Numerical study of turbulent flow under different flow mixing devices in a scaled-down reactor pressure vessel model

Abstract

Turbulent flow in reactor pressure vessel (RPV) of pressurized water reactor (PWR) is complicated because the complex geometry in RPV. The flow rates through fuel assemblies at core inlet are strongly influenced by different designs of flow mixing devices in lower plenum of RPV. For heat transfer during reactor operation, uniform flow rate at core inlet is an important design objective. For now, vortex suppression plate, flow skirt and semi-spherical perforated drum are three kinds of popular flow mixing devices in lower plenum. In this study, turbulent flow in a simplified and scaled-down RPV model with three kinds of simplified flow mixing devices was studied by computational fluid dynamics (CFD) methodology. The flow structures, pressure, Reynolds stresses and core flow rate in the RPV model were studied with validated turbulent model. The effect of three kinds of flow mixing devices on turbulent flow in lower plenum and flow rate at core inlet was studied in details. Among different turbulent models, the Reynolds stress model predicts turbulent flow well against experimental data. The separation vortices and high Reynolds stresses are generated by three jets from inlet nozzles and decay fast with flow development downwards in downcomer. In lower plenum, the flow separation vortices, flow bifurcation, jets and redirected flow improved the Reynolds stresses. The flow mixing devices have strong effect on turbulent anisotropic states and flow rate at core inlet. And smallest standard deviation of flow rates was found in case of flow skirt.