Abstract
Dry storage systems (DSSs) store spent nuclear fuel at many operating and decommissioned power reactor sites in the United States. Carbon steel, low-alloy steel, and stainless steel components are commonly used to construct DSSs. Some of the components are exposed to outdoor air and sheltered environments in which the materials may be susceptible to degradation. Potential aging mechanisms include general corrosion, pitting and crevice corrosion, galvanic corrosion, microbiologically influenced corrosion, stress corrosion cracking (SCC), creep, fatigue, thermal aging, radiation embrittlement, stress relaxation, and wear. This paper presents an assessment of these aging mechanisms based on review of literature and operating experience from nuclear and nonnuclear applications and their long-term effects on the integrity of DSSs. The results of this study indicate that the following mechanisms are credible for safely storing spent nuclear fuel during a 60-year timeframe: (i) general corrosion, pitting and crevice corrosion, galvanic corrosion, stress relaxation, and wear of carbon steel and low-alloy steel; (ii) wear of stainless steel; (iii) galvanic corrosion of stainless steel in contact with graphite; (iv) SCC of stainless steel welds and the weld heat affected zone; and (v) pitting and crevice corrosion of stainless steel as a precursor, or initiation site, for SCC. For weld-free austenitic stainless steel components or regions away from welds, such as the storage canister body, atmospheric SCC could be a credible aging mechanism provided sufficient tensile stresses exist. The results of this work are being used to inform recommendations for monitoring, inspection, and other activities to manage the aging of DSSs.
