In case of severe accident, complex thermal-hydraulics phenomena are expected to occur in the containment atmosphere. To investigate and understand these phenomena, fundamental for nuclear safety and design, major efforts are being spent all over the world. A new OECD project, named SETH-2, is conceived to generate relevant experimental data, useful to improve the modeling capabilities of the computer codes aimed to predict post-accident containment thermal-hydraulic conditions. The Commissariat a` l’Energie Atomique (CEA) contributes to the project performing experiments within the large scale MISTRA facility. Tests are proposed to investigate mixing phenomena promoted in a stratified containment. In particular, one of these test series concerns the interaction of buoyant jets with a stratified atmosphere. The present work is aimed to develop and validate computational tools useful to support the design of this experimental campaign and to analyze the actual MISTRA tests. In this aim, two different models have been implemented for turbulent buoyant jets in a stratified atmosphere: an engineering analytical model for a fast characterization of flow structures and a finite elements computational fluid dynamics (CFD) model that allows a detailed analysis of local phenomena. The models have been successfully validated for vertical buoyant jets in uniform atmosphere. Further experimental and numerical activities are illustrated, aimed to carry out the validation with stratified atmosphere and inclined injections.

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