7 - Molten core concrete interaction and ablation of sacrificial material in ex-vessel scenarios

Abstract

In a light water reactor, during severe accident progression, when the vessel failure occurs, the melt is ejected into the reactor cavity. In the reactors having no core catcher, the melt falls onto the concrete basemat and starts interacting with the concrete which is termed as molten core concrete interaction. In new advanced reactors, ex-vessel core catcher has been provided for stabilization and termination of core melts. In these reactors, the melt is ejected into the core catcher and falls on the sacrificial material. The thermal response of concrete and sacrificial material when high temperature melt falls on them is quite different. Nevertheless, both these phenomena of MCCI and sacrificial material ablation are very much important from the severe accident progression and termination point of view and needs in-depth understanding. This chapter discusses the phenomenology of molten core concrete interaction and sacrificial material ablation, experiments conducted towards MCCI and sacrificial material ablation with and without top flooding, modelling of the MCCI and sacrificial material ablation phenomena with property changes and validation with experimental data.