Potential adsorption and revolatilisation of ruthenium inside the containment in the case of a severe nuclear reactor accident

Titre du congrès :1st European Chemistry Congress Ville du congrès :Budapest Date du congrès :27/08/2006

During an hypothetical severe accident supposed to occur on a nuclear pressurized water reactor, Fission-Products (FPs) are released from fuel and reach the reactor containment. Over FPs, ruthenium is of particular importance due to its ability to form, under strong oxidizing conditions, highly reactive and volatile ruthenium tetroxide, RuO4. In addition to its chemical toxicity, RuO4 is a very hazardous radio-contaminant due to a high specific activity through Ru-106 and Ru-103. The life time of RuO4 and ruthenium oxide reactivity in the reactor containment have thus to be assessed in order to better estimate the ruthenium release outside the containment, i.e. the “source term”. RuO4 adsorption experiments, in conditions close to those prevailing in the reactor containment (stainless steel and paint substrates, temperature, atmosphere composition), have been performed by the French “Institut de Radioprotection et de Sureté Nucléaire” to determine deposition rate onto surfaces. Main results are presented. Revolatilisation phenomena have been also investigated. Ruthenium deposits onto surfaces have been at first submitted to an atmosphere containing either ozone or NOx (air radiolysis compounds), and next, gamma radiolysis tests have been also carried out. Various parameters have been studied like the dose, the temperature... Revolatilisation has been experimentally.