[en] Uranium dioxide is an oxygen excess, non-stoichiometric, fluorite material which exists over a wide range of compositions. At temperatures and oxygen activities that are relevant to its in-reactor behaviour, it has been reported that various types of point defects and clusters thereof may exist with different charge states and different compositions on both the anion and cation sublattices. These defects have a major influence on certain key engineering properties such as cation self -diffusion or creep. It is the aim of this work both to characterize the majority defects present in thermodynamically equilibrated samples and further our understanding of their impact upon uranium self -diffusion. To this end, three types of experiments were carried out. Neutron diffraction was used, as neutrons are sensitive to oxygen ions, to characterize samples with different oxygen to metal ratios at different temperatures. This work was carried out at Institut Laue Langevin in Grenoble on the D4c diffractometer which enables the determination of local atomic arrangements by means of the Pair Distribution Function analysis. Radial Distribution functions were modelled and compared to the experimental data. It is difficult to draw any firm conclusion about whether oxygen interstitials remain isolated or form clusters of ions in the low deviation from stoichiometry material as the system is extremely dilute. However, in samples containing much larger quantities of oxygen, results are consistent with the formation of clusters, either in a 2:2:2 type configuration or in the form of so-called cuboctahedron clusters, that are similar to those observed in U₄O₉. Positron Annihilation Spectroscopy was also carried out at CEMHTI, Orleans on samples originally equilibrated at high temperature but under different oxygen partial pressures and subsequently quenched. At high enough oxygen partial pressures, Doppler broadening and lifetime spectroscopy prove the emergence of a specific, uranium vacancy containing defect, with characteristics similar to the ones observed in irradiated material. Our results also highlight the specific effect of the presence of oxygen interstitials alone on Doppler broadening characteristics and confirm that their life -time properties are similar to those of the lattice. Uranium and oxygen defect concentrations are tentatively derived from interpreting the data using a trapping model. Finally, these results are complemented by uranium tracer diffusion experiments and attempt is made at interpreting changes in uranium self-diffusion coefficients based on our understanding of point defect behaviour. (author)