Numerical Simulation Of Turbulent Heat Transfer Of Liquid Lead-bismuth Eutectic(LBE)in Rod Bundle Channel

Among the fourth-generation nuclear reactors,the lead-cooled fast reactor has the most development potential and is expected to become the first reactor type to achieve industrial and commercial applications.Liquid lead-bismuth eutectic(LBE)as the coolant of leadbismuth reactor has the advantages of low melting point,high boiling point and good neutron performance.As the central part of lead-cooled fast reactor,wire-wrapped fuel assembly,the thermal-hydraulic characteristics of LBE in the fuel assembly are of great significance to the safety and economy of lead-cooled fast reactor.Therefore,it is necessary to study the law of heat transfer and flow of LBE in wire-wrapped fuel assemblies.In this paper,the computational fluid dynamics method is used to numerically study the thermal-hydraulic performance of liquid lead-bismuth eutectic in 19-pin fuel assemblies from different angles.The main research contents and conclusions are as follows:Evaluate different turbulence models and turbulent Prandtl number models,and select the most suitable turbulence model and turbulent Prandtl number model for wire-wrapped fuel assemblies.The calculation results were evaluated by friction coefficient correlation and heat transfer experiment correlation,and finally the SST k-ω turbulent model and Cheng-Tak turbulent Prandtl number model were selected for subsequent calculations.The surface temperature of the fuel rods in the fuel assembly was verified by using the experimental data in the literature,and the results showed that the errors of the calculation results were all less than 5%,which ensured the correctness of the numerical simulation method and grid.To explore the effect of the number of wire-wrapped on the thermal-hydraulic performance of fuel assemblies.The hydraulic performance,thermal performance and comprehensive performance of four fuel assemblies with different wire-wrapped numbers were compared and analyzed,and it was found that the number of wire-wrapped would affect the flow and heat transfer performance in the fuel assembly.Within the scope of the analysis,the increase in the number of wire-wrapped promotes the heat transfer performance of the fuel assembly and weakens the flow performance.The comprehensive performance analysis results of the four fuel assemblies show that the comprehensive performance of the multi wirewrapped fuel assembly is better than that of the single wire-wrapped fuel assembly.By comparing the flow and heat transfer performance of fuel assemblies with different structural parameters to study the influence of structural parameters on the flow and heat transfer performance of fuel assemblies.The analysis of the results shows that when the diameter of the fuel rod remains constant,changing the pitch and diameter ratio of the fuel assembly will affect the axial velocity distribution in the sub-channel and the heat transfer performance of the fuel assembly,but has little effect on the internal friction factor of the fuel assembly.Increasing the diameter of the wire-wrapped and decreasing the pitch of the wirewrapped will both strengthen the stirring effect of the winding wire and enhance the heat transfer performance of the component.But at the same time,it will also increase the internal resistance loss of the fuel assembly and reduce its flow performance.Therefore,when designing thermal-hydraulic design for wire-wound fuel assemblies,the diameter and pitch of the wire-wrapped should be within a reasonable range,so that the fuel assembly can obtain better thermal-hydraulic performance.Finally,the hot spot factor was introduced to evaluate the hot spot phenomenon in fuel assemblies with different structural parameters.