Coupled Analysis of Fuel Debris Distribution and Recriticality by both Multiphase/Multicomponent Flow and Continuous Energy Neutron Transport Monte Carlo Simulations

Abstract

To reveal the melting behaviors of core internals mechanistically and to reduce the uncertainties of existing severe accident analysis codes, a numerical simulation code for melt relocation and accumulation behaviors based on computational fluid dynamics named JUPITER has been developed by JAEA. In this paper, we performed a simulation of the accumulation and spreading of a melt to the pedestal region of a typical BWR containment vessel by JUPITER to consider a method for estimating the fuel debris composition. We performed recriticality analysis by the continuous energy neutron transport Monte Carlo code MVP using detailed fuel debris composition data obtained by JUPITER to evaluate recriticality for fuel debris. It was revealed that JUPITER has the potential to obtain a com-plicated fuel debris distribution mechanistically. Also, in effective multiplication factor analyses, we investigated the effect of parameters （ uranium enrichment, water content ratio and partitioning resolution in MVP analysis ） on the effective multiplication factor. It was also revealed that the partitioning resolution is one of the most important factors in JUPITER-MVP coupled analysis, and an appro-priate partitioning according to the inhomogeneity of the fuel debris distribution obtained by JUPITER will be very important.