Flash sintering of UO2 pellets for nuclear fuel and wasteform applications

Abstract

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 ~4µm, close to conventional sintering (CS). The optimised FS program reduced sintering temperature and cycle time by ~50% compared to CS. Scale up trials showed >96%TD pellets could be achieved for 11.3 and 14.125mm diameter green bodies, demonstrating typical fuel pellet diameters are feasible with FS. Gd doping experiments showed with 1wt.% Gd2O3 addition, a ~92%TD pellet with ~2µm grain size was obtainable, highlighting further optimisation is required for mixed oxide (MOx) materials.