抄録
Thermal fragmentation process plays a key role in Fuel Coolant Interaction (FCI) during NPP's severe accidents, which significantly affects the heat transfer and determines the ratio of heat transferred to mechanical energy. Although various thermal fragmentation models have been raised, the phenomenon is not well understood due to its complicated process. Unstable film boiling is one of the mechanisms that lead to thermal fragmentation of the melt. In this paper, thermal fragmentation process induced by unstable film boiling condition is discussed based on theoretical analysis, including a momentum equation for vapor film dynamics, an energy equation for each phase involved and some appropriate boundary conditions. The effects of the initial melt temperature, coolant temperature and ambient pressure on thermal fragmentation process are also investigated. In order to evaluate this fragmentation model, a set of experiments on typical simulant materials are introduced, which give the fragmentation time and the evolution of mixture region. The evaluation shows that the main results calculated from the model are consistent with the experimental data and reflect the fragmentation process well.
