Investigation of irradiated uranium-plutonium mixed oxide fuel by synchrotron based micro X-ray diffraction

Specimens of a 4.7 wt % plutonium MOX fuel, irradiated for a period of 6 years up to 60 MW d kg−1 were investigated using synchrotron based micro X-ray diffraction technique (μXRD). The μXRD measurements at the Swiss Light Source SLS with a beam spot size of about 2 μm × 2 μm were carried out on the center and periphery region on the cross section of the irradiated fuel, as well as on un-irradiated reference MOX material. The profiles of characteristic (111), (200), (220), (311) and (222) diffraction lines of the irradiated samples were analyzed in detail and compared with the data of the non-irradiated MOX material, revealing the lattice distortion and dilatation in the irradiated fuel matrix. Broadening of reflexes can be observed due to the increasing stress finally yielding strain up to fuel grain fracture. This phenomenon is quantified thanks to the analysis of the reflexes arcs fine structure. The sub-grain number per grain volume is analysed as a function of fuel location and history.