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ASTEC validation on PANDA tests

ASTEC validation on PANDA tests. A. BENTAIB , A. BLEYER Institut de Radioprotection et de Sûreté Nucléaire BP 17, 92262 Fontenay aux Roses Cedex, FRANCE. B. ATANASOVA INRNE-BAS Tzarigradsko shossee 72, 1784 Sofia, BULGARIA. Outline. Motivation. PANDA T9, T9bis and T25 analysis.

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ASTEC validation on PANDA tests

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  1. ASTEC validation on PANDA tests A. BENTAIB , A. BLEYERInstitut de Radioprotection et de Sûreté Nucléaire BP 17, 92262 Fontenay aux Roses Cedex, FRANCE B. ATANASOVA INRNE-BAS Tzarigradsko shossee 72, 1784 Sofia, BULGARIA

  2. Outline • Motivation • PANDA T9, T9bis and T25 analysis • Conclusions & perspectives

  3. H2 risk issues: Pressurized Water Reactors • 3 barriers between radioactive materials and • environment (« Defense in depth » principle) : • • Combustible clads • • Primary Circuit • • Containment • Volume : 50000 to 80000 m3 depending of thetype • Length scale : some cm to several meters • Double concrete containment or simple concretecontainment with liner (steel or composite)

  4. H2 Risk Issues: Pressurized Water Reactors Severe Accident: A severe accident is characterized by a reactor core uncovery leading to core degradation and Fission Products release into the containment atmosphere (loss of the two first barriers) Four main Phases : • Loss of Fuel coolantphase in the primarycircuit •Core uncovery and coredegradation phases • Core melt-throughandreactor core vessel failure • Core concreteinteraction and base mat penetration

  5. Hydrogen Risk evaluation for PWR: Needs • the composition of the gaseous mixture inside the containmentat each location and at each time (Distribution) • the effect of the mitigation means as spray, catalytic recombiners(Mitigation) • an estimation of the possible ignition of the gaseous mixture (Flammability limits) • an evaluation the propensity of a premixed flame to propagate inside thecontainment (Flame acceleration criteria) • the pressure and temperature loads due to combustion eventsinside the containment (Combustion)

  6. ASTEC : Accident Source Term Evaluation Code IRSN/GRS cooperation since 1996 for development of an integral code for LWR (present/future PWR, BWR, VVER) source term severe accident (SA) calculation • Main objectives: • Applications to PSA2, including uncertainty analysis, • Accident management studies, • Investigations of NPP behaviour in SA cond., including source term evaluation, • Support and interpretation of experiments, • Basis for a better understanding of SA physical phenomena. • Main requirements: • Comprehensive coverage of phenomena, account for their interactions. • "Reasonable" calculation time (fast-running code)  < 12h CPU for one day of accident simulated, • Accounting for safety systems and their availability (SAM), • High level of model validation, • Modularity, flexibility, user-friendliness, easy model incorporation. => ASTEC aim : becoming the european reference code for Severe Accidents

  7. Example of experimental programs in support of ASTEC validation TOSQAN (IRSN) ThAI (BT) MISTRA (CEA) PANDA (PSI) 7 m3 60 m3 100 m3 480 m3 Addressed phenomena : Condensation, Gas and Thermal stratification , stratification break-up, Spray effect, Scaling effect

  8. PANDA facility Operated by Paul Scherrer Institute (Switzerland) SETH configuration : Dimensions : Height 8 m, diameter 3.957 m, volume about 180 m³ Materials: Steel walls instrumentation: more than 275 TC and 47 sampling points for MS measurements

  9. Experiments • Main addressed phenomena • Steam and non-condensable gases mixing behavior • Thermal stratification phenomena • Characteristic of gas transportation between compartments • Steam condensation on the walls • Injection location effect

  10. PANDA nodalizationnear wall injection configuration • 50 zones • 10 vertical levels • Zones connected by flowpaths with area according geometry • Structures: heat exchange with atmosphere, condensation, heat capacity, heat losses to environment

  11. Test 9 and Test 9bis analysis • In the early phase the amount of steam is for both tests comparable over the Vessel 1 height • Later on, due to the on-set of condensation in Test 9bis the steam concentration at the top of vessel increases faster in Test 9 • Due to the evaporation of condensate water, steam concentration in lower becomes higher in test9bis

  12. Test 9bis: steam concentration (DW1) the condensate water drained to the lower part of DW1 leads to a sharp decrease of gas temperature at 4000 seconds. Afterwards and due to the difference between gas and wall temperature, steam evaporation occurs and generates an increase of gas temperature and steam concentration in the bottom of DW1

  13. Thermal stratification in DW1 Until 3000 s, the increase of gas temperature is comparable for both tests For test 9bis and after 3000 s, steam condensation induces a strong heat transfer and an increase of wall and gas temperature

  14. Thermal stratification in DW2

  15. Steam transport in IP steam is transported mainly in the top of the interconnecting pipe The on-set of condensation in Test 9bis determines similar observation as in Vessel 1

  16. Steam transport to DW2 • Sharp steam stratification is observed during the overall test period, between the regions above and under the interconnecting pipe height • The on-set of condensation in Test 9bis determines similar observation as in Vessel 1

  17. Steam at the venting location Until 3000 s, steam concentration at venting location is compared for both tests After 3000 s, The on-set of condensation in Test 9bis determines similar observation as in Vessel 1, Vessel 2 and IP.

  18. PANDA nodalizationcentral injection configuration ww • 53 zones with 12 vertical levels • Zones connected by flowpaths with area according geometry • Structures: heat exchange with atmosphere, condensation, heat capacity, heat losses to environment

  19. Test 25 analysis : pressure time evolution • Predicted pressure, gas composition and temperature in the vent are in good agreement with data

  20. Test 25 analysis: 1st Phase (time <815s)

  21. Test 25 analysis 1st Phase (2215<time <2815s)

  22. Test 25 analysis 1st Phase (4415<time <7015s)

  23. Test 25 analysis 2nd Phase (7415<time <14215s)

  24. Conclusions Results on gas temperature and gas concentration obtained with the ASTEC code for both tests T9, T9bis and Test25 are in good agreement with the experimental data: • gas mixing and stratification above and under the height of the DW interconnecting pipe have been well reproduced by the code. • the steam condensation effect on the thermal and the concentration front propagation in the two drywells and the interconnecting pipe have been well predicted by the calculation

  25. Conclusions The Astec validation process will continue by considering well instrumented experiments to check the effect of facility scale and to prepare rules and recommendations to best use of LP codes for reactor applications

  26. Thank you for your attention

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