Analysis of heat threshold in contact melting process

Abstract

In the processes of core meltdown under severe reactor accidents and nuclear waste self-burial, the main heat source is radioactive decay heat. Melting will cease when the heat generated by the source is insufficient to melt the surrounding medium. For contact melting induced by a decay heat source under the third-type boundary condition, the concept of heat threshold is proposed. This paper analyzes and calculates the heat threshold and the time to reach this threshold during the melting process of a spherical heat source under different conditions, discusses the main factors affecting the heat threshold. It is found that for contact melting with a heat source of finite heat capacity or decay heat, there will be cases of melting cessation or heat threshold; the heat threshold is mainly affected by the initial temperature of the heat source under severe reactor accidents; the rock thermal conductivity has a significant impact on the melting distance and heat threshold during the nuclear waste self-burial process.