Interim storage of spent fuel assemblies

Spent fuel discharged from light water reactors (LWR) is cooled at the reactor sites for at least 5 months to allow short-lived radioactive isotopes to decay. Recently, spent fuel has been considered as a possible waste form suitable for interim storage or even ultimate disposal. Several alternatives have been demonstrated or proposed for retrievable storage of spent fuel for periods of up to 100 years. These include storage in water-cooled basins, air-cooled vaults, concrete surface silos, geologic formations, or near-surface heat sinks. Water-cooled storage of spent fuel in near-surface cells of heavily reinforced concrete lined with stainless steel has been proven by about 30 years of operating experience at reactor sites and fuel reprocessing plants. Near-surface storage with forced-draft air cooling of HTGR (High Temperature Gas Reactor) fuels is being used by INEL (Idaho National Engineering Laboratory) and is feasible for unpackaged LWR fuel that has been out of the reactor at least 3 to 4 years. Natural-draft cooling of spent fuel has also been proposed, and demonstration programs are in progress for CANDU (Canada Deuterium Uranium) fuel. Spent fuel assemblies are sealed in thick low-carbon steel containers and placed in large cylindrical concrete housings (silos) located outdoors. The cooling is completely passive, requiring little maintenance and only minimal surveillance. Recent studies comparing the economics of interim storage of spent fuel (throwaway fuel cycle) with prompt chemical reprocessing conclude that disposal as fuel decreases the Nation's natural resources significantly and is not cost justified if both plutonium and uranium are recycled in the nuclear fuel cycle.