Numerical Study of Turbulent Heat Transfer of Annular Fuel Assembly in a Sodium-cooled Fast Reactor by a SST k-ω-kθ-εθ Model

Abstract

ABSTRACT The annular fuel has two cooling surfaces inside and outside, which can fully take away the heat of the fuel assemblies, and have strong advantages in safety and economy. It is urgent to conduct research on sodium-cooled fast reactor annular fuel assemblies. The Prandtl number Pr of liquid sodium is much less than 1 (Pr˂˂1). The problem is that using the traditional constant turbulent Prandtl number Pr t of 0.85 ~ 0.9, which is generally derived from the Reynolds analogy hypothesis suitable for conventional fluids, will greatly affect the accuracy of the numerical prediction of the thermal-hydraulic properties of liquid sodium in annular fuel assemblies. In order to address this issue, the turbulent heat transfer characteristics of the bare 7-pin annular fuel assembly and the annular fuel assembly with wire spacers for a sodium-cooled fast reactor are investigated by a SST k-ω-k θ -ε θ model, which couples the SST k-ω turbulence model with a two-equation k θ -ε θ heat flux model as a way to transport the turbulent stress and turbulent heat flux of liquid sodium. The open-source CFD software OpenFOAM is used for this calculation. In order to verify the validity of the present calculation method, some classical liquid metal heat transfer correlations are used to compare and analyze the results of the present calculation method (k θ -ε θ model), the results of the Reynolds analogy hypothesis (Pr t = 0.85 model), and the results of the turbulent Prandtl number correlation (Pr t =kays model). It is shown that the SST k-ω-Pr t = 0.85 model overestimates the Nusselt number Nu of the internal flow field and sub-channels of the annular fuel assembly. The SST k-ω-k θ -ε θ model agrees well with the SST k-ω-Pr t =Kays model in the internal flow field and sub-channels of the bare 7-pin annular fuel assembly and the annular fuel assembly with wire spacers. It suggests that the numerical calculation results of the SST k-ω-k θ -ε θ model are reliable in both the simple fuel assembly models and complex fuel assembly models. In brief, the SST k-ω-k θ -ε θ model is more capable of predicting the turbulent heat transfer characteristics of the bare 7-pin annular fuel assembly and the annular fuel assembly with wire spacers in sodium-cooled fast reactors. In addition, the thermal-hydraulic characteristics of annular fuel assemblies with wire spacers for sodium-cooled fast reactors have been investigated. This research can provide a reference for the study of turbulent heat transfer characteristics of annular fuel assemblies in sodium-cooled fast reactor.