Preparation of UC ceramic nuclear fuel microspheres by combination of an improved microwave-assisted rapid internal gelation with carbothermic reduction process

Uranium carbide (UC) ceramic microspheres filled into a cladding are a potential nuclear fuel format for nuclear reactors. Uniform sized ceramic UC microspheres with a diameter of 675 ± 10 µm were successfully prepared by an improved microwave-assisted rapid internal gelation process combined with carbothermic reduction. First of all, the nanoparticle carbon was dispersed into the HMUR stock solution, and the C-UO3·2H2O gelled microspheres were prepared using an improved microwave-assisted internal gelation process without cooling the initial stock solutions. Next, the gelled microspheres were subjected to a carbothermic reduction process to obtain ceramic UC microspheres. TG and XRD investigations indicated that the C-UO3·2H2O microspheres were firstly reduced into UO2 at a temperature of 700 °C, and were further converted into UC at 1500 °C in argon atmosphere. Crack-free ceramic UC microspheres with a smooth and metallic shiny surface were obtained at a sintering temperature of 1500 °C for 5 h with an initial C/U molar ratio of 3.5.