Spark plasma sintering of diamond-reinforced uranium dioxide composite fuel pellets

• Fabricated UO2–diamond composite fuel pellets using spark plasma sintering (SPS).
• Increased thermal conductivity by up to 41.6% compared to standard pure UO2 fuel.
• Investigated the effect of diamond particle size on properties of composites.

In an effort to increase the thermal conductivity of UO2 fuel pellets, high density UO2–5 vol% diamond composite pellets were fabricated using the spark plasma sintering (SPS) technique. Diamond particles with nano-size (0.25 μm) and several micro-sizes (3 μm, 12 μm and 25 μm) were mixed with UO2 powder and sintered using SPS at 1300–1600 °C with a hold time of 5 min. The resultant density, chemical reaction, microstructure, thermal conductivity and Young's modulus of the sintered pellets were investigated. The pellets with 3 μm diamond particles had a uniform distribution of particles as well as better thermal and mechanical properties compared to others. An increase in thermal conductivity of up to 41.6%, 38.3% and 34.2% at 100 °C, 500 °C and 900 °C, respectively, was measured in the UO2–diamond composite pellets compared to the pure UO2 fuel pellets.