Evolution of dislocation loops in irradiated α-Uranium: An atomistically-informed cluster dynamics investigation

An atomistically informed mean field cluster dynamics model has been presented to investigate the nucleation and growth of defect loops in irradiated α-U. TEM analysis of neutron irradiated α-U shows the evolution of SIA and vacancy loops on (010) and (100) crystallographic planes respectively, resulting in an anisotropic swelling of the face-centered orthorhombic crystal. The accumulation of such loops, on irradiation, has been closely estimated using the cluster dynamics model. Parameters of the model, namely, the binding energy of point defects, i.e., Ui and VU, to SIA and vacancy loops respectively and the diffusivity of point defects govern the energetics and kinetics of the defect clustering phenomenon. We have studied the crystallography of defect loops and computed the binding energy of point defects to such loops using an angular dependent EAM potential in classical MD simulations. Using bond-boost hyperdynamics in LAMMPS, the anisotropic diffusion of Ui and VU in α-U has been investigated. The mechanisms of point defect diffusion and the associated migration energies have also been reported and compared with previous DFT studies. Our CD model uses the computed parameters, within their error ranges, to predict the population of defect clusters with a dose-rate and temperature similar to the neutron irradiation experiments. The predictions show an accumulation of small sized vacancy loops along with a population of large and growing SIA loops which closely corresponds to the TEM observations.