Abstract: A storage system for storing spent nuclear fuel on site at a reactor complex includes a concrete storage cask adapted to receive fuel assemblies or loaded fuel canisters from the spent-fuel pool. The storage cask is sealed and maintained on site for a predetermined time period. The fuel assemblies or canisters can then be transferred from the concrete storage cask to a shipping container for shipment to a permanent disposal site, while the concrete casks can be reused or broken up so that the concrete can be used as fill or ballast. The fuel assemblies or canisters are removed from the pool and placed in the cask in a dry condition. Alternatively, the cask may be submerged in the fuel pool for loading. Preferably, the cask is sealed and backfilled with an inert gas. In one embodiment of the invention, the concrete storage cask is manufactured on site at the reactor complex.