Fabrication of Uranium Nitride Surrogate Nuclear Fuel

Uranium nitride (UN) is an advanced nuclear fuel candidate distinguished by its high uranium density of 13.5 g-U/cm³ and thermal conductivity of 13.6 W/m*K (300 °C, 95% TD), which improves with temperature. Accordingly, UN has the potential to serve as a replacement for traditional uranium dioxide (UO₂) fuel. While alternative consolidation methods such as Spark Plasma Sintering (SPS) may produce higher-density material, conventional sintering is currently the most feasible option for mass fuel fabrication. In this study, UN powder was synthesized from UO₂ and graphite precursors using the carbothermic reduction prior to nitriding method. This synthesis route leverages the existing UO₂ supply chain and is a commercially scalable synthesis route for metal nitrides. Disc shaped samples of 1 cm diameter and nominally 2 mm height were pressed at 350 MPa and densified to > 90% theoretical density using pressureless sintering for 3 hours at 1800 °C. Oxygen impurities were analyzed using combustion analysis and thermal diffusivity experiments were performed using Laser Flash Analysis (LFA). Results show that the fabricated UN is phase pure and the influence of oxygen levels on thermal diffusivity will inform manufacturing requirements moving forward.