Operation Extension of 900MWe NPPs: French TSO Main Conclusions regarding Long Term Sump Performance after a Loss of Coolant Accident

Jean-François Trigeol (1) , Pariaud Emilie (1) , Dixneuf Estelle (2) , Georges Repetto (3)

1 IRSN/PSN-EXP/SSyR/BECS - Bureau d'Evaluation de la Conception et du Fonctionnement des Systèmes
2 IRSN/PSN-EXP/SHOT - Service Homme Organisation Technologie
3 IRSN/PSN-RES/SIPR - Service de l'Ingénierie et des Projets de Recherche

During a Loss Of Coolant Accident (LOCA), water is injected by the Emergency Core Cooling System (ECCS) to ensure the long-term core coolability and by the Containment Spray System (CSS) to remove residual heat and to maintain containment integrity. After the drainage of the RWST (Refueling Water Storage Tank), water is taken from the containment sump in the lower part of the nuclear reactor building. A filtering system is implemented at the bottom of the containment to collect debris produced by the pipe break and the degradation of the ambient conditions inside the reactor building, and to minimize the amount of debris entering in the ECCS and CSS systems. Consequently, one of the major issues is the clogging of the filtering system due to physical and chemical conditions which can lead to an inadequate net positive suction head (NPSH) margin for the ECCS and CSS pumps and can affect the mechanical integrity of the strainers. Furthermore, despite the filtering system, a part of the debris bypassing the strainers is transported to the core. That might alter the fuel assembly coolability (downstream effects), which constitutes the second major issue. Since the Baresbäck incident in Sweden in 1992, which raised questions concerning the risk of strainers clogging at international level, sump performance has become a major concern in France, where this issue is common to all NPPs. In the framework of the operation extension of the French 900MWe NPPs beyond 40 operating years, EDF presented its safety demonstration based on studies and new experimental program on strainer clogging and fuel assembly coolability. IRSN conducted the evaluation of the EDF safety case and performed simultaneously its own tests on the VIKTORIA loop in Slovakia. IRSN provided its technical position in March 2020. The paper will present the French background and French Technical Safety Organization (IRSN) conclusions on sumps performance issue for the 4th periodic safety review of 900MWe NPPs dated the end of March, 2020.

Mots clés: Long term coolability LOCA sump filters clogging debris head losses; Long term coolability; LOCA; sump filters clogging; debris; head losses

Domaines: Sciences de l'ingénieur [physics]

Jean-François Trigeol, Pariaud Emilie, Dixneuf Estelle, Georges Repetto. Operation Extension of 900MWe NPPs: French TSO Main Conclusions regarding Long Term Sump Performance after a Loss of Coolant Accident. RCCS - 2021 - Specialist Workshop on Reactor core and containment cooling systems – long term management and reliability, OECD/NEA, Oct 2021, Virtual (on line), Slovakia. 5 p. ⟨irsn-04113763⟩