Information AboutUranium |
Uranium is a Chemical Element in the Periodic Table that has the symbol U and Atomic Number 92. Heavy, silvery-white, Metal lic, naturally Radioactive , Pyrophoric , toxic and Teratogenic , uranium belongs to the Actinide Series . Its isotopes 235U and to a lesser degree 233U are used as the fuel for Nuclear Reactor s and the explosive material for Nuclear Weapon s. Depleted Uranium is used in Incendiary Projectile Weapons . Uranium is commonly found in very small amounts in Rock s, Soil , Water , Plant s, and Animal s (including Human s). Notable characteristics When refined, uranium is a silvery white, weakly radioactive Metal , which is slightly softer than Steel . It is Malleable , Ductile , and slightly Paramagnetic . Uranium metal has very high Density , 65% more dense than Lead , but slightly less dense than Gold . When finely divided, it can react with cold water; in air, uranium metal becomes coated with uranium oxide. Uranium in ores can be extracted and chemically converted into Uranium Dioxide or other chemical forms usable in industry. Uranium metal has three Allotropic forms:
Its two principal isotopes are 235U and 238U . Naturally-occurring uranium also contains a small amount of the 234U isotope, which is a decay product of 238U. The isotope 235U or enriched uranium is important for both Nuclear Reactor s and Nuclear Weapon s because it is the only isotope existing in nature to any appreciable extent that is fissile, that is, fissionable by thermal Neutron s. The isotope 238U is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope 239Pu ( Plutonium ), which also is fissile. The artificial 233U isotope is also fissile and is made from Thorium-232 by Neutron bombardment. Uranium was the first element that was found to be fissile, i.e. upon bombardment with slow neutrons, its 235U isotope becomes the very short lived 236U, that immediately divides into two smaller nuclei, liberating energy and more neutrons. If these neutrons are absorbed by other 235U nuclei, a Nuclear Chain Reaction occurs and, if there is nothing to absorb some neutrons and slow the reaction, the reaction is explosive. The first atomic bomb worked by this principle ( Nuclear Fission ). A more accurate name for both this and the hydrogen bomb ( Nuclear Fusion ) would be "nuclear weapon", because only the nuclei participate. Applications Before Radiation was discovered, uranium was primarily used in small amounts for glass and pottery dyes (such as Uranium Glass and in Fiestaware ). After the discovery of uranium radiation, and especially after the discovery of Radium in uranium ores, these additional scientific and practical values of uranium were pursued. After the discovery in 1939 that it could undergo Nuclear Fission , uranium gained new importance on the world political scene as many scientists independently realized it could be used for Nuclear Power or even for weapons purposes. During the Manhattan Project , the wartime Allied program to develop the first Atomic Bomb s during World War II , the United States government bought up many reserves of uranium around the world and though the process of enriching it to applicable levels required gargantuan facilities (see Oak Ridge National Laboratory ). Eventually enough uranium, mainly from Democratic Republic of the Congo (Belgian Congo), was enriched for one atomic bomb, which was dropped on Hiroshima, Japan in 1945. The other nuclear weapons developed during the war used plutonium as their fissionable material, which itself requires uranium to produce. Initially it was believed that uranium was relatively rare, and that Nuclear Proliferation could be avoided by simply buying up all known uranium stocks, though within a decade large deposits of it were discovered in many places around the world. Enriched Uranium , which has been processed to have higher-than-natural levels of 235U, can be used for a variety of purposes relating to nuclear fission. Commercial Nuclear Power plants use fuel typically enriched to 2-3% 235U, though some reactor designs (such as the Candu reactors) can use Natural Uranium (unenriched, less than 1% 235U) fuel. Fuel used for United States Navy submarine reactors is typically highly enriched in 235U (the exact values are Classified Information ). In nuclear weapons uranium is also highly enriched, usually over 90% (again, the exact values are classified information) to a level known as "weapons grade". In a Breeder Reactor , 238U can also be converted into Plutonium . As uranium metal is very dense and heavy, Depleted Uranium (almost pure 238U with less than 0.2% 235U) is used by some Militaries as shielding to protect Tank s, and also in parts of Bullet s, Kinetic Energy Penetrator s and Missile s. It is additionally used in Helicopter s and Airplane s as counterweights on certain wing parts. Other uses include:
History The use of uranium, in its natural Oxide form, dates back to at least AD 79 , when it was used to add a yellow colour to Ceramic glazes (yellow glass with 1% uranium oxide was found near Naples , Italy ). When this was rediscovered, in the earlier part of the 19th century, the world’s only known source of uranium 'earths' were the old Hapsburg silver mines in Joachimsthal , Bohemia , and the local glassmaking industry kept a tight lid on the secret ingredient and its supply as long as it could. The Discovery of the element is credited to the German chemist Martin Heinrich Klaproth who in 1789 found uranium in a Mineral called Pitchblende . It was named after Uranus the planet , which had been discovered eight years earlier by William Herschel . It was first isolated as a Metal in 1841 by Eugene-Melchior Peligot . In 1850 the first commercial use of Uranium in glass was developed by Lloyd & Summerfield of Birmingham , England . Uranium was found to be Radioactive by French physicist Henri Becquerel in 1896 , who first discovered the process of radioactivity with uranium Mineral s. Codenames ''tuballoy'', ''depletalloy'' and ''oralloy'' During the Manhattan Project , the names ''tuballoy'' and ''oralloy'' were used to refer to natural uranium and enriched uranium respectively, originally for purposes of secrecy. These names are still used occasionally to refer to natural or enriched uranium. The names ''Q-metal'', ''depletalloy'', and ''D-38'', once applied to depleted uranium, have fallen into disuse. Bacterial Biochemistry It has been shown in some recent work at Manchester that Bacteria can reduce and fix uranium in Soil s. {Link without Title} Occurrence Uranium is a naturally occurring element found in low levels within all rock, soil, and water. This is the highest-numbered element to be found naturally in significant quantities on earth--- significant enough to have been utilized industrially since ancient times. It is considered to be more plentiful than Antimony , Beryllium , Cadmium , Gold , Mercury , Silver , or Tungsten and is about as abundant as Arsenic or Molybdenum . It is found in many minerals including Uraninite (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 Ore s (it is recovered commercially from these sources). The decay of uranium, convection, which in turn drives Plate Tectonics . Uranium ore is rock containing uranium mineralisation in concentrations that can be mined economically, typically 1 to 4 pounds of uranium oxide per ton or 0.05 to 0.20 percent uranium oxide. ''See also .'' Production and distribution See Also: Uranium Market Commercial-grade uranium can be produced through the Reduction of uranium Halide s with Alkali or Alkaline Earth Metal s. Uranium metal can also be made through Electrolysis of K U F 5 or UF4, dissolved in a molten CaCl2 and NaCl . Very pure uranium can be produced through the Thermal Decomposition of uranium halides on a hot filament. Owners and operators of U.S. civilian nuclear power reactors purchased from U.S. and foreign suppliers a total of 21,300 tons of uranium deliveries during 2001 . The average price paid was $26.39 per kilogram of uranium, a decrease of 16 percent compared with the 1998 price. In year 2001, the U.S. produced 1,018 tons of uranium from 7 mining operations, all of which are west of the Mississippi River . Uranium is distributed worldwide. Generally, large countries produce more uranium than smaller ones because the worldwide distribution of uranium is very roughly uniform. Canada is the world's largest producer of uranium, with the world's richest deposits in Saskatchewan . Saskatchewan, through three large mines in the Athabasca Basin region, produces over a quarter of the world's uranium. Because of this production, extra capacity, and the close government control of the industry the provincial government plays a central role in setting international uranium prices. Australia also has extensive uranium deposits making up approximately 40% of the world's known uranium reserves. The world's largest single uranium deposit is located at the Olympic Dam Mine in South Australia . [http://money.cnn.com/services/tickerheadlines/for5/200411231804DOWJONESDJONLINE000797_FORTUNE5.htm The ultimate supply of uranium is very large. It is estimated that for a ten times increase in price, the supply of uranium that can be economically mined is increased 300 times. See ''World Uranium Resources''.''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. Uranium exploration and mining The exploration and mining of radioactive ores in the United States began around the turn of the 20th Century . Sources for Radium (contained in uranium ore) were sought for use as luminous paint for watch dials and other instruments, as well as for health-related applications (some of which in retrospect were incredibly unhealthy). Because of the need for the element during World War II, the Manhattan Project contracted with numerous Vanadium mining companies in the American Southwest, and also purchased uranium ore from the Belgian Congo , through the Union Minière Du Haut Katanga , and in Canada from the Eldorado Mining And Refining Limited company, which had large stocks of uranium as waste from its Radium refining activities. American uranium ores mined in Colorado were primarily mixes of vanadium and uranium, but because of wartime secrecy the Manhattan Project would only publicly admit to purchasing the vanadium, and did not pay the uranium miners for the uranium ore (in a much later lawsuit, many miners were able to reclaim lost profits from the U.S. government). American uranium ores did not have nearly as high uranium concentrations as the ore from the Belgian Congo, but they were pursued vigorously to ensure nuclear self-sufficiency. Similar efforts were undertaken in the Soviet Union , which did not have native stocks of uranium when it started developing its own weapons program. Australia has the world's largest uranium reserves - 40 percent of the planet's known supply. Almost all the uranium is exported, but under strict International Atomic Energy Agency safeguards to satisfy the Australian people and government that none of the uranium is used in Nuclear Weapons . Australian uranium is used strictly for electricity production. The Olympic Dam operation run by BHP Billiton in South Australia is combined with mining of Copper , Gold , and Silver , and has reserves of global significance. There are three uranium mines in Australia, but more have been proposed. The most controversial was Jabiluka , to be built inside the World Heritage listed Kakadu National Park . The existing Ranger Uranium Mine is surrounded by the National Park as the mine area was not included in the original listing of the Park. In spite of Australia's huge reserves, Canada remains the largest exporter of uranium ore with mines located in Athabasca basin in northern Saskatchewan . Cameco , the world’s largest, low-cost uranium producer accounting for 18% of the world’s uranium production, operates 3 mines in the area. Rise, stagnation and renaissance of uranium mining In the beginning of the Cold War , to ensure adequate supplies of uranium for national defense, the United States Congress passed the U.S. Atomic Energy Act Of 1946 , creating the Atomic Energy Commission (AEC) which had the power to withdraw prospective uranium mining land from public purchase, and also to manipulate the price of uranium to meet national needs. By setting a high price for uranium ore, the AEC created a uranium "boom" in the early 1950s , which attracted many prospectors to the Four Corners Region of the country. Moab, Utah became known as the Uranium-capital of the world, when geologist Charles Steen discovered such an ore in 1952 , even though American ore sources were considerably less potent than those in the Belgian Congo or South Africa . At the height of the , these materials would potentially provide limitless source of energy. American military requirements declined in the as a result of industrial strains caused by the Energy Crisis , popular opposition, and finally the Three Mile Island nuclear accident in 1979 , all of which led to a ''de facto'' moratorium on the development of new nuclear reactor power stations. In Europe a mixed situation exists. Considerable nuclear power capacities have been developed, notably in Belgium , France , Germany , Spain , Sweden , Switzerland and the UK . In many countries development of Nuclear Power has been stopped by legal actions. In Italy the use of nuclear power has been barred by a Referendum in 1987 . In France and Switzerland the use of nuclear power continues, but there is little new demand that would stimulate the market for uranium. Since were higher, 43 US$/lb U3O8 is reported as the selling price for Australian uranium in 1978 by the Nuclear Information Centre . Uranium prices reached an all-time low in 2001, costing US$7/lb, but has since rebounded strongly. Uranium currently sells at US$37/lb and the price is rising fast. This is the highest price (adjusted for inflation et cetera) in more than 20 years {Link without Title} . The higher price has spurred new prospecting and reopening of old mines. Risks of uranium mining Because uranium ores emit in 1990. Compounds Uranium Tetrafluoride (UF4) is known as "green salt" and is an intermediate product in the production of uranium hexafluoride. Uranium Hexafluoride (UF6) is a white solid which forms a vapor at temperatures above 56 degrees Celsius. UF6 is the compound of uranium used for the two most common enrichment processes, Gaseous Diffusion enrichment and Gas Centrifuge enrichment. It is simply called "hex" in the industry. in a drum.]] , Uranyl Sulfate , Sodium Para-uranate , and Uranyl Peroxide , along with various Uranium Oxide s. Modern yellowcake typically contains 70 to 90 percent uranium oxide (U3O8) by weight. (Other uranium oxides, such as UO2 and UO3, exist; the most stable oxide, U3O8, is actually considered to be a 2:3 molar mixture of these.) Uranium Dioxide a black, crystalline powder, once used in the late 1800s to mid-1900s in ceramic glazes is now is used mainly as nuclear fuel, specifically in the form of fuel rods. Ammonium Diuranate is an intermediate product in the production of yellowcake, and is bright yellow in colour. Uranyl Nitrate (UO2(NO3)2) is an extraordinarily toxic, soluble uranium Salt . Uranium Rhodium Germanium (URhGe) is the first discovered alloy that becomes superconducting in the presence of an extremely strong electromagnetic field. Uranium Carbonate (UO2(CO3)) is found in both the mineral and organic fractions of coal and its fly ash and is the main component of uranium in mine tailing seepage water. ''See also .'' Combustion products : Isotopes Naturally occurring uranium is composed of three major Isotope s, 238U, 235U, and 234U, with 238U being the most abundant (99.3% Natural Abundance ). All three isotopes are Radioactive , creating Radioisotope s, with the most abundant and stable being 238U with a Half-life of 4.5 × 109 years, 235U with a half-life of 7 × 108 years, and 234U with a half-life of 2.5 × 105 years. 238U is an α emitter, Decaying into 206 Pb . Uranium isotopes can be separated to increase the concentration of one isotope relative to another. This process is called "enrichment" (see Enriched Uranium ). To be considered "enriched" the 235U fraction has to be increased to significantly greater than 0.711% (by weight) (typically to levels from 3% to 7%). 235U is typically the main fissile material for Nuclear Power reactors. Either 235U or 239Pu are used for making Nuclear Weapon s. The process produces huge quantities of uranium that is depleted of 235U and with a correspondingly increased fraction of 238U, called Depleted Uranium or "DU". To be considered "depleted", the 235U isotope concentration has to have been decreased to significantly less than 0.711% (by weight). Typically the amount of 235U left in depleted uranium is 0.2% to 0.3%. This represents anywhere from 28% to 42% of the original fraction of 235U. Given that the half life of 235U is considerably shorter than 238U, the "depleted" uranium is still significantly radioactive, as is the natural uranium after refining. Another way to look at this is as follows: Pressurised Heavy Water Reactor s (PHWR) use natural uranium (0.71% fissile material). From Pressurised Water Reactor s (PWRs) of typical design (most USA reactors are PWR) we note the fuel goes in with about 4% 235U and 96% 238U and comes out with about 1% 235U, 1% 239Pu and 95% 238U. If the 239Pu were removed (fuel reprocessing is not allowed in the USA) and this were added to the "depleted uranium" then we would have 1.2% fissile material in the reprocessed "depleted uranium" and at the same time have 1% fissile material in the left over "spent" fuel. Both of these would be considered "enriched" fuels for a PHWR style reactor. 233U, an artificial isotope, is used as a reactor fuel in India. It has also been used in atomic bombs. Precautions ''All isotopes and compounds of uranium are toxic, Teratogenic , and radioactive.'' In less than lethal doses toxicity is limited primarily to recoverable Kidney damage. Radiological effects are generally local because this is the nature of alpha radiation, the primary form from U-238 decay. Uranium compounds in general are poorly absorbed by the lining in the lungs and may remain a radiological hazard indefinitely. Uranyl (UO2+) ions, such as from Uranium Trioxide or uranyl nitrate and other hexavalent uranium compounds have been shown to cause birth defects and immune system damage in laboratory animals. Finely-divided uranium metal presents a fire hazard because uranium is Pyrophoric , so small grains will ignite spontaneously in air at room temperature. A person can be exposed to uranium by inhaling dust in air, or ingesting water and Food . The general population is exposed to uranium primarily through food and water; the average daily intake of uranium from food ranges from 0.07 to 1.1 micrograms per day. The amount of uranium in air is usually very small; however, people who live near government facilities that made or tested nuclear weapons, or facilities that mine or process uranium ore or enrich uranium for reactor fuel, may have increased exposure to uranium. Houses or structures which are over uranium deposits (either natural or man-made slag deposits) may have an increased incidence of exposure to Radon gas, a radioactive Carcinogen . Uranium can enter the body when it is inhaled or swallowed, or under rare circumstances it may enter through cuts in the Skin . Uranium does not absorb through the skin, and Alpha Particle s released by uranium cannot penetrate the skin, so uranium that is outside the body is much less harmful than it would be if it were inhaled or swallowed. When uranium enters the body it can lead to kidney damage. Uranium itself is not a chemical carcinogen. Uranium Mining carries the danger of airborne radioactive dust and the release of radioactive Radon gas and its Daughter Products (an added danger to the already dangerous activity of all Hard Rock Mining ). As a result, without proper Ventilation , uranium miners have a dramatically increased risk of later development of Lung Cancer and other Pulmonary diseases. There is also the possible danger of groundwater contamination with the toxic chemicals used in the separation of the uranium ore. See also
References
External links
|