RANS analysis with a dynamic model for turbulent Schmidt number ($Sc_t$) on density stratification erosion in a small rectangular vessel

Abstract

International audienceHydrogen behavior in a reactor containment vessel is one of significant issues in discussing a potential ofhydrogen combustion during a severe accident. Density stratification and its break-up are importantphenomena for discussing the hydrogen behavior. Many research projects to understand the stratificationbehavior have been performed with large scale test facilities. Many experiments with helium as alternategas of hydrogen focus on the stratification erosion by a vertical or horizontal jet. Turbulence transportphenomenon is one of the important factor in the stratification erosion behavior.A small scale test is a useful approach to develop a physical model for the stratification erosion because ofeasiness for detailed measurement. Thus, small scale experiments have been carried out in the ROSA-SAproject conducted at JAEA for study on containment thermalhydraulics during a severe accident. Arectangular vessel apparatus named VIMES (VIsualization and MEasurement system on Stratificationbehavior) is one of such facilities, which has a vessel made of acrylic plates for visualizing flow field withthe PIV measurement, whose volume is 4.05 m$^3$ (1.5m(L) × 1.5m(W) × 1.8m(H)).In this paper, we focus on Computational Fluid Dynamics (CFD) analysis on a density stratification erosionwith a vertical buoyant jet observed in the VIMES experiments. Comparative study between Large-eddysimulation (LES) and Reynolds-averaged Navier-Stokes (RANS) are also performed to validate thedynamic turbulence Schmidt number ($Sc_t$) formulation. The results have indicated that the dynamic Sctmodel is advantageous to predict the observed stratification erosion over the conventional model using aconstant value of Sct. This research is a collaboration activity between CEA and JAEA