Fabrication, defect chemistry and microstructure of Mn-doped UO₂

Mn-doped UO₂ is under consideration for use as an accident tolerant nuclear fuel. We detail the synthesis of Mn-doped UO₂ prepared via a wet co-precipitation method, which was refined to improve the yield of incorporated Mn. To verify the Mn-doped UO₂ defect chemistry, X-ray absorption spectroscopy at the Mn K-edge was performed, in addition to X-ray diffraction, Raman spectroscopy and high-energy resolved fluorescence detection X-ray absorption near edge spectroscopy at the U M₄-edge. It was established that Mn²⁺ directly substitutes for U⁴⁺ in the UO₂ lattice, accompanied by oxygen vacancy (O_v) charge compensation. In contrast to other divalent-element doped UO₂ materials, compelling evidence for U⁵⁺ in a charge compensating role was not found. This work furthers understanding of the structure and crystal chemistry of Mn-doped UO_2, which could show potential advantages as a novel efficient advanced nuclear fuel.