VICTOR HUGO SANCHEZ ESPINOZA and I. GÓMEZ-GARCÍA-TORAÑO IAEA Conference on Topical Issues in Nuclear Installation Safety: Safety Demonstration of Advanced Water Cooled Nuclear Power Plants, 6-9. June 2017 IAEA-CN-251 Analysis of PWR Severe Accident Sequences including Mitigative Measures to Prevent or Delay the Failure of Safety Barriers with the Severe Accident Code ASTEC VICTOR HUGO SANCHEZ ESPINOZA and I. GÓMEZ-GARCÍA-TORAÑO victor.sanchez@kit.edu

Content Motivation The European SA Reference Code ASTEC Selected Severe Accident sequences (with/without SAM) Conclusions and Outlook IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

Motivation Fukushima accidents showed necessity for review Re-evaluation of accident analysis methodologies Assessment of NPP safety status Review of SAMG Improvement of numerical simulation tools used for SAM e.g. ASTEC, MELCOR, etc. German activities in SA embedded in national (WASA-BOSS) and international projects (CESAM, FASNET, etc.) KIT participation of SAM-optimization for BWR within WASA-BOSS project KIT participation n SAM-optimization for PWR within EU CESAM project IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

The ASTEC Severe Accident Code IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

The European SA Reference Code ASTEC CPA Main Modules ICARE, CESAR, and CPA used in the PWR plant simulations ICARE CESAR Aim of code Explain the picture Modules that are important to us Features KIT contributed to the validation of Version 2.o and 2.1 using KIT facilities e.g. QUENCH, CORA IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

The ASTEC2.0 Simulation of PWR SA Sequences with and without SAMG IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

KIT Approach for PWR SA Simulations (1/3) Steps: Integral plant model Predict stationary plant conditions Extend model depending of scenarios Activate physical models for in-vessel phenomena IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

KIT Approach for PWR SA Simulations (2/3) Model Extension Reactor Protection System AM procedures Mobile equipment IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

KIT Approach for PWR SA Simulations (3/3) Physical phenomena: Chemical interactions Corium oxidation Material interactions (Ag-Fe-Ni-Zry) Movement of materials Stratification lower plenum Mechanical behaviour Vessel failure Core Ring 1 Core Ring 2 Core Ring 3 Core Ring 4 Core Ring 5 Core Ring 6

Investigated SA Scenarios with ASTEC2.0 IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

ASTEC V2.0 Simulations: Selected scenarios Medium Break LOCA (testing purposes) Small Break LOCA (risk core damage) Station Blackout (risk containment damage) Put the screen in white and do the bridge by word Hypotheses: No surge line failure No 100 K/h cooldown Passive seals MCPs No temp-induced SGTR I. Gómez García-Toraño, et. al (2017). Investigation of SAM measures during selected MBLOCA sequences along with Station Blackout in a generic Konvoi PWR using ASTECV2.0. Annals of Nuclear Energy, 105, 226–39. I. Gómez García-Toraño, et. al (2017). Analysis of primary bleed and feed procedures during selected SBLOCA sequences along with Station Blackout in a generic Konvoi PWR using ASTECV2.0. Annals of Nuclear Energy. Submitted. IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

Total Station Blackout Reference Sequence 6.14 RPV-failure at high P! 0.33 h: LL_SGA/B < 4 m 2.61 h: oxidation starts 3.4 h: Clad melting 3.84 h: first corium slump into LP 4.18 h: total core uncover IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

Total Station Blackout Potential Accident Management Measures (1/2) SAMGs SAMGs I. Gómez García-Toraño at. Al (2017) Assessment of selected SAM measures during a Station Blackout in a generic Konvoi PWR using ASTECV2.0. Annals of Nuclear Energy. Submitted. ~ 120 simulations performed IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

Total Station Blackout Potential Accident Management Measures (2/2) Reflooding with mobile equipment IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

Total Station Blackout Core Reflooding (after PSD) IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

Total Station Blackout Core Reflooding (after PSD) ✓ ✓ IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

Total Station Blackout Core reflooding (after PSD) ✓ ✓ Deployment order of mobile pumps within 1 h after SBO to prevent melting! IAEA Conference on Topical Issues in Nuclear Installation Safety, 6-9. June 2017

Conclusions Contribution to further development of SAMGs in Konvoi PWR Demonstration of ASTEC V2.0 capabilities to perform severe accident analysis in PWR Robustness, numerical stability (Version 2.1 is even better), etc. Contribution to further development of SAMGs in Konvoi PWR PBF should be initiated at CET=400 °C or with a 20 min delay by means of all pressurizer valves to delay vessel failure Reflooding should be started when CET=650 °C is reached with injection rates > 20 kg/s to prevent RPV-failure must occur 20-30 min before 20 ton of corium has been relocated into the LP to prevent RPV failure regardless of injected mass flow rate Outlook: Repeat plant simulations with latest ASTEC V2.1 using converted models (2.0 to 2.1) Strong cooperation with code developers and other R&D institutions needed KIT provide experimental data (QUENCH BWR, LIVE) for code validation