The tubes containing the uranium pellets 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. Nuclear waste is produced whenever we put nuclear fission to work. Fission occurs when atoms split and cause a nuclear reaction. At a nuclear power plant, fission happens under carefully controlled conditions inside a nuclear reactor.
Fission generates energy, including heat.
This heat is used to make steam, which turns turbines to make electricity. To understand how nuclear fuel generates electricity, think about how other power plants work. When electricity is generated at coal-fired plants, coal is burned to produce heat to make steam. At nuclear power plants, fission within the fuel pellets creates the heat used to make steam to turn turbines. Once a year, approximately one-third of the nuclear fuel inside a reactor is removed and replaced with fresh fuel.