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 deg. C in air and then calcined in O2 at 800 deg. C followed by reduction in 8%H2/92%N2 at 600 deg. 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 deg. 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