<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (August 2010) (Learn how and when to remove this template message) </Td> </Tr> <P> Nuclear fuel is a substance that is used in nuclear power stations to produce heat to power turbines . Heat is created when nuclear fuel undergoes nuclear fission . </P> <P> Most nuclear fuels contain heavy fissile elements that are capable of nuclear fission, such as uranium - 235 or plutonium - 239 . When the unstable nuclei of these atoms are hit by a slow - moving neutron, they split, creating two daughter nuclei and two or three more neutrons . These neutrons then go on to split more nuclei . This creates a self - sustaining chain reaction that is controlled in a nuclear reactor, or uncontrolled in a nuclear weapon . </P> <P> The processes involved in mining, refining, purifying, using, and disposing of nuclear fuel are collectively known as the nuclear fuel cycle . </P>

What is the fuel in a nuclear reactor