Uranium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical compounds, chemical elements canno ...
with the
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different ...
U and
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of ever ...
92. It is a silvery-grey
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typical ...
in the
actinide
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The info ...
series of the
periodic table
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
. A uranium atom has 92
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s and 92
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kno ...
s, of which 6 are
valence electron
In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, a shared pair for ...
s. Uranium is weakly
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
because all
isotopes of uranium
Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay pr ...
are unstable; the
half-lives of its naturally occurring isotopes range between 159,200 years and 4.5 billion years. The most common isotopes in
natural uranium are
uranium-238
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, i ...
(which has 146
neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...
s and accounts for over 99% of uranium on Earth) and
uranium-235
Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists ...
(which has 143 neutrons). Uranium has the highest
atomic weight of the
primordially occurring elements. Its
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematica ...
is about 70% higher than that of
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...
, and slightly lower than that of
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile m ...
or
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
. It occurs naturally in low concentrations of a few
parts per million in soil, rock and water, and is commercially
extracted from uranium-bearing
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ...
s such as
uraninite.
In nature, uranium is found as uranium-238 (99.2739–99.2752%), uranium-235 (0.7198–0.7202%), and a very small amount of
uranium-234 (0.0050–0.0059%). Uranium decays slowly by emitting an
alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 atomic nucleus, nucleus. They are generally produced in the process of alpha decay, but may ...
. The half-life of uranium-238 is about 4.47
billion
Billion is a word for a large number, and it has two distinct definitions:
*1,000,000,000, i.e. one thousand million, or (ten to the ninth power), as defined on the short scale. This is its only current meaning in English.
*1,000,000,000,000, i.e ...
years and that of uranium-235 is 704
million
One million (1,000,000), or one 1000 (number), thousand thousand, is the natural number following 100,000#900,000 to 999,999, 999,999 and preceding 1,000,001. The word is derived from the early Italian ''millione'' (''milione'' in modern Italian) ...
years, making them useful in dating the
age of the Earth
The age of Earth is estimated to be 4.54 ± 0.05 billion years This age may represent the age of Earth's accretion, or core formation, or of the material from which Earth formed. This dating is based on evidence from radiometric age-dating of ...
.
Many contemporary uses of uranium exploit its unique
nuclear properties. Uranium-235 is the only naturally occurring
fissile
In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typ ...
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass number ...
, which makes it widely used in
nuclear power plant
A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces ele ...
s and
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bo ...
s. However, because of the tiny amounts found in nature, uranium needs to undergo
enrichment so that enough uranium-235 is present. Uranium-238 is fissionable by fast neutrons, and is
fertile, meaning it can be
transmuted to fissile
plutonium-239
Plutonium-239 (239Pu or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main ...
in a
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from n ...
. Another fissile isotope,
uranium-233, can be produced from natural
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...
and is studied for future industrial use in nuclear technology. Uranium-238 has a small probability for
spontaneous fission
Spontaneous fission (SF) is a form of radioactive decay that is found only in very heavy chemical elements. The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 56 (e.g., iron-56); spontaneous breakdo ...
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
In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific n ...
. This generates the heat in nuclear power reactors, and produces the fissile material for nuclear weapons.
Depleted uranium (
238U) is used in
kinetic energy penetrator
A kinetic energy penetrator (KEP), also known as long-rod penetrator (LRP), is a type of ammunition designed to penetrate vehicle armour using a flechette-like, high-sectional density projectile. Like a bullet or kinetic energy weapon, this typ ...
s and
armor plating.
[.] Uranium is used as a colorant in
uranium glass, producing lemon yellow to green colors. Uranium glass fluoresces green in ultraviolet light. It was also used for tinting and shading in early
photography
Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed ...
.
The 1789
discovery of uranium in the mineral
pitchblende
Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium causes th ...
is credited to
Martin Heinrich Klaproth, who named the new element after the recently discovered planet
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of Cro ...
.
Eugène-Melchior Péligot was the first person to isolate the metal and its radioactive properties were discovered in 1896 by
Henri Becquerel
Antoine Henri Becquerel (; 15 December 1852 – 25 August 1908) was a French engineer, physicist, Nobel laureate, and the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie and P ...
. Research by
Otto Hahn,
Lise Meitner
Elise Meitner ( , ; 7 November 1878 – 27 October 1968) was an Austrian-Swedish physicist who was one of those responsible for the discovery of the element protactinium and nuclear fission. While working at the Kaiser Wilhelm Institute on rad ...
,
Enrico Fermi and others, such as
J. Robert Oppenheimer starting in 1934 led to its use as a fuel in the
nuclear power
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produc ...
industry and in ''
Little Boy
"Little Boy" was the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II, making it the first nuclear weapon used in warfare. The bomb was dropped by the Boeing B-29 Superfortress ''Enola Gay'' p ...
'', the
first nuclear weapon used in war. An ensuing
arms race
An arms race occurs when two or more groups compete in military superiority. It consists of a competition between two or more states to have superior armed forces; a competition concerning production of weapons, the growth of a military, and t ...
during the
Cold War
The Cold War is a term commonly used to refer to a period of Geopolitics, geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term ''Cold war (term), co ...
between the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
and the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived
plutonium-239
Plutonium-239 (239Pu or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main ...
. The security of those weapons is closely monitored. Since around 2000, plutonium obtained by dismantling Cold War-era bombs is used as fuel for nuclear reactors. The development and deployment of these
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from n ...
s continue on a global base as they are powerful sources of CO
2-free energy.
Characteristics

When
refined, uranium is a silvery white, weakly radioactive
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typical ...
. It has a
Mohs hardness of 6, sufficient to scratch glass and approximately equal to that of
titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosio ...
,
rhodium
Rhodium is a chemical element with the symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isot ...
,
manganese
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy ...
and
niobium
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs scale of mineral hardness, Mohs hardness rating similar ...
. It is
malleable,
ductile
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, slightly
paramagnetic, strongly
electropositive and a poor
electrical conductor
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gene ...
.
Uranium metal has a very high
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematica ...
of 19.1 g/cm
3, denser than
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...
(11.3 g/cm
3), but slightly less dense than
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
and
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile m ...
(19.3 g/cm
3).
Uranium metal reacts with almost all non-metal elements (with the exception of the
noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low che ...
es) and their
compounds, with reactivity increasing with temperature.
Hydrochloric and
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitr ...
s dissolve uranium, but non-oxidizing acids other than hydrochloric acid attack the element very slowly.
When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of
uranium oxide
Uranium oxide is an oxide of the element uranium.
The metal uranium forms several oxides:
* Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende)
* Diuranium pentoxide or uranium(V) oxide (U2O5)
* Uranium trioxide or ...
.
Uranium in ores is extracted chemically and converted into
uranium dioxide
Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear re ...
or other chemical forms usable in industry.
Uranium-235 was the first isotope that was found to be
fissile
In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typ ...
. Other naturally occurring isotopes are fissionable, but not fissile. On bombardment with slow neutrons, its uranium-235
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass number ...
will most of the time divide into two smaller
nuclei, releasing nuclear
binding energy
In physics and chemistry, binding energy is the smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts. In the former meaning the term is predominantly use ...
and more neutrons. If too many of these neutrons are absorbed by other uranium-235 nuclei, a
nuclear chain reaction
In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific n ...
occurs that results in a burst of heat or (in special circumstances) an explosion. In a nuclear reactor, such a chain reaction is slowed and controlled by a
neutron poison
In applications such as nuclear reactors, a neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section. In such applications, absorbing neutrons is normally an undesirable eff ...
, absorbing some of the free neutrons. Such neutron absorbent materials are often part of reactor
control rod
Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium. Their compositions include chemical elements such as boron, cadmium, silver, hafnium, or indium, that are capable of absorbing ...
s (see
nuclear reactor physics for a description of this process of reactor control).
As little as of uranium-235 can be used to make an atomic bomb.
The nuclear weapon detonated over
Hiroshima
is the capital of Hiroshima Prefecture in Japan. , the city had an estimated population of 1,199,391. The gross domestic product (GDP) in Greater Hiroshima, Hiroshima Urban Employment Area, was US$61.3 billion as of 2010. Kazumi Matsui ...
, called ''
Little Boy
"Little Boy" was the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II, making it the first nuclear weapon used in warfare. The bomb was dropped by the Boeing B-29 Superfortress ''Enola Gay'' p ...
'', relied on uranium fission. However, the first nuclear bomb (the ''Gadget'' used at
Trinity
The Christian doctrine of the Trinity (, from 'threefold') is the central dogma concerning the nature of God in most Christian churches, which defines one God existing in three coequal, coeternal, consubstantial divine persons: God the F ...
) and the bomb that was detonated over Nagasaki (''
Fat Man
"Fat Man" (also known as Mark III) is the codename for the type of nuclear bomb the United States detonated over the Japanese city of Nagasaki on 9 August 1945. It was the second of the only two nuclear weapons ever used in warfare, the firs ...
'') were both plutonium bombs.
Uranium metal has three
allotropic forms:
* α (
orthorhombic
In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a ...
) stable up to . Orthorhombic,
space group
In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unc ...
No. 63, ''Cmcm'',
lattice parameters ''a''= 285.4 pm, ''b'' = 587 pm, ''c'' = 495.5 pm.
* β (
tetragonal
In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square ...
) stable from . Tetragonal, space group ''P''4
2/''mnm'', ''P''4
2''nm'', or ''P''4''n''2, lattice parameters ''a'' = 565.6 pm, ''b'' = ''c'' = 1075.9 pm.
* γ (
body-centered cubic) from to melting point—this is the most malleable and ductile state. Body-centered cubic, lattice parameter ''a'' = 352.4 pm.
Applications
Military

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
Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosio ...
or
molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with l ...
. 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
Military vehicles are commonly armoured (or armored; see spelling differences) to withstand the impact of shrapnel, bullets, shells, rockets, and missiles, protecting the personnel inside from enemy fire. Such vehicles include armoured fighti ...
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).
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
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...
in halting radiation from strong sources such as
radium
Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather ...
.
Other uses of depleted uranium include counterweights for aircraft control surfaces, as ballast for missile
re-entry vehicles and as a shielding material.
Due to its high density, this material is found in
inertial guidance system
An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors (gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dire ...
s and in
gyroscopic
A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...
compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
es.
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.
[.] The main risk of exposure to depleted uranium is chemical poisoning by
uranium oxide
Uranium oxide is an oxide of the element uranium.
The metal uranium forms several oxides:
* Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende)
* Diuranium pentoxide or uranium(V) oxide (U2O5)
* Uranium trioxide or ...
rather than radioactivity (uranium being only a weak
alpha emitter).
During the later stages of
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
, the entire
Cold War
The Cold War is a term commonly used to refer to a period of Geopolitics, geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term ''Cold war (term), co ...
, 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
Plutonium-239 (239Pu or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main ...
derived from uranium-238. Later, a much more complicated and far more powerful type of fission/fusion bomb (
thermonuclear weapon
A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lowe ...
) was built, that uses a plutonium-based device to cause a mixture of
tritium
Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...
and
deuterium
Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one ...
to undergo
nuclear fusion
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manife ...
. 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 neutrons from the nuclear fusion process.
Civilian

The main use of uranium in the civilian sector is to fuel
nuclear power plant
A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces ele ...
s. One kilogram of uranium-235 can theoretically produce about 20
terajoules of energy (2
joule
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s), assuming complete fission; as much
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat ...
as 1.5 million kilograms (1,500
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...
s) of
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when de ...
.
Commercial
nuclear power
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produc ...
plants use fuel that is typically enriched to around 3% uranium-235.
The
CANDU
The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide ( heavy water) moderator and its use of (originally, natural) uranium fuel. C ...
and
Magnox designs are the only commercial reactors capable of using unenriched uranium fuel. Fuel used for
United States Navy
The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the worl ...
reactors is typically highly enriched in
uranium-235
Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists ...
(the exact values are
classified). In a
breeder reactor, uranium-238 can also be converted into
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits ...
through the following reaction:
: + n +

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
Fiestaware.
The discovery and isolation of
radium
Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather ...
in uranium ore (pitchblende) by
Marie Curie
Marie Salomea Skłodowska–Curie ( , , ; born Maria Salomea Skłodowska, ; 7 November 1867 – 4 July 1934) was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was the first ...
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. This left a prodigious quantity of uranium as a waste product, since it takes three tonnes of uranium to extract one
gram
The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram.
Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
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
Mauve (, ; , ) is a pale purple color named after the mallow flower (French: ''mauve''). The first use of the word ''mauve'' as a color was in 1796–98 according to the ''Oxford English Dictionary'', but its use seems to have been rare bef ...
, black, blue, red and other colors.

Uranium was also used in
photographic chemicals (especially
uranium nitrate as a
toner),
in lamp filaments for
stage lighting
Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts. bulbs, to improve the appearance of
dentures, and in the leather and wood industries for stains and dyes. Uranium salts are
mordants 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
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
es, isolated
cell organelle
In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the s ...
s and
macromolecule
A macromolecule is a very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. Th ...
s.
The discovery of the radioactivity of uranium ushered in additional scientific and practical uses of the element. The long
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...
of the isotope uranium-238 (4.47 years) makes it well-suited for use in estimating the age of the earliest
igneous rock
Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
s and for other types of
radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...
, including
uranium–thorium dating,
uranium–lead dating and
uranium–uranium dating. Uranium metal is used for
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30  ...
targets in the making of high-energy X-rays.
History
Pre-discovery use
The use of uranium in its natural
oxide
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the ...
form dates back to at least the year 79
CE, when it was used in the
Roman Empire
The Roman Empire ( la, Imperium Romanum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn Rhōmaíōn) was the post- Republican period of ancient Rome. As a polity, it included large territorial holdings around the Medit ...
to add a yellow color to
ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...
glazes.
Yellow glass with 1% uranium oxide was found in a Roman villa on Cape
Posillipo
Posillipo (; nap, Pusilleco ) is an affluent residential quarter of Naples, southern Italy, located along the northern coast of the Gulf of Naples.
From the 1st century BC the Bay of Naples witnessed the rise of villas constructed by elite Rom ...
in the
Bay of Naples, Italy, by R. T. Gunther of the
University of Oxford
, mottoeng = The Lord is my light
, established =
, endowment = £6.1 billion (including colleges) (2019)
, budget = £2.145 billion (2019–20)
, chancellor ...
in 1912.
[.] Starting in the late
Middle Ages
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
, pitchblende was extracted from the
Habsburg
The House of Habsburg (), alternatively spelled Hapsburg in Englishgerman: Haus Habsburg, ; es, Casa de Habsburgo; hu, Habsburg család, it, Casa di Asburgo, nl, Huis van Habsburg, pl, dom Habsburgów, pt, Casa de Habsburgo, la, Domus Hab ...
silver mines in
Joachimsthal,
Bohemia
Bohemia ( ; cs, Čechy ; ; hsb, Čěska; szl, Czechy) is the westernmost and largest historical region of the Czech Republic. Bohemia can also refer to a wider area consisting of the historical Lands of the Bohemian Crown ruled by the Boh ...
(now Jáchymov in the Czech Republic), and was used as a coloring agent in the local
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) ...
making industry.
In the early 19th century, the world's only known sources of uranium ore were these mines. Mining for uranium in the
Ore Mountains ceased on the German side after the Cold War ended and
SDAG Wismut was wound down. On the Czech side there were attempts during the uranium price bubble of 2007 to restart mining, but those were quickly abandoned following a fall in uranium prices.
Discovery

The
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
Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium causes th ...
in
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitr ...
and neutralizing the solution with
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkal ...
.
[.] Klaproth assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with
charcoal
Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, cal ...
to obtain a black powder, which he thought was the newly discovered metal itself (in fact, that powder was an oxide of uranium).
He named the newly discovered element after the planet
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of Cro ...
(named after the primordial
Greek god of the sky), which had been discovered eight years earlier by
William Herschel.
In 1841,
Eugène-Melchior Péligot, Professor of Analytical Chemistry at the
Conservatoire National des Arts et Métiers
A music school is an educational institution specialized in the study, training, and research of music. Such an institution can also be known as a school of music, music academy, music faculty, college of music, music department (of a larger ins ...
(Central School of Arts and Manufactures) in
Paris
Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. ...
, isolated the first sample of uranium metal by heating
uranium tetrachloride with
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
.
Henri Becquerel
Antoine Henri Becquerel (; 15 December 1852 – 25 August 1908) was a French engineer, physicist, Nobel laureate, and the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie and P ...
discovered
radioactivity by using uranium in 1896.
Becquerel made the discovery in Paris by leaving a sample of a uranium salt, K
2UO
2(SO
4)
2 (potassium uranyl sulfate), on top of an unexposed
photographic plate in a drawer and noting that the plate had become "fogged".
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
The Central Powers, also known as the Central Empires,german: Mittelmächte; hu, Központi hatalmak; tr, İttifak Devletleri / ; bg, Централни сили, translit=Tsentralni sili was one of the two main coalitions that fought in W ...
suffered a shortage of molybdenum to make artillery gun barrels and high speed tool steels they routinely substituted
ferrouranium alloys which present many of the same physical characteristics. When this practice became known in 1916 the USA government requested several prominent universities to research these uses for uranium and tools made with these formulas remained in use for several decades only ending when the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
and the
Cold War
The Cold War is a term commonly used to refer to a period of Geopolitics, geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term ''Cold war (term), co ...
placed a large demand on uranium for fission research and weapon development.
Fission research

A team led by
Enrico Fermi in 1934 observed that bombarding uranium with neutrons produces the emission of
beta rays (
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kno ...
s or
positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collides ...
s from the elements produced; see
beta particle
A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β ...
).
The fission products were at first mistaken for new elements with atomic numbers 93 and 94, which the Dean of the Faculty of Rome, Orso Mario Corbino, christened ''
ausonium'' and ''
hesperium'', respectively. The experiments leading to the discovery of uranium's ability to fission (break apart) into lighter elements and release
binding energy
In physics and chemistry, binding energy is the smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts. In the former meaning the term is predominantly use ...
were conducted by
Otto Hahn and
Fritz Strassmann
Friedrich Wilhelm Strassmann (; 22 February 1902 – 22 April 1980) was a German chemist who, with Otto Hahn in December 1938, identified the element barium as a product of the bombardment of uranium with neutrons. Their observation was the ke ...
[.] in Hahn's laboratory in Berlin.
Lise Meitner
Elise Meitner ( , ; 7 November 1878 – 27 October 1968) was an Austrian-Swedish physicist who was one of those responsible for the discovery of the element protactinium and nuclear fission. While working at the Kaiser Wilhelm Institute on rad ...
and her nephew, the physicist
Otto Robert Frisch, published the physical explanation in February 1939 and named the process "
nuclear fission
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of ra ...
". Soon after, Fermi hypothesized that the 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 the rare uranium isotope uranium-235.
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
Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists ...
sample in the Tate Laboratory. After mailed to
Columbia University
Columbia University (also known as Columbia, and officially as Columbia University in the City of New York) is a private research university in New York City. Established in 1754 as King's College on the grounds of Trinity Church in Manhat ...
's
cyclotron
A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Jan ...
,
John Dunning confirmed the sample to be the isolated fissile material on 1 March. Further work found that the far more common uranium-238 isotope can be
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
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produc ...
. 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
Haigerloch is a town in the north-western part of the Swabian Alb in Germany.
Geography Geographical location
Haigerloch lies at between 430 and 550 metres elevation in the valley of the Eyach river, which forms two loops in a steep shelly lime ...
, the site of the last German wartime reactor experiment.
On 2 December 1942, as part of the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
, another team led by Enrico Fermi was able to initiate the first artificial self-sustained
nuclear chain reaction
In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific n ...
,
Chicago Pile-1. An initial plan using enriched uranium-235 was abandoned as it was as yet unavailable in sufficient quantities. Working in a lab below the stands of
Stagg Field at the
University of Chicago
The University of Chicago (UChicago, Chicago, U of C, or UChi) is a private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park neighborhood. The University of Chicago is consistently ranked among the b ...
, the team created the conditions needed for such a reaction by piling together 400
short tons (360
metric tons
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...
) of
graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...
, 58 short tons (53 metric tons) of
uranium oxide
Uranium oxide is an oxide of the element uranium.
The metal uranium forms several oxides:
* Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende)
* Diuranium pentoxide or uranium(V) oxide (U2O5)
* Uranium trioxide or ...
, and six short tons (5.5 metric tons) of uranium metal, a majority of which was supplied by
Westinghouse Lamp Plant in a makeshift production process.
Nuclear weaponry

Two major types of atomic bombs were developed by the United States during
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
: a uranium-based device (codenamed "
Little Boy
"Little Boy" was the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II, making it the first nuclear weapon used in warfare. The bomb was dropped by the Boeing B-29 Superfortress ''Enola Gay'' p ...
") whose fissile material was highly
enriched uranium
Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238 ...
, and a plutonium-based device (see
Trinity test and "
Fat Man
"Fat Man" (also known as Mark III) is the codename for the type of nuclear bomb the United States detonated over the Japanese city of Nagasaki on 9 August 1945. It was the second of the only two nuclear weapons ever used in warfare, the firs ...
") whose plutonium was derived from uranium-238. The uranium-based Little Boy device became the first nuclear weapon used in war when it was detonated over the
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the nor ...
ese city of
Hiroshima
is the capital of Hiroshima Prefecture in Japan. , the city had an estimated population of 1,199,391. The gross domestic product (GDP) in Greater Hiroshima, Hiroshima Urban Employment Area, was US$61.3 billion as of 2010. Kazumi Matsui ...
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 approximately 75,000 people (see
Atomic bombings of Hiroshima and Nagasaki
The United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August 1945, respectively. The two bombings killed between 129,000 and 226,000 people, most of whom were civilians, and remain the on ...
).
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.
Reactors

The
X-10 Graphite Reactor at
Oak Ridge National Laboratory
Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research an ...
(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
Argonne National Laboratory is a science and engineering research national laboratory operated by UChicago Argonne LLC for the United States Department of Energy. The facility is located in Lemont, Illinois, outside of Chicago, and is the lar ...
'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. 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
Electricity is the set of physics, physical Phenomenon, phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagne ...
come from nuclear power generated by
BORAX-III, another reactor designed and operated by
Argonne National Laboratory
Argonne National Laboratory is a science and engineering research national laboratory operated by UChicago Argonne LLC for the United States Department of Energy. The facility is located in Lemont, Illinois, outside of Chicago, and is the lar ...
). The world's first commercial scale nuclear power station,
Obninsk
Obninsk (russian: О́бнинск) is a city in Kaluga Oblast, Russia, located on the bank of the Protva River southwest of Moscow and northeast of Kaluga. Population:
History
The history of Obninsk began in 1945 when the First Research In ...
in the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
, began generation with its reactor AM-1 on 27 June 1954. Other early nuclear power plants were
Calder Hall in England, which began generation on 17 October 1956,
and the
Shippingport Atomic Power Station in
Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Ma ...
, which began on 26 May 1958. Nuclear power was used for the first time for propulsion by a
submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
, the
USS ''Nautilus'', in 1954.
Prehistoric naturally occurring fission
In 1972, the French 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
Gabon (; ; snq, Ngabu), officially the Gabonese Republic (french: République gabonaise), is a country on the west coast of Central Africa. Located on the equator, it is bordered by Equatorial Guinea to the northwest, Cameroon to the nort ...
,
West Africa
West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, Mau ...
, collectively known as the
Oklo Fossil Reactors. The ore deposit is 1.7 billion years old; then, uranium-235 constituted about 3% of the total uranium on Earth.
This is high enough to permit a sustained nuclear fission chain reaction to occur, provided other supporting conditions exist. The capacity of the surrounding sediment to contain the
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
The Yucca Mountain Nuclear Waste Repository, as designated by the Nuclear Waste Policy Act amendments of 1987, is a proposed deep geological repository storage facility within Yucca Mountain for spent nuclear fuel and other high-level radi ...
.
Contamination and the Cold War legacy

Above-ground
nuclear tests by the Soviet Union and the United States in the 1950s and early 1960s and by
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area e ...
into the 1970s and 1980s
spread a significant amount of
fallout from uranium
daughter isotopes around the world. Additional fallout and pollution occurred from several
nuclear accidents.
Uranium miners have a higher incidence of
cancer
Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Poss ...
. An excess risk of lung cancer among
Navajo uranium miners, for example, has been documented and linked to their occupation.
The
Radiation Exposure Compensation Act
The United States Radiation Exposure Compensation Act (RECA) is a federal statute providing for the monetary compensation of people, including atomic veterans, who contracted cancer and a number of other specified diseases as a direct result of t ...
, a 1990 law in the US, required $100,000 in "compassion payments" to uranium miners diagnosed with cancer or other respiratory ailments.
During the
Cold War
The Cold War is a term commonly used to refer to a period of Geopolitics, geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term ''Cold war (term), co ...
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. Since the
break-up of the Soviet Union in 1991, an estimated 600 short tons (540 metric tons) of highly enriched weapons grade uranium (enough to make 40,000 nuclear warheads) have been stored in often inadequately guarded facilities in the
Russian Federation
Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eigh ...
and several other former Soviet states.
Police in
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an a ...
,
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entire ...
, and
South America on at least 16 occasions from 1993 to 2005 have
intercepted shipments of smuggled bomb-grade uranium or plutonium, most of which was from ex-Soviet sources.
From 1993 to 2005 the Material Protection, Control, and Accounting Program, operated by the
federal government of the United States
The federal government of the United States (U.S. federal government or U.S. government) is the national government of the United States, a federal republic located primarily in North America, composed of 50 states, a city within a feder ...
, spent approximately
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. ''Scientific American'' reported in February 2006 that in some of the facilities security consisted of chain link fences which were in severe states of disrepair. According to an interview from the article, one facility had been storing samples of enriched (weapons grade) uranium in a broom closet before the improvement project; another had been keeping track of its stock of nuclear warheads using index cards kept in a shoe box.
Occurrence
Origin
Along with all elements having
atomic weights higher than that of
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
, uranium is only naturally formed by the
r-process
In nuclear astrophysics, the rapid neutron-capture process, also known as the ''r''-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements ...
(rapid neutron capture) in
supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
e and
neutron star mergers. 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.
Besides the two extant primordial uranium isotopes,
235U and
238U, the r-process also produced significant quantities of
236U, which has a shorter half-life and so is an
extinct radionuclide
An extinct radionuclide is a radionuclide that was formed by nucleosynthesis before the formation of the Solar System, about 4.6 billion years ago, but has since decayed to virtually zero abundance and is no longer detectable as a primordial nu ...
, having long since decayed completely to
232Th. Uranium-236 was itself enriched by the decay of
244Pu, accounting for the observed higher-than-expected abundance of thorium and lower-than-expected abundance of uranium.
While the natural abundance of uranium has been supplemented by the decay of extinct
242Pu (half-life 0.375 million years) and
247Cm (half-life 16 million years), producing
238U and
235U respectively, this occurred to an almost negligible extent due to the shorter half-lives of these parents and their lower production than
236U and
244Pu, the parents of thorium: the
247Cm:
235U ratio at the formation of the Solar System was .
Biotic and abiotic

Uranium is a
naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is the 51st element in order of
abundance in the Earth's crust. Uranium is also the highest-numbered element to be found naturally in significant quantities on Earth and is almost always found combined with other elements.
The decay of uranium,
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...
, and
potassium-40
Potassium-40 (40K) is a radioactive isotope of potassium which has a long half-life of 1.25 billion years. It makes up about 0.012% (120 ppm) of the total amount of potassium found in nature.
Potassium-40 undergoes three types of radioactive de ...
in the Earth's
mantle is thought to be the main source of heat that keeps the Earth's
outer core
Earth's outer core is a fluid layer about thick, composed of mostly iron and nickel that lies above Earth's solid inner core and below its mantle. The outer core begins approximately beneath Earth's surface at the core-mantle boundary and e ...
in the liquid state and drives
mantle convection
Mantle convection is the very slow creeping motion of Earth's solid silicate mantle as convection currents carrying heat from the interior to the planet's surface.
The Earth's surface lithosphere rides atop the asthenosphere and the two form ...
, which in turn drives
plate tectonics
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
.
Uranium's average concentration in the
Earth's crust
Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
is (depending on the reference) 2 to 4 parts per million,
or about 40 times as abundant as
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical c ...
.
The Earth's crust from the surface to 25 km (15 mi) down is calculated to contain 10
17 kg (2 lb) of uranium while the
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
s may contain 10
13 kg (2 lb).
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
A fertilizer (American English) or fertiliser ( British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s), and its concentration in sea water is 3 parts per billion.
Uranium is more plentiful than
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times ...
,
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
,
cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
,
mercury, or silver, and it is about as abundant as
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...
or
molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with l ...
.
Uranium is found in hundreds of minerals, including uraninite (the most common uranium
ore),
carnotite,
autunite,
uranophane,
torbernite, and
coffinite.
Significant concentrations of uranium occur in some substances such as
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phos ...
rock deposits, and minerals such as
lignite
Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low he ...
, and
monazite sands in uranium-rich ores
(it is recovered commercially from sources with as little as 0.1% uranium
).

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). Recent research suggests that this pathway includes reduction of the soluble U(VI) via an intermediate U(V) pentavalent state.
Other organisms, such as the lichen ''Trapelia involuta'' or
microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s such as the
bacterium
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amo ...
''
Citrobacter
''Citrobacter'' is a genus of Gram-negative coliform bacteria in the family Enterobacteriaceae.
The species ''C. amalonaticus'', ''C. koseri'', and ''C. freundii'' can use citrate as a sole carbon source. ''Citrobacter'' species are differenti ...
'', can absorb concentrations of uranium that are up to 300 times the level of their environment. ''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
decontaminate uranium-polluted water.
The proteobacterium ''
Geobacter'' has also been shown to bioremediate uranium in ground water.
The mycorrhizal fungus
Glomus intraradices increases uranium content in the roots of its symbiotic plant.
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
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
''.
Plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
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.
Dry weight concentrations of uranium in
food
Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is in ...
plants are typically lower with one to two micrograms per day ingested through the food people eat.
Production and mining

Worldwide production of U
3O
8 (yellowcake) in 2013 amounted to 70,015
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...
s, of which 22,451 t (32%) was mined in
Kazakhstan
Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbek ...
. Other important uranium mining countries are
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
(9,331 t),
Australia
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country b ...
(6,350 t),
Niger
)
, official_languages =
, languages_type = National languages[Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south a ...](_blank)
(4,323 t) and
Russia
Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eigh ...
(3,135 t).
Uranium ore is mined in several ways: by
open pit,
underground,
in-situ leaching, and
borehole mining (see
uranium mining
Uranium mining is the process of extraction of uranium ore from the ground. Over 50 thousand tons of uranium were produced in 2019. Kazakhstan, Canada, and Australia were the top three uranium producers, respectively, and together account f ...
).
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.
[.] High-grade ores found in
Athabasca Basin deposits in
Saskatchewan
Saskatchewan ( ; ) is a province in western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on the south by the U.S. states of Montana and North Dak ...
, Canada can contain up to 23% uranium oxides on average. Uranium ore is crushed and rendered into a fine powder and then leached with either an
acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...
or
alkali
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a s ...
. The
leachate is subjected to one of several sequences of precipitation, solvent extraction, and ion exchange. The resulting mixture, called
yellowcake
Yellowcake (also called urania) is a type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before fu ...
, contains at least 75% uranium oxides U
3O
8. Yellowcake is then
calcined
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), gener ...
to remove impurities from the milling process before refining and conversion.
Commercial-grade uranium can be produced through the
reduction of uranium
halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluo ...
s with
alkali
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a s ...
or
alkaline earth metals.
Uranium metal can also be prepared through
electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
of or
, dissolved in molten
calcium chloride
Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide.
Cal ...
() and
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35. ...
(
NaCl) solution.
Very pure uranium is produced through the
thermal decomposition of uranium halides on a hot filament.
File:U production-demand.png, World uranium production (mines) and demand
File:Yellowcake.jpg, alt=A yellow sand-like rhombic mass on black background., Yellowcake
Yellowcake (also called urania) is a type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before fu ...
is a concentrated mixture of uranium oxides that is further refined to extract pure uranium.
Resources and reserves

It is estimated that 5.5 million tonnes of uranium exists in ore reserves that are economically viable at US$59 per lb of uranium,
while 35 million tonnes are classed as mineral resources (reasonable prospects for eventual economic extraction).
Prices went from about $10/lb in May 2003 to $138/lb in July 2007. This has caused a big increase in spending on exploration,
with US$200 million being spent worldwide in 2005, a 54% increase on the previous year.
This trend continued through 2006, when expenditure on exploration rocketed to over $774 million, an increase of over 250% compared to 2004. The
OECD
The Organisation for Economic Co-operation and Development (OECD; french: Organisation de coopération et de développement économiques, ''OCDE'') is an intergovernmental organisation with 38 member countries, founded in 1961 to stimulate e ...
Nuclear Energy Agency said exploration figures for 2007 would likely match those for 2006.
Australia has 31% of the world's known uranium ore reserves and the world's largest single uranium deposit, located at the
Olympic Dam Mine in
South Australia. There is a significant reserve of uranium in
Bakouma
Bakouma is a sub-prefecture in the prefecture of Mbomou in Central African Republic. The area is known for its prosperity of mineral resources which have for a long time remained unexploited.
History
Bakouma was founded in September 1892 when ...
, a
sub-prefecture in the
prefecture
A prefecture (from the Latin ''Praefectura'') is an administrative jurisdiction traditionally governed by an appointed prefect. This can be a regional or local government subdivision in various countries, or a subdivision in certain international ...
of
Mbomou in the
Central African Republic
The Central African Republic (CAR; ; , RCA; , or , ) is a landlocked country in Central Africa. It is bordered by Chad to the north, Sudan to the northeast, South Sudan to the southeast, the DR Congo to the south, the Republic of the Co ...
.
Some nuclear fuel comes from nuclear weapons being dismantled, such as from the
Megatons to Megawatts Program The Megatons to Megawatts Program, also called the United States-Russia Highly Enriched Uranium Purchase Agreement, was an agreement between Russia and the United States. The official name of the program is the "Agreement between the Government of t ...
.
An additional 4.6 billion tonnes of uranium are estimated to be dissolved in
sea water
Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...
(
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the nor ...
ese scientists in the 1980s showed that extraction of uranium from sea water using
ion exchangers was technically feasible).
There have been experiments to extract uranium from sea water, 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.
Supplies

In 2005, seventeen countries produced concentrated uranium oxides:
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
(27.9% of world production),
Australia
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country b ...
(22.8%),
Kazakhstan
Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbek ...
(10.5%),
Russia
Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eigh ...
(8.0%),
Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south a ...
(7.5%),
Niger
)
, official_languages =
, languages_type = National languages[Uzbekistan
Uzbekistan (, ; uz, Ozbekiston, italic=yes / , ; russian: Узбекистан), officially the Republic of Uzbekistan ( uz, Ozbekiston Respublikasi, italic=yes / ; russian: Республика Узбекистан), is a doubly landlocked co ...](_blank)
(5.5%), the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
(2.5%),
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...
(2.1%),
Ukraine
Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inva ...
(1.9%) and
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones an ...
(1.7%). In 2008 Kazakhstan was forecast to increase production and may have become the world's largest producer of uranium by 2009 with an expected production of 12,826 tonnes, compared to Canada with 11,100 t and Australia with 9,430 t. The predictions have come true. In 2019 Kazakhstan produces the largest share of uranium from mines 42% of world supply, followed by Canada (13%) and Australia (12%), Namibia (10%), Uzbekistan (6%), Niger (5%), Russia (5%), China (3%), Ukraine (1.5%), USA (0.12%), India (0.6%), Iran (0.13%), with total world production 54752 tonnes from mines.
However, it should be mentioned that in 2019 uranium was mined not only by conventional underground mining of ores 43% of production (54752 tonnes), where rock mineralised is removed from the ground, breaking it up and treating it to remove the minerals being sought but also by
in-situ leaching methods (ISL) 57% of world production (64,566 tonnes).
In the late 1960s, UN geologists also discovered major uranium deposits and other rare mineral reserves in
Somalia
Somalia, , Osmanya script: 𐒈𐒝𐒑𐒛𐒐𐒘𐒕𐒖; ar, الصومال, aṣ-Ṣūmāl officially the Federal Republic of SomaliaThe ''Federal Republic of Somalia'' is the country's name per Article 1 of thProvisional Constituti ...
. 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.
The ultimate available supply is believed to be sufficient for at least the next 85 years,
although some studies indicate underinvestment in the late twentieth century may produce supply problems in the 21st century.
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.
In other words, there is little high grade ore and proportionately much more low grade ore available.
Compounds
Oxidation states and oxides
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 , which dates to the days of the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
when was used as an analytical chemistry reporting standard.
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
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the ...
s are, respectively,
uranium dioxide
Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear re ...
() and
uranium trioxide
Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is the hexavalent oxide of uranium. The solid may be obtained by heating uranyl nitrate to 400 °C. Its most commonly encountered polymorph, γ-UO3, is ...
().
[.] Other
uranium oxide
Uranium oxide is an oxide of the element uranium.
The metal uranium forms several oxides:
* Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende)
* Diuranium pentoxide or uranium(V) oxide (U2O5)
* Uranium trioxide or ...
s such as uranium monoxide (UO), diuranium pentoxide (), and uranium peroxide () also exist.
The most common forms of uranium oxide are
triuranium octoxide
Triuranium octoxide (U3O8) is a compound of uranium. It is present as an olive green to black, odorless solid. It is one of the more popular forms of yellowcake and is shipped between mills and refineries in this form.
U3O8 has potential long-te ...
() and .
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.
At ambient temperatures, will gradually convert to . Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal.
Aqueous chemistry

Salts of many
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. ...
s of uranium are water-
soluble and may be studied in
aqueous solution
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...
s. The most common ionic forms are (brown-red), (green), (unstable), and (yellow), for U(III), U(IV), U(V), and U(VI), respectively.
[.] A few
solid
Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...
and semi-metallic compounds such as UO and US exist for the formal oxidation state uranium(II), but no simple ions are known to exist in solution for that state. Ions of liberate
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, ...
from
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
and are therefore considered to be highly unstable. The ion represents the uranium(VI) state and is known to form compounds such as
uranyl carbonate,
uranyl chloride and
uranyl sulfate. also forms
complexes with various
organic chelating agents, the most commonly encountered of which is
uranyl acetate.
Unlike the uranyl salts of uranium and
polyatomic ion uranium-oxide cationic forms, the
uranates, 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
In electrochemistry, and more generally in solution chemistry, a Pourbaix diagram, also known as a potential/pH diagram, EH–pH diagram or a pE/pH diagram, is a plot of possible thermodynamically stable phases (''i.e.'', at chemical equilibrium) ...
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.
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 reacts with
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, ...
to form
uranium hydride
Uranium hydride, also called uranium trihydride (UH3), is an inorganic compound and a hydride of uranium.
Properties
Uranium hydride is a highly toxic, brownish grey to brownish black pyrophoric powder or brittle solid. Its density at 20 ° ...
. 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
In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...
, and
halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluo ...
compounds.
[.] 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 °C.
Uranium carbides and
uranium nitrides are both relatively
inert semimetal
A semimetal is a material with a very small overlap between the bottom of the conduction band and the top of the valence band.
According to electronic band theory, solids can be classified as insulators, semiconductors, semimetals, or metal ...
lic compounds that are minimally soluble in
acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...
s, react with water, and can ignite in
air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
to form .
Carbides of uranium include uranium monocarbide (U
C), uranium dicarbide (), and diuranium tricarbide (). Both UC and are formed by adding carbon to molten uranium or by exposing the metal to
carbon monoxide
Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
at high temperatures. Stable below 1800 °C, is prepared by subjecting a heated mixture of UC and to mechanical stress.
[.] Uranium nitrides obtained by direct exposure of the metal to
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seven ...
include uranium mononitride (UN), uranium dinitride (), and diuranium trinitride ().
Halides

All uranium fluorides are created using
uranium tetrafluoride (); itself is prepared by hydrofluorination of uranium dioxide.
Reduction of with hydrogen at 1000 °C produces uranium trifluoride (). Under the right conditions of temperature and pressure, the reaction of solid with gaseous
uranium hexafluoride
Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
() can form the intermediate fluorides of , , and .
At room temperatures, has a high
vapor pressure
Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed pha ...
, 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:
: + 4 HF → + 2 (500 °C, endothermic)
: + → (350 °C, endothermic)
The resulting , a white solid, is highly
reactive (by fluorination), easily
sublimes (emitting a vapor that behaves as a nearly
ideal gas
An ideal gas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state, and is ...
), and is the most volatile compound of uranium known to exist.
One method of preparing
uranium tetrachloride () is to directly combine
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...
with either uranium metal or uranium hydride. The reduction of by hydrogen produces uranium trichloride () while the higher chlorides of uranium are prepared by reaction with additional chlorine.
All uranium chlorides react with water and air.
Bromide
A bromide ion is the negatively charged form (Br−) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardan ...
s and
iodides of uranium are formed by direct reaction of, respectively,
bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
and
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a v ...
with uranium or by adding to those element's acids.
Known examples include: , , , and . has never been prepared. Uranium oxyhalides are water-soluble and include , , , and . Stability of the oxyhalides decrease as the
atomic weight of the component halide increases.
Isotopes
Natural concentrations
Natural uranium consists of three major isotopes:
uranium-238
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, i ...
(99.28% natural abundance), uranium-235 (0.71%), and
uranium-234 (0.0054%). All three are
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
, emitting
alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 atomic nucleus, nucleus. They are generally produced in the process of alpha decay, but may ...
s, with the exception that all three of these isotopes have small probabilities of undergoing
spontaneous fission
Spontaneous fission (SF) is a form of radioactive decay that is found only in very heavy chemical elements. The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 56 (e.g., iron-56); spontaneous breakdo ...
. There are also four other trace isotopes: uranium-239, which is formed when
238U undergoes spontaneous fission, releasing neutrons that are captured by another
238U atom; uranium-237, which is formed when
238U captures a neutron but emits two more, which then decays to
neptunium-237
Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be ...
;
uranium-236, which occurs in trace quantities due to neutron capture on
235U and as a decay product of
plutonium-244
Plutonium-244 (244Pu) is an isotope of plutonium that has a half-life of 80 million years. This is longer than any of the other isotopes of plutonium and longer than any other actinide isotope except for the three naturally abundant ones: uraniu ...
; and finally, uranium-233, which is formed in the
decay chain
In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay direct ...
of neptunium-237. It is also expected that
thorium-232
Thorium-232 () is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half life of 14 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its decay ...
should be able to undergo
double beta decay
In nuclear physics, double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons, or vice versa, inside an atomic nucleus. As in single beta decay, this process allows the atom to move clos ...
, which would produce uranium-232, but this has not yet been observed experimentally.
The only significant deviation from the U-235 to U-238 ratio in any known natural samples occurs in
Oklo
Oklo is a region near the town of Franceville, in the Haut-Ogooué province of the Central African country of Gabon. Several natural nuclear fission reactors were discovered in the uranium mines in the region in 1972.
History
Gabon was a Fren ...
,
Gabon
Gabon (; ; snq, Ngabu), officially the Gabonese Republic (french: République gabonaise), is a country on the west coast of Central Africa. Located on the equator, it is bordered by Equatorial Guinea to the northwest, Cameroon to the nort ...
where
natural nuclear fission reactors consumed some of the U-235 some two billion years ago when the ratio of U-235 to U-238 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 reactors. The existence of such natural fission reactors which had been theoretically predicted beforehand was proven as the slight deviation of U-235 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 U-235) confirmed the theory by finding isotope ratios of common
fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release ...
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.
Uranium-238 is the most stable isotope of uranium, with a half-life of about 4.468 years, roughly the
age of the Earth
The age of Earth is estimated to be 4.54 ± 0.05 billion years This age may represent the age of Earth's accretion, or core formation, or of the material from which Earth formed. This dating is based on evidence from radiometric age-dating of ...
. Uranium-235 has a half-life of about 7.13 years, and uranium-234 has a half-life of about 2.48 years.
[.] Uranium-238 is usually an alpha emitter (occasionally, it undergoes spontaneous fission), decaying through the
uranium series
In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay directl ...
, which has 18 members, into
lead-206
Lead (82Pb) has four stable isotopes: 204Pb, 206Pb, 207Pb, 208Pb. Lead-204 is entirely a primordial nuclide and is not a radiogenic nuclide. The three isotopes lead-206, lead-207, and lead-208 represent the ends of three decay chains: the urani ...
, by a variety of different decay paths.
The decay chain of
235U, which is called the
actinium series
In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay directl ...
, has 15 members and eventually decays into lead-207.
The constant rates of decay in these decay series makes the comparison of the ratios of parent to
daughter elements useful in radiometric dating.
Uranium-234, which is a member of the uranium series (the decay chain of uranium-238), decays to lead-206 through a series of relatively short-lived isotopes.
Uranium-233 is made from
thorium-232
Thorium-232 () is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half life of 14 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its decay ...
by neutron bombardment, usually in a nuclear reactor, and
233U is also fissile.
Its decay chain forms part of the
neptunium series and ends at
bismuth-209 and
thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes and ...
-205.
Uranium-235 is important for both
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from n ...
s and
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bo ...
s, because it is the only uranium isotope existing in nature on Earth in any significant amount that is fissile. This means that it can be split into two or three fragments (
fission products
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release ...
) by thermal neutrons.
Uranium-238 is not fissile, but is a fertile isotope, because after
neutron activation
Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus decays immediately by emitti ...
it can be converted to plutonium-239, another fissile isotope. Indeed, the
238U nucleus can absorb one neutron to produce the radioactive isotope
uranium-239
Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay p ...
.
239U decays by
beta emission
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ex ...
to
neptunium
Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. Its position in the periodic table just after uranium, named after the planet Uranus, led to it being ...
-239, also a beta-emitter, that decays in its turn, within a few days into plutonium-239.
239Pu was used as fissile material in the first
atomic bomb
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bom ...
detonated in the "Trinity test" on 15 July 1945 in
New Mexico
)
, population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano)
, seat = Santa Fe, New Mexico, Santa Fe
, LargestCity = Albuquerque, New Mexico, Albuquerque
, LargestMetro = Albuquerque metropolitan area, Tiguex
, Offi ...
.
Enrichment

In nature, uranium is found as uranium-238 (99.2742%) and uranium-235 (0.7204%).
Isotope separation concentrates (enriches) the fissionable uranium-235 for nuclear weapons and most nuclear power plants, except for
gas cooled reactors and
pressurised heavy water reactors. Most neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the
nuclear chain reaction
In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific n ...
. 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%. 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 uranium-235 isotope concentration should be no more than 0.3%.
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.
The
gas centrifuge
A gas centrifuge is a device that performs isotope separation of gases. A centrifuge relies on the principles of centrifugal force accelerating molecules so that particles of different masses are physically separated in a gradient along the radiu ...
process, where gaseous
uranium hexafluoride
Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
() is separated by the difference in molecular weight between
235UF
6 and
238UF
6 using high-speed
centrifuge
A centrifuge is a device that uses centrifugal force to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby separating fluids of different densities (e.g. cream from milk) or l ...
s, is the cheapest and leading enrichment process.
[.] The
gaseous diffusion process had been the leading method for enrichment and was used in the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
. In this process, uranium hexafluoride is repeatedly
diffused through a
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical c ...
-
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic ...
membrane, and the different isotopes of uranium are separated by diffusion rate (since uranium-238 is heavier it diffuses slightly slower than uranium-235).
The
molecular laser isotope separation method employs a
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
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.
An alternative laser method of enrichment is known as
atomic vapor laser isotope separation (AVLIS) and employs visible
tunable lasers such as
dye lasers. Another method used is liquid thermal diffusion.
Human exposure
A person can be exposed to uranium (or its
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
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phos ...
fertilizer
A fertilizer (American English) or fertiliser ( British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
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
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when de ...
-fired power plant, facilities that mine or process uranium ore, or enrich uranium for reactor fuel, may have increased exposure to uranium.
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
The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...
(OSHA) has set the
permissible exposure limit for uranium exposure in the workplace as 0.25 mg/m
3 over an 8-hour workday. The
National Institute for Occupational Safety and Health
The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...
(NIOSH) has set a
recommended exposure limit
A recommended exposure limit (REL) is an occupational exposure limit that has been recommended by the United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country p ...
(REL) of 0.2 mg/m
3 over an 8-hour workday and a short-term limit of 0.6 mg/m
3. At levels of 10 mg/m
3, uranium is
immediately dangerous to life and health.
Most ingested uranium is excreted during
digestion
Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intes ...
. 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%.
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
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side ...
s, pose a more serious exposure hazard. After entering the bloodstream, the absorbed uranium tends to
bioaccumulate and stay for many years in
bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...
tissue because of uranium's affinity for phosphates.
Uranium is not absorbed through the skin, and
alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 atomic nucleus, nucleus. They are generally produced in the process of alpha decay, but may ...
s released by uranium cannot penetrate the skin.
Incorporated uranium becomes
uranyl ions, which accumulate in bone, liver, kidney, and reproductive tissues. Uranium can be decontaminated from steel surfaces
and
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
s.
Effects and precautions
Normal functioning of the
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...
,
brain
A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
,
liver
The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
,
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to ...
, and other systems can be affected by uranium exposure, because, besides being weakly radioactive, uranium is a
toxic metal.
Uranium is also a
reproductive toxicant.
Radiological effects are generally local because alpha radiation, the primary form of
238U 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.
Uranyl () ions, such as from
uranium trioxide
Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is the hexavalent oxide of uranium. The solid may be obtained by heating uranyl nitrate to 400 °C. Its most commonly encountered polymorph, γ-UO3, is ...
or
uranyl nitrate
Uranyl nitrate is a water-soluble yellow uranium salt with the formula . The hexa-, tri-, and dihydrates are known. The compound is mainly of interest because it is an intermediate in the preparation of nuclear fuels.
Uranyl nitrate can be prep ...
and other
hexavalent uranium compounds, have been shown to cause birth defects and immune system damage in laboratory animals. While the CDC has published one study that no human
cancer
Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Poss ...
has been seen as a result of exposure to natural or depleted uranium,
exposure to uranium and its decay products, especially
radon, are widely known and significant health threats.
Exposure to
strontium-90
Strontium-90 () is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. It undergoes β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine and ...
,
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.
Although accidental inhalation exposure to a high concentration of
uranium hexafluoride
Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
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.
Finely divided uranium metal presents a fire hazard because uranium is
pyrophoric; small grains will ignite spontaneously in air at room temperature.
Uranium metal is commonly handled with gloves as a sufficient precaution.
Uranium concentrate is handled and contained so as to ensure that people do not inhale or ingest it.
See also
*
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 engineering is the branch of engineering concerned with the application of breaking down atomic nuclei ( fission) or of combining atomic nuclei ( fusion), or with the application of other sub-atomic processes based on the principles of ...
*
Nuclear fuel cycle
*
Nuclear physics
Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter.
Nuclear physics should not be confused with atomic physics, which studies t ...
*
Quintuple bond (earlier thought to be a
Phi bond), in the molecule U
2
*
Thorium fuel cycle
*
World Uranium Hearing
Notes
References
*
*
External links
U.S. EPA: Radiation Information for Uranium from
World Nuclear Association
Nuclear fuel data and analysisfrom the
U.S. Energy Information Administration
Current market price of uraniumAnnotated bibliography for uranium from the Alsos Digital LibraryNLM Hazardous Substances Databank—Uranium, RadioactiveMining Uranium at Namibia's Langer Heinrich MineWorld Nuclear NewsATSDR Case Studies in Environmental Medicine: Uranium ToxicityU.S.
Department of Health and Human Services
The United States Department of Health and Human Services (HHS) is a cabinet-level executive branch department of the U.S. federal government created to protect the health of all Americans and providing essential human services. Its motto is ...
Uraniumat ''
The Periodic Table of Videos'' (University of Nottingham)
{{Authority control
Chemical elements
Actinides
Nuclear fuels
Nuclear materials
Suspected male-mediated teratogens
Manhattan Project