Experimental research of heat transfer in heavy metallic layer under different top boundary conditions

Abstract

The External Reactor Vessel Cooling (ERVC) is crucial to realizing In-Vessel Retention (IVR) strategy when reactor core degradation happens; consequently, fission products would be limited in Reactor Pressure Vessel (RPV). Because of the fission products in the lower head of RPV, vessel integrity is threatened. Due to the immiscibility of oxide and metal materials, the molten pool in the lower head of RPV would turn to a stratified configuration. Two-layer (light metallic layer atop of oxidic layer) and three-layer (light metallic layer, oxidic layer, heavy metallic layer) configurations have been proposed. The possible heavy metallic layer has a different shape, top boundary conditions, and decay heat compared with the other two layers. Thereby, the objective of the heavy metallic layer experiment is to study its heat transfer characteristics, and two possible top boundary conditions are performed. The heating cables simulating the decay heat are placed in a hemispheric test section (diameter = 2.4 m). Water is used as the experimental simulant with a height of 0.3 m. The experimental results demonstrate that increasing the top cooling rate, the ratio of top cooling power to sidewall cooling power, and the ratio of upward heat flux to sideward heat flux increase. In addition, they share almost the same trend. The central melt temperature rises with the height increment, and the maximum normalized temperature reaches about 1.3 for both top cooling and insulated boundary conditions. Thermal stratification is found in the experiment, and the possible natural convection is limited in the heavy metallic layer. Correlations of UCLA, Mini-ACOPO, and RASPLAV reasonably predict the heavy metallic layer's normalized sideward heat flux distribution.