Abstract
Cr-doped UO₂ fuels are increasingly adopted for their superior in-reactor performance compared to undoped UO₂, but their spent fuel behaviour, particularly potential Cr speciation and fission product reactivity, remains poorly understood. This investigation has used high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy to examine speciation of Cr and Pr/Gd within 200 ppm Cr-doped (U4.4+0.7Pr3+0.3)O2-x and 200 ppm Cr-doped (U4.4+0.7Gd3+0.3)O2-x compounds. Despite both being UO2 soluble and undersaturated, analysis indicates that Cr3+ and Pr3+/Gd3+ form perovskite type (Pr3+/Gd3+)Cr3+O3 phases, consistent with classical “grey phases” of spent fuel. The radiation tolerance of these phases was examined via swift heavy ion irradiations of PrCrO3 and GdCrO3 compounds where electron microscopy and grazing incidence synchrotron diffraction indicate significant amorphization but retention of the crystal structure. The investigation highlights the pertinence of considering the chemistry of dopants used for nuclear fuel enhancements regarding their speciation during irradiation and subsequent occurrence within spent fuel.
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The datasets generated and/or analyzed during the current study are not publicly available due to technical limitations related to the scale, variance and non-standardised format of the primary data files, but are available from the corresponding author on reasonable request.
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Acknowledgements
The authors are grateful to the funding and support from the Helmholtz Graduate School for Energy and Climate Research (HITEC) at Forschungszentrum Juelich GmbH. We acknowledge the European Synchrotron Radiation Facility (ESRF) and Helmholtz-Zentrum Dresden-Rossendorf for provision of synchrotron radiation facilities under proposal numbers A20-1-868 and CH-7424. The authors are grateful for assistance with ion irradiations from Prof. Christina Trautmann. The authors are grateful for support from the from the German Federal Ministry of Education and Research (BMBF), Project No. 02NUK088A.
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The project was conceived and developed by Gabriel L. Murphy. Research methodology, experimental planning and formal analysis were conducted by Daniil Shirokiy and Gabriel L. Murphy. Synthesis of materials was done by Daniil Shirokiy, Andrey Bukaemskiy and Maximillian Henkes. Synchrotron X-Ray diffraction was performed by Christoph Hennig, Daniil Shirokiy, Gabriel L. Murphy and Julien Marquardt. X-ray absorption spectroscopy measurements were performed by Kristina O. Kvashnina, Elena Bazarkina, Daniil Shirokiy, Julien Marquardt and Gabriel L. Murphy. Ion irradiation was performed by Julien Marquardt. Stopping range of ions in matter calculations were performed by Daniil Shirokiy and Andrew Ryan. Grazing incidence X-Ray diffraction was performed by Andrew Fitch, Christoph Hennig, Daniil Shirokiy, Mara McCleary and Gabriel L. Murphy. Electron microscopy imaging was performed by Martina Klinkenberg, Murat Güngör and Daniil Shirokiy. Manuscript writing, reviewing and editing was performed by Daniil Shirokiy, Gabriel L. Murphy and Dirk Bosbach with input from all authors.
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Shirokiy, D., Bukaemskiy, A., Henkes, M. et al. Speciation and radiation stability of Cr and Ln “Grey-Phases” within Cr-doped (Ln,U)O2 spent fuel model materials. npj Mater Degrad (2026). https://doi.org/10.1038/s41529-026-00752-5
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DOI: https://doi.org/10.1038/s41529-026-00752-5
