Sintering behavior and microstructural evolution of UO2-Gd2O3 fuel processed by spark plasma sintering

This study systematically examines the sintering behavior of pure UO 2 and UO 2 pellets containing 10 wt% Gd 2 O 3 processed via conventional sintering and Spark Plasma Sintering (SPS). The analysis focuses on densification mechanisms, microstructural evolution, and diffusion-driven features related to local Gd redistribution. The results indicate that, under conventional sintering conditions, the incorporation of Gd 2 O 3 promotes the development of Kirkendall-type porosity due to the disparity in diffusion rates between Gd 3+ and U 4+ cations. This effect leads to increased residual porosity and a consequent reduction in densification of the doped pellets. In contrast, SPS processing yields significantly enhanced densification, with relative densities exceeding 97% of the theoretical density, even in the presence of Gd 2 O 3 . The corresponding microstructures are characterized by a higher degree of compaction and a predominance of fine, isolated pores, indicative of improved sintering efficiency. Energy-dispersive X-ray spectroscopy (EDS) mapping reveals a heterogeneous spatial distribution of gadolinium in samples processed by both routes, reflecting limitations in powder mixing and diffusion homogenization. Although forced powder mixing contributes to improved microstructural uniformity, its effect on densification remains comparatively limited. Overall, the findings highlight the superior capability of SPS to mitigate diffusion-induced porosity and to promote enhanced densification and microstructural refinement in UO 2 -Gd 2 O 3 systems.