Containment Iodine Experiments in the SARNET2 Project
T. Haste1, A. Auvinen8, J. Colombani1, F. Funke3, G. Glowa2, S. Güntay7,
J. Holm5*, T. Kärkelä8, G. Langrock3, G. Poss4, B. Simondi-Teisseire1,
S. Tietze5 and G. Weber6
(1) IRSN, Cadarache; (2) AECL, Chalk River; (3) AREVA, Erlangen;
(4) Becker Technologies, Erlangen; (5) Chalmers University, Gothenburg;
(6) GRS, Garching; (7) PSI, Villigen; (8) VTT, Espoo
*present address - Vattenfall
ERMSAR 2012, Cologne March 21 – 23, 2012
Introduction

An important safety issue is how much iodine could be present in the
containment atmosphere, and hence be released to the environment in
the event of containment failure or venting:


Particularly gaseous organic iodine, difficult to remove by filtration;
This is extensively studied in SARNET WP8 experimentally and theoretically; this
presentation outlines the small-scale and semi-integral tests involved, discussing
present and future use of the data produced:

EPICUR tests by IRSN under ISTP, looking particularly at the reaction of iodine with
paints under irradiation and formation of volatile iodine species;

Small-scale experiments at Chalmers University, such as adsorption of molecular
iodine and methyl iodide on painted surfaces;

Small-scale experiments by VTT (EXSI programme), radiolytic oxidation of methyl
iodide in humid conditions, release of iodine from painted surfaces;

PSI experiments on the effect of impurities on iodine volatility from sump water;

THAI experiments in the Iod series made available to SARNET, looking at such matters
as iodine oxide formation/destruction and the interaction between iodine behaviour
and containment thermal hydraulics;

AECL experiments such as from the RTF series available to SARNET
ERMSAR 2012, Cologne March 21 – 23, 2012
2
EPICUR (1/2)

EPICUR allows measurement on-line of the release kinetics of the volatile
iodine species that are formed from solution or from surfaces:


An electro-polished stainless steel irradiation vessel (4.8 l) is connected
through electro-polished stainless-steel tubes to a selective iodine filtration
system (dedicated to aerosols, molecular iodine and organic iodide); its
temperature is regulated in the range 40 to 130°C; six 60Co elements used as
the radiation source deliver average dose rates of about 2 kGy.h-1 at the level
of the painted coupon
Tests studied organic iodide formation from painted coupons, loaded with
molecular I2 labelled with 131I, put in the containment atmosphere:

Three main parameters were studied; the initial concentration of iodine on
the coupon, the temperature and the relative humidity in the irradiation
vessel;

The irradiation phase lasted between 8 hours and 30 hours
ERMSAR 2012, Cologne March 21 – 23, 2012
3
EPICUR (2/2)

Results show that:
Knit-mesh (First + Second)

Volatilisation increases with
time but not linearly, whereas
the activity measured on the
quartz fibre filter reaches a
plateau;

Still volatilisation of iodine
after 8 hrs of irradiation but
with slower kinetics;

The initial concentration of
iodine on the coupon mainly
influences
the
organic
production rate
Total iodine fraction transfered on the filter stages

0
Impregnated charcoal
Quartz fiber filter
10
20
30
Time (hours)
On-line measurements for a 30 hr duration
irradiation test in EPICUR
Longer experiments being performed in the current OECD/STEM project
will allow determination of whether the second slower kinetics are
sustained and of what fraction of the deposited iodine is involved
ERMSAR 2012, Cologne March 21 – 23, 2012
4
Chalmers (1/2)

Quantification studies are in progress on the partitioning and gaseous amounts of
organic iodine species such as methyl and ethyl iodides (MeI & EtI) that can be
present in the containment during severe nuclear reactor accidents using:


Experimental data from the literature (R. Borkowski) and from new tests performed
at Chalmers (FOMICAG facility: 23-70°C; with new equipment, temperatures of up to
150/170°C in the gas phase can now be obtained);
The Chalmers Model, a kinetic model describing mass transfer of MeI between the
containment gas and aqueous phases and its hydrolysis in the aqueous phase;
―
―
Applicable to any gas-liquid system, so long as the surface area and S/V ratio are known;
Applicable to data of different origins MeI(g), MeI(aq) & I-(aq) - (only one species is
required for the calculations), and to other organic iodides such as EtI, or to other substances
with similar chemical behaviour;
giving:


Kinetic parameters for the mass transfer, hydrolysis and partitioning coefficient of
methyl iodide; quantification of 3 different iodine species involved in the
partitioning, namely MeI(g), MeI(aq) & I-(aq), and also enabling;
Correction of results used in MAAP (Borkowski) since both the mass transfer and
hydrolysis of MeI can now be fully described.
ERMSAR 2012, Cologne March 21 – 23, 2012
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Chalmers (2/2)

Studies on the formation of organic and inorganic iodine species on paint films:


The paint can absorb and therefore reduce the amount of gaseous iodine species
already in the containment which needs to be removed in Venturi scrubber systems,
but also:
The paint can act as a source of volatile iodine species:
―
―

Paint as an ab/adsorber:



Formation of volatile organics by irradiation and heat decomposition of resin and solvents:
Re-release of iodine species; gaseous in dry areas of the containment; aqueous in contact
with steam and water pools, potentially followed by revaporisation;
Teknopox Aqua VA epoxy paint ab/adsorbs, by physi- and chemi-sorption, inorganic
iodine species such as elemental iodine, iodine oxide aerosols and organic iodine
species such as methyl and ethyl iodide;
The uptake of those species is controlled by the presence of chlorine;
Paint as a contributor to the iodine source term:


Teknopox Aqua VA releases volatile organics which can react with iodine in the
gaseous phase (already at 50°C, without the presence of irradiation);
Iodine species taken up are partially re-released in their original form or
chemically modified (by reactions of the species with paint ingredients) in both the
aqueous and gaseous phases.
ERMSAR 2012, Cologne March 21 – 23, 2012
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VTT/Chalmers – NROI (Nordic research on
Radiolytical Oxidation of Iodine)
Reaction and
sampling
furnaces
FTIR
DMA + CPC
Gas traps
Control unit
ELPI
TEOM
ERMSAR 2012, Cologne March 21 – 23, 2012
VTT/Chalmers – NROI: Experiments

Radiolytical oxidation of
iodine by UV (185 nm);

Methyl iodide as precursor;

Detection of formed particles
and gaseous reaction
products;

Varied parameters:

Temperature (50, 90 and
120 ºC);

UV intensity and/or O3
conc.;

Humidity
ERMSAR 2012, Cologne March 21 – 23, 2012
VTT/Chalmers – NROI: Results/Conclusions

Instant and extensive particle
formation:

Increased with:
120 °C
500
Particle
m ass
(m g/m 3)
250
– Ozone concentration;
High UVC
– UV intensity;
0
0
No UVC
1
– Temperature;
5
10
Ozone level
Humidity:


No UVC
Increased size of particles;
Agglomeration important =>
Particle size increased when
residence time was increased
mol Iodine particles/mol iodine
gas

1.0E+02
Dry
Humid
1.0E+00
1.0E-02
1.0E-04
1.0E-06
0
1
ozone levels
ERMSAR 2012, Cologne March 21 – 23, 2012
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PSI sump chemistry studies - Introduction

PSI performed experimental and modelling studies on the radiolysis of
iodide, nitrate and nitrite ions in aqueous solution:

Iodine volatilization from irradiated pure iodide solutions with different
boundary conditions (pH, concentration, oxidizing conditions, etc) is well
researched and reactions leading to the volatilization are modelled;

Separate-effect and integral (Phébus) tests have showed the presence of high
enough nitrate/nitrite ion concentrations in the aqueous phase as a result of
irradiation of the moist air in the gas phase;

Aqueous nitrous oxide irradiation chemistry directly modifies aqueous iodine
radiation chemistry;

The PSI project investigated conditions especially which might lead to a
certain degree of suppression of the iodine volatilization.
ERMSAR 2012, Cologne March 21 – 23, 2012
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PSI sump chemistry studies - Data
Dose rate dependent %I2 yields from
N2O-sparged CsI solutions containing
initially nitrite ions

Dose rate dependent %I2 yields from
Air-sparged CsI solutions initially
nitrate ions
New PSI experimental data on the effect of
nitrate and nitrite ions on iodine volatilization
ERMSAR 2012, Cologne March 21 – 23, 2012
Sharp increase at 3.7 kGy
dose: potential consumption
of all the nitrite ions by
conversion to nitrate ions by
oxidation
11
PSI sump chemistry studies - Conclusions

Experimental results clearly show that, under prevailing conditions under
irradiation, nitrate and nitrite ions lower % I2 generation yields;

The degree of suppression depends on the initial concentrations of
nitrate/nitrite ions, pH, CsI concentration and the level of net oxidation of
the system determined by the sparging gas type;

Further experiments might be helpful to broaden the data base to cover
other relevant nitrate/nitrite ratios and low initial iodide concentrations and
under air sparging conditions.
ERMSAR 2012, Cologne March 21 – 23, 2012
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THAI iodine tests released to SARNET

THAI test facility (Thermal hydraulics, Hydrogen,
Aerosols, Iodine) operated by Becker Technologies
in co-operation with AREVA NP and GRS:

26 iodine and the 6 iodine aerosol tests;

Iod-9: I2 mass transfer from gas into a sump and I2
adsorption and desorption at steel exposed to gas
phase (Benchmark in SARNET);

Iod-11 and Iod-12: I2 transport in a 5-compartment
geometry with a stratified and later a mixed
atmosphere (Benchmark in SARNET2/WP8);

Iod-13 and Iod-14: IOx aerosol production at
different I2/O3 ratios and IOx aerosol behaviour
(SARNET2 /WP8)
ERMSAR 2012, Cologne March 21 – 23, 2012
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THAI Iod-14: IOx aerosol particle sizes and
concentrations

Injection of 1.61 g I2 into
60 m3 air/steam/ozone
(ozone to simulate air radiolysis
products and to produce IOx,
initial molar ratio O3/I2 ≈ 100);

Generation of IOx
aerosol with small
particles (MMD ≈ 0.2
µm);

IOx aerosol behaviour:

Particle growth by
agglomeration;

Deposition mainly by
diffusion
Results of THAI tests Iod-13 and Iod-14:
http://dx.doi.org/10.1016/j.nucengdes.2012.01.005
ERMSAR 2012, Cologne March 21 – 23, 2012
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AECL – RTF (1/2)

RTF was an AECL experimental programme to study post-accident
iodine behaviour;

RTF Test P9T3 has been made available to SARNET members:


Electropolished vessel;
Can be used to test our computer models, in particular, the;
– Temperature dependence of iodine volatility;
– pH dependence of iodine volatility
Temperature increased to 60oC
Temperature increased to 80oC
Temperature increased to 60oC
Temperature increased to 80oC
pH to 5
pH to 9
9.0E-06
8.0E-06
3.0E-10
7.0E-06
Concentration (mol/dm 3)
Concentration mol/dm 3
2.5E-10
2.0E-10
1.5E-10
6.0E-06
5.0E-06
4.0E-06
3.0E-06
1.0E-10
2.0E-06
5.0E-11
[I]gas (On-line)
[I]gas (Off-line)
1.0E-06
0.0E+00
0.0E+00
0
50
100
150
200
250
300
350
400
0
50
100
150
200
250
300
350
400
Time (h)
Time (h)
Total gas phase iodine concentration
Total aqueous phase iodine concentration
ERMSAR 2012, Cologne March 21 – 23, 2012
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AECL – RTF (2/2)



In addition to iodine behaviour, RTF tests can be used also to study
various post-accident phenomena:

Water radiolysis (H2 and H2O2 production);

Air radiolysis (nitrate and nitrite production);

Organic dissolution and radiolysis;
Several RTF tests are available to some SARNET members:

OECD ISP-41 (2 tests);

OECD BIP (5 tests);

PHEBUS FP (6 tests);

EPRI ACE Project (13 tests);
Some of the available RTF tests were performed with painted surfaces:

These will provide integral test results that are complementary to ongoing projects;

The EPICUR, OECD/BIP and OECD/STEM projects currently study the interactions of
iodine and paint.
ERMSAR 2012, Cologne March 21 – 23, 2012
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Use of data (1/2)

Three main areas are studied: iodine interaction with paint; iodine oxide
formation in the gas phase; and iodine volatility in the sump in the
presence of impurities:

Also 2 relevant benchmarks, on Phébus FPT3 and on THAI Iod11/12:

For iodine volatility in the sump, the main use of the PSI data has been
internal in formulating the PSIodine code as indicated above; they are
also being used by the National Nuclear Laboratory (NNL) to validate
their INSPECT/IODAIR code:

The presence of iodine oxides, has been observed and/or deduced in
experiments such as EXSI (VTT/Chalmers cooperation), RTF, THAI
(specifically tests Iod13 and 14), Phébus FPT2 and PARIS:

Data being analysed from a modelling perspective by IRSN, VTT and NNL;

A review is promised by AECL;

Further experiments are planned in OECD/STEM, this project is now in progress;

These studies should enable improvements in the treatment of iodine oxides in the
major codes.
ERMSAR 2012, Cologne March 21 – 23, 2012
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Use of data (2/2)
BIP
30°C
ambient R.H.
Closed vessel
EPICUR
80 < T°< 120°C
15 % < R.H. < 60 %
Range of [I]ads
investigated in
the past
10-6
FPT0
10-5
FPT2
10-4
FPT3
10-3
10-2
10-1
[I]ads (mol/m²)
FPT1
Range of iodine
loadings used in
EPICUR and BIP in
comparison with
Phébus FP data and
likely reactor severe
accident conditions
R.H. = Relative Humidity
Representative cases of reactor accidents

The most active topic is interactions of iodine with paints, involving data from the
ISTP/EPICUR and OECD/BIP:




The challenge is to simulate satisfactorily the results of both ISTP/EPICUR (short term)
and BIP (longer exposure times) tests using the same modelling assumptions;
This is not yet achieved; work in progress by IRSN and CIEMAT with ASTEC, by KINS
with RAIM, by NNL with their more detailed code INSPECT/IODAIR;
Review by USNRC on iodine reactions in general; update of MAAP4 planned using
EPICUR data, and AECL will further develop their organic iodide formation models;
The database will be enlarged in OECD/STEM (extending the timescale of the EPICUR
tests and examining high iodine concentrations), in OECD/THAI2 (I absorption on
surfaces) and in OECD/BIP2 (OrgI production from polymers and iodinated compounds)
ERMSAR 2012, Cologne March 21 – 23, 2012
18
Conclusions

The improvement of models on iodine behaviour helps to reduce the
uncertainties in source term evaluations for safety studies:


Most activity is centred on the reaction of iodine with paints (ISTP/
EPICUR, OECD/BIP):



Modelling actively continues, as not yet possible to simulate data at both short and
long exposure times with the same model; substantial experimental work to cover
gaps in the database under way in the OECD programmes BIP2, STEM and THAI2
(all outside the SARNET2 framework, and extending beyond the end of that project);
Iodine oxide data are available from EXSI, RTF and THAI, modelling in
progress at VTT, IRSN etc.:


Several partners are making progress and some plan further activities in this area;
Again, further data are expected from projects outside SARNET, e.g. OECD;
The PSI sump volatility data are the basis for a detailed model on the
effects of impurities, with independent analysis by NNL;
These experiments are an invaluable resource for continually improving
major codes such as ASTEC and MELCOR, now and beyond the end of
SARNET2, such as in OECD projects
ERMSAR 2012, Cologne March 21 – 23, 2012
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Acknowledgements

The EPICUR experimental programme was conducted within the
framework of the International Source Term Program (ISTP),
launched by IRSN, CEA and EdF, with contributions from the European
Commission (EC), the US Nuclear Regulatory Commission, the Atomic
Energy of Canada Limited, Suez-Tractebel, the Paul Scherrer Institute
and the Korean Consortium;

The THAI tests Iod 9, Iod 11, Iod 12, Iod 13 and Iod 14 released to
SARNET were funded by the German Federal Ministry of Economics
and Technology in the frame of the German reactor safety research
project 1501272;

The authors would also like to thank L. Bosland (IRSN) for supplying
the figure that was the original basis for the last figure and B.
Clément (IRSN) and S. Dickinson (NNL) for their careful reviews of
this work.
ERMSAR 2012, Cologne March 21 – 23, 2012
20