Nuclear fuel

Nuclear fuel is the fuel that is used in a nuclear reactor to sustain a nuclear chain reaction. These fuels are fissile, and the most common nuclear fuels are the radioactive metals uranium-235 and plutonium-239. All processes involved in obtaining, refining, and using this fuel make up a cycle known as the nuclear fuel cycle.

The nuclear fuel cycle consists of front-end steps that prepare uranium for use in nuclear reactors and back-end steps to safely manage, prepare, and dispose of used—or spent—but still highly radioactive spent nuclear fuel.

Uranium-235 is used as a fuel in different concentrations. Some reactors, such as the CANDU reactor, can use natural uranium with uranium-235 concentrations of only 0.7%, while other reactors require the uranium to be slightly enriched to levels of 3% to 5%. Plutonium-239 is produced and used in reactors (specifically fast breeder reactors) that contain significant amounts of uranium-238. It can also be recycled and used as a fuel in thermal reactors. Current research is being done to investigate how thorium-232 can be used as a fuel.

UUranium is the most widely used fuel by nuclear power plants for nuclear fission. Nuclear power plants use a certain type of uranium—U-235—as fuel because its atoms are easily split apart. Although uranium is about 100 times more common than silver, U-235 is relatively rare at just over 0.7% of natural uranium. Uranium concentrate is separated from uranium ore at uranium mills or from a slurry at in-situ leaching facilities. It is then processed in conversion and enrichment facilities, which increases the level of U-235 to 3%–5% for commercial nuclear reactors, and made into reactor fuel pellets and fuel rods in reactor fuel fabrication plants.

Nuclear fuel is loaded into reactors and used until the fuel assemblies become highly radioactive and must be removed for temporary storage and eventual disposal. Chemical processing of spent fuel material to recover any remaining product that could undergo fission again in a new fuel assembly is technically feasible, but it is not permitted in the United States.