Post-dryout heat transfer in a multi-dimensional porous bed

Abstract

Post-dryout behavior of a particulate debris bed was investigated numerically. A separate flow model using the concepts of relative permeabilities and the Leverett function was used to describe two-phase flow and heat transfer in the bed. The saturation distribution, liquid and vapor pressures and flows were calculated when heat generation rate (decay rate) was less than a critical value called the 'dryout heat flux'. When the heat generation rate was greater than the dryout heat flux, a dry zone was defined by extrapolating two-phase flow calculations. This is accomplished by solving the nonlinear partial differential equations governing pressures and temperature using an alternating direction implicit (ADI) method with an upwind scheme. Conduction, convection and radiation are taken into account in the dry zone. The maximum temperature in the bed, the melting heat fluxes, and the fractional contribution to heat transfer by conduction, convection and radiation for various bed configurations were investigated.