| Fuel coolant interaction(FCI)is a phenomenon that may occur in severe accidents of nuclear power plants.The high temperature and pressure load generated by the fine fragmentation process may cause the damage of the pressure vessel and even threaten the integrity of the containment.Although a lot of researches on FCI phenomenon have been carried out at home and abroad,its mechanisms have not been completely understood.Therefore,it is necessary to study the influencing factors of FCI phenomenon and develop corresponding models.A visual experimental device is used to conduct experimental research on the initial melt temperature,melt mass and coolant temperature that affect the thermal fine fragmentation process of FCI,from the perspective of the morphology of the experimental products and the state of the interaction process.Pb-Sn alloy is used as melt material in this small-scale fragmentation tests facility.The results show that as melt temperature increases,the degree of thermal fine fragmentation increases first and decreases later;when the initial amount of coolant is constant,the increase of melt mass may cause fragmentation degree to degrease;and the fragmentation degree increases with the increasement of the coolant subcooling.Based on the experimental phenomenon obtained by researchers,combined with the peeling mechanism of the boundary layer stripping,using a combination method of theoretical derivation and experimental fitting,the fine fragmentation rate model and debris model describing the hydrodynamic fine fragmentation phenomenon are obtained.The reliability of the model is verified by comparing with the international typical experimental data.Then based on the validated hydrodynamic fragmentation model obtained,coupled with the instantaneous heat transfer between the melt and the coolant,a dynamic model of the vapor film on the surface of the melt is established.Applied to the previous experimental conditions,combined with Rayleigh equation,through the dynamic change of the steam film,the peak pressure of steam explosion caused by the rapid expansion of the steam film on the surface of the melt is described.This model can provide a model basis for the development of large-scale safety analysis tools for nuclear power plants. |
