Investigation of the influence of off-stoichiometry on the radiation damage evolution in uranium dioxide

• A novel MD study of off-stoichiometry effect on radiation damage in UO2 is shown.
• Off-stoichiometry induces partial to total recovery of the initial damage.
• Recombination rates of cascade interstitials (UO2−x) or vacancies (UO2+x) are high.
• An increase in vacancy (UO2−x) or interstitial (UO2+x) clustering is observed.
• The results evidence the formation of “split-interstitial clusters” in UO2+x.

The work presented herein brings in valuable contribution to the study of radiation damage in uranium dioxide. In particular, the effect of off-stoichiometric compositions on the damage evolution during a displacement cascade has been investigated, which appears to be a novel study, to the best of literature review achieved. The study has been performed by means of molecular dynamics simulations and, using a powerful tool developed for the purpose, the damage has been analysed thoroughly as cascade-induced point defects and point defect clusters. The results have revealed first of all that the composition does not affect the damage development in the time frame corresponding to the thermal spike. Second of all, as the displacement cascade relaxes and persistent damage shows up in the structures, the results have indicated that off-stoichiometric compositions induced mitigation or even recovery of the damage created by the cascade, due to different mechanisms that depend on the nature and the amount of initial point defects distributed in the material due to off-stoichiometry. Third and last of all, it has been observed that the clustering behaviour in off-stoichiometric structures is also affected accordingly, and overall, the results have evidenced the formation in hyper-stoichiometric structures of interstitial clusters referred to as “split-interstitial clusters”, as alluded to in other very recent studies.