During in reactor operations, the slowing down of fission fragments generates most of the radiation damage in uranium dioxide. Fission fragments deposit their energy to both atomic and electronic subsystems through nuclear and electronic interactions. To study the possible synergistic effects of nuclear and electronic energy deposition on the microstructure, UO2 thin foils have been irradiated with 0.39 MeV Xe and/or 6 MeV Si ions at 298 K using single or dual beam ion irradiations. The evolution of extended defects was characterized by in situ Transmission Electron Microscopy. Results show a similar evolution with fluence increase, irrespective of the ion beam: a nucleation of small dislocation loop that increase in density up to a saturation value, followed by an increase of the average loop size. However, the kinetics differs according to the irradiation conditions. In the case of the dual beam irradiation, all the phenomena occur at a lower value of damage level. The local increase of the temperature along the 6 MeV Si ion path seems to lead to an enhanced defect mobility, as in the case of irradiations performed at higher temperatures.