NEUTRON RESIDUAL STRESS MAPPING OF REPAIRED SPENT NUCLEAR FUEL WELDED STAINLESS-STEEL CANISTERS

摘要

Abstract: Stress corrosion cracking (SCC) caused byatmospheric deposition and deliquescence of aggressivecompounds such as chloride-containing salts or oxidizedsulfur species may pose a potential issue to the extendedservice life of spent nuclear fuel (SNF) storage canisters.When a chemically susceptible material is exposed to ahostile environment (e.g., coastal salt air) for a sufficientlength of time, SCC may occur at locations on the canisterwhich have undergone high tensile residual stress. Theselocations are often found in weld zones and the heataffectedzones (HAZ) of welded joints. Ideally, these crackscould be repaired by traditional fusion welding techniques,but the highly localized heat input of the repair weldingmay introduce additional high tensile residual stress andcould increase the risk for future SCCs. This paperpresents the results of neutron residual stress mapping ofas-welded and repaired stainless steel specimens. The asweldedspecimens were provided by Sandia NationalLaboratories from a canister mock-up manufactured usingprocedures similar to those used for actual canisterproduction. ASME-qualified gas-tungsten arc welding(GTAW) was used to repair the specimens, and post-repairresidual stresses were measured using neutron diffractionat the Oak Ridge National Laboratory (ORNL) High FluxIsotope Reactor (HFIR). As-welded and repaired specimenresidual stress distributions are evaluated and compared.Significant residual stress profiles were identified from thereceived as-welded longitudinal weld sample. Thegenerated residual stress profile from neutron diffractionis similar to that of the Sandia residual stress data obtainedfrom deep-hole drilling. The GTAW-repaired specimenshowed a notable redistribution in residual stresses andeven introduced compressive stresses when compared withthe as-welded condition. It appears that groove excavationand the well-controlled GTAW heat input resulted in astress relief/annealing effect on the metal. The results ofthis comparison are expected to be used to guideimprovements in future repair welding techniques.