Development of a formulation to predict molten core spreading in an LWR severe accident

Abstract

Relocated corium into the Primary Containment Vessel (PCV) needs to be properly cooled to avoid or mitigate molten-core concrete interactions (MCCI) in the PCV in order to maintain its supporting capability for the reactor pressure vessel and to suppress combustible/non-condensable gas releases. To know how effective the cooling is, it became important to know the geometry of the relocated corium. The present study chooses to focus on the “Wet Cavity” strategy and to build a reliable tool to evaluate the corium coolability in such a case. To achieve this goal, a previously developed formulation built to predict the corium geometry under the “Dry Cavity” strategy was extended to the conditions used in the “Wet Cavity” strategy. This extension includes the effect of solidification and cooling from the water by using a newly developed expression for the dimensionless thickness s*, the water subcooling, and the melt’s super-heat. After the validation of the extended formulation was confirmed, potential restrictions and limitations were investigated.