Energetics and defect clustering trends for trivalent rare earth cations substituted in UO2

Trends in the energetics and defect clustering tendencies for UO2 compounds substituted with trivalent rare earth cations (M3+) are investigated computationally using methods based on density functional theory. Higher energetic stability of U1−xMxO2−0.5x solid solutions relative to constituent oxides and increased preference for higher oxygen coordination around the trivalent cation are found with increasing size of the M3+ species. The implications of the computational results for the effect of trivalent fission products on oxygen ion mobility in spent fuel are discussed.