Uranium (chemical element) Uranium (chemical element)
URANIUM (lat. Uranium), U (read "uranium"), a radioactive chemical element with atomic number 92, atomic mass 238.0289. Actinoid. Natural uranium is composed of a mixture of three isotopes: 238 U, 99.2739%, with a half-life T 1/2 = 4.51 10 9 years, 235 U, 0.7024%, half-life T 1/2 = 7.13 10 8 years, 234 U, 0.0057%, half-life T 1/2 = 2.45 10 5 years. 238 U (uranium-I, UI) and 235 U (actinuranium, AcU) are the ancestors of the radioactive series. Out of 11 artificially obtained radionuclides with mass numbers 227-240, long-lived 233 U ( T 1/2 = 1.62 10 5 years), it is obtained by neutron irradiation of thorium (cm. THORIUM).
Configuration of three outer electronic layers 5 s 2
p 6
d 10 f 3 6s 2
p 6
d 1 7 s 2
, uranium belongs to f-elements. It is located in the IIIB group in the 7th period of the periodic table of elements. In compounds, it exhibits oxidation states +2, +3, +4, +5 and +6, valencies II, III, IV, V and VI.
The radius of the neutral uranium atom is 0.156 nm, the ion radius is: U 3 + - 0.1024 nm, U 4 + - 0.089 nm, U 5 + - 0.088 nm and U 6+ - 0.083 nm. The energies of successive ionization of the atom are 6.19, 11.6, 19.8, 36.7 eV. Pauling electronegativity (cm. POLING Linus) 1,22.
Discovery history
Uranium was discovered in 1789 by the German chemist M.G. Klaproth (cm. KLAPROT Martin Heinrich) in the study of the mineral "resin blende". It was named after the planet Uranus, discovered by W. Herschel (cm. GERSHEL) in 1781. Uranium was obtained in the metallic state in 1841 by the French chemist E. Peligot (cm. PELIGO Eugene Melkjor) in the reduction of UCl 4 with metallic potassium. The radioactive properties of uranium were discovered in 1896 by the Frenchman A. Becquerel (cm. BECQUEREL Antoine Henri).
Initially, the atomic mass of 116 was attributed to uranium, but in 1871 D.I. Mendeleev (cm. MENDELEEV Dmitry Ivanovich) came to the conclusion that it should be doubled. After the discovery of elements with atomic numbers from 90 to 103, the American chemist G. Seaborg (cm. SEABORG Glenn Theodore) came to the conclusion that these elements (actinides) (cm. ACTINOIDS) it is more correct to place it in the periodic table in the same cell with element number 89 actinium. This arrangement is due to the fact that the actinides are completed 5 f-elector sublevel.
Being in nature
Uranium is a characteristic element for the granite layer and the sedimentary shell of the earth's crust. Content in the earth's crust is 2.5 · 10 -4% by weight. In seawater, the concentration of uranium is less than 10 -9 g / l; in total, seawater contains from 10 9 to 10 10 tons of uranium. Free uranium is not found in the earth's crust. About 100 uranium minerals are known, the most important of which are pitchblende U 3 O 8, uraninite (cm. URANINITE)(U, Th) O 2, uranium resin ore (contains uranium oxides of variable composition) and tyuyamunite Ca [(UO 2) 2 (VO 4) 2] · 8H 2 O.
Receiving
Uranium is obtained from uranium ores containing 0.05-0.5% U. Uranium extraction begins with obtaining a concentrate. Ores are leached with solutions of sulfuric, nitric acids or alkali. The resulting solution always contains impurities of other metals. When separating uranium from them, differences in their redox properties are used. Redox processes are combined with the processes of ion exchange and extraction.
From the resulting solution, uranium is extracted in the form of oxide or tetrafluoride UF 4, using the metallothermy method:
UF 4 + 2Mg = 2MgF 2 + U
The resulting uranium contains trace amounts of boron impurities. (cm. Boron (chemical element)),
cadmium (cm. CADMIUM) and some other elements, the so-called reactor poisons. By absorbing the neutrons generated during the operation of a nuclear reactor, they make uranium unsuitable for use as a nuclear fuel.
To get rid of impurities, uranium metal is dissolved in nitric acid to obtain uranyl nitrate UO 2 (NO 3) 2. Uranyl nitrate is extracted from an aqueous solution with tributyl phosphate. The purification product from the extract is again converted into uranium oxide or tetrafluoride, from which the metal is again obtained.
Part of the uranium is obtained by regenerating the spent nuclear fuel in the reactor. All uranium regeneration operations are carried out remotely.
Physical and chemical properties
Uranium is a silvery white shiny metal. Uranium metal exists in three allotropic (cm. ALLOTROPY) modifications. Up to 669 ° C stable a-modification with orthorhombic lattice, parameters a= 0.2854nm, v= 0.5869 nm and with= 0.4956 nm, density 19.12 kg / dm 3. From 669 ° C to 776 ° C stable b-modification with tetragonal lattice (parameters a= 1.0758 nm, with= 0.5656 nm). Up to a melting point of 1135 ° C, the g-modification with a cubic body-centered lattice ( a= 0.3525 nm). Evaporating temperature 4200 ° C.
The chemical activity of uranium metal is high. In air, it becomes covered with an oxide film. Powdered uranium is pyrophoric; during the combustion of uranium and the thermal decomposition of many of its compounds in air, uranium oxide U 3 O 8 is formed. If this oxide is heated in a hydrogen atmosphere (cm. HYDROGEN) at temperatures above 500 ° C, uranium dioxide UO 2 is formed:
U 3 O 8 + H 2 = 3UO 2 + 2H 2 O
If uranyl nitrate UO 2 (NO 3) 2 is heated at 500 ° C, then, decomposing, it forms uranium trioxide UO 3. In addition to uranium oxides of stoichiometric composition UO 2, UO 3 and U 3 O 8, uranium oxide with the composition U 4 O 9 and several metastable oxides and oxides of variable composition are known.
When uranium oxides are fused with oxides of other metals, uranates are formed: K 2 UO 4 (potassium uranate), CaUO 4 (calcium uranate), Na 2 U 2 O 7 (sodium diuranate).
Interacting with halogens (cm. HALOGENS), uranium gives uranium halides. Among them, hexafluoride UF 6 is a yellow crystalline substance that readily sublimates even at low heating (40-60 ° C) and is just as easily hydrolyzed with water. Uranium hexafluoride UF 6 is of the most practical importance. It is obtained by the interaction of uranium metal, uranium oxides or UF 4 with fluorine or fluorinating agents BrF 3, СCl 3 F (freon-11) or CCl 2 F 2 (freon-12):
U 3 O 8 + 6CCl 2 F 2 = UF 4 + 3COCl 2 + CCl 4 + Cl 2
UF 4 + F 2 = UF 6
or
U 3 O 8 + 9F 2 = 3UF 6 + 4O 2
Fluorides and chlorides are known that correspond to the oxidation states of uranium +3, +4, +5, and +6. Uranium bromides UBr 3, UBr 4, and UBr 5 were obtained, as well as uranium iodides UI 3 and UI 4. Uranium oxyhalides such as UO 2 Cl 2 UOCl 2 and others have been synthesized.
When uranium interacts with hydrogen, uranium hydride UH 3 is formed, which has high chemical activity. When heated, the hydride decomposes to form hydrogen and powdered uranium. During sintering of uranium with boron, borides UB 2, UB 4 and UB 12 arise, depending on the molar ratio of the reactants and the process conditions.
With carbon (cm. CARBON) uranium forms three carbides UC, U 2 C 3 and UC 2.
Interaction of uranium with silicon (cm. SILICON) silicides U 3 Si, U 3 Si 2, USi, U 3 Si 5, USi 2 and U 3 Si 2 were obtained.
Uranium nitrides (UN, UN 2, U 2 N 3) and uranium phosphides (UP, U 3 P 4, UP 2) were obtained. With gray (cm. SULFUR) uranium forms a series of sulfides: U 3 S 5, US, US 2, US 3 and U 2 S 3.
Uranium metal dissolves in HCl and HNO 3, slowly reacts with H 2 SO 4 and H 3 PO 4. There are salts containing the uranyl cation UO 2 2+.
In aqueous solutions, uranium compounds exist in oxidation states from +3 to +6. The standard oxidation potential of the U (IV) / U (III) pair is 0.52 V, the U (V) / U (IV) pair 0.38 V, the U (VI) / U (V) pair 0.17 V, the pair U (VI) / U (IV) 0.27. The U 3+ ion is unstable in solution, the U 4+ ion is stable in the absence of air. The UO 2 + cation is unstable and in solution disproportionates to U 4+ and UO 2 2+. U 3+ ions have a characteristic red color, U 4+ ions - green, UO 2 2+ ions - yellow.
In solutions, uranium compounds are most stable in the +6 oxidation state. All uranium compounds in solutions are prone to hydrolysis and complexation, most strongly - cations U 4+ and UO 2 2+.
Application
Uranium metal and its compounds are used mainly as nuclear fuel in nuclear reactors. A low-enriched mixture of uranium isotopes is used in stationary reactors of nuclear power plants. Highly enriched product - in nuclear reactors operating on fast neutrons. 235 U is the source of nuclear energy in nuclear weapons. 238 U serves as a source of secondary nuclear fuel - plutonium.
Physiological action
In micro amounts (10 -5 -10 -8%) it is found in tissues of plants, animals and humans. Mostly accumulated by some fungi and algae. Uranium compounds are absorbed in the gastrointestinal tract (about 1%), in the lungs - 50%. The main depots in the body: spleen, kidneys, skeleton, liver, lungs and broncho-pulmonary lymph nodes. Content in organs and tissues of humans and animals does not exceed 10 -7 years.
Uranium and its compounds are highly toxic. Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds the maximum permissible concentration in the air is 0.015 mg / m 3, for insoluble forms of uranium the maximum permissible concentration is 0.075 mg / m 3. When it enters the body, uranium acts on all organs, being a general cellular poison. The molecular mechanism of action of uranium is associated with its ability to suppress enzyme activity. First of all, the kidneys are affected (protein and sugar appear in the urine, oliguria). With chronic intoxication, disorders of the hematopoiesis and nervous system are possible.
encyclopedic Dictionary. 2009 .
U (Uran, uranium; at O = 16 atomic weight U = 240) the element with the highest atomic weight; all the elements, by atomic weight, are placed between hydrogen and uranium. This is the hardest member of the metal subgroup VI of group of the periodic system (see Chromium, ... ... Encyclopedic Dictionary of F.A. Brockhaus and I.A. Efron
Uranium (U) Atomic number 92 Appearance of a simple substance Properties of an atom Atomic mass (molar mass) 238.0289 a. e. m. (g / mol) ... Wikipedia
Uranium (lat. Uranium), U, a radioactive chemical element of the III group of the periodic system of Mendeleev, belongs to the actinide family, atomic number 92, atomic mass 238.029; metal. Natural urea consists of a mixture of three isotopes: 238U √ 99.2739% ... ... Great Soviet Encyclopedia
Uranium (chemical element)- Uranium (Uranium), U, a radioactive chemical element of the III group of the periodic system, atomic number 92, atomic mass 238.0289; refers to actinides; metal, tp 1135 ° C. Uranium is the main element of nuclear energy (nuclear fuel), it is used in ... ... The Illustrated Encyclopedic Dictionary Wikipedia
- (Greek uranos sky). 1) the god of the sky, the father of Saturn, the oldest of the gods, in Greek. mythol. 2) a rare metal, which in its pure state has the appearance of silvery leaves. 3) a large planet discovered by Herschel in 1781. Dictionary of foreign words included in ... ... Dictionary of foreign words of the Russian language
Uranus: * Uranus (mythology) is an ancient Greek god. Son of Gaia * Uranus (planet) planet of the solar system * Uranus (musical instrument) ancient Turkic and Kazakh musical wind instrument * Uranus (element) chemical element * Operation ... ... Wikipedia
- (Uranium), U, a radioactive chemical element of the III group of the periodic table, atomic number 92, atomic mass 238.0289; refers to actinides; metal, tp 1135shC. Uranium is the main element of nuclear energy (nuclear fuel), it is used in ... ... Modern encyclopedia
| U | 92 |
| 238,0289 | |
| 5f 3 6d 1 7s 2 | |
| Uranus | |
Uranus(old name Uranium) - chemical element with atomic number 92 in the periodic table, atomic mass 238.029; denoted by the symbol U ( Uranium) belongs to the actinide family.
Even in ancient times (1st century BC), natural uranium oxide was used to make yellow glaze for ceramics. Research into uranium has evolved like the chain reaction it generates. At first, information about its properties, like the first impulses of a chain reaction, came with long interruptions, from case to case. The first important date in the history of uranium is 1789, when the German natural philosopher and chemist Martin Heinrich Klaproth reduced the golden-yellow "earth" extracted from the Saxon resin ore to a black metal-like substance. In honor of the most distant planet known then (discovered by Herschel eight years earlier), Klaproth, considering the new substance an element, called it uranium.
For fifty years, Klaproth's uranium was considered a metal. Only in 1841, Eugene Melchior Peligot - French chemist (1811-1890)] proved that, despite its characteristic metallic luster, Klaproth's uranium is not an element, but an oxide UO 2... In 1840, Peligo managed to obtain real uranium, a heavy metal of steel-gray color, and to determine its atomic weight. The next important step in the study of uranium was made in 1874 by DI Mendeleev. Based on the periodic system he developed, he placed uranium in the farthest cell of his table. Previously, the atomic weight of uranium was considered equal to 120. The great chemist doubled this value. After 12 years, Mendeleev's foresight was confirmed by the experiments of the German chemist Zimmermann.
The study of uranium began in 1896: the French chemist Antoine Henri Becquerel accidentally discovered the Becquerel Rays, which Marie Curie later renamed radioactivity. At the same time, the French chemist Henri Moissant managed to develop a method for obtaining pure metallic uranium. In 1899, Rutherford discovered that the radiation of uranium preparations is inhomogeneous, that there are two types of radiation - alpha and beta rays. They carry different electrical charges; their range in matter and ionizing ability are far from the same. A little later, in May 1900, Paul Villard discovered a third type of radiation - gamma rays.
Ernest Rutherford carried out in 1907 the first experiments to determine the age of minerals in the study of radioactive uranium and thorium on the basis of the theory of radioactivity that he created jointly with Frederick Soddy (Soddy, Frederick, 1877-1956; Nobel Prize in Chemistry, 1921). In 1913 F. Soddy introduced the concept of isotopes(from the Greek ισος - "equal", "the same", and τόπος - "place"), and in 1920 predicted that isotopes can be used to determine the geological age of rocks. In 1928, Niggot implemented, and in 1939 A.O.K. Nier (Nier, Alfred Otto Carl, 1911 - 1994) created the first equations for calculating age and used a mass spectrometer for isotope separation.
In 1939, Frederic Joliot-Curie and German physicists Otto Frisch and Lisa Meitner discovered an unknown phenomenon that occurs with the uranium nucleus when it is irradiated with neutrons. An explosive destruction of this nucleus took place with the formation of new elements much lighter than uranium. This destruction was of an explosive nature, fragments of products scattered in different directions at tremendous speeds. Thus, a phenomenon called a nuclear reaction was discovered.
In 1939-1940. Yu. B. Khariton and Ya. B. Zel'dovich were the first to theoretically show that with a small enrichment of natural uranium with uranium-235, conditions can be created for the continuous fission of atomic nuclei, that is, to give the process a chain character.
Uraninite ore
Uranium is widespread in nature. The clarke of uranium is 1 · 10 -3% (wt.). The amount of uranium in the 20 km thick layer of the lithosphere is estimated at 1.3 · 10 14 tons.
The bulk of uranium is found in acidic rocks with a high silicon... A significant mass of uranium is concentrated in sedimentary rocks, especially those enriched in organic matter. Uranium is present in large quantities as an impurity in thorium and rare earth minerals (orthite, sphene CaTiO 3, monazite (La, Ce) PO 4, zircon ZrSiO 4, xenotime YPO4, etc.). The most important uranium ores are pitchblende (uranium pitch), uraninite and carnotite. The main minerals - satellites of uranium are molybdenite MoS 2, galena PbS, quartz SiO 2, calcite CaCO 3, hydromuscovite, etc.
| Mineral | The main composition of the mineral | Uranium content,% |
|---|---|---|
| Uraninite | UO 2, UO 3 + ThO 2, CeO 2 | 65-74 |
| Carnotite | K 2 (UO 2) 2 (VO 4) 2 2H 2 O | ~50 |
| Casolite | PbO 2 UO 3 SiO 2 H 2 O | ~40 |
| Samarskite | (Y, Er, Ce, U, Ca, Fe, Pb, Th) (Nb, Ta, Ti, Sn) 2 O 6 | 3.15-14 |
| Brannerite | (U, Ca, Fe, Y, Th) 3 Ti 5 O 15 | 40 |
| Tuyamunit | CaO 2UO 3 V 2 O 5 nH 2 O | 50-60 |
| Zeinerite | Cu (UO 2) 2 (AsO 4) 2 nH 2 O | 50-53 |
| Otenit | Ca (UO 2) 2 (PO 4) 2 nH 2 O | ~50 |
| Schreckingerite | Ca 3 NaUO 2 (CO 3) 3 SO 4 (OH) 9H 2 O | 25 |
| Uranofan | CaO UO 2 2SiO 2 6H 2 O | ~57 |
| Fergusonite | (Y, Ce) (Fe, U) (Nb, Ta) O 4 | 0.2-8 |
| Thorburnite | Cu (UO 2) 2 (PO 4) 2 nH 2 O | ~50 |
| Coffinite | U (SiO 4) 1-x (OH) 4x | ~50 |
The main forms of uranium occurrence in nature are uraninite, pitchblende (uranium pitch) and uranium black. They differ only in the forms of finding; there is an age dependence: uraninite is present mainly in ancient (Precambrian rocks), pitchblende - volcanogenic and hydrothermal - mainly in Paleozoic and younger high- and medium-temperature formations; uranium blacks - mainly in young - Cenozoic and younger formations - mainly in low-temperature sedimentary rocks.
The content of uranium in the earth's crust is 0.003%; it is found in the surface layer of the earth in the form of four types of deposits. First, these are veins of uraninite, or uranium resin (uranium dioxide UO2), very rich in uranium, but rarely found. They are accompanied by radium deposits, since radium is a direct product of the isotopic decay of uranium. Such veins are found in Zaire, Canada (Big Bear Lake), Czech Republic and France... The second source of uranium is conglomerates of thorium and uranium ore, together with ores of other important minerals. Conglomerates usually contain sufficient amounts of gold and silver, and uranium and thorium become accompanying elements. Large deposits of these ores are located in Canada, South Africa, Russia and Australia. The third source of uranium is sedimentary rocks and sandstones rich in the mineral carnotite (potassium uranyl vanadate), which contains, in addition to uranium, a significant amount vanadium and other elements. Such ores are found in the western states. USA... Iron uranium shale and phosphate ores constitute the fourth source of sediment. Rich deposits found in shales Sweden... Some phosphate ores in Morocco and the United States contain significant amounts of uranium, and phosphate deposits in Angola and the Central African Republic are even richer in uranium. Most lignites and some coals usually contain uranium impurities. Uranium-rich lignite deposits found in North and South Dakota (USA) and bituminous coals Spain and Czech Republic
Natural uranium consists of a mixture of three isotopes: 238 U - 99.2739% (half-life T 1/2 = 4.468 × 10 9 years), 235 U - 0.7024% ( T 1/2 = 7.038 × 10 8 years) and 234 U - 0.0057% ( T 1/2 = 2.455 × 10 5 years). The latter isotope is not primary, but radiogenic; it is part of the 238 U radioactive series.
The radioactivity of natural uranium is mainly due to the isotopes 238 U and 234 U, in equilibrium their specific activities are equal. The specific activity of the 235 U isotope in natural uranium is 21 times less than the activity of 238 U.
There are 11 known artificial radioactive isotopes of uranium with mass numbers from 227 to 240. The longest-lived of them is 233 U ( T 1/2 = 1.62 × 10 5 years) is obtained by irradiating thorium with neutrons and is capable of spontaneous fission by thermal neutrons.
Uranium isotopes 238 U and 235 U are the ancestors of two radioactive series. The finite elements of these series are isotopes lead 206 Pb and 207 Pb.
In natural conditions, isotopes are prevalent mainly 234 U: 235 U : 238 U= 0.0054: 0.711: 99.283. Half of the radioactivity of natural uranium is due to the isotope 234 U... Isotope 234 U formed by decay 238 U... For the latter two, in contrast to other pairs of isotopes and regardless of the high migratory capacity of uranium, the geographic constancy of the ratio is characteristic. The magnitude of this ratio depends on the age of the uranium. Numerous field measurements showed insignificant fluctuations. So in rolls, the value of this ratio relative to the standard varies within the range of 0.9959 -1.0042, in salts - 0.996 - 1.005. In uranium-containing minerals (pitchblende, uranium black, cirtolite, rare earth ores), the value of this ratio ranges from 137.30 to 138.51; moreover, the difference between the forms U IV and U VI has not been established; in sphene - 138.4. In some meteorites, a deficiency of the isotope was revealed 235 U... Its lowest concentration in terrestrial conditions was found in 1972 by the French explorer Boujigues in the town of Oklo in Africa (a deposit in Gabon). Thus, normal uranium contains 0.7025% of uranium 235 U, while in Oklo it decreases to 0.557%. This confirmed the hypothesis of the presence of a natural nuclear reactor leading to isotope burnup predicted by George W. Wetherill of the University of California at Los Angeles and Mark G. Inghram of the University of Chicago and Paul K. Kuroda), a chemist at the University of Arkansas, who described the process back in 1956. In addition, natural nuclear reactors were found in the same districts: Okelobondo, Bangombe, etc. At present, about 17 natural nuclear reactors are known.
The very first stage of uranium production is concentration. The rock is crushed and mixed with water. Heavy suspension components settle faster. If the rock contains primary uranium minerals, then they precipitate quickly: these are heavy minerals. Secondary uranium minerals are lighter; in this case, heavy waste rock settles earlier. (However, it is far from always really empty; it can contain many useful elements, including uranium).
The next stage is leaching of concentrates, transferring uranium into solution. Acid and alkaline leaching is used. The first is cheaper, since sulfuric acid is used to extract uranium. But if in the feedstock, as, for example, in uranium tar, uranium is in a tetravalent state, then this method is inapplicable: tetravalent uranium practically does not dissolve in sulfuric acid. In this case, one must either resort to alkaline leaching, or pre-oxidize uranium to a hexavalent state.
Acid leaching is also not used if the uranium concentrate contains dolomite or magnesite that react with sulfuric acid. In these cases, use caustic soda (hydroxide sodium).
Oxygen flushing solves the problem of uranium leaching from ores. A stream of oxygen is fed into a mixture of uranium ore with sulfide minerals heated to 150 ° C. In this case, sulfuric acid is formed from sulfurous minerals, which washes out uranium.
At the next stage, uranium must be selectively separated from the resulting solution. Modern methods - extraction and ion exchange - solve this problem.
The solution contains not only uranium, but also other cations. Some of them under certain conditions behave in the same way as uranium: they are extracted with the same organic solvents, settle on the same ion-exchange resins, and precipitate under the same conditions. Therefore, for the selective separation of uranium, it is necessary to use many redox reactions in order to get rid of one or another undesirable companion at each stage. On modern ion-exchange resins, uranium is released very selectively.
Methods ion exchange and extraction They are also good in that they allow enough to completely extract uranium from poor solutions (the uranium content is tenths of a gram per liter).
After these operations, uranium is converted into a solid state - into one of the oxides or into UF 4 tetrafluoride. But this uranium still needs to be cleaned of impurities with a large thermal neutron capture cross section - bora, cadmium, hafnium. Their content in the final product should not exceed one hundred thousandths and millionths of a percent. To remove these impurities, a commercially pure uranium compound is dissolved in nitric acid. In this case, uranyl nitrate UO 2 (NO 3) 2 is formed, which, upon extraction with tributyl phosphate and some other substances, is additionally purified to the required conditions. Then this substance is crystallized (or peroxide UO 4 · 2H 2 O is precipitated) and cautiously ignited. As a result of this operation, uranium trioxide UO 3 is formed, which is reduced with hydrogen to UO 2.
Uranium dioxide UO 2 at a temperature of 430 to 600 ° C is exposed to dry hydrogen fluoride to obtain tetrafluoride UF 4. Uranium metal is reduced from this compound using calcium or magnesium.
Uranium is a very heavy, silvery-white, shiny metal. In its pure form, it is slightly softer than steel, malleable, flexible, and has slight paramagnetic properties. Uranus has three allotropic forms: alpha (prismatic, stable up to 667.7 ° C), beta (quadrangular, stable from 667.7 ° C to 774.8 ° C), gamma (with a body-centered cubic structure existing from 774, 8 ° C to melting point).
Radioactive properties of some isotopes of uranium (natural isotopes are identified):
Uranium can exhibit oxidation states from + III to + VI. Uranium (III) compounds form unstable red solutions and are strong reducing agents:
4UCl 3 + 2H 2 O → 3UCl 4 + UO 2 + H 2
Uranium (IV) compounds are the most stable and form green aqueous solutions.
Uranium (V) compounds are unstable and easily disproportionate in aqueous solution:
2UO 2 Cl → UO 2 Cl 2 + UO 2
Chemically, uranium is a very active metal. It quickly oxidizes in air and becomes covered with an iridescent oxide film. Fine uranium powder ignites spontaneously in air, it ignites at a temperature of 150-175 ° C, forming U 3 O 8. At 1000 ° C, uranium combines with nitrogen to form yellow uranium nitride. Water is capable of corroding metal, slowly at low temperatures, and quickly at high temperatures, as well as when finely ground uranium powder. Uranium dissolves in hydrochloric, nitric and other acids, forming tetravalent salts, but does not interact with alkalis. Uranus displaces hydrogen from inorganic acids and saline solutions of metals such as Mercury, silver, copper, tin, platinumandgold... When shaken vigorously, uranium metal particles begin to glow. Uranium has four oxidation states - III-VI. Hexavalent compounds include uranium trioxide (uranyl oxide) UO 3 and uranyl uranium chloride UO 2 Cl 2. Uranium tetrachloride UCl 4 and uranium dioxide UO 2 are examples of tetravalent uranium. Substances containing tetravalent uranium are usually unstable and become hexavalent upon prolonged exposure to air. Uranyl salts such as uranyl chloride decompose in the presence of bright light or organics.
The greatest application is isotope uranium 235 U, in which a self-sustaining nuclear chain reaction is possible. Therefore, this isotope is used as fuel in nuclear reactors, as well as in nuclear weapons. The separation of the U 235 isotope from natural uranium is a complex technological problem (see isotope separation).
The isotope U 238 is capable of fission under the influence of bombardment with high-energy neutrons, this feature is used to increase the power of thermonuclear weapons (neutrons generated by a thermonuclear reaction are used).
As a result of the capture of a neutron with the subsequent β-decay, 238 U can be converted into 239 Pu, which is then used as a nuclear fuel.
Uranium-233, artificially obtained in reactors from thorium (thorium-232 captures a neutron and turns into thorium-233, which decays into protactinium-233 and then into uranium-233), may in the future become a widespread nuclear fuel for nuclear power plants (already now there are reactors using this nuclide as fuel, for example KAMINI in India) and the production of atomic bombs (critical mass about 16 kg).
Uranium-233 is also the most promising fuel for gas-phase nuclear rocket engines.
The main industry of uranium use is the determination of the age of minerals and rocks in order to determine the sequence of the course of geological processes. This is done by Geochronology and Theoretical Geochronology. The solution of the problem of mixing and sources of matter is also of great importance.
The solution to the problem is based on the equations of radioactive decay described by equations.
where 238 U o, 235 U o- modern concentrations of uranium isotopes; ; - decay constants atoms respectively of uranium 238 U and 235 U.
Their combination is very important:
.Due to the fact that rocks contain different concentrations of uranium, they have different radioactivity. This property is used in the selection of rocks by geophysical methods. This method is most widely used in petroleum geology for geophysical studies of wells, this complex includes, in particular, γ-logging or neutron gamma-ray logging, gamma-gamma ray logging, etc. With their help, reservoirs and seals are identified.
A small amount of uranium imparts a beautiful yellow-green fluorescence to the glass (Uranium glass).
Sodium uranate Na 2 U 2 O 7 was used as a yellow pigment in painting.
Uranium compounds were used as paints for painting on porcelain and for ceramic glazes and enamels (they are painted in colors: yellow, brown, green and black, depending on the oxidation state).
Some uranium compounds are photosensitive.
At the beginning of the 20th century uranyl nitrate It was widely used for enhancing negatives and coloring (toning) positives (photographic prints) in brown.
Uranium-235 carbide in an alloy with niobium carbide and zirconium carbide is used as a fuel for nuclear jet engines (the working fluid is hydrogen + hexane).
Alloys of iron and depleted uranium (uranium-238) are used as powerful magnetostrictive materials.
Depleted uranium
After the extraction of 235 U and 234 U from natural uranium, the remaining material (uranium-238) is called "depleted uranium", since it is depleted in the 235th isotope. According to some reports, about 560,000 tons of depleted uranium hexafluoride (UF 6) are stored in the United States.
Depleted uranium is two times less radioactive than natural uranium, mainly due to the removal of 234 U from it. Due to the fact that the main use of uranium is energy production, depleted uranium is a product of little use with low economic value.
Basically, its use is associated with the high density of uranium and its relatively low cost. Depleted uranium is used for radiation protection (oddly enough) and as ballast mass in aerospace applications such as aircraft steering surfaces. Each Boeing 747 contains 1,500 kg of depleted uranium for this purpose. This material is also used in high-speed gyro rotors, large flywheels, as ballast in space descent vehicles and racing yachts, when drilling oil wells.
The tip (insert) of a 30 mm projectile (GAU-8 cannon of the A-10 aircraft) with a diameter of about 20 mm made of depleted uranium.
The most famous use of depleted uranium is as cores for armor-piercing projectiles. When alloyed with 2% Mo or 0.75% Ti and heat treatment (quick quenching of metal heated to 850 ° C in water or oil, further holding at 450 ° C for 5 hours), uranium metal becomes harder and stronger than steel (tensile strength is higher 1600 MPa, despite the fact that for pure uranium it is equal to 450 MPa). Combined with its high density, this makes the hardened uranium ingot an extremely effective armor penetration tool, similar in efficiency to more expensive tungsten. The heavy uranium tip also alters the mass distribution of the projectile, improving its aerodynamic stability.
Similar alloys of the "Stabil" type are used in arrow-shaped, feathered shells of tank and anti-tank artillery guns.
The process of destruction of armor is accompanied by grinding a uranium blank into dust and igniting it in air on the other side of the armor (see Pyrophoricity). About 300 tons of depleted uranium remained on the battlefield during Operation Desert Storm (mostly the remains of shells from the 30mm GAU-8 cannon of the A-10 assault aircraft, each shell containing 272 g of uranium alloy).
Such shells were used by NATO troops in hostilities on the territory of Yugoslavia. After their application, the environmental problem of radiation pollution of the country's territory was discussed.
For the first time, uranium was used as a core for projectiles in the Third Reich.
Depleted uranium is used in modern tank armor such as the M-1 Abrams tank.
It is found in trace amounts (10 -5 -10 -8%) in tissues of plants, animals and humans. Mostly accumulated by some fungi and algae. Uranium compounds are absorbed in the gastrointestinal tract (about 1%), in the lungs - 50%. The main depots in the body: spleen, kidneys, skeleton, liver, lungs and broncho-pulmonary lymph nodes. The content in organs and tissues of humans and animals does not exceed 10 −7 g.
Uranus and its compounds toxic... Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds the maximum permissible concentration in the air is 0.015 mg / m³, for insoluble forms of uranium the maximum permissible concentration is 0.075 mg / m³. When it enters the body, uranium acts on all organs, being a general cellular poison. The molecular mechanism of action of uranium is associated with its ability to suppress enzyme activity. First of all, the kidneys are affected (protein and sugar appear in the urine, oliguria). With chronic intoxication, disorders of the hematopoiesis and nervous system are possible.
Production by countries in tonnes of U content for 2005-2006.
Production by company in 2006:
Cameco - 8.1 thousand tons
Rio Tinto - 7 thousand tons
AREVA - 5 thousand tons
Kazatomprom - 3.8 thousand tons
TVEL OJSC - 3.5 thousand tons
BHP Billiton - 3 thousand tons
Navoi MMC - 2.1 thousand tons ( Uzbekistan, Navoi)
Uranium One - 1,000 tons
Heathgate - 0.8 thousand tons
Denison Mines - 0.5 thousand tons
In the USSR, the main uranium ore regions were Ukraine (the Zheltorechenskoye, Pervomayskoye, etc.), Kazakhstan (North - Balkashinskoye ore field, etc.; South - Kyzylsai ore field, etc.; East; they all belong mainly to the volcanogenic-hydrothermal type); Transbaikalia (Antey, Streltsovskoe, etc.); Central Asia, mainly Uzbekistan with mineralization in black shale with the center in the city of Uchkuduk. There are a lot of small ore occurrences and manifestations. Transbaikalia remains the main uranium ore region in Russia. A deposit in the Chita region (near the city of Krasnokamensk) produces about 93% of Russian uranium. Production is carried out by the mine method of the Priargunskoye Industrial Mining and Chemical Association (PIMCU), which is part of JSC Atomredmetzoloto (Uranium Holding).
The remaining 7% is obtained by in-situ leaching of ZAO Dalur (Kurgan region) and OAO Khiagda (Buryatia).
The resulting ores and uranium concentrate are processed at the Chepetsk Mechanical Plant.
About a fifth of the world's uranium reserves (21% and 2nd place in the world) are concentrated in Kazakhstan. The total uranium resources are about 1.5 million tons, of which about 1.1 million tons can be mined by in-situ leaching.
In 2009, Kazakhstan came out on top in the world in uranium mining.
The main enterprise is the Eastern Mining and Processing Plant in the city of Zheltye Vody.
Despite the legends about tens of thousands of dollars per kilogram or even gram quantities of uranium, its real price on the market is not very high - unenriched uranium oxide U 3 O 8 costs less than 100 US dollars per kilogram. This is due to the fact that to launch a nuclear reactor on unenriched uranium, tens or even hundreds of tons of fuel are needed, and for the manufacture of nuclear weapons, a large amount of uranium must be enriched to obtain concentrations suitable for creating a bomb.
Where did uranium come from? Most likely, it appears in supernova explosions. The fact is that for the nucleosynthesis of elements heavier than iron, a powerful neutron flux must exist, which occurs just during a supernova explosion. It would seem that then, during condensation from the cloud of new star systems formed by it, uranium, having collected in the protoplanetary cloud and being very heavy, should sink in the depths of the planets. But this is not the case. Uranium is a radioactive element and it releases heat when it decays. Calculations show that if uranium were evenly distributed throughout the entire thickness of the planet, at least with the same concentration as on the surface, then it would emit too much heat. Moreover, its flux should weaken as the uranium is consumed. Since nothing of the kind is observed, geologists believe that at least a third of uranium, and perhaps all of it, is concentrated in the earth's crust, where its content is 2.5 ∙ 10 –4%. Why this happened is not discussed.
Where is uranium mined? There is not so little uranium on Earth - it is in 38th place in terms of abundance. Most of this element is found in sedimentary rocks - carbonaceous shale and phosphorites: up to 8 ∙ 10 –3 and 2.5 ∙ 10 –2%, respectively. In total, the earth's crust contains 10 14 tons of uranium, but the main problem is that it is very scattered and does not form powerful deposits. About 15 uranium minerals are of industrial importance. This is a uranium resin - its basis is tetravalent uranium oxide, uranium mica - various silicates, phosphates and more complex compounds with vanadium or titanium based on hexavalent uranium.
What are Becquerel rays? After Wolfgang Roentgen discovered X-rays, the French physicist Antoine-Henri Becquerel became interested in the glow of uranium salts, which occurs under the influence of sunlight. He wanted to know if there were any X-rays here as well. Indeed, they were present - the salt was illuminating the photographic plate through the black paper. In one of the experiments, however, the salt was not illuminated, and the photographic plate still darkened. When a metal object was placed between the salt and the photographic plate, there was less darkening under it. Consequently, the new rays did not arise at all due to the excitation of uranium by light and did not partially pass through the metal. They were called at first "Becquerel rays". Subsequently, it was discovered that these are mainly alpha rays with a small addition of beta rays: the fact is that the main isotopes of uranium emit an alpha particle during decay, and the daughter products also experience beta decay.
How high is the radioactivity of uranium? Uranium has no stable isotopes; they are all radioactive. The longest-lived is uranium-238 with a half-life of 4.4 billion years. Next comes uranium-235 - 0.7 billion years. They both undergo alpha decay and become the corresponding thorium isotopes. Uranium-238 makes up over 99% of all natural uranium. Due to its huge half-life, the radioactivity of this element is low, and in addition, alpha particles are not able to overcome the stratum corneum on the surface of the human body. They say that IV Kurchatov, after working with uranium, simply wiped his hands with a handkerchief and did not suffer from any diseases associated with radioactivity.
Researchers have repeatedly turned to the statistics of diseases of workers in uranium mines and processing plants. For example, here is a recent article by Canadian and American experts who analyzed data on the health of more than 17 thousand workers at the Eldorado mine in the Canadian province of Saskatchewan for 1950-1999 ( Environmental Research, 2014, 130, 43–50, DOI: 10.1016 / j.envres.2014.01.002). They proceeded from the fact that radiation acts most strongly on rapidly multiplying blood cells, leading to the corresponding types of cancer. Statistics showed that the incidence of various types of blood cancer among mine workers is lower than the average among Canadians. At the same time, the main source of radiation is not considered to be uranium itself, but the gaseous radon generated by it and its decay products, which can enter the body through the lungs.
Why is uranium harmful?? It, like other heavy metals, is highly toxic and can cause kidney and liver failure. On the other hand, uranium, being a scattered element, is inevitably present in water, soil and, concentrating in the food chain, enters the human body. It is reasonable to assume that in the course of evolution, living things have learned to neutralize uranium in natural concentrations. Uranium is the most dangerous in water, so the WHO set a limit: at first it was 15 μg / l, but in 2011 the standard was increased to 30 μg / g. As a rule, there is much less uranium in water: in the USA, on average, 6.7 μg / L, in China and France - 2.2 μg / L. But there are also strong deviations. So in some areas of California it is a hundred times more than the standard - 2.5 mg / l, and in southern Finland it reaches 7.8 mg / l. Researchers are trying to understand if the WHO standard is too strict when studying the effect of uranium on animals. Here is a typical job ( BioMed Research International, 2014, ID 181989; DOI: 10.1155 / 2014/181989). For nine months, French scientists watered rats with water with depleted uranium additives, and in a relatively high concentration - from 0.2 to 120 mg / l. The lower value is water near the mine, the upper one is not found anywhere - the maximum concentration of uranium, measured in Finland, is 20 mg / l. To the surprise of the authors - the article is called: "The unexpected absence of a noticeable effect of uranium on physiological systems ..." - uranium had practically no effect on the health of rats. The animals ate well, put on weight properly, did not complain of illness and did not die of cancer. Uranium, as it should be, was deposited primarily in the kidneys and bones and in a hundredfold less amount in the liver, and its accumulation, as expected, depended on its content in water. However, this did not lead to renal failure, or even to a noticeable appearance of any molecular markers of inflammation. The authors suggested starting a revision of the strict WHO guidelines. However, there is one caveat: the effect on the brain. In the brains of rats, uranium was less than in the liver, but its content did not depend on the amount in water. But uranium affected the work of the antioxidant system of the brain: the activity of catalase increased by 20%, glutathione peroxidase by 68–90%, the activity of superoxide dismutase dropped by 50% regardless of the dose. This means that uranium was clearly causing oxidative stress in the brain and the body was responding to it. Such an effect - a strong effect of uranium on the brain in the absence of its accumulation in it, by the way, as well as in the genitals - has been noticed before. Moreover, water with uranium at a concentration of 75-150 mg / L, which researchers from the University of Nebraska fed rats for six months ( Neurotoxicology and Teratology, 2005, 27, 1, 135-144; DOI: 10.1016 / j.ntt.2004.09.001), had an effect on the behavior of animals, mainly males, released into the field: they did not cross the lines like the control ones, stood up on their hind legs and cleaned their fur. There is evidence that uranium also leads to memory impairments in animals. The behavioral change correlated with the level of lipid oxidation in the brain. It turns out that the uranium water made rats healthy, but stupid. These data will still be useful to us in the analysis of the so-called Gulf War Syndrome.
Is uranium contaminating shale gas sites? It depends on how much uranium is in the gas-containing rocks and how it is associated with them. For example, Assistant Professor Tracy Bank of the University of Buffalo explored the shale rocks of the Marcellus deposit, which stretches from western New York through Pennsylvania and Ohio to West Virginia. It turned out that uranium is chemically bound precisely with the source of hydrocarbons (remember that related coal shale has the highest uranium content). Experiments have shown that the solution used for fracturing the formation perfectly dissolves uranium in itself. “When uranium in these waters comes to the surface, it can cause pollution of the surrounding area. It does not pose a radiation risk, but uranium is a poisonous element, ”notes Tracy Bank in an October 25, 2010 university press release. Detailed articles on the risk of environmental pollution by uranium or thorium in the extraction of shale gas have not yet been prepared.
Why is uranium needed? Previously, it was used as a pigment for making ceramics and colored glass. Now uranium is the basis of atomic energy and nuclear weapons. At the same time, its unique property is used - the ability of the nucleus to divide.
What is nuclear fission? The disintegration of the nucleus into two unequal large pieces. It is because of this property that during nucleosynthesis due to neutron irradiation, nuclei heavier than uranium are formed with great difficulty. The essence of the phenomenon is as follows. If the ratio of the number of neutrons and protons in the nucleus is not optimal, it becomes unstable. Usually such a nucleus ejects from itself either an alpha particle - two protons and two neutrons, or a beta particle - a positron, which is accompanied by the transformation of one of the neutrons into a proton. In the first case, an element of the periodic table is obtained, spaced two cells back, in the second - one cell forward. However, in addition to the emission of alpha and beta particles, the uranium nucleus is capable of fission - decaying into the nuclei of two elements in the middle of the periodic table, for example barium and krypton, which it does after receiving a new neutron. This phenomenon was discovered shortly after the discovery of radioactivity, when physicists exposed the newly discovered radiation to whatever they had to. This is how Otto Frisch, a participant in the events, writes about this ("Uspekhi fizicheskikh nauk", 1968, 96, 4). After the discovery of beryllium rays - neutrons - Enrico Fermi irradiated them, in particular, uranium in order to cause beta decay - he hoped to get the next, 93rd element, now called neptunium, at its expense. It was he who discovered a new type of radioactivity in irradiated uranium, which he associated with the appearance of transuranium elements. At the same time, the slowing down of neutrons, for which the beryllium source was covered with a layer of paraffin, increased this induced radioactivity. The American radiochemist Aristide von Grosse suggested that one of these elements was protactinium, but he was mistaken. But Otto Hahn, who was then working at the University of Vienna and considered protactinium discovered in 1917 to be his brainchild, decided that he was obliged to find out what elements were obtained in this case. Together with Lisa Meitner, at the beginning of 1938, Hahn suggested on the basis of the results of experiments that whole chains of radioactive elements are formed, arising from multiple beta decays of uranium-238 nuclei and its daughter elements that have absorbed a neutron. Soon, Lisa Meitner was forced to flee to Sweden, fearing possible reprisals from the Nazis after the Austrian Anschluss. Hahn, continuing his experiments with Fritz Strassmann, discovered that among the products there was also barium, an element with number 56, which in no way could be obtained from uranium: all the alpha decay chains of uranium end in much heavier lead. The researchers were so surprised by the result that they did not publish it, they only wrote letters to friends, in particular Lisa Meitner in Gothenburg. There, on Christmas Day 1938, her nephew, Otto Frisch, visited her, and while walking in the vicinity of the winter city - he was on skis, his aunt on foot - they discussed the possibility of the appearance of barium in the irradiation of uranium due to nuclear fission (for more information about Lisa Meitner, see “Chemistry and Life ", 2013, No. 4). Back in Copenhagen, Frisch literally on the ladder of a steamer leaving for the United States, caught Niels Bohr and told him about the idea of fission. Bohr slapped his forehead and said: “Oh, what fools we were! We should have noticed this earlier. " In January 1939, an article by Frisch and Meitner was published on the fission of uranium nuclei by neutrons. By that time, Otto Frisch had already set up a test experiment, as had many American groups that had received a message from Bohr. They say that physicists began to disperse to their laboratories right during his report on January 26, 1939 in Washington at the annual conference on theoretical physics, when they grasped the essence of the idea. After the discovery of fission, Hahn and Strassmann revised their experiments and found, just like their colleagues, that the radioactivity of irradiated uranium is associated not with transurans, but with the decay of radioactive elements formed during fission from the middle of the periodic table.
How is the chain reaction in uranium? Soon after the possibility of fission of uranium and thorium nuclei was experimentally proved (and there are no other fissile elements on Earth in any significant amount), Niels Bohr and John Wheeler, who worked at Princeton, and also independently of them the Soviet theoretical physicist J. I. Frenkel and the Germans Siegfried Flügge and Gottfried von Droste created the theory of nuclear fission. Two mechanisms followed from it. One is related to the threshold absorption of fast neutrons. According to him, to initiate fission, a neutron must have a fairly high energy, more than 1 MeV for the nuclei of the main isotopes - uranium-238 and thorium-232. At lower energies, the absorption of a neutron by uranium-238 has a resonant character. For example, a neutron with an energy of 25 eV has a capture area thousands of times larger than with other energies. At the same time, there will be no fission: uranium-238 will become uranium-239, which with a half-life of 23.54 minutes will turn into neptunium-239, the one with a half-life of 2.33 days - into long-lived plutonium-239. Thorium-232 will become uranium-233.
The second mechanism is the thresholdless absorption of a neutron, followed by the third more or less widespread fissile isotope - uranium-235 (as well as plutonium-239 and uranium-233, which are absent in nature): having absorbed any neutron, even a slow one, the so-called thermal, with energy as for molecules participating in thermal motion - 0.025 eV, such a nucleus will split. And this is very good: thermal neutrons have a capture cross section four times higher than fast, megaelectronvolt ones. This is the significance of uranium-235 for the entire subsequent history of atomic energy: it is it that ensures the multiplication of neutrons in natural uranium. After a neutron hit, the uranium-235 nucleus becomes unstable and quickly divides into two unequal parts. Several (on average 2.75) new neutrons are emitted along the way. If they fall into the nuclei of the same uranium, they will cause the multiplication of neutrons in geometric progression - a chain reaction will take place, which will lead to an explosion due to the rapid release of a huge amount of heat. Neither uranium-238 nor thorium-232 can work this way: after fission, neutrons with an average energy of 1–3 MeV are emitted, that is, if there is an energy threshold of 1 MeV, a significant part of neutrons will certainly not be able to cause a reaction, and there will be no multiplication. This means that these isotopes should be forgotten and neutrons will have to be slowed down to thermal energy so that they interact with the nuclei of uranium-235 as efficiently as possible. At the same time, their resonant absorption by uranium-238 should not be allowed: after all, in natural uranium this isotope is slightly less than 99.3% and neutrons more often collide with it, and not with the target uranium-235. And by acting as a moderator, it is possible to maintain the multiplication of neutrons at a constant level and prevent an explosion - to control a chain reaction.
The calculation carried out by Ya.B. Zeldovich and Yu.B. Khariton in the same fateful 1939 showed that for this it is necessary to use a neutron moderator in the form of heavy water or graphite and enrich natural uranium with uranium-235 by at least 1.83 times. Then this idea seemed to them pure fantasy: “It should be noted that approximately double enrichment of those rather significant amounts of uranium, which are necessary for the implementation of a chain explosion,<...>is an extremely cumbersome task close to practical impracticability. " Now this problem has been solved, and the nuclear industry is serially producing uranium for power plants, enriched with uranium-235 to 3.5%.
What is spontaneous nuclear fission? In 1940, G.N. Flerov and K.A. Since this fission also produces neutrons, if they are not allowed to fly away from the reaction zone, they will serve as initiators of the chain reaction. It is this phenomenon that is used to create nuclear reactors.
Why is nuclear power needed? Zeldovich and Khariton were among the first to calculate the economic effect of atomic energy ("Uspekhi fizicheskikh nauk", 1940, 23, 4). “... At the moment, it is still impossible to draw final conclusions about the possibility or impossibility of carrying out a nuclear fission reaction with infinitely branching chains in uranium. If such a reaction is feasible, then the rate of the reaction is automatically adjusted to ensure its smooth flow, despite the enormous amount of energy at the experimenter's disposal. This circumstance is extremely favorable for the energetic utilization of the reaction. Therefore, let us give - although this is a division of the skin of an unkilled bear - some numbers that characterize the possibilities of the energetic use of uranium. If the fission process is on fast neutrons, therefore, the reaction captures the main isotope of uranium (U238), then<исходя из соотношения теплотворных способностей и цен на уголь и уран>the cost of a calorie from the main isotope of uranium turns out to be about 4000 times cheaper than from coal (unless, of course, the processes of "combustion" and heat removal are significantly more expensive in the case of uranium than in the case of coal). In the case of slow neutrons, the cost of a "uranium" calorie (based on the above figures) will be, taking into account that the abundance of the U235 isotope is 0.007, is already only 30 times cheaper than a "coal" calorie, all other things being equal ”.
The first controlled chain reaction was carried out in 1942 by Enrico Fermi at the University of Chicago, and the reactor was controlled manually - pushing in and out the graphite rods when changing the neutron flux. The first power plant was built in Obninsk in 1954. In addition to generating power, the first reactors also worked for the production of weapons-grade plutonium.
How does a nuclear power plant work? Most reactors now run on slow neutrons. Enriched uranium in the form of a metal, an alloy, for example with aluminum, or in the form of an oxide is piled into long cylinders - fuel elements. They are installed in a certain way in the reactor, and rods from the moderator are introduced between them, which control the chain reaction. Over time, reactor poisons, the fission products of uranium, also capable of absorbing neutrons, accumulate in the fuel element. When the concentration of uranium-235 falls below the critical value, the element is decommissioned. However, it contains many fission fragments with strong radioactivity, which decreases over the years, which is why the elements release a significant amount of heat for a long time. They are kept in cooling tanks, and then either buried or they are trying to reprocess them - to extract unburned uranium-235, accumulated plutonium (it was used to make atomic bombs) and other isotopes that can be used. The unused part is sent to the burial grounds.
In so-called fast reactors, or breeder reactors, reflectors made of uranium-238 or thorium-232 are installed around the elements. They slow down and send too fast neutrons back into the reaction zone. Neutrons slowed down to resonant speeds absorb the named isotopes, turning, respectively, into plutonium-239 or uranium-233, which can serve as fuel for a nuclear power plant. Since fast neutrons react poorly with uranium-235, its concentration must be significantly increased, but this pays off with a stronger neutron flux. Despite the fact that breeder reactors are considered the future of nuclear power, because they provide more nuclear fuel than they consume, experiments have shown that they are difficult to manage. Now in the world there is only one such reactor - at the fourth power unit of the Beloyarsk NPP.
How is nuclear power criticized? Aside from accidents, the main point in the arguments of opponents of nuclear power today is the proposal to add to the calculation of its efficiency the costs of protecting the environment after decommissioning the plant and when working with fuel. In both cases, there are problems of reliable disposal of radioactive waste, and these are costs borne by the state. It is believed that if we shift them to the cost of energy, then its economic attractiveness will disappear.
There is also opposition among the supporters of nuclear energy. Its representatives point to the uniqueness of uranium-235, for which there is no replacement, because alternative isotopes fissile by thermal neutrons - plutonium-239 and uranium-233 - are absent in nature due to a half-life of thousands of years. And they get them just as a result of the fission of uranium-235. If it ends, the excellent natural source of neutrons for a nuclear chain reaction will disappear. As a result of such extravagance, mankind will be deprived of the opportunity in the future to involve thorium-232 into the energy cycle, the reserves of which are several times greater than that of uranium.
In theory, particle accelerators can be used to generate a flux of fast neutrons with megaelectronvolt energies. However, if we are talking, for example, about interplanetary flights on an atomic engine, then it will be very difficult to implement a scheme with a bulky accelerator. Depletion of uranium-235 puts an end to such projects.
What is Weapon-Grade Uranium? This is highly enriched uranium-235. Its critical mass - it corresponds to the size of a piece of substance in which a chain reaction occurs spontaneously - is small enough to make ammunition. Such uranium can be used to make an atomic bomb, as well as a fuse for a thermonuclear bomb.
What disasters are associated with the use of uranium? The energy stored in the nuclei of the fissile elements is enormous. Having escaped from control through an oversight or due to intent, this energy is capable of doing a lot of troubles. Two of the worst nuclear disasters occurred on August 6 and 8, 1945, when the US Air Force dropped atomic bombs on Hiroshima and Nagasaki, killing and injuring hundreds of thousands of civilians. Disasters on a smaller scale are associated with accidents at nuclear power plants and nuclear cycle enterprises. The first major accident happened in 1949 in the USSR at the Mayak plant near Chelyabinsk, where plutonium was produced; liquid radioactive waste got into the Techa river. In September 1957, an explosion occurred on it with the release of a large amount of radioactive material. Eleven days later, the British plutonium production reactor at Windscale burned down, the cloud with the explosion products dissipated over Western Europe. In 1979, a reactor burned down at the Trimale Island nuclear power plant in Pennsylvania. The most ambitious consequences were the accidents at the Chernobyl nuclear power plant (1986) and the nuclear power plant in Fukushima (2011), when millions of people were exposed to radiation. The first littered vast lands, releasing 8 tons of uranium fuel with fission products as a result of the explosion, which spread throughout Europe. The second polluted and, three years after the accident, continues to pollute the waters of the Pacific Ocean in the fishing areas. Dealing with the consequences of these accidents was very expensive, and if these costs were decomposed by the cost of electricity, it would have increased significantly.
A separate issue is the consequences for human health. According to official statistics, many people who survived the bombing or live in contaminated areas benefited from radiation - the former have a higher life expectancy, the latter have fewer cancers, and experts associate a slight increase in mortality with social stress. The number of people who died precisely from the consequences of accidents or as a result of their elimination is in the hundreds. Opponents of nuclear power plants point out that the accidents led to several million premature deaths on the European continent, they are simply invisible against the statistical background.
The withdrawal of lands from human use in accident zones leads to an interesting result: they become a kind of nature reserves where biodiversity grows. True, some animals suffer from radiation-related illnesses. The question of how quickly they will adapt to the increased background remains open. There is also an opinion that the consequence of chronic irradiation is "selection for a fool" (see "Chemistry and Life", 2010, No. 5): even at the embryonic stage, more primitive organisms survive. In particular, in relation to humans, this should lead to a decrease in mental abilities in the generation born in contaminated areas shortly after the accident.
What is depleted uranium? This is uranium-238, left over after the separation of uranium-235 from it. The volumes of waste from the production of weapons-grade uranium and fuel elements are large - in the United States alone, 600 thousand tons of hexafluoride of such uranium have accumulated (for problems with it, see "Chemistry and Life", 2008, No. 5). The content of uranium-235 in it is 0.2%. This waste must either be stored until better times, when fast reactors will be created and the possibility of reprocessing uranium-238 into plutonium will appear, or somehow used.
They found a use for him. Uranium, like other transition elements, is used as a catalyst. For example, the authors of the article in ACS Nano dated June 30, 2014, they write that a catalyst made of uranium or thorium with graphene for the reduction of oxygen and hydrogen peroxide "has enormous potential for energy applications." Because uranium is dense, it serves as ballast for ships and as counterweight for aircraft. This metal is also suitable for radiation protection in medical devices with radiation sources.
What weapons can be made from depleted uranium? Bullets and cores for armor-piercing shells. The calculation is as follows. The heavier the projectile, the higher its kinetic energy. But the larger the projectile, the less concentrated its impact. This means that heavy metals with a high density are needed. Bullets are made of lead (the Ural hunters at one time also used native platinum until they realized that it was a precious metal), while the cores of the shells were made of tungsten alloy. Environmentalists point out that lead contaminates the soil in places of hostilities or hunting and it would be better to replace it with something less harmful, for example, the same tungsten. But tungsten is not cheap, and uranium, similar in density, is a harmful waste. At the same time, the permissible contamination of soil and water with uranium is approximately two times greater than for lead. This happens because the weak radioactivity of depleted uranium (and it is also 40% less than that of natural) is neglected and a really dangerous chemical factor is taken into account: uranium, as we remember, is poisonous. At the same time, its density is 1.7 times that of lead, which means that the size of uranium bullets can be halved; uranium is much more refractory and solid than lead - it evaporates less when fired, and when it hits a target, it produces fewer microparticles. In general, a uranium bullet pollutes the environment less than a lead one, however, it is not known for certain about such use of uranium.
But it is known that depleted uranium plates are used to strengthen the armor of American tanks (this is facilitated by its high density and melting point), as well as instead of tungsten alloy in the cores for armor-piercing projectiles. The uranium core is also good because the uranium is pyrophoric: its hot small particles formed upon impact on the armor flare up and set everything on fire. Both applications are considered radiation safe. So, the calculation showed that, even after spending a year in a tank with uranium armor loaded with uranium ammunition, the crew will receive only a quarter of the allowable dose. And in order to get the annual allowable dose, it is necessary to fasten such an ammunition to the skin surface for 250 hours.
Shells with uranium cores - for 30-mm aircraft cannons or for subcaliber artillery - were used by the Americans in recent wars, starting with the 1991 Iraqi campaign. That year, they poured onto Iraqi armored units in Kuwait, and during their retreat, 300 tons of depleted uranium, of which 250 tons, or 780 thousand rounds, fell on aircraft cannons. In Bosnia and Herzegovina, during the bombing of the army of the unrecognized Republika Srpska, 2.75 tons of uranium were spent, and during the shelling of the Yugoslav army in the province of Kosovo and Metohija - 8.5 tons, or 31 thousand rounds. Since the WHO was by then concerned about the consequences of the uranium use, monitoring was carried out. It showed that one salvo consisted of approximately 300 rounds, of which 80% contained depleted uranium. 10% hit the targets, and 82% fell within 100 meters of them. The rest scattered within 1.85 km. A shell hitting a tank burned up and turned into an aerosol, and a uranium shell pierced through light targets like armored personnel carriers. Thus, one and a half tons of shells could turn into uranium dust in Iraq. According to the estimates of the specialists of the American strategic research center "RAND Corporation", more has turned into aerosol, from 10 to 35% of the uranium used. Croat Asaf Durakovic, a croat fighter with uranium munitions, who worked in a variety of organizations from King Faisal Hospital in Riyadh to the Washington Uranium Medical Research Center, believes that in 1991 only in southern Iraq, 3-6 tons of submicron uranium particles were formed, which scattered over a wide area , that is, uranium pollution there is comparable to that of Chernobyl.
Uranus is the seventh planet in the solar system and the third gas giant. The planet is the third largest and fourth in mass, and it got its name in honor of the father of the Roman god Saturn.
Exactly Uranus was honored to be the first planet discovered in modern history. However, in reality, his initial discovery as a planet did not actually take place. In 1781, the astronomer William Herschel while observing the stars in the constellation Gemini, he noticed some disc-shaped object, which he initially recorded as a comet, which he reported to the Royal Scientific Society of England. However, later Herschel himself was puzzled by the fact that the object's orbit turned out to be almost circular, and not elliptical, as is the case with comets. It was only when this observation was confirmed by other astronomers that Herschel came to the conclusion that he had actually discovered a planet, not a comet, and the discovery finally gained widespread acceptance.
After confirming the data that the discovered object is a planet, Herschel received an extraordinary privilege - to give it his name. Without hesitation, the astronomer chose the name of King George III of England and named the planet Georgium Sidus, which means “George's Star”. However, the name never received scientific recognition and scientists, for the most part, came to the conclusion that it is better to adhere to a certain tradition in the names of the planets of the solar system, namely, to name them after the ancient Roman gods. This is how Uranus got its modern name.
Currently, the only planetary mission that has managed to collect information about Uranus is Voyager 2.
This meeting, which took place in 1986, allowed scientists to obtain a large amount of data about the planet and make many discoveries. The spacecraft transmitted thousands of photographs of Uranus, its moons and rings. Despite the fact that many photographs of the planet showed almost nothing other than the blue-green color that could be observed from ground-based telescopes, other images showed the presence of ten previously unknown satellites and two new rings. No new missions to Uranus are planned for the near future.
Due to the dark blue color of Uranus, the atmospheric model of the planet turned out to be much more difficult to compile than models of the same or even. Fortunately, images from the Hubble Space Telescope have provided a broader view. More modern imaging technologies of the telescope made it possible to obtain much more detailed images than those of Voyager 2. So thanks to the Hubble photographs, it was possible to find out that latitudinal bands exist on Uranus, as well as on other gas giants. In addition, the speed of winds on the planet can reach over 576 km / h.
It is believed that the reason for the appearance of a monotonous atmosphere is the composition of its uppermost layer. The visible cloud layers are composed primarily of methane, which absorbs these observed red wavelengths. Thus, the reflected waves are represented in the form of blue and green.
Beneath this outer layer of methane, the atmosphere is composed of approximately 83% hydrogen (H2) and 15% helium, with a certain amount of methane and acetylene present. This composition is similar to that of other gas giants in the solar system. However, the atmosphere of Uranus is dramatically different in another respect. While the atmospheres of Jupiter and Saturn are predominantly gaseous, Uranus' atmospheres contain much more ice. Extremely low surface temperatures are evidence of this. Considering the fact that the temperature of the atmosphere of Uranus reaches -224 ° C, it can be called the coldest atmosphere in the solar system. In addition, the available data indicate that such an extremely low temperature is present practically around the entire surface of Uranus, even on the side that is not illuminated by the Sun.
Uranus, according to planetary scientists, consists of two layers: the core and the mantle. Current models suggest that the core is mainly composed of rock and ice and is about 55 times the mass. The planet's mantle weighs 8.01 x 10 to the power of 24 kg, or about 13.4 Earth masses. In addition, the mantle is composed of water, ammonia, and other volatile elements. The main difference between the mantle of Uranus and Jupiter and Saturn is that it is icy, albeit not in the traditional sense of the word. The fact is that the ice is very hot and thick, and the mantle is 5.111 km thick.
What's most amazing about Uranus's composition and what sets it apart from other gas giants in our stellar system is that it does not emit more energy than it receives from the Sun. Considering the fact that even one that is very close in size to Uranus produces about 2.6 times more heat than it receives from the Sun, scientists today are very intrigued by such a weak power generated by Uranus. At the moment, there are two explanations for this phenomenon. The first indicates that Uranus was exposed to a volumetric space object in the past, which led to the loss of most of the planet's internal heat (received during formation) into outer space. The second theory states that there is a certain barrier inside the planet that does not allow the internal heat of the planet to escape to the surface.
The very discovery of Uranus allowed scientists to expand the radius of the known solar system almost twice. This means that the average orbit of Uranus is about 2.87 x 10 to the 9 km power. The reason for such a huge distance is the duration of the passage of solar radiation from the Sun to the planet. Sunlight takes about two hours and forty minutes to reach Uranus, nearly twenty times longer than it takes sunlight to reach Earth. The huge distance also affects the length of the year on Uranus, it lasts almost 84 Earth years.
The eccentricity of Uranus's orbit is 0.0473, which is only slightly less than that of Jupiter - 0.0484. This factor makes Uranus the fourth of all the planets in the solar system in terms of a circular orbit. The reason for such a small eccentricity of the orbit of Uranus is the difference between its perihelion 2.74 x 10 to the power of 9 km and the aphelion of 3.01 x 109 km is only 2.71 x 10 to the power of 8 km.
The most interesting moment in the rotation of Uranus is the position of the axis. The fact is that the axis of rotation for every planet, except Uranus, is approximately perpendicular to their orbital plane, however, the axis of Uranus is tilted by almost 98 °, which actually means that Uranus rotates on its side. The result of this position of the planet's axis is that the north pole of Uranus is on the Sun for half of the planetary year, and the other half falls on the south pole of the planet. In other words, daytime in one hemisphere of Uranus lasts 42 Earth years, and nighttime, in the other hemisphere, the same. The reason why Uranus "turned on its side", scientists again call a collision with a huge cosmic body.
Considering the fact that the most popular of the rings in our solar system for a long time remained the rings of Saturn, the rings of Uranus could not be detected until 1977. However, the reason is not only this, there are two more reasons for such a late discovery: the distance of the planet from the Earth and the low reflectivity of the rings themselves. In 1986, the Voyager 2 spacecraft was able to determine the presence of two more rings on the planet, in addition to those known at the time. In 2005, the Hubble Space Telescope spotted two more. Today, planetary scientists know 13 rings of Uranus, the brightest of which is the Epsilon ring.
The rings of Uranus differ from the Saturnian ones in almost everything - from particle size to composition. First, the particles that make up Saturn's rings are small, a little more than a few meters in diameter, while Uranus's rings contain many bodies up to twenty meters in diameter. Second, the particles in Saturn's rings are mostly made of ice. The rings of Uranus, however, are composed of both ice and significant dust and debris.
William Herschel only discovered Uranus in 1781, as the planet was too dim to be noticed by representatives of ancient civilizations. Herschel himself initially believed that Uranus was a comet, but later revised his opinion and science confirmed the planetary status of the object. So Uranus became the first planet discovered in modern history. The original name proposed by Herschel was "George's Star" - in honor of King George III, but the scientific community did not accept it. The name "Uranus" was proposed by the astronomer Johann Bode, in honor of the ancient Roman god Uranus.
Uranus makes a revolution on its axis once every 17 hours and 14 minutes. Likewise, the planet rotates in a retrograde direction, opposite to the direction of the Earth and the other six planets.
It is believed that the unusual tilt of the axis of Uranus could cause a grand collision with another cosmic body. The theory is that the planet, which was supposedly the size of Earth, collided sharply with Uranus, which shifted its axis by almost 90 degrees.
Wind speed on Uranus can reach up to 900 km per hour.
Uranus is about 14.5 times the mass of Earth, making it the lightest of the four gas giants in our solar system.
Uranus is often referred to as the "ice giant". In addition to hydrogen and helium in the upper layer (like other gas giants), Uranus also has an ice mantle that surrounds its iron core. The upper atmosphere, composed of ammonia and ice-cold methane crystals, gives Uranus its characteristic pale blue color.
Uranus is the second least dense planet in the solar system, after Saturn.
In the message of the Iraqi ambassador to the UN Mohammed Ali al-Hakim dated July 9, it says that at the disposal of the extremists ISIS (Islamic State of Iraq and the Levant). The IAEA (International Atomic Energy Agency) hastened to declare that the previously used nuclear substances by Iraq have low toxic properties, and therefore materials seized by the Islamists.
A source in the US government familiar with the situation told Reuters that the uranium stolen by the militants is most likely not enriched, so it can hardly be used to make nuclear weapons. The Iraqi authorities have officially notified the United Nations of this incident and called on "to prevent the threat of its use," RIA Novosti reports.
Uranium compounds are extremely dangerous. About what exactly, as well as about who and how can produce nuclear fuel, tells AiF.ru.
Uranium is a chemical element with atomic number 92, a silvery-white glossy metal, in the periodic table of Mendeleev is designated by the symbol U. In its pure form, it is slightly softer than steel, malleable, flexible, is contained in the earth's crust (lithosphere) and in seawater, and in its pure form is practically does not occur. Nuclear fuel is made from uranium isotopes.
Uranium is a heavy, silvery-white, shiny metal. Photo: Commons.wikimedia.org / Original uploader was Zxctypo at en.wikipedia.
In 1938 the German physicists Otto Hahn and Fritz Strassmann irradiated the uranium nucleus with neutrons and made a discovery: capturing a free neutron, the uranium isotope nucleus fissions and releases enormous energy due to the kinetic energy of fragments and radiation. In the years 1939-1940 Julius Khariton and Yakov Zeldovich for the first time, they theoretically explained that with a small enrichment of natural uranium with uranium-235, it is possible to create conditions for the continuous fission of atomic nuclei, that is, to give the process a chain character.
Enriched uranium is uranium that is obtained using technological process of increasing the fraction of 235U isotope in uranium. As a result, natural uranium is separated into enriched uranium and depleted uranium. After the extraction of 235U and 234U from natural uranium, the remaining material (uranium-238) is called "depleted uranium" because it is depleted in the 235th isotope. According to some reports, about 560,000 tons of depleted uranium hexafluoride (UF6) are stored in the United States. Depleted uranium is two times less radioactive than natural uranium, mainly due to the removal of 234U from it. Due to the fact that the main use of uranium is energy production, depleted uranium is a product of little use with low economic value.
In nuclear power, only enriched uranium is used. The uranium isotope 235U has the greatest application, in which a self-sustaining nuclear chain reaction is possible. Therefore, this isotope is used as fuel in nuclear reactors and nuclear weapons. The separation of the U235 isotope from natural uranium is a complex technology that few countries can implement. Uranium enrichment makes it possible to produce atomic nuclear weapons - single-phase or single-stage explosive devices, in which the main energy output comes from the nuclear fission reaction of heavy nuclei with the formation of lighter elements.
Uranium-233, artificially obtained in reactors from thorium (thorium-232 captures a neutron and turns into thorium-233, which decays into protactinium-233 and then into uranium-233), may in the future become a widespread nuclear fuel for nuclear power plants (already now there are reactors using this nuclide as fuel, for example KAMINI in India) and the production of atomic bombs (critical mass about 16 kg).
The core of a 30 mm caliber projectile (GAU-8 cannon of the A-10 aircraft) with a diameter of about 20 mm from depleted uranium. Photo: Commons.wikimedia.org / Original uploader was Nrcprm2026 at en.wikipedia
10 countries providing 94% of world uranium production. Photo: Commons.wikimedia.org / KarteUrangewinnung
Uranium and its compounds are toxic. Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds, the maximum permissible concentration (MPC) in the air is 0.015 mg / m³, for insoluble forms of uranium, the maximum permissible concentration (MPC) is 0.075 mg / m³. When it enters the body, uranium acts on all organs, being a general cellular poison. Uranium is practically irreversible, like many other heavy metals, binds to proteins, primarily to the sulfide groups of amino acids, disrupting their function. The molecular mechanism of action of uranium is associated with its ability to suppress enzyme activity. First of all, the kidneys are affected (protein and sugar appear in the urine, oliguria). With chronic intoxication, disorders of the hematopoiesis and nervous system are possible.
Isotope - varieties of atoms of a chemical element that have the same atomic (ordinal) number, but different mass numbers.
An element of the III group of the periodic table, belonging to the actinides; heavy, weakly radioactive metal. Thorium has a number of applications in which it sometimes plays an irreplaceable role. The position of this metal in the periodic table of elements and the structure of the nucleus predetermined its use in the field of peaceful uses of atomic energy.
*** Oliguria (from the Greek oligos - small and ouron - urine) - a decrease in the amount of urine excreted by the kidneys.
