Mechanical response of UO2 single crystals submitted to low-energy ion irradiation

{111}- and {100}-oriented UO2 single crystals were irradiated with 500-keV Ce3+ ions in the 1014-9 × 1014 cm−2 fluence range. The irradiation-induced strain was monitored using high-resolution X-ray diffraction. A mechanical modelling dedicated to thin irradiated layers was applied to account for the reaction of the unirradiated part of the crystals. The elastic strain, which is confined along the surface normal of the samples, increases with ion fluence until it is dramatically relieved. This behaviour is observed for both orientations. While the measured elastic strain depends on the crystallographic direction, the strain due to irradiation defects only is found to be equal for both directions, with a maximum value of ∼0.5%. Strain relaxation takes place at the damage peak, but the in-plane lattice parameter of the irradiated layer remains unchanged and equal to that of the pristine material. Meanwhile, the strain at the damaged/pristine interface continues to increase.