A Comparative Study on the Effect of Heat Transfer BC between Debris and Lower Head of Reactor Vessel in Severe Accident

The objective of this paper is comparative study on the effect of thermal boundary condition in contact area between debris and lower head of nuclear reacto. It is focused on the structural integrity of lower head and ICI (In-Core Instrumentation) nozzle under pressure and thermal loadings in severe accident scenario. The core debris in severe core melting accident may be relocated to and accumulated in the reactor pressure vessel lower head. In case of insufficient cooling, the excessive heat would drive the overheating and melting of lower head, and hence govern the vessel failure mode and timing. The thermal and structural analyses are carried out to find the effect of boundary condition between debris and lower head in severe accident of reactor. It was found that the head temperature at the contact area heat up to melting temperature and the head causes damage. The standard of safety evaluation for structures in high temperature condition is using the strain. The strain value of result for structure is not exceeded allowable strain