Friction Stir Processing of Degraded Austenitic Stainless Steel Nuclear Fuel Dry Cask Storage System Canisters

Chloride-induced stress corrosion cracking (CISCC) of austenitic stainless steel dry cask storage system (DCSS) canisters has been identified as an industry concern. Typical DCSS canisters are constructed from Types 304 or 316 stainless steel or their variants via conventional fusion welding processes. The presence of residual tensile stress and Cr-carbide precipitation within the weld heat affected zone (HAZ) places canisters near salt-bearing environments at an elevated risk for CISCC. The current study evaluates the suitability of friction stir processing (FSP) to repair stress corrosion cracking (SCC) and remediate sensitized fusion weld HAZs. FSP was applied to furnace sensitized Type 304 specimens containing laboratory-generated SCC and evaluated using liquid penetrant inspection, phased array ultrasonic inspection, and optical microscopy. In addition, fusion welded Type 304L specimens were fabricated, subjected to FSP, and destructively analyzed via ASTM A262 and optical microscopy. Results demonstrate that FSP is a viable option for SCC repair and sensitization remediation.