This report summarizes research activities conducted at Argonne National Laboratory in support of the development, qualification and certification of additively manufactured (AM) metallic components to allow for innovative reactor design and licensing. In this program, AM 316L stainless steel (SS) was evaluated in both light water reactor (LWR) environments as well as at higher temperatures expected in advanced reactors.In order to assess the long-term performance of AM 316L SS as a structural material in hightemperature nuclear environment, fatigue and creep-fatigue tests were performed. The results were compared with conventionally made wrought 316L SS. It was found that fatigue lives of AM 316L SS were slightly lower than that of wrought 316L SS, and decreased with the increase of test temperature from 300 to 550°C. The specimens machined from printed rods performed somewhat worse than those machined from printed plates, and no obvious difference can be identified between the samples parallel and perpendicular to the build direction. While both fatigue strength and ductility contribute to the fatigue performance of AM materials, the temperature effect on the fatigue life manifested mainly thought its impact on fatigue ductility.The tests conducted at 550°C with a short hold time of 30 s did not deteriorate the fatigue performance of AM 316L SS at 0.2% and 0.3% strain amplitudes.The void distribution in a creep tested AM 316L specimen was characterized by synchrotron xray tomography and compared to that in a conventional 316L specimen tested under the same condition. Comparison was also made to the untested AM 316L material. It was discovered that the built-in voids from the LPBF process and the laser hatching pattern had critical roles in the creep performance of the AM material.The variable of void distributions at different locations of an AM 316L rod (4" long x 0.5" dia.) was also characterized by synchrotron x-ray tomography. Specimens were extracted from different locations on the rod. It was found that the top segment had a higher density of small voids than the bottom segment, leading to a slightly higher porosity level.