Study on Spacer Grid Span Pressure Loss Under High Reynolds Number Flow Condition

Pressure loss coefficient of spacer grid is used as a key parameter for PWR core thermal hydraulic design. It has been obtained by single-phase hydraulic testing for many years. However, it is necessary to develop design tool for precise estimation of pressure loss of spacer grids as well as hydraulic tests to meet the needs of the worldwide nuclear fuel market. Recently, Computational Fluid Dynamics (CFD) analysis has been applied for estimation of flow field in a fuel rod bundle. In this study, the numerical simulation in a range of bare rod Reynolds numbers of the reactor flow condition is performed to examine the applicability of the CFD model for estimating spacer grid span pressure loss. For verification of the numerical estimation, the span pressure loss of 5×5 rod bundle with spacer grid is measured in Nuclear Development Corporation (NDC) hydraulic test facility up to bare rod Reynolds number as high as 500,000. The simulation shows good agreement with experimental data in the range of Reynolds numbers. The CFD model is also utilized to investigate the pressure loss as a function of distance from last passed spacer grid and to discuss the turbulent flow characteristics in the rod bundle with spacer grid under high Reynolds number flow condition.