LAUSR

Abstract Irradiation of zirconium alloys by neutrons causes dimensional changes associated with the formation of dislocation loops. In undeformed single crystals of this hexagonal close-packed material, an expansion in the crystallographic -direction and a contraction in the -direction are observed as a function of neutron fluence consisting of three stages, namely a rapid initial change, followed by a plateau, and then an accelerated “breakaway” growth whilst the volume remains constant. Molecular dynamics simulations suggest an atomic-level explanation: the initial dimensional changes are related to the formation of -type nano-clusters of self-interstitial atoms (SIAs) while vacancies remain mostly isolated. In the plateau-region, formation of -type vacancy loops compensates for the effect of growing SIA clusters and SIA -loops. Upon further irradiation, vacancy loops grow while the anisotropically diffusing SIAs anneal preferentially vacancy -loops. By having a preferential vacancy sink on the basal plane and a net flow of interstitials to -loops, the dimensional changes accelerate, thus leading to breakaway growth. The present simulations yield values for the thermodynamic stability, strain fields, and their effect on dimensional changes for vacancy and -loops as a function of their size, thus providing critical input for continuum models of radiation-induced growth of zirconium.