Migration of gases around a cell containing high-activity vitrified wastes during the operational phase

Andra is studying the feasibility of constructing a repository for radioactive waste in the Callovo-Oxfordian mudstones. The high-activity, long-lived vitrified wastes, in particular, will be stored in cells that are about 40 m long, with a single access aperture from an access gallery. The wall of each cell will be supported by a steel sleeve. g as the access galleries are ventilated, corrosion of the steel sleeve by oxygen in air will be important. This study estimates the thickness of the steel sleeve corroded during this phase, in order to be able to design the sleeve with an appropriate initial thickness to maintain integrity. ition, at the end of the cell farthest from the ventilated access gallery, it is possible that the oxygen concentration will be so low that corrosion occurs under reducing (anaerobic) conditions. This chemical reaction produces hydrogen gas, which will migrate towards the access gallery. This study estimates the transfer rate of hydrogen to the access gallery, which is necessary to evaluate the fire and/or explosion hazards (a hydrogen–oxygen mixture is highly flammable and/or explosive at certain concentrations) and maintain operational safety. ically, we have developed a capability to simulate flows of multi-component (i.e. nitrogen, oxygen and hydrogen) gas in porous media, and then we have applied that capability to predict: first, the flow rate of hydrogen from each cell to the access gallery; second, the hydrogen (and oxygen) mole fractions in the annular void between the steel sleeve and the rock; and third, the corrosion rate of the metal sleeve along the cell.