Multiscale approach for determining hydrogen diffusivity in zirconium

Abstract

The current research presents an approach which is used to determine the diffusivity of hydrogen in the hexagonal close packed (hcp) zirconium crystal, using a combination of first principles calculations and kinetic Monte Carlo (KMC) simulations. Rate constants found through the energy landscapes of hydrogen motion between different interstitial sites in the zirconium lattice were used in KMC to determine the values of bulk diffusivity. We simulated a stress-free environment to eliminate the effect of stress. It is hypothesized that stress could act as a driving forces for diffusion. We found that hydrogen diffusivity in hcp Zr is closely isotropic, with a slightly higher diffusivity in the axis direction. The individual diffusion jumps were closely investigated to identify the reasons for the isotropic nature of the diffusivity in the anisotropic hcp Zr lattice. We also use this study to validate the modeling approach followed to extend it to other diffusion studies of similar nature, which comprises of clearly understood diffusion steps.