2017 | AFC ACCOMPLISHMENTS 69 Accomplishments: In this work, UO2-UB2 and UO2-UB4 composites and the end members UB2 and UB4 have been sintered by SPS at Rensselaer Polytechnic Institute (RPI) and the conditions necessary to produce high density pellets (>90% TD) have been assessed. Arc-melting was used to produce the UB2 and UB4 buttons that were then crushed, milled and sieved to prepare the UB2 and UB4 feedstocks used in this work. X-ray diffraction (XRD) characterization showed that phase-pure materials were obtained through this method.These feedstocks were blended with UO2.00 feedstock to create UO2 composites with 5, 15 and 30%wt of both UB2 and UB4 phases. Pure UB2 and UB4 samples were also prepared alongside the UO2-UB2 and UO2-UB4 composites. Various heating profiles were tested to optimize the sintering parameters during SPS. It was found that the sample composition heavily influ- enced the sintering temperature with pure borides requiring higher temperatures to sinter to high densi- ties.While the UO2-based composites sinter to high densities at 1773 K in 5 minutes, the pure UB2 and UB4 samples had to be sintered at 2023 K in order to achieve densities larger than 90%TD.A typical microstructure, taken in backscatter mode, from a polished UO2-30%wt UB2 sample is shown in Figure 1.The islands of UB2 are rounded indicating that it is possible the UB2 phase was partially melted during SPS.The distribution of the UB2 phase is shown to be fairly uniform and no additional phases are currently observed. Thermal diffusivity values collected from LFA measurements performed at LANL, for UO2-UB2 (squares) and UO2-UB4 (circles) composites, sintered at 1773 K are shown in Figure 2, together with reference data from Fink [1] for UO2 and from White [2] for UB2 as a function of temperature for the range of 300-873 K.The thermal diffusivity for all composite samples was increased, when compared to the diffusivity of UO2, and sample UO2-30%wt UB2 showcased the largest increase with respect to UO2. Uranium boride phases can be added to composite fuels to improve thermal conductivity and provide a built-in burnable poison.