2017 | AFC ACCOMPLISHMENTS 64 Transmission Electron Microscopy of Native Oxides of U-Si Compounds Principal Investigators: P. Edmondson Collaborators: A. Nelson, Q. Smith, D. Skitt, K.Terrani Figure 1. Scanning Transmission Election Microscopy (STEM) Energy Dispersive X-Ray Spectroscopy (EDS) maps recorded for U3Si2 sample showing chemical structure of native oxide layer. Various uranium-silicide compounds are of interest as Accident Tolerant Fuel (ATF) concepts and as constituents in fissile ceramic composites, but remain far less understood with respect to their basic structure and chemistry compared with more established fuels. One particular area that is not understood is the native oxides formed on these materials following fabrication. Oxidation is a known vulnerability of these fuels, and further oxidation of feedstock has been demonstrated to impair fabrication. A collaborative investiga- tion executed by Oak Ridge National Laboratory (ORNL) and Los Alamos National Laboratory (LANL) LANL utilized advanced characterization methods to assess the structure of the surface oxides of U-Si compounds. Unprecedented detail on chemistry and structure of the native oxide of these materials on the nanometer scale was provided by this work.This information is key for interpretation of degradation mechanisms relevant to light water reactor deployment of these materials. Project Description: Execution of basic studies to under- stand the fundamental processing- structure-property-performance