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.