Raman microspectrometric identification of corrosion products formed on UO2 nuclear fuel during leaching experiments

The corrosion of directly disposed spent nuclear fuel by contact with intruding groundwater will alter the physical and chemical properties of this material. Secondary phases which formed during alteration of UO2 surfaces were measured with Raman microspectrometry and the characteristic vibrational spectra of the materials were recorded. U phases were synthesized in hydrothermal autoclave syntheses. A Raman spectral library of UO2 corrosion phases was set up for the identification of unknown products found on altered nuclear fuel samples. In a case study, U peroxide (UO4) was identified by comparison with a natural sample as the main alteration phase by its characteristic O–O Raman vibration at 870 cm−1. The results demonstrate the differentiation between UO2 and its alteration products U(VI) oxyhydroxide and U(VI) peroxide (UO4) on one sample with a relatively quick, non-destructive, spatially resolving measurement method which delivers oxidation state and molecular bonding information. Implications for the analysis of complex heterogenous matrices are discussed.