Experimental Study of the Heat Transfer Performance and the Crust of the Two-Layer Stratified Melting Corium

Abstract During severe accidents, the molten core will relocate into the lower head of RPV. If the lower head of RPV does not receive sufficient cooling, it will be melted by the decay heat and eventually form a melt pool. To avoid radioactive material leakage due to overheating, the in-vessel melt retention (IVR) is applied by flooding the lower head with cooling water. In this study, a two-layer melt pool experimental system is established to simulate the lower head with IVR. The test section geometry is semicircular slice with cooling water channel at the side wall. Power-adjustable electrical heating rods are uniformly arranged in the lower-layer area. The thermal oil and the binary nitrate are simulants of the upper layer and lower layer respectively. The complex heat transfer in the two layers and between the outside cooling water is experimentally studied. It is found that the temperature in the lower-layer area is obviously higher due to electrical heating. As the temperature in the upper-layer area is below the melting temperature, there is crust at the interface. Besides, the heat flux density through the side wall is much higher at the upper layer due to stronger convective heat transfer.