ermsar 2012, cologne march 21 – 23, 2012 containment iodine experiments in the sarnet2 project t....

ERMSAR 2012, Cologne March 21 – 23, 2012

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 2

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

Introduction


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

EPICUR (1/2)


EPICUR (2/2)

On-line measurements for a 30 hr duration irradiation test in EPICUR

Results show that: 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

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

0 10 20 30

Time (hours)

To

tal i

od

ine

fra

ctio

n t

ran

sfer

ed o

n t

he

filt

er s

tag

es

Knit-mesh (First + Second)

Impregnated charcoal

Quartz fiber filter


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.

Chalmers (1/2)


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:― 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;

Paint as an ab/adsorber: 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.

Chalmers (2/2)


VTT/Chalmers – NROI (Nordic research on Radiolytical Oxidation

of Iodine)

DMA + CPC

FTIR

Reaction and sampling furnaces

Gas traps

Control unit

ELPI TEOM


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

VTT/Chalmers – NROI: Experiments


Instant and extensive particle formation:

Increased with:

– Ozone concentration;

– UV intensity;

– Temperature;

Humidity: Increased size of particles;

Agglomeration important => Particle size increased when residence time was increased

0 1 5 10

No UVC

High UVC0

250

500

Particle mass

(mg/m3)

Ozone level

120 °C

No UVC

1.0E-06

1.0E-04

1.0E-02

1.0E+00

1.0E+02

0 1 10

ozone levels

mo

l Io

din

e p

art

icle

s/m

ol i

od

ine

g

as

Dry

Humid

VTT/Chalmers – NROI: Results/Conclusions


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.

PSI sump chemistry studies - Introduction


New PSI experimental data on the effect of nitrate and nitrite ions on iodine volatilization

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

Sharp increase at 3.7 kGy dose: potential consumption of all the nitrite ions by conversion to nitrate ions by oxidation

PSI sump chemistry studies - Data


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.

PSI sump chemistry studies - Conclusions


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)


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

14

Results of THAI tests Iod-13 and Iod-14: http://dx.doi.org/10.1016/j.nucengdes.2012.01.005


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

AECL – RTF (1/2)

0.0E+00

1.0E-06

2.0E-06

3.0E-06

4.0E-06

5.0E-06

6.0E-06

7.0E-06

8.0E-06

9.0E-06

0 50 100 150 200 250 300 350 400

Time (h)

Con

cen

trat

ion

(m

ol/d

m3 )

Temperature increased to 60oC Temperature increased to 80oC pH to 5 pH to 9

0.0E+00

5.0E-11

1.0E-10

1.5E-10

2.0E-10

2.5E-10

3.0E-10

0 50 100 150 200 250 300 350 400

Time (h)

Con

cen

trat

ion

mol

/dm

3

[I]gas (On-line)

[I]gas (Off-line)

Temperature increased to 60oC Temperature increased to 80oC

Total gas phase iodine concentration Total aqueous phase iodine concentration


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.

AECL – RTF (2/2)


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.


Use of data (2/2)

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)

10-5 10-4 10-3 10-2 10-1 [I]ads (mol/m²) 10-6

BIP 30°C

ambient R.H. Closed vessel

EPICUR 80 < T°< 120°C

15 % < R.H. < 60 %

Representative cases of reactor accidents

FPT0 FPT2 FPT3

FPT1

Range of [I]ads investigated in

the past

R.H. = Relative Humidity

Range of iodine loadings used in EPICUR and BIP in comparison with Phébus FP data and likely reactor severe accident conditions


Conclusions

The improvement of models on iodine behaviour helps to reduce the uncertainties in source term evaluations for safety studies:

Several partners are making progress and some plan further activities in this area;

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.:

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


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.