Study on Heat Transfer Behavior in a Scaled Down Core Catcher using Simulant Corium Having Indirect Cooling and (Quasi) Volumetric Heat Source

To mitigate the consequence of severe accident involving core meltdown, many advanced reactors employ ex-vessel core catchers which stabilize and cool the corium for prolonged period by strategically flooding it. The cooling system for the core catcher is one of the key components in designing the core catcher. To understand the coolability of melt pool including the effects of decay heat, a simulated experiment was performed in a scaled down ex-vessel core catcher model (CCM) employing electrical heaters to simulate decay heat of 1 MW/m³. The experiment was carried out by melting about 25 liters of sodium borosilicate glass, as a mixture of corium and sacrificial material simulant, using cold crucible induction furnace at about 1200°C. The electrical heaters were turned on as the molten corium was poured in the CCM test vessel. K-type thermocouples were used to monitor melt pool temperature as well as the bulk water temperature at different locations with time. The results show that in presence of water outside of the CCM test vessel for the present geometry, coolability of melt pool including removal of decay heat is achievable with outside vessel temperatures not exceeding 100°C. A stable crust was observed at the top surface of the melt pool, which prevented water ingression into the molten corium.