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NEA/CSNI/R(2020)14
February 2023
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Behaviour of Iodine Project 3
Final Summary ReportNEA/CSNI/R(2020)14  1
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NEA/CSNI/R(2020)14
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Behaviour of Iodine Project 3: Final Summary Report

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BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT
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Table of contents

List of abbreviations and acronyms ..................................................................................................... 7
Executive summary................................................................................................................................ 9
1. Introduction...................................................................................................................................... 12
2. BIP-3 project description ................................................................................................................ 13
2.1. Overview ..................................................................................................................................... 13
2.2. BIP-3 experimental tests performed ............................................................................................ 14
2.3. BIP-3 experimental test matrix ................................................................................................... 15
2.4. Overview of BIP-3 Analytical Working Group (AWG) modelling exercises ............................ 21
2.4.1. Overview of the Stage 1 modelling exercise ........................................................................ 22
2.4.2. Overview of the Stage 2 modelling exercises....................................................................... 23
3. Experimental methodology ............................................................................................................. 25
3.1. Coupon preparation ..................................................................................................................... 25
3.1.1. Coupon fabrication, geometry and painting ......................................................................... 25
3.1.2. Paint ageing techniques and pre-treatments for Amerlock coupons ..................................... 25
3.1.3. Ageing tests with other painted coupons .............................................................................. 27
3.2. Iodine adsorption studies ............................................................................................................. 28
3.3. Irradiation tests to evaluate methyl iodide production ................................................................ 30
3.3.1. Irradiation vessels for RAD series tests ................................................................................ 30
3.3.2. Irradiation vessel for METH series tests............................................................................... 32
3.3.3. Gas phase analysis ................................................................................................................ 33
3.3.4. Iodine desorption and mass balance analyses ....................................................................... 33
3.3.5. Radiation dose rates .............................................................................................................. 34
4. Summary of BIP-3 experimental outcomes ................................................................................... 35
4.1. Adsorption capacity..................................................................................................................... 35
4.2. Paint ageing ................................................................................................................................. 36
4.3. Pre-exposure to reactive gases .................................................................................................... 39
4.4. Effect of water on methyl iodide production............................................................................... 41
4.5. Iodine interactions with surfaces other than paint ....................................................................... 41
4.6. Gas phase production of methyl iodide ....................................................................................... 42
5. Summary of BIP-3 AWG modelling outcomes ............................................................................. 44
6. Overall conclusions .......................................................................................................................... 47
7. Recommendations ............................................................................................................................ 49
8. References ......................................................................................................................................... 50

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List of figures
Figure 3.1. Set-up used for coupon pre-irradiations .............................................................................. 26
Figure 3.2. Coupons before and after the thermal cure processes ......................................................... 26
Figure 3.3. Ripolin coupons before and after irradiation ....................................................................... 27
Figure 3.4. Schematic diagram of the multiple coupon Radioiodine Adsorption Apparatus. RH, T
and P denote relative humidity, temperature and pressure transducers. UHP N2
corresponds to ultra-high purity nitrogen ............................................................................ 29
Figure 3.5. Top and side view of the adsorption cells ........................................................................... 29
Figure 3.6. Cross-sectional diagram of the sample chambers and detectors ......................................... 30
Figure 3.7. Irradiation vessel (shown pre-irradiation and without the coupon holders) ........................ 31
Figure 3.8. Irradiation vessel (shown post-irradiation and with coupons and holders) ......................... 31
Figure 3.9. Diagram of new O-ring free irradiation vessel .................................................................... 32
Figure 3.10. Photographs of the new O-ring free irradiation vessel and coupon holder design, withcomponents disassembled (left) and fully assembled (right) ............................................... 32
Figure 3.11. Irradiation vessel for gas phase experiments ..................................................................... 33
Figure 4.1. Correlation between the gaseous iodine loading concentration and the relative amountof iodine desorbed for sorption tests on Amerlock .............................................................. 35
Figure 4.2. Correlation between the gaseous iodine loading concentration and the measured
deposition velocity for sorption tests on Amerlock ............................................................. 36
Figure 4.3. Adsorption and desorption profiles for AD series tests performed on thermally-cured
Amerlock coupons, and for tests performed on pre-irradiated and thermally-cured
Amerlock coupons. .............................................................................................................. 37
Figure 4.4. Deposition velocities for Gehopon A0 (naturally-aged; solid black line) and Gehopon
A30 (thermally and naturally-aged; dashed black line) coupons measured as a functionof relative humidity at 80°C and 1×10-8 M I2. Deposition velocities for fresh Amerlock(blue solid line) are also shown for comparison .................................................................. 38
Figure 4.5. Summary of methyl iodide concentrations measured as a function of irradiation time
for tests with Amerlock coupons aged using pre-irradiation treatments, or the
combination of pre-irradiation and heat treatment, in the O-ring (solid lines) and O-ringfree (dashed lines) irradiation vessels .................................................................................. 39
Figure 4.6. Adsorption and desorption profiles for AD series tests performed on fresh Amerlock
coupons with and without a 4 h pre-exposure to either 245 ppm NO2 or Cl2 gas.
Temperature and humidity were maintained at 70 °C and 70%, respectively, and an I2
loading concentration of 1×10-8 M was used ....................................................................... 40
Figure 4.7. Methyl iodide production as a function of irradiation time for fresh, untreated Amerlock
coupons and for coupons pre-exposed to NO2 gas prior to iodine loading. Tests were
performed in the O-ring free irradiation vessel.................................................................... 40
Figure 4.8. Methyl iodide production measured during irradiation tests of gas-loaded coupons thatwere submerged in water for 16 hours immediately after loading (red) and after 76 hoursof irradiation (blue) .............................................................................................................. 41
Figure 4.9. Summary of methyl iodide concentrations measured as a function of irradiation time for
all BIP-3 tests performed on Amerlock coupons in the O-ring (solid lines) and O-ringfree (dashed lines) irradiation vessels .................................................................................. 42
Figure 4.10. CH4 concentrations measured as a function of irradiation time for various CH4/I2 gas
mixtures ............................................................................................................................... 43
Figure 4.11. CH3I concentrations measured as a function of time for various CH4/I2 gas mixtures.
Tests performed with irradiation are shown with solid lines, and tests performed in
the absence of radiation are shown with dotted lines........................................................... 43
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List of tables
Table 2.1. Test series completed within the BIP-3 project .................................................................... 16
Table 2.2. Summary of all TOC series tests performed in the BIP-3 project ........................................ 16
Table 2.3. Summary of all DES series tests performed in the BIP-3 project......................................... 16
Table 2.4. Summary of all AD series tests performed in the BIP-3 project. Unless otherwise
noted, each adsorption test was performed with three coupons ........................................... 19
Table 2.5. Summary of all RAD series tests performed in the BIP-3 project. Unless otherwise
noted, tests were performed with six iodine-loaded coupons in the irradiation vessel ........ 19
Table 2.6. Summary of all METH series tests performed in the BIP-3 project ..................................... 21
Table 2.7. Simulation base conditions for the Stage 1 co-operative sensitivity study ........................... 23
Table 2.8. Summary of experimental conditions for STEM Test LD3 and BIP-2 Test
RAD-EPICUR-A1 ................................................................................................................ 24

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List of abbreviations and acronyms
AECL

Atomic Energy of Canada Limited

ASTEC

A commercially-available severe accident analysis code (developed by IRSN, France)

AWG

Analytical Working Group

BIP

Behaviour of Iodine Project

CNL

Canadian Nuclear Laboratories (formerly AECL)

CNRA

Committee on Nuclear Regulatory Activities (NEA)

COCOSYS

A commercially-available severe accident analysis code (developed by GRS,
Germany)

CRPPH

Committee on Radiological Protection and Public Health (NEA)

ECD

Electron Capture Detector

FID

Flame ionisation detectorGC

Gas chromatography

GRS

Gesellschaft für Anlagen- und Reaktorsicherheit (Germany)

INSPAIR

A mechanistic iodine chemistry research code (developed by NNL, United Kingdom)

IOx

Iodine oxides

IRSN

Institut de Radioprotection et de Sûreté Nucléaire (France)

JAEA

Japan Atomic Energy Agency

KICHE(OrgIDB)

A mechanistic iodine chemistry research code (developed by JAEA, Japan)

LIRIC

Library of iodine reactions in containment, a phenomenological research code
(developed by AECL, now CNL, Canada)

MELCOR

A commercially-available severe accident code (developed by SNL, United States)

NEA

Nuclear Energy Agency

NNL

National Nuclear Laboratory (United Kingdom)

OECD

Organisation for Economic Co-operation and Development

ORGI

Organic iodide

PRG

Program review group

RH

Relative humidity

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT8 | NEA/CSNI/R(2020)14
RWMC

Radioactive Waste Management Committee (NEA)

SNL

Sandia National Laboratories (United States)

STEM

Source term evaluation and mitigation project (IRSN, France)

TCD

Thermal conductivity detector

THAI

Thermal-hydraulics Hydrogen Aerosol Iodine project

TIC

Total inorganic carbon

TOC

Total organic carbon

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 9

Executive summary
The present report summarises the main results and learnings from the third phase of the Nuclear
Energy Agency (NEA) Behaviour of Iodine Project (BIP-3), which was conducted between
2016 and 2019 by the Canadian Nuclear Laboratories (CNL).
An NEA state-of-the-art report on iodine chemistry published in February 2007 concluded that
there were still several aspects of iodine behaviour in containment during severe accidents thatwarranted further investigation. Over the past 25 years, there have been several NEA initiatives
and other programmes to enhance the understanding of iodine chemistry, including the Phébus
FP and International Source Term Project, the NEA Thermal-hydraulics Hydrogen Aerosol
Iodine (THAI) Projects, the NEA Source Term Evaluation and Mitigation (STEM) Projects andthe NEA Behaviour of Iodine Projects (BIP).
BIP was created to investigate the interactions between iodine and paint. The adsorption ofiodine onto epoxy paint and the subsequent radiolytic production and release of organic iodides
from painted containment surfaces were topics of particular interest. A database of iodine
deposition data was accumulated in BIP-1 and expanded in BIP-2, with experiments focused on
improving mechanistic understanding of the nature of the iodine-paint interactions.
A third phase of BIP was initiated by the NEA in 2016, with Canadian Nuclear Laboratories(CNL) 1 as the operating agent. Topics for BIP-3 were chosen to leverage the CNL’s existing
facilities and expertise. The BIP-3 experimental programme was structured to address importantand unresolved topics from the BIP-1 and BIP-2 programmes as well as knowledge gaps thatarise when attempting to extrapolate results to postulated nuclear accident conditions.
Additionally, collaborative analytical activities, co-ordinated through the BIP-3 Analytical
Working Group (AWG), were completed as part of the NEA BIP-3 scope of work.
Although other parameters were also studied, BIP-3 mainly focused on the effects of different
paint ageing strategies (natural, pre-irradiation, and thermal treatments) on iodine behaviour.
Specifically, the effects of ageing on the quantity of releasable organic products from the paint,
the iodine sorption behaviour, and the subsequent rate of radiolytic methyl iodide production
were evaluated. Studies relating to radiolytic CH3I production in the gas phase were also
performed. Several experiments also expanded on previous themes and topics of interest in
BIP-1 and BIP-2. The impact of pre-exposing painted coupons to reactive gases such as NO2
and Cl2 was studied using higher concentrations and longer exposure periods, and a final test
was performed to evaluate the role of water in the organic iodide production mechanism.
Finally, several scoping tests were performed to assist in the interpretation and modelling of BIP
and STEM data, including tests to evaluate iodine behaviour with glass and O-ring surfaces, aswell as tests exploring the sorption behaviour of iodine for a wide range of surface loading
concentrations and as a function of the gaseous iodine loading concentration.
The NEA BIP-3 project was initiated in January 2016 with signatories from 11 member
countries: Belgium, Canada, Finland, France, Germany, Japan, Korea, Sweden, Switzerland, theUnited Kingdom and the United States. The total project budget was established at
EUR 1 million, half of which was contributed by Canada (CNL) as the operating agent. All
project deliverables were originally intended to be completed by July 2019. However, a seriesof critical equipment failures in the last year of the project led to an extended schedule at no1. Previously Atomic Energy of Canada Limited (AECL).
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT10 | NEA/CSNI/R(2020)14
extra cost to the members; tests continued until the end of June 2019, and the associated analysis
and documentation activities continued through March 2020.
Overall, the BIP-3 programme has continued to enrich the database of iodine kinetic data
available for researchers and analysts in support of model development. Tests have affirmedthat paint is an important sink for iodine in containment, and have provided significant insights
into the role of paint ageing on iodine sorption and the production of organic iodide.
The iodine adsorption process was shown to depend on paint type, age, the presence ofcompeting reactive species, loading temperature, relative humidity and the I2 exposure
concentration. Specifically:•

Slower deposition velocity was generally observed on paints with increased age (naturalor simulated), and combined ageing strategies had a larger effect.

•

Increased paint age is believed to contribute to enhanced surface modification (throughchemical breakdown of components of the paint structure), such that the number ofavailable active sites for iodine adsorption are reduced.

•

Pre-exposures to reactive gases such as NO2 and Cl2 led to an induction period for iodine
adsorption, and initial iodine deposition rates were among the lowest observed in BIP.

•

Higher deposition velocities are observed under higher temperatures and relative
humidities.

•

Exposure to higher iodine loading concentrations leads to lower deposition velocities
and higher relative iodine desorption.

Key conclusions with respect to methyl iodide production were as follows:•

Lower CH3I production is observed for paint with increased ageing (natural or
simulated), and the combination of ageing strategies leads to a greater reduction.

•

Gas phase production of CH3I from the reaction of I2 and CH4 appears to be very small.

•

Other organic-based materials (O-ring) can contribute to CH3I production, particularly
over the long term.

•

The CH3I peak observed for aqueous loaded irradiation tests in BIP-1 and 2 experiments
appears to be associated with the aqueous adsorption process rather than the simple
presence of water in the paint matrix, and suggests the nature of the iodine-paint bondis different for gas and aqueous loaded tests.

Key conclusions from the AWG modelling exercises were as follows:•

All models predicted that the inclusion of organic iodide production from painted
surfaces would increase the total airborne iodine for a postulated accident scenario, andsimilar overall trends were predicted for iodine behaviour and volatility with respect tosump acidification.

•

Significant variations in general modelling capabilities and modelling strategies still
exist. In particular, there was little consistency among the models in the selection of I2
deposition velocity, or the treatment of mass transfer.

•

There was also a lack of consensus on which chemical processes were considered, andthe outcomes of those processes, such as consideration of the possible gas phase reactionof I2 with volatile organic compounds or gas phase formation of iodine oxides (IOx)
from the radiolysis of I2 or organic iodides.
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 11•

Differences in the phenomenology considered among the codes (particularly in the gas
phase) can strongly impact model predictions.

While BIP-3 experiments have shown that paint ageing can have a significant effect on iodine
sorption and organic iodide production, the overall consequences of this phenomenon on
predictions of iodine speciation and volatility should be assessed. The AWG modelling
exercises also revealed that there are considerable differences in the iodine phenomenology
considered and the treatment of key parameters in the different iodine-paint interaction models,
and this can strongly impact the model predictions. This indicates that continued refinement of
our understanding of fundamental iodine chemistry pathways is needed to ensure continued
model development is based on accurate mechanistic behaviour. Additionally, continued model
development efforts should endeavour to limit the potential for user effects to impact on modeloutcomes and, wherever possible, fitting parameters should be independent of the test
considered.
Gaps still remain in the understanding of iodine-paint interactions that can impact predictionsof iodine source term in containment. In particular, the relative importance of radiolytic gas
phase reactions between I2 and volatile organic compounds on methyl iodide production remains
unclear. Resolution will require additional tests with an improved analytical method. Tests toassess the organic iodide production from organics in containment other than paint (e.g. cablecoatings) could be considered in future research programmes to assist in model development
and to better quantify predictions of iodine source term.

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1. Introduction
The present report summarises the main results and learnings from the third phase of the Nuclear
Energy Agency (NEA) Behaviour of Iodine Project (BIP-3), which was conducted between
2016 and 2019 by the Canadian Nuclear Laboratories (CNL) to address knowledge gaps on
iodine behaviour in the containment of light water reactors during a severe accident. The focusof the experimental investigations was on iodine interaction with aged paints, the resulting
iodine trapping by the containment painted surfaces and on organic iodides formation in thecontainment. Such investigations are of specific relevance for developing models for the
calculation of radioactive iodine release to the environment in case of a severe accident.

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2. BIP-3 project description
2.1. Overview
Continued improvement of existing computer models to predict post-accident fission productbehaviour in containment relies on a comprehensive understanding of all relevant phenomena
and high-confidence data. Unexpected iodine behaviour observed during the international
Phébus FP programme highlighted the need for a greater understanding of iodine behaviour.
This conclusion was further captured in an NEA state-of-the-art report on iodine chemistry
published in February 2007 [1]. There have been several NEA initiatives to study the behaviourof iodine in containment including the THAI, STEM and BIP projects. The development of acomputational model that can universally reproduce the experimental observations from eachof these projects is the primary long-term goal. In support of this, experimental programmessuch as BIP have focused on collecting quantitative data that are necessary inputs for iodine
behaviour models (such as iodine deposition velocities onto various substrates) or that can beused to assist in model validation exercises, as well as qualitative data that can be used to guidemodel design and inform on plausible reaction pathways.
Although a few other containment surfaces have been tested, the BIP project has focused on
iodine retention and subsequent release from epoxy paint, which is a commonly used coating
within containment buildings throughout the world. Epoxy paint is a complex mixture ofpolymeric compounds, and the nature of iodine’s interaction with this surface is not fully
understood. The BIP projects have endeavoured to resolve some of these uncertainties. In BIP-1,
experiments investigating the role of water on the deposition velocities and formation of methyl
iodide from irradiated paint showed that adsorbed water strongly affected both the sorption andorganic iodide formation processes [2]. While BIP- 2 investigated the same processes, emphasis
was placed on developing a more detailed mechanistic understanding of the iodine-paintinteractions [3]. Experiments using various polymeric compounds as model compounds fordifferent structures within the paint demonstrated that the iodine adsorption and radiolyticallydriven organic iodide formation are not limited to a single functional group on the paint. Many
parts of the paint structure will participate in these processes, although some structures are more
important (e.g. the amide groups). The first experiments to study the effect of other gases withincontainment such as NO2 (formed by air radiolysis) or Cl2 (formed by degradation of cableinsulation) on the iodine-paint interaction were also performed in BIP-2, although no effect wasobserved at the relatively low concentrations studied.
In BIP-1 and BIP-2, a significant database of iodine deposition data and organic iodide
production data was accumulated. These data have contributed to the development of iodine
models at organisations around the world. However, many key questions surrounding iodine
behaviour in containment remain unresolved, and additional data are required to both improveknowledge of iodine-paint interactions and to assist in further model development and validation
activities [4].
BIP-3 focused on outstanding questions remaining from BIP-1 and 2 and addressed knowledge
gaps that arise when attempting to extrapolate results to postulated nuclear accident conditions.
Additionally, one of the conclusions made by delegates at the 2015 NEA International Iodine
Workshop (held in Marseille, France) was that the execution of collaborative analyticalactivities has been limited in recent years. In response, the BIP- 3 programme was structured toinclude both experimental and analytical activities within the scope of work.

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The main objectives for BIP-3 were to:•perform experiments that will resolve outstanding questions and improve thesimulations of BIP and STEM results, including:‒‒‒

improve our ability to simulate iodine adsorption and desorption on containment
surfaces;
predict CH3I behaviour under accident conditions;investigate the effect of paint ageing on these processes.

•

further investigate the effect of contaminants (NO2, Cl2);•

share simulation strategies through modelling exercises (with member participation).

2.2. BIP-3 experimental tests performed
Three main iodine phenomena were studied experimentally in BIP-3 in support of the project
objectives described previously, and are summarised below:
1. Iodine sorption onto painted surfaces. Tests have evaluated the effects of the following
parameters:•

paint ageing strategy (natural, pre-irradiation, thermal);•

substrate type (Amerlock, Ripolin, Epigrip and Gehopon paints; scoping tests withglass, O-ring materials);•presence of contaminant species (e.g. NO2, Cl2);•other parameters such as loading [I2], surface loading concentration, humidity,
temperature.

2. Radiolytic organic iodide production from iodine-loaded coupons. Tests have evaluatedthe effects of the following parameters:•

paint ageing strategy (e.g. natural, pre-irradiation, thermal);•presence of contaminant species (e.g. NO2, Cl2) during loading;•presence of water;•

revolatilisation from glass, or production from other available organic sources(O-ring).

3. The potential for gas phase CH3I production from I2 and CH4.
A particular focus of BIP-3 was to evaluate the influence of paint ageing and pre-treatment
strategies on sorption behaviour and organic iodide production [5]. To date, many iodine
experiments have used paint that could be considered quite fresh in comparison with in-service
containment coatings. Questions remain regarding the applicability of such results to in-service
containment coatings, which may be exposed to constant low-level operational radiation fields,
or may be decades old. Experiments in BIP-3 evaluated how different ageing strategies such asheat treatments, pre-irradiation and natural ageing impact the amount of releasable carbon fromthe paint, the rate of iodine adsorption onto the painted surface, and the production of methyl
iodide (as a surrogate for all volatile organic iodides) during irradiation of the test samples.
While most tests were performed with Amerlock painted coupons, a limited number of tests
with Gehopon, Ripolin, and Epigrip paints were also performed at the request of the programme
review group (PRG) members.

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Several experiments also expanded on previous themes and topics of interest in BIP-1 andBIP-2. A final test was performed to evaluate the role of water in the organic iodide production
mechanism, simulating the scenario of condensation or sprays in containment that will lead towetting of the painted walls after gaseous iodine loading. The impact of pre-exposing painted
coupons to reactive gases was also studied using higher concentrations and longer exposure
periods than those used for BIP-2 to determine if sufficiently high NO2 or Cl2 concentrations
will eventually start to compete with iodine for active sites on the paint.
Tests to assist in the interpretation and modelling of BIP and STEM data were also performed.
The interactions of iodine with glass and O-ring surfaces were explored. Iodine sorption studies,
methyl iodide production from the O-ring, and the revolatilisation of adsorbed iodine from glass
surfaces to generate methyl iodide (either through direct release of adsorbed CH3I, or release as
I2 with subsequent reaction with gaseous organic contaminants in air) were completed.
Experiments in BIP-3 also studied the sorption behaviour of iodine as a function of the total
iodine loading. These experiments were needed to determine whether the amount of physisorbed
iodine increases as the chemisorption sites become occupied. Given that paint is a major iodine
sink within containment, this information was considered important for model development.
Similarly, the importance of gas phase CH3I production from the irradiation of methane-iodine
gas mixtures has been debated in the open literature. Although it is generally believed that O2
will outcompete I2 for any •CH3 radicals, some references have suggested methyl iodide
production can be significant in such mixtures [6][7]. Tests were performed in BIP-3 to confirm
whether this process can significantly impact the gas phase speciation of iodine in post-accident
containment.
Overall, nearly 100 tests were performed in the BIP-3 programme, with approximately 25% of
the tests having been added to the test matrix over the project life. Detailed descriptions of thetests performed are provided in Section 2.3.

2.3. BIP-3 experimental test matrix
Five experimental series, in addition to a small number of scoping tests, were performed in the
BIP programme to address the phenomena identified in Section 2.2 and they are briefly
described in Table 2.1. A summary of specific tests performed in support of each series, alongwith relevant experimental details, are provided in Table 2.2 through Table 2.6.
For TOC, AD and RAD tests (Table 2.1) with Amerlock coupons, test names generally include
the test series (e.g. AD), the coupon pre-treatment description (e.g. NO2 to indicate a coupon
pre-exposed to NO2), and a serial number to identify replicate tests. As an example, AD-PRE1-2
represents the second replicate adsorption test for an Amerlock coupon that has been
pre-irradiated to 100 kGy total absorbed dose. For AD and RAD tests with other paint types, asimilar convention is used, except that an additional paint identifier is included after the test
series identifier. For example, RAD-RIP-PRE1-1 is the first replicate irradiation test performedon Ripolin coupons that have been pre-irradiated to 100 kGy total absorbed dose. The DES
series tests identify different target loadings using sequential numbering after the paintidentifier. For example, DES-AMER-2-1 is the first replicate of the DES series adsorption test
performed on an Amerlock coupon using target loading condition #2 (2E-04 mol/dm2). Because
the METH series tests (Table 2.1) do not involve painted coupons, a simple sequential
numbering scheme was used, with A, B, C, etc. used to identify replicate tests.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT16 | NEA/CSNI/R(2020)14
Table 2.1. Test series completed within the BIP-3 project
Test Series

Description

TOC

Solvent leaching tests performed on fresh and aged Amerlock coupons to evaluate the total organic carbon (TOC) and total
inorganic carbon (TIC) release to water following 302 hours of exposure.

DES

Adsorption tests performed on fresh Amerlock coupons to varied target I2 loading concentrations on the coupon surface.

AD

Adsorption tests performed on painted coupons, glass coupons or O-ring material under various conditions.

RAD

Irradiation tests performed on painted coupons or O-ring material to evaluate methyl iodide (CH3I) production with time.

METH

Irradiation tests (and select blank, non-irradiated tests) to evaluate the potential gaseous reaction between I2 and CH4 (asurrogate volatile organic compound).

Other

Scoping tests to evaluate other specific interactions, such as CH3I adsorption onto glass and O-ring surfaces; impact of thevessel rinsing procedure on iodine transfer to vessel O-ring.

Source: CNL, 2020.

Table 2.2. Summary of all TOC series tests performed in the BIP-3 project
Test name

Couponmaterial

Description

Blank (Room Temp.)

No coupons

Water at room temperature.

Blank (65 °C)

No coupons

Water at 65 °C

TOC-FRESH-1

Amerlock2 coupons, painted 2015, 60 mL water at 65 °C

TOC-2013-1

Amerlock2 coupons , painted 2013, 60 mL water at 65 °C

TOC-2009-1

Amerlock2 coupons, painted 2009, 60 mL water at 65 °C

TOC-TC1-1

Amerlock2 coupons, heat treatment 1 (130°C for 96 h), 60 mL water at 65 °C

TOC-TC2-1

Amerlock2 coupons, heat treatment 2 (130°C + water for 96 h), 60 mL water at 65 °C

TOC-PRE1-1

Amerlock2 coupons, pre-irradiation to 100 kGy, 60 mL water at 65 °C

TOC-PRE2-1

Amerlock2 coupons, pre-irradiation to 1 000 kGy, 60 mL water at 65 °C

Source: CNL, 2020.

Table 2.3. Summary of all DES series tests performed in the BIP-3 project
Test name
DES-AMER-1-1
DES-AMER-1-2
DES-AMER-2-1
DES-AMER-2-2
DES-AMER-3-1
DES-AMER-4-1
DES-AMER-4-2
DES-AMER-5-1
DES-AMER-5-2

Loading
temp.

Loading
RH

Loading
[I2]

(°C)

(%)

(M)

None

70

70

Amerlock

None

70

70

Amerlock

None

70

70

Couponmaterial

Pretreatment

Amerlock

Amerlock

None

70

70

Amerlock

None

70

70

1.00E-07
5.00E-08
2.00E-08
1.00E-08
2.00E-08
1.00E-09
1.00E-09
1.00E-09
1.00E-09

Target Iodine
Loading(mol/dm2)

Other information

2E-03

Painted 2015

2E-04

Painted 2015

2E-05

Painted 2015

2E-06

Painted 2015

2E-07

Painted 2015

Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 17

Table 2.4. Summary of all AD series tests performed in the BIP-3 project.
Unless otherwise noted, each adsorption test was performed with three coupons
Couponmaterial

Test name

Loading
temp.

Loading
RH

Loading
[I2]

(°C)

(%)

(M)

Other information

Tests related to ageing phenomena:
AD-FRESH-1

Amerlock

70

70

1E-08

Painted 2015

AD-FRESH-2

Amerlock

70

70

1E-08

Painted 2015

AD-FRESH2-1

Amerlock

70

70

1E-08

Painted 2018

AD-FRESH2-2

Amerlock

70

70

1E-08

Painted 2018

AD-FRESH2-3

Amerlock

70

70

5E-08

Painted 2018,
Higher iodine loading concentration

AD-FRESH2-80-1

Amerlock

80

15
40
60

1E-08

Painted 2018,
No desorption phase between loadings

AD-2013-1

Amerlock

70

70

1E-08

Painted 2013

AD-2009-1

Amerlock

70

70

1E-08

Painted 2009

AD-PRE1-1

Amerlock

70

70

1E-08

100 kGy pre-irradiation

AD-PRE2-1

Amerlock

70

70

1E-08

1 000 kGy pre-irradiation

AD-TC1-1

Amerlock

70

70

1E-08

Heat treatment 1(130°C for 96 h)

AD-TC1-2

Amerlock

70

70

1E-08

Heat treatment 1(130°C for 96 h)

AD-TC2-1

Amerlock

70

70

1E-08

Heat treatment 2(130°C + water, 96 h)

AD-PRE2TC2-1

Amerlock

70

70

1E-08

1 000 kGy pre-irradiation followed by heat
treatment 2 (130°C + water, 96 h)

AD-PRE2TC2-2

Amerlock

70

70

1E-08

1 000 kGy pre-irradiation followed by heat
treatment 2 (130°C + water, 96 h)

AD-PRE2TC3-1

Amerlock

70

70

1E-08

1 000 kGy pre-irradiation followed by heat
treatment 3 (160°C + water, 96 h)

Tests with other containment paints:
AD-RIP-PRE1-1

Ripolin

70

70

1E-08

100 kGy pre-irradiation

AD-RIP-PRE2-1

Ripolin

70

70

1E-08

250 kGy pre-irradiation

AD-RIP-PRE3-1

Ripolin

70

70

1E-08

500 kGy pre-irradiation

AD-RIP-PRE4-1

Ripolin

70

70

1E-08

1 000 kGy pre-irradiation

AD-EPI-2010-1

Epigrip

70

70

1E-08

Painted 2010,
Natural ageing

AD-GEH-A0-1

Gehopon

80

15
40
60

1E-08

Received 2013,
natural ageing,
no desorption phase between loadings

AD-GEH-A0-2(a)Gehopon

80

15
40
60

1E-08

Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT

Replicate with desorption phase,run performed with only two coupons

18 | NEA/CSNI/R(2020)14
Table 2.4. Summary of all AD series tests performed in the BIP-3 project.
Unless otherwise noted, each adsorption test was performed with three coupons (Continued)
Loading
temp.

Loading
RH

(°C)

(%)

Gehopon

80

15
40
60

1E-08

Received 2013, simulated ageing (155°C for 42 h),
no desorption phase between loadings.

Gehopon

80

15
40
60

1E-08

Replicate with desorption phase,run performed with only one coupon.

Test name

Couponmaterial

AD-GEH-A30-1

AD-GEH-A30-2(a)Loading [I2](M)

Other information

Tests with pre-exposures to reactive gases:
AD-NO2-1-1

Amerlock

70

70

1E-08

Painted2018,
Pre-exposure to 245 ppm NO2 at 70°C/70% RH for
4h.

AD-NO2-2-1

Amerlock

70

70

5E-08

Painted2018,
Pre-exposure to 245 ppm NO2 at 70°C/70% RH for
4h.

AD-Cl2-1-1

Amerlock

70

70

1E-08

Painted2018,
Pre-exposure to 245 ppm Cl2 at 70°C/70% RH for
4h.

Tests with materials other than paint:
AD-RIG-1

N/A(b)

70

70

1E-08

No coupons, empty sample chambers.

AD-RIG-2

Glass(c)

30

15
40
60

1E-08

Two glass coupons, one empty sample chamber.

AD-RIG-3(a,b,c)Glass(c)

30

60

1E-08

AD-RIG-4(a,b,c)Glass(c)

70

70

1E-08

AD-ORING-1

O-ring(d)

70

70

1E-08

Two glass coupons, one empty sample chamber.
(a) 1 h (b) 2 h and (c) 6 h loading times
Two glass coupons, one empty sample chamber.
(a) 1 h (b) 2 h and (c) 6 h loading times
Three silicone O-ring pieces.

Source: CNL, 2020.
(a)
(b)
(c)
(d)

Because of limited remaining Gehopon A0 and A30 coupon inventory, runs AD-GEH-A0-2 and AD-GEH-A30-2 werecompleted simultaneously by placing two A0 coupons and one A30 coupon in the available sample chambers.
No coupons were placed in the sample holders. Online measurements are representative of the iodine adsorbing onto
the empty sample holders.
Glass coupons were placed into two of the sample holders, while the remaining sample holder was left empty forcomparison.
Three 0.5 inch-long pieces of a silicone O-ring (the material used to seal the old BIP irradiation vessel) were placed
into the sample holders.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 19

Table 2.5. Summary of all RAD series tests performed in the BIP-3 project.
Unless otherwise noted, tests were performed with six iodine-loaded coupons in the irradiation
vesselTest name

Couponmaterial

Loading
temp. (a)(°C)

Loading
RH (b)(%)

Dose
rate(c)(kGy/h)Other information

RAD-FRESH-1

Amerlock

70

70

0.75

Painted 2015

RAD-FRESH2-1-NV

Amerlock

70

70

0.59

Painted 2018

70

70

0.53

Painted 2018
Phase 1: Irradiation of coupons after gas load

N/A

N/A

0.53

Phase 2: Irradiation of empty vessel (coupons removed) to check for
revolatilisation of deposits

RAD-FRESH2-2-NV

AmerlockRAD-2013-1

Amerlock

70

70

0.75

Painted 2013

RAD-2013-2

Amerlock

70

70

0.65

Painted 2013

RAD-2013-3-NV

Amerlock

70

70

0.57

Painted 2013

RAD-2009-1

Amerlock

70

70

0.74

Painted 2009

RAD-2009-2-NV

Amerlock

70

70

0.56

Painted 2009

RAD-PRE1-1

Amerlock

70

70

0.74

100 kGy pre-irradiation

RAD-PRE1-2

Amerlock

70

70

0.67

100 kGy pre-irradiation

RAD-PRE1-3-NV

Amerlock

70

70

0.60

100 kGy pre-irradiation

RAD-PRE1-4-NV

Amerlock

70

70

0.60

100 kGy pre-irradiation

RAD-PRE2-1

Amerlock

70

70

0.73

1 000 kGy pre-irradiation

RAD-PRE2-2

Amerlock

70

70

0.67

1 000 kGy pre-irradiation

RAD-PRE2-3-NV

Amerlock

70

70

0.57

1 000 kGy pre-irradiation

RAD-TC1-1

Amerlock

70

70

0.66

Dry heat treatment

RAD-TC2-1

Amerlock

70

70

0.72

Heat/steam treatment (130°C)

RAD-TC2-2-NV

Amerlock

70

70

0.55

Heat/steam treatment (130°C)

70

70

0.63

1 000 kGy pre-irradiation and heat/steam treatment (130°C)
Phase 1: Irradiation of coupons after gas load

N/A

N/A

0.63

Phase 2: Vessel O-ring from Phase 1 placed into a clean vessel (nocoupons) and irradiated

70

70

0.54

N/A

N/A

0.54

Phase 2: Irradiation of empty vessel (coupons removed) to check for
revolatilisation of deposits
Pieces of silicone O-ring, used to seal older irradiation vessel
design. Surface area of each piece was estimated to be 1.85 cm2.

RAD-PRE2TC2-1

RAD-PRE2TC3-1-NV

Amerlock

Amerlock

RAD-ORING-1-NV

SiliconeO-ring

70

70

0.58

RAD-RIP-FRESH-1

Ripolin

70

70

0.59

RAD-RIP-PRE1-1

Ripolin

70

70

0.65

RAD-RIP-PRE4-1

Ripolin

70

70

0.64

Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT

1 000 kGy pre-irradiation and heat/steam treatment (160°C)
Phase 1: Irradiation of coupons after gas load

No pre-irradiation applied
Coupons received July 2017
100 kGy pre-irradiation
1 000 kGy pre-irradiation
Phase 1: Irradiation of coupons after gas load

20 | NEA/CSNI/R(2020)14
Table 2.5. Summary of all RAD series tests performed in the BIP-3 project.
Unless otherwise noted, tests were performed with six iodine-loaded coupons in the irradiation
vessel (Continued)
Couponmaterial

Test name

RAD-PRE2TC3-1-NV

Loading
temp. (a)(°C)

Loading
RH (b)(%)

Dose
rate(c)(kGy/h)

70

70

0.54

N/A

N/A

0.54

Phase 2: Irradiation of empty vessel (coupons removed) to check for
revolatilisation of deposits
Pieces of silicone O-ring, used to seal older irradiation vessel design.
Surface area of each piece was estimated to be 1.85 cm2.

Amerlock

Other information
1 000 kGy pre-irradiation and heat/steam treatment (160°C)
Phase 1: Irradiation of coupons after gas load

RAD-ORING-1-NV

Silicone Oring

70

70

0.58

RAD-RIP-FRESH-1

Ripolin

70

70

0.59

RAD-RIP-PRE1-1

Ripolin

70

70

0.65

70

70

0.64

N/A

N/A

0.64

Phase 2: Vessel O-ring from Phase 1 placed into a clean vessel (nocoupons) and irradiated

70

70

0.65

16 h water soak after gas load

70

70

0.64

Phase 1: Irradiation after gas load

N/A

N/A

0.64

Phase 2: After Phase 1 irradiation, coupons are soaked in water for 16h, then irradiated a second time in a clean vessel (new O-ring).

70

70

0.52

RAD-RIP-PRE4-1

Ripolin

RAD-AMER-WET-1

Amerlock

RAD-AMER-WET-2

Amerlock

RAD-NO2-1-1-NV

RAD-NO2-2-1-NV

Coupons received July 2017
100 kGy pre-irradiation
1 000 kGy pre-irradiation
Phase 1: Irradiation of coupons after gas load

Coupon pre-exposure to 245 ppm NO2 at 70°C, 70% RH for 4 h,followed by I2 loading at 70°C, 70% RH, 1×10-8 M I2.
Phase 1: Irradiation of coupons after gas load.

Amerlock

Amerlock

No pre-irradiation applied

N/A

N/A

0.52

70

70

0.53

Phase 2: Irradiation of empty vessel (coupons removed) to check for
revolatilisation of deposits.
Coupon pre-exposure to 245 ppm NO2 at 70°C, 70% RH for 4 h,followed by I2 loading at 70°C, 70% RH, 5×10-8 M I2.
Phase 1: Irradiation of coupons after gas load.

RAD-AMER-WET-1

Amerlock

RAD-AMER-WET-2

Amerlock

RAD-NO2-1-1-NV

RAD-NO2-2-1-NV

N/A

N/A

0.64

Phase 2: Vessel O-ring from Phase 1 placed into a clean vessel (nocoupons) and irradiated.

70

70

0.65

16 h water soak after gas load.

70

70

0.64

Phase 1: Irradiation after gas load.

N/A

N/A

0.64

Phase 2: After Phase 1 irradiation, coupons are soaked in water for
16 h, then irradiated a second time in a clean vessel (new O-ring).

70

70

0.52

Phase 1: Irradiation of coupons after gas load.

Amerlock

Amerlock

Coupon pre-exposure to 245 ppm NO2 at 70°C, 70% RH for 4 h,followed by I2 loading at 70°C, 70% RH, 1×10-8 M I2.

N/A

N/A

0.52

70

70

0.53

Phase 2: Irradiation of empty vessel (coupons removed) to check for
revolatilisation of deposits.
Coupon pre-exposure to 245 ppm NO2 at 70°C, 70% RH for 4 h,followed by I2 loading at 70°C, 70% RH, 5×10-8 M I2.
Phase 1: Irradiation of coupons after gas load.

Source: CNL, 2020.
(a)

(b)
(c)

Temperature during the loading phase; samples were irradiated at ambient temperature.
Relative humidity during the loading phase; samples were irradiated with no control of humidity.
As measured by Fricke dosimetry.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 21

Table 2.6. Summary of all METH series tests performed in the BIP-3 project
Test name

CH4
(ppm)

I2
(M)

Cover gas

Water
(ml)

Dose rate(a)(kGy/h)Other information

METH-1

~7%

High

Air

0

0.82

I2(s) present in vessel.

METH-2

200

1e-6

Air

0

0.79

METH-2B

200

1e-6

Air

0

0.78

METH-2 Blank

200

1e-6

Air

0

0

METH-3

200

1e-6

N2

0

0.79

METH-3B

200

1e-6

N2

0

0.78

METH-4

200

1e-6

Air

5

0.79

METH-4B

200

1e-6

Air

5

0.78

METH-10

200

1e-7

Air

0

0.77

METH-10B

200

1e-7

Air

0

0.77

METH-10 Blank

200

1e-7

Air

0

0

METH-0

0

1e-7

Air

0

0.77

METH-11

200

1e-8

Air

0

0.77

METH-11B

200

1e-8

Air

0

0.77

METH-11 Blank

200

1e-8

Air

0

0

Non-irradiated blank.

Non-irradiated blank. Keptin dark.

Non-irradiated blank. Keptin dark.

Source: CNL, 2020.
(a)

Dose rate as measured by the Fricke dosimeter. An adjustment may be necessary to account for different mass-energy adsorption
coefficients between Fricke solution and air.

2.4. Overview of BIP-3 Analytical Working Group (AWG) modelling exercises
The BIP-3 AWG was assembled with the general mandate to encourage discussion of modelling
strategies and to provide guidance to ongoing experimental and code development work
regarding the two main aspects of the iodine-paint interaction studied across all of the BIP
programmes:
1.

iodine adsorption/desorption from surfaces, and2.

organic iodide production from irradiated epoxy surfaces.

The BIP-3 AWG scope of work was performed in conjunction with the OECD BIP-3 research
programme from January 2016 through June 2018 and involved the completion of two
independent modelling exercises where the BIP-3 members were encouraged to participate andshare modelling data for selected scenarios. The modelling exercises were performed in twostages, with Stage 1 being defined and led by the CNL (the operating agent) and Stage 2 being
led by staff from the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) who also chaired
the BIP-3 AWG meetings.
Stage 1:

Perform a co-operative sensitivity study based on a simple geometry and accident
scenario (the same geometry was also used for a STEM-2 AWG activity).

Stage 2:

Perform modelling of two selected benchmark tests: RAD-EPICUR-A1 from the
BIP-2 Programme, and LD3 from the STEM Programme.

Representative organisations from seven of the BIP-3 member countries participated in the
AWG modelling exercises. Six different computational codes were used to model the selected
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT22 | NEA/CSNI/R(2020)14
scenarios, including commercially-available severe accident codes, such as ASTEC, MELCOR,
and COCOSYS, and research codes or codes developed and maintained internally by theparticipating organisation, including LIRIC, INSPAIR and KICHE(OrgIDB). Detailed
descriptions of the respective codes and participant submissions are available in the AWG
Summary report [8]. A brief overview of the Stage 1 and Stage 2 modelling exercises is provided
in the sections below.

2.4.1. Overview of the Stage 1 modelling exercise
The main objective of the Stage 1 modelling exercise was to demonstrate the sensitivity of thesimulated total airborne iodine to the inclusion of sub-models related to the radiolytic formationof organic iodides from iodine-loaded paint.
A simple scenario was devised to include conditions somewhat representative of a severe
accident, while excluding issues that could complicate the iodine calculation and detract fromthe main objective. The simulation scenario assumed a loss of primary coolant followed by fuelfailure and release of fission products. Iodine chemistry occurring in the containment building
was calculated starting from a time when iodine-containing aerosols and other fission products
have settled and have been washed into a water pool. It was assumed that the majority of theiodine entered containment as non-volatile I−, although a small portion (~2.5%) was assumed toenter the containment building as I2. The conditions chosen for the Stage 1 simulation aresummarised in Table 2.7.
Participants were asked to perform simulations using the conditions outlined in Table 2.7 withand without the formation of organic iodide from irradiated painted surfaces being consideredin the simulation. The following outputs were requested for each modelling submission inStage 1:•

total gas phase iodine;•gas phase iodine speciation (I2, ORGI, IOx, etc.);•

total aqueous iodine;•aqueous iodine speciation (major species if available);•pool pH evolution (if pH is changing);•

surface loading (submerged surface, dry surface, etc.).

The objectives of this modelling exercise were to:•evaluate the significance of the iodine-paint interaction in available models to predict
iodine volatility;•

evaluate the relevance of gaseous radiolytic reactions involving organic compounds(like CH4) and gaseous I2 and the need to include these phenomena for future model
development;•

identify the remaining uncertainties in iodine-paint interaction models and gas phase
iodine chemistry.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 23

Table 2.7. Simulation base conditions for the Stage 1 co-operative sensitivity study
Parameter

Value

Rationale/Comments

Vessel geometry

CylinderA common containment shape

Total volume

352 000 m

Similar to CANDU 6 and French reactor designs

Water volume

3

2 000 mTotal of heat transport and emergency waterGas volume

50 000 m

Similar to CANDU 6 and French reactors

Water-gas interface area

1 350 m2

Cross-sectional area of a cylinder with a diameter of 41.46 m(CANDU 6)

Painted surface area (dry)

25 000 m2

Assume all surfaces are painted

Painted surface area (wet)1 350 mFloor area

3

2

Inert surface area

20m

Can consider as sensitivity case

Steel surface area

0 m2

Can consider as sensitivity case

Temperature

100 °C

Within the range of a severe accident

Relative humidity (RH)70 %RH might be higher in reality, but data is available at 70%

Dose rate to gas phase

1 kGy/hWithin the estimated range of post-accident dose rates

Dose rate to water

1 kGy/hWithin the estimated range of post-accident dose rates

Thermalhydraulics

Vigorous mixing in both phases

pH evolution

Controlled at 9.0 for 84 h, then stepchange and controlled at 5.0 for 84 h

Most reactor sumps will be initially alkaline, but will acidify
with time (e.g. organic radiolysis and nitric acid formation)

Initial water chemistry

Pure water

Avoid complications with trisodium phosphate (TSP), boric
acid, etc.

Initial iodine species

Aqueous: 1e-5 M I− (aq)Gas: 5e-9 M I2 (g)Atmosphere

Normal air (with no CO2)

Other chemical changes

None, other than what is needed toaffect the pH change

To maintain homogeneity~97.5% of the iodine enters containment as a soluble form
(e.g. CsI) and ~2.5% enters containment in the form of I2. Total
mass is 2 603.5 g iodine
CO2 not present to affect pH for simulation
For simplicity

Source: CNL, 2020.

2.4.2. Overview of the Stage 2 modelling exercises
Stage 2 of the BIP-3 AWG included the modelling of two benchmark tests related to iodinepaint interactions:
1.

STEM test LD3 (on-line test). This test was performed in the IRSN facility and the data
was released to BIP-3 AWG participants for use in this study [9].

2.

BIP-2 test RAD-EPICUR-A1 (batch test). This test was performed in the CNL iodine
research facility [10].

Specific details regarding the benchmark tests are described in the respective STEM and BIP-2
project reports [9][10]. A summary of the experimental conditions for the two benchmark tests
is provided in Table 2.8.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT24 | NEA/CSNI/R(2020)14
Table 2.8. Summary of experimental conditions for STEM Test LD3 and BIP-2 Test RADEPICUR-A1
Parameter

STEM, Test LD3

BIP-2, Test RAD-EPICUR-A1

Epoxy painted coupon surface (cm²)

50

30.4

Temperature (°C)

80 ± 2

80

Pressure (bars)

1.70 ± 0.05

1.0

Relative humidity (%)

60 ± 3

Ambient (not controlled)

Vessel volume (L)

4.8

0.93

Vessel surface (cm²)

1 550 (steel)

870 (glass)

Dose rate (Gy/s)

Gas phase: 0.46 ± 0.04
Coupon level: 0.33 ± 0.03

0.325

Initial [I]ads on the paint (mol/m2)(9.50 ± 0.20)x10-5

1.46x10-3

Gaseous flow rate in the vessel (L/min)

0.250 ± 0.0050Pre-irradiation sweeping phases (h)00Irradiation phase duration (h)30 h

138 h (loaded coupons)
142 h (non-loaded coupons)

Post-irradiation sweeping phases (h)5 h – air with 50% RH
1 h – dry air

0

Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 25

3. Experimental methodology
3.1. Coupon preparation
3.1.1. Coupon fabrication, geometry and painting
To maintain consistency with earlier work and allow direct comparisons to BIP-1 and BIP-2
results, the CNL standard coupon geometry of ½ inch (1.27 cm) diameter and ¼ inch (0.635 cm)
thickness was used whenever possible. The surface area of the CNL standard coupon geometry
is approximately 5.08 cm2. Coupons used in BIP-3 were fabricated from 304 L stainless steel,
and were subsequently painted using the methodology below. A small number of adsorption
tests were also performed using glass coupons (Schott Duran borosilicate glass) of the same
dimensions.
Painted coupons were prepared prior to the start of the BIP-3 project (2015) by spray-coatingwith the appropriate coating(s) according to the paint manufacturer’s specifications andallowing for the recommended curing times between successive layers. Amerlock 400 coupons
were prepared by coating the stainless steel coupons with three layers of the paint (no undercoat)to a total average thickness of 0.18 mm. This treatment was similar to that used for earlier
coupon batches painted for BIP-1 and BIP-2. The coupons painted in 2015 were consideredfresh (denoted “FRESH”) for subsequent experimental work.
At the conclusion of Year 2, the inventory of FRESH Amerlock coupons (painted in 2015) was
limited and a new batch of coupons was prepared to replenish the supply in accordance with themethod outlined above. To distinguish between the different batches of coupons, tests using the
new batch of coupons (painted 2018) were denoted “FRESH2”, or their use is otherwise notedin the test matrix information (Section 3.3).

3.1.2. Paint ageing techniques and pre-treatments for Amerlock coupons
The effect of different paint ageing techniques on the sorption behaviour and organic iodide
production arising from painted coupons was evaluated in BIP-3. The ageing strategies are
summarised in Sections 3.1.2.1 to 3.1.2.4 below.

3.1.2.1 Natural ageing of painted coupons
A limited stock of naturally-aged Amerlock coupons was available for testing. These coupons
were originally prepared for BIP-1 (painted 2009) and BIP-2 (painted 2013), and have been
stored in the laboratory. Freshly prepared Amerlock coupons (painted 2015, 2018) were also
used for comparison.

3.1.2.2 Pre-irradiation of painted coupons
Painted coupons (painted in 2015) were placed in a beaker (Figure 3.1) and irradiated within a
Gammacell-220 60Co irradiator 2 at a dose rate of 0.86 kGy/h up to total absorbed doses of
100 kGy (Pre-irradiation 1 [PRE1]) and 1 000 kGy (Pre-irradiation 2 [PRE2]).

2. The Gammacell-220 60Co irradiator was distributed by MDS Nordion.
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT26 | NEA/CSNI/R(2020)14
Figure 3.1. Set-up used for coupon pre-irradiations

Source: CNL, 2020.

3.1.2.3 Thermal curing pre-treatments
Thermal pre-treatments are often used to simulate the effects of paint ageing [11][12]. Twothermal curing strategies were selected for use in BIP-3: (1) thermal curing performed under dry
conditions, and (2) thermal curing performed in a water-saturated environment.
For Thermal Cure 1 (TC1), the coupons were placed into open glass vials and were heated to130±2 °C for 96 hours in an oven (ambient air conditions).
For Thermal Cure 2 (TC2), coupons were suspended in glass holders within a 2 L Autoclave
Engineers Hastalloy C autoclave outfitted with a 3 kW heater. Excess water was added(100 mL) to ensure saturated steam conditions upon heating and coupons were suspended well
above the water level. The temperature was increased to 130°C within about 2 h and wascontrolled at 130°C to within about 4°C. After 96 h the heating was discontinued and the vessel
was allowed to cool. Coupons were stored in capped glass vials until required for testing (within
2 days). The autoclave water was sampled at the end of the second run containing six coupons
for RAD-TC2-1. The total organic carbon was measured to be 118.4 mg C/L.
Coupons were observed to change colour as a result of the thermal curing process (Figure 3.2).
Figure 3.2. Coupons before and after the thermal cure processes

Untreated

ThermalCure 1(Dry)

ThermalCure 2(Saturated)

Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 27

Thermal Cure 2 affected the coating integrity in such a way that a small amount of theunderlying steel was visible after coupons were removed from the glass holders (coupons had
some adherence to the glass, and the coating chipped during manipulation).

3.1.2.4 Combined ageing strategies – Pre-irradiation and thermal curing
To determine if the combination of ageing methods would have an additive effect on iodine
sorption processes or organic iodide production, a small number of coupons were prepared using
both a pre-irradiation and a sequential thermal curing treatment.
Coupons that had been pre-irradiated to 1 000 kGy (PRE2) were subsequently heated for 96 h
in an autoclave at 130 °C under water-saturated conditions. This pre-treatment was defined as
PRE2TC2.
Additionally, coupons that had been pre-irradiated to 1 000 kGy (PRE2) were subsequently
heated for 96 h in an autoclave at 160 °C under water-saturated conditions (TC3). This pretreatment was defined as PRE2TC3.

3.1.3. Ageing tests with other painted coupons
The original BIP-3 proposal did not include tests with other containment paints. However, alimited number of tests were added in consultation with the PRG to determine if othercontainment paints demonstrate similar ageing effects as observed for Amerlock paint.

3.1.3.1 Epigrip – Natural ageing
An inventory of Epigrip-painted coupons, which had originally been prepared in 2010 for testingin BIP-1, was still available. These coupons had been stored in the laboratory. Experimental
results using the naturally-aged Epigrip coupons were compared to previous results from BIP-1.

3.1.3.2 Ripolin – Pre-irradiation
Ripolin-painted coupons were prepared by IRSN in France in accordance with the standard
coupon geometry for BIP-3 (see Section 3.1.1). The coupons were received by the CNL in
July 2017. Using the same process as described in Section 3.1.2.2, the Ripolin coupons were
irradiated at 0.65 kGy/h to total absorbed doses of 100, 250, 500 and 1 000 kGy. The irradiatedRipolin coupons were noted to be slightly darker in colour than coupons that were not irradiated(Figure 3.3).
Figure 3.3. Ripolin coupons before and after irradiation

Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT28 | NEA/CSNI/R(2020)14

3.1.3.3 Gehopon – Natural ageing and combined natural and simulated ageing
A limited number of Gehopon-painted coupons (A0 and A30) were available which hadoriginally been used for testing in BIP-2. Although prepared from the same batch, the A0
coupons remained untreated (natural ageing) while the A30 coupons had an artificial ageing
treatment applied prior to their shipment to the CNL (155 °C for 42 h) 3 that was intended tosimulate the effects of 30 years of ageing. Hence, the A30 coupons had experienced both
simulated and natural ageing processes.

3.2. Iodine adsorption studies
Iodine can be adsorbed onto the coupon surfaces in one of two ways: (1) aqueous phaseadsorption by immersing the samples in aqueous solutions containing iodine (as I2), and (2)adsorption of gas phase elemental iodine from a stream of flowing air containing iodine vapour.
For all experiments performed in BIP-3, only the gas phase adsorption technique was used.
Gas phase iodine adsorption and desorption onto surfaces were studied over a range of iodine
concentrations, relative humidities (RH) and temperatures. The sorption experiments werecarried out in the Radioiodine Adsorption Apparatus (Figure 3.4). In a typical test, three samples(in the form of coupons) were placed in glass flow cells (Figure 3.5) and exposed to a continuous
flow of air containing 131I-labelled I2, followed by purging with iodine-free air. The adsorption
cells are made of borosilicate glass to minimise iodine adsorption on the walls. The adsorption
cells are situated in a heated oven chamber for temperature control. The iodine activity
accumulated on each sample was continuously monitored during loading and purging using a
γ-counting detector situated outside the oven and directly beneath each adsorption cell, see
Figure 3.6. Small known fractions of the flows entering and leaving the adsorption cell were
diverted to charcoal traps (referred to as the inlet and outlet trap, respectively). The 131I activities
accumulated in these traps were continuously monitored to determine the iodine loading andrelease concentrations in the inlet gas and in the effluent. The adsorption cells are disassembled
at the end of each test and thoroughly cleaned before reuse. Further details of the experimental
set-up and procedures are provided in Reference [13].
The uncertainty for typical activity-based measurements has been estimated as less than 15%,
based on variations in the specific activity determined from a given batch of trace-labelled I2.
However, the uncertainty rises as the count rate becomes small.
Deposition velocities were extracted from the initial time periods of the collected adsorption
curves. The length of time used for the deposition velocity calculation varied, depending on thecurvature of the adsorption profiles and the data scatter, but was generally calculated from thefirst 3-6 hours of loading. After conversion to common units, the deposition velocity is
calculated by simply dividing the loading rate by the loading concentration (Equation 1). For
tests where desorption behaviour was monitored, the amount of desorbed iodine was also
estimated from the measured changes in online surface activity.
𝑚𝑚𝑚𝑚𝑚𝑚�
𝑑𝑑𝑑𝑑2 ∙𝑠𝑠
𝑚𝑚𝑚𝑚𝑚𝑚𝐺𝐺𝐺𝐺𝐺𝐺 𝑃𝑃ℎ𝑎𝑎𝑎𝑎𝑎𝑎 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 � 3 �
𝑑𝑑𝑚𝑚

𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐼𝐼2 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 �= 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣 �

𝑑𝑑𝑑𝑑
𝑠𝑠

�

(1)

3. Information regarding pre-treatment conditions were provided by GRS.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 29

Figure 3.4. Schematic diagram of the multiple coupon Radioiodine Adsorption Apparatus. RH, T
and P denote relative humidity, temperature and pressure transducers. UHP N2 corresponds toultra-high purity nitrogen

Source: CNL, 2020.

Figure 3.5. Top and side view of the adsorption cells

Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT30 | NEA/CSNI/R(2020)14
Figure 3.6. Cross-sectional diagram of the sample chambers and detectors

Source: CNL, 2020.

3.3. Irradiation tests to evaluate methyl iodide production
3.3.1. Irradiation vessels for RAD series tests
In these experiments, a glass vessel containing coupons that were pre-loaded with 131I-labelled
I2 (as described in Section 3.2) and laboratory air was irradiated in a Gammacell-220 60Co
irradiator for the purpose of evaluating the radiolytic formation of organic iodides. Six coupons
were used for each irradiation test. Because only three coupons can be loaded at a time in theRadioiodine Adsorption Apparatus, the iodine loading was performed in two phases. Onceloading of the first three coupons was complete, the coupons were transferred into scintillation
vials where they were stored for the duration of the iodine loading for the second set of coupons.
After the second loading phase was complete, all coupons were 𝛾𝛾-counted to quantify the initialiodine loading on each coupon. The iodine-loaded coupons were then transferred into theirradiation vessel.
In BIP-1 and BIP-2, coupon irradiation tests had been performed using a glass vessel with an
O-ring seal. This vessel was also used within the BIP-3 programme, and is described in
Section 3.3.1.1. However, during the BIP-3 programme it became important to design a newvessel to eliminate the need for an O-ring seal, so as to reduce any contribution the O-ring may
have on organic iodide production. The new O-ring free irradiation vessel is described in 3.3.1.2.
Tests performed in the new vessel have been denoted ‘NV’.

3.3.1.1 O-ring vessel for coupon irradiation tests
This vessel consists of upper and lower sections made from borosilicate glass (Schott Duran).
Coupons are placed on custom glass holders that are suspended within the irradiation vessel,
which is shown in Figure 3.7 and Figure 3.8. The two sections connect on inner and outer groundglass flanges. An O-ring (silicone) is positioned between the two ground glass surfaces. An
external compression clamp ensures positive contact between the upper and lower sections. The
upper section contains a screw cap port with a septum for gas sampling. With the coupon holders
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 31

and 6 coupons in place, the vessel volume contains 927 mL of gas space. The glass surface area(for the glassware shown in Figure 3.7) is estimated to be 870 cm2. This estimate excludes
contributions from the coupon holders.
Figure 3.7. Irradiation vessel (shown pre-irradiation and without the coupon holders)

Source: CNL, 2020.

Figure 3.8. Irradiation vessel (shown post-irradiation and with coupons and holders)

Source: CNL, 2020.

3.3.1.2 New irradiation vessel (without O-ring) for coupon irradiation tests
The O-ring was completely eliminated by designing a vessel with a 1 inch stainless steel tube
with a glass/metal joint as the coupon access port (Figure 3.9 and Figure 3.10). The coupons in
the most recent tests were held in a narrow glass holder, but were separated to promote contact
and free exchange with the gas space. This change in design added an additional stainless steel
surface area to the vessel, which may have retained a certain amount of iodine. However,previous tests performed in BIP-1 suggest the impact of this material addition to be small [14].
Complete elimination of the sampling septum was not possible because sample withdrawal is anecessary experimental activity. A stainless steel ball valve was added to separate the septum
from the main irradiated volume thus eliminating the possibility of the septum as a contributor
to radiolytic CH3I production. The stainless steel ball valve contains a small amount of a Teflonlike material as seating for the rotating ‘ball’, which is not visible when the valve is open or
closed, but could have a very small area in contact with the vessel atmosphere.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT32 | NEA/CSNI/R(2020)14
In order to accommodate the new valve/septum system, the height of the vessel needed to be
decreased to fit within the Gammacell sample chamber; however, the new vessel volume iscomparable to the previous vessel (1 060 mL compared to 927 mL for the O-ring vessel).
Figure 3.9. Diagram of new O-ring free irradiation vessel

Source: CNL, 2020.

Figure 3.10. Photographs of the new O-ring free irradiation vessel and coupon holder design, withcomponents disassembled (left) and fully assembled (right)

Source: CNL, 2020.

3.3.2. Irradiation vessel for METH series tests
A glass vessel (~1 L) optimised for gas experiments was used to study the gas phase productionof methyl iodide from I2 and CH4 mixtures (Figure 3.11). The vessel had an inlet and an outlet

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 33

to facilitate gas purging, and ball valves (in addition to the septum) to ensure leak tightness. Dueto the height of this vessel, and because the tests did not contain 131I tracer, an alternate
Gammacell located at the CNL site (with a similar dose rate) was used for these tests.
Figure 3.11. Irradiation vessel for gas phase experiments

Source: CNL, 2020.

3.3.3. Gas phase analysis
Sampling of the gas phase in the irradiation vessels was accomplished using a gas-tightsyringe via the available gas sampling septum. Methyl iodide concentrations were determined
by Gas Chromatography (GC). Gas samples were introduced into a 10 µL sample loop for
injection into an HP 7890 Gas Chromatograph outfitted with a 30 m Agilent J&W DB-VRX
capillary separation column (0.32 mm interior diameter) and an electron capture detector(ECD). The detection limit for CH3I by this method was about 10-12 M. The practical detection
limit, however, was higher (10-11 M) because of difficulties associated with reproducibility at
low concentrations. Based on repeated injections of standard concentration, the uncertainty wasestimated to be about 25% and increases for concentrations below 10-11 M.
For gas phase irradiation tests, the methane concentrations were also monitored with time.
Methane concentrations were determined using the same GC system as described above, except
a flame ionisation detector (FID), rather than an ECD, was used for the analysis. Because of thisdifference, methyl iodide and methane products could not be analysed simultaneously, andseparate injections for each analysis were required.

3.3.4. Iodine desorption and mass balance analyses
After gas phase analyses were completed, the irradiation vessel was opened and the coupons
were γ-counted to determine the amount of iodine desorbed by comparison to their pre-test
loading. The vessel was then washed with three rinses of 20 mL 0.05 M NaOH. The wash
solution was analysed for iodine content and was used for the mass balance calculation. The
coupon holders for the various irradiation design are not rinsed and are not included in the massbalance calculation; however, they do represent a small percentage of the surface area. After the
NaOH washes, the vessel was cleaned with methanol, acetone and propanol to dissolve any
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT34 | NEA/CSNI/R(2020)14
remaining organic residue. Prior to the next experiment, the vessel was washed with pure waterand baked at 500°C to remove residual organic contaminants.

3.3.5. Radiation dose rates
Dosimetry measurements were performed to estimate the dose rates to samples in BIP-3. The
dose rate was measured to be 0.84 kGy/h as of January 2016 using the Fricke dosimeter (ferrous
sulphate solutions). Dose rates for individual tests are provided in the data reports [13][15][16].
In BIP-1 and BIP-2, the dose rate was assigned a 17% uncertainty to account for variations in
repeated tests and differences in geometry. A similar uncertainty was assigned for BIP-3.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 35

4. Summary of BIP-3 experimental outcomesThis section provides an overview of the main experimental trends observed in BIP-3. Detailed
experimental descriptions and discussions of specific test results can be found in the data reports[13][15][16].

4.1. Adsorption capacity
A series of iodine sorption tests were performed in BIP-3 to evaluate whether the fraction ofphysisorbed iodine is dependent on the total loading achieved. Sorption tests were performed
for target loading concentrations spanning four orders of magnitude and, in order to achievethese loadings, the gaseous iodine concentration was also varied over two orders of magnitude.
Upon examination of the data, it was determined that the iodine sorption behaviour was strongly
associated with the gaseous iodine loading concentration used for the test. The dependence ofthe observed iodine desorption and the measured deposition velocity on the I2 loading
concentration are shown in Figure 4.1 and Figure 4.2, respectively.
In general, the relative amount of iodine desorption was observed to be greater for Amerlock
coupons having higher initial surface loadings. Slower deposition velocities and larger fractionsof desorbed iodine are measured when higher iodine gas concentrations were used duringloading. Higher I2 concentrations during loading appear to result in more loosely-bound or
physisorbed I2 on the paint surface.
Figure 4.1. Correlation between the gaseous iodine loading concentration and the relative amountof iodine desorbed for sorption tests on Amerlock

Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT36 | NEA/CSNI/R(2020)14
Figure 4.2. Correlation between the gaseous iodine loading concentration and the measured
deposition velocity for sorption tests on Amerlock

Source: CNL, 2020.

4.2. Paint ageing
Studies associated with evaluating the impact of different paint ageing strategies on iodine-paintinteractions were a primary focus of BIP-3, and included sorption, irradiation and leachingexperiments.
Natural ageing, pre-irradiation exposures to different adsorbed doses, and thermal curing
treatments with and without steam were selected as the ageing strategies of interest for
BIP-3. A limited number of tests were also performed on Amerlock painted coupons that had
been both pre-irradiated and thermally-cured; for subsequent discussion, these tests will betermed combined ageing tests.
Figure 4.3 shows the iodine adsorption and desorption profiles measured on Amerlock for fresh,
thermally-cured and combined ageing tests. As the deposition velocity is determined by theslope of the adsorption curve, it can be observed that the deposition velocity decreased slightly
with time for all tests. Increased coupon ageing was shown to reduce the deposition velocity ofiodine onto the paint, with thermal treatments involving water having a greater effect on theiodine deposition velocity than dry treatments. Combining ageing strategies appeared to havean additive effect, leading to greater reductions in deposition velocity than for any single ageing
method. Measured deposition velocities for combined ageing tests were among the lowest
measured across all BIP programmes.
Increased natural ageing and pre-irradiations to higher doses also reduced the deposition
velocity of iodine onto paint, albeit by a smaller amount than for strategies involving thermal
treatments. For all single-strategy ageing tests, the measured deposition velocities remained
within a factor of two of the values measured on fresh paint.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 37

Iodine adsorbed (mol/dm2)

Figure 4.3. Adsorption and desorption profiles for AD series tests performed on thermally-cured
Amerlock coupons, and for tests performed on pre-irradiated and thermally-cured Amerlock
coupons.

Adsorption Phase Desorption Phase

0

10

20

30

40

50
Time (h)

60

70

80

90

AD-FRESH-1

AD-FRESH-1

AD-TC1-2

AD-TC1-2

AD-TC2-1

AD-TC2-1

AD-PRE2TC2-1

AD-PRE2TC2-1

AD-PRE2TC3-1

AD-PRE2TC3-1

100

Source: CNL, 2020.
Note: The profile for a freshly painted coupon is also shown for comparison. Loading was performed at 70 °C
and 70% relative humidity with an I2 loading concentration of 1×10-8 M.

Consistent with previous BIP studies, very little iodine desorption was typically observed for all
single-strategy ageing tests, although combined ageing tests showed relatively higher fractionsof iodine to be desorbed. Because very low deposition rates were also observed in these tests,
this behaviour suggests that the surface modifications arising from combined ageing strategies(e.g. hydrolysis reactions, cleavage of functional groups, surface annealing) are sufficient tolead to a significant reduction in the number of active sites for iodine adsorption onto paint. As
a result, iodine is not strongly retained on the paint surface, and the iodine-paint interaction is
likely associated to a greater extent with physisorption.
The explanation that ageing-induced surface modifications are reducing the number of available
active sites for iodine chemisorption is supported by leaching tests that were performed on aged
Amerlock paint samples in 65°C water. Because of variations in paint thickness, correlations
regarding measurements of total organic carbon (TOC) for naturally-aged coupons could not bemade with confidence. However, coupons that were aged using pre-irradiations or thermal
treatments showed increased TOC releases into water compared to fresh coupons, suggestingthat these ageing mechanisms lead to break down of components of the paint structure. Preirradiations to higher doses, and the addition of steam during thermal treatments further
increased the TOC, indicating that surface modifications have occurred to a greater extent forthese samples.
In consultation with the PRG, additional tests with other containment paints were performed todetermine if similar ageing trends would be observed. Although the pre-irradiation of Ripolin
coupons up to 1 000 kGy did not appear to have any influence on iodine deposition velocity,
increased natural ageing of Epigrip coupons led to a decrease in measured deposition velocity,
consistent with the Amerlock observations. A small inventory of Gehopon coupons from BIP-2
was also available for testing. The A0 and A30 coupons were originally prepared from the samebatch; however, the A0 coupons remained untreated, while the A30 coupons were subjected toa thermal treatment to simulate 30 years of ageing prior to their shipment to the CNL. Figure 4.4
shows the trend in measured deposition velocity at 80°C as a function of relative humidity for
Gehopon A0 and A30 coupons, along with Amerlock coupons for comparison. The observation
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT38 | NEA/CSNI/R(2020)14
of increased deposition velocity with increased humidity is consistent with past BIP results.
From the figure, it is clear that ageing has a significant effect on the deposition velocity of iodine
onto Gehopon. The untreated A0 coupons show deposition velocities of a comparable range tofresh Amerlock; however, a considerable reduction in iodine adsorption rate is observed for theA30 coupons that were thermally aged.

Deposition Velocity (dm/s)

Figure 4.4. Deposition velocities for Gehopon A0 (naturally-aged; solid black line) and Gehopon
A30 (thermally and naturally-aged; dashed black line) coupons measured as a function of relative
humidity at 80°C and 1×10-8 M I2. Deposition velocities for fresh Amerlock (blue solid line) arealso shown for comparison

80 C - Fresh Amerlock
80 C - Gehopon A0
80 C - Gehopon A30

0

10

20

30

40

50

60

70

Relative Humidity (%)

Source: CNL, 2020.

The effect of paint ageing on radiolytic methyl iodide production was also studied in BIP-3. As
described in Section 3.3.1, coupon irradiation tests in BIP-3 were performed using two vessel
designs. To distinguish between tests in the different vessels in the figures, solid lines have beenused for tests performed in the traditional O-ring vessel and dashed lines are used for tests
performed in the O-ring free vessel. Methyl iodide production measured during the irradiationof Amerlock coupons aged using pre-irradiation treatments is shown in Figure 4.5. Methyl
iodide concentrations measured for fresh Amerlock and a combined ageing strategy test are also
shown for comparison. Coupons with increased pre-irradiation dose showed lower methyl
iodide production and reached lower steady-state concentrations, regardless of the test vessel
used (Figure 4.5). Similar to the iodine sorption tests discussed previously, combined ageing
strategy tests showed an additive effect, leading to further reductions in CH3I production.
Comparable trends were observed for naturally-aged and thermally-cured coupons.
The influence of paint ageing on the methyl iodide production can, once again, be explained bysurface modifications that are reducing the available chemisorption sites. Although the initialiodine loading for all coupon irradiation tests is nominally the same, a larger fraction of iodine
may be physisorbed rather than chemisorbed at active sites on the surface. As a result, theseiodine species cannot participate as effectively in chemical reactions with the paint, leading to
reductions in methyl iodide production.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 39

Figure 4.5. Summary of methyl iodide concentrations measured as a function of irradiation time
for tests with Amerlock coupons aged using pre-irradiation treatments, or the combination ofpre-irradiation and heat treatment, in the O-ring (solid lines) and O-ring free (dashed lines)
irradiation vessels
Solid Lines = O-ring vessel
Dashed Lines = New vessel

No Pre-irradiation

RAD-FRESH-1
RAD-FRESH2-1-NV
RAD-PRE1-1

CH3I Concentraton (M)100 kGy Pre-irradiation

RAD-PRE1-2
RAD-PRE1-3-NV
RAD-PRE1-4-NV
RAD-PRE2-1
RAD-PRE2-2

1000 kGy Pre-irradiation

RAD-PRE2-3-NV

1000 kGy + Heat Treatment 2 (130°C with Steam)
1000 kGy + Heat Treatment 3(160°C with Steam)
0

50

100

150

200

250

300

RAD-PRE2TC2-1
RAD-PRE2TC3-1-NV

350

Time (h)Source: CNL, 2020.

4.3. Pre-exposure to reactive gases
There is an ongoing concern that reactive species in the post-accident containment atmosphere(such as NO2 and Cl2) may compete with I2 for active sites on paint surfaces, which could impact
subsequent iodine-paint interactions. Preliminary tests were performed on this topic in BIP-2
and showed a negligible effect; however, the pre-exposure concentrations used were low(5 ppm) and the pre-exposure period may have been too short to see an effect. This topic wasfurther studied in BIP-3 using higher concentrations (up to 1 000 times larger than thesubsequent I2 loading concentration) and longer exposure periods than those used for BIP-2.
Figure 4.6 shows the iodine sorption behaviour onto Amerlock coupons with and without a 4 h
pre-exposure to either 245 ppm NO2 or Cl2 gas, measured under standard BIP loading conditions(70°C, 70% RH, 1×10-8 M I2). An induction period for iodine adsorption is observed for the preexposure tests, whereby the rate of iodine adsorption increases with loading time. Thisbehaviour appears to suggest that NO2 and Cl2 can adsorb onto, or react with, the paint during
the pre-exposure period and compete with I2 for adsorption sites upon initiation of the iodine
flow. Over time, the reactive species are eventually displaced from the sites, either throughthermal desorption or competitive interaction with I2, and the rate of iodine adsorption isobserved to increase. By examination of Figure 4.6, Cl2 appears to be more competitive thanNO2 for I2 adsorption sites. Given that Cl2 is a halogen, similarities to I2 with respect to its
reactivity and affinity for adsorption onto paint are expected.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT40 | NEA/CSNI/R(2020)14
Figure 4.6. Adsorption and desorption profiles for AD series tests performed on fresh Amerlock
coupons with and without a 4 h pre-exposure to either 245 ppm NO2 or Cl2 gas. Temperature andhumidity were maintained at 70 °C and 70%, respectively, and an I2 loading concentration of
1×10-8 M was used

Iodine adsorbed (mol/dm2)

Adsorption Phase Desorption Phase
AD-FRESH2-1

AD-FRESH2-1

AD-NO2-1-1

AD-NO2-1-1

AD-Cl2-1-1

AD-Cl2-1-1

Flow controller started
malfunctioning for AD-Cl2-1-1

0

5

10

15

20

25
Time (h)

30

35

40

45

50

Source: CNL, 2020.

The effect of NO2 pre-exposures on the subsequent methyl iodide production rate was also
evaluated in BIP-3, with results shown in Figure 4.7. In general, while the observed methyl
iodide concentrations are slightly lower for paint that has been pre-exposed to NO2, the preexposures appear to have only a small effect on subsequent CH3I production for coupon
irradiation tests.
Figure 4.7. Methyl iodide production as a function of irradiation time for fresh, untreated
Amerlock coupons and for coupons pre-exposed to NO2 gas prior to iodine loading. Tests were
performed in the O-ring free irradiation vessel

Fresh Amerlock

CH3I Concentration (M)Pre-exposure to 245 ppm NO2
I2 loading at 1E-8 M

RAD-FRESH2-1-NV
RAD-NO2-1-1-NV
RAD-NO2-2-1-NV

Pre-exposure to 245 ppm NO2
I2 loading at 5E-8 M

0

50

100

150

200

250

Time (h)Source: CNL, 2020.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 41

4.4. Effect of water on methyl iodide production
Previous tests in BIP-1 and BIP-2 showed elevated methyl iodide production at the start of an
irradiation when the coupons were loaded by submersion in an I2 solution. This results in a shortterm peak in the methyl iodide concentration. Two tests (RAD-AMER-WET-1 andRAD-AMER-WET-2, Figure 3.8) were performed in BIP-3 to conclude investigations of therole of water on methyl iodide production and to simulate the scenario of water condensing onto
containment walls after gaseous iodine loading has occurred. Submersion in water after gaseousiodine loading did not result in the same short-term methyl iodide peak that was seen for aqueous
loaded tests. The methyl iodide peak observed in BIP-1 and 2 experiments appears to be
associated with aqueous adsorption rather than the simple presence of water in the paint matrix,
and suggests the nature of the iodine-paint bond is different for gas and aqueous loaded tests.
Figure 4.8. Methyl iodide production measured during irradiation tests of gas-loaded coupons
that were submerged in water for 16 hours immediately after loading (red) and after 76 hours ofirradiation (blue)
Gas-loaded coupons removed and soaked in water for 16 h.
Irradiation resumed in a new vessel.

CH3I Concentration (M)Coupons loaded in the gas phase thensoaked in water for 16 h

RAD-AMER-WET-1
RAD-AMER-WET-2

0

50

100

150

200

250

Time (h)Source: CNL, 2020.

4.5. Iodine interactions with surfaces other than paintExperiments to evaluate the significance of iodine interactions with surfaces other than paint(glass, O-ring were performed in BIP-3 to assist in the interpretation and modelling of BIP and
STEM data and to provide insight into associated experimental uncertainties.
In general, the adsorption of iodine, as I2 or as CH3I, onto glass surfaces was shown to be
negligible under the conditions studied. However, scoping tests with other solid organic
surfaces, such as O-ring material, did show some affinity for the adsorption of these gaseousiodine species.
A selection of irradiation tests were also performed to evaluate the potential for CH3I releasefrom deposits on glass, or via reaction with other available reactive surfaces (O-ring).
Revolatilisation processes were studied as addendums to a limited number of coupon irradiation
tests, where the coupons were removed from the vessel, and a second irradiation phase was
performed. Iodine revolatilisation was observed in all cases, but for most tests, the CH3I
concentrations measured were somewhat lower than those observed at the conclusion of theprior irradiation phase, and decreased further with time. A redesigned test vessel (Figure 3.10)
was used for coupon irradiation tests performed towards the end of BIP-3. A comparison of all
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT42 | NEA/CSNI/R(2020)14
the methyl iodide production profiles that have been measured in BIP-3 (Figure 4.9) for
irradiated Amerlock coupons in the traditional O-ring vessel, shown with solid lines, and theredesigned O-ring free vessel, shown with dashed lines, has clearly demonstrated that thepresence of other organic materials, even in very small quantities, can contribute to methyl
iodide production during the later stages of the irradiation. While differences in the magnitudeof CH3I concentrations are observed between tests performed in the two irradiation vessels, thegeneral trends observed with respect to paint ageing remain consistent.

CH3I Concentration (M)Figure 4.9. Summary of methyl iodide concentrations measured as a function of irradiation time
for all BIP-3 tests performed on Amerlock coupons in the O-ring (solid lines) and O-ring free(dashed lines) irradiation vessels

0

50

100
150
Irradiation Time (h)

200

250

RAD-FRESH-1
RAD-FRESH2-1-NV
RAD-FRESH2-2-NV
RAD-2013-1
RAD-2013-2
RAD-2013-3-NV
RAD-2009-1
RAD-2009-2-NV
RAD-PRE1-1
RAD-PRE1-2
RAD-PRE1-3-NV
RAD-PRE1-4-NV
RAD-PRE2-1
RAD-PRE2-2
RAD-PRE2-3-NV
RAD-TC1-1
RAD-TC2-1
RAD-TC2-2-NV
RAD-PRE2TC2-1
RAD-PRE2TC3-1-NV
RAD-NO2-1-1-NV
RAD-NO2-2-1-NV
RAD-AMER-WET-1
RAD-AMER-WET-2

Source: CNL, 2020.

4.6. Gas phase production of methyl iodide
A gas phase reaction between I2 and volatile organic compounds, such as CH4, is consideredwithin some iodine behaviour models as a large contributor of methyl iodide in containment(refer to Section 5). The importance of this mechanism, however, is still under debate. The
possibility that organic iodides are radiolytically formed to a significant extent in the gas phaseis generally dismissed due to the large concentration of O2 relative to I2; O2 is expected tooutcompete I2 for any available •CH3 radicals that are formed. However, some references havesuggested methyl iodide production can be significant in such mixtures [6][7].
The CH4 and CH3I concentrations measured with time for irradiated mixtures of methane, air(or N2) and I2 are shown in Figure 4.10 and Figure 4.11, respectively. Methane is observed todegrade in the radiation field, but the degradation rate was not significantly influenced by thebalance gas or the presence of water. Additionally, the methane degradation rate did not
noticeably change with increased I2 concentration, despite the I2 concentration being varied bymore than two orders of magnitude. This suggests that methane removal is proceeding more
effectively through reaction with other available species, such as O2.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 43

Figure 4.10. CH4 concentrations measured as a function of irradiation time for various CH4/I2 gas
mixtures

METH-2 (1e-6 M I2)
METH-2B

Methane (ppm)

METH-3 (N2 cover, 1e-6 M I2)
METH-3B
METH-4 (5 mL water, 1e-6 M I2)
METH-4B
METH-10 (1e-7 M I2)
METH-10B
METH-11 (1e-8 M I2)
METH-11B

0

20

40

60

80
Time (h)

100

120

140

160

Source: CNL, 2020.

Figure 4.11. CH3I concentrations measured as a function of time for various CH4/I2 gas mixtures.
Tests performed with irradiation are shown with solid lines, and tests performed in the absence ofradiation are shown with dotted lines

METH-2 (1e-6 M I2)
METH-2B

Concentration CH3I (M)METH-2 Blank
METH-3 (N2 cover, 1e-6 M I2)
METH-3B
METH-4 (5 mL water, 1e-6 M I2)
METH-4B
METH-10 (1e-7 M I2)
METH-10B
METH-10 Blank
METH-0 (No Methane, 1e-7 M I2)
METH-11 (1e-8 M I2)
METH-11B
METH-11 Blank
0

20

40

60
80
Irradiation Time (h)

100

120

140

Source: CNL, 2020.

While the experiments appeared to show some conversion to methyl iodide in the radiation field,
closer examination of the trends in Figure 4.12 suggests any such conversion is small anddifficult to quantify. Increased measurement uncertainties for CH3I were noted for gas samples
with relatively high I2 concentrations, and an irradiation test performed without methane present
yielded comparable CH3I concentrations to most of the other irradiated CH4/I2 mixtures.
Ultimately, the contribution of this reaction pathway to CH3I production for irradiation tests
remains unclear, but it does not appear to be a significant contributor compared to the production
from painted coupons.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT44 | NEA/CSNI/R(2020)14

5. Summary of BIP-3 AWG modelling outcomes
Two modelling exercises were performed by the BIP-3 AWG. Six different computational codes
were used to model the selected scenarios, ranging from commercially-available severe accident
codes to research codes that have been developed and maintained internally by the participatingorganisations. While some of the codes are semi-empirical in nature and describe
phenomenological iodine-paint behaviour, others are significantly more detailed, with larger
reaction databases, and use a mechanistic approach to evaluate iodine-paint interactions.
Outcomes from the modelling studies will be only summarised. Specific details are provided in
the BIP-3 AWG Summary report [8].
The main objective of the Stage 1 exercise was to evaluate how sensitive the simulated
predictions of total airborne iodine are towards the inclusion or exclusion of sub-models related
to the radiolytic formation of organic iodides from iodine-loaded paint (ORGIPAINT) 4 using asimple postulated severe accident scenario.
In general, all models predicted that the inclusion of ORGIPAINT formation would increase thetotal airborne iodine. Similar trends in predicted iodine behaviour and volatility were also
observed with respect to the simulated sump acidification. However, the results also highlighted
other areas where significant variations in model capabilities or modelling strategies exist. In
particular, there was little consistency among the models in the selection of I2 deposition
velocity, or the treatment of mass transfer. There was also a lack of consensus on which chemical
processes were considered, and the outcomes of those processes. Specifically, the gas phaseformation of IOx from the radiolysis of I2 or ORGI, the gas phase reaction of I2 with volatileorganic products to generate ORGI, and the aqueous chemistry of iodine under irradiation at
100 °C were all addressed differently within the different models.
Key observations from the Stage 1 modelling exercise were:

4.

•

Despite the range of adsorption rates and mass transfer parameters used in the different
models, all models predicted that gaseous I2 entering the containment is largely adsorbedon the epoxy paint, and can be converted to IOx (rather than be transferred to the sump)when this process is considered.

•

The main sources of gaseous ORGI are attributed to the radiolytic reaction of I2 with thepaint surface, and for some models, a gas phase reaction of I2 with organics. Both ofthese pathways have been studied in part through the BIP-3 experimental programme.
However, the relative importance of the latter mechanism remains unclear.

•

Variation of the selected I2(g) deposition velocity was shown to lead to opposite trends
in ORGI concentration in different codes. This deviation highlights how different
approaches to modelling ORGI formation, including the iodine phenomenology that is
considered (especially in the gas phase), strongly impact model predictions. Thissuggests some fundamental iodine chemistry pathways should be revisited to ensure that
continued model development is based on accurate mechanistic understanding.

For simplicity, organic iodides (ORGI) formed radiolytically from painted surfaces with adsorbed
iodine are termed ORGIPAINT. Codes may include organic iodide production by other means, such asradiolytic formation in the sump (ORGISUMP), radiolytic formation in the gas phase (ORGIGAS) andthermal formation in all phases.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 45

The main objective of the Stage 2 exercise was to more critically evaluate predictions from thedifferent iodine-paint interaction models in comparison to available experimental data from two
selected benchmark tests: the STEM LD3 test, and the BIP-2 RAD-EPICUR-A1 test.
STEM experiments have shown that organic and inorganic iodine species are quickly released
during the first 10 to 15 hours of irradiation and then the release rate decreases significantly for
longer irradiation times. BIP-2 experiments have shown that the gaseous organic iodide
concentration increases quickly during the first hours of irradiation and reaches a steady stateover the long term. The steady state is interpreted to be the result of an equilibrium between
organic iodide formation reactions and organic iodide decomposition. The main ORGI
formation routes in the gas phase were considered to be release from painted surfaces; however,the BIP-3 AWG modelling efforts and further investigations in the BIP-3 experimental
programme have shown that other mechanisms are also likely to have played a role in the tests.
Iodine interaction (as both I2 and ORGI) with the BIP-2 vessel O-ring and the gaseous radiolytic
reaction of I2 with volatile organic compounds are postulated as alternative sources, but there is
still no consensus on the importance of each of these mechanisms.
Key findings from the Stage 2 modelling exercise were as follows:•

Although the STEM LD3 test data are generally well modelled by the codes, there is noconsensus on the reactions and processes that are considered. From one code to another,I2 desorption is not always considered in the same way and ORGI release models arevery different (e.g. consideration of gaseous reactions between I2 and volatile organics).
The experimental data collected in recent phases of the STEM and BIP projects should
help developers refine and validate their iodine-paint interaction models for iodine
adsorption and release.

•

Modelling results for the CH3I production in the second irradiation phase of the
RAD-EPICUR-A1 test varied widely among codes, and deviated considerably from themeasured experimental values, with both overestimation and underestimation of the
CH3I concentrations observed. This suggested that other sinks or sources of CH3I exist
beyond I2 revolatilisation from IOx deposits on glass followed by adsorption andreaction with the paint surface. Four additional mechanisms were proposed, and arelisted below. Each mechanism has been addressed in part through the BIP-3
experimental programme, and recommendations related to these possible mechanistic
pathways are considered in Section 7.
1.

Radiolytic gas phase reactions between I2 and organic compounds released by the
paint.

2.

Adsorption/desorption processes involving CH3I with glass vessel or O-ring
surfaces.

3.

Chemical reactions between the paint and deposited IOx on the paint surface.

4.

Chemical reactions between I2 and/or CH3I and the rubber O-ring employed to seal
the vessel.

It is clear from the observations described above that the nature of the test (batch or on-line),
and the uncertainties therein, should be considered in our interpretation of the data. However,the differences in the phenomenology considered among the codes (particularly in the gas phase)
can strongly impact model predictions. This indicates that continued refinement of ourunderstanding of fundamental iodine chemistry pathways is needed to ensure continued model
development is based on accurate mechanistic behaviour. Furthermore, development efforts
should endeavour to limit the potential for user effects to impact on model outcomes.
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT46 | NEA/CSNI/R(2020)14
Specifically, parameter values should be, as much as possible, non-user dependent, and fitting
parameters should be independent of the test considered.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 47

6. Overall conclusions
As with its predecessor projects, BIP-3 has continued to expand the available database of iodine
deposition data and organic iodide production that can be used towards the development andvalidation of iodine models. A number of research topics were selected for study to enhance
understanding of iodine-paint interactions that may occur in containment, particularly withrespect to ageing processes or reactive gas exposure, and to assist in the interpretation oflaboratory experiments, including the quantification of uncertainties.
BIP-1 and BIP-2 showed that higher temperatures and relative humidities yield higher rates ofiodine adsorption onto paint, with iodine being strongly retained. In BIP-3, exposures using
higher iodine loading concentrations were correlated with reduced iodine deposition velocity,and increased relative iodine desorption. This is thought to be associated with a larger fractionof iodine being more loosely-bound, or physisorbed to the paint, under these conditions. As aresult, the effectiveness of paint as an iodine sink in containment is somewhat dependent on theconditions of iodine exposure (i.e. I2 concentration).
Most of the other phenomena studied in BIP-3, including paint ageing and reactive gas preexposures, also led to reduced rates of I2 adsorption onto Amerlock paint. Aside frompre-irradiated Ripolin, the other containment paints studied seemed to demonstrate similar
trends in iodine deposition with respect to ageing. These data suggest that aged paint is a lesseffective iodine sink than fresh paints, and could contribute to increased airborne iodine incontainment. However, it appears that nearly all of the iodine adsorption rates measured for
different paints and ageing strategies in BIP-3 fall within the range of deposition velocity values
that are currently applied in iodine chemistry models, and, aside from combined ageing tests
and tests with pre-exposures to reactive gases, the iodine adsorption rates measured forAmerlock coupons spanned only a factor of two.
Coupon irradiation tests performed in BIP-3 showed that methyl iodide production from iodineloaded paint was generally reduced as a function of age, with the combination of ageing
strategies leading to a greater reduction. This implies that, for aged paint, a larger fraction of thevolatile iodine in containment may remain as I2, which is more easily trapped than CH3I withconventional filtration systems.
The gas phase production of methyl iodide from the irradiation of I2 and CH4 gas mixtures was
also evaluated in BIP-3. Some iodine behaviour models consider this reaction to be a large
contributor of methyl iodide in containment. While low CH3I concentrations were detected inthese irradiation tests, large experimental uncertainties were assigned to the measurements(owing to the high I2 concentrations). Examination of the data trends appears to suggest that thisreaction is not a significant contributor to gaseous CH3I compared to the production frompainted coupons. However, the overall contribution of this reaction pathway to CH3I production
remains unclear.
The production or release of methyl iodide through interactions with other surfaces of the BIP
irradiation vessel were also explored in BIP-3. The revolatilisation of iodine from deposits on
glass produced detectable concentrations of methyl iodide that decreased with further irradiation
time. Additionally, the presence of other organically-based materials, even in very small
quantities, were shown to contribute to methyl iodide production in irradiation tests, particularly
over the long term. Coupon irradiation tests performed in a redesigned vessel that minimised
uncertainties associated with organically-based seals yielded lower methyl iodide
concentrations than comparable tests in the previous vessel, although general trends with respect
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT

48 | NEA/CSNI/R(2020)14
to paint ageing remained consistent among the two vessels. This observation may also help torationalise some of the deviations observed between model simulations and BIP-2 experimental
data through the AWG.
It should be noted that the organic iodide production rates from the irradiation of iodine-loaded
paint measured in BIP-1 and BIP-2 are among the lowest in the available literature [4], andconcentrations observed from recent BIP-3 tests are lower still. In part this can be attributed to
the fact that BIP measures methyl iodide as a surrogate for all organic iodides. While the recent
BIP-3 coupon irradiation tests may be considered optimised for separate effects testing of
iodine-paint interactions, other solid organics will be present in containment (such as cablecoatings). The interaction of iodine with these materials, and how these interactions may
contribute to the iodine source term, is not necessarily well understood. In the context of model
development, some consideration should be given to the level of conservatism appropriate forsuch methyl iodide production mechanisms.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORTNEA/CSNI/R(2020)14 | 49

7. Recommendations
The BIP-3 programme has demonstrated that paint ageing can have a significant effect on iodine
sorption and organic iodide production. The overall consequences of this phenomenon on
predictions of iodine speciation and volatility should be assessed in full scale accident analyses.
The relative importance of radiolytic gas phase reactions between I2 and volatile organic
compounds on methyl iodide production remains unclear. Resolution will require additional
tests with an improved analytical method.
The presence of other organically-based materials was shown to contribute in part to the longterm methyl iodide production for coupon irradiation tests in BIP-3. Tests to assess the organic
iodide production that may arise from organics in containment other than paint (e.g. cablecoatings) could be considered to assist in future model development and to better quantify
predictions of iodine source term.
The redesigned BIP-3 irradiation vessel minimised uncertainties associated with organicallybased seals and was better able to isolate the methyl iodide production arising from iodine-paintinteractions. A future modelling exercise could be considered using a benchmark test performedin this vessel.
In general, the AWG modelling exercises revealed that differences in the phenomenology
considered among the codes (particularly in the gas phase) can strongly impact model
predictions. This indicates that continued refinement of our understanding of fundamental
iodine chemistry pathways is needed to ensure continued model development is based on
accurate mechanistic behaviour. Additionally, continued model development efforts should
endeavour to limit the potential for user effects to impact on model outcomes, and wherever
possible, fitting parameters should be independent of the test considered.

BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT

50 | NEA/CSNI/R(2020)14

8. References[1]

NEA (2007), State of the Art Report on Iodine Chemistry, NEA/CSNI/R(2007)1, OECD
Publishing, Paris, www.oecd-nea.org/jcms/pl_18434.

[2]

NEA (2012), OECD/NEA Behaviour of Iodine Project: Final Summary Report,
NEA/CSNI/R(2011)11, OECD Publishing, Paris, www.oecd-nea.org/jcms/pl_19098.

[3]

NEA (2016), The Main Outcomes of the OECD Behaviour of Iodine Project, in“Proceedings of the OECD-NEA International Iodine Workshop, 30 March 30 to 1 April
2015, Marseille, France”, NEA/CSNI/R(2016)5, OECD Publishing, Paris, pp. 153-164,
www.oecd-nea.org/jcms/pl_19702.

[4]

Bosland, L. et al. (2014), “Iodine-paint interactions during nuclear reactor severe
accidents”, Ann. Nucl. Energy, 74, 184.

[5]

NEA (2016), The Behaviour of Iodine Project: A Proposal for BIP-3, in “Proceedings of
the OECD-NEA International Iodine Workshop, March 30 to April 1, 2015, Marseille,
France”, NEA/CSNI/R(2016)5, OECD Publishing, Paris, pp. 165-171, www.oecdnea.org/jcms/pl_19702.

[6]

Bartoníček, B. and A. Habersbergerová (1986), “Investigation of the Formation
Possibilities of Alkyl Iodides”, Nuclear Power Plants. Radiat. Phys. Chem., 28(5), 591.

[7]

Bartoníček, B. and A. Habersbergerová (1987), Formation of Methyl Iodide by Ionizing
Radiation. Proc. of the 4th Working Meeting on Radiation Interactions, Leipzig,
Germany,p. 49.

[8]

Yakabuskie, P.A., G.A. Glowa and L. Bosland (2020), Behaviour of Iodine Project 3:
Outcomes of the Analytical Working Group. Canadian Nuclear Laboratories R&D
Report, Canadian Nuclear Laboratories, 153-126530-440-023.

[9]Fillet, S. et al. (2012), LD1, LD2, LD3 STEM/EPICUR tests report – Formation andrelease of volatile species from painted coupons, IRSN Report, Institut deRadioprotection et de Sûreté Nucléaire, IRSN-SAG-SEREX 2012-057 STEM no6.

[10]

Glowa, G.A. et al. (2014), Behaviour of Iodine Project 2: Final Report, Atomic Energyof Canada Limited Report, 153-126530-440-019.

[11]

AFNOR (1996), Peintures pour l’industrie nucléaire: essai de tenue à des conditions
accidentelles de référence (réacteur à eau sous pression) et de réparabilité, Association
Française de Normalisation, AFNOR NF T30–900, ISSN 0335–3931.

[12]

ASTM (2008), Standard test method for evaluating coatings used in light-water nuclear
power plants at simulated design basis accident (DBA) conditions, American Society for
Testing and Materials International, ASTM-D3911-08.

[13]

Yakabuskie, P.A. et al. (2017), Behaviour of Iodine Project 3: Year 1 Report, Canadian
Nuclear Laboratories R&D Report.

[14]

Glowa, G.A. et al. (2011), Behaviour of Iodine Project: Final Report on Iodine
Adsorption Studies, Atomic Energy of Canada Limited Report, 153-126530-440-013.

[15]

Yakabuskie, P.A., G.A. Glowa and D. Boulianne (2018), Behaviour of Iodine Project
3: Year 2 Report, Canadian Nuclear Laboratories R&D Report, 153-126530-440-021.

[16]

Yakabuskie, P.A., D. Boulianne and J. Nakamura (2020), Behaviour of Iodine Project
3: Year 3 Report, Canadian Nuclear Laboratories R&D Report, 153-126530-440-022.
BEHAVIOUR OF IODINE PROJECT 3: FINAL SUMMARY REPORT