OECD/NEA ThAI Project

Progress in nuclear reactor containment safety research has led to a deeper understanding of the phenomena that may occur under potential accident conditions. However, there is still a need for additional information due to limitations in experimental databases. The uncertainties are related to the distribution of combustible hydrogen and to the behaviour of fission products, in particular iodine and aerosols.

In the case of hydrogen, uncertainties emerge mainly in the determination of conditions for the occurrence of deflagration flames and in the performance of devices designed to reduce the concentration of hydrogen gas developed in a hypothetical accident, such as passive autocatalytic recombiners. Some concern also prevails regarding the applicability of several previous experiments where helium was used to simulate hydrogen. The relevance to reactor safety is connected with the destructive potential of fast deflagrations.

In the case of fission products, a number of transport processes have not yet been investigated to a level of detail sufficient to set up reliable transport models. Such processes include the exchange of iodine between a turbulent atmosphere and the walls, relocation by wash-down, i.e. washing of walls by condensate water, airborne chemical reaction of iodine with radiolytic ozone, and aerosol re-suspension from a boiling sump. The control of volatile radioactive species is relevant to the potential accident source term and radioactivity management. The proposed experiments are designed to fill these knowledge gaps by delivering data for the evaluation and simulation of the hydrogen and fission product interactions mentioned above, thereby supporting the validation of accident simulation codes and models. The work during the first part of the project has concentrated on the specifications of the first
tests of the test matrix and performance of first mixing tests.

The experiments will be conducted in the THAI facility in Frankfurt, the name of which is an acronym for "Thermal-hydraulics, Hydrogen, Aerosols, Iodine".

Project participants