Optical dilatometry and sintering studies of Cr2O3-doped UO2

Abstract

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.