Uranium dioxide (UO2) is the primary fuel material that is used in current nuclear reactors. As one of the most fundamental material parameters, grain boundary (GB) energy strongly influences many fuel properties, and the influences depend on the characters and properties of individual GBs. Using molecular dynamics simulations, a high throughput survey of GB energy in UO2 was carried out for the purpose of elucidating the roles of GB geometry such as misorientation and inclination, as well as the bonding nature of UO2, in affecting GB energy. GB energies in CeO2 were calculated as well for comparison with UO2 to investigate the generality of GB energy anisotropy in fluorite phase oxides. The results show significant GB energy anisotropy in both UO2 and CeO2 that is associated with the cubic symmetry of the fluorite structure. More interestingly, the GB anisotropy is found to be dependent not only on the crystal structure but also the ionic bonding. As such, the GB energy anisotropy in fluorite oxides has significant differences compared with that in fcc metals. The data obtained and the increased knowledge on GB anisotropy will facilitate GB engineering for nuclear fuels with improved properties.

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Grain boundary (GB) energies have an effect on the frequency with which certain GBs are present in a material. Since GBs have a direct impact on a material's properties, knowledge of GB energies is useful in determining those properties. This knowledge is difficult to establish due to an incomplete understanding of the atomic structure of a GB. Previous research has successfully created an interpolation function for the GB energies of face-centered cubic (fcc) metals. An extension of this work was recently done by creating an interpolation function for uranium dioxide (UO 2 ), which has a fluorite crystal structure. This work improves the accuracy of that function. Molecular dynamics (MD) simulations were used to calculate more accurate GB energies for UO 2 , and new fitting parameters were calculated from those results. Comparison with previous work shows an overall improvement. * For cubic crystals, rotations of 90°, 180°, or 120°about any 〈100〉, 〈110〉, or 〈111〉 axis respectively is a symmetry operation. Thus, the 〈100〉 set is four-fold symmetric (360°/90°= 4), the 〈110〉 set is two-fold symmetric (360°/180°= 2), and the 〈111〉 set is three-fold symmetric (360°/120°= 3).