Atomic-level simulation methods are used to determine the interaction of a metallic fission product, Ru4+, with the core of ao/2〈1 1 0〉{1 1 0} and ao/2〈1 1 0〉{0 0 1} edge dislocations in UO2, experimentally the most active slip systems. Specifically, the segregation behavior of Ru4+ is examined at the cationic substitution site; comparisons are made with both continuum-elastic results and with the results of atomistic simulations on strained single crystals. The results on strained single crystals suggest that segregation behavior is a strong function of the elastic strain field around the detailed atomic structure at the dislocation core. Furthermore, the segregation is affected by the orientation of the dislocation and electrostatic interactions at the atomic defect site.