Investigation of the mechanical properties of ZrO2-doped UO2 ceramic pellets by indentation technique

ZrO2-doped UO2 ceramic pellets have been identified as a high performance nuclear fuel in LWR due to its desirable properties. Mechanical properties such as hardness, elastic modulus and fracture toughness, as well as microstructure of ZrO2-doped UO2 ceramics containing 0, 10, 15 and 20 wt% ZrO2 were investigated by Vickers micro-indentation technique, X-ray diffraction and scanning electron microscopy, respectively. The lattice parameter of the ZrO2-doped UO2 ceramics linearly decreases as a function of the ZrO2 content and follows Vegard's law, indicating the formation of a complete solid solution between the ZrO2 and UO2 up to 20 wt% of the ZrO2 content. The average grain size was typically between 20 and 30 μm with no dopant additions and gradually decreased to about 10 μm for additions of 20 wt% ZrO2. Additionally, the addition of ZrO2 will significantly increase the hardness and elastic modulus of UO2 ceramic by approximately 16.4% and 14.5% with the ZrO2 contents increasing from 0 to 20 wt%, respectively. Furthermore, the fracture toughness of UO2 ceramic was considerably decreased by the addition of ZrO2 dopant, which is evidently contrary to the hardness and elastic modulus.