Modeling oxidic molten core-concrete interaction in WECHSL Original Research Article

The WECHSL code aims at modeling the physical and chemical phenomena governing the molten core-concrete interaction in a severe reactor accident, when the molten core has penetrated the pressure vessel. Attention has recently been drawn to the influence of the melt properties, among others of the viscosity of oxidic melts, on the heat transfer, and on the melt behavior during MCCI. In the first step, the viscosity model in WECHSL was changed in order to better fit the experimental viscosities. To take into account the variation of the viscosity with temperature, an iterative scheme has been introduced in WECHSL to determine the gradient from the pool bulk temperature to the interface temperature in the melt boundary layer. In addition, the influence of porosity of the melt on the thermal conductivity was modeled. Finally, a method was implemented to correct the heat transfer relations. In this paper the WECHSL code including the above modifications is applied to a PWR accident scenario.