Synthesis of the OECD/NEA-PSI CFD benchmark exercise

• A benchmark exercise on stratification erosion in containment was conducted using a test in the PANDA facility.
• Blind calculations were provided by nineteen participants.
• Results were compared with experimental data.
• A ranking was made.
• A large spread of results was observed, with very few simulations providing accurate results for the most important variables, though not for velocities.

The third International Benchmark Exercise (IBE-3) conducted under the auspices of OECD/NEA is based on the comparison of blind CFD simulations with experimental data addressing the erosion of a stratified layer by an off-axis buoyant jet in a large vessel. The numerical benchmark exercise is based on a dedicated experiment in the PANDA facility conducted at the Paul Scherrer Institut (PSI) in Switzerland, using only one vessel. The use of non-prototypical fluids (i.e. helium as simulant for hydrogen, and air as simulant for steam), and the consequent absence of the complex physical effects produced by steam condensation enhanced the suitability of the data for CFD validation purposes. The test started with a helium–air layer at the top of the vessel and air in the lower part. The helium-rich layer was gradually eroded by a low-momentum air/helium jet emerging at a lower elevation. Blind calculation results were submitted by nineteen participants, and the calculation results have been compared with the PANDA data. This report, adopting the format of the reports for the two previous exercises, includes a ranking of the contributions, where the largest weight is given to the time progression of the erosion of the helium-rich layer. In accordance with the limited scope of the benchmark exercise, this report is more a collection of comparisons between calculated results and data than a synthesis. Therefore, the few conclusions are based on the mere observation of the agreement of the various submissions with the test result, and do not entail any interpretation of the discrepancies, which is left to the individual participants.