Mechanical properties of Urania-Zirconia solid solutions with tetragonal and monoclinic structures

Ikeuchi, Hirotomo  ; Yano, Kimihiko ; Ogino, Hideki; Matsunaga, Junji*

Mechanical properties (micro-hardness, elastic modulus, and fracture toughness) of fuel debris are essential information for defueling work in the Fukushima Daiichi NPP. The Urania-Zirconia solid solution, (U,Zr)O, is expected to be separated into cubic phase with low Zr contents and tetragonal or monoclinic phase with high Zr contents during cooling process. In this study, the properties of tetragonal and monoclinic phase are investigated. The (UZr)O samples (x=0.85 for tetragonal phase and 0.95 for monoclinic phase) were prepared by sintering the compacted mixture of UO and ZrO powders at maximum 2673 K. The micro-hardness of samples was lower than what has been expected from trend of cubic phase. The elastic modulus was comparable with cubic phase. The fracture toughness of the tetragonal phase was higher than the other two phases. The stress-induced martensitic transformation around the indent is expected to increase the fracture toughness.