  Under irradiation, Zr and Zr alloys undergo growth in the absence of applied
stress. This phenomenon is thought to be associated with the anisotropy of
diffusion of either or both radiation-induced point defects and defect
clusters. In this work, molecular dynamic simulations are used to study the
anisotropy of diffusion of self-interstitial atom clusters. Both
near-equilibrium clusters generated by aggregation of self-interstitial atoms
and cascade-induced clusters were considered. The cascade-induced clusters
display more anisotropy than their counterparts produced by aggregation. In
addition to 1-dimensional diffusing clusters, 2-dimensional diffusing clusters
were observed. Using our molecular dynamic simulations, the input parameters
for the "self-interstitial atom cluster bias" rate-theory model were estimated.
The radiation-induced growth strains predicted using this model are largely
consistent with experiments, but are highly sensitive to the choice of
interatomic interaction potential.
