Synthesis and structural characterization of single lanthanide-doped UO2 prepared by co-precipitation and spark plasma sintering

The characterization of irradiated nuclear fuel is experimentally challenging due to its radiological hazards and complex microstructure, making simulated fuels (simfuels) valuable model systems for controlled studies of fission product behavior in UO 2 . In this study, five UO 2 -based samples doped with 1 wt% of individual lanthanides (La, Ce, Pr, Nd, and Gd) were synthesized to investigate lattice evolution and charge compensation associated with lanthanide incorporation. Precursor powders were produced by co-precipitation from uranyl nitrate and lanthanide nitrate solutions using ammonium hydroxide, followed by calcination to U 3 O 8 , reduction in hydrogen to doped UO 2 , and pellet fabrication by spark plasma sintering (SPS). Structural characterization by synchrotron high-resolution powder X-ray diffraction (HR-PXRD) at the ESRF BM20 beamline confirmed single-phase fluorite UO 2 for all compositions and revealed systematic lattice parameter variations consistent with substitutional incorporation of the lanthanide dopants. The measured lattice parameters showed excellent agreement with values calculated using the hard-sphere model based on ionic radii for the fluorite structure, further supporting lanthanide incorporation and charge-compensation effects in the doped lattice. Complementary SEM observations showed dense pellet microstructures with grain sizes of approximately 1–5 µm, consistent with the high relative densities measured by helium pycnometry. LA-ICP-MS measurements showed stable Ln/ 235 U signal ratios during ablation, indicating no evidence of large scale heterogeneity across the analysed pellet surfaces. These results demonstrate that the combined co-precipitation and SPS route produces structurally well-defined lanthanide-doped UO 2 materials suitable for studying dopant–matrix interactions and as potential matrix-matched reference materials for nuclear analytical applications.