Investigations on in-vessel melt retention by external cooling for a generic VVER-1000 reactor. (January 2015)

• Record Type: Journal Article
• Authors: Tusheva, P.; Altstadt, E.; Willschütz, H.-G.; Fridman, E.; Weiß, F.-P.
• Is Part Of: Annals of nuclear energy. Volume 75(2015:Jan.)
• Page Start: 249
• Page End: 260
• Publication Date: 2015-01
• Subjects: Corium -- In-vessel melt retention -- External flooding -- Segregated pool -- Heat transfer -- Finite element analysis; Nuclear energy -- Periodicals; Nuclear engineering -- Periodicals; 621.4805
• DOI: 10.1016/j.anucene.2014.07.044
• Languages: English
• ISSNs: 0306-4549

Abstract

Highlights: Analysis of in-vessel melt retention after station blackout for a generic PWR VVER-1000. FE-modelling of the thermal behaviour of a segregated molten pool. Parameter studies on the thickness of the metal layer of the molten corium. FE-modelling of the thermo-mechanical behaviour of the reactor pressure vessel. Abstract: External or internal hazards, combined with multiple failures of components and safety systems or human errors can lead to a reactor core melt. In that case the reactor pressure vessel is the last barrier to keep the molten materials inside the reactor and to prevent further challenges to the nuclear power plant structures and consequently to the environment. In-vessel melt retention by external vessel cooling is a possible mitigative severe accident measure. Up to the moment it is not considered as a severe accident management strategy for VVER-1000 reactors. In this paper we analyse the possibility of in-vessel melt retention for a generic pressurized water VVER-1000 reactor during the late in-vessel phase of a postulated station blackout scenario. We developed a numerical model describing the thermal behaviour of a segregated molten pool situated in the lower plenum of the reactor pressure vessel and the thermo-mechanic behaviour of the vessel wall. The finite element code ANSYS® was used for the simulations. The results show that the highest thermo-mechanical loads are observed in the vertical part of the vessel wall, which is in contact with the molten metal. Parameter studies on the thickness of the metal layer have also been performed. Without flooding, the vessel wall will fail, as the necessary temperature for a balanced heat release from the external surface via radiation is near to or above the melting point of the steel. However, the external flooding could help the retention of the corium within the reactor pressure vessel.