High-level radioactive waste is produced at commercial nuclear power plants and at nuclear materials production defense facilities.
Nuclear fuel is made of solid pellets of enriched uranium.
The pellets are sealed in tubes, which are bundled together to form a nuclear fuel assembly. The assemblies are put inside a nuclear reactor and used to generate heat to make electricity. The fuel will be used until it is spent or no longer efficient in generating heat. Once a year, approximately one-third of the nuclear fuel inside a reactor is removed and replaced by new fuel assemblies. It is highly radioactive and is the primary form of high-level nuclear waste.