Simulation Study On Heat Transfer Characteristics Of Fast Reactor Spent Fuel Assembly During External Transportation Process

During the external transportation process,the fast reactor spent fuel assembly will be exposed to the gas region which has weak heat transfer characteristics.At this time,if a shutdown accident caused by mechanical failure of the transport device happens,the internal temperature of the spent fuel assembly will increase due to the lack of effective cooling.Once the maximum temperature of the cladding material exceeds the allowable limited temperature,it will damage due to the failure of cladding material and results in the leakage of radioactive substances.Therefore,it is necessary to study the heat transfer characteristics of spent fuel assembly discharged from the fast reactor during external transportation process.In this paper,by pre-analysis of the transportation cases,two types of typical shutdown cases are selected,that is the shutdown conditions of the spent fuel assembly in the conveyance of transportation room and the shutdown conditions of the spent fuel assembly above the sodium level.Reasonable modeling of heat transfer in the fast reactor spent fuel assembly is the key point of numerical simulation.In this paper,the whole spent fuel assembly is regarded as a six prism solid region and the equivalent heat conductivity model is used to describe the heat transfer process inside the spent fuel assembly.In order to evaluate the applicability of the equivalent heat conductivity model,Sanchezexperimental formula,Manteufel formula and two region model are verified and evaluated.Compared with the Sanchez experimental formula,the simulation results show that the two region model is a reasonable conservative model,because it can reflect the influence of external conditions on the internal heat transfer of spent fuel assemblies more sensitively.In addition,in order to describe the flow and heat transfer phenomena outside the spent fuel assembly,the corresponding turbulence model,the experimentally empirical correlation of natural convection heat transfer and the radiation heat transfer model are also selected.The simulation results of the shutdown condition of the conveyance of transportation room show that the main mechanism of heat transfer is radiation when the cooling of spent fuel assembly is completely dependent on natural convection,therefore,inlet conditions and turbulence models have little effect on the prediction of maximum temperature.However,the convection heat transfer of gas increases significantly under forced convection,so that the maximum temperature of the spent fuel assembly is reduced significantly.The influence of blowing speed on the maximum temperature of spent fuel assembly can be better predicted by the two region model.In addition,by several simplified assumptions and space independent verification,the heat transfer of the spent fuel assembly in the shutdown condition above the sodium level is preliminarily analyzed.