Radiation damage in uranium dioxide: Coupled effect between electronic and nuclear energy losses

A coupling between the nuclear and electronic energy losses occur in the nuclear fuel (UO2) during in-reactor operations. However, the underlying mechanisms involved are still to be investigated. In this work, synergistic effects of nuclear and electronic energy losses have been investigated by irradiating crystals with single (900 keV I ions or 27 MeV Fe ions) and dual (900 keV I ions and 27 MeV Fe ions, simultaneously) ion beams at the JANNUS-Saclay facility. The damage build-up kinetic was in situ characterized by Raman spectroscopy. The microstructure evolution was determined by transmission electron microscopy (TEM) observations and by X-ray diffraction (XRD) analysis. Results show that both crystalline disorder and strain level are lower under dual-beam compared to the single-beam ion irradiations. Indeed, the dual-beam irradiation induces a transition from the formation of dislocation loops to dislocation lines. This result can be explained, in the framework of the thermal spike model, by a local increase of the temperature along the high-energy ion path. This temperature increase likely induces an enhanced defect migration leading to defect rearrangement.