Numerical Simulation of Molten Salt Spreading Behavior under the Salt Spill Accident of Molten Salt Reactor

To simulate the process of a severe accident in a molten salt reactor involving a molten salt leak, two-dimensional and three-dimensional analyses have been performed for the case where molten salt leaks vertically onto a flat surface. We analyzed the spreading behavior as the molten salt, in its liquid form, leaks and solidifies due to heat loss at the bottom and top surfaces of the molten salt. Although it is an axisymmetric problem centered on the axis of the discharge nozzle, it was observed that as the molten salt solidifies, it forms local irregular crusts on the surface, resulting in non-uniform flow resistance in the circumferential direction. Consequently, in three-dimensional analysis, the molten salt does not spread uniformly in the circumferential direction. By comparing the two-dimensional and three-dimensional analysis results for the spreading distance of the molten salt, which is a critical parameter in the severe accident analysis of molten salt reactors, we evaluated the applicability of the two-dimensional analysis on the simulation of molten salt spreading problem with various boundary conditions.