Oxide-dispersion strengthened (ODS) ferritic-martensitic (F-M) alloys are leading candidates for structural components in fusion and fast fission reactors, because of their high-temperature strength, dimensional stability, and low activation. The large number of interfaces in F-M ODS alloys serve as point defect sinks, limiting the concentration of vacancies available to coalesce into bubbles or voids, thus increasing the radiation resistance of these materials. However, a high density of interfaces could be adverse to radiation tolerance if considerable radiation-induced segregation (RIS) were to occur at the interfaces. Lower-Cr F-M ODS alloys (i.e. those steels containing ~8-10 wt% Cr in bulk) could be attractive for nuclear applications because brittle, Cr-rich a’ phases have only been observed in higher-Cr F-M alloys. But on the other hand, the extent of Cr enrichment at grain boundaries is greater in the lower-Cr F-M alloys than in the higher-Cr F-M alloys. Recent studies on the irradiation response of F-M ODS alloys to have focused almost exclusively on higher-Cr ODS steels such as MA957 and 14YWT (both ~14 wt% Cr). Only limited work has been published on the irradiation response of the lower-Cr F-M ODS alloys. This project aims to characterize the irradiation response of lower-Cr F-M ODS alloys, including the phase stability, evolution of the oxide dispersoids, microstructure, and RIS. The specimens to be studied are a model Fe-9Cr ODS alloy and 9YWT, each previously irradiated with 5.0 MeV Fe++ ions to 100 dpa at 400°C. A sample of the same heat of the Fe-9Cr ODS alloy (sample library #023-331), which has been irradiated in the Advanced Test Reactor to 3 dpa at 500°C, will also be characterized. This project presents a rare opportunity to compare irradiation effects in the Fe-9Cr ODS alloy across two dose rates, without being affected by heat-to-heat variability. A combination of transmission electron microscopy (TEM) and local electrode atom probe (LEAP) analyses will provide a thorough characterization of the irradiated microstructure, phases, and grain boundary RIS. This proposal requests access to the Microscopy and Characterization Suite (MaCS) at the Center for Advanced Energy Studies (CAES), for 6 days on the FEI Quanta focused ion beam, 4 days on the CAMECA 4000X HR LEAP, and 6 days on the FEI Tecnai TEM.