Taking into account the gas diffusion parallel and perpendicular to the bundle axis, a two-dimensional model combining the non-conservative level set method and the steady-state diffusion equation is presented for evolving pore structure in the bundle cross-section. Parametric studies have been conducted to determine the sensitivity of residual porosity within the bundle to the structure parameters. Sheldon and Besmann's approach is revised and more realistic approximated expressions depicting the accessible and total porosity evolution inside the bundle are given. Such expression can serve as useful estimate of pore structure evolution for modeling the CVI process. (C) 2011 Elsevier Ltd. All rights reserved.