Preliminary feasibility study of post-flooding ex-vessel corium cooling strategy by CFD spreading simulations and concrete ablation analysis

This preliminary study examines the feasibility of adopting a post-flooding strategy as molten corium cooling for APR1400 plants. We address negative effects of a steam explosion and unevenly spread corium that are associated with the current pre-flooded cavity strategies. In this research, we assess the feasibility of the post-flooding strategy in two steps. First, we use three-dimensional (3D) CFD methodology to simulate molten corium spreading in the dry cavity of an APR1400 plant. In the second step, we perform ablation depth analysis with respect to the time taken to flood the cavity, based on OECD/MCCI project results with safety margin. The CFD simulation shows molten corium to be evenly spread in a uniform thickness of about 35 cm in the dry cavity. Our analysis results indicate that the integrity of the steel liner beneath the sacrificial concrete can be maintained during ex-vessel corium cooling if water is supplied into the cavity within 7.4 h of the vessel being breached. Therefore, the CFD corium spreading simulations and the leak tightness assessment confirms the feasibility of adopting the post-flooding strategy of molten corium cooling for APR1400 plants evading the risks of steam explosion.