First-principles modeling of He-clusters in UO2

We have investigated the behavior of He in UO₂, using the projector-augmented-wave (PAW) method and the generalized gradient approximation (GGA) based on the density functional theory. Total energy calculations with atomic relaxation included have been performed in a 96-atom large supercell. We have found that He has a strong tendency to form a cluster in vicinity of an octahedral interstitial site (OIS) in the UO₂ matrix. In addition, the strain energy produced by a He-cluster was found to be sufficient to create point defects of the host atoms in UO₂. Our study suggests that He-clusters and He-induced point defects play an important role for the local mechanical properties of UO₂.