Studtite Formation Assessed by Raman Spectroscopy and ¹⁸O Isotopic Labeling during the Oxidative Dissolution of a MOX Fuel

Abstract

The formation of studtite was studied during the oxidative dissolution of a MIMAS MOX fuel disk in aerated water enriched in 18O under a γ radiation source, coupling Raman spectroscopy and solution analyses. The use of isotopic labeling enabled the reactions responsible for the precipitation of studtite to be followed. At the beginning of the experiment, different 18O enrichments in the uranyl and peroxide bonds of the studtite were observed. While the uranyl bond was primarily enriched in 18O, the peroxide bond contained large amounts of 16O. This result suggests an oxygen contribution coming from different radiolytic species for each bond: H2O2 and radicals. The comparison with a UO2 sample leached in similar conditions ruled out a role of Pu α self-irradiation in this different behavior. Nevertheless, the influence of the MOX MIMAS heterogeneous microstructure and chemistry was observed with the preferential dissolution of the UO2 grains, the Pu-rich areas being much more stable with regard to the dissolution. In addition, the studtite first precipitated preferentially on the Pu-poor areas of the sample before covering the entire surface, including the plutonium-enriched aggregates, at the end of the experiment.

Gamma-Ray-Induced Formation of Uranyl Peroxide Cage Clusters

“…This change is most likely due to a shift of the bridging hydroxyl between uranyl ions that is present in U 24 but definite assignment is beyond the scope of this paper. These shifts are in agreement with previous labeling studies done on uranyl peroxides. , The assembly reaction proceeds directly from the monomer to the cluster as shown by the isosbestic point just under 800 cm –1 in Figure and does so at a consistent rate as seen by the uniformly changing intensities of the bands over time.…”

“…These shifts are in agreement with previous labeling studies done on uranyl peroxides. 36,38 The assembly reaction proceeds directly from the monomer to the cluster as shown by the isosbestic point just under 800 cm −1 in Figure 2 and does so at a consistent rate as seen by the uniformly changing intensities of the bands over time.…”

Oxidative dissolution of (U,Ce)O2 materials in aqueous solutions containing H2O2

“…Indeed the zones with low plutonium 30,84 or cerium contents (this study) dissolved preferentially and were the place of the precipitation of studtite whereas the zones with higher cerium and plutonium contents remained unchanged.…”

Superoxide Radicals in Uranyl Peroxide Solids: Lasting Signatures Identified by Electron Paramagnetic Resonance Spectroscopy

“…The authors have cited additional references within the Supporting Information (Ref. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]).…”