Diffusion in Undoped and Cr₂O₃ Doped Crystalline and Amorphous UO₂

Insoluble dopants such as chromia, Cr₂O₃, and alumina, Al₂O₃, are often added to urania fuel to promote grain growth during sintering, increasing fission product retention and burn-up of the fuel pellet. Migration of these dopants towards more favourable regions, such as grain boundaries, in the fuel is observed. Dopants may alter the structure formed along the grain boundaries, creating amorphous or disordered regions. Due to their disordered nature, diffusion along the grain boundaries may differ to that observed in the bulk, which is crystalline. Previous modelling work on undoped zirconia has shown that oxygen diffusion in amorphous systems is much faster than that observed in the crystalline counterpart, and this may also be true for other oxides, such as urania. This work focuses on using molecular dynamics modelling to simulate crystalline and amorphous, undoped and Cr₂O₃ doped, UO₂ systems. A range of temperatures and chromia concentrations will be considered throughout, and diffusion of all species will be computed. Comparisons will then be made with the crystalline and amorphous counterparts, to observe whether diffusion is impacted based on the structure of the system, and how this may relate to potential amorphous grain boundary formation in doped UO₂ fuel pellets.