Achieving a better understanding of the Irradiation Assisted Stress Corrosion Cracking (IASCC)resistance is one of the issues to improve the durability of Pressurized Water Reactors. To do so,assessing the interaction of irradiation defects with oxidation of internal vessel bolts, made up of316L alloy, is crucial. Indeed, some recent studies [1-2] seem to indicate that irradiation modifiesthe kinetics and the nature of the oxides formed. The properties of oxide films formed, includingmorphology, thickness, structure and chemical compositions are thought to play a crucial role inthe oxidation process, especially at the initial stages and at crack tips. To study at best the IASCCmechanisms, one should focus on the investigation of the oxidation occurring at the crack tips. Ascracks will further propagate, they will present at crack tips oxidized areas analogous to theoxidation first stages. Hence, to emulate the oxidation at the cracks tips, short times oxidationswere carried out in simulated PWR environment. They allowed to investigate the oxidation firststages on surface oxides and especially the oxides formation and growth.First, the characterization of the oxide layers formed on unirradiated 316L stainless steel insimulated primary environment will be presented. Their nature, structure and morphology both onthe surface and at grain boundaries were investigated. Indeed, since the main bolt cracks appearsto be intergranular ones, attention was drawn on grain boundaries oxidations. The effect ofcrystallographic orientation of the underlying metal grain on the oxide scales and oxidation kineticwas thoroughly studied and will be presented.Second, the irradiation effect on the oxidation kinetics of the austenitic 316L exposed to primarywater have been studied. Synthetic proton pre-irradiations were chosen to emulate the neutronirradiation and still induced similar changes in the materials (dislocation loops, Radiation InducedSegregation (RIS), cavities). The oxide morphology, thickness and composition both on thesurface and at grain boundaries have been characterized from macroscopic investigationstechniques (optical microscopy, Gazing Incidence X-Ray diffraction (GIXRD), Ramanspectroscopy) to microscopic ones (SEM-EBSD, TEM, STEM-EDX-EELS). Then, results on theIrradiation Assisted Corrosion (IAC) experiment of a sample oxidized under proton flux will bepresented.
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