Abstract: During vitrified industry process, the melted glass will be fractured after it is poured into the canister. When this fractured glass is disposed in deep geological media, it will be altered for contacting aqueous solution. Glass alteration involves several mechanisms, applied to a reactive surface area that must be accurately determined. This will allow computing the quantities of altered glass and the amount of radionuclides released from the package depending on the environmental conditions. This work researched a fractured full scale glass block after 1 147 d static leaching test at 90 ℃. Through a stereological approach, the fracture ratio of the full scale glass block is estimated to 41±13. About (3.88±1.20)×10^-4m³ glass volume equating (0.28±0.09)% of the full glass block were altered. These calculations are consistent with the data obtained from the leaching solution. It is also found that most of the cracks (>80%) had a gel layer less than 10 μm thick. This kind of cracks led to only 30% of the total alteration surface. On the other hand, the cracks whose gel layer thickness are larger than 10 μm, and play a major role on the global alteration. The results of this work are in good agreement with those from archaeological glass blocks.