Effects of irradiation on mechanical properties of nuclear UO2 fuels evaluated by Vickers indentation at room temperature

•Irradiation effect on hardness and apparent fracture toughness of UO2 fuels was studied using a large number of Vickers tests.•The Vickers hardness of UO2 quickly increased with the local burnup but decreased when the fuel restructured into the HBS.•The Vickers fracture toughness of the non-restructured doped UO2 increased quickly during the first irradiation cycle but was then constant with increasing local burnup. In the HBS, the fracture toughness was shown to be difficult to determine from indentation tests.