In the context of the geological disposal of vitrified radioactive waste, cracks are expected at the full scale of the glass blocks. To simulate glass alteration in cracks, static dissolution experiments were conducted with confined SM539 glass powder, at 30 °C in a synthetic young cementitious water. Short and long-term glass dissolution rates were determined and compared with those measured in similar experiments with dispersed glass powder. A long-term rate ~ 10 times lower was found, which might be due to a limited access of the solution to the glass surface area, resulting in a much higher local SA/V and faster increase of local concentrations of leached glass constituents, with possibly a lower local pH. In both types of experiments, the altered glass powder was characterised by XRD and SEM-EDX. Some glass particles showed the presence of an amorphous multi-layer and of fibrous and spherical secondary phases.