Fracture properties of an irradiated PWR UO₂ fuel evaluated by micro-cantilever bending tests

For the first time, fracture properties of a UO₂ fuel preliminary irradiated in a Pressurized Water Reactor (PWR) were characterized by bending tests. Measurements were made at room temperature and at a local scale on micro-cantilevers. Notched and un-notched specimens were prepared with a Focalized Ion Beam (FIB) microscope. Some cantilevers were milled into single grains of the polycrystalline UO₂ fuel sample with specific crystallographic orientations chosen with Electron Backscatter Diffraction (EBSD) measurements, others were milled in order to test grain boundaries. Then, every specimen was tested up to failure with a nano-indenter in situ of the SEM/FIB chamber. The resulting brittle fracture parameters (fracture toughness and fracture stress) are compared and discussed. Grain boundaries exhibit a significantly lower fracture resistance than grains, and {111} crystallographic planes appear weaker than {100} and {110} planes in single grains. (author)