Recent experimental studies suggest that thin films of a nano-porous complex oxide 12CaO center dot 7Al(2)O(3) (C12A7) are unusually stable under bombardment with energetic Ar+ ions [M. Miyakawa et al., J. Appl. Phys. 97 (2005) 023510.]. We employ classical Molecular Dynamics to study the processes induced by knock-on collisions of Ar+ with the C 12A7 lattice. Our results suggest that such collisions predominantly affect the anion sublattice and form Frenkel defect pairs. We find that most of these Frenkel pairs are unstable and readily recombine with the extra-framework O2- ions present in the lattice at stoichiometric concentrations of similar to 1.2 x 10(21) cm(-3). This process is further facilitated by fast diffusion of the extra-framework O2- ions. These results provide a useful insight in the design of new radiation-resistant materials. (c) 2007 Elsevier B.V. All rights reserved.