The time dependence of proton irradiation effect on the intergranular oxidation of 316 L stainless steel in high-temperature hydrogenated water

The time dependence of proton irradiation effect on the intergranular oxidation of 316 L stainless steel in simulated PWR primary water was clarified for the first time by ruling out the interference from grain boundary structure dependence. Interestingly, proton irradiation has an acceleration effect on the intergranular oxidation of 316 L stainless steel after shorter-term oxidation (less than 500 h) but a mitigation effect at later stage (more than 500 h). It was found that Cr depletion at the pristine grain boundary due to radiation-induced segregation (RIS) plays a dominant role at the early stage of oxidation, resulting in a deeper intergranular oxidation than in the non-irradiated region. Nevertheless, the Cr content at the intergranular oxide tip in the irradiated region builds up faster than in the non-irradiated region with time due to the enhanced solute (especially Cr) diffusivity in the irradiated region. The positive effect of enhanced Cr diffusivity on resistance to intergranular oxidation gradually dominates after longer-term immersion and eventually leads to a shallower intergranular oxide penetration in the irradiated region. The faster intergranular oxidation in irradiated region due to RIS at the early stage partly explains the accelerated crack propagation of irradiated material as the oxidation condition at the crack tip is similar to that at the early stage.