Surface Interaction of PuO2, UO2+x and UO3 with Water Ice

Synthesis and multi-scale properties of PuO2 nanoparticles: recent advances and open questions

Due to the increased attention given to actinide nanomaterials, the question of their structure-property relationship is on the spotlight of recent publications. Plutonium oxide (PuO₂) particularly plays a central role in nuclear energetics and a comprehensive knowledge about its properties when nanosizing is of paramount interest to understand its behaviour in environmental migration schemes but also for the development of advanced nuclear energy systems underway. The element plutonium further stimulates the curiosity of scientists due to the unique physical and chemical properties it exhibits around the periodic table. PuO₂ crystallizes in the fluorite structure of the face-centered cubic system for which the properties can be significantly affected when shrinking. Identifying the formation mechanism of PuO₂ nanoparticles, their related atomic, electronic and crystalline structures, and their reactivity in addition to their nanoscale properties, appears to be a fascinating and challenging ongoing topic, whose recent advances are discussed in this review.

Water on Actinide Dioxide Surfaces: A Review of Recent Progress

The fluorite structured actinide dioxides (AnO2), especially UO2, are the most common nuclear fuel materials. A comprehensive understanding of their surface chemistry is critical because of its relevance to the safe handling, usage, and storage of nuclear fuels. Because of the ubiquitous nature of water (H2O), its interaction with AnO2 has attracted significant attention for its significance in studies of nuclear fuels corrosion and the long-term storage of nuclear wastes. The last few years have seen extensive experimental and theoretical studies on the H2O–AnO2 interaction. Herein, we present a brief review of recent advances in this area. We focus on the atomic structures of AnO2 surfaces, the surface energies, surface oxygen vacancies, their influence on the oxidation states of actinide atoms, and the adsorption and reactions of H2O on stoichiometric and reduced AnO2 surfaces. Finally, a summary and outlook of future studies on surface chemistry of AnO2 are given. We intend for this review to encourage broader interests and further studies on AnO2 surfaces.

Direct observation of pure pentavalent uranium in U2O5 thin films by high resolution photoemission spectroscopy

Thin films of the elusive intermediate uranium oxide U₂O₅ have been prepared by exposing UO₃ precursor multilayers to atomic hydrogen. Electron photoemission spectra measured about the uranium 4f core-level doublet contain sharp satellites separated by 7.9(1) eV from the 4f main lines, whilst satellites characteristics of the U(IV) and U(VI) oxidation states, expected respectively at 6.9(1) and 9.7(1) eV from the main 4f lines, are absent. This shows that uranium ions in the films are in a pure pentavalent oxidation state, in contrast to previous investigations of binary oxides claiming that U(V) occurs only as a metastable intermediate state coexisting with U(IV) and U(VI) species. The ratio between the 5f valence band and 4f core-level uranium photoemission intensities decreases by about 50% from UO₂ to U₂O₅, which is consistent with the 5f ² (UO₂) and 5f ¹ (U₂O₅) electronic configurations of the initial state. Our studies conclusively establish the stability of uranium pentoxide.