2016 | ANNUAL REPORT 57 precipitates, and voids.All of these experiments were conducted at the Microscopy and Characterization Suite (MaCS) at the Center for Advanced Energy Studies (CAES). This project will contribute to the scientific community in numerous ways. First, this project will help us gain a deeper understanding of the mechanisms of Si-Ni-Mn clustering in b.c.c. Fe-Cr alloys. More specifically, this project will help us understand the role of Si-Ni-Mn clustering in the irradiation stability of oxide nanoparticles in ODS steels. Stability of these oxide nanoparticles is critical to the long-term material integrity of ODS alloys in cladding and structural components in fission and fusion reactors. Second, this project presents a rare and unique opportunity to compare neutron, proton, and self-ion irradiation effects in identical heats of a model Fe-9Cr ODS alloy at identical irradiation temperatures and doses.This comparison offers great opportunity to help us understand fundamental differences in the creation of irradiation damage between neutrons, protons, and self-ions.Third, results of this project will be relevant to all ODS and other nanostructured alloys based on the b.c.c Fe-Cr matrix, which are of growing interest to the U.S. Department of Energy Office of Nuclear Energy due to their enhanced radiation resistance. Last, this project will enable a graduate student to utilize state-of-the-art ion beam irradiation techniques toward developing his thesis. Accomplishments The atomic level resolution of APT with Interactive Analysis and Visualization Software (IVAS) cluster analysis enabled both the characterization of the irradiation induced dissolution of oxide nanoclusters and the irradiation induced formation of Si-, Ni-, and Mn-rich clusters.The three- dimensional reconstructions of the neutron-, proton-, and self-ion- irradiated specimens all exhibit clustering ofTi, O, andY atoms along withTiO,YO, FeO, and CrO compounds at coincident locations in the matrix.There is also visual evidence of clustering among the Si, Mn, and Ni atoms at the same locations. Multiple localized electron atom probe (LEAP) tips were analyzed from each of the as-received and irradiated specimens. Representative atom distribution maps, as created by APT analysis and 3D reconstruction, are shown in the attached figures. Quantitative chemical analysis, enabled by the APT IVAS software, confirms the visual evidence of Si, Mn, and Ni clustering. For example, the fraction of all detected Si, Mn, and Ni atoms that are found in clusters (i.e. percent clustered) increases with irradiation. In addition, the in-cluster composition of Si, Mn, and Ni increase with all types of irradiation, while the matrix composition of Si decreases, further affirming that these species cluster during irradiation. Oxide nanoparticles co-evolve with Si, Mn, and Ni radiation induced segregation in ODS alloys.