In dry storage vaults, the spent fuel is stored in a reinforced concrete building, whose exterior structure serves as the radiation barrier, and whose interior has large numbers of cavities suitable for spent fuel storage units. These cavities contain metallic cylinders in which externally air is insufflated or sometimes the air circulation is natural. Spent fuel is received (either dry or wet) at a vault facility using transfer or transportation casks. The fuel is typically stored in sealed metal storage tubes or storage cylinders, which may hold one or several fuel assemblies. These cylinders provide containment of the radioactive material in the spent fuel. Shielding is provided by the exterior structure. Heat removal is normally accomplished by forced or natural convection of air or gas over the exterior of the fuel containing units or storage cavities, and subsequently exhausting this air directly to the outside atmosphere or dissipating the heat via a secondary heat removal system.
Thus, vault systems typically also require cranes or fuel-handling machines. Typical features of vaults are their modularity, which facilitates incremental capacity extension, separated shielding and containment functions, capability for containment monitoring, and a vertical fuel loading methodology.