2017 | AFC ACCOMPLISHMENTS 78 introduced into the material either by feedstock synthesis, ageing, fabri- cation, or other means is quickly incorporated as UO2. Feedstocks were produced containing nomi- nally 2000, 4000, 6000, 8000, and 10,000 weight percent oxygen. For the U3Si2+O system, these levels of oxygen correspond to volume fractions of approximately 2, 4, 6, 8, and 10% UO2 within the uncertainty of the synthesis method (+/- 2%). The oxygen-containing feedstocks were then fabricated into pellets using the standard U3Si2 sintering procedure.This yielded property measurement samples of better than ninety percent theoretical density sized to accommodate a range of techniques.The initial focus of investigation was thermal conduc- tivity.The thermal conductivity of U3Si2 is far superior to UO2; this provides one of the main advan- tages for a U3Si2 fuel as centerline temperatures and stored energy is significantly reduced. However, the incorporation of oxygen as UO2 into U3Si2 pellets poses a concern for reactor operation as the UO2 would be expected to degrade thermal conductivity through either presence of the oxide phase or by internal cracking that could be caused by thermal expansion mismatch between the two materials. The results of laser flash analysis examination of a number of U3Si2 samples containing varying oxide contents are plotted in Figure 1. Thermal diffusivity is a measure of a number of intrinsic mate- rial behaviors that affect heat transfer. Perturbations to thermal diffusivity correlate directly to thermal conductivity when mate- rial composition is not significantly