Numerical Investigation On Heat Transfer Of Spent Fuel Assembly Of Sodium Cooled Fast Reactor In Argon Atmosphere

Spent fuel assembly of sodium cooled fast reactor will be exposed to the argon atmosphere in reactor building during the unloading process.Staying in argon atmosphere for a long time will lead to the excess of designed limited temperature for wrappers due to the poor heat transfer property of gas.For the purpose of predicting the heat transfer of spent fuel assembly in argon atmosphere,a method was used for decoupling heat transfer inside and outside the spent fuel assembly.In order to develop the predicting method for heat transfer inside the spent fuel assembly,a radiative heat transfer model using fuel rods as control volumes and a computing model for calculating the rod-rod view factors and rod-edge view factors were built.Based on these models,a steady state numerical analysis program for predicting the heat transfer inside the spent fuel assembly was developed,and can be used to predict the temperature of fuel rods inside the assembly.Comparing the predicting results and experimental data,the reliability of code was confirmed.Calculation under different conditions had been performed for the sensitivity analysis of wall temperature,heating power and surface emissivity,after the reliability confirmed.Calculation results showed that both the temperature of assembly and rapidity will rise with increment of wall temperature.While only taking the temperature gradient between the fuel rods and wall into consideration,the gradient both with rapidity will decline with increment of wall temperature.The temperature will rise with increment of heating power,while rapidity will decline.For surface emissivity,both temperature and rapidity will decline with increment.CFD analysis method was used to investigate the natural convective heat transfer of spent fuel assembly in the large space,for analysis of heat transfer between wall of assembly and argon atmosphere.Volume heat source was used to simulate the decay power of assembly and effective thermal conductivity model was used to simulate the heat transfer inside the assembly.The convective heat transfer outside the assembly was determined by correlation for natural convection of vertical cylinder in large space and radiative heat transfer was determined by surface emissivity calculated from experimental data.The predicting results were smaller than experimental data for wall temperature with minor deviation,but the deviation between predicting results and experimental data for center temperature was huge.In addition,using Manteufel correlation to meliorate the predicting results of CFD and calculating the center temperature from the wall temperature of CFD results,the revised results had minor deviation with experimental data.CFD analysis method was used to investigate the natural convective heat transfer of spent fuel assembly with tube in argon atmosphere.The realizable K-Epsilon two-layer model was used to describe the flow of gas in the tube.The bottom of the tube was velocity inlet and the top of the tube was pressure outlet.The influence of inlet velocity for heat transfer property of assembly was analyzed.The results showed that the center temperature,wall temperature and tube temperature of assembly will decline with the increment of velocity.The heat taken away from gas flow in the tube possessed the portion of total heat loss about 33%,45%,57% with the velocity of 0.5m/s,1.0m/s,1.5m/s.It was the dominated way of heat dissipation with high inlet velocity.