Fabrication, defect chemistry and microstructure of Mn-doped UO 2 .

Mn-doped UO 2 is under consideration for use as an accident tolerant nuclear fuel. We detail the synthesis of Mn-doped UO 2 prepared via a wet co-precipitation method, which was refined to improve the yield of incorporated Mn. To verify the Mn-doped UO 2 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 M 4 -edge. It was established that Mn 2+ directly substitutes for U 4+ in the UO 2 lattice, accompanied by oxygen vacancy (O v ) charge compensation. In contrast to other divalent-element doped UO 2 materials, compelling evidence for U 5+ 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.