To fully understand how the high-temperature ultrafine-precipitate-strengthened (HT-UPS) austenitic stainless steel responds to a sodium cooled fast reactor (SFR) relevant irradiation condition, it is proposed to utilize the transmission electron microscopy (TEM) and atom probe tomography (APT) at MaCS/CAES to quantitatively analyze the neutron irradiation induced defects such as dislocation loops, voids, radiation-induced precipitates and the RIS. TEM disk samples (as-received, 3dpa/500°C and 3dpa/500°C + ann. at 600°C) are available to this project. Complemented by the far-field high-energy X-ray diffraction microscopy (FF-HEDM) measurement at APS/ANL, the anticipated outcome from this project will provide a fundamental understanding of the irradiation effects on this material’s microstructure and microchemistry at multi-scale (nano to meso). The results will further help to understand the mechanical responses of neutron microstructure to an in-situ high energy X-ray tensile test. The project is fully aligned with the DOE-NE’s missions via supporting the advanced reactor concepts (ARC), advanced small modular reactors (aSMR), and nuclear energy advanced modeling and simulations (NEAMS) programs. The proposed period of experiment is FIB for 2 days, Tecnai TEM for 2 days, and LEAP for 4 days.The research will be completed within six months after the proposal is approved and granted instrument time.

HT-UPS austenitic stainless steel has a significantly improved high temperature creep resistance, and the material has been considered as a candidate structure material for the sodium cooled fast reactor. A complete understanding of material’s microstructural changes and phase evolutions from neutron irradiation will directly benefit the nuclear materials modeling and efforts to design alloys with improved irradiation performance. This proposed research is fully aligned with DOE NE’s missions as exemplified in programs of light water reactor sustainability (LWRS), advanced reactor concepts (ARC), advanced small modular reactors (aSMR), and nuclear energy advanced modeling and simulations (NEAMS).