Irradiation damage and IASCC of printed 316L for use as fuel cladding

Additive manufacturing is an area of increasing interest to the nuclear industry. It offers a number of benefits over traditional manufacturing methods, such as the ability to create complex geometries without the need for welds. In addition to the potential for creating nuclear structural components, additive manufacturing may be used to create novel fuel/cladding designs. However, printed steel behaves differently than traditional wrought material. A number of industries are already studying the effects of the printed microstructures on mechanical properties. For cladding material and some structural nuclear components, however, the nuclear industry must also understand the material response to irradiation. This work examines the irradiation damage and the irradiation assisted stress corrosion cracking behavior of both proton irradiated (1 and 5 dpa) printed 316L steel and wrought 316L steel that were irradiated side by side at the Michigan Ion Beam Laboratory. As orientation with respect to the build direction can affect the mechanical properties of printed metal, specimens were taken from multiple orientations within the printed steel. For the IASCC testing, specimens were strained to 4% in simulated BWR NWC water (288°C, 0.2 µS/cm). TEM, SEM and X-ray microCT were used to examine coupons of the material as well as tensile bars used in the IASCC testing. This work found that the wrought 316L was more susceptible to IASCC than the printed steel, however, significant IASCC was observed in the printed steel when tested with the tensile axis in line with the build direction. TEM observations have shown significantly fewer radiation induced voids forming in the printed steel, likely due to the preexisting void network acting as sinks to point defects. The lower density of voids is believed to be contributing to the IASCC resistance by decreasing the localization of deformation in the irradiated specimens.