Quantification of irradiation-induced defects IN UO2 using Raman and positron annihilation spectroscopies

In UO2, Raman spectroscopy has recently put into evidence the existence of a specific signature, referred to as the triplet defect bands, which is characteristic to irradiation damages. In this work, we perform a detailed experimental analysis to investigate how this Raman signature can be used to characterize irradiated nuclear fuels. For this purpose, an electron irradiation experiment of sintered UO2 disks coupled with ex situ Raman and positron annihilation spectroscopy measurements were carried out. The obtained findings showed that the Raman defect bands take their origin from the ballistic collisions of the incident electrons with the U and O atoms and are due to the formation of point defects. These defects induce the re-arrangement of UO2 lattice atoms and give rise to domains with symmetry lower than Fm-3m with the loss of one or more symmetry elements, such as translational symmetry, centering F, mirror or rotational symmetry operations.