Analysis of heat transfer and solidification within CANDU corium

Severe nuclear accidents which result in substantial damage to the reactor core have the potential to release radiation into the environment if the integrity of the reactor vessel is not maintained. In the event of a full loss of core cooling, the expected failure mechanism for Canada Deuterium Uranium (CANDU) calandria vessels is thermal stresses, which are influenced by the heat transfer within the corium. The current study uses computational fluid dynamics (CFD) to simulate the fluid flow, heat transfer, and crust formation in the corium using of full-scale CANDU calandria vessel. Uncertainties in the boundary conditions are considered with a sensitivity analysis. Results indicate that about 90% of the corium volume is in the mushy and solid form. The heat flux over the majority of the vessel wall is below the critical heat flux values and reaches the maximum value at the edge of the step region.