PARIS project: Radiolytic oxidation of molecular iodine in containment during a nuclear reactor severe accident: Part 2. Formation and destruction of iodine oxides compounds under irradiation – Experimental results modelling
Abstract In the case of a severe accident in a nuclear Light Water Reactor (LWR), the high radiation fields reached in the reactor containment building due to the release of fission products from the reactor core would induce air radiolysis. The air radiolysis products (ARP) could, in turn, oxidise gaseous molecular iodine (I2) into aerosol-borne iodine–oxygen–nitrogen compounds, abbreviated as iodine oxides (IOx). These reactions involve the conversion of a gaseous iodine compound resulting in a change of the iodine depletion rate from the containment atmosphere. Kinetic data were produced within the first part of PARIS project on the air radiolysis products formation and destruction. The second part of the PARIS project as presented in this paper deals with the impact of the ARP on the conversion of I2 into IOx. The objective was to provide a database to develop new or to validate existing kinetic models of formation and destruction of iodine oxides. The iodine tests of the PARIS project, performed at very low, realistic iodine concentrations, constitute an important database to further develop or validate empirical and mechanistic models on radiolytic I2 oxidation. In the presence of painted surface areas or silver aerosol surface areas, radiolytic I2 oxidation is negligible compared to I2 adsorption on these surfaces for the conditions examined. However, radiolytic I2 oxidation remains very efficient if surface areas are small or if they are made of the relatively non-reactive stainless steel.