SiC whisker strengthened UO2–Mo composite pellets with superior thermal-mechanical properties

Abstract UO2–Mo composites are expected to be candidate materials for use as enhanced thermal fuel in the next generation of high-level safety reactors. Nevertheless, the UO2 matrix tends to create micro-cracks caused by thermal stress generated during the sintering process. A novel type of UO2–Mo-SiCw composite is fabricated by spark plasma sintering (SPS) to enhance the thermal-mechanical properties of UO2. In the composite, SiCw is dispersed uniformly in the UO2 matrix to form microspheres, and Mo is distributed in a three-dimensional network to form heat-conduction channels. Micro-cracks in the UO2 matrix are significantly suppressed in the UO2–Mo composite, since only a small amount of SiCw is incorporated into the UO2. Indentation testing indicates a great capability of the SiCw to sharply enhance the crack propagation resistance of the UO2 matrix. The estimated indentation fracture toughness reaches 0.91 MPa m1/2 with the incorporation of 0.5 vol% SiCw, representing a 68.5% improvement over the value of 0.54 MPa m1/2 obtained for the UO2–Mo composite. The thermal conductivity of the UO2–4Mo composite at 1000 °C was enhanced by approximately 54.3%, 60.1% and 67.2% for a SiCw content of 0.5, 2, and 4 vol%, respectively, compared with pure UO2. These results provide new insight for further improving the safety and lifespan of UO2 fuel in reactors.