The THAI project - Thermal-hydraulics, Hydrogen, Aerosols, Iodine - is an international project organized under the auspices of the OECD. The IRSN is actively participating in this project by performing the pre-calculations and the post-calculations of the tests with the ASTEC and TONUS codes. The purpose of THAI is to perform thermal-hydraulic experiments to settle the questions concerning the distribution, combustion and mitigation of hydrogen, and those concerning the behaviour of the aerosols and the fission products, and iodine in particular.

Initiated on January 1st 2007 for a period of three years, THAI brings together international experts from nine countries of Europe, Asia and America (Germany, Canada, Korea, Finland, France, Hungary, the Netherlands, Switzerland, and the Czech Republic).

The test matrix achieved for this facility comprises both separate and coupled effects tests and integral tests. The experimental programme thus defined concerns:

• The hydrogen risk by proposing tests specific to hydrogen distribution and combustion, and the impact of the recombiners designed to prevent hydrogen build-up. The first distribution tests confirmed the hypothesis that helium could be considered a good hydrogen simulant. The combustion tests are designed to make up for the lack of results on slow hydrogen flame propagation (two tests have been chosen to be used in the ISP49 (International Standard Problem) benchmark organized under the auspices of the OECD). The recombiner tests are designed to study, among other things, the impact of an oxygen deficit on the effectiveness of the recombiners and the possibility of them initiating ignition.
• The behaviour of iodine in the containment and how it interacts with the recombiner.
• The washing out of fission products and their entrainment towards the containment sump by films of condensates on steel or painted surfaces.