Investigating The Thermal Hydraulic Performance Of Combined Split And Swirl Vanes Using Star-Ccm+

ABSTRACT

For effective evacuation of heat from nuclear fuels and increasing the Critical Heat Flux (CHF) of nuclear fuel bundles, mixing vanes are attached to spacer grids in fuel assemblies. However, the presence of spacer grids increases the pressure drop across the fuel bundle which has economic implications on the operations of Nuclear Power Plants (NPPs) in general. Nuclear fuel vendors are therefore continually improving upon the designs of mixing vanes in order to improve the thermal hydraulic efficiency of fuel assemblies. Numerical simulation was conducted in this study to analyse the thermal hydraulic performance of a 1200 mm long 5 5 fuel assembly supported by split and swirl vanes at varying spacer gaps of 350 mm and 530 mm. This numerical simulation was performed using STAR-CCM+ CFD code. The Shear Stress Turbulence (SST) was adopted for a single phase (liquid) isothermal coolant in this study. The objective of this study was to validate the simulation results with experimental data obtained from the Korean Atomic Energy Institute. The present study also investigated the effects of spacer gaps and mixing vanes on the velocity and turbulence of the flow through the fuel bundle. Validation of split vane data of all velocity components showed good correlation with experimental results; however simulation data of the swirl vane showed poor correlation with experimental results. The split vane produced a higher effect on the turbulence of the flow than the swirl vane. Also the 350 mm split-swirl fuel bundle produced a higher turbulence than the 530 mm split-swirl arrangement. Also the 530 mm swirl-split fuel bundle had a higher effect on turbulence than the 350 mm swirl-split vane arrangement. In effect the split-swirl 530 mm produced the highest turbulence than the swirl-split 350mm, swirl-split 350 mm and swirl-split 530 mm fuel bundles.