Flow characteristics inside a single basket containing a nuclear fuel assembly

The flow characteristics inside a fuel basket containing a spent nuclear fuel assembly were analyzed in this study. The geometry of a nuclear fuel assembly is very complicated; hence, a porous media model and an effective thermal conductivity were used to simplify the fuel assembly geometry. The permeability was calculated in three different ways, namely, a theoretical approach using the friction factor assuming laminar flow, a computational fluid dynamics (CFD) calculation using shear stress, and a CFD calculation using pressure drop. The results of the CFD calculations by shear stress and pressure drop showed a good agreement. The result of the theoretical approach was 30% less than the CFD results because the theoretical approach did not fully consider the flow resistance resulting from the complex geometry of the spacer grid and the fuel rods. The calculations were repeated using simplified models based on the repeated geometry in the system. The simplified model with periodic boundary conditions was used to accurately calculate the permeability while increasing the CFD calculation efficiency.