Study On The Flow And Heat Transfer Characteristics Of Liquid Lead-bismuth Eutectic In Plate-type Fuel Assembly And Upper Plenum

The lead cooled fast reactor in the form of plate-type fuel assembly has the characteristics of reproducing nuclear fuel,easy miniaturization and high-power density,and has a great prospect in military development.The plate-type fuel assembly and upper plenum are the key structures of lead cooled fast reactor,the thermal hydraulic research of liquid lead-bismuth eutectic in them is the most important to improve the cost performance and reliability of lead cooled fast reactor.As the common coolant of lead cooled fast reactor,liquid lead-bismuth eutectic has unique thermophysical properties.The key to accurately describe its thermal hydraulic characteristics is to select appropriate turbulent Prandtl number model and RANS turbulence model.Based on the existing experimental data,the accuracy and applicability of turbulent Prandtl number models and RANS turbulence models are verified by large eddy simulation,and the influence of computational domain and thermal boundary condition on the local thermal state is explored;Based on large eddy simulation and the optimization models,the flow and heat transfer of liquid lead-bismuth eutectic in plate-type fuel assembly,jet mixing and thermal mixing behavior in upper plenum are accurately predicted.The following are the research points and relevant conclusions:(1)Based on Pacio experiment,the accuracy and applicability of turbulent Prandtl number models and RANS models for liquid lead-bismuth eutectic are evaluated.After comprehensively temperature error,customized fitting degree Θ and Ф,it is decided to select the best performing Cheng model in combination with SST k-ω model for subsequent research.(2)Based on large eddy simulation and Pacio experiment,the influence of computational domain and thermal boundary condition on local thermal state is explored,which provides a reference for the accuracy verification of SST k-ωmodel in plate-type fuel assembly and the investigation of the influence of solid domain.Four large eddy simulation schemes with different calculation domain and thermal boundary condition are designed,and the accuracy of local thermal state of each scheme is analyzed emphatically.The fluid-solid conjugate scheme under large eddy simulation is used as the reference for verifying the simulation accuracy RANS model in plate-type fuel assembly and determining the computational domain.(3)The accuracy of SST k-ω model and solid domain for simulating plate-type fuel assembly is evaluated,the flow and heat transfer characteristics of lead-bismuth eutectic in plate-type fuel assembly and the role of the relevant parameters are explored based on the optimal models.For the plate-type fuel assembly,the SST k-ω model can accurately predict the flow and heat transfer process of liquid lead-bismuth eutectic by simulating the pure fluid domain;Increasing mass flow rate,gap width,heat flow density and inlet temperature can increase the comprehensive heat transfer coefficient,but the increase of the latter three will increase the maximum fluid temperature,which is not conducive to the core safety;The reverse flow can only reduce the maximum temperature at low mass flow rate,without other effects.(4)Based on the optimal models and large eddy simulation,the flow and heat transfer laws and the spatiotemporal evolution process of liquid lead-bismuth eutectic in upper plenum are captured,and the feasibility of RANS model replacing LES is analyzed.Increasing the inlet temperature difference and inlet velocity difference can both enhance the disturbance and mixing degree of the fluid in upper plenum,but also increase the pressure and its fluctuation,in which the influence of inlet velocity is obviously stronger than that of inlet temperature.Both the steady state simulation of SST k-ωmodel and the transient simulation of large eddy model can accurately capture the macroscopic and time-averaged characteristics of the velocity field,temperature field and pressure field in upper chamber,but large eddy model can further capture the temporal and spatial evolution of jet mixing,thermal mixing and pressure fluctuation.In this paper,the turbulent Prandtl number model and RANS turbulence model suitable for liquid lead-bismuth eutectic are optimized,the influence of computational domain and thermal boundary conditions on local thermal state is explored,the thermal hydraulic characteristics of liquid lead-bismuth eutectic in plate-type fuel assembly and upper plenum are explored,and the optimal engineering CFD simulation scheme is provided,which provides theoretical support for the scientific research and engineering application of plate-type fuel assembly and upper plenum in lead cooled fast reactor.