Experimental study of natural convection heat transfer phenomena in two-layer corium pools

During a postulated core melt down accident, the corium pool stratification phenomenon will directly affect the thermal load on reactor pressure vessel (RPV). The focusing effect of upper metal layer may result in a sharp increase of wall heat flux. In-vessel retention (IVR) has been proposed as an effective strategy to mitigate the consequence of severe accident in pressurized water reactors (PWRs). In this study, several tests have been conducted on the large-scale 2D COPRA facility, which concerned with the natural convection behavior in a two-layer molten pool. The test section is a 1/4 circular slice with an inner radius of 2.2 m and the working fluid is a binary mixture of 20%NaNO₃-80%KNO₃. The melt pool is divided into two parts and electrical heating is applied in the lower part to simulate the internally heated oxide pool. Applying different heating powers and top boundary conditions, experimental data showed that the cooling boundary played an important role on the temperature of metal layer and the heat flux along vessel wall, as well as the crust thickness. Results from the two-layer corium pool experiment will provide basic and useful information for posttest studies of stratification effect.