Investigation on entropy generation and flow characteristics of 7-pin sodium cooled wrapped-wire fuel bundle

Abstract

The fuel assembly of sodium-cooled fast reactor (SFR) is considered a compact heat interchanger with the intricate flow. The wire-wrapped make a great difference on the secondary flow and transverse momentum mixing. The investigations on fully developed convective heat transfer in a 7-pin fuel bundle with wrapped-wire are conducted for particular Reynolds number from 2 × 104 to 2 × 105, and heat flux at 500 to 1500 kW/m2 employing commercial computational fluid dynamic (CFD) code based on the finite volume method (FVM). The SST k-ω turbulent model and periodic boundary conditions are adopted at the inlet and outlet to obtain the fully developed fluid field and capture the detailed information in the near-wall region. The model validation and mesh independence verification are conducted, and the maximum error is 10.3%. The results are analyzed in view of sensitivities of secondary flow and thermodynamic irreversibility to mass flow rate and heat flux from the local and systemic scales by means of the entropy generation analysis approach. The axial profiles of secondary flow and entropy generation rate under different working conditions are studied. The results indicate that due to the helical structure of the wrapped-wire, the secondary flow, and entropy generation present similar periodical fluctuation and symmetric distributions in axial direction. Also, the secondary flow enhance has an impact on the heat transfer. The thermal irreversibility is also analyzed, and the result shows that heat conduction is the leading cause of the irreversible losses. Ep decreases with the Reynolds number, and increases with heat flux, which means the better thermal economic performance occurs at lower velocity and higher heat flux.