Abstract

During the severe accident condition involving the core melt, stabilization and cooling the molten corium for long duration is the primary requirement. To address this challenge, core catcher systems are being installed inside the containment of the advanced nuclear reactors. Few ex-vessel core catcher designs incorporate special refractory sacrificial material, which on interaction with molten corium, ablate and reduce the enthalpy of the molten pool. During the interaction, the components of ablated sacrificial material and molten corium are stratified in different layers due to density difference between them, i.e., the low density oxidic components stratify in the top layer while higher density metallic components stratify in the bottom layers in the melt pool. This manuscript presents the material characterization of the stratified melt pool after cooling in an experiment involving interaction of approx. 550kg of molten simulant corium with approx. 150kg of sacrificial material in a scaled down V-shaped ex-vessel core catcher vessel. The cooling strategy in the experiment was similar to prototypic reactor conditions. After cooling and stratification of the melt pool, solid samples from different locations and different heights were collected for SEM-EDS analysis for characterizations. The phenomena of melt inversion were verified in the post-test analysis.

Keywords: Severe accident; Melt inversion; Corium-sacrificial material interaction