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Iodine Behavior in Containment

Jungsook Clara WrenAECL Chalk River Laboratories

Presented to US Nuclear Regulatory CommissionWashington DC

May 6-7, 2003

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Background

• Iodine is the single most important nuclide with potential for public dose in the event of a severe core damage accident

• AECL recognized the importance very early− Mechanistic approach to fully understanding release fraction

• Not bounding• Based on fundamental understanding coupled with validation

tests− AECL established a program over 20 years ago

• Results− Best models in the world− Well validated− High confidence, Low uncertainty

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Iodine Volatility in Containment

• Iodine would be released from fuel into containment mainly as CsI (& HI), which would dissolve as non-volatile iodide upon contact with water.

• However, under the oxidizing and high radiation environment following an accident, non-volatile iodide would react and become volatile and partition into the gas phase.

• The primary concern is the time dependent concentration of gaseous iodine as a result of the radiolytic production in containment following an accident.

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Iodine Interconversion and Mass Transport

I−−−−, I3−−−−, HOI, IOx−−−−

I(con)

Iaq(ad)

Ig(ad)

I2(aq) RI(aq)

I2(g) RI(g)

Accident Conditions

• DR <<<< 10 kGy/h• T <<<< 130oC• pH: 11 – 5 • Initial concentration

<<<< 10−−−−4 [I−−−−] M• Condensing• Variety of surfaces

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Information Required

• Fraction of iodine in the gas phase as a function of time− Rate of interconversion of non-volatile iodine (I−−−−, I3−−−−, etc) to

volatile species (I2 & RI) in water

− Rate of transport of volatile iodine species between the aqueous and gas phases and surfaces

Pg 6

Complexity of the Iodine System

Iodine conversion via rxns with water radiolysis products, •OH, •O2

−−−−, H2O2

Inter-dependenthomogeneous, heterogeneous processes I−−−−, I3−−−−, HOI, IOx

−−−−

I(con)

Iaq(ad)

Ig(ad)

I2(aq) RI(aq)

I2(g) RI(g)

I−−−−, I3−−−−, HOI, IOx−−−−

I(con)

Iaq(ad)

Ig(ad)

I2(aq) RI(aq)

I2(g) RI(g)

Iodine in various oxidation states

Continuous radiation

Inter-dependent rxns, having different dependences on conditional parameters

Large no. of rxnsto model

Effects of organic impurities & trace metal ions

The kinetics of each rxn path needed to model

Difficult to separate the effects of individual factors

Difficult to extract a scaling factor

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AECL’s Iodine Program Components

• Engineering-scale integrated-effects tests in the Radioiodine Test Facility (RTF)

• Supporting bench-scale tests to separate and quantify individual effects

• Development and validation of containment iodine behavior models, LIRIC & IMOD, for safety analysis

• International collaboration− EPRI ACE and ACEX contracts− Leading the International Standard Problem (ISP) on iodine

code comparison exercises− COG-IPSN information exchange

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RTF Program

• RTF− Miniature containment, which could simulate a wide range of

post- accident conditions − The most important integrated facility in the world designed to

examine the iodine chemistry and transport processes together

• Objectives− Evaluate the relative importance of various processes− Effects of individual components in an integrated test facility − Unforeseen phenomena

• Significant contributions to understanding− Revealed the importance of many unexpected phenomena that

were not previously observed in large-scale or bench-scale studies

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Supporting Bench-Scale R&D Areas

• Objectives:− To aid in the interpretation of the RTF test results − To develop models that would have solid technical

basis for their predictable capability

• Study Components:1. Aqueous Phase Chemistry

a. Inorganic Iodine Reactionsb. Steady-State Water Radiolysisc. Reactions of Organic Impurities and Organic Iodides

2. Aq-Gas Phase Partitioning3. Iodine – Surface Interaction

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Model Development & Validation

• LIRIC− A comprehensive mechanistic model, consisting of about 200

chemical reactions and transport equations − Epitome of our current understanding− Performs well when tested against bench-scale and RTF tests

carried out over a wide range of conditions

• IMOD− Constructed based on extensive LIRIC analysis and simulations

of various RTF tests − A smaller, simpler model, but maintains many of the capabilities

of LIRIC− Integrated into a larger safety analysis code

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RTF Program

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I−−−−, I3−−−−, HOI, IOx−−−−

I(con)

Iaq(ad)

Ig(ad)

I2(aq) RI(aq)

I2(g) RI(g)

I−−−−, I3−−−−, HOI, IOx−−−−

I(con)

Iaq(ad)

Ig(ad)

I2(aq) RI(aq)

I2(g) RI(g)

Main Vessel

Radioiodine Test Facility

Pg 13

RTF Schematic

DO

ORP

pH

AAIS

Gas Recirculation Loop

H2 Sensor

AqueousRecirculation

Loop

Gas Ventilation LoopCharcoal Filter

AqueousSampling

Loop

Lead Canister

GasSampling

Loop

Main Vessel

pH control

pH

OnlineGamma

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Radioiodine Test Facility

• Main features − Well instrumented and controlled− A replaceable 340 L vessel − Provides many combinations of

• Reaction media (gas, water, surfaces)• Conditions (pH, T, radiation dose, chemical additives)

− Equipped with on-line sensors and off-line measurements• On-line: [I(g)], [I(aq)], pH, DO • Off-line: iodine speciation, organic and anions, trace metals

Pg 15

Typical RTF Test

I2(g)

I (ad)

RI(g)

RII2

Radiation Field

I (ad)

I (g):I2

HVRILVRI

I (aq):I2RI

I−−−−CsI Injection

Organic ImpuritiesMetal Ions

Pg 16

50 RTF Tests

• Type of Vessel Surface− Stainless Steel (electropolished, untreated)− Organic Coatings on carbon steel or concrete

(Vinyl, Epoxy, Polyurethane)− Inorganic Coatings (zinc primer)

• Radiation on, Radiation off• pH controlled, pH uncontrolled

− pH range: 4.5 – 10.5• Temperature

− constant throughout exp; 25, 60, 90oC− steps from 25 to 80oC

• Condensing, Non-condensing• Organic and Inorganic Additives

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Technical Contributions of the RTF Program1. The Effect of Radiation

• The RTF test program provided concrete data, showing that iodine behavior in the presence of a steady-state radiation source dramatically differs from that of non-radiolyticconditions

• The gas phase iodine concentrations and iodine speciation observed in the RTF tests were very different from those predicted from the equilibrium thermodynamic calculations.

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Effect of Radiation (Vinyl Vessel, 25oC, DR = 0 or 1.4 kGy/h)

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

0 10 20 30 40 50 60 70 80 90 100

Time (h)

Gas

Pha

se Io

dine

Con

cent

ratio

n (M

)

Radiation Source PresentNo Radiation Source

Radiation

No Radiation

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• The RTF studies firmly established the effect of pH on iodine volatility in a containment-like vessel.

• [I(g)] increases by a factor of 5 – 10 with a decrease in pH by one unit. A higher dependence at a lower temperature.

• The early assessments emerged following the TMI accident postulated that a sufficiently high pH in containment water would keep iodine trapped in the containment sump water as I−−−−.

• However, the observed pH dependence of iodine volatility was different from those predicted from the equilibrium thermodynamic calculations.

Technical Contributions of the RTF Program2. The Effect of pH

Pg 20

Effect of pH (Stainless Steel Vessel, 60oC, DR = 0.78 kGy/h)

4

5

6

7

8

9

10

0 100 200 300 400 500

Time (h)

pH

1.0E-14

1.0E-12

1.0E-10

1.0E-08

Gas

Pha

se Io

dine

Con

cent

ratio

n (m

ol/d

m3)

pHTotal Gas Phase Iodine

pH [I(g)]

Pg 21

• The RTF program demonstrated that containment surfaces have a major influence on iodine behavior, especially under radiationconditions.

• Surfaces influence iodine volatility through more ways than simply iodine deposition and reactions on surfaces.

• In a radiation field, the surfaces may govern − The pH of the sump water − Iodine speciation in water, hence, the partitioning of iodine

between the gas phase, the aqueous phase and surfaces

Technical Contributions of the RTF Program3. The Effect of Surface

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Effect of SurfaceOrganic- vs. Inorganic-Based Paint

-14

-13

-12

-11

-10

-9

-8

-7

0 10 20 30 40 50 60 70 80 90 100Time (h)

Log

Gas

Pha

se Io

dine

Con

cent

ratio

n

zinc-primer coatingVinyl coating

Vinyl Coated

Zinc-primer Coated

Tests at 25oC, DR ~ 1.5 kGy/h

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Organic Surfaces on pH & [I(g)]

-12

-11

-10

-9

-8

-7

-6

-5

-4

0 2 4 6 8 10 12 14 16 18 20

Time (h)

Log

Gas

Pha

se Io

dine

Con

cent

ratio

n

0

2

4

6

8

10

pH

VinylEpoxyPolyurethane

EpoxyPolyurethane

Vinyl

Tests at 25oC, DR ~ 1.5 kGy/h

Surface affects iodine volatility, mainly via its impact on pH

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1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

0 10 20 30 40 50 60 70 80 90 100

Time (h)

Gas

Pha

se Io

dine

Con

cent

ratio

n (M

)

pH UncontrolledpH Controlled at 10pH Uncontrolled (No Radiation Source)

Radiation, pH = 10

Radiation, pH uncontrolled

No Radiation

Effect of pH under Radiation(Vinyl Vessel, 25oC, DR = 0 or 1.4 kGy/h)

Pg 25

Cause for the pH Change in Organic VesselsMEK addition in an RTF test (zinc-primed, 25oC, ~1.8 kGy·h-1)

0

2E-11

4E-11

6E-11

8E-11

1E-10

1.2E-10

1.4E-10

1.6E-10

1.8E-10

2E-10

170 220 270 320 370 420 470 520

Time (h)

Gas

Pha

se Io

dine

Con

cent

ratio

n (m

ol/d

m3 )

0

2

4

6

8

10

pH a

nd D

isso

lved

Oxy

gen

(ppm

)

[Ig]

DO

pH

MEK AdditionMEK addition to water

pH

DO

[I(g)]

Pg 26

Organic Concentrations in Water

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

3.00E-03

0 50 100 150 200 250 300 350 400 450 500

Time (h)

Con

cent

ratio

n (m

ol/d

m3 )

MEKMIBK

MIBK Addition

MIBK

MIBK addition

MEK

Vinyl Vessel, 25oC, No RadiationIn radiation: [Org] <<<< detection limit

pH change due to organic impurities dissolved from surface into water

Pg 27

pH Change due to Slow, Continuous MIBK Addition(Electropolished SS vessel, 25oC, ~0.6 kGy·h-1)

6

6.5

7

7.5

8

8.5

9

9.5

10

10.5

11

0 50 100 150 200 250 300

Time (h)

pH

Experimental Data (pH offset by 0.2 units)

IMOD-2.0

Slow MIBK Addition Fast (5X) MIBK AdditionpHControl

pHControl

pHControl

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Organic Iodide Production(Vinyl Vessel, 25oC, DR ~ 1.4 kGy/h)

-10.5

-10

-9.5

-9

-8.5

-8

0 20 40 60 80 100Time (h)

Log

of C

once

ntra

tion

Aqueous Phase Speciation

Organic Iodide

I2

-9.5

-9.3

-9.1

-8.9

-8.7

-8.5

-8.3

-8.1

0 20 40 60 80 100Time (h)

Log

of C

once

ntra

tion

Gas Phase Speciation

I2

Organic Iodide

Aqueous Concentrations Gaseous Concentrations

Organic Iodide

I2

I2

Organic Iodide

− A variety of organic iodides could be formed − Ave. volatility of organic iodide <<<< volatility of CH3I, ≈≈≈≈ I2

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793 ×××× 10-10ZincYes

821 ×××× 10-10ZincNo

866 ×××× 10-10Stainless SteelYes

52 ×××× 10-10Vinyl at pH 10Yes

877 ×××× 10-9EpoxyYes

923 ×××× 10-9PolyurethaneYes

124 ×××× 10-11VinylNo

788 ×××× 10-9VinylYes

% Iodine Lost to Surface

Maximum Gas Phase Iodine Concentration

(mol⋅⋅⋅⋅dm-3)

Vessel SurfaceRadiation Field

Surface Loading Observed in the RTF (1)

Pg 30

• Surface adsorption is greater in the presence of radiation, except for the test with the zinc primer surface.− In the absence of radiation, adsorption occurred mainly in the

aqueous phase. − In the presence of radiation, the iodine adsorption occurred mainly

in the gas phase and was more significant.

• The observed surface loading was related to the gas phase iodineconcentration. − The concentration was higher in the presence of radiation− Equally significant on bare stainless steel and painted surfaces− When the pH was kept high, the surface loading was significantly

reduced.

Surface Loading Observed in the RTF (2)

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• The prevalent presumption was that iodine volatility would increase considerably with an increase in temperature− Mainly based on the fact that the partition coefficients of volatile

iodine species (I2 and organic iodides) would decrease exponentially with increasing temperature.

• The RTF tests show that iodine volatility is relatively insensitive to temperature − The hydrolysis rates of I2 and organic iodides to non-volatile iodide

in solution increases exponentially with T, effectively counterbalancing the partitioning behavior.

− Temperature also affects the net surface adsorption rates of iodine species

Technical Contributions of the RTF Program4. The Effect of Temperature

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0.0E+00

5.0E-11

1.0E-10

1.5E-10

2.0E-10

2.5E-10

3.0E-10

3.5E-10

4.0E-10

0 50 100 150 200 250 300

Time (h)

Con

cent

ratio

n (m

ol/d

m3 )

25oC 80oC60oC

Effect of Temperature (Stainless Steel Vessel, DR = 0.67 kGy/h)

Total Gas Phase Iodine Concentration

Pg 33

Effect of Temperature (Stainless Steel Vessel, DR = 0.67 kGy/h)

0.E+00

1.E-06

2.E-06

3.E-06

4.E-06

5.E-06

6.E-06

7.E-06

8.E-06

9.E-06

0 50 100 150 200 250 300

Time (h)

Con

cent

ratio

n (m

ol/d

m3 )

Total Aqueous Phase Iodine Concentration

Pg 34

Other RTF Studies

• The effect of silver, boric acid, organic polymers and hydrazine additives on iodine chemistry

• The role of condensation and aqueous-gas phase mass transfer on iodine mass transport

Pg 35

Summary of the RTF Program (1)

• The RTF studies have identified the key processes that must be considered in determining iodine volatility under post-accident containment conditions, and the parameters to which these processes are sensitive.

• Iodine volatility increases dramatically in the presence of radiation

• Iodine volatility increases with a decrease in pH− Thermodynamic considerations do not explain the quantitative

effect of pH on iodine volatility observed in the RTF

• Iodine volatility does not vary appreciably with temperature. − This observation was contrary to the early assumption that

temperature would increase iodine volatility substantially.

Pg 36

• Surfaces (particularly organic) play a significant role in determining iodine volatility, through their indirect impacts on pH and iodine speciation and by adsorbing significant amount of iodine− The surface impact on pH is the result of organic impurities

dissolved from the surface into the aqueous phase.− Under radiolysis conditions, a variety of organic iodides could be

formed in the presence of organic-based painted surface. Most of these organic iodides are, however, far less volatile than CH3I.

• Containment surfaces can absorb considerable amount of iodine, providing “iodine sinks”

Summary of the RTF Program (2)

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Supporting Bench-Scale Program

Pg 38

Supporting Bench-Scale R&D Areas

• Aqueous Phase Chemistry1. Inorganic Iodine Reactions2. Water Radiolysis3. Reactions of Organic Impurities and Organic Iodides

• Source of organic compounds dissolved in water• Radiolytic decomposition of organic impurities• Organic iodide formation and decomposition

• Aq-Gas Phase Partitioning

• Iodine – Surface Interaction

Pg 39

• The most fundamental process determining iodine volatility− Non-volatile iodine species are continually converted to I2,

which then undergoes various reactions, including• conversion back to non-volatile species, • aqueous-gas phase interfacial mass transfer, • organic iodide formation, etc.

• As many as 80 reactions have been used to describe this process under the post-accident containment conditions− Thermal iodine reactions and equilibria− Reactions of iodine species and water radiolysis products

Aqueous Chemistry 1. Inorganic Iodine Reactions (1)

Pg 40

Aqueous Chemistry 1. Inorganic Iodine Reactions (2)

• Key oxidation reactionsI– + •OH •I + OH– : rate determining•I + •I I2

• Key reduction reactionsI2 + H2O HOI + I– + H+

I2 + •O2– •I2– + O2

I2 + H2O2 2I– + 2 H+ + O2

• Modeling iodine behavior requires quantitative description of the I2 production in the aqueous phase.− Reaction kinetics as a function of T, pH, [I–]o, dose rate, etc.

Pg 41

Aqueous Chemistry1. Inorganic Iodine Reactions (3)

• Key AECL Contributions

− Critical review of all the potential inorganic iodine reactions and their rates & equilibrium constants, Keq

• The reaction mechanisms, individual rate constants and their dependence on pH and temperature are well established.

− Established the reaction mechanism and kinetics, e.g.,• HOI disproportionation (to I−−−− and IO3

−−−−) and iodine equilibria• Reduction of I2 by H2O2

• T dependence of Keq of the iodine hydrolysis

Pg 42

Aqueous Chemistry2. Water Radiolysis Reactions

• Containment water subjected to continuous irradiation:

H2O •OH, eaq–, •H, H2, H2O2, HO2•

• The water radiolysis products react with each other, dissolved O2(DO), iodine, metal ions and organic impurities

• Modeling iodine behavior requires quantitative description of the behavior of water radiolysis products

• AECL’s work− A water radiolysis model for continuous irradiation constructed.− The sub-model in LIRIC has been validated for its ability to

model H2 production, radiolysis of organics, iodine behavior

Pg 43

• Organic impurities dissolved in water significantly affect iodine volatility

− Organic impurities decompose by radiolytic reactions to organic acids and CO2, affecting

• the behavior of water radiolysis products• pH

− Organic radicals react with I2 to form organic iodides• Some organic iodides are more volatile and more difficult to

remove than I2

Aqueous Chemistry3. Organic Reactions (1)

Pg 44

Aqueous Chemistry3. Organic Reactions (2)

• Key organic processes to consider for iodine modelinga. Sources of organic compounds dissolved in waterb. Radiolytic decomposition of organic impuritiesc. Organic iodide formation, decomposition and aqueous-gas

phase partitioning

• These processes are complex• The additional challenge is how to handle a wide range of

organic impurities and organic iodides

Pg 45

a. Sources of Dissolved Organic Compounds

• Organic compounds that would have a significant effect on iodinebehavior are dissolved organic compounds

• A major source of dissolved organic impurities is organic solvents trapped in paint matrix− Paint- or other organic-polymers do not dissolve easily in water

• AECL’s work on organic solvent release from a painted surface into the aqueous phase− The release kinetics follows a first-order kinetics− The k depends on water diffusion thru the pores in the paint matrix,

and is a function of T and paint thickness− Various paints and solvents show same kinetic behavior− The absolute amount released depends on paint aging

Pg 46

MIBK Release from Epoxy Surface into Water Observed vs. Calculated Using the Dissolution Sub-Model

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400 500time (h)

Nor

mal

ized

Con

cent

ratio

n

60oC

25oC

90oC

70oC

40oC

Pg 47

b. Radiolytic Decomposition of Organic Impurities

• Dissolved organic impurities decompose by radiolyticreactions to organic acids and CO2, affecting− the behavior of water radiolysis products− pH

• Iodine models need a simple, generalized organic radiolysis sub-model to handle a large number of organic types

• The objectives of the sub-model is to predict− pH of the containment sump water − Concentrations of organic radicals− Concentrations of water radiolysis products, such as

•OH, •O2–, etc

Pg 48

Detailed exp. using MEKMEK, its decomposition

products, pH as a function of dose under various environment Full MEK Model

130 rxns of organics with water radiolysis productsLiterature review

Simple sets of exp. using various org. (RH)

RH & pH as a function of dose

Generic Org. Rad. ModelGENORG for LIRIC, ORAD for IMOD

Iodine Behavior ModelsLIRIC and IMOD

Other Sub-Models

Model validation using RTF Tests

Simplified MEK Model7 rxns + 4 equilibria

Model analysis

Organic Radiolysis Model Development Steps

Pg 49

Full MEK Model

pH[MEK] vs DR[Int. Prod.]

Common Objectives

� pH� [Wat. Rad. Prod.]� [Org Radical]

Simplified MEK Model

Full Water Radiolysis Model


GENORG for LIRIC


ORAD for IMOD

[Wat. Rad. Prod.] as a function of [Org], DRpH & [Org]

vs DR

Validation

Objectives of Organic Radiolysis Sub-Models

Pg 50

Radiolytic Decomposition of MEKMEK Behavior

0

200

400

600

800

1000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000Dose (Gy)

Conc

entr

atio

n (

µµ µµmol

·dm

-3) MEK

Full MEK Model Simple MEK Model

Pg 51

0

10

20

30

40

50

60

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Dose (Gy)

Aceta

ldeh

yde,

Form

aldeh

yde,

and

3-Hy

drox

y-2-

buta

none

Con

cent

ratio

n (m

icrom

olar

)

0

100

200

300

400

500

600

700

800

Aceti

c Acid

Con

cetra

tion

(micr

omola

r)

Acetic Acid

Formaldehyde

Acetaldehyde3-Hydroxy-2-butanone

Radiolytic Decomposition of MEKObserved Intermediate Decomposition Products

MEK 3-OH-2-butanone Acetaldehyde Formaldehyde CO22,3-butanedione Acetic Acid Formic Acid

(4-C RH) (4-C RH with O) (2-C RH with O) (1-C RH with O)

Pg 52

MEK Model Simulations

0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Dose (Gy)

Conc

entr

atio

n (

µµ µµmol

·dm

-3)


3-Hydroxy-2-Butanone

Pg 53



3

4

5

6

7

8

9

10

0 1000 2000 3000 4000 5000 6000 7000 8000

Dose (Gy)

pH

pH

Pg 54

Full MEK Model Prediction

With MEK Without MEK

1.E-15

1.E-14

1.E-13

1.E-12

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Dose (Gy)

Conc

entr

atio

n OH

, H an

d e

- aq (m

ol/d

m3 )

e-aq

H

OH••••OH

••••H

eaq−−−−

Pg 55



1.E-15

1.E-14

1.E-13

1.E-12

0 1000 2000 3000 4000 5000 6000 7000 8000

Dose (Gy)

Con

cent

ratio

n O

H a

nd e- aq

(mol

/dm

3 )

OH

e-aq

Gen Org Model

••••OH

eaq−−−−

Pg 56


Full MEK Model Simple MEK Model Gen Org Model

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-020 1000 2000 3000 4000 5000 6000 7000 8000

Dose (Gy)

Con

cent

ratio

n H

2O2 a

nd H

O2/O

2- (mol

/dm

3 )

H2O2

O2-/HO2

H2O2

O2−−−−/HO2

Pg 57

Generic Organic Radiolytic Decomposition ModelpH Simulations of RTF Tests

6

6.5

7

7.5

8

8.5

9

9.5

10

10.5

0 50 100 150 200 250 300Time (h)

pH

Experimental Data

IMOD-2.0

Slow MIBK Addition Fast (5X) MIBK AdditionpHControl

pHControl

pHControl

C1 = 5 x 104 s-1 and C1 = 1 x 104 s-1

7

7.5

8

8.5

9

9.5

10

10.5

0 50 100 150 200 250 300

Time (h)

pH

Experimental data

IMOD-2.0

Pg 58

Organic Iodide Behavior

• Processes to be modeled− Organic iodide formation− Decomposition by hydrolysis− Decomposition by radiolysis− Aqueous-gas phase partitioning

• A wide range of organic iodides• The rates of these processes were measured on a wide

range of organic iodides as a function of T• A review of the rates shows that RI can be grouped into High

& Low Volatility organic iodides, HVRI & LVRI

Pg 59

Aqueous-Gas Phase Partitioning

• I2 and RI partition with the gas phase according to− Mass transfer across the aqueous-gas phase interface − Henry’s Law constants

• A first order mass transfer rate based on a two-resistance model is adequate

• AECL’s studies concentrate on− Building database on the partitioning coefficients of organic

compounds and organic iodides− Developing a sound strategy for grouping of the organic

species

Pg 60

Surface Interactions

• Containment surfaces include stainless steel, aluminum, painted steel, painted concrete, plastics

• Dry, submerged, condensing films

• Some of the surfaces change their characteristics during iodine adsorption (e.g., Stainless Steel)

• Most surface interaction can be adequately described using a simple first order rate equation

• AECL’s studies concentrate on building database on the adsorption rate constants

Pg 61

Iodine Behavior ModelsLIRIC and IMOD

Pg 62

LIRIC(Library of Iodine Reactions in Containment)

• Comprehensive mechanistic model, consisting of about 300 chemical reactions and physical processes

• Epitome of our current understanding

• Has successfully simulated RTF tests performed over a wide range of conditions

• Has been available for the support of safety analysis

• Due to its complexity and size, integration of LIRIC into a safety analysis code is undesirable.

Pg 63

LIRIC-3.x

Gas PhaseAqueous Phase

Water radiolysis reactions (~40 rxns)

Inorganic iodine reactions (~80 rxns)

Organic reactions

SurfacesDry, wet, submerged(SS, Al, Paints, Polymers)

Dissolution

Radiolytic decomposition

Organic iodide behavior

Mass transfer

All volatile species(I2, HVRI, LVRI,

H2, O2, CO2) Ads Des

Condensate flow

Des

Ads

Pg 64

Mechanistic LIRIC Model Simple Iodine Model

• LIRIC has reproduced various bench-scale and RTF test results performed over a wide range of conditions, indicating the key processes determining iodine volatility are adequately modelled in LIRIC

• Sensitivity analysis and simulations of various RTF tests using LIRIC have enabled us to construct IMOD, which is smaller and very simple, but maintains many of the capabilities of LIRIC.

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IMOD-2.x

Aqueous Phase Gas Phase

SurfacesDry, wet, submerged(SS, Al, Paints, Polymers)

Mass transfer

Volatile Iodines(I2, HVRI, LVRI) Ads Des

Condensate Flow

Des

Ads

NONVOLI(aq) I2(aq) I2(aq) HVRI(aq), LVRI(aq)HVRI(aq), LVRI(aq) NONVOLI(aq)

Organic DissolutionRadiolytic decompositionAcid-Base Equilibria

Total 16 reactions

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Performance of LIRIC-3.3 & IMOD-2.1

• Have reproduced the results of RTF tests performed over a wide range of conditions to within ~ experimental uncertainties

• Comparisons over a set of results, not just one parameter − Gas phase total iodine concentration − Aqueous phase total iodine concentration − Iodine speciation; I2 and Organic Iodides in the presence of

painted surfaces− pH evolution, when pH was not controlled

• Outside the RTF conditions, IMOD-2.1 results are comparable with LIRIC-3.3 results

• Testing the models against two CAIMAN tests are underway throughISP-41F Phase 2

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IMOD Simulations of an RTF Test(10-5 M CsI, 60°°°°C, 0.6 kGy/h, Epoxy painted vessel)

pH

6

7

8

9

10

11

0 100 200 300

Time(h)

pH

observedcalculated

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[I(aq)]

0.E+00

2.E-06

4.E-06

6.E-06

8.E-06

1.E-05

0 100 200 300

Time (h)

Tot

al Io

dine

in th

e A

queo

us P

ha (

Mol

arity

)

observedcalculated

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[I(g)]

1.0E-11

1.0E-10

1.0E-09

1.0E-08

0 100 200 300

Time (h)

To

tal I

odin

e in

the

Ga

s P

(mol

arit

y)

observedcalculated

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[HVRI(g)] and [LVRI(g)]

1.E-12

1.E-11

1.E-10

1.E-09

0 100 200 300

Time(h)

Org

anic

Iodi

de in

the

Gas

Pha

se (m

olar

ity)

LVRI observedHVRI observedcalculated

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Summary

• AECL’s integral approach has contributed significantly to understanding of iodine behavior in containment− Mechanistic approach based on fundamental understanding

coupled with validation tests

• AECL has robust models (IMOD-2 & LIRIC 3)− Models & their components (sub-models) have solid bases− Well validated− High confidence, Low uncertainty

• The results are highly relevant to Severe Core Damage Accidents− Safety analysis− Accident management

iodine behavior in containment. - nrc: home pagelvri i (aq): i2 ri i − csi injection organic...

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