Editing Nuclear fuel cycle (section)

==Basic concepts==
[[File:Spent Fuel Storage (25865854820).png|thumb|left| The lifecycle of fuel in the present US system. If put in one place the total inventory of spent nuclear fuel generated by the commercial fleet of power stations in the United States, would stand {{convert|25|ft|order=flip}} tall and be {{convert|300|ft|order=flip}} on a side, approximately the footprint of one [[American football field]].<ref name="Generation Atomic">{{Cite web|title=Why Nuclear – Generation Atomic|date=26 January 2021 |url=https://generationatomic.org/why-nuclear/|access-date=2021-06-27|language=en-US}}</ref><ref name="npr.org">{{Cite news|title=Nuclear Waste May Get A Second Life|url=https://www.npr.org/templates/story/story.php?storyId=125740818|access-date=2021-06-27|website=NPR.org|language=en}}</ref>]]
[[Nuclear power]] relies on fissionable material that can sustain a [[nuclear chain reaction|chain reaction]] with [[neutron]]s. Examples of such materials include [[uranium]] and [[plutonium]]. Most nuclear reactors use a [[Neutron moderator|moderator]] to lower the [[kinetic energy]] of the neutrons and increase the probability that [[Nuclear fission|fission]] will occur. This allows reactors to use material with far lower concentration of [[fissile]] [[isotopes]] than are needed for [[nuclear weapon]]s.  [[Graphite]] and [[heavy water]] are the most effective moderators, because they slow the neutrons through collisions without absorbing them. [[Nuclear reactor technology|Reactors]] using [[Heavy water reactor|heavy water]] or graphite as the moderator can operate using [[natural uranium]].

A [[light water reactor]] (LWR) uses water in the form that occurs in nature, and requires fuel enriched to higher concentrations of fissile isotopes. Typically, LWRs use uranium [[Enriched uranium|enriched]] to 3–5% [[U-235]], the only fissile isotope that is found in significant quantity in nature. One alternative to this low-enriched uranium (LEU) fuel is [[MOX fuel|mixed oxide]] (MOX) fuel produced by blending plutonium with natural or depleted uranium, and these fuels provide an avenue to utilize surplus [[weapons-grade]] plutonium. Another type of MOX fuel involves mixing LEU with [[Thorium fuel cycle|thorium]], which generates the fissile isotope [[Uranium-233|U-233]]. Both plutonium and U-233 are produced from the absorption of neutrons by [[irradiating]] [[fertile material]]s in a reactor, in particular the common uranium isotope [[Uranium-238|U-238]] and [[thorium]], respectively, and can be separated from spent uranium and thorium fuels in [[Nuclear reprocessing|reprocessing plants]].

Some reactors do not use moderators to slow the neutrons. Like nuclear weapons, which also use unmoderated or "fast" neutrons, these [[fast-neutron reactor]]s require much higher concentrations of fissile isotopes in order to sustain a chain reaction. They are also capable of [[Breeder reactor|breeding]] fissile isotopes from fertile materials; a [[breeder reactor]] is one that generates more fissile material in this way than it consumes.

During the nuclear reaction inside a reactor, the fissile isotopes in nuclear fuel are consumed, producing more and more [[Nuclear fission product|fission products]], most of which are considered [[radioactive waste]]. The buildup of fission products and consumption of fissile isotopes eventually stop the nuclear reaction, causing the fuel to become a [[spent nuclear fuel]]. When 3% enriched LEU fuel is used, the spent fuel typically consists of roughly 1% U-235, 95% U-238, 1% plutonium and 3% fission products. Spent fuel and other high-level radioactive waste is extremely hazardous, although nuclear reactors produce orders of magnitude smaller volumes of waste compared to other power plants because of the high energy density of nuclear fuel. Safe management of these byproducts of nuclear power, including their storage and disposal, is a difficult problem for any country using nuclear power{{Citation needed|date=October 2019}}.