2017 | AFC ACCOMPLISHMENTS 65 linkages for proposed ATF concepts is a key component of their deployment. High density fuels such as U3Si2 provide advantages, but are far less understood than UO2. Execution of a science-based fuel development campaign to advance the technical readiness level of these systems requires understanding of their basic structure and chemistry. Surface oxidation is a fundamental challenge to deployment of U3Si2. While previous studies of elevated temperature oxidation behavior have been performed, the structure of the as-fabricated surface oxide (i.e. native oxide) of U3Si2 and other compounds in the U-Si system has not been previously investigated. This is of particular relevance to development of industrial processing methods for these systems. Oxida- tion of powder feedstocks has been found to significantly retard sintering kinetics; storage of U3Si2 powders in even very low oxygen environments (e.g. inert gloveboxes) will result in oxidation, and degrade the product densities achieved through sintering operations. As the oxide structure formed at ambient temperatures was not previously understood, it was not possible to develop more robust processing steps or other mitigation techniques.The results of this work address this gap and demonstrate the potential for state of the art charac- terization at lower length scales to address similar challenges in fuel development. Accomplishments: Specimens of U3Si5 and U3Si2 were prepared using reference fabrication processes at LANL and shipped to ORNL. At ORNL, the samples were polished and subsequently imaged using electron backscatter diffraction (EBSD).The results of the EBSD exam- ination for U3Si5 provided important insights into another previously unknown aspect of U3Si5 behavior, as the micro cracking observed in U3Si5 samples was correlated to a specific crystallographic orientation.This data will assist in future studies of the elevated temperatures phase transfor- mations in this portion of the U-Si phase diagram. Following EBSD, focused ion beam (FIB) lift outs were performed to prepare foils for transmission electron microscopy (TEM). BothTEM and