Simulation on the Process of Core Molten Pool Formation and Corium Relocation in the Core Region

Abstract Accurately estimating the moment on which the core melt relocates to the lower head in severe accidents is crucial for evaluating the effectiveness of the In-Vessel Retention (IVR) strategy. However, the collapse and fragmentation of the fuel rods as well as the melting and re-solidification of the core material during the core degradation process lead to complex changes in the core geometry, making it difficult to accurately simulate the relocation process of the melt in the core. Based on TMI-2 and Phebus FPT series experiments, a porous media model with transient flow and heat transfer both in the rod bundle region and debris bed region was established in this paper. The VOF and LEVEL SET methods were used to track the movement front of the corium in the core, as well as the coalescence process of local separate molten pools to form a large-scale core molten pool. Moreover, the efficient and stable IDEAL segregated algorithm was adopted to deal with the coupling problem of flow and heat transfer. The VOF and LEVEL SET methods were verified by the dam break problem, and the deviation of the results is within 10%. Using the above methods, the formation of a large-scale molten pool in the core and the relocation process of corium in the core region were simulated.