Modeling of fuel-to-steel heat transfer in core disruptive accidents

Abstract

A mathematical model for direct-contact boiling heat transfer between immiscible fluids was developed and tested experimentally. The model describes heat transfer from a hot fluid bath to an ensemble of droplets of a cooler fluid that boils as it passes through the hot fluid. The mathematical model is based on single bubble correlations for the heat transfer and a drift-flux model for the fluid dynamics. The model yields a volumetric heat transfer coefficient as a function of the initial diameter, velocity and volume fraction of the dispersed component. An experiment was constructed to boil cyclopentane droplets in water. The mathematical and experimental results agreed reasonably well. The results were applied to investigate the possibility of steel vaporization during a hypothetical core disruptive accident in a liquid metal fast breeder reactor. The model predicts that substantial steel vaporization may occur in core disruptive accidents, if the steel reaches its saturation temperature rapidly enough. The potential importance of steel vaporization is dependent on the accident scenario.