He, Kr and Xe diffusion in ZrN – An atomic scale study

The atomic scale diffusion mechanisms for He, Kr and Xe in the nitride fuel component ZrN are developed from first principles. The vacancy formation energies reveal a prevalent N vacancy concentration in the material. However, a high N self-diffusion barrier hinders vacancy-aided Kr and Xe diffusion. High, attractive binding energies of interstitial Xe and Kr to a N vacancy effectively eliminate interstitial diffusion mechanism for these gases. In comparison, He exhibits considerable degrees of freedom, as it is weekly bound to a N vacancy, enhances N-vacancy aided diffusion, has the lowest interstitial migration barrier, and has the capacity to be reintroduced into the ZrN lattice as an interstitial. N self-diffusion barriers are lowered if the diffusing N is in close proximity to a substitutional atom. The obtained results suggest a high release of He, while the majority of Kr and Xe is retained, in agreement with experiments.