The overall objective of the THAI-2 project is to address open questions concerning the behaviour of hydrogen, iodine and aerosols in the containment of water-cooled reactors during design-basis or severe accident typical conditions. The understanding of the processes taking place during such events is essential for evaluating the challenge posed on containment integrity (hydrogen) and for evaluating the amount of airborne radioactivity (iodine and aerosols), which may be present inside a containment during such severe accidents with core damage. The project is to generate valuable data for evaluating the hydrogen deflagration behaviour during spray operation and its effective removal by PARs. Concerning fission products, the project will focus on the interaction of molecular iodine with nonreactive and reactive aerosol particles. Another important issue related to iodine behaviour is to quantify the release of gaseous iodine from a flashing jet, representing a PWR design basis accident scenario (steam generator tube rupture during reactor shutdown sequence). An extensive analytical effort will accompany the experimental programme consisting of code calculations to support test design for pre-test assessments, result evaluation and extrapolation to reactor conditions.