ERMSAR 2012, Cologne March 21 – 23, 2012 Source term assessment with ASTEC and associated uncertainty analysis using SUNSET tool K. Chevalier-Jabet 1, F. Cousin 1, L. Cantrel 1, C. Séropian 1 (1) IRSN, Cadarache

ERMSAR 2012, Cologne March 21 – 23, 2012 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 1

ERMSAR 2012, Cologne March 21 – 23, 2012 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 2

ERMSAR 2012, Cologne March 21 – 23, 2012 Joint IRSN/GRS development from Provides models for most phenomena of a severe accident  enables source term assessment 2.Integrates up-to date models developed on the basis of R&D programs  enables uncertainty analysis in association with SUNSET tool 3

ERMSAR 2012, Cologne March 21 – 23, 2012 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 4

ERMSAR 2012, Cologne March 21 – 23, 2012 Iodine behaviour models of ASTEC In RCS : iodine speciation  modelled with SOPHAEROS module : chemical speciation, retention, aerosol size distribution  Lack of knowledge on thermodynamic/thermokinetics properties Impacts the iodine gaseous mass fraction at the break : CHIP experiment, (T.Haste Presentation S3.1 ) ; [ 5% -> 95%] 5

ERMSAR 2012, Cologne March 21 – 23, 2012 Iodine behaviour models of ASTEC In containment : modelled with IODE module 1. Species accounted for :  GAS : I, CH3I, I2, HI, IO3  SUMPS : I-, IO3-, I2, CH3I, AgI, HIO  Aerosols computed by CPA 2. Reactions accounted for : mass transfer, thermal reactions, radiolytic reactions Lack of knowledge :  Organic iodides formation/release rate : uncertainty range ~2 decades  related to iodide oxides behaviour:  Ozone production rate influence : uncertainty range ~2 decades  iodide oxides deposition rate : uncertainty range [1  4] factor 6

ERMSAR 2012, Cologne March 21 – 23, 2012 The competition between formation/destruction phenomena governs the volatile iodine amount in the containment Liquid phase Volatile species are transferred to the gaseous phase (I 2, RI) Ag 2 O 2 O AgI(  ) Ag (  If Ag is present, iodides ions can form insoluble compounds (AgI…) Gaseous phase A trapped fraction of I 2 is converted into RI, that are destructed into IO x I 2 reacts with surfaces (adsorption, desorption) Iodide ions are oxidized by water radicals (OH ° ) and form I 2 that can be hydrolised, adsorbed on immersed paint, or react with organics in solution to form organic iodides RI  ROH H 2 O OH - R RI  ROH H 2 O OH - R -  IO 3 I H 2 O HOI  3 I H 2 O  2 aerosol type pH M Ag /M I Th. conditions of the sump  ½ ½ % I gaseous /I tot I- Iodine aerosols sediment and settle on walls. If soluble (CsI…), they form iodide ions (I-) in the aqueous phase. The insoluble aerosols (AgI…) stay in the bottom of the sump gazeux aérosols I I circuit Iodine oxides sediment and settle on the surfaces (walls, surface developed by aerosols in suspension) Volatile iodine reacts with air radiolytic products, and oxidizes a fraction of I 2 and RI => formation of iodine oxides (considered as fine particles) RI O IO 3 3 H 2 O (v) IO 3 3 H 2 O (v)  K ads /k des I 2 7

ERMSAR 2012, Cologne March 21 – 23, 2012 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 8

ERMSAR 2012, Cologne March 21 – 23, 2012 SOURCE term assessment for a 1300 MWe PWR : various scenarios SEQUENCES Containment Spray System Safety Injection ISMP Safety Injection Low Pressure Break location Loss of feedwater in steam generator – 1 lost at 1 dayNO Direct mode only Hot Leg Loss of feedwater in steam generator – 2 NO Direct mode only Hot Leg Loss of coolant break size of 12 ’’ NO Direct mode only Cold Leg Loss of coolant break size of 2’’ NO Cold Leg Source term computation : full accidental scenario computation Uncertainty assessment for this scenario 9

ERMSAR 2012, Cologne March 21 – 23, 2012 Scenario related variability Depending on the scenario the iodine release ranges from ~0.1g to ~5g. Loss FWSG ; CSS Loss FWSG ; no CSS 12’’ LOCA2’’ LOCA RCS Retention : 53% Initial gaseous fraction at the break : 7.2 % RCS Retention : 55% Initial gaseous fraction at the break : 2 % RCS Retention : 9% Initial gaseous fraction at the break : 10 % 10

ERMSAR 2012, Cologne March 21 – 23, 2012  0 h 20 minPrimary motopumps shutdown  2 h 29 minSafety injections starting  2 h 40 minSteam generator isolation  2 h 46 minPressuriseur POR Valves opening  2 h 56 minStart of SM release  3 h 6 minAccumulators discharge  3 h 7 minStart of FP release  4 h 3 minSafety injections lost  6 h 10 minTotal dewatering of core  7 h 11 minVessel rupture  ~ 3 daysFiltered containment venting system activation  ~ 6 daysBasemat rupture Uncertainty assessment scenario : loss of FWSG without CSS 11

ERMSAR 2012, Cologne March 21 – 23, 2012 XiXi XnXn X1X1   Y p (  Xi Yp Uncertainties Sensitivity LHS sampling Astec runs over sampled variables Sunset uncertainty assessment and sensitivity assessment SUNSET 12

ERMSAR 2012, Cologne March 21 – 23, 2012  The majority of the release is due to FCV  Uncertainty range ~20 at least (to be compared to scenario variability)  Most influent parameters  gaseous iodine mass fraction  iodide oxides deposition rate  To a lesser extent,  organic formation rate in the containment gas phase  ozone formation reaction rate 3.8 g 84 g 13

ERMSAR 2012, Cologne March 21 – 23, 2012 Source term computation : full accidental scenario computation The release after containment venting is due to gaseous species Containment filtered venting 14

ERMSAR 2012, Cologne March 21 – 23, 2012 Source term computation : full accidental scenario computation During core degradation, iodine species in the containment are essentially iodine oxides and molecular iodine 15

ERMSAR 2012, Cologne March 21 – 23, 2012 Source term computation : full accidental scenario computation At 1 day iodine oxides prevail for all situations 16

ERMSAR 2012, Cologne March 21 – 23, 2012 Source term computation : full accidental scenario computation 3 bodies system 17

ERMSAR 2012, Cologne March 21 – 23, 2012 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 18

ERMSAR 2012, Cologne March 21 – 23, 2012 Conclusion  Uncertainties on iodine phenomenology knowledge have an important impact, in the same order of magnitude as the variability due to the scenario.  Gaseous iodine mass fraction and iodine oxide mass deposition rate are the major contributors to these uncertainties  To a lower extent organic iodides formation rate and ozone formation rate have contributions of some importance.  These results confirm that the R&D efforts made by IRSN together with many partners in the ISTP and SARNET frames are focused on key issues. 19

ERMSAR 2012, Cologne March 21 – 23, 2012 Conclusion  Sensitivity analysis module of SUNSET helps to establish ranking of the studied effects, disregarding the complexity of the problem.  Regarding uncertainty propagation, interesting complements of this study – The addition of other epistemic uncertainties would be of some interest, as the ones related to MCCI – introduction of stochastic uncertainties, and the combined analysis of both epistemic-stochastic influences 20

ERMSAR 2012, Cologne March 21 – 23, 2012 Thank you for your attention

ERMSAR 2012, Cologne March 21 – 23, 2012 ADDITIONAL SLIDES

ERMSAR 2012, Cologne March 21 – 23, 2012 Source term computation : full accidental scenario computation 1 day2 days3 days6 days Iodine gaseous mass fraction at primary circuit break Iodine oxides deposition rate in containment Organic iodine formation rate in containment atmosphere Organic iodine formation rate in containment sumps Organic compound release rate in containment atmosphere Organic compound release rate from sumps Ozone formation rate (forward reaction) Ozone formation rate (backward reaction) Table of partial correlation coefficients for iodine release in environment vs. the different uncertain parameters

ERMSAR 2012, Cologne March 21 – 23, 2012 Source term computation : full accidental scenario computation table of partial correlation coefficient for different iodine amounts in the containment versus the iodine partition at the primary break Effect of gaseous mass fraction on iodine amount at … 1 day2 days6 days in/on … Immerged surfaces Emerged surfaces Gas phase (organic iodine) Gas phase (molecular iodine) Gas phase (Iodine oxides) Sumps (I - ) Sumps (iodine oxides) Sumps (molecular iodine) Sumps (organic iodine) Sumps (AgI)

ERMSAR 2012, Cologne March 21 – 23, 2012 ASTEC models the transport in the reactor coolant system (RCS) of vapours and aerosols formed by condensation of material released from the degraded core.  Computes retention of radionuclides in the RCS  Computes aerosol size distribution and chemical speciation of aerosol and vapour phases along the RCS  Deals with the speciation of approximately 800 species

ERMSAR 2012, Cologne March 21 – 23, 2012 Liquid phase  hydrolysis of I 2 and RI  disappearance of HOI  oxidation of I - by O 2  reactions with Ag  formation of RI Thermal reactions : Gas phase  oxidation of I 2 by O 3 in I x O y  formation of RI Radiolytic reactions : Liquid phase  oxidation of I - in I 2  radiolytic reduction of IO 3 -  formation/destruction of RI Gas phase  formation/destruction of RI in I y O x  formation of O 3 Mass transfer processes : Liquid – gas (I2, IO3-, RI) Liquid – surfaces (I 2 : steel, paint, concrete) Gas – surfaces (I 2 : steel, paint, concrete) ASTEC a SA integral code : presentation of FP related modules – chemistry in containment

ERMSAR 2012, Cologne March 21 – 23, 2012 Uncertainty distributions Uncertain variableDistribution Gaseous iodine mass fraction at primary circuit breakUniform law [min = 0.05; max = 0.95] Iodine oxides deposition rate in containmentMultiplying factor of the default value (16h -1 ): uniform law [min = 0.5 ; max = 2] ; Ozone formation rates (forward and backward reactions)Multiplying factor of the default kinetics constants: Log normal law [ µ = 0 ;  1 ] ; Organic iodine formation rate in containment atmosphere and sumps Multiplying factor of the default kinetics constant: Log normal law [ µ = 0 ;  1 ] ; Release rate from paints of organic compounds that may react with molecular iodine in containment atmosphere and sumps to form organic iodides Multiplying factor of the default kinetics constant: Log normal law [ µ = 0 ;  1 ] ; Method : Latin Hypercube, size = 100

ERMSAR 2012, Cologne March 21 – 23, 2012 Source term computation : full accidental scenario computation Source Term Sand bed filter Chimney Containment Auxiliary building Direct Containment leak Direct leak (no filtering) U5 french procedure Leak to EEE (90 %) Double containment EEE (PWR 1300 and 1450) Iodine Filter Filtered leak No filtered leak Filtered leak Iodine Filter Filtered and direct leaks to environment

ERMSAR 2012, Cologne March 21 – 23, 2012 Scenario related variability  Aerosols masses in environment are significant as long as the CSS does not work  For a LFWSG, the gaseous release is higher when CSS does not work  The location of the break has a strong influence on RCS retention  Depending on the scenario the iodine release ranges from ~0.1g to ~5g.  The gaseous mass fraction at primary break is a function of break size, location and other scenario effects.  The calculated gaseous iodine mass fraction seems to be low, though, especially when compared to the orders of magnitudes obtained in PHEBUS experiments, which confirms the importance of the on-going CHIP experiments in the frame of the ISTP program [5]. Loss FWSG ; CSS Loss FWSG ; no CSS 12’’ LOCA2’’ LOCA RCS Retention : 53% Gaseous fraction : 7.2 % RCS Retention : 55% Gaseous fraction : 2 % RCS Retention : 9% Gaseous fraction : 10 %