Numerical study on the thermal hydraulic characteristics in mixed pattern of wire-wrapped bundle for fast reactor annular fuel assembly

Abstract

The annular fuel has dual-cooled surfaces internally and externally. Compared with traditional cylindrical fuel, the annular fuel can take away the heat fully generated by the fuel pellets, reduce the surface temperature of the fuel assembly and improve the safety of the reactor effectively. In order to increase the power density of sodium-cooled fast reactors and flatten the coolant temperature, the numerical study is performed on a 7-pin fuel bundle annular fuel assembly for the Sodium-cooled Fast Reactor by using CFD. In this research, a new mixed pattern is developed. It is not wire-wrapped in the middle rod and the winding directions of the outer wire-wrapped bundle are clockwise and anticlockwise alternately. By comparison with the temperature field, flow field, and pressure drop of no wire-wrapped bundle, traditional pattern and mixed pattern, the results are clear that the mixed pattern flattens the coolant temperature gradient. The mixed pattern increases the transverse velocity of the coolant due to the clockwise and anticlockwise alternate winding directions of the wire-wrapped bundle. The mixed pattern reduces the pressure drop by about 10% compared with the traditional pattern. The winding direction and the number of wires are important factors, which affect the coolant thermal–hydraulic behavior. And through qualitative analysis, the influence share of each factor has been obtained. Finally, it is feasible to increase the power density by 30%. The research provides a reference for the optimization design of the fuel assembly.