Investigation of Fuel Melt and Grid Plate Interaction Moments After CDA in FBRs

Abstract

During core disruptive accident (CDA) in a typical medium-sized fast breeder reactor (FBR), a significant amount of corium (core melt) relocates to the bottom plate of the grid plate after melting structures above it. The ability of the bottom plate to resist or delay relocation has been investigated in the current study. The effect of corium entrapped between subassembly (SA) foot and sleeve is analyzed in addition to which stays over bottom plate. Melt-through of the sleeve is also studied along with a bottom plate to investigate the relative melting rates of both. Towards this, a computer code has been developed in FORTRAN 90 which solves two-dimensional transient energy equations to analyze melting of bottom plate in both radial and axial directions. It is found that there is no melting of the bottom plate happening in the radial direction. This is due to the lesser heat capacity of core melt entrapped in clearance compared to the melt settled over the surface of the bottom plate. It is also found from these studies that due to the faster melting of the sleeve compared to the bottom plate, the melt-through time of a bottom plate reduced significantly. This is due to the melting of relatively thinner sleeves earlier compared to the bottom plate of the grid plate.