Flow characteristic inside a single basket includes a fuel assembly

Flow characteristics inside a fuel basket containing a spent nuclear fuel assembly were analyzed. Since the geometry of a nuclear fuel assembly is very complicated, a porous media model and effective thermal conductivity were used to simplify the fuel assembly geometry. The permeability was calculated in three different ways. These included a theoretical approach using the friction force 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 good agreement. The result of the theoretical approach was 50% less than the CFD results. This was because the theoretical approach did not fully consider the flow resistance resulting from the complex geometry of the spacer grid and fuel rods. (author)