TRANSIENT BEHAVIORS OF HEAVY METALLIC LAYER AND EFFECTS OF PR ON THE HEAT TRANSFER CHARACTERISTICS

Transient behavior and heat transfer characteristics of the multi-layer corium pool is a significant problem that arises in the In-Vessel Retention analysis of the nuclear reactor severe accident. According to the results of the OECD MASCA project, a heavy metallic layer with internal heat source and high thermal conductivity may form on the bottom of the lower head of the reactor pressure vessel (RPV). Based on the existing empirical relationships, the CHF (critical heat flux) at the bottom of the outer wall of the RPV is smaller. Therefore, the heavy metallic layer may cause failure of the RPV. Some numerical simulations based on the newly disclosed heavy metallic layer heat transfer experiment were conducted to investigate the heat transfer characteristics and effects of changes in internal heat source. Water, molten salt or other low melting point solutions are usually used as simulation materials in the heat transfer characteristics experiments because of the high melting point and radioactivity of the real heavy metallic layer materials. However, the physical properties, especially the Prandtl number, of these materials are quite different from real materials, which may affect heat transfer characteristics, such as Nu distribution. Therefore, the effects of the Pr on the heat transfer characteristics of the heavy metallic layer were also investigated in this study.