Simulating Molten Corium Concrete Interaction: A Multiphase Approach with OpenFOAM

In a severe accident, the reactor core may melt to form corium, a mixture of molten fuel and structural materials. If not adequately cooled, corium can breach the reactor pressure vessel and interact with containment concrete, leading to Molten Corium–Concrete Interaction (MCCI). Accurate modeling of MCCI is essential for assessing containment integrity. While previous studies have relied on experimental programs and lumped-parameter system codes, such approaches have limited capability to resolve detailed flow dynamics, phase interactions, and spatial heterogeneity. Existing CFD-based investigations often focus primarily on corium spreading, overlooking other key MCCI mechanisms. This study presents a novel multiphase CFD framework for simulating natural convection, phase change, mass mixing, and phase-specific decay heat generation during MCCI. The model is implemented in OpenFOAM and first validated against a phase change material melting experiment, demonstrating strong agreement with experimental melt-front evolution. The validated framework is then applied to the COMET-L2 experiment, incorporating simultaneous phase transitions between concrete, oxide, and metal phases. Time-step and mesh sensitivity studies are performed to ensure numerical robustness. The simulations successfully reproduce key MCCI phenomena, including concrete ablation, crust formation, oxide relocation, and metal penetration, providing improved physical insight into corium thermal behavior during MCCI events.