Optical dilatometry and sintering studies of Cr2O3-doped UO2

Optical dilatometry has been used to study the sintering behaviour of Cr2O3-doped UO2 and such observations have been compared to undoped UO2, enabling a visual and measurable comparison of their behaviour during this important manufacturing step. Sintering UO2 and Cr2O3-doped UO2 pellets at different temperatures allowed for grain nucleation and growth to be assessed. Optical dilatometry was implemented to visually assess differences in the densification of UO2 and Cr2O3-doped UO2. The rate of sintering and extent of shrinkage was found to be higher for the doped pellet, with the Cr2O3-doped pellet decreasing in volume by ∼40 %, compared to only ∼20 % for the undoped pellet. The temperature at which shrinkage commenced was also approximately 100 – 200 °C lower for the doped sample than for the undoped variant. This indicates that there is a difference between the sintering processes of the two systems. The possible contribution of the CrUO4 secondary phase to large grain growth has also been examined through Differential Scanning Calorimetry (DSC) in reducing conditions. A change occurring at approximately 1250 °C for CrUO4 was observed. This temperature corresponds to the end of shrinkage and start of grain growth for Cr2O3-doped UO2 pellets, as shown in the optical dilatometry experiments, which could be indicative of the commencement of the large-grain growth process.