Thermodynamic model of the oxidation of Ln-doped UO2
V L Vinograd1, A A Bukaemskiy2, G Deissmann2
1Institute of Energy and Climate Research-Nuclear Waste Management (IEK-6), Forschungszentrum Jülich GmbH, Jülich, Germany. v.vinograd@fz-juelich.de.
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.
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