Nuclear Science User Facilities 70 Characterization on the Bor-60 Neutron Irradiated Austenitic Stainless Steels and Cast Stainless Steel YongYang – University of Florida – The work was planned to system- ically characterize the 316 SA and 304 SA stainless steels and CF‑3 cast stainless steels irradiated to 45 dpa at 320°C in the Bor-60 reactor. Both transmission electron microscopy and atom probe tomography were used to study the irradiated induced nano-sized features, including disloca- tion, phase separation, and precipi- tates.The output from the execution of proposed study fills the existing knowledge gap by providing a more systematic study, at an atomic level, on neutron irradiation effects in light water reactor (LWR) internal struc- tural materials at LWR relevant condi- tions. By correlating the microstruc- ture study with selected mechanical tests, this proposed research provides a fundamental understanding of the response of austenitic stainless steels, cast stainless steel (welds) during the designed 40-year reactor life, and, more relevantly, during the extended life of 60 years and beyond. Figure 1. Spinodal decomposition in the ferrite phases of CF3 Cast Stainless Steel irradiated to 5, 10, 20 and 40 dpa, respectively.