Numerical Modeling Of Heat-up And MeltingProcesses In Internally Heated Debris Bed AndReactor Vessel Lower Plenum

Abstract

The paper considers the two-dimensional thermal processes in internally heated oxidic debris beds in the lower plenum of a light water reactor vessel during the course of severe accidents with core meltdown and relocation. Heat transfer and phase change processes in debris beds and vessel lower head wall are investigated numerically with a particular emphasis on the dynamic characteristics of thermal transients in question. The main purpose of the work is to develop an appropriate modeling approach, which enables the analysis of complicated physical processes (involving dynamic changes of bed porosity, anisotropic heat transfer in remelting beds with internal energy sources) in complex domains of debris bed and vessel lower head wall. The natural convection heat transfer in the forming melt pools are described by means of an originally developed effective conductivityconvectivity approach. A multi-block control-volume numerical scheme for two-dimensional cartesian or cylindrical non-orthogonal geometries has been developed and applied to predict heat transfer in the solid or porous core debris beds and forming melt pools.