Three-dimensional experiment of heat transfer for molten oxidic pool

Abstract

The effectiveness of in-vessel retention (IVR) of core melt during severe accident in light water reactor strongly depends on whether the heat removed from boundaries could exceed the heat generated in the molten pool in lower head of reactor pressure vessel (RPV). Natural convection in the oxidic pool plays a key role in determining the heat transfer behavior inside the molten pool. A Molten pool Oxide-layer heat tRaNsfer experiment (MORN) facility was built to investigate the heat transfer characteristic of the molten oxidic pool with the intention to verify the heat transfer correlation of the pool. The test facility consists of a three dimensional hemisphere test section with an inner radius of 0.4 m. The outer boundary of the test section could be cooled by different methods (radiation or convection), so as to study the influence of external cooling condition on the crust formation of oxidic pool. Three kinds of material have been chosen as the simulants. They are water, NaNO3/KNO3(mole ratio 1:4) and a non-eutectic binary mixture of calcium-boron oxide (30 wt%CaO-70 wt%B2O3) respectively. At first period, several water and salt experiments with the melt height of 340 mm were performed and the data were analyzed. Though the normalized temperature distribution of the pool was nearly the same between water and salt experiments, the heat flux across the side wall differed much. The heat flux distribution of the water experiment rose nearly linearly with polar angle till to the melt surface. The heat flux of salt experiment at the low angle was larger than that of water, decreased slightly with angle increasing and then rose quickly till to the melt surface. This is consistent with the LIVE and COPRA experiments with the same boundary condition. The maximum normalized heat flux of the water experiment was approximate 1.6 and that of the salt experiment was about 2.2. The downward heat transfer of MORN is smaller than the correlation derived by COPO, mini-ACOPO and BALI experiments, but is consistent as LIVE, COPRA experiment.