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The analysis on a density stratification layer consisting of multiple gases in the reactor containment vessel is important for the safety assessment of sever accidents. The JAEA (Japan Atomic Energy Agency) has started the project on the containment thermal hydraulics. We carried out CFD (computational fluid dynamics) analyses in order to investigate the erosion of the density stratification layer by a vertical buoyant jet under this project. We used the RANS (Reynolds averaged numerical simulation) and LES (large eddy simulation) models to analyze the erosion of a density stratification layer by a vertical buoyant jet in a small vessel which represents a containment vessel. This numerical study calculates the turbulent mixing of a two-component (air and helium) gas mixture. The turbulence models used for the RANS analyses are two types of k-e models. The first model is the low Reynolds number k-e model developed by Launder and Sharma. The second model is modified from the first model in order to accurately consider the turbulent production and damping in a stratification layer. The results indicated while the erosion rate calculated by the low-Re k-e model was much faster than that of the LES model, the modified k-e model could calculate the erosion rate similar to the LES result.

A Study on Improvement of RANS Analysis for Erosion of Density Stratified Layer of Multicomponent Gas by Buoyant Jet in a Containment Vessel