vi AbstractIn several coneepts of future Boiling WaterReactors, emergency coolmg of the reactor and

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In the frame of the OECD/SETH-2 project, an experimental programme is being carried out in parallel in the PANDA facility at the Paul Scherrer Institute and in the MISTRA facility at the Commissariat à l'Energie Atomique. Part of the program focuses on gas stratification break-up induced by mass sources and similar tests have been performed in both facilities. Indeed, the scaling effect of the phenomena involved in the erosion of a gas stratified layer can be assessed. Depending on the interaction Froude number, different regimes have been identified including pure diffusive mixing, global dilution or slow erosion processes. These phenomena are driven by different time scales. Small value of the non-dimensional number leads to mixing process driven by molecular diffusion. When the interaction Froude number is increased to large values, the dilution process can be described by a global time scale based on volumetric mixing provided that the air entrainment by the jet is taken into account. The intermediate case with two layers is more complicated and a single time scale cannot be derived. These test results with high-quality measurements can be regarded as a good basis for CFD models verification.

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