Preparation of (U,Pu)O2 pellets through sol–gel microsphere pelletization technique

Mixed uranium–plutonium oxide microspheres were prepared by internal gelation process using feed solution of optimized composition. In the feed, total metal concentration was maintained at 1.5 M and hexamethylenetetramine (HMTA)-urea to metal mole ratio (R) was kept at 1.0. The gel particles obtained from each batch were dried and heated at 250 °C in air and then calcined in O2 at 800 °C followed by reduction in 8%H2/92%N2 at 600 °C for 1 h to obtain soft (U,Pu)O2 microspheres containing 4 mol% Pu. The soft (U,Pu)O2 microspheres were directly taken for the preparation of pellets. The microspheres were characterized with respect to surface area, tap density, crush strength and O/M ratio. X-ray diffraction analysis of the mixed oxide microspheres was carried out to identify the phases. The mixed oxide pellets were characterized for their density and micro-homogeneity. The sintering behaviour was studied by dilatometric investigations. The green pellets were sintered in 8%H2/92%N2 at 1600 °C for 2 h. The density of the sintered pellet was found to be 10.40 ± 0.05 g/cm3 with grains in the size range of 3–6 μm with an excellent micro-homogeneity.