“…These predictions should be based on studies of the diffusivities of Ca 2+ ions in both the Na-bentonite and the altered bentonite. Although extensive studies have been performed for the diffusion of radionuclides in bentonite (Bourg et al, 2008, Glaus et al, 2007, Gonzalez-Sanchez et al, 2008, Kozaki et al, 2008, Melkior et al, 2009, there are few studies on the diffusivities of Ca 2+ ions in compacted bentonite (Kozaki et al, 2001a) and the effects of exchangeable cations on diffusion of radionuclides (Choi and Oscarson, 1996, Kozaki et al, 1999a, 2005 The diffusion mechanism of Ca 2+ ions in compacted montmorillonite discussed in this paper is based on these experimental data.…”