Modeling of molten corium oxidation in the presence of an oxide crust on the melt surface

In the case of a severe accident at a nuclear power plant with light-water reactors, the most effective method for localization of the formed melt (corium) is its retention in the cooled reactor vessel whose integrity depends on the heat flux from the melt to the vessel. One of the critically important processes in this case is the oxidation of the melt by water vapor or air–vapor mixture, which may significantly increase the heat load on the reactor vessel due to the heat of exothermal reactions of oxidation of reducing agents present in the melt, the decrease in the thickness of the metallic part of the molten pool, and the release of hydrogen, which depend on the oxidation rate. In analysis of the melt oxidation conditions, it is considered that for the generally accepted scenarios of a severe accident, the most realistic situation is the presence of the solid-phase oxide layer (oxide crust) on the melt surface. In these conditions, based on the diffusion model, we propose a dependence for calculating the oxidation rate for the corium melt and its validation using the obtained experimental data.