Numerical analysis of natural convection behavior in density stratification induced by external cooling of a containment vessel

Ishigaki, Masahiro* ; Abe, Satoshi  ; Hamdani, A.  ; Hirose, Yoshiyasu  

It is essential to improve computational fluid dynamics (CFD) analysis accuracy to estimate thermal flow in a containment vessel during a severe accident. Previous studies pointed out the importance of the influence of initial and boundary conditions on the CFD analysis. The purpose of this study is to evaluate the influence of initial and boundary conditions by numerical analysis of natural convection experiments in a large containment vessel test facility CIGMA(Containment InteGral effects Measurement Apparatus). A density stratification layer was initially formed in the vessel using helium and air, and external cooling of the vessel surface-induced natural convection. In this study, we carried out numerical simulations of the density stratification erosion driven by the natural convection using the RANS (Reynolds averaged Navier-Stokes) model. As a result, the temperature boundary condition of the small internal structure in the vessel had a significant influence on the fluid temperature distribution in the vessel. The erosion velocity of the density stratification layer changed depending on the initial gas concentration distribution. Then, appropriate settings of the temperature and gas concentration conditions are necessary for accurate analysis.