The viscoplastic behavior of uranium dioxide (UO2) single crystal is of great interest to perform predictive multiscale modeling of the nuclear fuel. Here, a viscoplastic model is built considering dislocation glide in ½<110>{100} and ½<110>{110} slip systems. The constitutive law parameters are determined adjusting the temperature dependency of the experimental critical resolved shear stress for both principal slip modes. Crystal plasticity finite element simulations of single crystal compression tests show a reasonable agreement with experimental viscoplastic anisotropy of UO2. However, for specific orientations where ½<110>{111} slip is observed experimentally, significant differences remain between experimental and computed compression stresses. Therefore, the role of ½<110>{111} slip is investigated based on a parametric study that provides new insights on UO2 plastic deformation. Several parameterizations of ½<110>{111} slip are tested highlighting the complexity of UO2 viscoplastic behavior. Significant improvements are still required to explain all simulation-experiment gaps.