  Helium diffusion in metals is the basic requirement of nucleation and growth
of bubble, which gives rise to adverse degradation effects on mechanical
properties of structural materials in reactors under irradiation. Lattice based
Kinetic Monte Carlo approach is widely adopted to study the evolution of
helium-vacancy clustering. However, the imple-mentation of Arrhenius law to
prediction the event rate of single interstitial helium solute diffusion in
metal is not always appropriate due to low-energy barrier. Based on a
stochastic model, a modified formula is derived from the Brownian motion upon a
cosine-type potential. Using the parameters obtained from molecular dynamics
simulation for the diffusivity of single helium solute in BCC W, the prediction
of our model is consistent with the results from dynamical simulation and
previous model. This work would help to develop a more accurate KMC scheme for
the growth of helium-vacancy clusters, as well as other low-energy reactions in
materials science.
