Characterization of irradiated AISI 316L stainless steel disks removed from the Spallation Neutron Source

Abstract Disk-shaped samples were removed from the first and second operational target modules at the Spallation Neutron Source for post-irradiation examination to assess the extent of radiation-induced changes in mechanical properties and the amount of cavitation-induced erosion to the AISI 316L stainless steel target vessel. Characterization techniques performed include: high-resolution photography of the disk specimens, ultrasonic cleaning to remove mercury residue and surface oxides, surface profile mapping of cavitation pits using high frequency ultrasonic testing, high-resolution surface replication, and scanning electron microscopy accompanied by energy dispersive spectroscopy. The target disk samples were machined using wire electrical discharge machining to produce microstructural and mechanical test specimens for tensile testing, Rockwell Superficial hardness testing, and Vickers microhardness testing. The effectiveness of the cleaning procedure was evident in the pre- and post-cleaning photography, and provided accurate photographs of areas on each disk that facilitated the creation of detailed machining maps. Due to the limited amount of material available and the unique geometry of the disks, test specimen design and development of fixturing for machining operations were critical aspects of this work; multiple designs were considered and refined during mock-up testing on unirradiated disks. The techniques used to successfully machine and test the various specimens will be presented along with a summary of important findings from the laboratory characterizations.