The effect of pre-sintering UO2 granules on the microstructure and the thermal conductivity of UO2–Mo composites fabricated by spark plasma sintering (SPS).

Uranium dioxide (UO 2) is the standard fuel used in light water reactors (LWRs). However, it has a low thermal conductivity that ultimately limits its performance both during normal operation and in accident conditions. Adding a material with high thermal conductivity is a potential approach to enhance the thermal conductivity of UO 2. Forming an interconnected structure of high-conductivity material can significantly enhance the overall thermal conductivity of the composite. Molybdenum (Mo) has been used as an additive material in UO 2 composites previously. A new method for the fabrication of interconnected UO 2− Mo composites using pre-sintered UO 2 granules to improve the continuity of Mo channels was investigated in this study. UO 2 –10 wt% Mo composites were produced using UO 2 granules and 1073 K and 1473 K pre-sintered UO 2 granules, followed by spark plasma sintering (SPS) of the mixtures at 1473 K for 5 min. The composites were characterised using scanning electron microscopy and X-ray diffractometry and their thermal conductivities were measured by the laser flash method and compared with a reference UO 2 pellet. At a maximum measurement temperature of 1073 K, a 52 % increase in thermal conductivity was observed in the composites containing UO 2 without pre-sintering, and UO 2 pre-sintered at 1073 K. The increase was 31 % for composites manufactured from UO 2 pre-sintered at 1473 K. These results suggest that higher temperature pre-sintering may be detrimental to forming interconnected Mo structures. [ABSTRACT FROM AUTHOR]