Modelling Mass Transfer and Mixing of Corium with Concrete during Molten Corium-Concrete Interaction: Impact of Concrete Thermal Conductivity

Molten corium, a mixture of nuclear fuel, claddings, and structural elements, would form after the meltdown of a reactor core in the event of a severe accident at a nuclear power plant. This paper presents the development and implementation of a new numerical mixing model in OpenFOAM for a comprehensive analysis of concrete ablation during the Molten Corium-Concrete Interaction (MCCI) process. The well-researched CCI-2 experiment served as the model's benchmark during model validation. The model can forecast heat transfer, concrete ablation, phase change, mass transfer, and mixing of concrete and corium. Additionally, the effect of concrete thermal conductivity was investigated to study its impact on concrete ablation. We observed significant low concrete ablation, controlled temperature, velocity and density field for concrete with low thermal conductivity. Accordingly, the ablation of concrete decreased by 61 and 58 %, when the thermal conductivity was decreased to 1.5 and 1.0 W/m.K, respectively from 2.0 W/m.K. Our results also revealed that the melted concrete and corium, even though, having different densities, form a single phase/mixer that could enhances the ablation of concrete.