In this work, both 22Na based positron lifetime spectroscopy (PALS) and slow positron beam based Doppler annihilation-ray broadening spectrometry (SPBDB) have been used to characterize respectively the bulk and the first micron under the surface of sintered UO 2 disks that have been polished and annealed at high temperature (1700 °C/24 h/ArH 2 ). Results show the presence of negative ions that are tentatively identified to negatively charged oxygen atoms located in interstitial sites. The positron annihilation characteristics in the UO 2 lattice have been determined and are equal to S L (UO 2 ) = 0.371(5), W L (UO 2 ) = 0.078(7), τ L (UO 2 ) = 169 ± 1 ps. Such disks have been irradiated at room temperature with electrons and α particles at different fluences. After irradiation, SPBDB and PALS measurements show the formation of U-related vacancy defects after a 2.5 MeV electrons irradiation whereas no defects are detected for an irradiation at 1 MeV.

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