Source term assessment with ASTEC and associated uncertainty analysis using SUNSET tool

Transcription

1 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

2 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 1

3 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 2

4 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

5 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 4

6 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%] WALL Sorbtion cooler Condensation Deposition Inlet flow Supersaturated vapours Aerosol Gas phase Nucleation chemical reactions Agglomeration Release 5

7 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: 1. Ozone production rate influence : uncertainty range ~2 decades 2. iodide oxides deposition rate : uncertainty range [1 4] factor 6

8 aerosol type % I gaseous /I tot 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 I gazeux I aérosols Volatile iodine reacts with air radiolytic products, and oxidizes a fraction of I 2 and RI => formation of iodine oxides (considered as fine particles) O 3 IO 3 H 2 O (v) I 2 Gaseous phase g RI K ads /k des I 2 reacts with surfaces (adsorption, desorption) Iodine oxides sediment and settle on the surfaces (walls, surface developed by aerosols in suspension) 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 ph If Ag is present, iodides ions can form insoluble compounds (AgI ) I- Ag 2 O IO 3 HOI AgI ( ) - 3 g g H 2 O I 2 Ag R g Liquid phase RI H 2 O OH - ROH t ½ A trapped fraction of I 2 is converted into RI, that are destructed into IO x Volatile species are transferred to the gaseous phase (I 2, RI) Th. conditions of the sump M Ag /M I The competition between formation/destruction phenomena governs the volatile iodine amount in the containment 7

9 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 8

10 Source term computation : full accidental scenario computation 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 day NO Loss of feedwater in steam generator 2 NO NO Loss of coolant break size of 12 Loss of coolant break size of 2 NO Direct mode only Direct mode only Direct mode only Direct mode only Hot Leg Hot Leg Cold Leg NO NO NO Cold Leg Uncertainty assessment for this scenario 9

11 Scenario related variability 12 LOCA 2 LOCA Loss FWSG ; CSS Loss FWSG ; no CSS 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 % Depending on the scenario the iodine release ranges from ~0.1g to ~5g. 10

12 Uncertainty assessment scenario : loss of FWSG without CSS 0 h 20 min Primary motopumps shutdown 2 h 29 min Safety injections starting 2 h 40 min Steam generator isolation 2 h 46 min Pressuriseur POR Valves opening 2 h 56 min Start of SM release 3 h 6 min Accumulators discharge 3 h 7 min Start of FP release 4 h 3 min Safety injections lost 6 h 10 min Total dewatering of core 7 h 11 min Vessel rupture ~ 3 days ~ 6 days Filtered containment venting system activation Basemat rupture 11

13 SUNSET Uncertainties a= 0.5, X 1 Y p (a) Yp X i Sensitivity Xi X n XnYp corr ( X n, Y p ) = Xn Yp LHS sampling Astec runs over sampled variables Sunset uncertainty assessment and sensitivity assessment 12

14 Iodine in environment (kg) 7.0E E E E E E E E+00 1E+00 1E-01 1E-02 1E-03 1E-04 1E-05 Iodine in environment (percentiles) Time (s) 84 g 3.8 g minimum 5% percentile median 95% percentile maximum 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 13

15 Iodine aerosol mass (kg) 0.0E E+05 Source term computation : full accidental scenario computation Source term computation : full accidental scenario computation 2.0E E E E E E+05 Gaseous Iodine mass (kg) 0.0E E E E E E E E+05 Iodine aerosols masses in containment (percentiles) Total gaseous iodine mass in containment (percentiles) 1.E E+02 1.E+01 1.E+00 1.E-01 minimum 5% percentile median 95% percentile maximum 1.00E E E-01 1.E-02 1.E-03 1.E E E E-04 minimum 5% percentile median 95% percentile maximum 1.E E-05 Time (s) Containment filtered venting Time (s) Containment filtered venting The release after containment venting is due to gaseous species 14

16 IxOy mass fraction 0.0E E+05 Source term computation : full accidental scenario computation Source term computation : full accidental scenario computation 2.0E E E E E E+05 I2 mass fraction 0.0E+00 CH3I mass fraction 0.0E E E E E E E E E E E E E E E+05 IxOy mass fraction in containment gas phase (percentiles) I2 mass fraction in containment gas phase (percentiles) 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 2E-01 1E-01 1E-02 minimum 5% percentile median 95% percentile maximum 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 2E-01 1E-01 1E-02 minimum 5% percentile median 95% percentile maximum Time (s) CH3I mass fraction in containment gas phase (percentiles) Time (s) During core degradation, iodine species in the containment are essentially iodine oxides and molecular iodine 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 2E-01 1E-01 1E-02 minimum 5% percentile median 95% percentile maximum Time (s) 15

17 IxOy mass fraction 0.0E E+05 Source term computation : full accidental scenario computation Source term computation : full accidental scenario computation 2.0E E E E E E+05 I2 mass fraction 0.0E+00 CH3I mass fraction 0.0E E E E E E E E E E E E E E E+05 IxOy mass fraction in containment gas phase (percentiles) I2 mass fraction in containment gas phase (percentiles) 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 2E-01 1E-01 1E-02 minimum 5% percentile median 95% percentile maximum 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 2E-01 1E-01 1E-02 minimum 5% percentile median 95% percentile maximum Time (s) CH3I mass fraction in containment gas phase (percentiles) Time (s) At 1 day iodine oxides prevail for all situations 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 2E-01 1E-01 1E-02 minimum 5% percentile median 95% percentile maximum Time (s) 16

18 IxOy mass fraction 0.0E E+05 Source term computation : full accidental scenario computation Source term computation : full accidental scenario computation 2.0E E E E E E+05 I2 mass fraction 0.0E+00 CH3I mass fraction 0.0E E E E E E E E E E E E E E E+05 IxOy mass fraction in containment gas phase (percentiles) I2 mass fraction in containment gas phase (percentiles) 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 2E-01 1E-01 1E-02 minimum 5% percentile median 95% percentile maximum 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 2E-01 1E-01 1E-02 minimum 5% percentile median 95% percentile maximum Time (s) CH3I mass fraction in containment gas phase (percentiles) Time (s) 3 bodies system 9E-01 8E-01 7E-01 6E-01 5E-01 4E-01 3E-01 minimum 5% percentile median 95% percentile maximum 2E-01 1E-01 1E-02 Time (s) 17

19 CONTENTS 1. Assessing source term with ASTEC 2. Iodine related models and associated uncertainties 3. Source term assessment 4. Conclusion 18

20 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

21 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

22 Thank you for your attention

23 ADDITIONAL SLIDES

24 Source term computation : full accidental scenario computation Source term computation : full accidental scenario computation 1 day 2 days 3 days 6 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

25 Source term computation : full accidental scenario computation Source term computation : full accidental scenario computation Effect of gaseous mass fraction on iodine amount at 1 day 2 days 6 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) table of partial correlation coefficient for different iodine amounts in the containment versus the iodine partition at the primary break

26 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 WALL Sorbtion cooler Condensation Deposition Inlet flow Supersaturated vapours Aerosol Gas phase Nucleation chemical reactions Agglomeration Release

27 ASTEC a SA integral code : presentation of FP related modules chemistry in containment 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 : Radiolytic reactions : Gas phase oxidation of I 2 by O 3 in I x O y formation of RI 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)

28 Uncertainty distributions Uncertain variable Distribution Gaseous iodine mass fraction at primary circuit break Uniform law [min = 0.05; max = 0.95] Iodine oxides deposition rate in containment Ozone formation rates (forward and backward reactions) Organic iodine formation rate in containment atmosphere and sumps 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 value (16h -1 ): uniform law [min = 0.5 ; max = 2] ; Multiplying factor of the default kinetics constants: Log normal law [µ = 0 ; = 1 ] ; Multiplying factor of the default kinetics constant: Log normal law [µ = 0 ; = 1 ] ; Multiplying factor of the default kinetics constant: Log normal law [µ = 0 ; = 1 ] ; Method : Latin Hypercube, size = 100

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

30 Scenario related variability 12 LOCA 2 LOCA Loss FWSG ; CSS Loss FWSG ; no CSS RCS Retention : 53% RCS Retention : 55% Gaseous fraction : 7.2 % Gaseous fraction : 2 % Aerosols masses in environment are significant as long as the CSS does not work RCS Retention : 9% Gaseous fraction : 10 % 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 ERMSAR seems to 2012, be low, Cologne though, especially March 21 when 23, compared 2012 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].