Evaluation of the Impact That PARs Have on the Hydrogen Risk in the Reactor Containment: Methodology and Application to PSA Level 2

This paper presents a methodology and its application to a Level 2 Probabilistic Safety Assessment (PSA-2), to evaluate the impact of the Passive Autocatalytic Recombiners (PARs) on the hydrogen risk in the reactor containment in case of a severe accident. Among the whole set of accidental scenarios calculated in the framework of the PSA-2, nine have been selected as representative in terms of the in-vessel hydrogen production rate and in-vessel total produced hydrogen mass. Five complementary scenarios have been added as representative of the core reflooding situations. For this set of selected scenarios the evolution of the conditions in the containment (i.e., pressure, temperature, and composition) during the in-vessel phase of the accident has been evaluated by means of a lumped parameter approach. The use of spray systems in the containment has also been considered as well as the presence of recombiners. Moreover, the ignition by recombiners of the flammable atmosphere has been considered

Study of the stability of CsI and iodine oxides (IOx) aerosols and trapping efficiency of small aerosols on sand bed and metallic filters under irradiation

International audienceThe decomposition of deposited CsI and iodine oxides (IOx) aerosols deposited on sand bed and on a metallic filter has been pursued under irradiation at 120°C. On the sand, it was found that CsI aerosols are decomposed by the irradiation and the temperature effect into an inorganic specie assumed to be molecular iodine. The temperature effect might be due to surface effects of the sand grains as CsI aerosols are usually stable at this temperature. IOx aerosols are expected to be well retained by the sand filter (DF > 100) as long as the sand height is high enough (> 60 cm). IOx are also decomposed by the temperature and irradiation. The humidity is also expected to have a significant influence on their decomposition. On the metallic filter, despite both species are expected to be significantly decomposed, very few gaseous iodine release from the filter was observed. The gaseous iodine species produced by the aerosols decomposition is assumed to be quickly adsorbed on the steel wires even if a slow desorption is also expected