Abstract

ASME Boiler and Pressure Vessel Code Section XI Code Case N-860 provides inspection requirements and evaluation standard for welded stainless steel canisters used for spent nuclear fuel storage. The Code Case defines an initial inspection interval and populations then defines examination requirements that are based on the primary degradation mechanism, chloride induced stress corrosion cracking (CISCC). Additional examination requirements are based on the results of the initial screening examination. This paper summarizes the technical basis for the examinations and the evaluation criteria defined in Code Case N-860. Technical basis information for topics related to the inservice inspection and the flaw evaluation of canisters are described. The topics related to inservice inspection include: 1) the reasons for and the basis of requirements for the site susceptibility of the canister installations, 2) the inspection intervals required by the Code Case, 3) the inspection sample population required by the Code Case, 4) the methods and acceptance criteria for visual examinations required by the Code Case, and 5) the size and location of the required inspection region for supplemental examinations. The topics related to the flaw evaluation include: 1) a summary of the crack growth rate technical basis, and 2) background related to flaw size evaluation for spent fuel canisters.

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