2017 | AFC ACCOMPLISHMENTS 59 Accomplishments: Sample fabrication took place in the Fuel Research Laboratory at Los Alamos National Laboratory (LANL). The material chosen for initial investigation was U3Si2 given its prevalence across a range of Accident Tolerant Fuel (ATF) concepts. In addition, U3Si and USi were included in the study given their presence in U3Si2 as common impurity phases. Samples of U3Si2 containing varying levels of oxygen were also included in the study to assess the impact of oxidation on mechanical properties. The RUS along with (Figure 1) both quasi-static and continuous stiffness nanoindentation measurements were performed at LANL. Results of nano- mechanical testing (Figure 2) high- light properties determined as a func- tion of depth in these materials. Use of both RUS and nanoindentation have provided a number of mechanical and elastic properties for these compounds that were previously unavailable. Hardness is a critical component in post-irradiation examination and provides insight into chemical and microstructural evolutions of fuel following burnup. Elastic and bulk moduli are essential parameters that link strain to stress; determining the impact that the temperature gradients present in operating fuel will have on stress and in turn fuel pellet fracture requires these data. Finally, the funda- mental elastic constants as provided by RUS are essential inputs to density functional theory and other modeling efforts.The availability of these param- eters for U3Si2 and other fuel materials will improve the ability of companion modeling and simulation efforts to capture and predict the behaviors of these materials.These measurements will be extended to fuel operating temperatures in the coming year.