The diffusion behaviours of oxygen and uranium were evaluated for the bulk and grain-boundaries of uranium dioxide using molecular dynamics simulations. This showed that oxygen behaved like a liquid in a superionic state at high temperatures and migrated on sub-lattice sites accompanying formation of lattice defects such as Frenkel defects at intermediate temperatures. The formation energies of Frenkel and Schottky defects were compared to literature data, and the migration energies of oxygen and uranium were estimated by introducing vacancies into the super-cell. For grain boundaries modelled by the coincidence-site lattice theory, molecular dynamics calculations showed that the grain-boundary energy and diffusivities of oxygen and uranium increased with misorientation angle. By analysing grain-boundary structures such as pair-correlation functions, it was also shown that the disordered phase was present for uranium as well as oxygen in grain boundaries; especially for a large misorientation angle. Hence, grain-boundary diffusion was much higher than bulk diffusion of oxygen or uranium.

Molecular Dynamics Analysis of Diffusion of Uranium and Oxygen Ions in Uranium Dioxide. T.Arima, K.Yoshida, K.Idemitsu, Y.Inagaki, I.Sato: IOP Conference Series - Materials Science and Engineering, 2010, 9[1], 012003