Safety evaluation of core components exposed to air during an LBLOCA

An analysis was performed to determine the peak heat structure temperature of internal reactor components during the gamma-heating phase of a large-break loss-of-coolant accident (LBLOCA) in a heavy-water reactor. During this phase, the reactor is scrammed, the coolant in the moderator tank is replaced by air, and fuel and control rod tubes are cooled internally by forced convection via the emergency core-cooling system (ECCS) water. However, the safety rods, reflector assemblies, and tank wall continue to heat up as a result of gamma deposition and relatively low heat transfer rates; heat transfer in the safety rods, reflector assemblies, and the tank wall occurs primarily from natural/mixed convection and radiation heat transfer. The ECCS discharges at the top of the moderator tank in the form of droplets and film. Thus, the gamma-heating phase of the LBLOCA is characterized by natural/mixed air convection heat transfer, conduction heat transfer, droplet flow, thermal radiation heat transfer, and air-droplet interfacial heat transfer