Nuclear Fuel Cycle
The nuclear fuel cycle (chain) is a series of different stages that a nuclear fuel progresses through from its creation to its safe disposal. It includes front end steps (preparing the fuel), service period steps (usage of the fuel during the reactor process) and the back end steps (steps needed to safely dispose of or reprocess the fuel). In case the spent nuclear fuel is not recycled or reprocessed, the cycle is termed an open fuel cycle. In contrast, if the fuel is reprocessed, the cycle is called a closed fuel cycle. The nuclear fuel cycle includes steps that involve generation of electricity from nuclear fuels in a nuclear power reactor.
Nuclear power is obtained from fissionable material which can sustain a chain reaction with neutrons. Such fissionable materials (nuclear fuels) include uranium and plutonium. Most reactors use a substance called a moderator which reduced the kinetic energy of the neutrons and increase the probability of fission occurring. Examples of moderators include heavy water and graphite.
The front end of the nuclear fuel chain includes mining, conversion, enriching the fuel, and fabrication of the fuel. At present, the isotopes of uranium and plutonium that are used as fuels are uranium-235, uranium-238 and plutonium-239. Thorium can also be used as a nuclear fuel.