Friction stir welding (FSW) is a cutting-edge technique enabling potential on-site repairs. However, there are knowledge gaps regarding the impact of neutron damage after welding. The Oak Ridge National Laboratory (ORNL) team has successfully demonstrated helium-contained, crack-free FSW on irradiated stainless steel. The welding utilized HFIR-irradiated 304L stainless steel containing different helium levels. For this project, coupons from these welds will be re-irradiated using Fe self-ion irradiation. The self-ion irradiation will be performed using an accelerator at Texas A&M University. The sequence of HFIR irradiation, FSW, accelerator Fe ion irradiation, and characterization provides useful data to evaluate the overall performance of FSW welds. The main benefit is to use a hybrid neutron + ion irradiation to extend the damage level beyond that attained in HFIR, as a fast and low-cost testing method. For post-welding accelerator irradiation, the irradiation includes several temperatures allowing for the consideration of temperature shifting effects (caused by the large dpa rate difference between reactor irradiation and accelerator irradiation). The temperature matrix considers the uncertainty of the currently available temperature shifting model, for the benefit of creating additional useful data for the future hybrid reactor + accelerator irradiation experimental designs. The project involves sample cutting at Oak Ridge National Laboratory, accelerator irradiation at Texas A&M University, and structural characterization at Idaho National Laboratory. The FSW welds are ready and available for the project.

The proposed work directly aligns with the mission of the U.S. Department of Energy (DOE), Office of Nuclear Energy (NE), which aims to advance U.S. nuclear power to meet the nation's energy needs by enhancing the long-term viability and competitiveness of the existing U.S. reactor fleet. The lack of data on the neutron irradiation effects on FSW welds is crucial for the nuclear industry to consider adoption of FSW as an on-site in-vessel repairing solution. The project's impact extends to fundamental studies, optimization, and commercialization of FSW. Additionally, it will have implications for safety analysis and qualification processes.