In many countries using nuclear energy high-level wastes resulting from the reprocessing of nuclear spent fuel is being confined in a highly-resistant glass matrix. In France, the resulting highly radioactive glass, named R7T7, is cooled in stainless steel canisters and stored on-site waiting for final geological disposal. For geological disposal the waste package will be encapsulated in carbon steel container and then sent to a multi-barrier underground disposal facility located in an argillaceous Callovo-Oxfordian (COx) layer. This confinement system should limit both the glass alteration by surrounding ground waters and the release of the radioactive elements from the glass matrix, although the alteration of the glass by surrounding ground waters cannot be excluded for long-term. It is expected after closure of the disposal facility that the glass will be firstly in contact with water vapour before complete saturation of the void spaces. In fact, the anoxic corrosion of metallic components will lead to a massive production of hydrogen that will probably prevent a fast saturation of the glass container with the surrounding ground waters. Consequently, a phenomenon of glass vapour hydration may occur for several thousands of years before the glass becomes completely submerged by groundwater. Various studies have been conducted to better understand the hydration of nuclear glasses [1−۵] and their natural analogues such as obsidian [6−۱۱]. During the hydration process, a thin film of water is firstly sorbed or condensed on the surface of the glass [12]. The thickness of the sorbed film of water mainly depends on the temperature and relative humidity (RH), the latter was controlled by varying the concentration of NaCl in the solution [13]. The condensed water diffuses and reacts via a hydrolysis and ion exchange mechanism. This leads to the transfer of glass components to the glass surface. The glass surface-area-to-liquid volume (S/V) ratio is estimated to be high under water vapour hydration (in the order of 108 m-1 ) [12]. This estimation is based on the sorption curve of water on the SRL glass as a function of the relative humidity. The thin film of water became rapidly saturated with dissolved glass constituents leading for certain glass compositions to higher local pH values and then the increase of solubility of the silicate glasses network. An alteration layer grows on the corroded glass surface; it is mainly composed of hydration gel, pore water and crystalline alteration products. The thickness of the alteration layer and the nature of secondary phases precipitated on the external surface depend on experimental conditions (time, temperature, RH, pH) and glass composition.