What is Spent Nuclear Fuel?
Spent nuclear fuel (SNF) is irradiated fuel or targets containing uranium, plutonium, or thorium that is permanently withdrawn from a nuclear reactor or other neutron irradiation facility following irradiation, the constituent elements of which have not been separated by reprocessing. Such materials include essentially intact fuel and disassembled or damaged units and pieces, and the following:
- Irradiated reactor fuel, production targets, slugs, and blankets presently in storage or that will be accepted for storage at DOE facilities
- Debris, small pieces of fuel, and cut up assemblies that contain reportable quantities of uranium, thorium, or plutonium subject to evaluation of their waste classification.
A large number of different SNF types are stored within the DOE complex. Of the different types, several categories of DOE-owned SNF may be defined. These are:
- Materials production fuels
This category includes those nuclear fuels, drivers, and targets that historically have been processed by the DOE to recover valuable materials. Examples of SNF existing today include the N-reactor fuel stored at Hanford and the K/L/P reactor fuel and targets stored at Savannah River.
- Naval nuclear propulsion fuel
Like the first category, Naval nuclear propulsion SNF has historically been processed to recover valuable materials. Following the phaseout of processing, however, some Naval SNF remains in storage at the Idaho National Laboratory (INL), and additional quantities will be placed into storage as fuel is withdrawn from vessels.
DOE-sponsored nuclear research activities, both in the U.S. and overseas. SNF from research reactors is currently stored at a number of DOE sites (primarily Hanford, Idaho, and Savannah River) and at numerous (primarily active) university and government research reactor sites within the U.S. Additional research reactor SNF is being returned to the U.S. from foreign research reactors. Examples of research reactor SNF being stored within the DOE complex include the Experimental Breeder Reactor - II (EBR-II) fuel at Idaho, the Molten Salt Reactor Experiment (MSRE) fuel at Oak Ridge, and the High Flux Beam Reactor (HFBR) fuel at the Brookhaven National Laboratory.
A small quantity of SNF is currently stored within the DOE complex from small, specialty type reactors. An example is the SNF from the space program (i.e., SNAP fuel).
- Commercial nuclear power reactor fuels
Some SNF from early (or demonstration) commercial power reactors (Shippingport, Peach Bottom, Fort St. Vrain, etc.) is stored within the DOE complex, primarily at Idaho and West Valley. Also included in this category is the Three-Mile Island Unit 2 (TMI) fuel debris that is stored at Idaho.
DOE facilities that come under the SNF program include those conditioning and storage facilities within which DOE-owned SNF currently resides and new facilities that are brought online to affect the mission of providing safe, interim storage.
What does nuclear fuel look like?
Nuclear fuel is a solid material like coal or wood. It is not a liquid or a gas like oil or propane. Fuel rods or plates (elements) are bundled together and structurally reinforced to form a fuel assembly, typically containing 50-300 fuel elements. These assemblies are installed in a nuclear reactor. The size and form of a nuclear fuel assembly depends on the type of reactor in which it will be used. The Department of Energy (DOE) manages many different types of nuclear fuel assemblies, ranging from small ones weighing about 2 pounds, to some that weigh almost half a ton.
How is SNF handled and stored?
After spent nuclear fuel is removed from the reactor, it is placed inside concrete basins of water within the reactor facility. The water cools the spent nuclear fuel and shields workers from radiation. The "wet" method of storing spent nuclear fuel is not intended to be permanent. As the basins reach their storage capacity, some of the spent fuel must be moved to make room for future spent fuel when it is removed from the reactor.
Spent nuclear fuel that has been cooled may be moved to a "dry" storage area. Using remotely handled equipment, the spent fuel is removed from the pool, dried, and placed in specially designed canisters. The canisters are either stored in a shielded container or in a shielded vault-type dry storage facility where the circulation of air provides cooling. Dry storage reduces corrosion concerns associated with extended storage of fuel under water, provides all the safety characteristics of wet storage, and is less expensive to operate.