Thermodynamic model of the oxidation of Ln-doped UO2

Abstract

Ln-doped UO2 is often considered as a model system of spent nuclear fuel (SNF) helping to reveal effects of fission and activation products on its chemical stability. Comparing thermodynamics of UO2-UO3 and LnO1.5-UO2-UO3 systems provides a means to understand the phenomenon of an increased resistivity of Ln-doped UO2 to oxidation in air relative to pure UO2. Here a thermodynamic model is developed and is applied to investigate detailed phase changes occurring along the oxidation of Ln-doped fluorite to U3O8. The study proposes that an enhanced resistivity to oxidation of Ln-doped UO2 is likely caused by a thermodynamically driven partitioning of Ln between a fluorite-type phase and a U3O8 polymorph, which at ambient temperatures becomes hindered by slow diffusion.

Long-term, sustainable solutions to radioactive waste management

“…Finally, spent nuclear fuel itself can be considered as a suitable wasteform, leading to its direct storage in geological repositories. In this context, Vinograd and co-workers 6 questioned the reactivity of Ln-doped UO 2 samples, as model compounds for SNF, towards oxidation in air. They showed that OPEN EDITORIAL 1 Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany.…”

“…5 Pacific Northwest National Laboratory, 902 Battelle Blvd, Richland, WA 99354, USA. 6 Massachusetts Institute of Technology, Cambridge, MA, USA. 7 Investing in fundamental research and the development of new technologies for waste treatment and disposal can lead to more efficient and cost-effective methods.…”

“…Finally, spent nuclear fuel itself can be considered as a suitable wasteform, leading to its direct storage in geological repositories. In this context, Vinograd and co-workers 6 questioned the reactivity of Ln-doped UO 2 samples, as model compounds for SNF, towards oxidation in air. They showed that the partitioning of lanthanide cations between the original fluorite-type phase and the oxidized U 3 O 8 enhanced the resistivity to oxidation, thus contributing to the chemical durability of the ceramic.…”