Assessment of corium concrete interaction and impact of water ingression mechanism using top flooding strategy for a small PWR with MELCOR 2.2

Molten Corium Concrete Interaction (MCCI) process is a critical phenomenon in the management of the late phase of a severe accident. Determination of water ingression (WI) and melt eruption (ME) impact on the ablation process is necessary for the assessment of cavity erosion. A model is developed to study the MCCI for Siliceous (SIL) and Limestone Common Sand (LCS) concretes in dry and water-filled cavities using MELCOR 2.2 code for a small PWR. It is found in this study that the ablated volume is greater in the SIL as compared to the LCS concrete. WI and ME were able to successfully halt the ablation process for LCS concrete under water flooding. Even with WI, SIL concrete ablation cannot be completely stopped in the axial and radial directions. In terms of concrete ablation, the cavity constructed with LCS is found to be safer than the cavity constructed with SIL concrete.