Investigation of large-scale gas mixing and stratification phenomena related to LWR containment studies in the PANDA facility

The thermal-hydraulic processes governing the containment response to postulated accidents and the mixing and distribution of hydrogen following a severe accident are relevant issues identified by several international expert groups as 'research needs' for current and advanced LWRs. The development and validation of modern computational codes that will accurately predict gas distribution in LWR containments is required for analyses related to safety, design and operational issues in current and advanced reactors. This objective requires the availability of separate-effect test data collected in facilities where the 3D distribution of the relevant variables is measured with sufficient resolution and accuracy and tests are performed under well-controlled initial and boundary conditions. Within the scope of the OECD project 'SETH', a series of 25 tests has been initiated in the large-scale thermal-hydraulic facility PANDA, in order to investigate mixing and stratification phenomena in a large multi-compartment gas volume approaching the dimensions of actual containment compartments. This experimental programme investigates jets and plumes and the resulting propagation of stratification fronts. The presentation of the first results from this test series demonstrates the value of these new data for code validation purposes.