Quality of several vitrified radwastes specimens was demonstrated on their hydrolytic resistance. The type of water corrosion mechanism and structural features were also elucidated. The time dependence of the corrosion process proved two subsequent mechanisms of water attack. The first stage is controlled by diffusion. Later the silicate matrix is damaged and its surface layer dissolved. Ultimately, the quality of glass is evaluated from the point of view of possible radioactivity releases.