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{{about|the chemical element}}
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{{Infobox uranium}}
'''Uranium''' is a [[chemical element]] with the [[chemical symbol|symbol]] '''U''' and [[atomic number]] 92. It is a silvery-grey [[metal]] in the [[actinide]] series of the [[periodic table]]. A uranium atom has 92 [[proton]]s and 92 [[electron]]s, of which 6 are [[valence electron]]s. Uranium [[radioactive decay|radioactively decays]], usually by emitting an [[alpha particle]]. The [[half-life]] of this decay varies between 159,200 and 4.5&nbsp;billion years for different [[isotopes of uranium|isotopes]], making them useful for dating the [[age of the Earth]]. The most common isotopes in [[natural uranium]] are [[uranium-238]] (which has 146 [[neutron]]s and accounts for over 99% of uranium on Earth) and [[uranium-235]] (which has 143 neutrons). Uranium has the highest [[atomic weight]] of the [[primordial nuclide|primordially]] occurring elements. Its [[density]] is about 70% higher than that of [[lead]] and slightly lower than that of [[gold]] or [[tungsten]]. It occurs naturally in low concentrations of a few [[Parts-per notation#Parts-per expressions|parts per million]] in soil, rock and water, and is commercially [[uranium mining|extracted]] from uranium-bearing [[mineral]]s such as [[uraninite]].<ref>{{cite web|title=Uranium |url=https://www.britannica.com/science/uranium |website=Encyclopaedia Britannica|access-date=22 April 2017}}</ref>

Many contemporary uses of uranium exploit its unique [[atomic nucleus|nuclear]] properties. Uranium-235 is the only naturally occurring [[fissile]] [[isotope]], which makes it widely used in [[nuclear power plant]]s and [[nuclear weapon]]s. However, because of the low abundance of uranium-235 in natural uranium (which is, overwhelmingly, mostly uranium-238), uranium needs to undergo [[uranium enrichment|enrichment]] so that enough uranium-235 is present. Uranium-238 is fissionable by fast neutrons and is [[fertile material|fertile]], meaning it can be [[Nuclear transmutation|transmuted]] to fissile [[plutonium-239]] in a [[nuclear reactor]]. Another fissile isotope, [[uranium-233]], can be produced from natural [[thorium]] and is studied for future industrial use in nuclear technology. Uranium-238 has a small probability for [[spontaneous fission]] or even induced fission with fast neutrons; uranium-235, and to a lesser degree uranium-233, have a much higher fission cross-section for slow neutrons. In sufficient concentration, these isotopes maintain a sustained [[nuclear chain reaction]]. This generates the heat in [[nuclear reactor|nuclear power reactors]] and produces the fissile material for nuclear weapons.  The primary civilian use for uranium harnesses the heat energy to produce electricity. [[Depleted uranium]] ({{sup|238}}U) is used in [[kinetic energy penetrator]]s and [[vehicle armour|armor plating]].{{sfn|Emsley|2001|p=479}}

The 1789 [[discovery of the chemical elements|discovery]] of uranium in the mineral [[uraninite|pitchblende]] is credited to [[Martin Heinrich Klaproth]], who named the new element after the recently discovered planet [[Uranus]]. [[Eugène-Melchior Péligot]] was the first person to isolate the metal, and its radioactive properties were discovered in 1896 by [[Henri Becquerel]]. Research by [[Otto Hahn]], [[Lise Meitner]], [[Enrico Fermi]] and others, such as [[J. Robert Oppenheimer]] starting in 1934 led to its use as a fuel in the [[nuclear power]] industry and in ''[[Little Boy]]'', the [[Atomic bombings of Hiroshima and Nagasaki|first nuclear weapon used in war]]. An ensuing [[arms race]] during the [[Cold War]] between the [[United States]] and the [[Soviet Union]] produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived [[plutonium-239]]. Dismantling of these weapons and related nuclear facilities is carried out within various [[nuclear disarmament]] programs and costs billions of dollars. Weapon-grade uranium obtained from nuclear weapons is diluted with uranium-238 and reused as fuel for nuclear reactors. [[Spent nuclear fuel]] forms [[radioactive waste]], which mostly consists of uranium-238 and poses a significant health threat and [[Uranium in the environment|environmental impact]].

==Characteristics==
[[File:Nuclear fission.svg|thumb|left|upright|A neutron-induced nuclear fission event involving uranium-235|alt=A diagram showing a chain transformation of uranium-235 to uranium-236 to barium-141 and krypton-92]]
Uranium is a silvery white, weakly radioactive [[metal]]. It has a [[Hardnesses of the elements (data page)|Mohs hardness]] of 6, sufficient to scratch glass and roughly equal to that of [[titanium]], [[rhodium]], [[manganese]] and [[niobium]]. It is [[malleability|malleable]], [[ductility|ductile]], slightly [[paramagnetism|paramagnetic]], strongly [[electronegativity|electropositive]] and a poor [[electrical conductivity|electrical conductor]].<ref name="SciTechEncy" /><ref name="LANL">{{cite book |author=Hammond, C. R. |title=The Elements, in Handbook of Chemistry and Physics |edition=81st |publisher=CRC press |date=2000 |isbn=978-0-8493-0481-1 |url=http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elements.pdf}}</ref> Uranium metal has a very high [[density]] of 19.1&nbsp;g/cm{{sup|3}},<ref>{{cite web |title=Uranium |url=http://www.rsc.org/periodic-table/element/92/uranium |publisher=Royal Society of Chemistry}}</ref> denser than [[lead]] (11.3&nbsp;g/cm{{sup|3}}),<ref>{{cite web |title=Lead |url=http://www.rsc.org/periodic-table/element/82/lead |publisher=Royal Society of Chemistry}}</ref> but slightly less dense than [[tungsten]] and [[gold]] (19.3&nbsp;g/cm{{sup|3}}).<ref>{{cite web |title=Tungsten |url=http://www.rsc.org/periodic-table/element/74/tungsten |publisher=Royal Society of Chemistry}}</ref><ref>{{cite web |title=Gold |url=http://www.rsc.org/periodic-table/element/79/gold |publisher=Royal Society of Chemistry}}</ref>

Uranium metal reacts with almost all non-metallic elements (except [[noble gas]]es) and their [[chemical compound|compounds]], with reactivity increasing with temperature.<ref name="ColumbiaEncy">{{cite encyclopedia |title=uranium |encyclopedia=Columbia Electronic Encyclopedia|url=http://www.answers.com/uranium |publisher=Columbia University Press |edition=6th |access-date=27 September 2008|archive-date=27 July 2011|archive-url=https://web.archive.org/web/20110727194715/http://www.answers.com/uranium|url-status=dead}}</ref> [[Hydrochloric acid|Hydrochloric]] and [[nitric acid]]s dissolve uranium, but non-oxidizing acids other than hydrochloric acid attack the element very slowly.<ref name="SciTechEncy" /> When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of [[uranium oxide]].<ref name="LANL" /> Uranium in ores is extracted chemically and converted into [[uranium dioxide]] or other chemical forms usable in industry.

Uranium-235 was the first isotope that was found to be [[fissile]]. Other naturally occurring isotopes are fissionable, but not fissile. On bombardment with slow neutrons, uranium-235 most of the time splits into two smaller [[atomic nucleus|nuclei]], releasing nuclear [[binding energy]] and more neutrons. If too many of these neutrons are absorbed by other uranium-235 nuclei, a [[nuclear chain reaction]] occurs that results in a burst of heat or (in some circumstances) an explosion. In a nuclear reactor, such a chain reaction is slowed and controlled by a [[neutron poison]], absorbing some of the free neutrons. Such neutron absorbent materials are often part of reactor [[control rod]]s (see [[nuclear reactor physics]] for a description of this process of reactor control).

As little as {{cvt|15|lb}} of uranium-235 can be used to make an atomic bomb.<ref name="EncyIntel">{{cite encyclopedia |encyclopedia=Encyclopedia of Espionage, Intelligence, and Security|publisher=The Gale Group, Inc. |title=uranium |url=http://www.answers.com/uranium|access-date=27 September 2008|archive-date=27 July 2011|archive-url=https://web.archive.org/web/20110727194715/http://www.answers.com/uranium|url-status=dead}}</ref> The nuclear weapon detonated over [[Hiroshima]], called ''[[Little Boy]]'', relied on uranium fission. However, the first nuclear bomb (the ''Gadget'' used at [[Trinity (nuclear test)|Trinity]]) and the bomb that was detonated over Nagasaki (''[[Fat Man]]'') were both plutonium bombs.

Uranium metal has three [[allotropy|allotropic]] forms:<ref>{{cite book |url=https://books.google.com/books?id=KWGu-LYMYjMC&pg=PA108 |page=108 |title=Applications of Texture Analysis |author=Rollett, A. D. |publisher=John Wiley and Sons |date=2008 |isbn=978-0-470-40835-3}}</ref>
* α ([[orthorhombic]]) stable up to {{convert|668|C}}. Orthorhombic, [[space group]] No. 63, ''Cmcm'', [[lattice parameter]]s ''a''&nbsp;= 285.4&nbsp;pm, ''b''&nbsp;= 587&nbsp;pm, ''c''&nbsp;= 495.5&nbsp;pm.<ref name="Grenthe">{{cite book|last1=Grenthe |first1=Ingmar |first2=Janusz |last2=Drożdżyński |first3=Takeo |last3=Fujino |first4=Edgar C. |last4=Buck |author-link5=Thomas Albrecht-Schönzart |first5=Thomas E. |last5=Albrecht-Schmitt |first6=Stephen F. |last6=Wolf |contribution=Uranium |title=The Chemistry of the Actinide and Transactinide Elements |editor1-first=Lester R. |editor1-last=Morss |editor2-first=Norman M. |editor2-last=Edelstein |editor3-first=Jean |editor3-last=Fuger |edition=3rd |date=2006 |volume=5 |publisher=Springer |location=Dordrecht, the Netherlands |pages=52–160 |url=http://radchem.nevada.edu/classes/rdch710/files/thorium.pdf |doi=10.1007/1-4020-3598-5_5 |url-status=dead |archive-url=https://web.archive.org/web/20160307160941/http://radchem.nevada.edu/classes/rdch710/files/Thorium.pdf |archive-date=7 March 2016 |isbn=978-1-4020-3555-5 }}</ref>
* β ([[tetragonal]]) stable from {{convert|668|to|775|C}}. Tetragonal, space group ''P''4<sub>2</sub>/''mnm'', ''P''4<sub>2</sub>''nm'', or ''P''4''n''2, lattice parameters ''a''&nbsp;= 565.6&nbsp;pm, ''b''&nbsp;= ''c''&nbsp;= 1075.9&nbsp;pm.<ref name="Grenthe" />
* γ ([[body-centered cubic]]) from {{convert|775|C}} to melting point—this is the most malleable and ductile state. Body-centered cubic, lattice parameter ''a''&nbsp;=&nbsp;352.4&nbsp;pm.<ref name="Grenthe" />

==Applications==

===Military===
[[File:30mm DU slug.jpg|thumb|left|Various militaries use depleted uranium as high-density penetrators.|alt=Shiny metallic cylinder with a sharpened tip. The overall length is 9&nbsp;cm and diameter about 2&nbsp;cm.]]

The major application of uranium in the military sector is in high-density penetrators. This ammunition consists of [[depleted uranium]] (DU) alloyed with 1–2% other elements, such as [[titanium]] or [[molybdenum]].<ref>{{cite web |url=http://www.gulflink.osd.mil/du_ii/du_ii_tabe.htm#TAB_E_Development_of_DU_Munitions|title=Development of DU Munitions |year=2000|work=Depleted Uranium in the Gulf (II)|publisher=Gulflink, official website of Force Health Protection & Readiness}}</ref> At high impact speed, the density, hardness, and [[pyrophoricity]] of the projectile enable the destruction of heavily armored targets. Tank armor and other removable [[vehicle armor]] can also be hardened with depleted uranium plates. The use of depleted uranium became politically and environmentally contentious after the use of such munitions by the US, UK and other countries during wars in the Persian Gulf and the Balkans raised questions concerning uranium compounds left in the soil (see [[Gulf War syndrome]]).<ref name="EncyIntel" />

Depleted uranium is also used as a shielding material in some containers used to store and transport radioactive materials. While the metal itself is radioactive, its high density makes it more effective than [[lead]] in halting radiation from strong sources such as [[radium]].<ref name="SciTechEncy" /> Other uses of depleted uranium include counterweights for aircraft control surfaces, as ballast for missile [[atmospheric reentry|re-entry vehicles]] and as a shielding material.<ref name="LANL" /> Due to its high density, this material is found in [[inertial guidance system]]s and in [[gyroscope|gyroscopic]] [[compass]]es.<ref name="LANL" /> Depleted uranium is preferred over similarly dense metals due to its ability to be easily machined and cast as well as its relatively low cost.{{sfn|Emsley|2001|p=480}} The main risk of exposure to depleted uranium is chemical poisoning by [[uranium oxide]] rather than radioactivity (uranium being only a weak [[alpha decay|alpha emitter]]).

During the later stages of [[World War II]], the entire [[Cold War]], and to a lesser extent afterwards, uranium-235 has been used as the fissile explosive material to produce nuclear weapons. Initially, two major types of fission bombs were built: a relatively simple device that uses uranium-235 and a more complicated mechanism that uses [[plutonium-239]] derived from uranium-238. Later, a much more complicated and far more powerful type of fission/fusion bomb ([[thermonuclear weapon]]) was built, that uses a plutonium-based device to cause a mixture of [[tritium]] and [[deuterium]] to undergo [[nuclear fusion]]. Such bombs are jacketed in a non-fissile (unenriched) uranium case, and they derive more than half their power from the fission of this material by [[fast neutron]]s from the nuclear fusion process.<ref>{{cite web
 |url=https://fas.org/nuke/intro/nuke/design.htm
 |title=Nuclear Weapon Design
 |publisher=Federation of American Scientists
 |date=1998
 |access-date=19 February 2007
 |url-status=dead
 |archive-url=https://web.archive.org/web/20081226091803/https://fas.org/nuke/intro/nuke/design.htm
 |archive-date=26 December 2008
}}</ref>

===Civilian===
The main use of uranium in the civilian sector is to fuel [[nuclear power plant]]s. One kilogram of uranium-235 can theoretically produce about 20&nbsp;[[terajoules]] of energy (2{{e|13}}&nbsp;[[joule]]s), assuming complete fission; as much [[energy]] as 1.5&nbsp;million kilograms (1,500 [[tonne]]s) of [[coal]].{{sfn|Emsley|2001|p=479}}

Commercial [[nuclear power]] plants use fuel that is typically enriched to around 3% uranium-235.{{sfn|Emsley|2001|p=479}} The [[CANDU reactor|CANDU]] and [[Magnox]] designs are the only commercial reactors capable of using unenriched uranium fuel. Fuel used for [[United States Navy]] reactors is typically highly enriched in [[uranium-235]] (the exact values are [[classified information|classified]]). In a [[breeder reactor]], uranium-238 can also be converted into plutonium-239 through the following reaction:<ref name="LANL" />

:{{nuclide|link=yes|uranium|238}} + n {{Bigmath|→}} {{nuclide|link=yes|uranium|239}} + γ {{overunderset|{{Bigmath|→}}|β<sup>−</sup>|&nbsp;}} {{nuclide|link=yes|neptunium|239}} {{overunderset|{{Bigmath|→}}|β<sup>−</sup>|&nbsp;}} {{nuclide|link=yes|plutonium|239}}

[[File:U glass with black light.jpg|thumb|right|Uranium glass glowing under [[ultraviolet|UV light]]|alt=A glass place on a glass stand. The plate is glowing green while the stand is colorless.]]
Before (and, occasionally, after) the discovery of radioactivity, uranium was primarily used in small amounts for yellow glass and pottery glazes, such as [[uranium glass]] and in [[Fiesta (dinnerware)|Fiestaware]].<ref>[http://www.hlchina.com/gmastatement.html "Statement regarding the ''Good Morning America'' broadcast," The Homer Laughlin China Co.] {{webarchive|url=https://web.archive.org/web/20120401000958/http://www.hlchina.com/gmastatement.html |date=1 April 2012 }}, 16 March 2011, accessed 25 March 2012.</ref>

The discovery and isolation of [[radium]] in uranium ore (pitchblende) by [[Marie Curie]] sparked the development of uranium mining to extract the radium, which was used to make glow-in-the-dark paints for clock and aircraft dials.<ref>{{cite web |url=https://www.newscientist.com/article/mg15520902.900-dial-r-for-radioactive.html |title=Dial R for radioactive – 12 July 1997 – New Scientist |publisher=Newscientist.com |access-date=12 September 2008}}</ref><ref>{{cite web |title=Uranium Mining |url=https://www.atomicheritage.org/history/uranium-mining |website=Atomic Heritage Foundation |access-date=23 December 2020}}</ref> This left a prodigious quantity of uranium as a waste product, since it takes three tonnes of uranium to extract one gram of radium. This waste product was diverted to the glazing industry, making uranium glazes very inexpensive and abundant. Besides the pottery glazes, [[uranium tile]] glazes accounted for the bulk of the use, including common bathroom and kitchen tiles which can be produced in green, yellow, [[mauve]], black, blue, red and other colors.

[[File:Uranium ceramic - Flickr - Sencer Sarı.jpg|thumb|The uranium glaze on a Sencer Sarı ceramic glowing under [[Ultraviolet|UV light]].]]

[[File:Vacuum capacitor with uranium glass.jpg|thumb|Uranium glass used as lead-in seals in a vacuum [[capacitor]]|alt=A glass cylinder capped on both ends with metal electrodes. Inside the glass bulb there is a metal cylinder connected to the electrodes.]]
Uranium was also used in [[photography|photographic]] chemicals (especially [[uranium nitrate]] as a [[toner]]),<ref name="LANL" /> in lamp filaments for [[stage lighting]] bulbs,<ref name="epa">{{cite web |title=EPA Facts about Uranium |url=http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/Uranium%20Fact%20Sheet%20final.pdf |access-date=20 September 2014 |publisher=U.S. Environmental Protection Agency |archive-date=29 November 2014 |archive-url=https://web.archive.org/web/20141129061718/http://www.epa.gov/superfund/health/contaminants/radiation/pdfs/Uranium%20Fact%20Sheet%20final.pdf}}</ref> to improve the appearance of [[dentures]],<ref>{{cite web |url=https://orau.org/health-physics-museum/collection/consumer/ceramics/uranium-containing-dentures.html |title=Uranium Containing Dentures (ca. 1960s, 1970s) |publisher=[[Oak Ridge Associated Universities]] |website=ORAU Museum of Radiation and Radioactivity |date=1999 |access-date=11 October 2021}}</ref> and in the leather and wood industries for stains and dyes. Uranium salts are [[mordant]]s of silk or wool. [[Uranyl acetate]] and [[uranyl formate]] are used as electron-dense "stains" in [[transmission electron microscopy]], to increase the contrast of biological specimens in ultrathin sections and in [[negative staining]] of [[virus]]es, isolated [[cell organelle]]s and [[macromolecule]]s.

The discovery of the radioactivity of uranium ushered in additional scientific and practical uses of the element. The long [[half-life]] of uranium-238 (4.47{{e|9}} years) makes it well-suited for use in estimating the age of the earliest [[igneous rock]]s and for other types of [[radiometric dating]], including [[uranium–thorium dating]], [[uranium–lead dating]] and [[uranium–uranium dating]]. Uranium metal is used for [[X-ray]] targets in the making of high-energy X-rays.<ref name="LANL" />

==History==

===Pre-discovery use===
The use of [[pitchblende]], uranium in its natural [[oxide]] form, dates back to at least the year 79 AD, when it was used in the [[Roman Empire]] to add a yellow color to [[ceramic]] glazes.<ref name="LANL" /> Yellow glass with 1% uranium oxide was found in a Roman villa on Cape [[Posillipo]] in the [[Gulf of Naples|Bay of Naples]], Italy, by R. T. Gunther of the [[University of Oxford]] in 1912.{{sfn|Emsley|2001|p=482}} Starting in the late [[Middle Ages]], pitchblende was extracted from the [[Habsburg]] silver mines in [[Jáchymov|Joachimsthal]], [[Bohemia]] (now Jáchymov in the Czech Republic) in the [[Ore Mountains]], and was used as a coloring agent in the local [[glass]]making industry.{{sfn|Emsley|2001|p=477}} In the early 19th century, the world's only known sources of uranium ore were these mines.

===Discovery===
[[File:Uranus_Voyager2_color_calibrated.png|thumb|left|upright|The planet [[Uranus]], which uranium is named after]]
The [[discovery of the chemical elements|discovery]] of the element is credited to the German chemist [[Martin Heinrich Klaproth]]. While he was working in his experimental laboratory in [[Berlin]] in 1789, Klaproth was able to precipitate a yellow compound (likely [[sodium diuranate]]) by dissolving [[pitchblende]] in [[nitric acid]] and neutralizing the solution with [[sodium hydroxide]].{{sfn|Emsley|2001|p=477}} Klaproth assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with [[charcoal]] to obtain a black powder, which he thought was the newly discovered metal itself (in fact, that powder was an [[oxide of uranium]]).{{sfn|Emsley|2001|p=477}}<ref>{{cite journal
| title = Chemische Untersuchung des Uranits, einer neuentdeckten metallischen Substanz
| author = Klaproth, M. H.
| journal = Chemische Annalen
| volume = 2
| date = 1789
| pages = 387–403
| author-link = Martin Heinrich Klaproth}}</ref> He named the newly discovered element after the planet [[Uranus]] (named after the primordial [[Uranus (mythology)|Greek god of the sky]]), which had been discovered eight years earlier by [[William Herschel]].<ref>{{cite encyclopedia|edition=4th|title=Uranium|encyclopedia=The American Heritage Dictionary of the English Language |publisher=Houghton Mifflin Company|url=http://www.answers.com/uranium|access-date=15 January 2007|archive-date=27 July 2011 |archive-url=https://web.archive.org/web/20110727194715/http://www.answers.com/uranium|url-status=dead}}</ref>

In 1841, [[Eugène-Melchior Péligot]], Professor of Analytical Chemistry at the [[Conservatoire National des Arts et Métiers]] (Central School of Arts and Manufactures) in [[Paris]], isolated the first sample of uranium metal by heating [[uranium tetrachloride]] with [[potassium]].{{sfn|Emsley|2001|p=477}}<ref>{{cite journal| title=Recherches Sur L'Uranium
| author=Péligot, E.-M. |journal=[[Annales de chimie et de physique]]
| volume=5 |issue=5 |date=1842
| pages=5–47 |url=http://gallica.bnf.fr/ark:/12148/bpt6k34746s/f4.table}}</ref>

[[File:Becquerel plate.jpg|thumb|[[Henri Becquerel]] discovered [[radioactivity]] by exposing a [[photographic plate]] to uranium in 1896.|alt=Two fuzzy black features on a fuzzy white paper-like background. There is a handwriting at the top of the picture.]]
[[Henri Becquerel]] discovered radioactivity by using uranium in 1896.<ref name="ColumbiaEncy" /> Becquerel made the discovery in Paris by leaving a sample of a uranium salt, K{{sub|2}}UO{{sub|2}}(SO{{sub|4}}){{sub|2}} (potassium uranyl sulfate), on top of an unexposed [[photographic plate]] in a drawer and noting that the plate had become "fogged".{{sfn|Emsley|2001|p=478}} He determined that a form of invisible light or rays emitted by uranium had exposed the plate.

During World War I when the [[Central Powers]] suffered a shortage of molybdenum to make artillery gun barrels and high speed tool steels, they routinely used [[ferrouranium]] alloy as a substitute, as it presents many of the same physical characteristics as molybdenum. When this practice became known in 1916 the US government requested several prominent universities to research the use of uranium in manufacturing and metalwork. Tools made with these formulas remained in use for several decades,<ref>{{cite web|url=https://books.google.com/books?id=-5c7AQAAMAAJ&q=ferrouranium+artillery&pg=PA367|title=The Electric Journal|date=10 April 1920|publisher=Westinghouse Club |via=Google Books}}</ref><ref>{{cite book |url=https://books.google.com/books?id=kfvBmuFOAiEC&pg=PA8 |title=Preparation of ferro-uranium |first1=Horace Wadsworth |last1=Gillett |first2=Edward Lawrence |last2=Mack |date=10 April 1917 |series=Technical Paper 177 – U.S. Bureau of Mines |publisher=U.S. Govt. print. off. |via=Google Books}}</ref> until the [[Manhattan Project]] and the [[Cold War]] placed a large demand on uranium for fission research and weapon development.

===Fission research===
[[File:UraniumCubesLarge.jpg|thumb|Cuboids of uranium produced during the Manhattan Project]]
A team led by [[Enrico Fermi]] in 1934 found that bombarding uranium with neutrons produces [[beta decay|beta rays]] ([[electron]]s or [[positron]]s from the elements produced; see [[beta particle]]).{{sfn|Seaborg|1968|p=773}} The fission products were at first mistaken for new elements with atomic numbers 93 and 94, which the Dean of the [[Sapienza University of Rome]], [[Orso Mario Corbino]], named [[ausenium and hesperium]], respectively.<ref>{{cite web
 |url          = https://www.nobelprize.org/nobel_prizes/physics/laureates/1938/fermi-lecture.pdf
 |last         = Fermi
 |first        = Enrico
 |date         = 12 December 1938
 |title        = Artificial radioactivity produced by neutron bombardment: Nobel Lecture
 |publisher    = Royal Swedish Academy of Sciences
 |access-date  = 14 June 2017
 |archive-url  = https://web.archive.org/web/20180809111423/https://www.nobelprize.org/nobel_prizes/physics/laureates/1938/fermi-lecture.pdf
 |archive-date = 9 August 2018
 |url-status     = dead
}}</ref><ref>{{cite journal |author=De Gregorio, A. |title=A Historical Note About How the Property was Discovered that Hydrogenated Substances Increase the Radioactivity Induced by Neutrons |date=2003 |pages=41–47 |volume=19 |journal=Nuovo Saggiatore |arxiv=physics/0309046 |bibcode=2003physics...9046D}}</ref><ref>{{cite web |author=Nigro, M. |title=Hahn, Meitner e la teoria della fissione |url=http://www.brera.unimi.it/SISFA/atti/2003/312-321NigroBari.pdf |date=2004 |access-date=5 May 2009 |archive-date=25 March 2009 |archive-url=https://web.archive.org/web/20090325120427/http://www.brera.unimi.it/SISFA/atti/2003/312-321NigroBari.pdf |url-status=dead}}</ref><ref>{{cite web| author=van der Krogt, Peter |url=http://elements.vanderkrogt.net/element.php?sym=Pu |title=Elementymology & Elements Multidict |access-date=5 May 2009}}</ref> The experiments leading to the discovery of uranium's ability to fission (break apart) into lighter elements and release [[binding energy]] were conducted by [[Otto Hahn]] and [[Fritz Strassmann]]{{sfn|Seaborg|1968|p=773}} in Hahn's laboratory in Berlin. [[Lise Meitner]] and her nephew, physicist [[Otto Robert Frisch]], published the physical explanation in February 1939 and named the process "[[nuclear fission]]".<ref>{{cite journal
| title = Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction
| author1 = [[Lise Meitner|Meitner, L.]]
| author2 = [[Otto Frisch|Frisch, O.]]
| journal = Nature
| volume = 143
| date = 1939
| pages = 239–240
| doi = 10.1038/224466a0
| url = http://www.atomicarchive.com/Docs/Begin/Nature_Meitner.shtml |bibcode = 1969Natur.224..466M
| issue=5218| s2cid = 4188874
}}</ref> Soon after, Fermi hypothesized that fission of uranium might release enough neutrons to sustain a fission reaction. Confirmation of this hypothesis came in 1939, and later work found that on average about 2.5 neutrons are released by each fission of uranium-235.{{sfn|Seaborg|1968|p=773}} Fermi urged [[Alfred O. C. Nier]] to separate uranium isotopes for determination of the fissile component, and on 29 February 1940, Nier used an instrument he built at the [[University of Minnesota]] to separate the world's first [[uranium-235]] sample in the Tate Laboratory. Using [[Pupin Hall|Columbia University]]'s [[cyclotron]], [[John R. Dunning|John Dunning]] confirmed the sample to be the isolated fissile material on 1 March.<ref>{{cite web|title=Alfred O. C. Nier |url=https://www.aps.org/programs/outreach/history/historicsites/nier.cfm |website=www.aps.org|access-date=2016-12-04}}</ref> Further work found that the far more common uranium-238 isotope can be [[Nuclear transmutation|transmuted]] into plutonium, which, like uranium-235, is also fissile by thermal neutrons. These discoveries led numerous countries to begin working on the development of nuclear weapons and [[nuclear power]]. Despite fission having been discovered in Germany, the ''[[Uranverein]]'' ("uranium club") Germany's wartime project to research nuclear power and/or weapons was hampered by limited resources, infighting, the exile or non-involvement of several prominent scientists in the field and several crucial mistakes such as failing to account for impurities in available graphite samples which made it appear less suitable as a [[neutron moderator]] than it is in reality. Germany's attempts to build a [[natural uranium]] / [[heavy water]] reactor had not come close to reaching criticality by the time the Americans reached [[Haigerloch]], the site of the last German wartime reactor experiment.<ref>{{cite web|author=Manfred Popp |url=https://www.spektrum.de/news/hitlers-atombombe-warum-es-sie-nicht-gab/1423529 |title=Wissenschaftsgeschichte: Hitlers Atombombe – warum es sie nicht gab – Spektrum der Wissenschaft |publisher=Spektrum.de |date=2016-09-21 |access-date=2022-02-25}}</ref>

On 2 December 1942, as part of the [[Manhattan Project]], another team led by Enrico Fermi was able to initiate the first artificial self-sustained [[nuclear chain reaction]], [[Chicago Pile-1]]. An initial plan using enriched uranium-235 was abandoned as it was as yet unavailable in sufficient quantities.<ref>{{cite web |url=http://large.stanford.edu/courses/2013/ph241/masters1/ |title=Chicago Pile One|website=large.stanford.edu|access-date=2016-12-04}}</ref> Working in a lab below the stands of [[Stagg Field]] at the [[University of Chicago]], the team created the conditions needed for such a reaction by piling together 360 tonnes of [[graphite]], 53 tonnes of [[uranium oxide]], and 5.5 tonnes of uranium metal, most of which was supplied by [[Westinghouse Lamp Plant]] in a makeshift production process.{{sfn|Seaborg|1968|p=773}}<ref>{{cite journal |last=Walsh |first=John |title=A Manhattan Project Postscript |journal=Science |date=19 June 1981 |volume=212 |pages=1369–1371 |bibcode=1981Sci...212.1369W |pmid=17746246 |url=http://pbadupws.nrc.gov/docs/ML0533/ML053340429.pdf |access-date=23 March 2013 |publisher=AAAS |doi=10.1126/science.212.4501.1369 |issue=4501}}</ref>

===Nuclear weaponry===
[[File:Atomic cloud over Hiroshima - NARA 542192 - Edit.jpg|thumb|upright|[[Mushroom cloud]] over Hiroshima after the dropping of the uranium-fired '[[Little Boy]]'|alt=White fragmentred mushroom-like smoke cloud evolving from the ground.]]
Two types of atomic bomb were developed by the United States during [[World War II]]: a uranium-based device (codenamed "[[Little Boy]]") whose fissile material was highly [[enriched uranium]], and a plutonium-based device (see [[Trinity test]] and "[[Fat Man]]") whose plutonium was derived from uranium-238. Little Boy became the first nuclear weapon used in war when it was detonated over [[Hiroshima]], [[Japan]], on 6 August 1945. Exploding with a yield equivalent to 12,500 tonnes of [[TNT]], the blast and thermal wave of the bomb destroyed nearly 50,000 buildings and killed about 75,000 people (see [[Atomic bombings of Hiroshima and Nagasaki]]).{{sfn|Emsley|2001|p=478}} Initially it was believed that uranium was relatively rare, and that [[nuclear proliferation]] could be avoided by simply buying up all known uranium stocks, but within a decade large deposits of it were discovered in many places around the world.<ref>Helmreich, J.E. ''Gathering Rare Ores: The Diplomacy of Uranium Acquisition, 1943–1954'', Princeton UP, 1986: ch. 10 {{ISBN|0-7837-9349-9}}</ref>

===Reactors===
[[File:First four nuclear lit bulbs.jpeg|thumb|Four light bulbs lit with electricity generated from the first artificial electricity-producing nuclear reactor, [[Experimental Breeder Reactor I|EBR-I]] (1951)|alt=An industrial room with four large illuminated light bulbs hanging down from a bar.]]
The [[X-10 Graphite Reactor]] at [[Oak Ridge National Laboratory]] (ORNL) in Oak Ridge, Tennessee, formerly known as the Clinton Pile and X-10 Pile, was the world's second artificial nuclear reactor (after Enrico Fermi's Chicago Pile) and was the first reactor designed and built for continuous operation. [[Argonne National Laboratory]]'s [[Experimental Breeder Reactor I]], located at the Atomic Energy Commission's National Reactor Testing Station near [[Arco, Idaho]], became the first nuclear reactor to create electricity on 20 December 1951.<ref>{{cite web |url=http://www.ne.anl.gov/About/reactors/frt.shtml |title=Reactors Designed by Argonne National Laboratory: Fast Reactor Technology |publisher=U.S. Department of Energy, Argonne National Laboratory |date=2012 |access-date=25 July 2012}}</ref> Initially, four 150-watt light bulbs were lit by the reactor, but improvements eventually enabled it to power the whole facility (later, the town of Arco became the first in the world to have all its [[electricity]] come from nuclear power generated by [[BORAX-III]], another reactor designed and operated by [[Argonne National Laboratory]]).<ref>{{cite web |url=http://web.em.doe.gov/tie/history.html |title=History and Success of Argonne National Laboratory: Part 1 |publisher=U.S. Department of Energy, Argonne National Laboratory |date=1998 |access-date=28 January 2007 |archive-url=https://web.archive.org/web/20060926155637/http://web.em.doe.gov/tie/history.html |archive-date=26 September 2006 |url-status=dead}}</ref><ref>{{cite web |title=Reactors Designed by Argonne National Laboratory: Light Water Reactor Technology Development |publisher=U.S. Department of Energy, Argonne National Laboratory |date=2012 |url=http://www.ne.anl.gov/About/reactors/lwr3.shtml#fragment-5 |access-date=25 July 2012}}</ref> The world's first commercial scale nuclear power station, [[Obninsk Nuclear Power Plant|Obninsk]] in the [[Soviet Union]], began generation with its reactor AM-1 on 27 June 1954. Other early nuclear power plants were [[Calder Hall nuclear power station|Calder Hall]] in England, which began generation on 17 October 1956,<ref>{{cite news |title=1956: Queen switches on nuclear power |date=17 October 1956 |work=[[BBC News]] |url=http://news.bbc.co.uk/onthisday/hi/dates/stories/october/17/newsid_3147000/3147145.stm |access-date=28 June 2006}}</ref> and the [[Shippingport Atomic Power Station]] in [[Pennsylvania]], which began on 26 May 1958. Nuclear power was used for the first time for propulsion by a [[submarine]], the [[USS Nautilus (SSN-571)|USS ''Nautilus'']], in 1954.{{sfn|Seaborg|1968|p=773}}<ref>{{cite web |title=STR (Submarine Thermal Reactor) in "Reactors Designed by Argonne National Laboratory: Light Water Reactor Technology Development" |publisher=U.S. Department of Energy, Argonne National Laboratory |url=http://www.ne.anl.gov/About/reactors/lwr3.shtml#fragment-2 |date=2012 |access-date=25 July 2012}}</ref>

===Prehistoric naturally occurring fission===
{{Main|Natural nuclear fission reactor}}
In 1972, French physicist [[Francis Perrin (physicist)|Francis Perrin]] discovered fifteen ancient and no longer active natural nuclear fission reactors in three separate ore deposits at the [[Oklo mine]] in [[Gabon]], Africa, collectively known as the [[Natural nuclear fission reactor|Oklo Fossil Reactors]]. The ore deposit is 1.7&nbsp;billion years old; then, uranium-235 constituted about 3% of uranium on Earth.<ref name="OCRWM">{{cite web |title=Oklo: Natural Nuclear Reactors |work=Office of Civilian Radioactive Waste Management |url=http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml |archive-url=https://web.archive.org/web/20040603085718/http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml |archive-date=3 June 2004 |access-date=28 June 2006}}</ref> This is high enough to permit a sustained chain reaction, if other supporting conditions exist. The capacity of the surrounding sediment to contain the health-threatening [[nuclear waste]] products has been cited by the U.S. federal government as supporting evidence for the feasibility to store spent nuclear fuel at the [[Yucca Mountain nuclear waste repository]].<ref name="OCRWM" />

===Contamination and the Cold War legacy===
[[File:US and USSR nuclear stockpiles.svg|thumb|U.S. and USSR/Russian nuclear weapons stockpiles, 1945–2005|alt=A graph showing evolution of number of nuclear weapons in the US and USSR and in the period 1945–2005. US dominates early and USSR later years with and crossover around 1978.]]
Above-ground [[nuclear testing|nuclear tests]] by the Soviet Union and the United States in the 1950s and early 1960s and by [[France]] <!-- SEE TALK and [[Israel]] -->into the 1970s and 1980s{{sfn|Emsley|2001|p=480}} spread a significant amount of [[nuclear fallout|fallout]] from uranium [[daughter isotope]]s around the world.<ref>{{cite journal |author=Warneke, T. |author2=Croudace, I. W. |author3=Warwick, P. E. |author4=Taylor, R. N. |name-list-style=amp |title=A new ground-level fallout record of uranium and plutonium isotopes for northern temperate latitudes |journal=Earth and Planetary Science Letters| date=2002 |volume=203 |issue=3–4 |pages=1047–1057 |doi=10.1016/S0012-821X(02)00930-5 |bibcode=2002E&PSL.203.1047W}}</ref> Additional fallout and pollution occurred from several [[nuclear and radiation accidents|nuclear accidents]].<ref>{{cite magazine |url=http://www.time.com/time/photogallery/0,29307,1887705,00.html |archive-url=https://web.archive.org/web/20090328130544/http://www.time.com/time/photogallery/0,29307,1887705,00.html |url-status=dead |archive-date=28 March 2009 |title=The Worst Nuclear Disasters |magazine=Time |date=25 March 2009 |access-date=24 May 2010}}</ref>

Uranium miners have a higher incidence of [[cancer]]. An excess risk of lung cancer among [[Navajo people|Navajo]] uranium miners, for example, has been documented and linked to their occupation.<ref name="Gilliland et al 2000">{{cite journal |journal=Journal of Occupational and Environmental Medicine |author=Gilliland, Frank D. |author2=Hunt, William C. |author3=Pardilla, Marla |author4=Key, Charles R. |title=Uranium Mining and Lung Cancer Among Navajo Men in New Mexico and Arizona, 1969 to 1993 |date=March 2000 |volume=42 |issue=3 |pages=278–283 |pmid=10738707 |doi=10.1097/00043764-200003000-00008}}</ref> The [[Radiation Exposure Compensation Act]], a 1990 law in the US, required $100,000 in "compassion payments" to uranium miners diagnosed with cancer or other respiratory ailments.<ref name="ajph.org">{{cite journal |title=The History of Uranium Mining and the Navajo People |doi=10.2105/AJPH.92.9.1410 |publisher=Ajph.org |pmid=12197966 |date=2002 |last1=Brugge |first1=Doug |last2=Goble |first2=Rob |journal=American Journal of Public Health |volume=92 |issue=9 |pages=1410–1419 |pmc=3222290}}</ref>

During the [[Cold War]] between the Soviet Union and the United States, huge stockpiles of uranium were amassed and tens of thousands of nuclear weapons were created using enriched uranium and plutonium made from uranium. After the [[Collapse of the Soviet Union (1985–1991)#Dissolution of the USSR|break-up of the Soviet Union]] in 1991, an estimated 600&nbsp;short tons (540&nbsp;metric tons) of highly enriched weapons grade uranium (enough to make 40,000 nuclear warheads) had been stored in often inadequately guarded facilities in the [[Russia|Russian Federation]] and several other former Soviet states.<ref name="EncyIntel" /> Police in [[Asia]], [[Europe]], and [[South America]] on at least 16 occasions from 1993 to 2005 have [[nuclear espionage|intercepted shipments]] of smuggled bomb-grade uranium or plutonium, most of which was from ex-Soviet sources.<ref name="EncyIntel" /> From 1993 to 2005 the [[Material Protection, Control, and Accounting Program]], operated by the [[federal government of the United States]], spent about US$550 million to help safeguard uranium and plutonium stockpiles in Russia. This money was used for improvements and security enhancements at research and storage facilities.<ref name="EncyIntel" />

Safety of nuclear facilities in Russia has been significantly improved since the stabilization of political and economical turmoil of the early 1990s. For example, in 1993 there were 29 incidents ranking above level 1 on the [[International Nuclear Event Scale]], and this number dropped under four per year in 1995–2003. The number of employees receiving annual radiation doses above 20 [[Sievert|mSv]], which is equivalent to a single full-body [[CT scan]],<ref>{{cite journal |pmid=9166072 |year=1997 |last1=Van Unnik |first1=J. G. |last2=Broerse |first2=J. J. |last3=Geleijns |first3=J. |last4=Jansen |first4=J. T. |last5=Zoetelief |first5=J. |last6=Zweers |first6=D. |title=Survey of CT techniques and absorbed dose in various Dutch hospitals |volume=70 |issue=832 |pages=367–371 |journal=The British Journal of Radiology|doi=10.1259/bjr.70.832.9166072 }} (3000 examinations from 18 hospitals)</ref> saw a strong decline around 2000. In November 2015, the Russian government approved a federal program for nuclear and radiation safety for 2016 to 2030 with a budget of 562 billion rubles (ca. 8 billion [[USD]]). Its key issue is "the deferred liabilities accumulated during the 70 years of the nuclear industry, particularly during the time of the Soviet Union". About 73% of the budget will be spent on decommissioning aged and obsolete nuclear reactors and nuclear facilities, especially those involved in state defense programs; 20% will go in processing and disposal of nuclear fuel and radioactive waste, and 5% into monitoring and ensuring of nuclear and radiation safety.<ref>[https://world-nuclear.org/information-library/country-profiles/countries-o-s/russia-nuclear-fuel-cycle.aspx Russia's Nuclear Fuel Cycle]. World Nuclear Association. Updated December 2021.</ref>

==Occurrence==
Uranium is a [[natural abundance|naturally occurring]] element found in low levels in all rock, soil, and water. It is the highest-numbered element found naturally in significant quantities on Earth and is almost always found combined with other elements.<ref name="LANL" /> Uranium is the [[Abundance of elements in Earth's crust|48th most abundant element]] in the Earth’s crust.<ref>{{Cite book |last=Emsley |first=John |url=https://books.google.com/books?id=j-Xu07p3cKwC&dq=%2248th+most+abundant+element%22&pg=PA480 |title=Nature's Building Blocks: An A-Z Guide to the Elements |date=2003 |publisher=Oxford University Press |isbn=978-0-19-850340-8 |language=en}}</ref> The decay of uranium, [[thorium]], and [[potassium-40]] in Earth's [[mantle (geology)|mantle]] is thought to be the main source of heat<ref>{{cite magazine |url=https://www.newscientist.com/article/mg18725103-700-first-measurements-of-earths-core-radioactivity/ |title=First measurements of Earth's core radioactivity |magazine=New Scientist |last=Biever |first=Celeste |date=27 July 2005 |access-date=July 7, 2022 }}</ref><ref>{{cite web |url=https://physicsworld.com/a/potassium-40-heats-up-earths-core/ |title=Potassium-40 heats up Earth's core |work=physicsworld.com |date=7 May 2003 |access-date=14 January 2007}}</ref> that keeps the Earth's [[Structure of the Earth|outer core]] in the liquid state and drives [[mantle convection]], which in turn drives [[plate tectonics]].

Uranium's [[Abundance of elements in Earth's crust|concentration in the Earth's crust]] is (depending on the reference) 2 to 4 parts per million,<ref name="SciTechEncy">{{cite encyclopedia |edition=5th |title=Uranium |encyclopedia=The McGraw-Hill Science and Technology Encyclopedia |publisher=The McGraw-Hill Companies, Inc. |isbn=978-0-07-142957-3 |year=2005 |url-access=registration |url=https://archive.org/details/mcgrawhillconcis00newy}}</ref>{{sfn|Emsley|2001|p=480}} or about 40 times as abundant as [[silver]].<ref name="ColumbiaEncy" /> The Earth's crust from the surface to 25&nbsp;km (15&nbsp;mi) down is calculated to contain 10{{sup|17}}&nbsp;kg (2{{e|17}}&nbsp;lb) of uranium while the [[ocean]]s may contain 10{{sup|13}}&nbsp;kg (2{{e|13}}&nbsp;lb).<ref name="SciTechEncy" /> The concentration of uranium in soil ranges from 0.7 to 11 parts per million (up to 15 parts per million in farmland soil due to use of phosphate [[fertilizer]]s),<ref>Schnug, E., Sun, Y., Zhang, L., Windmann, H., Lottermoser, B.G., Ulrich, A. E., Bol, R., Makeawa, M., and Haneklaus, S.H. (2023) "Elemental loads with phosphate fertilizers – a constraint for soil productivity?" In: Bolan, N.S. and Kirkham, M.B. (eds.) ''Managing Soil Constraints for Sustaining Productivity''. CRC Press.</ref> and its concentration in sea water is 3 parts per billion.{{sfn|Emsley|2001|p=480}}

Uranium is more plentiful than [[antimony]], [[tin]], [[cadmium]], [[mercury (element)|mercury]], or silver, and it is about as abundant as [[arsenic]] or [[molybdenum]].<ref name="LANL" />{{sfn|Emsley|2001|p=480}} Uranium is found in hundreds of minerals, including uraninite (the most common uranium [[ore]]), [[carnotite]], [[autunite]], [[uranophane]], [[torbernite]], and [[coffinite]].<ref name="LANL" /> Significant concentrations of uranium occur in some substances such as [[phosphate]] rock deposits, and minerals such as [[lignite]], and [[monazite]] sands in uranium-rich ores<ref name="LANL" /> (it is recovered commercially from sources with as little as 0.1% uranium<ref name="ColumbiaEncy" />).

===Origin===
Like all elements with [[atomic weight]]s higher than that of [[iron]], uranium is only naturally formed by the [[r-process]] (rapid neutron capture) in [[supernova]]e and [[neutron star merger]]s.<ref>{{cite web |url=http://herschel.jpl.nasa.gov/chemicalOrigins.shtml |title=History/Origin of Chemicals |publisher=NASA |access-date=1 January 2013}}</ref> Primordial thorium and uranium are only produced in the r-process, because the [[s-process]] (slow neutron capture) is too slow and cannot pass the gap of instability after bismuth.<ref name="B2FH">{{cite journal | author1=Burbidge, E. M. | author2=Burbidge, G. R. | author3=Fowler, W. A. | author4=Hoyle, F. | year=1957 | title=Synthesis of the Elements in Stars | journal=[[Reviews of Modern Physics]] | volume=29 | issue=4 | page=547 | bibcode=1957RvMP...29..547B | doi=10.1103/RevModPhys.29.547 | doi-access=free }}</ref><ref>{{cite book|last=Clayton|first=Donald D.|author-link=Donald D. Clayton|title=Principles of Stellar Evolution and Nucleosynthesis|publisher=Mc-Graw-Hill|location=New York |date=1968|pages=577–91|isbn=978-0226109534}}</ref> Besides the two extant primordial uranium isotopes, {{sup|235}}U and {{sup|238}}U, the r-process also produced significant quantities of [[uranium-236|{{sup|236}}U]], which has a shorter half-life and so is an [[extinct radionuclide]], having long since decayed completely to {{sup|232}}Th. Further uranium-236 was produced by the decay of [[plutonium-244|{{sup|244}}Pu]], accounting for the observed higher-than-expected abundance of thorium and lower-than-expected abundance of uranium.<ref name="thoruranium">{{cite journal |last1=Trenn |first1=Thaddeus J. |date=1978 |title=Thoruranium (U-236) as the extinct natural parent of thorium: The premature falsification of an essentially correct theory |journal=Annals of Science |volume=35 |issue=6 |pages=581–97 |doi=10.1080/00033797800200441}}</ref> While the natural abundance of uranium has been supplemented by the decay of extinct [[plutonium-242|{{sup|242}}Pu]] (half-life 375,000&nbsp;years) and {{sup|247}}Cm (half-life 16&nbsp;million years), producing {{sup|238}}U and {{sup|235}}U respectively, this occurred to an almost negligible extent due to the shorter half-lives of these parents and their lower production than {{sup|236}}U and {{sup|244}}Pu, the parents of thorium: the {{sup|247}}Cm/{{sup|235}}U ratio at the formation of the Solar System was {{val|7.0e-5|1.6}}.<ref>
{{cite journal |last1=Tissot |first1=François L. H. |last2=Dauphas |first2=Nicolas |last3=Grossmann |first3=Lawrence |date=4 March 2016 |title=Origin of uranium isotope variations in early solar nebula condensates |journal=Science Advances |volume=2 |issue=3 |doi=10.1126/sciadv.1501400|pmid=26973874 |pmc=4783122 |arxiv=1603.01780 |bibcode=2016SciA....2E1400T |page=e1501400}}</ref>

===Biotic and abiotic===
{{Main|Uranium in the environment}}
[[File:Pichblende.jpg|thumb|Uraninite, also known as pitchblende, is the most common ore mined to extract uranium.|alt=A shiny gray 5-centimeter piece of matter with a rough surface.]]

[[File:Evolution of Earth's radiogenic heat.svg|thumb|right|The evolution of Earth's [[radiogenic heat]] flow over time: contribution from {{sup|235}}U in red and from {{sup|238}}U in green]]

Some bacteria, such as ''[[Shewanella putrefaciens]]'', ''[[Geobacter metallireducens]]'' and some strains of ''[[Burkholderia fungorum]]'', use uranium for their growth and convert U(VI) to U(IV).<ref>{{cite journal |doi=10.1016/j.oregeorev.2004.10.003 |title=Evidence of uranium biomineralization in sandstone-hosted roll-front uranium deposits, northwestern China |date=2005 |last1=Min |first1=M. |last2=Xu |first2=H. |last3=Chen |first3=J. |last4=Fayek |first4=M. |journal=Ore Geology Reviews |volume=26 |page=198 |issue=3–4 |bibcode=2005OGRv...26..198M}}</ref><ref>{{cite journal |doi=10.1371/journal.pone.0123378 |pmid=25874721 |pmc=4395306 |year=2015 |last1=Koribanics |first1=N. M. |title=Spatial Distribution of an Uranium-Respiring Betaproteobacterium at the Rifle, CO Field Research Site |journal=PLOS ONE |volume=10 |issue=4 |pages=e0123378 |last2=Tuorto |first2=S. J. |last3=Lopez-Chiaffarelli |first3=N. |last4=McGuinness |first4=L. R. |last5=Häggblom |first5=M. M. |last6=Williams |first6=K. H. |last7=Long |first7=P. E. |last8=Kerkhof |first8=L. J. |bibcode=2015PLoSO..1023378K |doi-access=free}}</ref> Recent research suggests that this pathway includes reduction of the soluble U(VI) via an intermediate U(V) pentavalent state.<ref name="Renshaw">{{cite journal |last1=Renshaw |first1=J. C. |last2=Butchins |first2=L. J. C. |last3=Livens |first3=F. R. |last4=May |first4=I. |last5=Charnock |first5=J. M. |last6=Lloyd |first6=J. R. |display-authors=3 |title=Bioreduction of uranium: environmental implications of a pentavalent intermediate |journal=Environmental Science & Technology |date=June 2005 |volume=39 |issue=15 |pages=5657–5660 |doi=10.1021/es048232b |pmid=16124300|bibcode=2005EnST...39.5657R }}</ref><ref name="Vitesse">{{cite journal |last1=Vitesse |first1=GF |last2=Morris |first2=K |last3=Natrajan |first3=LS |last4=Shaw |first4=S |title=Multiple Lines of Evidence Identify U(V) as a Key Intermediate during U(VI) Reduction by Shewanella oneidensis MR1 |journal=Environmental Science & Technology |date=January 2020 <!--|volume=preprint--> |volume=54 |issue=4 |pages=2268–2276 |doi=10.1021/acs.est.9b05285 |pmid=31934763 |bibcode=2020EnST...54.2268V |doi-access=free }}</ref>
<!-- NEEDS CITE
Some recent work at [[Manchester]] has shown that [[bacteria]] can reduce and fix uranium in [[soil]]s. This research is continuing at the [[University of Plymouth]] by Dr. Keith Roach and S. Handley.
/NEEDS CITE -->
Other organisms, such as the [[lichen]] ''Trapelia involuta'' or [[microorganism]]s such as the [[bacterium]] ''[[Citrobacter]]'', can absorb concentrations of uranium that are up to 300 times the level of their environment.{{sfn|Emsley|2001|pp=476 and 482}} ''Citrobacter'' species absorb [[uranyl]] ions when given [[glycerol phosphate]] (or other similar organic phosphates). After one day, one gram of bacteria can encrust themselves with nine grams of uranyl phosphate crystals; this creates the possibility that these organisms could be used in [[bioremediation]] to [[radioactive contamination|decontaminate]] uranium-polluted water.{{sfn|Emsley|2001|p=477}}<ref>{{cite journal
| title = Uranium bioaccumulation by a ''Citrobacter'' sp. as a result of enzymically mediated growth of polycrystalline {{chem|HUO|2|PO|4}}
| author = Macaskie, L. E.
| author2 = Empson, R. M.
| author3 = Cheetham, A. K.
| author4 = Grey, C. P.
| author5 = Skarnulis, A. J.
| name-list-style = amp
| journal = Science
| volume = 257
| issue = 5071
| date = 1992
| pages = 782–784
| doi = 10.1126/science.1496397
| pmid = 1496397 |bibcode = 1992Sci...257..782M}}</ref>
The proteobacterium ''[[Geobacter]]'' has also been shown to bioremediate uranium in ground water.<ref name="AndersonVrionis2003">{{cite journal |last1=Anderson |first1=R. T. |last2=Vrionis |first2=H. A. |last3=Ortiz-Bernad |first3=I. |last4=Resch |first4=C. T. |last5=Long |first5=P. E. |last6=Dayvault |first6=R. |last7=Karp |first7=K. |last8=Marutzky |first8=S. |last9=Metzler |first9=D. R. |last10=Peacock |first10=A. |last11=White |first11=D. C. |last12=Lowe |first12=M. |last13=Lovley |first13=D. R. |title=Stimulating the ''in situ'' activity of ''Geobacter'' species to remove uranium from the groundwater of a uranium-contaminated aquifer |journal=Applied and Environmental Microbiology |volume=69 |issue=10 |date=2003 |pages=5884–5891 |doi=10.1128/AEM.69.10.5884-5891.2003 |pmc=201226 |pmid=14532040|bibcode=2003ApEnM..69.5884A }}</ref> The mycorrhizal fungus ''[[Glomus intraradices]]'' increases uranium content in the roots of its symbiotic plant.<ref>{{Cite journal |title=Metals, minerals and microbes: geomicrobiology and bioremediation |journal=Microbiology |author=Gadd, G. M. |volume=156 |issue=Pt 3 |date=March 2010 |pages=609–643|pmid=20019082 |doi=10.1099/mic.0.037143-0 |doi-access=free }}</ref>

In nature, uranium(VI) forms highly soluble carbonate complexes at alkaline pH. This leads to an increase in mobility and availability of uranium to groundwater and soil from nuclear wastes which leads to health hazards. However, it is difficult to precipitate uranium as phosphate in the presence of excess carbonate at alkaline pH. A ''[[Sphingomonas]]'' sp. strain BSAR-1 has been found to express a high activity [[alkaline phosphatase]] (PhoK) that has been applied for bioprecipitation of uranium as uranyl phosphate species from alkaline solutions. The precipitation ability was enhanced by overexpressing PhoK protein in ''[[E. coli]]''.<ref>
{{cite journal
|author=Nilgiriwala, K.S.
|author2=Alahari, A.
|author3=Rao, A. S.
|author4=Apte, S.K.
|name-list-style=amp
|date=2008
|title=Cloning and Overexpression of Alkaline Phosphatase PhoK from ''Sphingomonas'' sp. Strain BSAR-1 for Bioprecipitation of Uranium from Alkaline Solutions
|journal=Applied and Environmental Microbiology
|volume=74
|issue=17
|pages=5516–5523
|doi=10.1128/AEM.00107-08
|pmid=18641147
|pmc=2546639
|bibcode=2008ApEnM..74.5516N
}}</ref>

[[Plant]]s absorb some uranium from soil. Dry weight concentrations of uranium in plants range from 5 to 60 parts per billion, and ash from burnt wood can have concentrations up to 4 parts per million.{{sfn|Emsley|2001|p=477}} Dry weight concentrations of uranium in [[food]] plants are typically lower with one to two micrograms per day ingested through the food people eat.{{sfn|Emsley|2001|p=477}}

===Production and mining===

{{Main|Uranium mining}}

Worldwide production of uranium in 2021 was 48,332 [[tonne]]s, of which 21,819 t (45%) was mined in [[Kazakhstan]]. Other important uranium mining countries are [[Namibia]] (5,753&nbsp;t), [[Canada]] (4,693&nbsp;t), [[Australia]] (4,192&nbsp;t), [[Uzbekistan]] (3,500&nbsp;t), and [[Russia]] (2,635&nbsp;t).<ref name="WNA-WUM">{{cite web |url=https://world-nuclear.org/information-library/nuclear-fuel-cycle/mining-of-uranium/world-uranium-mining-production.aspx |title=World Uranium Mining |publisher=World Nuclear Association |access-date=31 January 2023 }}</ref>

Uranium ore is mined in several ways: [[open-pit mining|open pit]], [[underground mining (soft rock)|underground]], [[in-situ leach]]ing, and [[borehole mining]].{{sfn|Emsley|2001|p=479}} Low-grade uranium ore mined typically contains 0.01 to 0.25% uranium oxides. Extensive measures must be employed to extract the metal from its ore.{{sfn|Seaborg|1968|p=774}} High-grade ores found in [[Athabasca Basin]] deposits in [[Saskatchewan]], Canada can contain up to 23% uranium oxides on average.<ref>{{cite web |url=http://www.investcom.com/moneyshow/uranium_athabasca.htm |title=Athabasca Basin, Saskatchewan |access-date=4 September 2009}}</ref> Uranium ore is crushed and rendered into a fine powder and then leached with either an [[acid]] or [[alkali]]. The [[leachate]] is subjected to one of several sequences of precipitation, solvent extraction, and ion exchange. The resulting mixture, called [[yellowcake]], contains at least 75% uranium oxides U{{sub|3}}O{{sub|8}}. Yellowcake is then [[calcined]] to remove impurities from the milling process before refining and conversion.<ref>{{cite book |url=https://books.google.com/books?id=F7p7W1rykpwC&pg=PA75 |pages=74–75 |title=Hydrometallurgy in extraction processes |volume=1 |author=Gupta, C. K. |author2=Mukherjee, T. K. |name-list-style=amp |publisher=CRC Press |date=1990 |isbn=978-0-8493-6804-2}}</ref>

Commercial-grade uranium can be produced through the [[redox|reduction]] of uranium [[halide]]s with [[alkali metal|alkali]] or [[alkaline earth metal]]s.<ref name="LANL" /> Uranium metal can also be prepared through [[electrolysis]] of {{chem|KUF|5}} or
[[Uranium tetrafluoride|{{chem|UF|4}}]], dissolved in molten [[calcium chloride]] ({{chem|CaCl|2}}) and [[sodium chloride]] ([[sodium|Na]]Cl) solution.<ref name="LANL" /> Very pure uranium is produced through the [[thermal decomposition]] of uranium [[halide]]s on a hot filament.<ref name="LANL" />

<gallery mode=packed heights=200px>
U production-demand.png|World uranium production (mines) and demand<ref name="WNA-WUM" />
Yellowcake.jpg|alt=A yellow sand-like rhombic mass on black background.|[[Yellowcake]] is a concentrated mixture of uranium oxides that is further refined to extract pure uranium.
Uranium production, OWID.svg|Uranium production 2015, in tonnes<ref>{{cite web |title=Uranium production |url=https://ourworldindata.org/grapher/uranium-production |website=Our World in Data |access-date=6 March 2020}}</ref>
</gallery>

===Resources and reserves===
[[File:Uranium prices.webp|thumb|upright=2|Uranium price 1990–2022.]]
It is estimated that 6.1&nbsp;million tonnes of uranium exists in ores that are economically viable at US$130 per kg of uranium,<ref name=res/> while 35&nbsp;million tonnes are classed as mineral resources (reasonable prospects for eventual economic extraction).<ref name="IAEAResourcesDemand" />

Australia has 28% of the world's known uranium ore reserves<ref name=res>{{cite web |url=https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/uranium-resources/supply-of-uranium.aspx |title=Uranium Supplies: Supply of Uranium – World Nuclear Association |website=www.world-nuclear.org}}</ref> and the world's largest single uranium deposit is located at the [[Olympic Dam, South Australia|Olympic Dam]] Mine in [[South Australia]].<ref>{{cite web|title=Uranium Mining and Processing in South Australia |publisher=South Australian Chamber of Mines and Energy |date=2002 |url=http://www.uraniumsa.org/processing/processing.htm |access-date=14 January 2007 |url-status=dead |archive-url=https://web.archive.org/web/20120106005859/http://www.uraniumsa.org/processing/processing.htm |archive-date=6 January 2012 }}</ref> There is a significant reserve of uranium in [[Bakouma]], a [[sub-prefecture]] in the [[prefecture]] of [[Mbomou]] in the [[Central African Republic]].<ref>{{cite news |date=2011 |url=https://www.reuters.com/article/idAFL5E7M34T920111103 |title=Areva suspends CAR uranium mine project |last1=Ngoupana |first1=P.-M. |last2=Felix |first2=B. |editor-last=Barker |editor-first=A. |work=Central African Republic News |access-date=7 March 2020}}</ref>

Some uranium also originates from dismantled nuclear weapons.<ref>{{cite web |url=https://world-nuclear.org/information-library/nuclear-fuel-cycle/uranium-resources/military-warheads-as-a-source-of-nuclear-fuel.aspx |title=Military Warheads as a Source of Nuclear Fuel |work=World-nuclear.org |access-date=24 May 2010}}</ref> For example, in 1993–2013 Russia supplied the United States with 15,000 tonnes of low-enriched uranium within the [[Megatons to Megawatts Program]].<ref>{{cite web |url=http://www.usec.com/megatonstomegawatts.htm |title=Megatons to Megawatts|publisher=U.S. Enrichment Corp.|url-status=dead|archive-url=https://web.archive.org/web/20080716044207/http://www.usec.com/megatonstomegawatts.htm|archive-date=July 16, 2008}}</ref>

An additional 4.6&nbsp;billion tonnes of uranium are estimated to be dissolved in [[sea water]] ([[Japan]]ese scientists in the 1980s showed that extraction of uranium from sea water using [[ion exchange]]rs was technically feasible).<ref name="UseaWater">{{cite web |title=Uranium recovery from Seawater |url=http://www.jaea.go.jp/jaeri/english/ff/ff43/topics.html |access-date=3 September 2008 |publisher=Japan Atomic Energy Research Institute |date=23 August 1999 |archive-url=https://web.archive.org/web/20091017081215/http://www.jaea.go.jp/jaeri/english/ff/ff43/topics.html |archive-date=17 October 2009 |url-status=dead}}</ref><ref name="stanfordCohen">{{cite web |title=How long will nuclear energy last? |url=http://www-formal.stanford.edu/jmc/progress/cohen.html |access-date=29 March 2007 |date=12 February 1996 |url-status=dead |archive-url=https://web.archive.org/web/20070410165316/http://www-formal.stanford.edu/jmc/progress/cohen.html |archive-date=10 April 2007 }}</ref> There have been experiments to extract uranium from sea water,<ref>{{Cite journal |doi=10.1002/cjce.5450620416 |title=Extraction of uranium from sea water using biological origin adsorbents |year=1984 |last1=Tsezos |first1=M. |last2=Noh |first2=S. H. |journal=The Canadian Journal of Chemical Engineering |volume=62 |issue=4| pages=559–561}}</ref> but the yield has been low due to the carbonate present in the water. In 2012, [[ORNL]] researchers announced the successful development of a new absorbent material dubbed HiCap which performs surface retention of solid or gas molecules, atoms or ions and also effectively removes toxic metals from water, according to results verified by researchers at [[Pacific Northwest National Laboratory]].<ref>{{cite web |url=http://www.ornl.gov/info/press_releases/get_press_release.cfm?ReleaseNumber=mr20120821-00 |title=ORNL technology moves scientists closer to extracting uranium from seawater |publisher=Oak Ridge National Laboratory, United States |date=21 August 2012 |access-date=22 February 2013 |archive-url=https://web.archive.org/web/20120825192521/http://www.ornl.gov/info/press_releases/get_press_release.cfm?ReleaseNumber=mr20120821-00 |archive-date=25 August 2012 |url-status=dead}}</ref><ref>{{cite web |title=Fueling nuclear power with seawater |publisher=Pnnl.gov |date=21 August 2012 |url=http://www.pnnl.gov/news/release.aspx?id=938 |access-date=22 February 2013}}</ref>

===Supplies===
{{Main|Uranium market}}
{{see also|2000s commodities boom}}
[[File:MonthlyUraniumSpot.png|thumb|right|Monthly uranium spot price in US$ per pound. The [[Uranium bubble of 2007|2007 price peak]] is clearly visible.<ref name="uraniumingo">{{cite web |url=http://www.uranium.info/prices/monthly.html |archive-url=https://web.archive.org/web/20071212170510/http://www.uranium.info/prices/monthly.html |archive-date=12 December 2007 |title=NUEXCO Exchange Value (Monthly Uranium Spot)}}</ref>]]
In 2005, ten countries accounted for the majority of the world's concentrated uranium oxides: [[Canada]] (27.9%), [[Australia]] (22.8%), [[Kazakhstan]] (10.5%), [[Russia]] (8.0%), [[Namibia]] (7.5%), [[Niger]] (7.4%), [[Uzbekistan]] (5.5%), the [[United States]] (2.5%), [[Argentina]] (2.1%) and [[Ukraine]] (1.9%).<ref>{{cite web |url=http://www.uxc.com/fuelcycle/uranium/production-uranium.html |title=World Uranium Production |publisher=UxC Consulting Company, LLC |access-date=11 February 2007 |archive-date=27 February 2007 |archive-url=https://web.archive.org/web/20070227140531/http://www.uxc.com/fuelcycle/uranium/production-uranium.html |url-status=dead}}</ref> In 2008, Kazakhstan was forecast to increase production and become the world's largest supplier of uranium by 2009;<ref>{{cite web |author=Mithridates |url=http://www.pagef30.com/2008/07/kazakhstan-to-surpass-canada-as-worlds.html |title=Page F30: Kazakhstan to surpass Canada as the world's largest producer of uranium by last year (2009) |website=Mithridates.blogspot.com |date=24 July 2008 |access-date=12 September 2008}}</ref><ref>{{cite web |url=http://www.zaman.com.tr/haber.do?haberno=717292 |title=Kazakistan uranyum üretimini artıracak|publisher=Zaman Gazetesi |work=Zaman.com.tr |language=tr|access-date=12 September 2008|date=28 July 2008|url-status=dead|archive-url=https://web.archive.org/web/20090113013838/http://www.zaman.com.tr/haber.do?haberno=717292|archive-date=13 January 2009}}</ref> Kazakhstan has dominated the world's uranium market since 2010. In 2021, its share was 45.1%, followed by Namibia (11.9%), Canada (9.7%), Australia (8.7%), Uzbekistan (7.2%), Niger (4.7%), Russia (5.5%), China (3.9%), India (1.3%), Ukraine (0.9%), and South Africa (0.8%), with a world total production of 48,332 tonnes.<ref name="WNA-WUM"/> Most uranium was produced not by conventional underground&nbsp;mining of ores (29% of production), but by [[in situ leach]]ing (66%).<ref name="WNA-WUM"/><ref>{{cite web|title=In Situ Leach Mining (ISL) of Uranium – World Nuclear Association |website=www.world-nuclear.org |url=https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/mining-of-uranium/in-situ-leach-mining-of-uranium.aspx|access-date=2021-05-06}}</ref>

In the late 1960s, UN geologists discovered major uranium deposits and other rare mineral reserves in [[Somalia]]. The find was the largest of its kind, with industry experts estimating the deposits at over 25% of the world's then known uranium reserves of 800,000 tons.<ref name="Bufais">{{cite news|title=Big Uranium Find Announced in Somalia|url=https://news.google.com/newspapers?id=hbVWAAAAIBAJ&pg=7276%2C235261|access-date=16 May 2014|newspaper=The New York Times|date=16 March 1968}}</ref>

The ultimate available supply is believed to be sufficient for at least the next 85 years,<ref name="IAEAResourcesDemand">{{cite web| title=Global Uranium Resources to Meet Projected Demand |url=http://www.iaea.org/newscenter/news/2006/uranium_resources.html |access-date=29 March 2007 |publisher=International Atomic Energy Agency |date=2006}}</ref> though some studies indicate underinvestment in the late twentieth century may produce supply problems in the 21st century.<ref name="MITfuelSupply">{{cite web| title=Lack of fuel may limit U.S. nuclear power expansion |url=https://news.mit.edu/2007/fuel-supply |access-date=29 March 2007 |work=Massachusetts Institute of Technology |date=21 March 2007}}</ref>
Uranium deposits seem to be log-normal distributed. There is a 300-fold increase in the amount of uranium recoverable for each tenfold decrease in ore grade.<ref>{{cite journal
| title = World Uranium Resources
|journal = Scientific American |volume = 242|issue = 1| author = Deffeyes, Kenneth S.
| author2 = MacGregor, Ian D.
| name-list-style = amp
| date = January 1980
| page = 66
|osti = 6665051|bibcode = 1980SciAm.242a..66D|doi = 10.1038/scientificamerican0180-66}}</ref>
In other words, there is little high grade ore and proportionately much more low grade ore available.

==Compounds==
{{Main|Uranium compounds}}
[[File:Uranium reactions.svg|thumb|upright=1.5|right|Reactions of uranium metal]]

===Oxidation states and oxides===

====Oxides====
{{See also|Uranium oxide}}
{{multiple image
| align = right
| total_width = 340
| image1 = U3O8lattice.jpg
| alt1 = Ball and stick model of layered crystal structure containing two types of atoms.
| caption1 = 
| image2 = UO2lattice.jpg
| alt2 = Ball and stick model of cubic-like crystal structure containing two types of atoms.
| caption2 = 
| footer = [[Triuranium octoxide]] (left) and [[uranium dioxide]] (right) are the two most common uranium oxides.
}}

Calcined uranium yellowcake, as produced in many large mills, contains a distribution of uranium oxidation species in various forms ranging from most oxidized to least oxidized. Particles with short residence times in a calciner will generally be less oxidized than those with long retention times or particles recovered in the stack scrubber. Uranium content is usually referenced to {{chem|U|3|O|8}}, which dates to the days of the [[Manhattan Project]] when {{chem|U|3|O|8}} was used as an analytical chemistry reporting standard.<ref>{{Cite book |last1=Kloprogge |first1=J. Theo |last2=Ponce |first2=Concepcion P. |last3=Loomis |first3=Tom A. |title=The periodic table : nature's building blocks : an introduction to the naturally occurring elements, their origins and their uses |date=2021 |publisher=Elsevier |isbn=978-0-12-821538-8 |location=Amsterdam |pages=861–862 |oclc=1223058470}}</ref>

[[Phase (matter)|Phase relationships]] in the uranium-oxygen system are complex. The most important oxidation states of uranium are uranium(IV) and uranium(VI), and their two corresponding [[oxide]]s are, respectively, [[uranium dioxide]] ({{chem|UO|2}}) and [[uranium trioxide]] ({{chem|UO|3}}).{{sfn|Seaborg|1968|p=779}} Other [[uranium oxide]]s such as [[uranium monoxide]] (UO), [[diuranium pentoxide]] ({{chem|U|2|O|5}}), and [[uranium peroxide]] ({{chem|UO|4|·2H|2|O}}) also exist.

The most common forms of uranium oxide are [[triuranium octoxide]] ({{chem|U|3|O|8}}) and {{chem|UO|2}}.<ref name="ANL-Chem">{{cite web |title=Chemical Forms of Uranium |publisher=Argonne National Laboratory |url=http://web.ead.anl.gov/uranium/guide/ucompound/forms/index.cfm |access-date=18 February 2007 |archive-url=https://web.archive.org/web/20060922180607/http://web.ead.anl.gov/uranium/guide/ucompound/forms/index.cfm |archive-date=22 September 2006 |url-status=dead}}</ref> Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octoxide is (depending on conditions) the most stable compound of uranium and is the form most commonly found in nature. Uranium dioxide is the form in which uranium is most commonly used as a nuclear reactor fuel.<ref name="ANL-Chem"/> At ambient temperatures, {{chem|UO|2}} will gradually convert to {{chem|U|3|O|8}}. Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal.<ref name="ANL-Chem"/>

====Aqueous chemistry====
[[File:U Oxstufen.jpg|thumb|left|upright=0.85|Uranium in its oxidation states III, IV, V, VI]]
Salts of many [[oxidation state]]s of uranium are water-[[solubility|soluble]] and may be studied in [[aqueous solution]]s. The most common ionic forms are {{chem|U|3+}} (brown-red), {{chem|U|4+}} (green), {{chem|UO|2|+}} (unstable), and {{chem|UO|2|2+}} (yellow), for U(III), U(IV), U(V), and U(VI), respectively.{{sfn|Seaborg|1968|p=778}} A few [[solid]] and semi-metallic compounds such as UO and [[Uranium monosulfide|US]] exist for the formal oxidation state uranium(II), but no simple ions are known to exist in solution for that state. Ions of {{chem|U|3+}} liberate [[hydrogen]] from [[water]] and are therefore considered to be highly unstable. The {{chem|UO|2|2+}} ion represents the uranium(VI) state and is known to form compounds such as [[uranyl carbonate]], [[uranyl chloride]] and [[uranyl sulfate]]. {{chem|UO|2|2+}} also forms [[complex (chemistry)|complexes]] with various [[organic compound|organic]] [[chelation|chelating]] agents, the most commonly encountered of which is [[uranyl acetate]].{{sfn|Seaborg|1968|p=778}}

Unlike the uranyl salts of uranium and [[polyatomic ion]] uranium-oxide cationic forms, the [[uranate]]s, salts containing a polyatomic uranium-oxide anion, are generally not water-soluble.

====Carbonates====
The interactions of carbonate anions with uranium(VI) cause the [[Pourbaix diagram]] to change greatly when the medium is changed from water to a carbonate containing solution. While the vast majority of carbonates are insoluble in water (students are often taught that all carbonates other than those of alkali metals are insoluble in water), uranium carbonates are often soluble in water. This is because a U(VI) cation is able to bind two terminal oxides and three or more carbonates to form anionic complexes.

{|class="wikitable" style="text-align:center; float:center"
|+[[Pourbaix diagram]]s<ref name="medusa">Puigdomenech, Ignasi (2004) [https://www.kth.se/che/medusa/chemeq-1.369367 ''Hydra/Medusa Chemical Equilibrium Database and Plotting Software'']. [[KTH Royal Institute of Technology]]</ref>
|-
|width=50% |[[File:Uranium pourdaix diagram in water.png|center|190x180px|alt=A graph of potential vs. pH showing stability regions of various uranium compounds]]
|width=50% |[[File:Uranium pourdiax diagram in carbonate media.png|center|190x180px|alt=A graph of potential vs. pH showing stability regions of various uranium compounds]]
|-
|Uranium in a non-complexing aqueous medium<br/>(e.g. [[perchloric acid]]/sodium hydroxide).<ref name="medusa" />
|Uranium in carbonate solution
|-
|[[File:Uranium fraction diagram with no carbonate.png|center|250x180px|alt=A graph of potential vs. pH showing stability regions of various uranium compounds]]
|[[File:Uranium fraction diagram with carbonate present.png|center|250x180px|alt=A graph of potential vs. pH showing stability regions of various uranium compounds]]
|-
|Relative concentrations of the different chemical forms of uranium in a non-complexing aqueous medium<br/>(e.g. [[perchloric acid]]/sodium hydroxide).<ref name="medusa" />
|Relative concentrations of the different chemical forms of uranium in an aqueous carbonate solution.<ref name="medusa" />
|}

====Effects of pH====
The uranium fraction diagrams in the presence of carbonate illustrate this further: when the pH of a uranium(VI) solution increases, the uranium is converted to a hydrated uranium oxide hydroxide and at high pHs it becomes an anionic hydroxide complex.

When carbonate is added, uranium is converted to a series of carbonate complexes if the pH is increased. One effect of these reactions is increased solubility of uranium in the pH range 6 to 8, a fact that has a direct bearing on the long term stability of spent uranium dioxide nuclear fuels.

===Hydrides, carbides and nitrides===
Uranium metal heated to {{convert|250|to|300|C|F}} reacts with [[hydrogen]] to form [[uranium hydride]]. Even higher temperatures will reversibly remove the hydrogen. This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium [[carbide]], [[nitride]], and [[halide]] compounds.{{sfn|Seaborg|1968|p=782}} Two crystal modifications of uranium hydride exist: an α form that is obtained at low temperatures and a β form that is created when the formation temperature is above 250&nbsp;°C.{{sfn|Seaborg|1968|p=782}}

[[Uranium carbide]]s and [[uranium nitride]]s are both relatively [[Chemically inert|inert]] [[semimetal]]lic compounds that are minimally soluble in [[acid]]s, react with water, and can ignite in [[air]] to form {{chem|U|3|O|8}}.{{sfn|Seaborg|1968|p=782}} Carbides of uranium include uranium monocarbide (U[[carbon|C]]), uranium dicarbide ({{chem|UC|2}}), and diuranium tricarbide ({{chem|U|2|C|3}}). Both UC and {{chem|UC|2}} are formed by adding carbon to molten uranium or by exposing the metal to [[carbon monoxide]] at high temperatures. Stable below 1800&nbsp;°C, {{chem|U|2|C|3}} is prepared by subjecting a heated mixture of UC and {{chem|UC|2}} to mechanical stress.{{sfn|Seaborg|1968|p=780}} Uranium nitrides obtained by direct exposure of the metal to [[nitrogen]] include uranium mononitride (UN), uranium dinitride ({{chem|UN|2}}), and diuranium trinitride ({{chem|U|2|N|3}}).{{sfn|Seaborg|1968|p=780}}

===Halides===
[[File:Uranium hexafluoride crystals sealed in an ampoule.jpg|thumb|[[Uranium hexafluoride]] is the feedstock used to separate uranium-235 from natural uranium.|alt=Snow-like substance in a sealed glass ampoule.]]
<!--[[File:Uranium-hexafluoride-2D-V2.svg|thumb|upright|[[Uranium hexafluoride]] is the feedstock used to separate uranium-235 from natural uranium.|alt=Skeletal diagram of a chemical compound having a uranium atom in its center bonded to 6 fluorine atoms.]]-->
All uranium fluorides are created using [[uranium tetrafluoride]] ({{chem|UF|4}}); {{chem|UF|4}} itself is prepared by hydrofluorination of uranium dioxide.{{sfn|Seaborg|1968|p=782}} Reduction of {{chem|UF|4}} with hydrogen at 1000&nbsp;°C produces [[uranium trifluoride]] ({{chem|UF|3}}). Under the right conditions of temperature and pressure, the reaction of solid {{chem|UF|4}} with gaseous [[uranium hexafluoride]] ({{chem|UF|6}}) can form the intermediate fluorides of {{chem|U|2|F|9}}, {{chem|U|4|F|17}}, and [[Uranium pentafluoride|{{chem|UF|5}}]].{{sfn|Seaborg|1968|p=782}}

At room temperatures, {{chem|UF|6}} has a high [[vapor pressure]], making it useful in the [[gaseous diffusion]] process to separate the rare uranium-235 from the common uranium-238 isotope. This compound can be prepared from uranium dioxide and uranium hydride by the following process:{{sfn|Seaborg|1968|p=782}}

:{{chem|UO|2}} + 4 HF → {{chem|UF|4}} + 2 {{chem|H|2|O}} (500&nbsp;°C, endothermic)
:{{chem|UF|4}} + {{chem|F|2}} → {{chem|UF|6}} (350&nbsp;°C, endothermic)

The resulting {{chem|UF|6}}, a white solid, is highly [[chemical reaction|reactive]] (by fluorination), easily [[sublimation (chemistry)|sublimes]] (emitting a vapor that behaves as a nearly [[ideal gas]]), and is the most volatile compound of uranium known to exist.{{sfn|Seaborg|1968|p=782}}

One method of preparing [[uranium tetrachloride]] ({{chem|UCl|4}}) is to directly combine [[chlorine]] with either uranium metal or uranium hydride. The reduction of {{chem|UCl|4}} by hydrogen produces [[uranium trichloride]] ({{chem|UCl|3}}) while the higher chlorides of uranium are prepared by reaction with additional chlorine.{{sfn|Seaborg|1968|p=782}} All uranium chlorides react with water and air.

[[Bromide]]s and [[iodide]]s of uranium are formed by direct reaction of, respectively, [[bromine]] and [[iodine]] with uranium or by adding {{chem|UH|3}} to those element's acids.{{sfn|Seaborg|1968|p=782}} Known examples include: [[Uranium(III) bromide|{{chem|UBr|3}}]], [[Uranium(IV) bromide|{{chem|UBr|4}}]], [[Uranium(III) iodide|{{chem|UI|3}}]], and [[Uranium(IV) iodide|{{chem|UI|4}}]]. {{chem|UI|5}} has never been prepared. Uranium oxyhalides are water-soluble and include [[Uranyl fluoride|{{chem|UO|2|F|2}}]], {{chem|UOCl|2}}, [[Uranyl chloride|{{chem|UO|2|Cl|2}}]], and [[Uranyl bromide|{{chem|UO|2|Br|2}}]]. Stability of the oxyhalides decrease as the [[atomic weight]] of the component halide increases.{{sfn|Seaborg|1968|p=782}}

==Isotopes==
{{main|Isotopes of uranium}}
<!--[[File:Uranium enrichment proportions.svg|thumb|upright=0.55|Pie-graphs showing the relative proportions of uranium-238 (blue) and uranium-235 (red) at different levels of enrichment]]-->
Uranium, like all elements with an atomic number greater than 82, has no [[stable isotope]]s. All isotopes of uranium are [[radioactive]] because the [[strong nuclear force]] does not prevail over [[electromagnetic repulsion]] in nuclides containing more than 82 protons.<ref name="beiser">{{cite book|title=Concepts of Modern Physics|chapter-url=http://phy240.ahepl.org/Concepts_of_Modern_Physics_by_Beiser.pdf |year=2003|publisher=[[McGraw-Hill Education]]|isbn=978-0-07-244848-1|chapter=Nuclear Transformations|pages=432–434 |edition=6th |first=A. |last=Beiser |access-date=4 July 2016|archive-date=4 October 2016|archive-url=https://web.archive.org/web/20161004204701/http://phy240.ahepl.org/Concepts_of_Modern_Physics_by_Beiser.pdf|url-status=dead}}</ref> Nevertheless, the two most stable isotopes, {{sup|238}}U and {{sup|235}}U, have [[half-life|half-lives]] long enough to occur in nature as [[primordial radionuclide]]s, with measurable quantities having survived since the formation of the Earth.<ref name=primU>{{cite journal |first1= I. U. |last1= Roederer |first2=K. |last2=Kratz |first3=A. |last3=Frebel |first4=N. |last4=Christlieb |first5=B. |last5=Pfeiffer |first6=J. J. |last6=Cowan |first7=C. |last7=Sneden |title=The end of nucleosynthesis: Production of lead and thorium in the early galaxy |date=2009 |journal=The Astrophysical Journal |volume=698 |number=2 |pages= 1963–1980 |doi=10.1088/0004-637X/698/2/1963|arxiv= 0904.3105 |bibcode= 2009ApJ...698.1963R |hdl= 2152/35050 |s2cid= 14814446 }}</ref> These two [[nuclide]]s, along with [[thorium-232]], are the only confirmed primordial nuclides heavier than nearly-stable [[bismuth-209]].{{NUBASE2020|ref}}{{refn|name=pu244}}

[[Natural uranium]] consists of three major isotopes: uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). There are also five other trace isotopes: uranium-240, a decay product of [[plutonium-244]];{{refn|name=pu244}} uranium-239, which is formed when {{sup|238}}U undergoes spontaneous fission, releasing neutrons that are captured by another {{sup|238}}U atom; uranium-237, which is formed when {{sup|238}}U captures a neutron but emits two more, which then decays to [[neptunium-237]]; [[uranium-236]], which occurs in trace quantities due to neutron capture on {{sup|235}}U and as a decay product of plutonium-244;{{refn|name=pu244|The occurrence of plutonium-244 as a primordial nuclide is disputed, though some reports of its detection have also been attributed to infall from the [[interstellar medium]].<ref name="PRC">{{cite journal|last=Lachner|first=J. |display-authors=etal|date=2012|title=Attempt to detect primordial {{sup|244}}Pu on Earth|journal=Physical Review C|volume=85|issue=1|page=015801| doi=10.1103/PhysRevC.85.015801|bibcode=2012PhRvC..85a5801L}}</ref><ref name="WallnerFaestermann2015">{{cite journal |last1=Wallner |first1=A. |last2=Faestermann |first2=T. |last3=Feige |first3=J. |last4=Feldstein |first4=C. |last5=Knie |first5=K. |last6=Korschinek |first6=G. |last7=Kutschera |first7=W. |last8=Ofan |first8=A. |last9=Paul |first9=M. |last10=Quinto |first10=F. |last11=Rugel |first11=G. |last12=Steier |first12=P. |title=Abundance of live 244Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis |journal=Nature Communications |volume=6 |year=2015 |page=5956 |issn=2041-1723 |doi=10.1038/ncomms6956 |pmid=25601158 |pmc=4309418 |arxiv=1509.08054 |bibcode=2015NatCo...6.5956W}}</ref>}} and finally, [[uranium-233]], which is formed in the [[decay chain]] of neptunium-237. Additionally, [[uranium-232]] would be produced by the [[double beta decay]] of natural [[thorium-232]], though this energetically possible process has never been observed.<ref name="Tretyak2002">{{Cite journal
 |last1=Tretyak |first1=V.I. 
 |last2=Zdesenko |first2=Yu.G. 
 |year=2002
 |title=Tables of Double Beta Decay Data — An Update
 |journal=[[At. Data Nucl. Data Tables]] |volume=80 |issue=1 |pages=83–116
 |doi=10.1006/adnd.2001.0873
|bibcode=2002ADNDT..80...83T }}</ref>

Uranium-238 is the most stable isotope of uranium, with a half-life of about {{val|4.463|e=9}} years,{{NUBASE2020|ref}} roughly the [[age of the Earth]]. Uranium-238 is predominantly an alpha emitter, decaying to thorium-234. It ultimately decays through the [[uranium series]], which has 18 members, into [[lead-206]].<ref name="ColumbiaEncy" /> Uranium-238 is not fissile, but is a fertile isotope, because after [[neutron activation]] it can be converted to plutonium-239, another fissile isotope. Indeed, the {{sup|238}}U nucleus can absorb one neutron to produce the radioactive isotope [[uranium-239]]. {{sup|239}}U decays by [[beta emission]] to [[neptunium]]-239, also a beta-emitter, that decays in its turn, within a few days into plutonium-239. {{sup|239}}Pu was used as fissile material in the first [[atomic bomb]] detonated in the "[[Trinity test]]" on 16 July 1945 in [[New Mexico]].{{sfn|Seaborg|1968|p=773}}

Uranium-235 has a half-life of about {{val|7.04|e=8}} years; it is the next most stable uranium isotope after {{sup|238}}U and is also predominantly an alpha emitter, decaying to thorium-231.{{NUBASE2020|ref}} Uranium-235 is important for both [[nuclear reactor]]s and [[nuclear weapon]]s, because it is the only uranium isotope existing in nature on Earth in significant amounts that is fissile. This means that it can be split into two or three fragments ([[fission products]]) by thermal neutrons.<ref name="ColumbiaEncy" /> The decay chain of {{sup|235}}U, which is called the [[actinium series]], has 15 members and eventually decays into lead-207.<ref name="ColumbiaEncy" /> The constant rates of decay in these decay series makes the comparison of the ratios of parent to [[decay product|daughter elements]] useful in radiometric dating.

Uranium-236 has a half-life of {{val|2.342|e=7}} years{{NUBASE2020|ref}} and is not found in significant quantities in nature. The half-life of uranium-236 is too short for it to be primordial, though it has been identified as an [[extinct radionuclide|extinct]] progenitor of its alpha decay daughter, thorium-232.<ref name="thoruranium"/> Uranium-236 occurs in [[spent nuclear fuel]] when neutron capture on {{sup|235}}U does not induce fission, or as a decay product of [[plutonium-240]]. Uranium-236 is not fertile, as three more neutron captures are required to produce fissile {{sup|239}}Pu, and is not itself fissile; as such, it is considered long-lived radioactive waste.<ref name=236U>{{cite journal |title = Alpha-particle emission probabilities of {{sup|236}}U obtained by alpha spectrometry |journal = Applied Radiation and Isotopes |volume = 87 |pages = 292–296 |year = 2014 |issn = 0969-8043 |doi = 10.1016/j.apradiso.2013.11.020 |first1=M. |last1=Marouli |first2=S. |last2=Pommé |first3=V. |last3=Jobbágy |first4=R. |last4=Van Ammel |first5=J. |last5=Paepen |first6=H. |last6=Stroh |first7=L. |last7=Benedik|pmid = 24309010 }}</ref>

Uranium-234 is a member of the uranium series and occurs in equilibrium with its progenitor, {{sup|238}}U; it undergoes alpha decay with a half-life of 245,500 years{{NUBASE2020|ref}} and decays to lead-206 through a series of relatively short-lived isotopes.

Uranium-233 undergoes alpha decay with a half-life of 160,000 years and, like {{sup|235}}U, is fissile.<ref name="LANL" /> It can be bred from [[thorium-232]] via neutron bombardment, usually in a nuclear reactor; this process is known as the [[thorium fuel cycle]]. Owing to the fissility of {{sup|233}}U and the greater natural abundance of thorium (three times that of uranium),<ref name="iaea2022">{{cite report |title=Near Term and Promising Long Term Options for the Deployment of Thorium Based Nuclear Energy |publisher=International Atomic Energy Agency |date=2022 |location=Vienna |url=https://www-pub.iaea.org/MTCD/Publications/PDF/TE-2009web.pdf}}</ref> {{sup|233}}U has been investigated for use as nuclear fuel as a possible alternative to {{sup|235}}U and {{sup|239}}Pu,<ref name="Forsburg 1999">{{cite journal |author1=Forsburg, C. W. |author2=Lewis, L. C. |title=Uses For Uranium-233: What Should Be Kept for Future Needs? |publisher=Oak Ridge National Laboratory |journal=Ornl-6952 |date=24 September 1999 |url=http://moltensalt.org/references/static/downloads/pdf/ORNL-6952.pdf}}</ref> though is not in widespread use {{as of|lc=y|2022}}.<ref name="iaea2022"/> The decay chain of uranium-233 forms part of the [[neptunium series]] and ends at nearly-stable bismuth-209 (half-life {{val|2.01|e=19|u=years}}){{NUBASE2020|ref}} and stable [[thallium]]-205.

[[Uranium-232]] is an alpha emitter with a half-life of 68.9 years.{{NUBASE2020|ref}} This isotope is produced as a byproduct in production of {{sup|233}}U and is considered a nuisance, as it is not fissile and decays through short-lived alpha and [[gamma radiation|gamma emitter]]s such as [[thallium-208|{{sup|208}}Tl]].<ref name="Forsburg 1999"/> It is also expected that thorium-232 should be able to undergo [[double beta decay]], which would produce uranium-232, but this has not yet been observed experimentally.{{NUBASE2020|ref}}

All isotopes from {{sup|232}}U to {{sup|236}}U inclusive have minor [[cluster decay]] branches (less than {{val|e=-10}}%), and all these bar {{sup|233}}U, in addition to {{sup|238}}U, have minor [[spontaneous fission]] branches;{{NUBASE2020|ref}} the greatest [[branching ratio]] for spontaneous fission is about {{val|5|e=-5}}% for {{sup|238}}U, or about one in every two million decays.<ref>{{cite book |last=Goffer |first=Zvi |year=2006 |title=Archaeological Chemistry |page=106 |publisher=[[Wiley (publisher)|Wiley]] |edition=2nd |isbn=978-0-471-91515-7}}</ref> The shorter-lived trace isotopes {{sup|237}}U and {{sup|239}}U exclusively undergo [[beta decay]], with respective half-lives of 6.752 days and 23.45 minutes.{{NUBASE2020|ref}}

In total, 28 isotopes of uranium have been identified, ranging in [[mass number]] from 214<ref>{{cite journal |title=New α -Emitting Isotope 214 U and Abnormal Enhancement of α -Particle Clustering in Lightest Uranium Isotopes |year=2021 |url=https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.126.152502 |doi=10.1103/PhysRevLett.126.152502 |access-date=15 May 2021|last1=Zhang |first1=Z. Y. |last2=Yang |first2=H. B. |last3=Huang |first3=M. H. |last4=Gan |first4=Z. G. |last5=Yuan |first5=C. X. |last6=Qi |first6=C. |last7=Andreyev |first7=A. N. |last8=Liu |first8=M. L. |last9=Ma |first9=L. |last10=Zhang |first10=M. M. |last11=Tian |first11=Y. L. |last12=Wang |first12=Y. S. |last13=Wang |first13=J. G. |last14=Yang |first14=C. L. |last15=Li |first15=G. S. |last16=Qiang |first16=Y. H. |last17=Yang |first17=W. Q. |last18=Chen |first18=R. F. |last19=Zhang |first19=H. B. |last20=Lu |first20=Z. W. |last21=Xu |first21=X. X. |last22=Duan |first22=L. M. |last23=Yang |first23=H. R. |last24=Huang |first24=W. X. |last25=Liu |first25=Z. |last26=Zhou |first26=X. H. |last27=Zhang |first27=Y. H. |last28=Xu |first28=H. S. |last29=Wang |first29=N. |last30=Zhou |first30=H. B. |journal=Physical Review Letters |volume=126 |issue=15 |page=152502 |pmid=33929212 |arxiv=2101.06023 |bibcode=2021PhRvL.126o2502Z |s2cid=231627674 |display-authors=1 }}</ref> to 242, with the exception of 220.{{NUBASE2020|ref}}<ref name=U241>{{cite journal |title = Discovery of New Isotope {{sup|241}}U and Systematic High-Precision Atomic Mass Measurements of Neutron-Rich Pa-Pu Nuclei Produced via Multinucleon Transfer Reactions |author1= Niwase, T. |author2=Watanabe, Y. X. |author3=Hirayama, Y. |author4=Mukai, M. |author5=Schury, P. |author6=Andreyev, A. N. |author7=Hashimoto, T. |author8=Iimura, S. |author9=Ishiyama, H. |author10=Ito, Y. |author11=Jeong, S. C. |author12=Kaji, D. |author13=Kimura, S. |author14=Miyatake, H. |author15=Morimoto, K. |author16=Moon, J.-Y. |author17=Oyaizu, M. |author18=Rosenbusch, M. |author19=Taniguchi, A. |author20=Wada, M. |display-authors=3 |journal = Physical Review Letters |volume = 130 |issue = 13 |pages = 132502-1–132502-6 |year = 2023 |doi = 10.1103/PhysRevLett.130.132502|pmid= 37067317 |s2cid= 257976576 |bibcode= 2023PhRvL.130m2502N |url= https://eprints.whiterose.ac.uk/197980/1/PhysRevLett.130.132502.pdf }}</ref> Among the uranium isotopes not found in natural samples or nuclear fuel, the longest-lived is {{sup|230}}U, an alpha emitter with a half-life of 20.23 days.{{NUBASE2020|ref}} This isotope has been considered for use in [[targeted alpha-particle therapy]] (TAT).<ref name="230Pa">{{cite journal |last1=Mastren |first1=T. |last2=Stein |first2=B. W. |last3=Parker |first3=T. G. |last4=Radchenko |first4=V. |last5=Copping |first5=R. |last6=Owens |first6=A. |last7=Wyant |first7=L. E. |last8=Brugh |first8=M. |last9=Kozimor |first9=S. A. |last10=Noriter |first10=F. M. |last11=Birnbaum |first11=E. R. |last12=John |first12=K. D. |last13=Fassbender |first13=M. E. |title=Separation of protactinium employing sulfur-based extraction chromatographic resins |journal=Analytical Chemistry |date=2018 |volume=90 |issue=11 |pages=7012–7017 |doi=10.1021/acs.analchem.8b01380 |pmid=29757620 |osti=1440455 |url=https://www.researchgate.net/publication/325135604 |issn=0003-2700}}</ref> All other isotopes have half-lives shorter than one hour, except for {{sup|231}}U (half-life 4.2 days) and {{sup|240}}U (half-life 14.1 hours).{{NUBASE2020|ref}} The shortest-lived known isotope is {{sup|221}}U, with a half-life of 660 nanoseconds, and it is expected that the hitherto unknown {{sup|220}}U has an even shorter half-life.<ref name=Khuyagbaatar>{{Cite journal |last=Khuyagbaatar |first=J. |display-authors=et al |date=11 December 2015 |title=New Short-Lived Isotope <sup>221</sup>U and the Mass Surface Near ''N'' = 126 |journal=Physical Review Letters |volume=115 |issue=24 |pages=242502 |doi=10.1103/PhysRevLett.115.242502 |pmid=26705628 |bibcode=2015PhRvL.115x2502K |s2cid=12184696 |url=https://lup.lub.lu.se/record/8311218}}</ref> The proton-rich isotopes lighter than {{sup|232}}U primarily undergo alpha decay, except for {{sup|229}}U and {{sup|231}}U, which decay to [[isotopes of protactinium|protactinium isotopes]] via [[positron emission]] and [[electron capture]], respectively; the neutron-rich {{sup|240}}U, {{sup|241}}U, and {{sup|242}}U undergo [[beta decay]] to form [[isotopes of neptunium|neptunium isotopes]].{{NUBASE2020|ref}}<ref name=U241/>

===Enrichment===
{{Main|Enriched uranium}}
[[File:Gas centrifuge cascade.jpg|thumb|Cascades of [[gas centrifuge]]s are used to enrich uranium ore to concentrate its fissionable isotopes.|alt=A photo of a large hall filled with arrays of long white standing cylinders.]]
In nature, uranium is found as uranium-238 (99.2742%) and uranium-235 (0.7204%). [[Isotope separation]] concentrates (enriches) the fissile uranium-235 for nuclear weapons and most nuclear power plants, except for [[gas cooled reactor]]s and [[pressurized heavy water reactor]]s. Most neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the [[nuclear chain reaction]]. The concentration and amount of uranium-235 needed to achieve this is called a '[[critical mass]]'.

To be considered 'enriched', the uranium-235 fraction should be between 3% and 5%.<ref>{{cite web |title=Uranium Enrichment |url=http://web.ead.anl.gov/uranium/guide/depletedu/enrich/index.cfm |access-date=11 February 2007 |publisher=Argonne National Laboratory |archive-url=https://web.archive.org/web/20070124232415/http://web.ead.anl.gov/uranium/guide/depletedu/enrich/index.cfm |archive-date=24 January 2007 |url-status=dead}}</ref> This process produces huge quantities of uranium that is depleted of uranium-235 and with a correspondingly increased fraction of uranium-238, called depleted uranium or 'DU'. To be considered 'depleted', the {{sup|235}}U concentration should be no more than 0.3%.<ref name="paducah">{{cite news |url=http://www.wise-uranium.org/dhap991.html |title=Depleted Uranium: a by-product of the Nuclear Chain |access-date=31 July 2009 |publisher=Laka Foundation |author=Diehl, Peter |url-status=dead |archive-url=https://archive.today/20130113114319/http://www.wise-uranium.org/dhap991.html |archive-date=13 January 2013}}</ref> The price of uranium has risen since 2001, so enrichment tailings containing more than 0.35% uranium-235 are being considered for re-enrichment, driving the price of [[depleted uranium hexafluoride]] above $130 per kilogram in July 2007 from $5 in 2001.<ref name="paducah" />

The [[gas centrifuge]] process, where gaseous [[uranium hexafluoride]] ({{chem|UF|6}}) is separated by the difference in molecular weight between {{sup|235}}UF{{sub|6}} and {{sup|238}}UF{{sub|6}} using high-speed [[centrifuge]]s, is the cheapest and leading enrichment process.{{sfn|Emsley|2001|p=478}} The [[gaseous diffusion]] process had been the leading method for enrichment and was used in the [[Manhattan Project]]. In this process, uranium hexafluoride is repeatedly [[diffusion|diffused]] through a [[silver]]-[[zinc]] membrane, and the different isotopes of uranium are separated by diffusion rate (since uranium-238 is heavier it diffuses slightly slower than uranium-235).{{sfn|Emsley|2001|p=478}} The [[molecular laser isotope separation]] method employs a [[laser]] beam of precise energy to sever the bond between uranium-235 and fluorine. This leaves uranium-238 bonded to fluorine and allows uranium-235 metal to precipitate from the solution.{{sfn|Emsley|2001|p=479}} An alternative laser method of enrichment is known as [[atomic vapor laser isotope separation]] (AVLIS) and employs visible [[tunable laser]]s such as [[dye laser]]s.<ref>{{cite book |editor=[[F. J. Duarte|Duarte, F. J.]] |editor2=Hillman, L. W. |title=Dye Laser Principles |publisher=Academic |date=1990 |page=413 |isbn=978-0-12-222700-4 |url=http://www.opticsjournal.com/dlp.htm |url-status=dead |archive-url=https://web.archive.org/web/20100917020215/http://www.opticsjournal.com/dlp.htm |archive-date=17 September 2010}}</ref> Another method used is liquid thermal diffusion.<ref name="SciTechEncy" />

The only significant deviation from the {{sup|235}}U to {{sup|238}}U ratio in any known natural samples occurs in [[Oklo]], [[Gabon]], where [[natural nuclear fission reactor]]s consumed some of the {{sup|235}}U some two billion years ago when the ratio of {{sup|235}}U to {{sup|238}}U was more akin to that of [[low enriched uranium]] allowing regular ("light") water to act as a [[neutron moderator]] akin to the process in humanmade [[light water reactor]]s. The existence of such natural fission reactors which had been theoretically predicted beforehand was proven as the slight deviation of {{sup|235}}U concentration from the expected values were discovered during [[uranium enrichment]] in France. Subsequent investigations to rule out any nefarious human action (such as stealing of {{sup|235}}U) confirmed the theory by finding isotope ratios of common [[fission product]]s (or rather their stable daughter nuclides) in line with the values expected for fission but deviating from the values expected for non-fission derived samples of those elements.

==Human exposure==
A person can be exposed to uranium (or its [[decay product|radioactive daughters]], such as [[radon]]) by inhaling dust in air or by ingesting contaminated water and food. The amount of uranium in air is usually very small; however, people who work in factories that process [[phosphate]] [[fertilizer]]s, live near government facilities that made or tested nuclear weapons, live or work near a modern battlefield where depleted uranium [[weapons]] have been used, or live or work near a [[coal]]-fired power plant, facilities that mine or process uranium ore, or enrich uranium for reactor fuel, may have increased exposure to uranium.<ref name="EPA-Rad">{{cite web |date=16 February 2023 |title=Radionuclide Basics: Uranium |publisher=U.S. Environmental Protection Agency |url=https://www.epa.gov/radiation/radionuclide-basics-uranium |access-date=19 April 2023}}</ref><ref name="ATSDR-ToxFAQ">{{cite web |title=ToxFAQ for Uranium |url=https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsDetails.aspx?faqid=439&toxid=77 |access-date=19 April 2023 |publisher=Agency for Toxic Substances and Disease Registry |date=18 March 2014}}</ref> Houses or structures that are over uranium deposits (either natural or man-made slag deposits) may have an increased incidence of exposure to radon gas. The [[Occupational Safety and Health Administration]] (OSHA) has set the [[permissible exposure limit]] for uranium exposure in the workplace as 0.25&nbsp;mg/m{{sup|3}} over an 8-hour workday. The [[National Institute for Occupational Safety and Health]] (NIOSH) has set a [[recommended exposure limit]] (REL) of 0.2&nbsp;mg/m{{sup|3}} over an 8-hour workday and a short-term limit of 0.6&nbsp;mg/m{{sup|3}}. At 10&nbsp;mg/m{{sup|3}}, uranium is [[IDLH|immediately dangerous to life and health]].<ref>{{cite web |date=30 October 2019 |title=CDC – NIOSH Pocket Guide to Chemical Hazards – Uranium (insoluble compounds, as U) |url=https://www.cdc.gov/niosh/npg/npgd0650.html |access-date=19 April 2023 |website=National Institute for Occupational Safety and Health}}</ref>

Most ingested uranium is excreted during [[digestion]]. Only 0.5% is absorbed when insoluble forms of uranium, such as its oxide, are ingested, whereas absorption of the more soluble [[uranyl]] ion can be up to 5%.{{sfn|Emsley|2001|p=477}} However, soluble uranium compounds tend to quickly pass through the body, whereas insoluble uranium compounds, especially when inhaled by way of dust into the [[lung]]s, pose a more serious exposure hazard. After entering the bloodstream, the absorbed uranium tends to [[bioaccumulation|bioaccumulate]] and stay for many years in [[bone]] tissue because of uranium's affinity for phosphates.{{sfn|Emsley|2001|p=477}} Incorporated uranium becomes [[uranyl]] ions, which accumulate in bone, liver, kidney, and reproductive tissues.<ref>{{cite book |last=Permyakov |first=Eugene |title=Metalloproteomics |publisher=John Wiley & Sons |place=Hoboken |date=2009 |isbn=978-0-470-44774-1 |oclc=609844907 |page=564}}</ref>

Radiological and chemical toxicity of uranium combine by the fact that elements of high atomic number Z like uranium exhibit phantom or secondary radiotoxicity through absorption of natural background gamma and X-rays and re-emission of photoelectrons, which in combination with the high affinity of uranium to the phosphate moiety of DNA cause increased single and double strand DNA breaks.<ref>Busby, C. and Schnug, E. (2008). "Advanced biochemical and biophysical aspects of uranium contamination". In: De Kok, L.J. and Schnug, E. (Eds) ''Loads and Fate of Fertilizer Derived Uranium''. Backhuys Publishers, Leiden, The Netherlands. {{ISBN| 978-90-5782-193-6}}</ref>

Uranium is not absorbed through the skin, and [[alpha particle]]s released by uranium cannot penetrate the skin.<ref name="epa" />

Uranium can be decontaminated from steel surfaces<ref name="Francis">{{cite journal |pmid=16053105 |date=2005 |last1=Francis |first1=A. J. |last2=Dodge |first2=C. J. |last3=McDonald |first3=J. A. |last4=Halada |first4=G. P. |title=Decontamination of uranium-contaminated steel surfaces by hydroxycarboxylic acid with uranium recovery |volume=39 |issue=13 |pages=5015–21 |journal=Environmental Science & Technology |doi=10.1021/es048887c |bibcode=2005EnST...39.5015F}}</ref> and [[aquifer]]s.<ref>{{Cite journal |last1=Gandhi |first1=T. Pushparaj |last2=Sampath |first2=Prasanna Venkatesh |last3=Maliyekkal |first3=Shihabudheen M. |date=2022-06-15 |title=A critical review of uranium contamination in groundwater: Treatment and sludge disposal |journal=The Science of the Total Environment |volume=825 |pages=153947 |pmid=35189244 |doi=10.1016/j.scitotenv.2022.153947 |bibcode=2022ScTEn.82553947G |s2cid=246988421 |issn=1879-1026}}</ref><ref>{{Cite journal |last1=Prusty |first1=Sourav |last2=Somu |first2=Prathap |last3=Sahoo |first3=Jitendra Kumar |last4=Panda |first4=Debasish |last5=Sahoo |first5=Sunil Kumar |last6=Sahoo |first6=Shraban Kumar |last7=Lee |first7=Yong Rok |last8=Jarin |first8=T. |last9=Sundar |first9=L. Syam |last10=Rao |first10=Koppula Srinivas |date=December 2022 |title=Adsorptive sequestration of noxious uranium (VI) from water resources: A comprehensive review |journal=Chemosphere |volume=308 |issue=Pt 1 |pages=136278 |doi=10.1016/j.chemosphere.2022.136278 |issn=1879-1298 |pmid=36057349|bibcode=2022Chmsp.30836278P |s2cid=251999162 }}</ref>

===Effects and precautions===
Normal functioning of the [[kidney]], [[brain]], [[liver]], [[heart]], and other systems can be affected by uranium exposure, because, besides being weakly radioactive, uranium is a [[Metal toxicity|toxic metal]].{{sfn|Emsley|2001|p=477}}<ref name="Craft04">{{cite journal
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| journal = Journal of Toxicology and Environmental Health Part B: Critical Reviews
| date = 2004
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| doi = 10.1080/10937400490452714| bibcode = 2004JTEHB...7..297C
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| citeseerx = 10.1.1.535.5247
| s2cid = 9357795
}}</ref><ref name="ATSDR">{{cite report |title=Toxicological Profile for Uranium |chapter=2. Relevance to Public Health |pages=11–38 |chapter-url=http://www.atsdr.cdc.gov/toxprofiles/tp150-c2.pdf |url=https://wwwn.cdc.gov/TSP/ToxProfiles/ToxProfiles.aspx?id=440&tid=77 |author=Agency for Toxic Substances and Disease Registry (ATSDR) |location=Atlanta, GA| publisher=U.S. Department of Health and Human Services, Public Health Service| id=CAS# 7440-61-1 |date=February 2013}}</ref> Uranium is also a [[reproductive toxicant]].<ref name="Hindin2005">{{cite journal |doi=10.1186/1476-069X-4-17 |last1=Hindin |first1=Rita|last2=Brugge |date=2005 |first2=D. |last3=Panikkar |first3=B. |title=Teratogenicity of depleted uranium aerosols: A review from an epidemiological perspective |journal=Environ Health |volume=4 |issue=1 |page=17 |pmid=16124873|pmc=1242351 |bibcode=2005EnvHe...4...17H |doi-access=free }}</ref><ref>{{cite journal
| author = Arfsten, D. P.
| author2 = Still, K. R.
| author3 = Ritchie, G. D.
| date = 2001
| title = A review of the effects of uranium and depleted uranium exposure on reproduction and fetal development
| journal = Toxicology and Industrial Health
| volume = 17
| pages = 180–91
| doi = 10.1191/0748233701th111oa
| issue = 5–10
| pmid = 12539863| bibcode = 2001ToxIH..17..180A
| s2cid = 25310165
}}</ref> Radiological effects are generally local because alpha radiation, the primary form of {{sup|238}}U decay, has a very short range, and will not penetrate skin. Alpha radiation from inhaled uranium has been demonstrated to cause lung cancer in exposed nuclear workers.<ref>{{cite journal |last1= Grellier |first1= James
|last2= Atkinson|first2= Will
|last3= Bérard|first3= Philippe
|last4= Bingham|first4= Derek
|last5= Birchall|first5= Alan
|last6= Blanchardon|first6= Eric
|last7= Bull|first7= Richard
|last8= Guseva Canu|first8= Irina
|last9= Challeton-de Vathaire|first9= Cécile
|last10= Cockerill|first10=Rupert
|last11= Do|first11=Minh T
|last12= Engels|first12= Hilde
|last13= Figuerola|first13= Jordi
|last14= Foster|first14= Adrian
|last15= Holmstock|first15= Luc
|last16= Hurtgen|first16= Christian
|last17= Laurier|first17= Dominique
|last18= Puncher|first18= Matthew
|last19= Riddell |first19= Tony
|last20= Samson |first20= Eric
|last21= Thierry-Chef |first21= Isabelle
|last22= Tirmarche |first22= Margot
|last23= Vrijheid |first23= Martine
|last24= Cardis |first24= Elisabeth|date= 2017|title= Risk of lung cancer mortality in nuclear workers from internal exposure to alpha particle-emitting radionuclides.|journal= Epidemiology|volume= 28|issue= 5|pages= 675–684|doi= 10.1097/EDE.0000000000000684|pmc= 5540354 |pmid=28520643}}</ref> While the CDC has published one study that no human [[cancer]] has been seen as a result of exposure to natural or depleted uranium,<ref name="ATSDR-PHS">{{cite web |url=https://www.atsdr.cdc.gov/ToxProfiles/tp150-c1-b.pdf |title=Public Health Statement for Uranium |publisher=CDC |access-date=5 May 2023}}</ref> exposure to uranium and its decay products, especially [[radon]], is a significant health threat.<ref>[https://www.cdc.gov/niosh/pgms/worknotify/fernald.html Radon Exposures to Workers at the Fernald Feed Materials Production Center]. Page reviewed: April 8, 2020. U.S. National Institute for Occupational Safety and Health (NIOSH)</ref> Exposure to [[strontium-90]], [[iodine-131]], and other fission products is unrelated to uranium exposure, but may result from medical procedures or exposure to spent reactor fuel or fallout from nuclear weapons.<ref>Chart of the Nuclides, US Atomic Energy Commission 1968</ref>

Although accidental inhalation exposure to a high concentration of [[uranium hexafluoride]] has resulted in human fatalities, those deaths were associated with the generation of highly toxic hydrofluoric acid and [[uranyl fluoride]] rather than with uranium itself.<ref>{{cite book |url=https://books.google.com/books?id=qDf3AO8nILoC&pg=PA1468 |page=1468 |title=Medical Toxicology |author=Dart, Richard C.|publisher=Lippincott Williams & Wilkins |date=2004 |isbn=978-0-7817-2845-4}}</ref> Finely divided uranium metal presents a fire hazard because uranium is [[pyrophoricity|pyrophoric]]; small grains will ignite spontaneously in air at room temperature.<ref name="LANL" />

Uranium metal is commonly handled with gloves as a sufficient precaution.<ref name="DOH.WA">{{cite web |publisher=Washington State Department of Health, Office of Radiation Protection |url=http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs27uran.htm |title=Radiation Fact Sheets #27, Uranium (U) |date=2010 |access-date=23 August 2011 |archive-url=https://web.archive.org/web/20110928164044/http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs27uran.htm |archive-date=28 September 2011 |url-status=dead}}</ref> Uranium concentrate is handled and contained so as to ensure that people do not inhale or ingest it.<ref name="DOH.WA" />

==See also==
{{div col}}
* [[K-65 residues]]
* [[List of countries by uranium production]]
* [[List of countries by uranium reserves]]
* [[List of uranium projects]]
* [[Lists of nuclear disasters and radioactive incidents]]
* [[Nuclear and radiation accidents and incidents]]
* [[Nuclear engineering]]
* [[Nuclear fuel cycle]]
* [[Nuclear physics]]
* [[Quintuple bond]] (earlier thought to be a [[phi bond]]), in the molecule U{{sub|2}}
* [[Thorium fuel cycle]]
* [[World Uranium Hearing]]
{{div col end}}

==Notes==
{{Notelist}}

==References==
{{reflist}}

==Sources cited==
* {{Cite book |date=2001 |chapter=Uranium |chapter-url=https://books.google.com/books?id=j-Xu07p3cKwC |title=Nature's Building Blocks: An A to Z Guide to the Elements |publisher=[[Oxford University Press]] |location=[[Oxford]] |isbn=978-0-19-850340-8 |author-link=John Emsley |first=John |last=Emsley |pages=[https://archive.org/details/naturesbuildingb0000emsl/page/476 476–482]|url=https://archive.org/details/naturesbuildingb0000emsl/page/476 }}
* {{Cite book |title=The Encyclopedia of the Chemical Elements |chapter=Uranium |date=1968 |author-link=Glenn T. Seaborg |first=Glenn T. |last=Seaborg |publisher=Reinhold Book Corporation |location=[[Skokie, Illinois]] |pages=773–786 |lccn=68029938}}

==External links==
{{Commons category|Uranium}}
{{Wiktionary|uranium}}
* [http://www.eia.gov/nuclear/ Nuclear fuel data and analysis] from the [[U.S. Energy Information Administration]]
* [http://www.wise-uranium.org/umaps.html World Uranium deposit maps]
* {{cite EB9 |wstitle = Uranium |volume= XXIV  |last= Dittmar |first= William  |author-link= William Dittmar| page=7 |short=1 }}
* [https://web.archive.org/web/20051214080409/http://alsos.wlu.edu/qsearch.aspx?browse=science%2FUranium Annotated bibliography for uranium from the Alsos Digital Library]
* [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+uranium,+radioactive NLM Hazardous Substances Databank – Uranium, Radioactive]
* [https://www.cdc.gov/niosh/npg/npgd0650.html CDC – NIOSH Pocket Guide to Chemical Hazards]
* [https://www.atsdr.cdc.gov/csem/csem.html ATSDR Case Studies in Environmental Medicine: Uranium Toxicity] U.S. [[Department of Health and Human Services]]
* [http://www.periodicvideos.com/videos/092.htm Uranium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)

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{{Uranium compounds}}
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[[Category:Uranium| ]]
[[Category:Chemical elements]]
[[Category:Actinides]]
[[Category:Nuclear fuels]]
[[Category:Nuclear materials]]
[[Category:Suspected male-mediated teratogens]]
[[Category:Manhattan Project]]
[[Category:Pyrophoric materials]]