Study of γ-ray irradiation effects on corrosion resistance of alloys for storage of high-level waste packages, (1)

The effects of γ-ray irradiation on corrosion resistance have been studied about candidate alloys as high-level waste canisters, overpacks and storage fasility materials. The purpose of this study is to evaluate integrity of alloys in the view of safety evaluation for interim storage systems such as water and air cooling system. Stress corrosion cracking (SCC) test has been carried out and the double U-bend type specimens were used. The alloys tested were Type 304 ss, Type 304L ss, Type 304EL ss, Type 309s ss, Incoloy 825, Inconel 600, Inconel 625 and SMA 50. Sensitized Type 304 ss, Type 304L ss and Type 309s ss have been found to be susceptible to SCC because of radiolysis in boiling deionized water with γ-ray irradiation but not without irradiation. It was also confirmed that they were susceptible to SCC under the existence of a little chloride ion and dissolved oxygen even without γ-ray irradiation. Fractographic observation revealed that the cracking mode was completely intergranular. The other alloys were not susceptible to SCC, but SMA 50 rusted over its surface. On the other hand, no alloy was susceptible to SCC in atmosphere at room temperature even with γ-ray irradiation. This study was carried out in corporation at JAERI and Kobe Steel Ltd. (author)