Water on Actinide Dioxide Surfaces: A Review of Recent Progress

Abstract

<jats:p>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.</jats:p>

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

“…It is expected that the selective adsorption of ligands on the desired surface would also control the morphology of nanocrystals that are formed. 19,173 Simulations performed by Zhang et al indicated that interactions between the PuO 2 (111) surface and H 2 O are higher than those observed with CO 2 under similar ( P , T ) conditions. 174…”

“…Particularly, it has been demonstrated that water can be present as adsorbed hydroxyl groups on the ( 110) and (100) surfaces, even at elevated temperatures and pressures. 19,173 In contrast, the interaction of H 2 O with PuO 2 bulk surface has been experimentally reported to generate H 2 gas as well as an overstoichiometric oxide PuO 2+x containing Pu(VI) moieties. 175 Using X-ray and ultra-violet photoelectron spectroscopies (XPS and UPS, respectively), Gouder et al investigated the behaviour of a PuO 2 thin lm surface in contact with water.…”

“…MOX is a ceramic made out of a mixture of depleted uranium and plutonium dioxides both crystallizing in the fluorite structure of the face-centered cubic system ( Fm 3̄ m space group). 19,20 Current MOX fuel used in some PWR reactors has a plutonium mass level (Pu/(U+Pu)) lower than 10%, whereas future nuclear reactors, such as sodium-cooled fast reactors, would burn more Pu, necessitating a 30% mass level in nuclear fuel. 21 Current fuel preparation, based upon the precipitation and calcination of oxalate precursors, can lead to localized fuel heterogeneities responsible for the decrease of the fuel performance during operation (release of fission gas, fuel swelling, dislocation, etc. )…”

Charge Localization and Magnetic Correlations in the Refined Structure of U3O7

“…A significant body of work has been published on the thermodynamics of the U–O binary system as well as on the oxidation kinetics of UO 2 under dry and wet conditions. − Oxidation alters the original fluorite-type crystal lattice by forming oxygen defects and defect clusters . At temperatures above 700 K, a wide nonstoichiometric solid solution phase field (UO 2+ x ) gradually develops, but at lower temperatures only slight deviations from stoichiometry (0 < x < 0.03) can occur .…”

Thermodynamic non-ideality and disorder heterogeneity in actinide silicate solid solutions

“…For instance, U can be involved in redox reactions leading to the more mobile uranyl-based species, but Th remains tetravalent, so the dissolution rate of uranothorite could be enhanced due to the nanoscale heterogeneity in the material. Plus, these small sized heterogeneities could also yield a significant amount of highly active sites in the interfaces or surfaces, which can act as catalysts for reactions with the aqueous solution to promote dissolution [92][93][94] . As a consequence, the heterogeneity can potentially introduce the incongruent corrosion process and induce intragranular stress in the bulk structure due to dislocation activity.…”