzO t--, I r O K + H+ -1 -1 kf = 5.76 x 1 0 - k, = 2 x 101° dm3 mol s (5.65)

- [?OH- - Iz + OH- J -1 -1 k r = 5 x 10 k r = 8 x 10~drn'rnol s (5.66)

LOH- - HO1 + 1- k f= 1.36 x 106 k , = I x 10' dm3 mol-' s-' (5.67)

HO1 - HHt + 01- kr = 1 x 1 O-' k, = 1 x 10" dm3 mol-' s-' (5.68)

HO1 + O H H1O + 01- 10 k t = 2 x 10 kr=1 .56r 10'drn3m01-'s-' (5.69)

The tz is reduced indirectly through reaction with hydrogen peroside ( H 2 0 1 ) :

I ,OK t HZ02 <-> 1- + 10IH + HZO kf = 2 x kr = 3-3 x 10' dm3 mol-' s-' (5.70)

I O z H + O K + I - + 0 2 + H 2 0 k = 3 x 109 dm3 mol-' Y' (5.71)

Numerous other reactions occur and these may be important under some conditions.

However. the above reactions typicaiIy dominate in aerated solutions [ILCI.

5.6.3 Organic Compound Reactions

Due to the large varie. of different organic compounds that may be present in containment.

it \\-ould be untèasible to develop a mechanistic model that represents the contribution of

each individual organic compound. Specifically, not enough mechanistic detail is known to

develop such a rigorous model and considerable amounts of new experimental data would be

required. E-lence. in this model a semi-mechanistic approach is taken in which generic

reactions are used to represent diffèrent types of organic compounds (alkyl halides.

carbonyIs, and aromatics).

The semi-mechanistic model contains the major radiolysis reactions for different

classes of organic compounds in aqueous solutions as well as the formation and destruction

of organic iodides. The objective is to include the rnost important processes while

simultaneously keeping the mode1 simple. Due to the generic nature of the model, the rate

constants are in terms of their approximate magnitudes. The values selected For the rate

constants are discussed in Appendix H.

5.6.3.1 Alhyl Halides

Alkyl halides are rapidly dechlorinated through their reaction with the hydrated electron and

hydrogen atom. They c m also react with OH or O?- resulting in hydrogen abstraction.

The follouings represent aikyl halide reactions in the rnodel:

RCl + e-., - K + CI- k = 1 x 1 o9 dm3 mol-' s-' (5.73)

R C l + H - - - + R ' + C I - + K T k = 1 x 10' dm3 mol-' s-' (5.73)

RC1+ OH - KC1+ H20 k = 1 x 10' dm3 mol-' s-' (5.74)

RCl +O2-- R'Cl+ HO2- - 1 - 1 k = I x 10~drn'mol s (5.75)

It should be noted that multi-chloro organïc compounds are treated the sarne as single-chforo

molecules in the model.

5.6.3.2 Carbonyls

The mechanistic details for the radiolytic decomposition of the carbonyl radicals t e give aIkyI

radicais are not known (see Section 3-32!). For simplicity. a semi-mechanistic approach to

modeling is taken in which the detailed steps required for the formation of alkyl radicais are

neglected and. instead- simple two-step reactions are used. The first step describes the

scavenging of OH and H. while the second step, with a srnaller rate constant. descnbes the

production O Falkyl radicals.

The followings represent carbonyl reactions in the model:

RCHO + e-,, --+ RCOH? + O K k = 5 x l o9 dm3 mol-' s-'

RCHO + OH 4 RCO' +- H20 k = 5 x 1o8 dm3 mol-' s-'

RCHO + H --+ RCO' + Hz k = j x 10' dm' mol-' s-l

RCOH2 + RCOH2 - RCOH + PRODUCT k = 5 x 10' dm3 mol-' s-'

RC0'-R+CO

5.6.3.3 Aromatics

Aromatic compounds react with OH to form the hydroxy-cyclohexadienyl radical. This

radical reacts with O2 usually leading to the formation of hydrosy lated species. The reaction

of aromatics ~ i t h Oz- is included in the model to compensate for the scavenging of al1 the

OH by aromatics. In the absence of this reaction. the scavenging of more than 99% of OH by

aromatics (dépending on the 1- concentration) leads to an unrealistic decrease in iodine

volatilization by a few orders of magnitude. The reaction of Oz- with phenolic compounds at

relatively high rates has been reported [61]. The rate constant used in the model for 0:'

reaction with aromatics is much higher than that reported for its reaction with phenolic

compounds. The effect of this somewhat arbitrary selection of the rate constant was

esamined in ternis of a sensitivity analysis.

The followings represent arornatic reactions in the model:

AR + OH - AROH k = 5 x 109 dm3 mol-' s-l

AR+s‘,-ARHt0E-r k = 1 x 10' dm3 mol-' s-'

AR+H-ARH k = 1 x lo9 dm3 mol-' s-'

AR + 02-- PRODUCT k = 1 x lo7 dm3 mol-' s-'

AROH + 0 2 4 PHOH + HO2 k = 5 x 10' dm3 mol-' s-'

ARH+O2-i\JC+HO2 k = 1 x lo9 dm3 mol-' ç-'

PHOH -+ OH v PRODUCT k = 1 x l ~ ' ~ d r n ~ r n o l - ' s - '

PHOH + Oz-- PRODUCT k = 1 x 10' dm3 mol-' s-'

5-6.3.4 Organic Iodides

The organic iodide reaction set simulates the tbrmation and destruction of organic iodides.

The following reactions were incorporated in the model to represent thrsr processes:

Alkyl radicals and alkyl halide radicals that are produced fiom the radiolysis of

aqueous carbonyis and alkyl halides react tvith iodine species in the following manner:

R+I-,-RI k = 3 x 1 o9 dm3 mol-' s-' (5.89)

R+I-Ri k = 1 x lo9 dm3 mol-' s-' (5.90)

RtHOI-RI+OH k = 1 x lo9 dm3 mol-' s-' (5.9 1 )

The organic iodides formed from the above reactions are decomposed via reaction with water

radiolysis products and by hydrolysis:

EU+OH-R+HOI k = 1 x 1 0'"dm3 mol-' s-' ( 5 -92)

RI + e-,,- R + 1- -1 -1 k = 2 x 1 0 ' ~ d r n ~ r n o l s (5.93)

R Z + H - R + I - + H ~ k = 5 x 1 o6 dm3 moi-' s-' (5.94)

R I - + H ~ O ~ R O H + I - + H ~ k = 2 x 1 0 - ~ dm3 mol-' S-' ( 5 -95)

There are other organic radical reactions that are important, such as organic radical

dimerisation and reactions with hydrogen atoms. In the presence of oxygen. organic radicals

will react rapidly with O? to produce peroxy radicals. The dissociation of the peroq radicals

back to oxygen and an organic radical is also possible. The organic perosides react to forrn

aldehydes. alco ho 1s. and organic acids, which also undergo decomposition until they are

eventually converted to carbon dioside. During, this process m e r radicals will be formed

(see reactions 5-76-5.80). This kvas represented in the model using a reverse reaction for

reaction 5.98:

R+R-R, k = 1 x 10' dm' mol-' s-' (5.96)

R + H ---+ RH k = 1 x 10' dm3 mol-1 r1 ( 5 -97)

R + O 1 e R O - , k f = 3 x 109dm3mol-'s- 'k,=1s-' (5.98)

The hydroxylated compounds. formed through the radiolysis of aqueous aromatic solutions.

react with iodine and form non-volatile iodophenolic compounds. The iodophenolic

compounds then dissociate by reacting with water radiolysis products:

PHOH t HO1 - IPHOH k = 1 x l O' dm; mol-' s-' (5.99)

IPHOH + e-,, - 1- + PRODUCT k = 1 x 109 dm3 mol-' S-' (5.100)

IPHOH + OH - PRODUCT k = I x 10" dm3 mol-' s-' (5.101)

IPHOH + H ---+ PRODUCT k = 1 x 1 o9 dm3 mol-' s-l (5.102)

I Os'

5.7 Mode1 Evaluation

n i e model was evaluated through a comparison with the experimental results. Major parts of

the model, including mass transfer parameters. cvater radiolysis reactions. iodine reactions

and organic iodide reactions were evaluated separately.

5.7.1 Mass Transfer Parameters

PUi effort was made in order to compare the model and experimental results in terms of the

sensitivity to mass transfer coefficients. The overall mass transfer coetrfrcient was increased

2.5 times by altering the liquid phase mass transfer coefficient in the modeI. The model aIso

shocved a 2.5 fold increase in iodine volatilization rate. This was in agreement with the

esperimental results. A sirniiar increase in iodine volatilization rate \vas observed in

rxperiments in which the liquid phase mass transfer coefficient kvas increased through higher

agitation (Section 4.1.5). This confirmed that both experimental and model volatilization

rates wrre directly proportional to the mass transfer rate for the conditions of this esperiment.

5.7.2 Water Radiolysis Reactions

The simulation of water radiolysis reactions in the presence of iodine reactions was evaluated

in terms of the concentration of hydrogen peroxide. the only readiiy measured water

radiolysis product. A comparison of the mode1 simulation and esperimental measurements

showed similar behaviour with reasonable agreement (Figure 5.27).

Time (min) 1 anModel 9 Emenment I

Figure 5.27 Cornparison of the modeling and expetimental results of' hydrogen peroside concentration (iodine concentration 1 O" MI pH 5 )

5.7.3 Iodine Voiatilization

Iodine reactions were evaluated by comparing the volatilization rates obsewed through

rnodeling and experiments. The mode1 predicted a gradua1 increase in the iodine

volatilization rate at the beginning of radiation. approaching a constant value over time. A

similar behaviour kvas observed in the experiments (Figure 5.28). This behaviour is a result

of the time required for hydrogen peroside to accumutate in the solution.

O 100 200 300 400 500 600 700 800 900 1000

Time (min)

Figure 5.28 Cornparison of the modeLing and experimental results of total volatilized iodine (modeling iodine concentration 0.6 x IO-' M. experimental iodine concentration 1 x IO-' M. pH 5. pH 5 )

Iodine volatilization rates predicted by the model at various iodine concentrations and

pH values were compared with the esperimental results (Appendis 1). -A strong dependence

of the volatilization rate on iodine concentration was predicted by the model under acidic and

neutral conditions (Figure 5.29). However. unlike the esperiments. the model did not show

this dependence under basic conditions.

C d 1E4 M CSI 1 E-5 M Csl 1 E-6 M

1 O Modeling O Experimental

Fi_rure 5.29 Cornparison of the modeling and experimental resuIts of iodine volatilization rate at dif'ferent 1- concentrations (pH 7)

The model predicted the dependence of the volatilization rate on the solution pH with

reasonable accuracy for an 1- concentration 1 O-' M (Figure 5.30)- However. the model over

estimated the volatilization rates for acidic 1 oI' M iodine solutions.

1 O Modeiing O Experimental

Figure 5.30 Cornparison of the rnodeling and experimental results of iodine volatilization rate at different pH values (iodine concentration 10" M)

The rate of iodine volatilization predicted by the model at pH 5 changed dramatically

ovcr the iodine concentration range of 1 x IO-' to 0.5 x IO-' M. The model over estirnated

the volatilization rate at 1 x IO-' M iodine concentration but once the concentration

decreased to O.> x 10-' MI the volatilization rate approached a constant value (the value used

in Figure 5-30) and mode1 generated resuits were in agreement with those of the experiments.

The drarnatic changes in iodine volatilization rates predicted by the model for pH 5

solutions, with 1- concentrations ranging from 1 x 10-' to 0.5 x IO" M is probably due to an

incomplete representation of one of the processes in the model which is particularly

important under these conditions. For example phosphate buffer may play an important role

in determining the volatilization rate under acidic conditions. In particular. phosphate likel y

cataiyses the reduction of I2 by Hz02 (Equation 5.70) under acidic conditions.

A sensitivity analysis was perfomed in which the rate constant of reaction 5.70 was

increased by nvo orders of magnitude, This increase eliminated the dramatic change in

iodine volatilization rate over the concentration range of 1 x 10-' to 0.5 x 10-' M. This

indicated that the representation of the Iz reduction by HzOz used in the mode1 was likely

incomplete, causing the model to overestimate volatilization rate for pH 5 solution with

concentrations above 0.5 x IO-' M. This possibility was further explored by adding the

mechanism proposed by Bal1 et. ai. [56] to represent the catalysis of this process by

phosphate. Addition of these reactions into the model also reduced the volatilization rate for

pH 5 solution with concentrations above 0.5 x IO-' M. thereby eliminating the dramatic

change over the concentration range of 1 x 10-5 to 0.5 x 10-' M. However. these reactions

also caused the volatilization rate at pH 7 to decrease by over an order of magnitude. This

finding was inconsistent with the observation in this work that adding phosphate to a pH 7

solution only decreased the volatilization rate by 40% (Section 5.1.4). As a result. further

work is required on understanding the role of phosphate and hence the phosphate catalysis

reactions were not incorporated into the model.

The majority of the experiments in the presence of organics were perfomed at pH 5.

with an I- concentration of IO-' M. Therefore. for cornparison of rnodeling simulation with

experiments in the presence of organics. organic compounds present in the system were

considered when a constant volatilization rate was obtained.

5.7.1 Iodine Volatilization Rate in the Presence of Organics

In generai, the predicted iodine volatilization rate and changes in molecular iodine

concentration, as weIl as organic iodide formation were in reasonable agreement with the

esperimental results for al1 types oforganics (IO-.' M) (Figure 5.3 1 and Appendis 1).

Halides Carbonyls Aromatics

L O Modeling O Experimental

Figure 5.3 1 Cornparison of the modeling and experimental results of iodine volatilization rate in the presence of organics (iodine concentration IO-' M. pH 5 )

5.7.4.1 Alhyl Halides

Significant - increases in the iodine volatiIization rate and airbome molecular iodine

concentration at al1 pH values and iodine concentrations, which were observed

experimentally, were predicted by the model. The model ais0 predicted the formation of a

considerable amount of organic iodide in the system. However. the model tended to over

estimate the total airborne concentration for neutral and basic pH values (Figure 5-37). It is

due to considerable formation of organic iodides in the solutions at neutral and high pH

values, calculated by the model. Sensitivity analysis indicated that the volatilization rate

does not strongly depend on the rate constant of the reaction of aikylhalides with Oz-

(Equarion 5. 75). For example, increasing the rate constant of this reaction from 1 x 1 O' to

1 x 10' dm3 mol-' s-' caused an increase in the volatilization rate by a factor of two for the 1-

IO-' M. pH 5 solution.

O Modeling OExperimental 1 Fioure 5-32 Cornparison of the modeling and experimental results of iodine voIatilization rate in the presence of alkyl halides (iodine concentration 10-' M)

5.7.4.2 Carbonyls

The model predicted an increase in total iodine volatilization and a decrease in airborne

molecuiar iodine concentration, as was observed experirnentally. The majority of the

airborne iodine was predicted to be in an organic form, which is in agreement with the

experiments. Quantitative agreement between the model and expenments was also

reasonable for 10-' M iodine at al1 pH values (Figure 5.33). It should be rnentioned that

organic iodide concentration, and therefore the volatilization rates predicted by the mode1

were not constant during the initial addition of carbonyIs. However, the values reached a

steady state as time progressed. This might be due to the pseudo-mechanistic approach to the

reaction mechanism. Sensitivity analysis indicated that the reverse reaction for the organic

radical reaction cvith O? (Equation 5.98) is important in modeling a system containing

carbonyls. In the absence of this back reaction. the majority of organic radicals will be

scavenged by oxygen. causing no appreciable organic iodide formation in the systems.

Omitting the reverse reaction causes the model to under predict the volatilization rate for

carbonyl systerns. by more than an order of magnitude.

I O Modeling O Experimental

Figure 5.33 Cornparison of the m o d e h g and experimental results of iodine volatilization rate in the presence of carbonyls (iodine concentration IO-' M)

5-7.4-3 Aromatics

The model predicted that the iodine volatilization rate to decrease under acidic conditions and

kcrease under basic conditions. The same behaviour was observed in the experiments.

Furthemore, the rnodel did not show any significant formation of iodo-organics in the

system under acidic conditions, also in agreement with the experiments. Quantitative

agreement between the mode1 and experiments was reasonable for 10-' M iodine at al1 pH

values (Figure 5-34}. Sensitivity analysis indicated that the reaction of aromatics with O?-

(Equation 5.84) plays an important role in determining the volatilization rate, predicted by

the model. in aromatic systems. The rate constants for the reactions ofaromatics and 1- with

hydroxyl radicals are similar. Thus, in the absence of this reaction scavenging of the

majority of OH by aromatics leads to a decrease in iodine volatilization rate. For example, in

the absence of this reaction, the volatilization rate predicted by the model decreases by three

orders of magnitude for the r 10-' M' pH 5 solution.

Figure 5.34 Cornparison of the modeling and experimental results of iodine volatilization rate in the presence of arornatics (iodine concentration 10-' M)

5.7.4.4 Mixture of Various Organics

Evaluation of the predicted iodine volatilization rates in the presence of a mixture of orpnics

c m be a valuable way for mode1 evaluation. A comparison of the mode1 predictions and

experimentally O btained results were within reasonable agreement (Figure 5.3 5) .

Ar + RCOH Ar + RCI Ar + RCI + RCOH

1 O Modeling O Experimental 1

Figure 5.35 Comparison of the modeling and expenmentai results of iodine vo1atilization rate in the presence of organics (iodine concentration 10-' MI pH 5 )

5.7.4.5 Summary of the Results

A cornparison of the results obtained through modeling and experïmentation. for a wide

4 range of iodine concentrations (1 0 . 10-j. and 1 O" M) and pH (5. 7. and 9). in the presence

and absence of organics are provided in Figure 5.36. [t is seen that the majorïty of the data

points lie behveen the two diagonal lines. indicating the results are in agreement within an

order of magnitude. These results are satisfactory? considering the relatively simple nature of

the rnodel.

I .OOE-12 1.00E-11 1.00E-10 1 .OOE-O9 1.00E-08

Volatilization Rate (exp erim en&)

, No Org. , RCI , RCHO ,Ar

F i y r e 5.36 Cornparison of the modeling and experimental results of iodine volatilization rate (mol/rnin). for a wide range of iodine concentration (1 O-'. 1 O-'. 10" M) and pH (5. 7. 9). in the absence and presence of organics (IO-' M)

5.8 Application of the Results in Real Reactor Accidents

The results of this work will assist in evaluatinz the radiological consequences of a reactor

accident. The quantification of iodine volatilization rates under various conditions provided

valuable information on the preferred chemical conditions in a reactor containment following

an accident. This includes the advantage of maintaining basic pH conditions and avoiding

alkyl halides and ketone based solutions in reactor containment, in order to reduce

radioiodine vo latility under reactor accident conditions. The net vo latilization rate values

obtained from the experiments however. may not be used directly to estimate iodine

volatilization rates under reai reactor accident conditions. Parameters such as radiation dose

rate. rnass transfer coefficients, and gadliquid surface area. which were constant in these

esperiments. will affect the volatilization rates. These parameters can be taken into account

by using the model developed through Sus study. However. it remains to be demonstrated

that this model will satisfactorily simulate iodine behaviour for conditions beyond those

esarnined in this study. Given the mechanistic basis of the model. there is good reason to

believe that it will perform well over a wide range of conditions. This hypothesis shouId be

tested by validating the model against esperimental data obtained in otl~er Iaboratories. Once

validated. the model c m be incorporated into a more elaborated code. containing al1 the

pertinent physical phenornena. in order to predict the radiological consequences following a

reactor accident.

6 CONCLUSIONS AND RECOMMENDATIONS

This research made a significant contribution to the understanding of iodine behaviour in the

presence of organic compounds as it relates to a nuclear reactor accident. The important role

of organics &-ith respect to both aqueous phase iodine chemistry and iodine volatility was

demonstrated and evaiuated under a wide range of chernical conditions relevant to reactor

accidents. Irradiated iodine solutions were anaiyzed in the presence of various organics and

the types of organic iodides formed in the gas and liquid phases were identified and

interpreted. In addition, a generic mode1 of iodine volatility in the presence of organics was

developed and evaluated through a cornparison with these new esperimeiitai results. which

represents one of the most important contributions of this research. The following

conclusions can be drawn from this research:

1. Radiation is a very important factor influencing aqueous phase iodine chemistry. Iodine

volatilization rate and organic iodide formation drarnatically increase in the presence of

radiation. It is recornrnended that M e r experiments be conducted to study the impact of

the radiation dose rate on iodine volatility and organic iodide formation.

2. Iodine volatilization rates are nearly proportional to the iodine concentration over the

range of concentrations and pH values exarnined in the study. Further experiments are

recornmended to see if this reiationship can be expanded to the Lower iodine

concentrations that may arise following less serious reactor accidents.

3. pH is a very important factor that influenced iodine volatility for al1 the conditions

examined. Volatilization rate increases substantially with a decrease in pH.

4. From the last 3 conclusions @io, 1-3), it appears that the absence of irradiation. Iow

iodine concentrations. and a high pH constitute favorable conditions for minimizing iodine

volatility in a reactor containment following an accident. The radiation dose rate and

iodine concentration depend on the extent of fuel failure and hence are not controllable

following an accident. However. basic conditions in the containment aqueous phase can

be obtained through a deliberate alkalination and the addition of buffers.

5. A study of irradiated iodine solutions containing various al-1 halides. carbonyls. and

aromatics indicate that these organics can be classified into groups. based on their distinct

impact on iodine radiation chemistry. Additional research on the impact of otlier types of

organics ( cg . alcohols) should be conducted in order to deterrnine if such a classification

can be M e r estended.

6. The presence of alkyl halides. including 1-1.1 -trichloroethane. dichloromethane, and

trichloroethylene, greatly increases iodine volatilization rates. A significant increase in

organic iodide formation and in molecular iodine formation occurs in the presence of these

organics and airborne iodine is predominantly in an organic forni. The impact of

trichloroethane on the iodine volatilization rate is more pronounced at lower iodine

concentrations and locver pH values.

7. The inclusion of carbonyls. including methyl ethyl ketone. methyl isobutyl ketone. and

diethyl ketone, significantIy increases iodine volatilization rates. A considerable increase

in organic iodide formation' but a decrease in molecuIar iodine formation occurs in the

presence of these organics. The majority of the airborne iodine is in organic forms. The

impact of methyl ethyl ketone on iodine volatilization rate is more pronounced at lower

iodine concentrations.

8. The addition of aromatics, including toluene- benzene. and styrene decreases iodine

vo latilization rates (r 1 O-' M. pH 5). There is no si_enificant formation of organic iodides

in the systems and rnolecular iodine formation decreases in the presence of these organics.

Iodine volatilization rates in solutions containing toluene decrease under acidic conditions.

but increase under basic conditions at low iodine concentrations. Toluene is more

effective in reducing iodine volatilization at higher iodine concentrations and lower pH

values, while it causes a greater increase in volatilization at lower iodine concentrations

and higher pH values.

9. The impact of organics on iodine volatility is influenced by the presence of other organics.

Iodine volatilization in the presence of carbonyls and alkyl halides is substantially reduced

by introducing aromatics to the system, either prior to or afier addition of those organics.

Further research is recommended on the effectiveness of iodine volatility abatement

methods, such as the addition of reducing agents or radical scavengers. particularly in the

presence of organic compounds.

10. From the last 3 conclusions (No. 5-9). it appears that given the option. materials

containing aromatics are a better choice than those containing alkyI halides and carbonyls

for use in containment, with regard to their impact on iodine volatility. The importance of

this conclusion is apparent, considering that paints (likely the main sources of organics)

used in containment, c m contain various organic ingredients. In some cases aromatics are

the main constituent, while in others alkyl chlorides or carbonyis are the main component.

As the previous conclusion (No. 9) suggests. under some conditions. release of aromatics

to the post-accident reactor pool might be considered as one of the reactor safety features.

11. Irradiation of iodine solutions containing multi-chloro alkyl chlorides leads to the

formation of chloro-iodo organics. Chloro-iodomethane is fonned in the presence of

dichloromethane. While, dichloro-iodoethane and dichloro-iodoethylene are forrned in the

presence of trichloroethane and trichloroethylene, respectively. It appears that the organic

iodides forrned in the irradiated systems have a similar rno1ecula.r structure as that of the

original alkyl chloride with the exception of the replacement of a chlorine by iodine (Le.

RCl" - RCI(n-llI).

12. Irradiation of iodine solutions containing carbonyls leads to the formation of alkyl

iodides. Iodomethane and iodoethane are formed in the presence of methyl ethyl ketone.

while only iodoethane is formed in the presence of diethyl ketone. iodomethane and C,H91

are h n e d in the presence of methyl isobutyl ketone. It appears ttiat organic iodides

formed in the irradiated systems are alkyl iodides with the sarne alkyl groups in their

molecules. as those of in the original carbonyl molecules (Le. R-CO-R' - -+ Ri &

KI).

13. The ability to classi6 organic compounds based on their distinct impact on iodine

behaviour. and to predict the types of organic iodides which are formed in imadiated

systems (Conclusions No. 11-12). provides valuable information in determining the

feasibility of using a generic approach to modeling the impact of organics. Another

advantage of these predictions is determining the specific types of alkyl halides and

carbonyls that should be avoided in containment to prevent the formation of undesired

organic iodides. A fûrther advantage of these predictions is that the possible sources of

organic contamination that lead to production of volatile organic iodides c m be

deterrnined, through analyzing and identiQing the type of organic iodides which are

formed in medium and large scale experiments designed to simulate reactor accidents.

14. The kinetic-based modeI, containing a mechanistic description of iodine chemistry and

oeneric semi-mechanistic reactions for various types of organics. provides a reasonable - description of the esperimental results. The model could be refined by conducting M e r

research on the radiolysis of iodine solutions containing organic cornpounds with an

emphasis on kinetic rneasurements, as these would be a great value in improving the

kinetic-based model. Specifically the following areas of uncertainties are recommended

for fùrther investigations. Iodine reactions under basic conditions. the role of buffer

reactions. the mechanisms of alkyl radical formations in radiolysis of carbonyl solutions.

scavenging of organic radicals with oxygen (R + O2 - RO1). and any reactions that

compensate scavenging the majority of OH radicals in the presence of aromatics.

NOMENCLATURE

AC E

D EK.

IPC

LOCA

LMEK

!WB K

RTF

TCA

TEDA

Advanced Containment Experiments

diethyl ketone

iodine partition coefficient

Loss-Of-Coolant Accident

methyl ethyl ketone

methyI isobutyl ketone

Radioiodine Test Facility

trichloroethane

triethy lenediamine

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APPENDIX A: Caiculation of Mass Transfer Coefficients

A.1 Liquid Side Mass Transfer Coefficient

The Liquid side mass transfer coefficient (k,) was evaluated by examining the mass transfer of

oxygen from the gas to the liquid phase. A dissolved oxygen level of near O ppm was

obtained by bubbIing nitrogen through the liquid, air was then added to the vessel's gas

phase. The dissolved oxygen concentration in the liquid phase was measured at various time

intervais. Figure A.1 shows the trend of dissolved oxygen concentration for two diffèrent

mass transfer conditions (stir rates of 1 10 and 380 rpm).

Time (min) --

380 RPM o 110 RPM

F i ~ u r e A. I Dissolved oxygen concentrations under various mass transfer conditions (stir rates of 1 10 and 380 rpm)

The mass balance equation for dissolved oxygen in the Iiquid phase is given as:

d[02]!dt = - I.6, ([oz] - [O11 *)

Where;

[O,'J = dissolved oxygen concentration

[Od* = equilibrium dissolved oxygen concentration (8.7 ppm)

t = tirne

E& = overall liquid side mass transfer coefficient (l/KoL = l/k, + Wk3 -

A = interfacial area (1 dm')

V = volume (0.7 dm3)

k, = liquid side mass transfer coeffkient

kg = gas side rnass transfer coefficient -

H = partition coefficient

The value of partition coefficient of dissolved osygen (H = 3-65 x IO-') permits the

following approximation:

I K o L l/kl

Tlieretbre Equation A.1 can be written as:

d[OIJ/dt = k, A N ([07]* - [OZ])

Solving Equation A.3 for k, yields;

k, = -V/(At) x ln (([O3]* - [O7])/[O2J*)

The values of (In (([OJ* - [02])/[02]*))/t can be obtained from the ope of th

Figure A.2. These values were calcuIated to be -0.045 and -0.120 mir? for the stir rates of

1 10 and 380 rprn, respectively.

Time (min) 1 o 380 RPM o 110 RPM 1

Figure A-2 ln (([O2]* - [O2])/[O2]*) under various mass transfer conditions (stir rates of 1 10 and 380 rpm)

Therefore. lkom Equation A.4. the liquid side mass transfer coeffkients for osygen are:

k, = 0.045 x 02/60 = 1.5 x IO-' dm/s for stir rate of 1 10 rpm

kl = 0.120 x 02/60 = 4.5 x IO-' d d s for stir rate of 380 rpm

The liquid side mass transfer of iodine is reIated to the liquid side rnass transfer of

oxygen by the following equation:

(ki- 12Y(kl. 02) = (~:ruLr-1d/(D~waier-02) (A.5)

Where? D is diffusion coefficient. The value of n is 1 if film theory is used and 0.5 if the

penetration theory is used. In most practical correlations, n is taken to be 0.67. Since the

difision coeficient of iodine and oxygen in water are sirnilar (1.2 x 1 0 ~ ~ crn2/s), the

obtained mass transfer values for oxygen can be used for iodine.

k,-12 = 1.5 x 10-l d d s for stir rate of 1 10 rpm

k,. ,, = 4.5 1 o4 d d s for stir rate of 380 rpm

A.2 Gas Side Mass Transfer Coefficient

The gas side mass transfer coefficient in the system was evduated b y measuring the change

in the relative hurnidity of the air passed through the vessel. T h e rate of evaporation of

water. which is proportional to the gas side mass transfer coefficient, was determined based

on the change in relative hurnidity and the known flow rate.

The mass batance equation for W1O in the gas phase is given as:

d[H-O],/dt = k, - A N ([H-O]* - @320],) - F N ([H,Oj, - [H2OIi)

Where :

[H@] * = saturated E i ?O concentration

[H20Ii = input HzO concentration

[H20], = output H,0 concentration

kz - = gas side mass transfer coefficient

A = interfacial area (1 dm')

V = volume (0.65 dm')

F = flow rate

At steady state conditions:

d[HTO],/dt = O

From the ideal-gas law:

p3zo] = P m

P is related to P,,, by:

P = Pm. (RH)

8 Where, RH is relative humidity.

Replacing Equations A.7, A.8, and A-9 at A.6 yields:

k, A (1 - RH,) = F (RH, - RHi) a (A. 10)

Where RHi and RH, are the input and output relative humidities at steady state conditions.

Solving Equation A. 10 for Ku yields: a

k, - = (F/A) x (RH, - RHi)/( 1 - RH,) (A. 1 1)

In this test A = 1 dm2_ F = O. 1 dm%, RHi and RH, were measured to be 0.4 and 0.8.

respectively and were not changed by changing of the stir rates. Therefore. from A. 1 1. the

j a s side mass transfer coefficient for H 2 0 is:

kg = (0.111) x (0.8 - 0.4)/(1 - 0.8) = 2 x 10-' dm/s

The gas side mass transfer of iodine is related to the Cas side mass transfer of o

following equation:

(kg. ~ 2 0 ) = ('n.L\ir-[Z)/(~n:\ir-m)

[gen by the

(A. 13)

The difision coefficients of iodine and H1O in air are 0.082 and 0.23 crnl/s. respectively.

There fore :

0.67 - k,. 12 - ks- x (0.082/0.23) - 0.2 x 0.49 -

ko- ,, = 1 x 1 O-' d m / s -

APPENDIX B: Calibration Data and Graphs

Calibration cunre for calculating mo1ecuIar iodine concentration

0.00E+00 2.00E-96 4.00E-06 6.00E-06 8.00E-06 1.00E-05 1 -20E-05

Molecular lodine Concentration (M)

Esperirnentai data:

I7 Concentration (Liquid Phase) Absorbante (590 nm)

Regression data: R' = 0.98

Pararneter Estimate Locver 95% Upper 95%

Slope 167814 143 566 192062

Intercept 0-1 1 -0 .O0 0.23

- - --

Reported extinction coefficient: 90000 (M x cm) -' [l]

Calibration c u v e for calculating hydrogen peroxide concentration

0.00E+O0 1.00E-05 2.00E-05 3.00E-05 4.00E-05 5.00E-05 6.00E-05

Hydrogen Peroxide Concentration (M)

Experimental data:

HzOz Concentration (Liquid Phase) Absorbante (350 nm)

Regression data: R' = 0.99

Parameter Estimate Lower 95% Upper 95%

Slope 25 168 25034 35303

Reported extinction coefficient: 26400 (M x cm) '' [2 ]

Calibration curve for caiculating iodomethane concentration

0-00E+00 5.00E-07 1 .OOE-06 1 SOE-06 2.00E-06 2.50E-06 3.00E-06

Gas Phase lodomethane Concentration (M)

Experïmental data:

CH31 Concentration (Gas Phase) Peak Area

Regression data: R' = 0.99

Parameter Estimate Lower 95% Upper 95%

Slope 3.85E10 3.67ElO 4.02E 10

Intercept 950 -1351 3253

Calibration curve for calculating iodoethane concentration

0.00€+00 5.00E-07 7 -00E-06 1.50E-06 2-00E-06 2-50E-06 3.00E-06

Gas Phase lodomethane Concentration (M)

Experimental data:

I - -

C,H,I Concentration (Gas Phase) Peak Area

Regression data: R' = 0.99

Parameter Estimate Lower 95% Upper 95%

Intercept 793 -2 128 3715

References:

1. J.W.T Spinks, and R.J. Woods; htrodzrcrion (O Radiation Chernistiy: Third Edition.

John Wiley & Sons: New York. 255. 1990

2. A.P. Black and G,P Whittle, J, Am. Water Works Assoc., 59, 47 1-490, ( 1 967)

APPENDIX C: Iodine VoIatiIization Rates

Table C. 1 iodine volatilization rates (movmin) at various 1- concentrations and pH values.

Table C.3 fodine volatilization rates (moVmin) in the presence of va~5ous organics (r

iodine Concentration

1E-4 M

concentration 1 O-' M_ organic concentration 1 0-3 M- pH 5 )

1 Organic type Organic 1 Before Addition 1 Afier Addition

pH = -5

9E-IO

AIkyl Halides

p H = 6

SE-10

p H = 7

2E-10

tric hloroethane

p H = 8

1E-IO

of Organics 1 -4E-IO

trichloroethy lene

Carbonyls

pH = 9

6E-11

of Organics 1 E-8

I I I

1.8E-10

methyl ethyl ketone

7.OE-9

methyl isobutyl ketone

Arornatics

1.2E- 10 4.SE- 10

1.7E-IO

35E-IO

6.1E-11

4.2E- 1 1

3.OE-11

diethyl ketone

styrene

toluene

benzene

3.7E-10

t

1 -4E- 10

1.4E-10

1.3E-10

1.8E-10

Table C.3 Iodine volatilization rates (moVmin) at pH = 5 in the presence of methyl ethyl ketone at various concentrations

Table C.4 Iodine volatiIization rates (mournin) at pH = 5 in the presence of trichloroethane at various concentrations

Iodine Conc.

1E-4 M

Table C.5 Iodine volatilization rates (mol/min) at pH = 5 in the presence of toluene at

No Organic

9.5E-I0

Iodine Conc.

1E-4 M

1E-5 M

1E-6 bl

various concentrations

Organic lE-6 M 9.7E-10

No Orsanic

9.2E-10

I .4E- 10

1-3E-1 1

Iodine Conc.

1E-4 M

Organic 1E-5 M 9.8E-10

Organic 1E-6 M 9.2E-10

1.4E-10

1 -3E-11

No Organic

7.4E-10

Organic l E - 4 M 1.1 E-9

Organic iE-5 M 9.2E-10

1.4E-I0

1.3E-11

Organic 1E-3 M 1.9E-9

Organic 1E-6 M 7.3 E-1 0

Organic I E - 4 M 4.OE-9

2.1E-I0

1.8E-1 1

Organic 1E-3 M 3.5E-8

12E-8

7.8E-11

Organic 1E-5 M 7.2E- 1 0

Organic 1E-4 M 6.OE-10

Organic 1E-3 M 2-7E-10

Table C.6 Iodine volatilization rates (moumin) in the absence and presence of organics at various 1- concentrations and pH values.

Cs1 Conc- PH No Organic MEK TCA Toluene (Ml 1E-3 M lE-3 M 1E-3 M

Table C -7 Cornparison of replicate results for iodine volaûlization rates at various conditions

1- lE-CM/ 22E-9 MEK 1E-3 MI

MEK 1E-2 M 1- LE-5 W 1.3E-IO

MEK IE-4 M

TCA 1E-3 M

Table C.8 Regression analysis dada of the volatilization rates. The dope of "activity/time" was converted to "accumulate volatilized iodine/time", in order to calculate the volatilization rates. The conversion factors were different for various tests. depending on the initial iodine concentration, initiai activity of the tracer, and the efficiency of the detector.

Slope (activityltime)

128.8

3 O .3

22.1

13.4

4.5

1.9

1 522

27.1

7.2

155.6

45.9

7-4

1665.9

34.2

6.8

2403.2

1 16.3

7.9

R Square

0.99

0.99

0.99

0.99

0.98

0.93

0-99

0.99

0.98

0.94

0.97

0.8 1

0.99

0.99

0.94

0.99

0.99

0.98

I Conditions

1- 1E-.CM, pH5

1- IE-5 M, pH 5

1- IE-6 M, pH 5

1 - l E 4 M , p H 5 MEK 1 E-3 M

1- 1 E 4 M . pH7 MEK 1E-3 M

1- 1E-4 M: pH 9 MEK IE-3 M

1-1E-5MTpH5 MEK 1E-3 M

1- 1E-5 M? pH 7 iMEK 1E-3 M

1- ZE-5 LM, pH 9 MEK 1E-3 M

1- 1E-6 M. pH 5 MEK 1E-3 M

1- 1 E-6 M. pH 7 MEK lE-3 M

1- LE-6 M t p H 9 MEK 1E-3 M

1- lE-4 M, pH 5 TCA 1E-3 M

1- 1E-4 M, pH 7 TCA 1E-3 M

1- 1E-4M, p H 9 TCA 1 E-3 M

1- 1E-5 M, pH 5 TCA 1E-3 M

1- 1E-5 M, pH 7 TCA 1E-3 M

1- 1E-5 M1 pH 9 TCA 1E-3 M

Data Points

141

8 1

71

32

30

17

2 1

33

41

41

19

30

7

12

8

8

12

9

Lower 95%

127.8

30.2

21.9

12.9

3-7

1.6

148.7

26.1

6.9

143.7

42.1

6.0

1571.2

33.1

5.1

2268.2

114.1

7 .O

Upper 93%

129-7

30.4

22.2

13-8

4 -4

- 7 .- 7

155-7

38.0

7 -6

167.5

49.8

8 -8

1760.5

35.3

8 -4

2536.4

118.5

8 -5

Conditions Data Points R Square

1- IE-6 M, pH 5 TCA IE-3 M

TCA lE-3 M 1- lE-6 M, pH 9 11 0 -99

TCA 1E-3 M 1 1- 1 E - 4 M O p H 5 5 1 0.96 Toluene 1 E-3 M 1- 1 E - 4 M T p H 7 34 0.99 Toluene 1 E-3 M 1- L E 4 Mt pH 9 34 0.93 Toluene I E-3 M 1- 1E-5M.pH5 Toluene 1 E-3 M 1- 1E-5 M , p H 7 Toluene 1 E-3 M 1- 1E-5M,pH9 40 0.99 Toluene 1 E-3 M 1- 1E-6 M, pH 5 8 1 0.99 Toluene 1 E-3 M 1- 1E-6 M. pH 7 3 1 0.99 Toluene 1 E-3 M 1- lE-6 M, pH 9 3 1 0.99 Toluene 1E-3 M 1- 1E-5 M, pH 5 19 0.99 MIBK 1 E-3 M

1- 1E-5 M. pH 5 13 0.98 DEK LE-3 M

1- 1E-5 M, pH 5 11 0.99 DCM 1E-3 M

1- 1E-5 MI pH 5 10 O -99 TCAthyl. 1E-3 M 1- lE-5 M, pH 5 27 O -99 Benzene IE-3 M 1- 1E-5 M, p H 5 41 0.98 Styrene 1 E-3 M

S lope Lower 95% (activityk ime)

Upper 95%

APPENDIX D: Statistical Analysis of Data

Table D. 1 Statistical data of the volatilization rates (moVmin), pH 5

Standard ~ev ia t ion l

Confidence Level

I l 1

1.3E-10

Standard DeviationJ 1 15%

2.7E-11

18%

2.17E-12

l m 0

Table D.2 Statistical data of the liyuid molecular iodine concentrations (M), 1- 1E-5 M,

No Organic MEK Z E-3 M

Standard ~eviation'

Standard DeviationJ (%)

1.12E-7

+95% Confidence Level

5-83E-8

2% 4%

1.39E-7 7.23E-8

Table D.3 Statisticai data of the iodomethane and iodoethane concentrations (M) in the presence of MEK I E-3 M, 1- 1 E-5 M, pH 5

Iodomethane Iodoethane

Standard ~eviation'

Standard Deviation' (%)

4.6E-8

f 95% Confidence Level

1 -8 E-8

35% 22%

1.1 E-7 4.5E-8

APPENDK E: Identification of the Types of Organic Iodides in the Solutions Containing Alkyl Halides

A gas chromatograph with a mass selective detector was used to identiQ the organic

iodides in the gas phase of the sarnples containing various alkyl halides. The spectrums

of the mass peak and the relative abundance of each mass have been provided in Fi, wres

E. 1-E.9. The organic iodides can be distinguished from other organics by their relatively

high mass abundance at 1 3 7 , which is equivalent to the iodine atomic weight.

Chloroiodomethane:

Figures E. 1-E.3 show the spectnims of the sample containing dichloromethane (CH,Cl,). - -

In addition to this chernical, chloroiodomethane (CH2C11), and moIecular iodine (II) were

identifîed in the system. Relative mass abundance of the CHJl, CHICLI. and II are

provided in Figures E. 1-E.3, respectively. The rnass peak of chloroiodomethane was

identified by the mass spectrometer (MS) Iibrary.

Dichloroiodoethane:

Figures E-4-E.6 show the spectrums of the sample containing 1.1.1 -trichioroethane

(C,H3C13), Besides this chernical. dichloroiodoethane (CIH3CIII), and molecular iodine

(Il) were identified in the system. Relative mass abundance of the C,H3C13. C2H,CL21.

and I7 are provided in Figures E.4-E.6, respectively. T h e mass peak of

dichloroiodoethane was not registered and hence not identified by the MS library. This

chemical was identified based on its spectrum that illustrates the relative abundance mass

(Figure E.5). The rnass abundance spectra of this chemical has a relatively high mass

abundance at 61 (for C-CC1) and 97 (for C-CCI2) which is similar to that of C2H3C13

structure of this chemicai has some similarity to that of C,H3C13 m d can be ionized to C-CC1

and C-CC12. Furthemore, this chemical has a high relative mass abundance at 137

indicating the presence of iodine in its rnolecular stluc~ure. Finally. the rnass abundance at

1 89 represents C-CC11 radical.

Two other peaks found in the mass s p e c t m (at 2.1 and 4.3 min) are not organic

iodide and therefore will not be discussed here.

Dichloroiodoethylene:

Figures E.7-E.9 show the spectnims of the sample containing tricidoroethylene (C2HC13).

Besides this chemical. dichloroiodoethyIene (C2HCl&, and molecular iodine (I?) were

identified in the system. Relative mass abundance of the C2HC1,, C2HCIII. and I I are

provided in Figures E.7-E.9, respectively. The mass peak of dicnloroiodoethylene was not

registered and hence not identified by the MS Iibrary. This chemical was identified based on

its spectnim that illustrates the relative abundance mass (Figure E.8). The mass abundance

spectra of this chemical has a relativeIy high mass abundance at 60 (for C=CCl) and 95 (for

C=CC12) which is sirnilar to that of C,HC13 (Figure E.7). This indicates that the molecular

structure of this chemical has some simiIarity to that of C2HC13 and c m be ionized to C=CCI

and C=CCI,. In addition. this chemical has a high relative mass abundance at 117 indicating

the presence of iodine in its molecular structure. Finally, Trichloroethylene has its highest

mass abundance at 130. which is equivalent to the molecular weight of a trichloroethyiene

radicaI, C1C=CC12 (Figure E.7). This chemical has its highest mass abundance at 222, which

is equivalent to the molecular weight of a dichloroiodoethylene radical CIC=CCII (Figure

E.8).

The other peak found in the mass spectrum (at 3.2 min) is not an organic iodide and

therefore \vil1 not be discussed here,

Figure E. 1 Mass peak spectrum of the sample containing dichloromethane, with the relative mass abundance spectnun of CH,CI, - -

120000

1 OOOOO

Figure E.2 Mass peak spectrum of the sarnple containing dichloromethane. with the relative mass abundance spectrum of CH2C11

Figure E.3 Mass peak spectrum of the sarnple containing dichloromethane. with the relative rnass abundance spectnim of Il

Figure E.4 Mass peak spectnim of the sample containing trichloroethane. with the relative mass abundance spectrum of C2H3C1,

Figue E S Mass peak specmim of the sarnple containing trichloroethane, with the relative mass abundance spectnim of C2H3CI2I

Figure E.6 Mass peak specirum of the sample containing trichloroethane. with the relative mass abundance specûum of I2

Figure E.7 Mass peak spectrum of the sarnple containing trichloroethylene, with the relative mass abundance spectrurn of C2HC13

Fizure E.8 Mass peak spectrum of the sarnple containing trichloroethylene. with the relative mass abundance spectnun of CIHClzl

Figure E.9 Mass peak spectrurn of the sample containing trichioroethylene. with the relative mass abundance spectnun of I2

APPENDIX F: Model of Iodine Radiation Chemistry in the Presence of Organics

* MODEL FOR SI!HULATING RADIATION CHEMISTRY OF IODINE IN THE PRESENCE OF ORGANIC COMPOUNDS (ALK-C HALIDES, CARBONYLS , AROMATICS

* THE MODEL CONTAINS : MECHANISTIC RADIOLYSIS REACTIONS OF WATER, MECHANISTIC RADIOLYSIS AND THERMAL REACTIONS OF IODINE, GENERIC SEMI-MECHANISTIC REACTIONS OF ORGANIC COMPOUNDS, INTERFACIAL GAS /LIQUID MASS TRANSFER

* INPUT: pH, 1- CONCENTRATION, ORGANIC CONCENTRATION, DOSE RATE, MASS T W S FER PARAMETERS

* NO TEMPERATURE VARIATION

* SIMULTAION OF GAMMA CELL EXPERIMENTS WITH CONSTANT FLOW BASED ON GEOMETRY OF STIRRED VESSEL IN GAMMA CELL

* EDITED AUGUST 1998 BY FARIBORZ TAGHIPOUR;

* PARAMETERS : AGL AN DR FLOW Gx

KTG KTL VG VL

GAS /LIQUID INTERFACIAL AREA ( am2 ) AVOGADRO CONSTANT (6.022E23) DOSE RATE (kGr/hr) GAS PHASE FLOW RATE (L/s) G VALUE " T m YIELD OF WATER RADIOLYSIS PRODUCTS" OF THE COMPONENT x (number of molecules formed per 100 eV) LIQUID-GAS PARTITION COEFFICIENT OF THE COMPONENT x GAS SIDE MASS TRANSFER COEFFICIENT (drn/s) LIQUID SIDE MASS TRANSFER COEFFICIENT (dm/s) GAS PHASE VOLUME (dm3 ) LIQUID PHASE VOLUME (dm3 ) ;

COMPILE INSTANT ;

OPEN 6 "VOUPUT4 . LOG" ;

OPEN 7 "VEO1.OUT " ; OPEN 8 'IVE02 .OUT " ; OPEN 9 "VE03.0UT " ; OPEN 10 "VEO4 .OUT" ; OPEN 11 "VSOS.OUT" ; OPEN 12 "VEO6. OUT" ;

PERMIT + - ;

VARIABLE 12G 12 1- 13- 01- HO1 I 12- 10-2 IO2H E- HO2 O- H H2 OH 02 - 03- IG I20H- 102 OH- 02 02G H2G H02- H202 H203 TRAP;

VAFtI-ABLE CH3 R PHOH RI ROH IPHOH PRODUCT HOIR CO RIG IPHG ARH AROH RCO RCOH2 RO2 CL-;

PARAMETER R1 R2 R3 R4 R18 RI9 R20 R32 R33 R34 R46 R47 R4ô R60 R61 R62 Fi74 R75 R76 R88 R89 R90 RIA RIB R1C RIO RIP R1Q

R5 R6 R7 R8 R9 R10 RI1 RI2 R13 R14 R1S R16 R17 R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R35 R36 R37 R38 R39 R40 R41 R42 R43 R44 R45 R49 R50 R51 R52 R53 R54 R55 R S 6 R57 R58 R59 R63 R64 R65 R66 R67 R68 R69 R70 R71 R72 R73 R77 878 R79 R80 R8L R82 RB3 R84 R85 R86 R87 R91 R92 R93 R94 R95 R96 R97 R98 R99 RlOO RID RIE R1F R1G RIH R1I R1J R1K R1L RIM RIN R1R RV2 RI2 R02- R12- RI3- RH02 RI-;

PARAMETER H20 55.51DO 8 Ht PH 5 IO- IE-4 M O ;

P M T E R RH O.OE-O RCOH 0-OE-O AR 0.OE-3 RCL 0.OE-3 ;

PARAMETER AN 6.023323 DR 0.15 PR;

PARAMETER GE- 2.75 GH 0-63 GH2 0-45 GOH 3.12 GH202 0.58 GH+ 2.7;

PARAMETER AGL 1.03 VL 0.25 VG 0.75 AGW ;

PARAMETER HE02 2.6354E-2 HEH2 1.7569E-2 HE12 80 HE1 1.85 HERI 4 HEIPH 10000;

PARAMETER KTlLG KTlGL KTSLG KT2GL KT3LG KT3GL KT4LG KT4GL KTSLG KT5GL ISWX SE-4 ISUMG 1E-25 ISUM PCI FI TF1 TOT ORGIG REMOV KTL 1.5E-4 KTG 1-2E-1 FLOW 7e-2 KVENT ;

COMPILE GENERAL ;

* MASS TRANSFER PARAMETERS; KTlGL=KTL*AGL/VL; KTlLG=KTL*AGL/VG; KT2GL=AGL/(VLf (l/KTL + EFEI2/KTG) ) ; KT2LG=AGL/ (VG* (~/KTL + HEI~/KTG) ) ;

KT~GL=AGL/ (VL* (l/KTL + HEI/KTG) ) ; KT3LG=AGL/ (VG* (~/KTL t HEI/KTG) ) ; KTQGL=AGL/ (VL* (~/KTL + HERI/KTG) ) ;

KT~LG=AGL/ (VG* (~/KTL + HERI/KTG) ) ; KTSGL=AGL/ (VL* (l/KTL + HEIPH/KTG) ) ; KTSLG=AGL/ (VG* (~/KTL + HEIPH/KTG) ) ;

COMPILE GENE-;

* VARIOUS TOTALS FOR KEEPING TRACK OF TECE MASS BALANCE; ISUMG = 2*12G + IG + RIG + IPHG; ISUM = 2*12 + HO1 + 1- t 3*I3- + 01- + I + 2*12-

i- 10-2 + RI + IPHOH; ORGIG = RIG + IPHG; FI = 2'12 + HO1 + 01- ; TF1 = 2*12 + HO1 + 01- + I + 2*13- + 12-; TOT = ISUMGfVG + ISUMfVL + TRAP ;

* BALANCE ON THE OVERALL RATE O F CHANGE OF SELECTED SPECIES BY SUMMING THE RATES OF THE RELEVANT REACTIONS ;

RI2 = RSO + R33 + R1L + R 4 0 - R27 - R 2 8 - R30 - R39 - R 4 2 - RIM; RO2- = R9 + R25 - R4 - RI1 - R17 - R21 - R23 - R41 - R42 - R43 ; RI- = 2fR41 + R43 -+ R 4 4 + R 4 5 + R 4 7 + R48 + R51 + R28 + R37

- R 3 1 - R34 - R27 - R46; RH02 = R3 + R 1 6 + R 2 3 + R47 - R5 - R18 - R21 - 2*R22 - R39 - R 4 0 ;

* THE NET RATE OF PRODUCTION OF VOLATILE IODINE (moles/rnin); rernov = rv2*60; ** -

COMPILE I N I T I A L ;

H+ = 10.0(- PH) ; OH- = I.OE-14/H+ ; 0 2 = DO*2-5E-4/8; 02G = 02/HE02; ISUMG = 1E-25; 1- = IO-; **;

COMPILE EQUATIONS;

* FORMATION OF NATER RADIOLYSIS PRODUCTC; R I A % PR*GE-: =E-; R I B % PR*GH : =H; R l C % PRfGH2 : =H2 ; R1D % PR*GOH: =OH; RIE % PRkGH202 : =HZ02 ; R I F % PRfGH+: =H+;

* INTERFACIAL TRANSFER OF 02 AND H2; R1G % KTlGL* (02G*HE02 - 02) : =O2 ; RlE % KTlLG* (O2 - 02G*HE02 ) : =02G ; R I 1 % KTlGL* (H2G*HEH2 - H2) :=H2; R1J % KTlLG* (H2 - H2G*HEH2 ) : =H2G;

* INTERFACIAL TRANSFER AND VENTING OF AIRBOIXNE IODINE; RIK % KT2GL* (I2G * HE12 - 12) : =12 ; R1L % KTSLG* (12 - 12G * m12) - KVENT*I2G:=LISG; RIM % KT3GL*(IG * EEEI - 1) :=I; RLN % KT3LG*(I - IG * HEI) - KVENT*IG:=IG; R10 % KT4GL* (RIG * HERL - RI) : =RI ; RIP % KT4LG* (RI - RIG * =RI) - KVENT*RIG:=EIG; RIQ % KTSGL* (IPHG * EIEIPH - IPHOH) :=IPHOH; RIB % KTSLG* (IPHOH - IPHG * HEIPH) - KVENT*IPHG:=IPHG;

* ACCUMULATION OF IODINE ON THE CHARCOAL TRPS ; W 2 % KVENT*VG* (2*12G + IG + RIG + IPHG) : =TRAP;

* CHEMICAL REE+CTIONS ;

* WATER RADIOLYSIS REACTIONS * -----------------,---------- RI % 5.5OE+09 : OH + OH R2 % 3.00E+10 : OH + E- R3 % 2.50Et10 : OH + H R4 % 1.80E+10 : OH + 0- R5 % 6.00E+09 : OH + HO2 R6 % 8.00E+09 : OH + 02- R7 % 8.50Ec09 : OH + 03- R8 % 2-70Ec07 : OH + B202 R9 % 7.50E+09 : OH tH02- R10 % 4.20Ec07 : OH + H2

. - - r

H202 - * ; OH- - * ; Et20 - * ; HO2 -

II

H203 - * ; OH- + 02 - * ; HO2 + 02- ; HO2 + 02- + El+ ; * ;

H20 + 02- r

H 2 0 + H ; * ;

= H2 + OH- -t O R - - + ; 1

= OH- + H2 - * ; = OH- + OH- - * . = H02- + OH- - + ; = O H +OH- - * ; = O - +OH- - * ; = H . * - = 02- - * ;

R19 % 5 .50E+09 : H + H = H2 - * ; R20 % 1.00Et10 : H + HO2 = H202 - * ; R21 % 2.00E-i-10 : H + 02- = HO2- - . A - ;

R22 % 9.00Et07 t H +Hz02 = H 2 O + O H - * ; R23 % 1.50Et07 : H + OH- = E- + H20 . * ; R24 % 2.00Et10 : H + 02 = 02- + H+ . * ; R25 % 1.99Et10 : H + O- = OH- - * -

R26 % 1.29E+08 : O- + O- = H202 + OH- + OH- - * ; R27 % 6.00E+08 : O- + 02- = 02 + OH- + OH- - * . r

R28 % 7,00E+08 : O- + 03- = 02- + 02- r . * . t

R29 % 5.00E+08 : 0- + H202 = 02- + H20 . - A - - R30 % 4.00Et08 : O- + HO2 = OH- + O 2 . * - R31 % 3.60Et09 : 0- + O2 = 03- t . * - r

H 2 0 2 + 02 - * ; 0 2 + H02- - * ; 02 + H 2 0 - . * - .

1

O- + 02 - * ; OH + O 2 ; * ;

H+ + H02- - * . r

H 2 0 2 ; * BOYO ; H+ t OH- - * ; H 2 0 ; * DRA; O- + H 2 0 . i r e , 1

OH + O H - r - + . r

K+ + 0 2 - - * - , r

HO2 r - * ;

*R59 % 4 . 0 0 E - 0 2 % 4 . 4 0 3 + 1 2 : 12 + H z 0 = HO1 + 1- + H + ;

R 6 0 t 5.76E-02 % 2 . 0 0 E + 1 0 : 1 2 + H 2 0 = 1 2 0 H - + R+ ; * ; R 6 1 % 8 .OE+08 % 5 . 0 0 E + 0 4 : 1 2 + OH- = 1 2 0 H - - x - 1

R 6 2 % 1 , 3 6 E + 0 6 % 4 . 0 0 E t 0 8 : 12OH- = HO1 + 1- ; * ; R 6 3 % 1 . 0 0 E - 0 1 % 1 . 0 0 E + 1 0 : HO1 = H+ + 01- ; * ; R64 % 2.00E+10 % 1 . 5 6 E t 0 5 : HO1 + OH- = H2O + 01- ; * ;

*REACTIONS OF H 2 0 2 *-------------------------. R 6 5 % 2 . 0 2 E + 0 6 % 1 . 3 0 E t 0 7 / 5 5 . 5 : I 2 0 H - + H202 = 1- t I 0 2 H + H 2 0 ; * ; R66 % 3.OE+09 : I O 2 H t OH- = 0 2 + H 2 0 + 1- - * ;

"ORGANIC IODIDE FORMATION AND DESTRUCTION REACTIONS * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - R 6 7 % 1 . 2 0 E + 0 8 : RH + OH = R + H2O ; * ;

TIME OH H 0 2 - H 2 0 2 E- 02; **; PSTREAM 3 9; TIME ISUM ISUMG; **; PST= 4 1 0 ; TIMF, REMOV TRAP ; ** - , PSTREAM S 11;

TIME 1 2 G 1 2 1- 13- 01- HO1 12- ; **; PSTREAM 6 12; KTL KTG FLOW ; **;

COMPILE OUT; P C I = ISUM/ISUMG ; PSTREAM 1;

PSTREAM 2 ; PSTREAM 3 ; PSTREAM 4 ;

PSTPcEAM 5 ; **;

COMPILE CHANGE; RCL = 0 . O E - 3 ; RCOH = 0 .OE-3 ; AR = 0 . O E - 3 ; RESTART ; *-* -

I

WHEN TIME = 1 . 0 + 5 E 2 + 3 0 0 CALL OUT; TIME = 5E4 CALL CHANGE; TIME = 1 5 . O E 4 % ; **;

BEGIN; STOP;

APPENDIX G: Relationships Between the Governing Equations in the Mode1

Figure G.1 provides a simple representation of the relationships between the governing

squations in the model. For simplicity in this description, I2 is only produced through

reaction G.1 and consumed through reaction G.2. These two processes involve a number of

reactions in the actual rnodel- The Iz produced in the liquid phase is transferred to the gas

phase by mass transfer.

1- + OH - 12 + PRODUCTS

1, + O-? ---+ ri + 0 2

Figure G. 1 A simple presentation of chemical reactions and mass transfer in the system

To calculate the gas and aqueous phase concentrations of iodine. a combination of

chernical reactions and mass transfer can be considered as follows.

dl?x$dt = &L m~ ([Id - [IIG~) - F2C3lNG

d[IlJ/dt = k1 117 [OH1 - k II4 [O-il - &L ML, NI2 J - H f l z ~ 1 )

where:

CIzG] and Cfz,] = gas and aqueous phase concentrations of I2

[rl, [ O a , and = the concentrations of 1-, OH, and Ob2, respectively

F = flow rate

J&, = overall liquid side mass transfer coefficient

A = interfacial area

V, and V, = gas and aqueous phase volumes

k , and k, = the rate constants ofreactions G.1 and G.2, respectively

H = partition coeff~cient

t = time

For water radiolysis products such as OH, their radiolytic production should also be

considered? in addition to their subsequent reactions.

d[OH]/dt = (Dose rate x G,d - k, [ I l [OH]

Where Go,, is the yieId for OH production as a result ofabsorbed radiation.

APPENDM H: Rate Constants of Organic Reactions

Due to the generic nature of the organic iodide reactions in the model, the rate constants of

these reactions are in terms of their approximate magnitudes. The values implemented for

the rate constants have been justified here. The rate constants for the generic reactions were

estirnated fiom values obtained for specific organics with similar molecular structures to that

of the --generic" organic. An example of the rate constant for each reaction is provided

below.

Atkyl Halides

RCl + e-,, - R' + Cl-

CH,Cl, + e-., ---+ CHzCl + Cl-

RCI + OH - EX1 + H20

CH2C12 + OH - CHzCl + Cl-

k = 1 x 10' dm3 mol-' s-'

k = 9 x 107 dm3 mol-' s-' [3]

k = 1 x 10' dm' mol-' s-'

k = value estimated [4]

Carbonyls

RCHO + e-,q + RCOH2 + O H k = 5 x 10' d d mol-' s-' ( 5 -76)

CH3COC2Hï + e-, ---+ CH3COHC2Hj + O H k = 4.9 x 109 dm' mol-' s-' [5] (H.5)

RCHO + OH - RCO' + HzO k = 5 x 10' dm3 mol-' s-' (5.77)

CH3COC2Hj + OH - CH3COWCIH4 + H 2 0 k = 7 x 10' dm3 mol-' S-l [j] (Hm

RCHO + H - RCO' + H2 k = 5 x 10' dm3 mol-' s-' (5.78)

CH3COC2H, + H ---+ CH3CO'C2H, + H2 k = 3 x 10' dm3 mol-' s-' [6] (H.7j

RCOH, + RCOH, - RCOH + PRODUCT k = 5 x 10' dm3 mol-' s-' (5.79)

2 CH3COHCH3 - CH3CHOHCHj + CH3COCH3 k = 7 x 108 dm3 mol-' s-' [7] (H.8)

RC0'- R + C O k = 1 x 10' dm3 mol-' s-' (5.80)

from decornposition of CH3COHC2H, - k = 3 x 10' dm3 mol-' s-' [8] (H.9)

Aromatics

AR+OH- AROH -1 -1 k = 5 ~ 1 0 ~ d m ~ m o l s (5.8 1)

C6H6 + OH - Hydroxylcyclohexadienyl k = 7.9 x 1 o9 dm3 mol-' s-l [9] (H. 10)

AR+e-,- AP3I-t O H k = 1 x 10' dm3 mol-' s-' (5.82)

C6H6 + e- ,, - [C6H6] '- k = 9 x 106 dm3 mol-' S-' [1 O] (H.11)

AR-~H-AEZH k = I x 109 dm3 mol-' S-'

C,H6 t H - Cyclohexadienyl k = 1.1 x log mol-' s-' [ l 11

AR + Oz- - PRODUCT k = 1 x 10' dm3 mol-' s-'

frorn: C6H3(OH)3 +- O?-+ Dihydrosyphenoxyl k = 3.4 x 105 dm3 mol-' s-' [12]

AROH +- O2 - PHOH + HO2 k = j x 10' dm3 mol-' s-'

Hydrosycyclohesadienyl+ O2 - Products k = 3.1 x 10' dm' mol-' s-' [ 131

.4RH+O2-AR+HO2 k = 1 x 1 o9 dm3 mol-' s-'

Cl-cfohesadienyl+ O2 - Products k = 1.6 x lo9 dm' mol-' s-' [11]

PHOH -+ OH -----+ PRODUCT k = 1 x 10" dm' mol-' s-'

C,H,OH + OH - Dihydrosylcyclohexadienyl k = 6.6 x log dm3 mol-' s-' [15]

PHOH + O--- PRODUCT k = 1 x 10'dm3rnol - 1 s - 1

H3

(5-83)

(H. 12)

('5 - 84)

(H. 13)

(5.85)

(H- 14)

(5.86)

(H. 15)

(5.87)

(H. 16)

(5.85)

C6HjOH i- OH ---+ Product

Organic Iodides

R + Iz- RI

CH; + 1, - CH;I

k = 5.8 x 10' dm' mol-' s-' [16] (H. 17)

k = 3 x 1 o9 dm3 mol-' S-' (5.89)

k = 2 . 7 5 ~ 1 0 ~ d m ~ m o l - ~ s - ~ [ 1 7 ] ( H M )

EU+OH-HOIR

CH31 +- OH - Product

CH; +CH;

k = 1 x 20' dm3 mol-' s-'

k = 1 x 10' dm3 mol-' s-' [18]

( 5 -90)

(H. 19)

- [ - 1 k = 1 x 1 0 ' ~ d m ~ r n o l s ( 5 -94)

k = 1.2 x 101° dm3 mol-' s-' [21] (H.23)

k = 2 x 1 O-' dm3 rno 1- ' s- ' (5.95)

k = 2 x IO-' dm3 mol-' s-' [18] (H.24)

R + H - W

fi-om: CH3 + CH3 - CH3CH3

k = j x lo9/l dm3 mol-' S-' (5.98)

k = 4 x 1 o9 dmi mol-' s-' [23] (H.27)

PHOH + HO1 ---+ IPHOH k = 1 x 10' dm3 ma 1-L s-' (5.99)

C6HjOH + HO1 - C6H40HI k = value estimated [W] (H-28)

IPHOH + e-, - 1- + PRODUCT k = 1 x 1 o9 dm' mol-' s-l (5.100)

frorn: ClC,H,OH -+ e-,, - CI- + HOC6H, k = 4.4 x 10' dm3 mol-' s-' [25] (H.29)

lPHOH + OH - PRODUCT k = 1 x 10" dm3 mol-' s-' (5.101)

from: CiC6H,0H + OH w Addition k = 1.2 x 10" dm3 mol-' s-' [25] (H.30)

IPHOH + H - PRODUCT k = 1 x 1 0' dm3 mol-' s-' (5.102)

from: CLC,H,OH + H ---+ Addition k = 1.5 x lo9 dm3 mol-' s-' [25] (H.3 1)

References:

Balkas. T.I.. Int. J. Radiat. Phys. Chem. 4(2): 199-208 (7972)

Neta. P,; Fessenden, R, W . Schuler, R.H.. J. Phys. Chern. 75(11): 1654-66 (1 97 1 )

Haag, W.R.; Yao, C.C.D., Environ. Sci. Technol. 26(5): 1005-13 (1 992)

Getoff. N., Radiat. Phys. Chem. 35(l-3): 432-39 (1 990)

Mezyk, S.P., Cm. J. Chem. 72(4): 11 16-9 (1994)

Mezyk. S.P.; Bartels, D-M,, Can. J. Chem. 72(12): 25 16-20 (1994)

Spinks, 1. W. T: Woods, R. J-T Intr-odtiction ro Rndkltion Chemisrty, Wiley, New York,

326- 1990

Finlayso-pitts, B. J-, Atmospheric Chernistry: Fzindarnentuls and Ekperimentul

Techniques, Wiley, New York, 429, 1986

Ashton. L.; Buuton, G.V.; Stuart, C.R-, J- Chem. Soc., Faraday Trans. 91(1 1): 163 1-3

(1995)

Koehler, G.; Solar, S.: Getoff? N.; Holnvarth, A.R.; Schaffner. K., J. Photochem. 28(3):

383-9 1 (1 985)

Roduner, E.: Bartels, D.M., Ber. Bunsenges. Phys. Chem. 96(8): 1037-42 (1992)

Deeble, D.J.; Parsons. B.J.; Phillips, G.O.; Schuchmann, H . 2 : von Sonntag, C.. Int. J.

Radiat. Biol. 54(2): 179-93 (1 988)

Pan, X.-M.; von Sonntag' C., Z. Naturforsch., B, Chem. Sci. 45B(9): 1337-40 (1990)

Maillard, B.; Ingold, K.U.; Scaiano, J-C., J. Am. Chem. Soc. 105(15): 5095-9 (1983)

Field, R.J.; Raghavan, N.V, Brummer, KG., J. Phys. Chem. 86(13): 2443-9 (1982);

Kem. Koezl. 59(1-2): 235-50 (1983)

Tsujimoto. Y.; Hashizume' H.; Yamazaki. M., Int. J. Biochem. 25(4): 491-4 (1993)

Mezyk, S.P.: Madden, K.P., J. Phys-Chem. 100: 9360-64 (1996)

Evans, G.J: Melnyk. A.; Paquette, J.; Sagert, N.H., The LIRIC Database, WB-90-234

( 1990)

Mohan, H,; Asrnus, K.D., J, Phys. Chem. 92(188): (1988)

Mezyk, S.P.: Radiat. Phys. Chem. 49(4): 437-43 (1997)

Mezyk, S.P.; Bartels, D.M-, J. Phys. Chem. 98(41): 10578-83 (1994)

Getoff, N., Appl. Radiat. Isot. 40(7): 585-94 (1989)

Marcha., A.; Kelley, D.G.; Bakac, A.; Espenson, J.H., J. Phys. Chem. 95(11): 4440-1

(1991)

Wren, J-C.; Paquette, J.; Wren. D.J.: Sanipelli, G.G.. "The Formation and VoIatility of

Organic Iodides", Proc. of The Speciaiists' workshop on iodine chemistry in reactor

safety, Hmvell, England, September 1 1-12, 1985; AERE R 1 1974: (1986)

Getoff, N.F Solar. S., Radiat. Phys. Chem. 28(5-6): 44-50 (1986)

APPENDK 1: Comparison of Modeling and Experimental Results

Table I. 1 Comparison of modeling and expenmental Results of iodine volatiIization rate Liquid Mass Transfer coefficient: 1 -5E-4, Gas Mass Transfer coefficient: 1 E- 1 dm/s

1 (LMT 4.5 E-4)

Conditions

p H 5 / r L E 4 M

Table 1.2 Modeling results of airbome iodine concentrations in the presence of organics at 1- 0.5 E-5 M, pH 5

Experiment (movmin) 9.OE-10

Modeling (rnoI/min)

2E-8

Conditions

No Organic

RCI 1 E-3 M

RCHO 1E-3 M

Aromatic 1E-3 hl

I2G (Ml

1.5 E-1 1

3 E-IO

5 E-13

9 E-12

ORG-IG (MI

O

2 E-9

1 E-10

1 E-12

IG (M)

2 E-12

2 E-12

7 E-13

1 E-13

Volatilization (mo Vmin) 1.3 E-10

1.3 E-8

3 E-10

9 E-11