1. Introduction
At equilibrium all materials are characterized by presence of
vacancies. Although the equilibrium concentration of vacancies is
in general small, extra concentrations may be generated by various
processes when the material is acted upon by external agents, such
as quenching, irradiation, oxidation, corrosion, and stress [1,2].
Condensation and configuration of vacancy clusters play an important
role in the evolution of damage in a variety of materials