Numerical Investigation on the Vortex-Flow Characteristics in Rod Bundles with Mixing-Vane Spacer Grids

In nuclear reactor fuel assemblies, spacer grids are installed among the rod bundles to support the fuel rods and affect the flow field between rods. Mixing vanes, as a swirling device, are set on the upper apex of the spacer grid. Vortexes produced by mixing vanes move along the axial direction in subchannels and enhance the forced convection heat transfer between the rods and cooling-fluid medium. In this paper, a numerical simulation method was used to investigate vortex motion produced by typical AFA-3G spacer grids in a 5×5-rod bundle by Star-CCM+ software. The shear-stress transport k-ω model was used to simulate turbulence phenomena. A dimensionless parameter, Se, based on the absolute vorticity flux, was reported to specify the intensity of secondary flow. Its physical meaning is the ratio of inertial force to viscous force induced by secondary flow. The results are helpful to take advantage of spacer grids in a much more effective way in pressurized water reactors.