The modeling of reactor pressure vessel failure modes during core meltdown accidents of BWRs

The consequences of core meltdown accidents strongly depend on whether the reactor pressure vessel (RPV) fails when in contact with molten corium and, if so, what the timing and modes of the failure are. In particular, the proper modeling of the events which may lead to the vessel failure is very important for obtaining a realistic assessment of the fission product release for source term evaluations. The purpose of this paper is to present the overall model of the phenomena expected to occur in the lower plenum of a BWR following the hypothetical release of molten debris from the reactor core. Mechanistic models have been developed for the heat transfer and phase change phenomena between the melt, solid vessel structures and any water which may be present. The present model was extensively tested and implemented in the APRIL computer code, where it interacts with other in-vessel and out-of-vessel models.