The conditions of continued dry storage of the spent nuclear fuel in multipurpose canisters render the canisters, a component for confinement in dry storage cask systems, susceptible to chloride-induced stress corrosion cracking (SCC). The requisite conditions involve deposits of chloride-bearing marine salts and/or dust that deliquesce on the external surface of the cooling canister to create brine at weld residual stress regions. The subcritical crack growth rate at this “dry salt” condition, investigated by several researchers, has shown a relatively slow growth rate compared to chloride-cracking under aqueous conditions. A new SCC growth rate test specimen configuration has been developed to enable an initially dried salt assemblage to deliquesce under temperature and humidity conditions to load the fatigue pre-cracked, wedge-opening-loaded (WOL) specimen with the brine and enable measurements of crack growth rate (da/dt) under falling stress intensity factor, KJ, conditions. The application of the results to a canister weldment with a residual stress profile to predict crack extension in time is described. The results are evaluated in terms of development of acceptance standards for this type of flaw, should SCC be identified and characterized through inservice inspection (ISI).

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