'Uranium' ()is a white/black
metallic
chemical element in the
actinide series of the
periodic table that has the
symbol 'U' and
atomic number 92. It has 92
protons and
electrons, 6 of them
valence electrons. It can have between 141 and 146
neutrons, with 143 and 146 in its most common isotopes. Uranium has the highest atomic weight of the naturally occurring elements (see
plutonium). Uranium is approximately 70% more
dense than
lead and is weakly
radioactive. It occurs naturally in low concentrations (a few
parts per million) in soil, rock and water, and is commercially extracted from uranium-bearing
minerals such as
uraninite (see
uranium mining).
In nature, uranium atoms exist as
uranium-238 (99.275%),
uranium-235 (0.711%), and a very small amount of
uranium-234 (0.0058%). Uranium decays slowly by emitting an
alpha particle. The
half-life of uranium-238 is about 4.47
billion years and that of uranium-235 is 704
million years,
[1] making them useful in dating the
age of the Earth (see
uranium-thorium dating,
uranium-lead dating and
uranium-uranium dating). Along with
thorium and
plutonium, uranium is one of the three
fissile elements, meaning it can easily break apart to become lighter elements. While uranium-238 has a small probability to fission spontaneously or when bombarded with fast neutrons, the much higher probability of uranium-235 and to a lesser degree
uranium-233 to fission when bombarded with slow neutrons generates the heat in
nuclear reactors used as a source of power, and provides the fissile material for
nuclear weapons. Both uses rely on the ability of uranium to produce a sustained
nuclear chain reaction.
Depleted uranium (uranium-238) is used in
kinetic energy penetrators and
armor plating.
[2]
Uranium is used as a colorant in
uranium glass, producing orange-red to lemon yellow hues. It was also used for tinting and shading in early
photography. The 1789
discovery of uranium in the mineral
pitchblende is credited to
Martin Heinrich Klaproth, who named the new element after the planet
Uranus. Eugène-Melchior Péligot was the first person to isolate the metal, and its radioactive properties were uncovered in 1896 by
Antoine Becquerel. Research by
Enrico Fermi and others starting in 1934 led to its use as a fuel in the nuclear power industry and in ''
Little Boy'', the
first nuclear weapon used in war. An ensuing
arms race during the
Cold War between the
United States and the
Soviet Union produced tens of thousands of nuclear weapons that used
enriched uranium and uranium-derived plutonium. The security of those weapons and their fissile material following the
breakup of the Soviet Union in 1991 along with the legacy of
nuclear testing and
nuclear accidents is a concern for public health and safety.
Characteristics
An induced nuclear fission event involving uranium-235
When
refined, uranium is a silvery white, weakly radioactive
metal, which is slightly softer than
steel,
[3] strongly
electropositive and a poor
electrical conductor.
It is
malleable,
ductile, and slightly
paramagnetic.
Uranium metal has very high
density, being approximately 70% more dense than
lead, but slightly less dense than
gold.
Uranium metal reacts with nearly all nonmetallic elements and their
compounds, with reactivity increasing with temperature.
[4] Hydrochloric and
nitric acids dissolve uranium, but nonoxidizing acids 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 in ores is extracted chemically and converted into
uranium dioxide or other chemical forms usable in industry.
Uranium was the first element that was found to be
fissile. Upon bombardment with slow
neutrons, its
uranium-235 isotope becomes a very short-lived uranium-236 isotope, which immediately divides into two smaller
nuclei, releasing nuclear
binding energy and more neutrons. If these neutrons are absorbed by other uranium-235 nuclei, a
nuclear chain reaction occurs and, if there is nothing to absorb some neutrons and slow the reaction, the reaction is explosive. As little as 15 lb (7 kg) of uranium-235 can be used to make an atomic bomb.
[5] The first atomic bomb worked by this principle (nuclear fission).
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. At high impact speed, the density, hardness, and flammability of the projectile enable destruction of heavily armored targets. Tank armor and the removable armor on combat vehicles are also hardened with depleted uranium (DU) plates. The use of DU became a contentious political-environmental issue after the use of DU munitions by the US, UK and other countries during wars in the Persian Gulf and the Balkans raised questions of 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.
Other uses of DU 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 devices and in
gyroscopic compasses.
DU is preferred over similarly dense metals due to its ability to be easily machined and cast as well as its relatively low cost.
[6] Counter to popular belief, the main risk of exposure to DU is chemical poisoning by uranium oxide rather than radioactivity (uranium being only a weak
alpha emitter).
During the later stages of
World War II, the entire
Cold War, and to a much lesser extent afterwards, uranium was used as the fissile explosive material to produce
nuclear weapons. Two major types of fission bombs were built: a relatively simple device that uses
uranium-235 and a more complicated mechanism that uses
uranium-238-derived
plutonium-239. Later, a much more complicated and far more powerful fusion bomb that uses a plutonium-based device in a uranium casing to cause a mixture of
tritium and
deuterium to undergo
nuclear fusion was built.
[7]
Civilian
The most visible civilian use of uranium is as the thermal power source used in
nuclear power plants.
The main use of uranium in the civilian sector is to fuel commercial
nuclear power plants; by the time it is completely fissioned, one kilogram of uranium can theoretically produce about 20
trillion joules of energy (20 joules); as much
electricity as 1500
tonnes of
coal.
Generally this is in the form of
enriched uranium, which has been processed to have higher-than-natural levels of uranium-235 and can be used for a variety of purposes relating to nuclear fission.
Commercial
nuclear power plants use fuel that is typically enriched to around 3% uranium-235,
though some reactor designs (such as the
CANDU reactors) can use unenriched uranium fuel. Fuel used for
United States Navy reactors is typically highly enriched in uranium-235 (the exact values are
classified). In a
breeder reactor, uranium-238 can also be converted into
plutonium through the following reaction:
U(n, gamma) -> U -(beta)-> Np -(beta)-> Pu.
Prior to the discovery of
radiation, uranium was primarily used in small amounts for yellow glass and pottery dyes (such as
uranium glass and in
Fiestaware). Uranium was also used in
photographic chemicals (esp.
uranium nitrate as a
toner),
in lamp filaments, 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 stains in
transmission electron microscopy, to increase the contrast of biological specimens in ultrathin sections and in
negative staining of
viruses, isolated
cell organelles and
macromolecules.
The discovery of the radioactivity of uranium ushered in additional scientific and practical uses of the element. The long
half-life of the isotope uranium-238 (4.51 years) makes it well-suited for use in estimating the age of the earliest
igneous rocks and for other types of
radiometric dating (including
uranium-thorium dating and
uranium-lead dating). Uranium metal is used for
X-ray targets in the making of high-energy X-rays.
History
Pre-discovery use
The use of uranium in its natural
oxide form dates back to at least the year 79, when it was used to add a yellow color to
ceramic glazes.
[3] Yellow glass with 1% uranium oxide was found in a
Roman villa on Cape
Posillipo in the
Bay of Naples,
Italy by R. T. Gunther of the
University of Oxford in 1912.
[9] Starting in the late
Middle Ages,
pitchblende was extracted from the
Habsburg silver mines in
Joachimsthal,
Bohemia (now Jáchymov in the
Czech Republic) and was used as a coloring agent in the local
glassmaking industry.
In the early 19th century, the world's only known source of uranium ores were these old mines.
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 in
nitric acid and neutralizing the solution with
sodium hydroxide.
[10] Klaproth mistakenly assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with
charcoal to obtain a black powder, which he thought was the newly discovered metal itself (in fact, that powder was an oxide of uranium).
He named the newly discovered element after the planet
Uranus, which had been discovered eight years earlier by
William Herschel.
[12]
In 1841,
Eugène-Melchior Péligot, who was Professor of Analytical Chemistry at the
Conservatoire des arts et métiers (Central School of Arts and Manufactures) in
Paris, isolated the first sample of uranium metal by heating
uranium tetrachloride with
potassium.
[13] Uranium was not seen as being particularly dangerous during much of the 19th century, leading to the development of various uses for the element. One such use for the oxide was the aforementioned but no longer secret coloring of pottery and glass.
Antoine Becquerel discovered
radioactivity by using uranium in 1896.
Becquerel made the discovery in Paris by leaving a sample of uranium 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.
Fission research
A team led by
Enrico Fermi in 1934 observed that bombarding uranium with
neutrons produces the emission of
beta rays (
electrons or
positrons; see
beta particle).
The fission products were at first mistaken for new elements of atomic numbers 93 and 94, which the Dean of the Faculty of Rome, Orso Mario Corbino, christened ''
ausonium'' and ''
hesperium'', respectively.
[14][15][16][17] The experiments leading to the discovery of uranium's ability to
fission (break apart) into lighter elements and release
binding energy were conducted by
Otto Hahn and
Fritz Strassmann[18] in Hahn's laboratory in Berlin.
Lise Meitner and her nephew, physicist
Otto Robert Frisch, published the physical explanation in February 1939 and named the process '
nuclear fission'.
[19] 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 1/2 neutrons are released by each fission of the rare uranium isotope
uranium-235.
Further work found that the far more common
uranium-238 isotope can be
transmuted into
plutonium, which, like uranium-235, is also fissionable by thermal neutrons.
On
2 December 1942, another team led by Enrico Fermi was able to initiate the first artificial
nuclear chain reaction. Working in a lab below the stands of
Stagg Field at the
University of Chicago, the team created the conditions needed for such a reaction by piling together 360 tonnes of
graphite, 53 tonnes of
uranium oxide, and 5.5 tonnes of uranium metal.
Later researchers found that such a chain reaction could either be controlled to produce usable energy or could be allowed to go out of control to produce an explosion more violent than anything possible using
chemical explosives.
Bombs and reactors
Two major types of atomic bomb were developed in the
Manhattan Project during
World War II: a
plutonium-based device (see
Trinity test and '
Fat Man') whose plutonium was derived from uranium-238, and a uranium-based device (nicknamed '
Little Boy') whose fissile material was highly
enriched uranium. The uranium-based Little Boy device became the first nuclear weapon used in war when it was detonated over the
Japanese city of
Hiroshima 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).
Four light bulbs lit with electricity generated from the first artificial electricity-producing
nuclear reactor,
EBR-I (1951)
at the
Idaho National Laboratory(INL) near
Arco, Idaho became the first functioning artificial nuclear reactor 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 whole town of Arco became the first in the world to have all its
electricity come from nuclear power).
[20] The world's first commercial scale nuclear power station,
Calder Hall in England, began generation on
17 October 1956.
[21] Another early power reactor was the
Shippingport Reactor in
Pennsylvania, which began electricity production in 1957. Nuclear power was used for the first time for propulsion by a
submarine, the
USS ''Nautilus'', in 1954.
Fifteen ancient and no longer active
natural nuclear fission reactors were found in three separate ore deposits at the
Oklo mine in
Gabon,
West Africa in 1972. Discovered by French physicist
Francis Perrin, they are collectively known as the
Oklo Fossil Reactors. The ore they exist in is 1.7 billion years old; at that time, uranium-235 constituted about three percent of the total uranium on Earth.
[22] This is high enough to permit a sustained nuclear fission chain reaction to occur, providing other conditions are right. The ability of the surrounding sediment to contain the
nuclear waste products in less than ideal conditions has been cited by the U.S. federal government as evidence of their claim that the
Yucca Mountain facility could safely be a repository of waste for the
nuclear power industry.
Cold War legacy and waste
U.S. and USSR/Russian nuclear weapons stockpiles, 1945–2006
During the
Cold War between the Soviet Union and the United States, huge stockpiles of uranium were amassed and tens of thousands of nuclear weapons were created using enriched uranium and plutonium made from uranium.
Since the
break-up of the Soviet Union in 1991, an estimated 540 tonnes 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 and several other former Soviet states.
Police in
Asia,
Europe, 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, spent approximately
US $550 million to help safeguard uranium and plutonium stockpiles in Russia.
The improvements made provided repairs and security enhancements at research and storage facilities. ''Scientific American'' reported in February of 2006 that some of the facilities had been protected only by 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 prior to the improvement project; another had been keeping track of its stock of nuclear warheads using index cards kept in a shoe box.
[23]
Above-ground
nuclear tests by the Soviet Union and the United States in the 1950s and early 1960s and by
France into the 1970s and 1980s
spread a significant amount of
fallout from uranium daughter isotopes around the world.
[24] Additional fallout and pollution occurred from several
nuclear accidents.
The
Windscale fire at the
Sellafield nuclear plant in 1957 spread
iodine-131, a short lived radioactive isotope, over much of
Northern England.
The
Three Mile Island accident in 1979 released a small amount of
iodine-131. The amounts released by the partial meltdown of the Three Mile Island power plant were minimal, and an environmental survey only found trace amounts in a few field mice dwelling nearby. As I-131 has a half life of slightly more than eight days, any danger posed by the radioactive material has long since passed for both of these incidents.
The
Chernobyl disaster in 1986, however, was a complete core breach meltdown and partial detonation of the reactor, which ejected iodine-131 and
strontium-90 over a large area of Europe. The 28 year half-life of strontium-90 means that only recently has some of the surrounding countryside around the reactor been deemed safe enough to be habitable.
Occurrence
Biotic and abiotic
Main articles: Uranium in the environment
Uraninite, also known as Pitchblende, is the most common ore mined to extract uranium.
Uranium is a
naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is also the highest-numbered element to be found naturally in significant quantities on earth and is always found combined with other elements.
Along with all elements having
atomic weights higher than that of
iron, it is only naturally formed in
supernova explosions.
[25] The decay of uranium,
thorium and
potassium-40 in the Earth's
mantle is thought to be the main source of heat
[26][27] that keeps the
outer core liquid and drives
mantle convection, which in turn drives
plate tectonics.
Its average concentration in the
Earth's
crust is (depending on the reference) 2 to 4 parts per million,
[28] or about 40 times as abundant as
silver.
The Earth's crust from the surface to 25 km (15 mi) down is calculated to contain 10 kg (2 lb) of uranium while the
oceans may contain 10 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
fertilizers), and 3 parts per billion of sea water is composed of the element.
It is more plentiful than
antimony,
tin,
cadmium,
mercury, or silver, and it is about as abundant as
arsenic or
molybdenum.
It is found in hundreds of minerals including
uraninite (the most common uranium
ore),
autunite,
uranophane,
torbernite, and
coffinite.
Significant concentrations of uranium occur in some substances such as
phosphate rock deposits, and minerals such as
lignite, and
monazite sands in uranium-rich ores
(it is recovered commercially from these sources with as little as 0.1% uranium
).
''
Citrobacter'' species can have concentrations of uranium in their bodies 300 times higher than in the surrounding environment.
Some
microorganisms, such as the lichen ''
Trapelia involuta'' or the bacterium ''
Citrobacter'', can absorb concentrations of uranium that are up to 300 times higher than their environment.
[29] ''Citrobactor'' species absorb
uranyl ions when given
glycerol phosphate (or other similar organic phosphates). After one day, one gram of bacteria will encrust themselves with nine grams of uranyl phosphate crystals; this creates the possibility that these organisms could be used to
decontaminate uranium-polluted water.
s absorb some uranium from the soil they are rooted in. 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 plants are typically lower with one to two micrograms per day ingested through the food people eat.
Production and mining
Yellowcake is a concentrated mixture of uranium oxides that is further refined to extract pure uranium.
Uranium ore is mined in several ways: by
open pit,
underground, in-situ
leaching, and
borehole mining (see
uranium mining).
Low-grade uranium ore typically contains 0.1 to 0.25% of actual uranium oxides, so extensive measures must be employed to extract the metal from its ore.
[31] High-grade ores found in Athabasca Basin deposits in
Saskatchewan, Canada can contain up to 70% uranium oxides, and therefore must be diluted with waste rock prior to milling. Uranium ore is crushed and rendered into a fine powder and then leached with either an
acid or
alkali. The leachate is then subjected to one of several sequences of precipitation, solvent extraction, and ion exchange. The resulting mixture, called
yellowcake, contains at least 75% uranium oxides. Yellowcake is then
calcined to remove impurities from the milling process prior to refining and conversion.
Commercial-grade uranium can be produced through the
reduction of uranium
halides with
alkali or
alkaline earth metals.
Uranium metal can also be made through
electrolysis of or , dissolved in a molten
calcium chloride () and
sodium chloride (
NaCl) solution.
Very pure uranium can be produced through the
thermal decomposition of uranium halides on a hot filament.
Resources and reserves
It is estimated that there is 4.7 million tonnes of uranium ore reserves (economically mineable) known to exist, while 35 million tonnes are classed as mineral resources (reasonable prospects for eventual economic
extraction).
[ An additional 4.6 billion tonnes of uranium are estimated to be in sea water (Japanese scientists in the 1980s proved that extraction of uranium from sea water using ion exchangers was feasible).][ Uranium recovery from Seawater ][ How long will nuclear energy last? ]
Exploration for uranium is continuing to increase with US$200 million being spent world wide in 2005, a 54% increase on the previous year.
Australia has 38% of the world's uranium ore resources—the most of any country.[ Australia's Uranium and Who Buys It ] In fact, the world's largest single uranium deposit is located at the Olympic Dam Mine in South Australia.[32] Almost all the uranium is exported, under strict International Atomic Energy Agency safeguards to satisfy the Australian people and government that none of the uranium is used in nuclear weapons. As of 2006, the Australian government was advocating an expansion of uranium mining, although issues with state governments and indigenous interests complicate the issue.[33]
The largest single source of uranium ore in the United States was the Colorado Plateau located in Colorado, Utah, New Mexico, and Arizona. The U.S. federal government paid discovery bonuses and guaranteed purchase prices to anyone who found and delivered uranium ore, and was the sole legal purchaser of the uranium. The economic incentives resulted in a frenzy of exploration and mining activity throughout the Colorado Plateau from 1947 through 1959 that left thousands of miles of crudely graded roads spider-webbing the remote deserts of the Colorado Plateau, and thousands of abandoned uranium mines, exploratory shafts, and tailings piles. The frenzy ended as suddenly as it had begun, when the U.S. government stopped purchasing the uranium.
Supply
2.PNG)
Uranium output in 2005
In 2005, seventeen countries produced concentrated uranium oxides, with Canada (27.9% of world production) and Australia (22.8%) being the largest producers and Kazakhstan (10.5%), Russia (8.0%), Namibia (7.5%), Niger (7.4%), Uzbekistan (5.5%), the United States (2.5%), Ukraine (1.9%) and China (1.7%) also producing significant amounts.[34] The ultimate supply of uranium is believed to be very large and sufficient for at least the next 85 years[ Global Uranium Resources to Meet Projected Demand ] although some studies indicate underinvestment in the late twentieth century may produce supply problems in the 21st century.[ Lack of fuel may limit U.S. nuclear power expansion ] It is estimated that for a ten times increase in price, the supply of uranium that can be economically mined is increased 300 times.[35]
Compounds
Oxidation states and oxides
Ions that represent the four different oxidation states of uranium are soluble and therefore can be studied in aqueous solutions. They are: U (red), U (green), {{chem|UO|2| (unstable), and (yellow).[36] A few solid 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 U liberate hydrogen from water and are therefore considered to be highly unstable. The {{chem|UO|2| ion represents the uranium(VI) state and is known to form compounds such as the carbonate, chloride and sulfate. {{chem|UO|2| also forms complexes with various organic chelating agents, the most commonly-encountered of which is uranyl acetate.
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 particles that have long retention times or are recovered in the stack scrubber. While uranium content is referred to for content, to do so is inaccurate and dates to the days of the Manhattan project when was used as an analytical chemistry reporting standard.
Phase relationships in the uranium-oxygen system are highly complex. The most important oxidation states of uranium are uranium(IV) and uranium(VI), and their two corresponding oxides are, respectively, uranium dioxide () and uranium trioxide ().[37] Other uranium oxides such as uranium monoxide (UO), diuranium pentoxide (), and uranium peroxide () are also known to exist.
The most common forms of uranium oxide are triuranium octaoxide () and the aforementioned .[38] Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octaoxide 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.
Hydrides, carbides and nitrides
Uranium metal heated to 250 to 300°C (482 to 572°F) reacts with hydrogen to form uranium hydride. Even higher temperatures will reversibly remove the hydrogen. This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium carbide, nitride, and halide compounds.[39] 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 semimetallic compounds that are minimally soluble in acids, react with water, and can ignite in air to form .
Halides
All uranium fluorides are created using uranium tetrafluoride (); itself is prepared by hydrofluorination of uranium dioxide.
At room temperatures, has a high vapor pressure, making it useful in the gaseous diffusion process to separate highly valuable uranium-235 from the far more common uranium-238 isotope. This compound can be prepared from uranium dioxide and uranium hydride by the following process:
The resulting white solid is highly reactive (by fluorination), easily sublimes (emitting a nearly perfect gas vapor), and is the most volatile compound of uranium known to exist.
One method of preparing uranium tetrachloride () is to directly combine chlorine 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.
Bromides and iodides of uranium are formed by direct reaction of, respectively, bromine and iodine with uranium or by adding to those element's acids.
Isotopes
Pie-graphs showing the relative proportions of uranium-238 (blue) and uranium-235 (red) at different levels of enrichment
Natural concentrations
Main articles: Isotopes of uranium
Naturally occurring uranium is composed of three major isotopes, uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). All three isotopes are radioactive, creating radioisotopes, with the most abundant and stable being uranium-238 with a half-life of 4.51 years (close to the age of the Earth), uranium-235 with a half-life of 7.13 years, and uranium-234 with a half-life of 2.48 years.[41]
Uranium-238 is an α emitter, decaying through the 18-member uranium natural decay series into lead-206.
The isotope uranium-235 is important for both nuclear reactors and nuclear weapons because it is the only isotope existing in nature to any appreciable extent that is fissile, that is, can be broken apart by thermal neutrons.
Enrichment
Main articles: Enriched uranium
Cascades of
gas centrifuges are used to enrich uranium ore to concentrate its fissionable isotopes.
Enrichment of uranium ore through isotope separation to concentrate the fissionable uranium-235 is needed for use in nuclear power plants and nuclear weapons. A majority of neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the nuclear chain reaction needed for these applications. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass.'
To be considered 'enriched', the uranium-235 fraction has to be increased to significantly greater than its concentration in naturally-occurring uranium. Enriched uranium typically has a uranium-235 concentration of between 3 and 5%.[42] The 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 has to have been decreased to significantly less than its natural concentration. Typically the amount of uranium-235 left in depleted uranium is 0.2% to 0.3%.[43] As the price of uranium has risen since 2001, some enrichment tailings containing more than 0.35% uranium-235 are being considered for re-enrichment, driving the price of these depleted uranium hexafluoride stores above $130 per kilogram in July, 2007 from just $5 in 2001.[44]
The gas centrifuge process, where gaseous uranium hexafluoride () is separated by weight using high-speed centrifuges, has become the cheapest and leading enrichment process (lighter concentrates in the center of the centrifuge).[45] The gaseous diffusion process was the previous leading method for enrichment and the one used in the Manhattan Project. In this process, uranium hexafluoride is repeatedly diffused through a silver-zinc membrane, and the different isotopes of uranium are separated by diffusion rate (uranium 238 is heavier and thus diffuses slightly slower than uranium-235).
Precautions
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 fertilizers, live near government facilities that made or tested nuclear weapons, live or work near a modern battlefield where depleted uranium weapons have been used, or live or work near a coal-fired power plant, facilities that mine or process uranium ore, or enrich uranium for reactor fuel, may have increased exposure to uranium.[46][47] 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.
Almost all uranium that is ingested is excreted during digestion, but up to 5% is absorbed by the body when the soluble uranyl ion is ingested while only 0.5% is absorbed when insoluble forms of uranium, such as its oxide, are ingested.
Effects
The greatest health risk from large intakes of uranium is toxic damage to the kidneys, because, in addition to being weakly radioactive, uranium is a toxic metal.[48][49]
Although accidental inhalation exposure to a high concentration of uranium hexafluoride has
resulted in human fatalities, those deaths were not associated with uranium itself.[53] Finely-divided uranium metal presents a fire hazard because uranium is pyrophoric, so small grains will ignite spontaneously in air at room temperature.
See also
★ Nuclear engineering
★ Nuclear fuel cycle
★ Nuclear physics
★ K-65 residues
★ List of uranium mines
Notes
1. WWW Table of Radioactive Isotopes
2. Emsley, ''Nature's Building Blocks'' (2001), page 479
3. Uranium
4. uranium Columbia Electronic Encyclopedia
5. uranium Encyclopedia of Espionage, Intelligence, and Security
6. Emsley, ''Nature's Building Blocks'' (2001), page 480
7. Nuclear Weapon Design
8. Uranium
9. Emsley, ''Nature's Building Blocks'' (2001), page 482
10. Emsley, ''Nature's Building Blocks'' (2001), page 477
11. Chemische Untersuchung des Uranits, einer neuentdeckten metallischen Substanz, M. H. Klaproth, , , Chemische Annalen, 1789
12. Uranium The American Heritage Dictionary of the English Language
13. Recherches Sur L'Uranium, E.-M. Péligot, , , Annales de chimie et de physique, 1842
14. Fermi, E.; ''Artifical radioactivity produced by neutron bombardment'', Nobel prize address, 12 December 1938
15. De Gregorio, A. ''A Historical Note About How the Property was Discovered that Hydrogenated Substances Increase the Radioactivity Induced by Neutrons'' (2003)
16. Nigro, M,; ''Hahn, Meitner e la teoria della fissione'' (2004)
17. Peter van der Krogt, Elementymology & Elements Multidict
18. Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 773
19. Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction, L. Meitner, O. Frisch, , , Nature, 1939
20. History and Success of Argonne National Laboratory: Part 1
21. 1956:Queen switches on nuclear power
22. Oklo: Natural Nuclear Reactors
23. Glaser, Alexander and von Hippel, Frank N. "Thwarting Nuclear Terrorism" Scientific American Magazine, February 2006
24. A new ground-level fallout record of uranium and plutonium isotopes for northern temperate latitudes, T. Warneke, I. W. Croudace, P. E. Warwick, R. N. Taylor, , , Earth and Planetary Science Letters, 2002
25. WorldBook@NASA: Supernova
26. First measurements of Earth's core radioactivity, Biever, Celeste, , , ,
27. Potassium-40 heats up Earth's core
28. Uranium The McGraw-Hill Science and Technology Encyclopedia
29. Emsley, ''Nature's Building Blocks'' (2001), pages 476 and 482
30.
31. Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 774
32. Uranium Mining and Processing in South Australia
33. "Nuclear Balance of Power", ''BRW'', 26 Oct. 2006, pp. 41–44
34. World Uranium Production
35. "World Uranium Resources", by Kenneth S. Deffeyes and Ian D. MacGregor, ''Scientific American'', January, 1980, page 66, argues that the supply of uranium is very large.
36. Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 778
37. Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 779
38. Chemical Forms of Uranium
39. Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 782
40. Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 780
41. Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 777
42. Uranium Enrichment
43. Lawmakers back plan for Paducah plant work
44. dummytext
45. Emsley, ''Nature's Building Blocks'' (2001), page 478
46. Radiation Information for Uranium
47. ToxFAQ for Uranium
48. Depleted and natural uranium: chemistry and toxicological effects, E. S. Craft, A. W. Abu-Qare, M. M. Flaherty, M. C. Garofolo, H. L. Rincavage, M. B. Abou-Donia, , , Journal of Toxicology and Environmental Health Part B: Critical Reviews, 2004
49. Toxicological Profile for Uranium
50. Arfsten, D.P.; K.R. Still; G.D. Ritchie (2001) "A review of the effects of uranium and depleted uranium exposure on reproduction and fetal development," ''Toxicology and Industrial Health,'' vol. 17, pp. 180–91
51. Public Health Statement for Uranium
52. Chart of the Nuclides, US Atomic Energy Commission 1968
53. Kathren and Moore 1986; Moore and Kathren 1985; USNRC 1986
References
''Full reference information for multi-page works cited''
★ Nature's Building Blocks: An A to Z Guide to the Elements, John Emsley, , , Oxford University Press, 2001,
★ ''The Encyclopedia of the Chemical Elements'', Glenn T. Seaborg, , , Reinhold Book Corporation, 1968, LCCCN 68-29938
External links
★ Public Health Statement for Uranium
★ Uranium Resources and Nuclear Energy
★ U.S. EPA: Radiation Information for Uranium
★ "What is Uranium?" from Uranium Information Centre, Australia
★ Nuclear fuel data and analysis from the U.S. Energy Information Administration
★ Australia's Uranium Information Centre
★ Current market price of uranium
★ World Uranium deposit maps
★ Annotated bibliography for uranium from the Alsos Digital Library
★ NLM Hazardous Substances Databank — Uranium, Radioactive
2.PNG)
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