Basic mechanisms of Frenkel pair recombinations in UO2 fluorite structure calculated by molecular dynamics simulations

In the present paper, the analysis of Frenkel pair recombinations is investigated by empirical-potential-molecular dynamics simulations. Frenkel pairs with separation distance between the vacancy and the interstitial up to 1.5 times the lattice parameter have been studied. For each Frenkel pair, their lifetimes as a function of the temperature and their migration paths are analyzed. For both uranium and oxygen defects, the picture of the recombination is rather complex and depends on the separation distance and the structure. A thermal dependence on the recombination lifetimes is found in separation distance larger than 7 A. The energy that an interstitial must overcome to recombine with a vacancy is lower than the migration energy of the diffusion. This recombination activation energy is also related to the pathways of the vacancy hops during the recombinations. Recombination distances are discussed and compared with the results from previous displacement cascade simulations. Finally, the role of Frenkel pair recombinations on the resistance to amorphization in UO2 is discussed