On the use of the MISTRA coupled effect test facility for the validation of containment thermal-hydraulics codes

Twenty four years after the Three Mile Island Accident, Hydrogen risk remains a safety issue for current and future Pressurized Water Reactors (PWR). The formation of a combustible gas mixture in the complex geometry of a reactor containment depends on the understanding of hydrogen production, complex 3D flow due to gas/steam injection, natural convection, heat transfer by condensation on walls and effect of mitigation devices. Lumped parameter safety codes mainly developed for full containment analysis are not able to accurately predict the local gas mixing within the containment. 3D CFD codes are required but a thorough validation process on well-instrumented experimental data is necessary before they can be used with a high degree of confidence. The MISTRA coupled effect test facility has been recently built at CEA to fulfill these objectives: numerous measurement points in the gaseous volume (temperature and gas concentration) and the use of Laser technology (L.D.V. and P.I.V.) provide suitable experimental data for code validation. The in-house CEA-IRSN CAST3M/TONUS code is developed and validated against experimental data provided by this facility. Some of these tests have been proposed to the international community for code benchmarking (MICOCO benchmark and OECD/ISP47 exercise). Finally, extrapolation to global containment scale requires the validation of the code on more complex flow patterns and a detailed investigation of scaling effects. These two items will be the guidelines of future MISTRA tests