The first dry storage systems were single purpose systems for storing of spent fuel, in most cases, away from the reactor (AFR). Typically, vaults, silos and non­transportable casks were used. In the last few decades, development has shifted towards multipurpose storage containers.

Vaults

Vaults consist of above or below ground reinforced-concrete buildings containing arrays of storage cavities suitable for containment of one or more fuel assemblies. Shielding is provided by the exterior structure. Heat removal is normally accomplished by forced or natural convection of air or gas (nitrogen or helium) over the exterior of the fuel-containing units or storage cavities and exhausting the air directly to the outside atmosphere or, where another gas is used, dissipating the heat via a secondary heat removal system.8 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 technology. Spent fuel is received either wet or dry to such a facility using transportation casks. Spent fuel is transferred to a metal-lined storage tube (single fuel element) or a cylinder (multi-element canister), which is housed within a concrete storage cavity in the vault structure. After transferring the fuel, the storage tubes are dried and sealed; they are usually backfilled with inert gas to prevent oxidation of the spent fuel in storage.