Analysis of gas entrainment phenomenon from free liquid surface for a sodium-cooled fast reactor design. Velocity profile and Strouhal number in a flow field

Gas entrainment (GE) from cover gas, which is an inert gas to cover sodium coolant in the reactor vessel, is one of the key issues for Sodium-cooled fast reactors (SFRs) design to prevent unexpected effects to core reactivity. In this research series, evaluation method has been investigated for surface dimple depth growth of unstable drifting vortex dimples on the liquid surface in the reactor vessel. By using a computational fluid dynamics (CFD) code, analyses have been conducted to estimate the drifting vortex on water experiments in a circulating water tunnel. The unstable drifting flow vortexes on the water surface were generated as wake vortexes behind a plate obstacle. Downward flow velocity was induced by the bottom slit's flow passing along the flow channel. In the previous study, the initial conditions of the gas entrainment were evaluated based on existing non-dimensional numbers method by using the STREAM-VIEWER code. However, the CFD predication accuracy of the detailed flow field itself was not clear especially for vortex frequency in the wake flow and detailed velocity profiles in the flow channel. In this study, to clarify the accuracy of CFD analysis, Strouhal numbers of vortex frequency and detailed flow velocity profiles were compared with experimental data which were measured by Particle Image Velocimetry (PIV) method. As the results, the Strouhal numbers of the vortex frequency behind the plate obstacle reasonably agreed with the experimental data. (author)