Defect study in Xe-irradiated UO2 by XRD, TEM and PAS

Transmission electron microscopy (TEM), X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS) characterizations were combined on polycrystalline UO 2 disks, implanted with low energy xenon ions, to probe the microstructural transformations due to irradiation by taking advantage of their different sensitivities to radiation damage. While XRD provides information on elastic strain (and thus free swelling) and microstrains, PAS is sensitive to vacancy defects and TEM allows the direct observation of extended defects (dislocations and vacancy objects). These data were gathered in order to understand mechanisms involved in the damage build up in UO 2 . At a very low damage level, an increase of the free swelling is highlighted along with first vacancy defects, and then with interstitials dislocation loops. At a higher damage level, dislocation lines appear through loop interactions, inducing a small free swelling relaxation associated with an increase of microstrains. The results of this extensive experimental study are then discussed in the light of literature data.