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URANIUM Basic information

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URANIUM Chemical Properties

Melting point:
314-316°C (dec.)
Boiling point:
4160.06°C (estimate)
1.01 g/mL at 25 °C
storage temp. 
silvery-white orthorhombic crystals
EPA Substance Registry System
Uranium (7440-61-1)

Safety Information

Hazard Codes 
Risk Statements 
Safety Statements 
UN 3264 8/PG 3
WGK Germany 
HS Code 

URANIUM Usage And Synthesis


Uranium-238 has a half-life of 4.468 billion years over which time it decays into stable lead-206. This process can be used to date ancient rocks by comparing the ratio of the isotope lead-206, the last isotope in the uranium decay series, to the level of uranium-238 in the sample of rock to determine its age.


Uranium is a silver-white, lustrous, heavy, mildly radioactive metal. Its appearance will change upon exposure to air or water, as oxidation occurs. Its colour darkens through brass, from brown to charcoal grey. Powders, fines, chips, or turnings oxidise rapidly, yielding a dull or flat dark grey or brown colour. Uranium is almost as hard as steel and much denser than lead. Natural uranium is used to make fuel for nuclear power plants; depleted uranium is the leftover product. Some alloys will oxidise more slowly, retaining the silver-white and then brassy colour. No odour is found. Uranium is used as an abundant source of concentrated energy. Uranium occurs in most rocks in concentrations of 2–4 parts per million and is as common in the Earth’s crust as tin, tungsten, and molybdenum. Uranium occurs in seawater and can be recovered from the oceans.
Uranium is a naturally occurring radioactive element. Natural uranium is a mixture of three isotopes: 234U, 235U, and 238U. The most common isotope is 238U; it makes up about 99% of natural uranium by mass. Depleted uranium is a mixture of the same three uranium isotopes except that it has very little 234U and 235U. It is less radioactive than natural uranium. The high density of uranium means that it also finds uses in the keels of yachts and as counterweights for aircraft control surfaces, as well as for radiation shielding. Uranium metal is known to react dangerously with carbon tetrachloride, chlorine, fluorine, nitric acid, nitric oxide, selenium, sulphur, and water (in finely divided form). On decomposition with fire, it produces uranium metal fume and/or oxide. Radioactive progenies (daughters), thorium-234, protactinium-234, and protactinium-234m (metastable), are produced by natural radioactive decay; they are the source of the majority of the penetrating radiation. These isotopes can be concentrated in situations where the metal is melted, condensed, or dissolved, potentially elevating the observed external dose rate. Many industries involved in mining, milling, and processing of uranium can also release it into the environment. Inactive uranium industries may continue to release uranium into the environment.

Chemical Properties

Dense, silvery solid. Strongly electropositive, ductile and malleable, poor conductor of electricity. Forms solid solutions (for nuclear reactors) with molybdenum, niobium, titanium, and zirconium. The metal reacts with nearly all nonmetals. It is attacked by water, acids, and peroxides, but is inert toward alkalies. Green tetravalent uranium and yellow uranyl ion (UO2 ++) are the only species that are stable in solution.

Chemical Properties

Uranium is a silver-white, malleable, ductile, lustrous solid. Weakly radioactive but must be handled with caution. A combustible solid in the form of powder or turnings. Insoluble in water.

Physical properties

Uranium occurs in nature as a mixture of numerous uranium oxides. Triuranium octaoxide, U3O8, is the most stable and common chemical form of uranium oxide found naturally; uranium dioxide (UO2) and uranium trioxide (UO3) are also commonly found in uranium ores. Triuranium octaoxide, which is a complex oxide composed of the oxides U2O5 and UO3, is a dark-green to black solid most commonly found in the mineral pitchblende. Uranium dioxide produces U3O8 when oxidized: 3UO2 + O2 → U3O8. Uranium trioxide is reduced to U3O8 when heated above 500°C: 6UO3 → 2U3O8 + O2. The structure of U3O8 is pentagonal bipyramidal, containing repeating UO7 units.

Physical properties

Uranium is the fourth metal in the actinide series. It looks much like other actinide metallicelements with a silvery luster. It is comparatively heavy, yet malleable and ductile. It reactswith air to form an oxide of uranium. It is one of the few naturally radioactive elementsthat is fissionable, meaning that as it absorbs more neutrons, it “splits” into a series of otherlighter elements (lower atomic weights) through a process of alpha decay and beta emissionthat is known as the uranium decay series, as follows: U-238→ Th-234→Pa-234→U-234→Th-230→Ra-226→Rn-222→Po-218→Pb-214 & At-218→Bi-214 & Rn-218→Po-214→Ti-210→Pb-210→Bi-210 & Ti-206→Pb-206 (stable isotope of lead, 82Pb).Uranium’s melting point is 1,135°C, its boiling point is about 4,100°C, and its density isabout 19g/cm3, which means it is about 19 times heavier than water.


There are total of 26 isotopes of uranium. Three of these are considered stablebecause they have such long half-lives and have not all decayed into other elements and thus still exist in the Earth’s crust. The three are uranium-234, with a half-life of2.455×10+5 years, which makes up 0.0054% of the uranium found on Earth; uranium-235, with a half-life of 703.8×10+6years, which accounts for 0.724% of the Earth’s uranium;and uranium-238m with a half-life of 4.468×10+9years, which makes up most ofthe Earth’s supply of uranium at 99.2742% of the uranium found naturally.

Origin of Name

Named for the planet Uranus.


Uranium is the 44th most abundant element on Earth. It is found mainly in theore pitchblende, but can also be extracted from ores such as uraninite (UO2), carnotite[K2(UO2)2VO4], autunite [Ca(UO2)2(PO4)2], phosphate rock [Ca3(PO4)2], and monazitesand. These ores are found in Africa, France, Australia, and Canada, as well as in Colorado andNew Mexico in the United States. Today, most uranium is sold both to governments and onthe black market as “yellow cake” (triuranium octoxide U3O8). This form can be converted touranium dioxide (UO2), which is a fissionable compound of uranium mostly used in nuclearelectrical power plants. Only 0.7204% of uranium is the isotope U-235, which is fissionableand can be used in nuclear power plants. Although U-235 is capable of producing enough freeneutrons to sustain a nuclear chain reaction, it is very difficult to obtain enough U-235 for thispurpose. To produce an adequate supply for the first atomic (nuclear) bombs, a large gaseousdiffusion plant was constructed that separated small amounts of U-235 from nonfissionableisotopes and their ores by using the differences in their atomic weights. The plant used porousmembranes that, through diffusion, allow the lighter U-235 atoms to pass through the poreswhile the heavier U-238 does not. Thus, the U-235 is separated and concentrated from theheavier U-238. The common uranium isotope U-238 can be converted to plutonium-239 in“breeder” nuclear reactors. Pu-239 is fissionable and is often used in the production of nuclearbombs as well as in nuclear power plants. Another form of uranium (U-233) that is not foundin nature can be artificially produced by bombarding thorium-232 with neutrons to producethorium-233, which has a half-life of 22 minutes and decays into protactinium-233 with ahalf-life of 27 days. Pa-233 then, through beta decay, transmutes into uranium-233. Just onepound of U-233 in nuclear reactors produces energy equal to 1,500 tons of coal.


Uranium reacts with most nonmetallic elements to form a variety of compounds, all ofwhich are radioactive. It reacts with hot water and dissolves in acids, but not in alkalis (bases).Uranium is unique in that it can form solid solutions with other metals, such as molybdenum,titanium, zirconium, and niobium.
Because the isotope uranium-235 is fissionable, meaning that it produces free neutronsthat cause other atoms to split, it generates enough free neutrons to make it unstable. Whenthe unstable U-235 reaches a critical mass of a few pounds, it produces a self-sustaining fissionchain reaction that results in a rapid explosion with tremendous energy and becomesa nuclear (atomic) bomb. The first nuclear bombs were made of uranium and plutonium.Today, both of these “fuels” are used in reactors to produce electrical power. Moderators(control rods) in nuclear power reactors absorb some of the neutrons, which prevents the mass from becoming critical and thus exploding. Although some countries have overcome theirfear of nuclear power and generate a large portion of their electricity through nuclear reactors,the United States, after developing nuclear power plants 40 to 50 years ago, has stopped thecontinued expansion of nuclear power plants. Despite the experience of the Three-Mile Islandevent that spread no more radiation than what people living at high altitudes receive, nuclearpower plants are safer than coal-fired electrical generation plants (there are fewer accidents)and they are far less damaging to the quality of air. Plans are being currently developed in theUnited States for the construction of nuclear power plants that utilize improved technologiesto meet the ever-increasing energy demands of U.S. citizens, while improving the quality ofour air and water.


Yellow-colored glass, containing more than 1% uranium oxide and dating back to 79 A.D., has been found near Naples, Italy. Klaproth recognized an unknown element in pitchblende and attempted to isolate the metal in 1789. The metal apparently was first isolated in 1841 by Peligot, who reduced the anhydrous chloride with potassium. Uranium is not as rare as it was once thought. It is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, davidite, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. Large deposits of uranium ore occur in Utah, Colorado, New Mexico, Canada, and elsewhere. Uranium can be made by reducing uranium halides with alkali or alkaline earth metals or by reducing uranium oxides by calcium, aluminum, or carbon at high temperatures. The metal can also be produced by electrolysis of KUF5 or UF4, dissolved in a molten mixture of CaCl2 and NaCl. High-purity uranium can be prepared by the thermal decomposition of uranium halides on a hot filament. Uranium exhibits three crystallographic modifications as follows: α--688℃--→β--776℃--→γ Uranium is a heavy, silvery-white metal that is pyrophoric when finely divided. It is a little softer than steel, and is attacked by cold water in a finely divided state. It is malleable, ductile, and slightly paramagnetic. In air, the metal becomes coated with a layer of oxide. Acids dissolve the metal, but it is unaffected by alkalis. Uranium has twenty-three isotopes, one of which is an isomer and all of which are radioactive. Naturally occurring uranium contains 99.2745% by weight 238U, 0.720% 235U, and 0.0055% 234U. Studies show that the percentage weight of 235U in natural uranium varies by as much as 0.1%, depending on the source. The U.S.D.O.E. has adopted the value of 0.711 as being their “official” percentage of 235U in natural uranium. Natural uranium is sufficiently radioactive to expose a photographic plate in an hour or so. Much of the internal heat of the Earth is thought to be attributable to the presence of uranium and thorium. 238U, with a half-life of 4.46 × 109 years, has been used to estimate the age of igneous rocks. The origin of uranium, the highest member of the naturally occurring elements — except perhaps for traces of neptunium or plutonium — is not clearly understood, although it has been thought that uranium might be a decay product of elements of higher atomic weight, which may have once been present on Earth or elsewhere in the universe. These original elements may have been formed as a result of a primordial “creation,” known as “the big bang,” in a supernova, or in some other stellar processes. The fact that recent studies show that most trans-uranic elements are extremely rare with very short half-lives indicates that it may be necessary to find some alternative explanation for the very large quantities of radioactive uranium we find on Earth. Studies of meteorites from other parts of the solar system show a relatively low radioactive content, compared to terrestrial rocks. Uranium is of great importance as a nuclear fuel. U can be converted into fissionable plutonium by the following reactions: 238U(n,γ)→239U--β--→239Np--β--→239Pu
This nuclear conversion can be brought about in “breeder” reactors where it is possible to produce more new fissionable material than the fissionable material used in maintaining the chain reaction. 235U is of even greater importance, for it is the key to the utilization of uranium. 235U, while occurring in natural uranium to the extent of only 0.72%, is so fissionable with slow neutrons that a self-sustaining fission chain reaction can be made to occur in a reactor constructed from natural uranium and a suitable moderator, such as heavy water or graphite, alone. 235U can be concentrated by gaseous diffusion and other physical processes, if desired, and used directly as a nuclear fuel, instead of natural uranium, or used as an explosive. Natural uranium, slightly enriched with 235U by a small percentage, is used to fuel nuclear power reactors for the generation of electricity. Natural thorium can be irradiated with neutrons as follows to produce the important isotope 233U. 232Th(n,γ)→233Th--β--→233Pa--β--→233U While thorium itself is not fissionable, 233U is, and in this way may be used as a nuclear fuel. One pound of completely fissioned uranium has the fuel value of over 1500 tons of coal. The uses of nuclear fuels to generate electrical power, to make isotopes for peaceful purposes, and to make explosives are well known. The estimated world-wide production of the 437 nuclear power reactors in operation in 1998 amounted to about 352,000 megawatt hours. In 1998 the U.S. had about 107 commercial reactors with an output of about 100,000 megawatt-hours. Some nuclear-powered electric generating plants have recently been closed because of safety concerns. There are also serious problems with nuclear waste disposal that have not been completely resolved. Uranium in the U.S. is controlled by the U.S. Nuclear Regulatory Commission, under the Department of Energy. Uses are being found for the large quantities of “depleted” uranium now available, where uranium-235 has been lowered to about 0.2%. Depleted uranium has been used for inertial guidance devices, gyrocompasses, counterweights for aircraft control surfaces, ballast for missile reentry vehicles, and as a shielding material for tanks, etc. Concerns, however, have been raised over its low radioactive properties. Uranium metal is used for X-ray targets for production of high-energy X-rays. The nitrate has been used as photographic toner, and the acetate is used in analytical chemistry. Crystals of uranium nitrate are triboluminescent. Uranium salts have also been used for producing yellow “vase-line” glass and glazes. Uranium and its compounds are highly toxic, both from a chemical and radiological standpoint. Finely divided uranium metal, being pyrophoric, presents a fire hazard. The maximum permissible total body burden of natural uranium (based on radiotoxicity) is 0.2 μCi for soluble compounds. Recently, the natural presence of uranium and thorium in many soils has become of concern to homeowners because of the generation of radon and its daughters (see under Radon). Uranium metal is available commercially at a cost of about $6/g (99.7%) in air-tight glass under argon.


Labelled quinolone antibacterial.


235U in nuclear power reactors and nuclear weapons. Uranium depleted of 235U to manufacture of armor-piercing ammunition, in inertial guidance devices and gyro compasses, as a counterweight for missile reentry vehicles, as radiation shielding material, and x-ray targets.


Uranium is a white radioactive metallic element found in pitchblende ore, also known as uraninite. Uranyl chloride and uranyl nitrate are two uranium compounds used in photography.


The most common use of uranium is to convert the rare isotope U-235, which is naturallyfissionable, into plutonium through neutron capture. Plutonium, through controlled fission,is used in nuclear reactors to produce energy, heat, and electricity. Breeder reactors convertthe more abundant, but nonfissionable, uranium-238 into the more useful and fissionableplutonium-239, which can be used for the generation of electricity in nuclear power plants orto make nuclear weapons.
Although uranium forms compound with many nonmetallic elements, there is not muchuse for uranium outside the nuclear energy industry. Depleted uranium has had most of theU-235 removed from it through decay processes. It finds uses as armor-piercing antitankshells, ballast for missile reentry systems, glazes for ceramics, and shielding against radiation.An increasing concern is the possibility that terrorists can construct “dirty bombs” that useconventional explosives to spread “spent” radioactive materials that are still radioactive enoughto inflict harm to people exposed to the bomb’s blast and those downwind of the explosion,as well at to the environment.
Uranium-238 has a half-life of 4.468 billion years over which time it decays into stablelead-206. This process can be used to date ancient rocks by comparing the ratio of the isotopelead-206, the last isotope in the uranium decay series, to the level of uranium-238 inthe sample of rock to determine its age. This system has been used to date the oldest rockson Earth as being about 4.5 billion years old, which is about the time of the formation ofour planet.

Production Methods

Uranium is best known as a fuel for nuclear power plants. To prepare this fuel, uraniumores are processed to extract and enrich the uranium. The process begins by mining uraniumrichores and then crushing the rock. The ore is mixed with water and thickened to form aslurry. The slurry is treated with sulfuric acid and the product reacted with amines in a series ofreactions to give ammonium diuranate, (NH4)2U2O7. Ammonium diuranate is heated to yieldan enriched uranium oxide solid known as yellow cake. Yellow cake contains from 70–90%U3O8 in the form of a mixture of UO2 and UO3. The yellow cake is then shipped to a conversionplant where it can be enriched.
Natural uranium consists of different isotopes of uranium. Natural uranium is 0.7% U-235and 99.3% U-238. Uranium-238 is nonfissionable, and therefore naturally occurring uraniummust be enriched to a concentration of approximately 4% to be used as fuel for nuclearreactors or 90% for weapons-grade uranium. Yellow cake is shipped to conversion plants for enrichment. The process involves dissolving yellow cake in nitric acid to produce uranylnitrate hexahydrate, UO2(NO3)2?6H2O. The uranyl nitrate solution is purified and heatedto extract UO3, which is then reduced to UO2 with H2: UO3(s) + H2(g)→ UO2(s) + H2O(g).To enrich uranium, the solid uranium oxide is fluorinated to put it into a gaseous phase byreacting with hydrogen fluoride: UO2(s) + 4HF(g) → UF4(s) + 4H2O(g). Uranium tetrafluoride,UF4, is combined with fluorine gas to yield uranium hexafluoride, UF6: UF4(s) + F2(g) → UF6(g).Uranium hexafluoride is a white crystalline solid at standard temperature and pressure, butit sublimes to a gas at 57°C. The U-235 in uranium hexafluoride can be enriched by several methods based on the difference in masses of the uranium isotopes. Two common methodsare gaseous diffusion and gas centrifuge.


A toxic radioactive silvery element of the actinoid series of metals. Its three naturally occurring radioisotopes, 238U (99.283% in abundance), 235U (0.711%), and 234U (0.005%), are found in numerous minerals including the uranium oxides pitchblende, uraninite, and carnotite. The readily fissionable 235U is a major nuclear fuel and nuclear explosive, while 238U is a source of fissionable 239Pu. Symbol: U; m.p. 1132.5°C; b.p. 3745°C; r.d. 18.95 (20°C); p.n. 92; r.a.m. 238.0289.


uranium: Symbol U. A white radioactivemetallic element belonging to the actinoids; a.n. 92; r.a.m. 238.03;r.d. 19.05 (20°C); m.p. 1132±1°C; b.p.3818°C. It occurs as uraninite, fromwhich the metal is extracted by anion-exchange process. Three isotopesare found in nature: uranium–238(99.28%), uranium–235 (0.71%), anduranium–234 (0.006%). As uranium–235 undergoes nuclear fissionwith slow neutrons it is the fuel usedin nuclear reactors and nuclearweapons; uranium has therefore assumedenormous technical and politicalimportance since their invention.It was discovered by Martin Klaproth(1747–1817) in 1789.

General Description

A silver-gray radioactive metal. Radioactive materials emit ionizing radiation that can only be detected using special instruments. Exposure to intense levels of radiation or prolonged exposure to low levels is harmful. Film is also damaged by radiation.

Air & Water Reactions

Highly flammable. Ignites spontaneously in air.

Reactivity Profile

URANIUM is a reducing agent. Ignites spontaneously in air. Ignites in warm nitric oxide [Katz and Rabinowitch 1951]. Reacts with incandescence with hot selenium or with boiling sulfur [Mellor 12:31-2. 1946-47]. An explosion occurred when carbon tetrachloride was used to put out a fire involving a small amount of uranium [Allison 1970].


All compounds as well as metallic uranium are radioactive—some more so than others. Themain hazard from radioactive isotopes is radiation poisoning. Of course, another potentialhazard is using fissionable isotopes of uranium and plutonium for other than peaceful purposes,but such purposes involve political decisions, not science.

Health Hazard

Radiation presents minimal risk to transport workers, emergency response personnel and the public during transportation accidents. Packaging durability increases as potential hazard of radioactive content increases. Undamaged packages are safe. Contents of damaged packages may cause higher external radiation exposure, or both external and internal radiation exposure if contents are released. Low radiation hazard when material is inside container. If material is released from package or bulk container, hazard will vary from low to moderate. Level of hazard will depend on the type and amount of radioactivity, the kind of material it is in, and/or the surfaces it is on. Some material may be released from packages during accidents of moderate severity but risks to people are not great. Released radioactive materials or contaminated objects usually will be visible if packaging fails. Some exclusive use shipments of bulk and packaged materials will not have "RADIOACTIVE" labels. Placards, markings and shipping papers provide identification. Some packages may have a "RADIOACTIVE" label and a second hazard label. The second hazard is usually greater than the radiation hazard; so follow this GUIDE as well as the response GUIDE for the second hazard class label. Some radioactive materials cannot be detected by commonly available instruments. Runoff from control of cargo fire may cause low-level pollution.

Safety Profile

A highly toxic element on an acute basis. The permissible levels for soluble compounds are based on chemical toxicity, whereas the permissible body level for insoluble compounds is based on radiotoxicity. The high chemical toxicity of uranium and its salts is largely shown in kidney damage, which may not be reversible. Acute arterial lesions may occur after acute exposures. The most soluble uranium compounds are UF6, UO2(NO3)2, U02Cl2, UO2F2, and uranyl acetates, sulfates, and carbonates. Some moderately soluble compounds are UF4, UO2, UO4, (NH4)2 U2O7, UO3, and uranyl nitrates. The rapid passage of soluble uranium compounds through the body tends to allow relatively large amounts to be absorbed. Soluble uranium compounds may be absorbed through the skin. The least soluble compounds are high-F2ed UO2, U3O8, and uranium hydrides and carbides. The high toxicity effect of insoluble compounds is largely due to lung irradation by inhaled particles. This material is transferred from the lungs of animals quite slowly. A very dangerous fire hazard in the form of a solid or dust when exposed to heat or flame. It can react violently with air, Cl2, F2, HNO3, NOx Se, S, water, NH3, BrF3, trichloroethylene, nitryl fluoride. During storage it may form a pyrophoric surface due to effects of air and moisture. Depleted uranium (the 238U by-product of the uranium enrichment process, with relatively low radioactivity) is used in armor-piercing shells, ship or aircraft ballast, and counterbalances. Uranium is also used in making colored ceramic glazes.

Potential Exposure

The primary use of natural uranium is in nuclear energy as a fuel for nuclear reactors, in plutonium production, and as feeds for gaseous diffusion plants. It is also a source of radium salts. Uranium compounds are used in staining glass, glazing ceramics; and enameling; in photographic processes; for alloying steels; and as a catalyst for chemical reactions; radiation shielding; and aircraft counterweights. Uranium presents both chemical and radiation hazards, and exposures may occur during mining, processing of the ore, and production of uranium metal.


Smoking Interaction in Lung Cancer. Generally, exposure response curves for nonsmokers were linear for both respiratory cancer and “other respiratory disease”; cigarette smoking by both whites and nonwhites elevates and distorts the linearity and raises respiratory cancer/1000 person-years from 1.5 for nonsmokers at WLM of 2100 to 8.2 for those who smoked 1–19 cigarettes/ day and to 13 for those who smoked more than 20 a day for the same WLM of 2100.


UN2979 Uranium metal, pyrophoric, requires a shipping label of “RADIOACTIVE, SPONTANEOUSLY COMBUSTIBLE.” It falls in Hazard Class 7. UN2909 Radioactive material, excepted package-articles manufactured from natural uranium or depleted uranium or natural thorium, Hazard class: 7-Radioactive material; Labels: None. Uranyl nitrate, solid, requires a shipping label of “RADIOACTIVE, OXIDIZER.” It falls in Hazard Class 7. Uranyl nitrate hexahydrate solution, requires a shipping label of “CORROSIVE.” It falls in Hazard Class 7.


Uranium: Metal powder is radioactive, pyrophoric (ignites spontaneously in air), and a strong reducing agent. Keep away from chlorine, fluorine, nitric acid; nitric oxide; selenium, sulfur, carbon dioxide; carbon tetrachloride. Complete coverage of uranium metal scrap or turnings with oil is essential for prevention of fire.

Waste Disposal

Disposal of wastes containing uranium (uranium and compounds) should follow guidelines set forth by the nuclear regulatory commission. Contact the nuclear regulatory commission regarding disposal notification. Recovery for reprocessing is the preferred method. Processes are available for uranium recovery from process wastewaters and process scrap. Burial at an authorized radioactive burial site.



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