Lattice strain mapping of cracks and indentations in UO2 using synchrotron microdiffraction

Fractures and cracks commonly found in UO2 fuel in nuclear reactors have been studied for decades. In this study, an advanced synchrotron micro X-ray diffraction (μXRD) technique was used to study lattice strain development in cracking and indentation regions of micro-indented UO2 materials. A stoichiometric UO2 sample prepared by spark plasma sintering (SPS) was indented with a microscale Vickers indenter. The cracks and other defects on the sample surface observed in scanning electron microscope were correlated to the micro-diffraction measurements by Laue diffraction signal intensities, so that the lattice strains developed in those microstructures could be precisely mapped. The highest and lowest strained areas were found near the indentation tip and within the “open” crack, respectively. Induced by the residual stress, the lattice strain near the indentation was found to progressively decrease radially from the indentation boundary.