Raman microspectroscopic studies of unirradiated homogeneous (U0.76Pu0.24)O2+x: the effects of Pu content, non‐stoichiometry, self‐radiation damage and secondary phases

In this study, micro‐Raman spectroscopy technique was implemented to characterize an unirradiated homogeneous Gigondas (U0.76Pu0.24)O2+x sample, which had been stored for 30 years at room temperature under air. The impacts of Pu content, deviation from stoichiometry, self‐radiation damage and formation of secondary phases were assessed by comparing the Raman spectra of the aged Gigondas with an annealed sample [(U0.76Pu0.24)O2]. The Pu content of the sample was measured by electron probe microanalysis technique, while the stoichiometry of the annealed Gigondas sample was determined by the results of electron probe microanalysis technique and X‐ray diffraction. Two methods were proposed to explain the Raman spectrum of the aged Gigondas sample. They considered the presence of MO2+x phase and the mixture of MO2+x and M4O9 (M: U and Pu) phases respectively. Formation of the secondary phases, which were detected on the surface of the aged Gigondas sample, could be mostly due to alpha radiolysis. It was suggested that self‐radiation damage up to about 0.6 dpa leads to a shift of MO2+x T2g band by about 1 to 2 cm−1 towards lower wavenumbers. Copyright © 2017 John Wiley & Sons, Ltd. Characterization of the radioactive materials by Raman spectroscopy needs special attention. The present study aims at giving a general guidance for the characterization of U‐Pu mixed oxides with Raman spectroscopy by comparing the Raman spectrum of annealed (U0.76Pu0.24)O2 and 30‐year‐old (U0.76Pu0.24)O2+x samples. It has been pointed out that before analysing Raman spectra, Pu content, concentration of decay products, level of radiation damage, storage conditions, non‐stoichiometry and formation of secondary phases should be taken into consideration.