Abstract : During the deep geological disposal, stainless steel containers of the vitrified waste will be put in carbon steel overpacks. After the closing of the storage site, overpacks will be in contact with a humid air and a radioactive medium. After hundred years, overpacks could be in contact with water radiolysis in an anoxic medium.
In this context, my PhD work is a fundamental study which is the understanding of the corrosion mechanisms of pure iron under proton irradiation. This corrosion is affected by the contact of iron with different atmospheres (air, nitrogen) and water.
In the case of the atmospheric iron corrosion under irradiation, we have study the influence of the proton beam flux. During this work, we have characterized the structure of the oxides formed at the iron surface. The structure formed doesn't correspond to iron oxides and hydroxides indexed. However, we have shown that the oxide structure is close to that of lepidocrocite and bernalite. Moreover, we have determined the oxygen diffusion coefficient in iron under irradiation and we have shown that the irradiation accelerates of 6 orders of magnitude the iron corrosion.
In addition, the irradiations which were realized in different gas have put in evidence the negligible role of nitrates, and the importance of the O2/H2O coupling on the iron corrosion. Finally, we have shown the influence of the relative humidity, the maximum of the corrosion being observed for a relative humidity close to 45%.
In the case of the iron corrosion in aqueous media under irradiation, the influence of the oxygen dissolved in water has been studied using a surface marker. We have put in evidence that the corrosion is twice more significant in aerated medium than in deaerated medium. Moreover, the influence of radicals has been shown. An irradiated sample is more corroded than a sample put in contact with a H2O2 solution. Finally, the follow-up of the iron potential under irradiation have shown the majority role of the oxidant radicals on the iron corrosion.