NEA Thermal-hydraulics, Hydrogen, Aerosols and Iodine Project Phase 3 (THAI-3)

The experimental investigations carried out in the frame of the THAI (2007-09) and THAI-2 (2011-14) projects contributed significantly to hydrogen and fission-product-related issues in a water-cooled reactor containment in accident conditions. The tests were conducted in the 60 m³ stainless-steel THAI vessel. For THAI-3 the facility has been enhanced to a linked, two-vessel apparatus named THAI+ with a total enclosed volume of 80 m3.

THAI provided an experimental database devoted to the spatial distribution of hydrogen in containment, its removal by passive autocatalytic recombiners (PARs) and slow hydrogen combustion processes in accident conditions. Concerning fission products (FPs), the programme focused on iodine and aerosol interaction with PARs and a scoping test on a wash-down of soluble aerosol from walls by condensate film.

THAI-2 addressed additional experimental and analytical needs regarding hydrogen-related issues: PAR performance under different thermal-hydraulic conditions including the effect of reduced oxygen content in the air on PAR onset and ignition behaviour; one test series focused on investigating hydrogen deflagration during water-spray operation. Experimental investigations related to FPs focused on the interaction of gaseous iodine with tin oxide and silver aerosols and the release of gaseous iodine from a flashing jet.

Remaining open issues related to hydrogen and FPs are being investigated in THAI-3 benefiting from the enhanced capabilities of the THAI+ facility where the following experiment series will be performed:

  1. PAR performance in the adverse conditions of counter-current flow;
  2. hydrogen combustion and flame propagation in a two-compartment system and looking in particular at the impact of higher flow velocities of the unburned gas on flame acceleration;
  3. FP re-entrainment from water pools at elevated temperature;
  4. resuspension of FP deposits (aerosol and molecular iodine) due to a highly-energetic event, e.g. hydrogen deflagration.

Experiments on the performance of PARs were completed in 2016.


Belgium, Canada, China, Czech Republic, Finland, France, Germany, Hungary, India, Japan, Korea, Luxembourg, Slovak Republic, Sweden, Switzerland and the United Kingdom.

Project Period

1 February 2016 to 31 July 2019


EUR 4.75 million

Related links

Last updated: 31 October 2018