[en] In deionized water the pH of leachates of most nuclear waste glasses rapidly rise to 9.7 or above. However, in a repository situation bicarbonate buffering is an important consideration. Systematic experiments in controlled pH are reported, designed to explore the effect of pH on glass dissolution mechanisms. The glass WV205 exhibited matrix dissolution from essentially time zero when placed in a pH 10 buffer. However, diffusion controlled dissolution was seen in pH 8.5 up to 120 days. The longevity of the diffusion stage suggests direct transition to the saturation controlled leaching stage instead of the conventional diffusion/matrix dissolution/saturation progression