ABSTRACT
The ex-vessel phenomenology of a severe Light-Water Reactor accident after release of the core melt from the reactor pressure vessel is very much affected by the melt concrete interaction. The experimental melt/concrete investigations were separated into the thermohydraulic behavior of erosion processes on the one side and the aerosol release on the other side. WECHSL has been developed specifically for melt/concrete interaction in two-dimensional cylinder geometry. In the course of the WECHSL code validation, improvements were introduced concerning mainly heat transfer and solidification phenomena, oxidation behavior, void behavior and details of cavity formation late in the interaction phase. One of the key phenomena during melt concrete interaction is the heat transfer from the melt to the decomposing concrete. Depending on the gas flux of the decomposing concrete and the inclination of the surface, heat transfer is controlled by a gas film, nucleate boiling, or transition type of heat transfer.
