Development of maintenance technique for materials of core components in light-water reactor using ion-beam irradiation

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Austenitic stainless steel is used extensively in the core components of light water reactors (LWRs). Irradiation assisted stress corrosion cracking (IASCC) is one of the major concerns of stainless steel in LWR environment. Radiation induced segregation (RIS), that represents chromium depletion and nickel enrichment, caused by neutron irradiation is regarded as one of controlling factors of IASCC. To estimate the effect of chromium depletion at grain boundaries on corrosion behavior, the electrochemical potentiokinetic reactivation (EPR) test is very useful. In order to study the neutron irradiation effect of neutron, energetic particle beam irradiation using accelerators have been performed as simulation experiments. Since the corrosion behavior evaluated by EPR test is affected by chemical properties from the surface to 2-3μm depth of the austenitic stainless steel, the light ion irradiation can introduce enough damage level and damage area to evaluate the corrosion behavior of irra … More diated surface including grain boundaries. The purposes of this study are to establish the testing method using miniature size specimens for ion-irradiation experiments and to clarify the change in corrosion behavior of irradiated stainless steel caused by displacement damage under controlled irradiation conditions such as temperature and fluence.The corrosion behavior of type 304 austenitic stainless steel irradiated with hydrogen ion was investigated using EPR testing combined with TEM observation after irradiation at 300℃, 400℃ and 500℃ up to 0.1, 0.5 and 1 dpa. The results are summarized as follows ;1.It was confirmed that 3 mm disk specimens could be used to estimate corrosion behavior of austenitic stainless steel using EPR test.2.In the specimens irradiated at 300℃ and 400℃, the surface pitting was observed within grains after EPR testing. No etching trenches at and around grain boundaries were observed, nevertheless RIS was occurred in the specimens irradiated at 400℃ to 0.1dpa. So it was suggested that the corrosion resistance at grain boundaries after ion irradiation was still maintained.3.In the specimens irradiated at 500℃, etching trenches at and around grain boundaries were observed, and surface pits were absent. The width of etching trenches and the reactivation ratio increased with irradiation dose. It was suggested that high-temperature irradiation enhanced RIS and also the recovery of damage defects and therefore it suppressed the chemical activation within grains.4.The correlation between the changes in corrosion properties and the development of RIS and microstructures was discussed.Based on these results, it is concluded that hydrogen ion beam irradiation combined with EPR test is valuable to estimate neutron irradiation induced corrosion behavior of austenitic stainless steel. Less