Localized Corrosion Prediction for Nuclear Waste Disposal Container Materials

by Guen Nakayama, IHI, Tokyo, Japan,
Masatsune Akashi, IHI, Tokyo, Japan,

Abstract: When the bentonite is used in the geological disposal of high-level wastes as a buffer material to stand between containers and host rocks, thereby turning the pH of the groundwater slightly alkaline. In this slightly alkaline condition, stainless alloys, e.g., austenitic stainless steels or titanium alloys, and even carbon steels are in the passivity region. Although the uniform corrosion rate is ignorably small for these materials in such circumstances, they are liable to localized corrosion, i.e., pitting corrosion, crevice corrosion, or stress-carbon cracking. Their safety usage domains can be quantitatively defined on the notion of the critical potential of initiating the localized corrosion, VC, with VC > ESP, the free-corrosion potential terminally attained in the environment concerned. The critical potential that brings a propagating corrosion crevice into repassivation and arrest, ER,CREV, can well be used in assessment for the critical potential for crevice corrosion, VC,CREV. An allowable service limits diagram that has been drawn on this basis for interplay of the environment temperature and the chloride ion concentration is presented for several stainless alloys. Similarly, the critical potential for stress-corrosion cracking has also been discussed.

Subject Headings: Corrosion | Waste disposal | Alloys | Radioactive wastes | Rocks | Groundwater | Alkalinity

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