Thermodynamic model of the oxidation of Ln-doped UO2

V L Vinograd; A A Bukaemskiy; G Deissmann; G Modolo

doi:10.1038/s41598-023-42616-x

Thermodynamic model of the oxidation of Ln-doped UO₂

Sci Rep. 2023 Oct 20;13(1):17944. doi: 10.1038/s41598-023-42616-x.

Authors

V L Vinograd¹, A A Bukaemskiy², G Deissmann², G Modolo²

Affiliations

¹ Institute of Energy and Climate Research-Nuclear Waste Management (IEK-6), Forschungszentrum Jülich GmbH, Jülich, Germany. v.vinograd@fz-juelich.de.
² Institute of Energy and Climate Research-Nuclear Waste Management (IEK-6), Forschungszentrum Jülich GmbH, Jülich, Germany.

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 LnO_1.5-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.