Flash sintering of UO2 pellets for nuclear fuel and wasteform applications

Flash sintering (FS) has been shown to enhance the sintering kinetics in UO2. Using a bespoke AC-FS furnace, high density UO2 pellets, >95 % theoretical density (TD) have been produced followed by scale up and Gd2O3 doping trials. Increasing furnace temperature during FS increases pellet density to a plateau, however, increasing hold time and maximum current both increased the density of UO2 samples to >95 % TD and grain size to similar to 4 mu m, close to conventional sintering (CS). The optimised FS program reduced sintering temperature and cycle time by similar to 50 % compared to CS. Scale up trials showed >96 %TD pellets could be achieved for 11.3 and 14.125 mm diameter green bodies, demonstrating typical fuel pellet diameters are feasible with FS. Gd doping experiments showed with 1 wt% Gd2O3 addition, a similar to 92 %TD pellet with similar to 2 mu m grain size was obtainable, highlighting further optimisation is required for mixed oxide (MOx) materials.