Modelling of UO2 mechanical behavior requires detailed knowledge of the local stresses and strains during the fuel's operation in normal and accident conditions. Therefore, a crystal plasticity formulation is proposed for polycrystalline UO2. The model contains a dislocation-density-based formulation including three slip families and their interactions. The model is parametrized with single crystal and polycrystal experimental data using an optimization scheme. The model's capability to represent yield point, strain hardening behavior, temperature and strain rate dependencies are evaluated. Finally, different approaches to include porosity at the polycrystal are analyzed to assess the effect of porosity on homogenized macro-scopic stress-strain behavior, and stress/strain localization at the grain level.