Main outcomes of OECD/NEA THAI-2 project on hydrogen risk and source term investigations: Data application for code validation and containment safety assessment

During a core-melt accident, apart from hydrogen, radioactive gases and aerosols are released into the containment, the behaviour of which is of significant importance for determining the radiological source term. The investigation of in-containment combustible gases and fission product behaviour was the subject of the OECD/NEA THAI-2 project conducted during 2011–2014. The project focused on experiments on hydrogen behaviour i.e., deflagration in the presence of spray and passive autocatalytic recombiners (PARs) performance in O₂-lean atmosphere, on the interaction of molecular iodine with reactive (silver) and non-reactive (tin oxide) aerosol particles to assess the effect on a potential source term, and on the quantification of the release of gaseous iodine from a flashing jet, representing a PWR steam generator tube rupture scenario during reactor shutdown. The project was supported by 11 countries involving safety organizations, regulatory bodies, research laboratories, universities and industries. The experimental programme of the OECD/NEA THAI-2 project strongly contributed to the validation and further development of advanced lumped parameter and computational fluid dynamic codes used for reactor applications by e. g. providing experimental data for code benchmark exercises. The present paper summarizes the key findings of the project and highlights the importance of project results for mitigation of hydrogen risk and source term related issues. Furthermore, the use of project results by the project partners for code validation and reactor analyses towards management and mitigation of a severe accident in light water reactors is discussed with selected examples.