Fabrication of UO2–Mo composite fuel pellets with enhanced thermal conductivity by using wet mixing

Uranium dioxide (UO₂) is the standard nuclear fuel for light water reactors (LWRs) due to its operational experience, irradiation stability, and ease of manufacture. However, its low thermal conductivity results in a high temperature gradient across the pellet in-service, leading to thermal stresses, deformation, and cracking. This study explores the addition of a high thermal conductivity molybdenum phase as a nano-powder, which is trialled alongside pre-sintered UO 2 granules to improve the thermal conductivity of the resulting pellet. UO 2 - 10 wt. % Mo composite pellets were fabricated by dispersing UO₂ granules and nano-Mo powder in ethanol during mixing, followed by ethanol evaporation and subsequent Spark Plasma Sintering (SPS) at 1473 K with a 5-minute hold. Pellet microstructures were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Pellet thermal conductivity was measured by the laser flash method. Significant improvements in thermal conductivity were observed in the as-manufactured pellets with increases of up to 75% at 1073K for the pellets produced from nano-Mo and pre-sintered UO 2 granules compared to a pure UO₂ pellet. These results highlight the effectiveness of nano-Mo addition and the pre-sintering of UO 2 granules in enhancing the thermal performance of UO₂-based nuclear fuel composites.