Uranium in nature. Uranus: facts and facts

Uranium is not a very typical actinide; its five valence states are known - from 2+ to 6+. Some uranium compounds have a characteristic color. Thus, solutions of trivalent uranium are red, tetravalent uranium is green, and hexavalent uranium - it exists in the form of uranyl ion (UO 2) 2+ - colors the solutions yellow... The fact that hexavalent uranium forms compounds with many organic complexing agents, turned out to be very important for the extraction technology of element No. 92.

It is characteristic that the outer electron shell of uranium ions is always completely filled; The valence electrons are in the previous electron layer, in the 5f subshell. If we compare uranium with other elements, it is obvious that plutonium is most similar to it. The main difference between them is the large ionic radius of uranium. In addition, plutonium is most stable in the tetravalent state, and uranium is most stable in the hexavalent state. This helps to separate them, which is very important: the nuclear fuel plutonium-239 is obtained exclusively from uranium, ballast from the energy point of view of uranium-238. Plutonium is formed in a mass of uranium, and they must be separated!

However, first you need to get this very mass of uranium, going through a long technological chain, starting with ore. Typically a multi-component, uranium-poor ore.

Light isotope of a heavy element

When we talked about obtaining element No. 92, we deliberately omitted one important stage. As you know, not all uranium is capable of supporting a nuclear chain reaction. Uranium-238, which accounts for 99.28% of the natural mixture of isotopes, is not capable of this. Because of this, uranium-238 is converted into plutonium, and the natural mixture of uranium isotopes is sought to either be separated or enriched with the isotope uranium-235, which is capable of fissioning thermal neutrons.

Many methods have been developed for separating uranium-235 and uranium-238. The gas diffusion method is most often used. Its essence is that if a mixture of two gases is passed through a porous partition, then the light will pass faster. Back in 1913, F. Aston partially separated neon isotopes in this way.

Most uranium compounds under normal conditions are solids and can be converted into a gaseous state only at very high temperatures, when there can be no talk of any subtle processes of isotope separation. However, the colorless compound of uranium with fluorine, UF 6 hexafluoride, sublimes already at 56.5 ° C (at atmospheric pressure). UF 6 is the most volatile uranium compound and is best suited for separating its isotopes by gaseous diffusion.

Uranium hexafluoride is characterized by high chemical activity. Corrosion of pipes, pumps, containers, interaction with the lubrication of mechanisms - a small but impressive list of troubles that the creators of diffusion plants had to overcome. We encountered even more serious difficulties.

Uranium hexafluoride, obtained by fluoridation of a natural mixture of uranium isotopes, from a “diffusion” point of view, can be considered as a mixture of two gases with very similar molecular masses - 349 (235 + 19 * 6) and 352 (238 + 19 * 6). The maximum theoretical separation coefficient in one diffusion stage for gases that differ so slightly in molecular weight is only 1.0043. In real conditions this value is even less. It turns out that it is possible to increase the concentration of uranium-235 from 0.72 to 99% only with the help of several thousand diffusion steps. Therefore, uranium isotope separation plants occupy an area of several tens of hectares. The area of porous partitions in the separation cascades of factories is approximately the same order of magnitude.

Briefly about other isotopes of uranium

Natural uranium, in addition to uranium-235 and uranium-238, includes uranium-234. The abundance of this rare isotope is expressed as a number with four zeros after the decimal point. A much more accessible artificial isotope is uranium-233. It is obtained by irradiating thorium in the neutron flux of a nuclear reactor:

232 90 Th + 10n → 233 90 Th -β-→ 233 91 Pa -β-→ 233 92 U
According to all the rules of nuclear physics, uranium-233, as an odd isotope, is divided by thermal neutrons. And most importantly, in reactors with uranium-233, expanded reproduction of nuclear fuel can (and does) occur. In a conventional thermal neutron reactor! Calculations show that when a kilogram of uranium-233 burns up in a thorium reactor, 1.1 kg of new uranium-233 should accumulate in it. A miracle, and that’s all! We burned a kilogram of fuel, but the amount of fuel did not decrease.

However, such miracles are only possible with nuclear fuel.

The uranium-thorium cycle in thermal neutron reactors is the main competitor of the uranium-plutonium cycle for the reproduction of nuclear fuel in fast neutron reactors... Actually, only because of this, element No. 90 - thorium - was classified as a strategic material.

Other artificial isotopes of uranium do not play a significant role. It is only worth mentioning uranium-239 - the first isotope in the chain of transformations of uranium-238 plutonium-239. Its half-life is only 23 minutes.

Isotopes of uranium with a mass number greater than 240 do not have time to form in modern reactors. The lifetime of uranium-240 is too short, and it decays before it has time to capture a neutron.

In the super-powerful neutron fluxes of a thermonuclear explosion, a uranium nucleus manages to capture up to 19 neutrons in a millionth of a second. In this case, uranium isotopes with mass numbers from 239 to 257 are born. Their existence was learned from the appearance of distant transuranium elements - descendants of heavy uranium isotopes - in the products of a thermonuclear explosion. The “founders of the genus” themselves are too unstable to beta decay and pass into higher elements long before the products of nuclear reactions are extracted from the rock mixed by the explosion.

Modern thermal reactors burn uranium-235. In already existing fast neutron reactors, the energy of the nuclei of a common isotope, uranium-238, is released, and if energy is true wealth, then uranium nuclei will benefit humanity in the near future: the energy of element N° 92 will become the basis of our existence.

It is vitally important to ensure that uranium and its derivatives burn only in nuclear reactors of peaceful power plants, burn slowly, without smoke and flame.

ANOTHER SOURCE OF URANIUM. Nowadays, it has become sea water. Pilot-industrial installations are already in operation for extracting uranium from water using special sorbents: titanium oxide or acrylic fiber treated with certain reagents.

WHO HOW MUCH. In the early 80s, uranium production in capitalist countries was about 50,000 g per year (in terms of U3Os). About a third of this amount was provided by US industry. Canada is in second place, followed by South Africa. Nigor, Gabon, Namibia. Of the European countries, France produces the most uranium and its compounds, but its share was almost seven times less than the United States.

NON-TRADITIONAL CONNECTIONS. Although it is not without foundation that the chemistry of uranium and plutonium is better studied than the chemistry of traditional elements such as iron, chemists are still discovering new uranium compounds. So, in 1977, the journal “Radiochemistry”, vol. XIX, no. 6 reported two new uranyl compounds. Their composition is MU02(S04)2-SH20, where M is a divalent manganese or cobalt ion. X-ray diffraction patterns indicated that the new compounds were double salts, and not a mixture of two similar salts.

Where did uranium come from? Most likely, it appears during supernova explosions. The fact is that for the nucleosynthesis of elements heavier than iron, there must be a powerful flow of neutrons, which occurs precisely 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 a protoplanetary cloud and being very heavy, should sink into the depths of the planets. But that's not true. Uranium is a radioactive element and when it decays it releases heat. 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, it would emit too much heat. Moreover, its flow should weaken as uranium is consumed. Since nothing like this has been 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. And most of this element is found in sedimentary rocks - carbonaceous shales 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 dispersed and does not form powerful deposits. Approximately 15 uranium minerals are of industrial importance. This is uranium tar - 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's rays? After the discovery of X-rays by Wolfgang Roentgen, French physicist Antoine-Henri Becquerel became interested in the glow of uranium salts, which occurs under the influence of sunlight. He wanted to understand if there were X-rays here too. Indeed, they were present - the salt illuminated the photographic plate through the black paper. In one of the experiments, however, the salt was not illuminated, but the photographic plate still darkened. When a metal object was placed between the salt and the photographic plate, the darkening underneath was less. Therefore, new rays did not arise due to the excitation of uranium by light and did not partially pass through the metal. They were initially called “Becquerel’s rays.” It was subsequently 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 radioactive is 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 isotopes of thorium. Uranium-238 makes up more than 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 penetrate the stratum corneum on the surface of the human body. They say that after working with uranium, I.V. Kurchatov 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. Here, for example, is a recent article by Canadian and American specialists who analyzed health data of more than 17 thousand workers at the Eldorado mine in the Canadian province of Saskatchewan for the years 1950–1999 ( Environmental Research, 2014, 130, 43–50, DOI:10.1016/j.envres.2014.01.002). They proceeded from the fact that radiation has the strongest effect on rapidly multiplying blood cells, leading to the corresponding types of cancer. Statistics have shown that mine workers have a lower incidence of various types of blood cancer than the average Canadians. In this case, the main source of radiation is not considered to be uranium itself, but the gaseous radon it generates 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 dispersed 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 process of evolution, living beings have learned to neutralize uranium in natural concentrations. Uranium is the most dangerous in water, so the WHO set a limit: initially 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 whether the WHO standard is too strict by studying the effect of uranium on animals. Here is a typical job ( BioMed Research International, 2014, ID 181989; DOI:10.1155/2014/181989). French scientists fed rats water with added depleted uranium for nine months, and in relatively high concentrations - from 0.2 to 120 mg/l. The lower value is water near the mine, while the upper value 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, gained weight properly, did not complain of illness and did not die from cancer. Uranium, as it should be, was deposited primarily in the kidneys and bones and in a hundred times smaller quantities in the liver, and its accumulation expectedly depended on the content in the water. However, this did not lead to renal failure or even the noticeable appearance of any molecular markers of inflammation. The authors suggested that a review of the WHO's strict guidelines should begin. However, there is one caveat: the effect on the brain. There was less uranium in the rats' brains than in the liver, but its content did not depend on the amount in the water. But uranium affected the functioning of the brain’s antioxidant system: the activity of catalase increased by 20%, glutathione peroxidase by 68–90%, and the activity of superoxide dismutase decreased by 50%, regardless of the dose. This means that uranium clearly caused oxidative stress in the brain and the body responded to it. This effect - the strong effect of uranium on the brain in the absence of its accumulation in it, by the way, as well as in the genitals - was noticed before. Moreover, water with uranium in 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), affected the behavior of animals, mainly males, released into the field: they crossed lines, stood up on their hind legs and preened their fur differently than the control ones. There is evidence that uranium also leads to memory impairment in animals. Behavioral changes were correlated with levels of lipid oxidation in the brain. It turns out that the uranium water made the rats healthy, but rather stupid. These data will be useful to us in the analysis of the so-called Gulf War Syndrome.

Does uranium contaminate shale gas development sites? It depends on how much uranium is in the gas-containing rocks and how it is associated with them. For example, Associate Professor Tracy Bank of the University at Buffalo studied the Marcellus Shale, which stretches from western New York through Pennsylvania and Ohio to West Virginia. It turned out that uranium is chemically related precisely to the source of hydrocarbons (remember that related carbonaceous shales have the highest uranium content). Experiments have shown that the solution used during fracturing perfectly dissolves uranium in itself. “When the uranium in these waters reaches the surface, it can cause contamination of the surrounding area. This does not pose a radiation risk, but uranium is a poisonous element,” notes Tracy Bank in a university press release dated October 25, 2010. No detailed articles have yet been prepared on the risk of environmental contamination with uranium or thorium during shale gas production.

Why is uranium needed? Previously, it was used as a pigment for making ceramics and colored glass. Now uranium is the basis of nuclear energy and atomic weapons. In this case, its unique property is used - the ability of the nucleus to divide.

What is nuclear fission? The decay of a 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. Typically, such a nucleus emits 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 emitting 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, having received a new neutron. This phenomenon was discovered shortly after the discovery of radioactivity, when physicists exposed the newly discovered radiation to everything they could. Here is how Otto Frisch, a participant in the events, writes about this (“Advances in Physical Sciences,” 1968, 96, 4). After the discovery of beryllium rays - neutrons - Enrico Fermi irradiated uranium with them, in particular, to cause beta decay - he hoped to use it to obtain the next, 93rd element, now called neptunium. 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, slowing down the neutrons, for which the beryllium source was covered with a layer of paraffin, increased this induced radioactivity. American radiochemist Aristide von Grosse suggested that one of these elements was protactinium, but he was wrong. 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. Together with Lise Meitner, at the beginning of 1938, Hahn suggested, based on experimental results, that entire chains of radioactive elements are formed due to multiple beta decays of the neutron-absorbing nuclei of uranium-238 and its daughter elements. Soon Lise Meitner was forced to flee to Sweden, fearing possible reprisals from the Nazis after the Anschluss of Austria. Hahn, having continued his experiments with Fritz Strassmann, discovered that among the products there was also barium, element number 56, which in no way could be obtained from uranium: all chains of alpha decays of uranium end with 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 to Lise Meitner in Gothenburg. There, at Christmas 1938, her nephew, Otto Frisch, visited her, and, walking in the vicinity of the winter city - he on skis, the aunt on foot - they discussed the possibility of the appearance of barium during the irradiation of uranium as a result of nuclear fission (for more information about Lise Meitner, see “Chemistry and Life ", 2013, No. 4). Returning to Copenhagen, Frisch literally caught Niels Bohr on the gangway of a ship departing for the United States and told him about the idea of fission. Bohr, slapping himself on the forehead, said: “Oh, what fools we were! We should have noticed this earlier." In January 1939, Frisch and Meitner published an article on the fission of uranium nuclei under the influence of neutrons. By that time, Otto Frisch had already carried out a control experiment, as well as many American groups who received the 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 transuraniums, but with the decay of radioactive elements formed during fission from the middle of the periodic table.

How does a chain reaction occur in uranium? Soon after the possibility of fission of uranium and thorium nuclei was experimentally proven (and there are no other fissile elements on Earth in any significant quantity), Niels Bohr and John Wheeler, who worked at Princeton, as well as, independently of them, the Soviet theoretical physicist Ya. I. Frenkel and the Germans Siegfried Flügge and Gottfried von Droste created the theory of nuclear fission. Two mechanisms followed from it. One is associated with the threshold absorption of fast neutrons. According to it, 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, neutron absorption by uranium-238 has a resonant character. Thus, a neutron with an energy of 25 eV has a capture cross-sectional area that is thousands of times larger than with other energies. In this case, 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, which, with a half-life of 2.33 days, will turn into long-lived plutonium-239. Thorium-232 will become uranium-233.

The second mechanism is the non-threshold absorption of a neutron, it is followed by the third more or less common fissile isotope - uranium-235 (as well as plutonium-239 and uranium-233, which are not found in nature): by absorbing any neutron, even a slow one, the so-called thermal one, 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-sectional area four times higher than fast, megaelectronvolt neutrons. This is the significance of uranium-235 for the entire subsequent history of nuclear energy: it is it that ensures the multiplication of neutrons in natural uranium. After being hit by a neutron, the uranium-235 nucleus becomes unstable and quickly splits into two unequal parts. Along the way, several (on average 2.75) new neutrons are emitted. If they hit the nuclei of the same uranium, they will cause neutrons to multiply exponentially - a chain reaction will occur, 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 like that: after all, during fission, neutrons are emitted with an average energy of 1–3 MeV, that is, if there is an energy threshold of 1 MeV, a significant part of the neutrons will certainly not be able to cause a reaction, and there will be no reproduction. This means that these isotopes should be forgotten and the neutrons will have to be slowed down to thermal energy so that they interact as efficiently as possible with the nuclei of uranium-235. At the same time, their resonant absorption by uranium-238 cannot 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 - control the chain reaction.

A calculation carried out by Ya. B. Zeldovich and Yu. B. Khariton in the same fateful year of 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 at least 1.83 times. Then this idea seemed to them pure fantasy: “It should be noted that approximately double the enrichment of those rather significant quantities of uranium that are necessary to carry out a chain explosion,<...>is an extremely cumbersome task, close to practical impossibility.” Now this problem has been solved, and the nuclear industry is mass-producing uranium enriched with uranium-235 to 3.5% for power plants.

What is spontaneous nuclear fission? In 1940, G. N. Flerov and K. A. Petrzhak discovered that the fission of uranium can occur spontaneously, without any external influence, although the half-life is much longer than with ordinary alpha decay. Since such fission also produces neutrons, if they are not allowed to escape from the reaction zone, they will serve as the initiators of the chain reaction. It is this phenomenon that is used in the creation of nuclear reactors.

Why is nuclear energy needed? Zeldovich and Khariton were among the first to calculate the economic effect of nuclear energy (Uspekhi Fizicheskikh Nauk, 1940, 23, 4). “...At the moment, it is still impossible to make 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 reaction rate is automatically adjusted to ensure its smooth progress, despite the enormous amount of energy at the experimenter’s disposal. This circumstance is extremely favorable for the energy use of the reaction. Let us therefore present - although this is a division of the skin of an unkilled bear - some numbers characterizing the possibilities of the energy use of uranium. If the fission process proceeds with 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 approximately 4000 times cheaper than from coal (unless, of course, the processes of “combustion” and heat removal turn out to be much 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, 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 graphite rods in and out as the neutron flux changed. The first power plant was built in Obninsk in 1954. In addition to generating energy, the first reactors also worked to produce weapons-grade plutonium.

How does a nuclear power plant operate? Nowadays, most reactors operate on slow neutrons. Enriched uranium in the form of a metal, an alloy such as aluminum, or an oxide is placed in long cylinders called fuel elements. They are installed in a certain way in the reactor, and moderator rods are inserted between them, which control the chain reaction. Over time, reactor poisons accumulate in the fuel element - uranium fission products, which are also capable of absorbing neutrons. When the concentration of uranium-235 falls below a critical level, the element is taken out of service. However, it contains many fission fragments with strong radioactivity, which decreases over the years, causing the elements to emit a significant amount of heat for a long time. They are kept in cooling pools, and then either buried or tried to be processed - to extract unburned uranium-235, produced plutonium (it was used to make atomic bombs) and other isotopes that can be used. The unused part is sent to 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 back into the reaction zone neutrons that are too fast. Neutrons slowed down to resonant speeds absorb these isotopes, turning into plutonium-239 or uranium-233, respectively, 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 energy, since they produce more nuclear fuel than they consume, experiments have shown that they are difficult to manage. Now there is only one such reactor left in the world - at the fourth power unit of the Beloyarsk NPP.

How is nuclear energy criticized? If we do not talk about accidents, then the main point in the arguments of opponents of nuclear energy today is the proposal to add to the calculation of its efficiency the costs of protecting the environment after the station is decommissioned and when working with fuel. In both cases, the task of reliable disposal of radioactive waste arises, and these are costs borne by the state. There is an opinion that if you transfer them to the cost of energy, then its economic attractiveness will disappear.

There is also opposition among supporters of nuclear energy. Its representatives point to the uniqueness of uranium-235, which has no replacement, because alternative isotopes fissile by thermal neutrons - plutonium-239 and uranium-233 - due to their half-life of thousands of years, are not found in nature. And they are obtained precisely as a result of the fission of uranium-235. If it runs out, a wonderful natural source of neutrons for a nuclear chain reaction will disappear. As a result of such wastefulness, humanity will lose the opportunity in the future to involve thorium-232, the reserves of which are several times greater than uranium, into the energy cycle.

Theoretically, particle accelerators can be used to produce a flux of fast neutrons with megaelectronvolt energies. However, if we are talking, for example, about interplanetary flights on a nuclear engine, then implementing a scheme with a bulky accelerator will be very difficult. The depletion of uranium-235 puts an end to such projects.

What is weapons-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 produce ammunition. Such uranium can be used to make an atomic bomb, and also as a fuse for a thermonuclear bomb.

What disasters are associated with the use of uranium? The energy stored in the nuclei of fissile elements is enormous. If it gets out of control due to oversight or intentionally, this energy can cause a lot of trouble. The two 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. Smaller scale disasters are associated with accidents at nuclear power plants and nuclear cycle enterprises. The first major accident occurred in 1949 in the USSR at the Mayak plant near Chelyabinsk, where plutonium was produced; Liquid radioactive waste ended up in the Techa River. In September 1957, an explosion occurred on it, releasing a large amount of radioactive material. Eleven days later, the British plutonium production reactor at Windscale burned down, and the cloud with the explosion products dispersed over Western Europe. In 1979, a reactor at the Three Mail Island Nuclear Power Plant in Pennsylvania burned down. The most widespread consequences were caused by the accidents at the Chernobyl nuclear power plant (1986) and the Fukushima nuclear power plant (2011), when millions of people were exposed to radiation. The first littered vast areas, releasing 8 tons of uranium fuel and decay products as a result of the explosion, which spread across Europe. The second polluted and, three years after the accident, continues to pollute the Pacific Ocean in fishing areas. Eliminating the consequences of these accidents was very expensive, and if these costs were broken down into the cost of electricity, it would increase significantly.

A separate issue is the consequences for human health. According to official statistics, many people who survived the bombing or living in contaminated areas benefited from radiation - the former have a higher life expectancy, the latter have less cancer, and experts attribute some increase in mortality to social stress. The number of people who died precisely from the consequences of accidents or as a result of their liquidation amounts to hundreds of people. Opponents of nuclear power plants point out that the accidents have led to several million premature deaths on the European continent, but they are simply invisible in the statistical context.

Removing 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 diseases. 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 fools” (see “Chemistry and Life”, 2010, No. 5): even at the embryonic stage, more primitive organisms survive. In particular, in relation to people, 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, remaining 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 such uranium hexafluoride 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 neutron reactors will be created and it will be possible to process uranium-238 into plutonium, or used somehow.

They found a use for it. 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 use in the energy sector.” Because uranium has a high density, it serves as ballast for ships and counterweights 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 projectiles. The calculation here 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 high density are needed. Bullets are made of lead (Ural hunters at one time also used native platinum, until they realized that it was a precious metal), while the shell cores are made of tungsten alloy. Environmentalists point out that lead contaminates the soil in places of military operations or hunting and it would be better to replace it with something less harmful, for example, 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 twice as high as for lead. This happens because the weak radioactivity of depleted uranium (and it is also 40% less than that of natural uranium) is neglected and a truly dangerous chemical factor is taken into account: uranium, as we remember, is poisonous. At the same time, its density is 1.7 times greater than that of lead, which means that the size of uranium bullets can be reduced by half; uranium is much more refractory and hard than lead - it evaporates less when fired, and when it hits a target it produces fewer microparticles. In general, a uranium bullet is less polluting than a lead bullet, although such use of uranium is not known for certain.

But it is known that plates made of depleted uranium are used to strengthen the armor of American tanks (this is facilitated by its high density and melting point), and also instead of tungsten alloy in cores for armor-piercing projectiles. The uranium core is also good because uranium is pyrophoric: its hot small particles formed upon impact with the armor flare up and set fire to everything around. Both applications are considered radiation safe. Thus, the calculation showed that even after sitting for a year in a tank with uranium armor loaded with uranium ammunition, the crew would receive only a quarter of the permissible dose. And to get the annual permissible dose, you need to screw such ammunition to the surface of the skin for 250 hours.

Shells with uranium cores - for 30-mm aircraft cannons or artillery sub-calibers - have been used by the Americans in recent wars, starting with the Iraq campaign of 1991. That year they rained down on Iraqi armored units in Kuwait and during their retreat, 300 tons of depleted uranium, of which 250 tons, or 780 thousand rounds, were fired at aircraft guns. 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 region of Kosovo and Metohija - 8.5 tons, or 31 thousand rounds. Since WHO was by that time concerned about the consequences of the use of uranium, monitoring was carried out. He showed that one salvo consisted of approximately 300 rounds, of which 80% contained depleted uranium. 10% hit targets, and 82% fell within 100 meters of them. The rest dispersed within 1.85 km. A shell that hit a tank burned up and turned into an aerosol; the uranium shell pierced through light targets like armored personnel carriers. Thus, at most one and a half tons of shells could turn into uranium dust in Iraq. According to experts from the American strategic research center RAND Corporation, more, from 10 to 35% of the used uranium, turned into aerosol. Croatian anti-uranium munitions activist Asaf Durakovic, who has worked in a variety of organizations from Riyadh's King Faisal Hospital to the Washington Uranium Medical Research Center, estimates that in southern Iraq alone in 1991, 3-6 tons of submicron uranium particles were formed, which were scattered over a wide area , that is, uranium contamination there is comparable to Chernobyl.

URANIUM (chemical element) URANIUM (chemical element)

URANIUM (lat. Uranium), U (read “uranium”), radioactive chemical element with atomic number 92, atomic mass 238.0289. Actinoid. Natural uranium consists 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%, with half-life T 1/2 = 7.13 10 8 years, 234 U, 0.0057%, with half-life T 1/2 = 2.45 10 5 years. 238 U (uranium-I, UI) and 235 U (actinouranium, AcU) are the founders of the radioactive series. Of the 11 artificially produced radionuclides with mass numbers 227-240, the 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. Located in group IIIB in the 7th period of the periodic table of elements. In compounds it exhibits oxidation states +2, +3, +4, +5 and +6, valences II, III, IV, V and VI.
The radius of a neutral uranium atom is 0.156 nm, the radius of ions: 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. Electronegativity according to Pauling (cm. PAULING Linus) 1,22.
History of discovery
Uranium was discovered in 1789 by the German chemist M. G. Klaproth (cm. KLAPROT Martin Heinrich) when studying the mineral “resin blende”. He was named in honor of the planet Uranus, discovered by W. Herschel (cm. HERSCHEL) in 1781. In the metallic state, uranium was obtained in 1841 by the French chemist E. Peligot (cm. PELIGOT Eugene Melchior) when reducing UCl 4 with potassium metal. The radioactive properties of uranium were discovered in 1896 by the Frenchman A. Becquerel (cm. BECQUEREL Antoine Henri).
Initially, uranium was assigned an atomic mass of 116, but in 1871 D. I. Mendeleev (cm. MENDELEEV Dmitry Ivanovich) I 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) concluded that these elements (actinides) (cm. ACTINOIDS) It is more correct to place it in the periodic table in the same cell with element No. 89 actinium. This arrangement is due to the fact that actinides undergo completion of 5 f-electronic sublevel.
Being in nature
Uranium is a characteristic element for the granite layer and sedimentary shell of the earth's crust. The content in the earth's crust is 2.5·10 -4% by weight. In sea water, the concentration of uranium is less than 10 -9 g/l; in total, sea water contains from 10 9 to 10 10 tons of uranium. Uranium is not found in free form in the earth's crust. About 100 uranium minerals are known, the most important of which are pitchblende U 3 O 8 and 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.
Receipt
Uranium is obtained from uranium ores containing 0.05-0.5% U. Extraction of uranium begins with the production of 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 ion exchange and extraction processes.
From the resulting solution, uranium is extracted in the form of oxide or tetrafluoride UF 4 using the metallothermic method:
UF 4 + 2Mg = 2MgF 2 + U
The resulting uranium contains small amounts of boron impurities (cm. BOR (chemical element)), cadmium (cm. CADMIUM) and some other elements, so-called reactor poisons. By absorbing neutrons produced during the operation of a nuclear reactor, they make uranium unsuitable for use as nuclear fuel.
To get rid of impurities, uranium metal is dissolved in nitric acid, producing 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 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 forms (cm. ALLOTROPY) modifications. The a-modification with an orthorhombic lattice is stable up to 669°C, parameters A= 0.2854nm, V= 0.5869 nm and With= 0.4956 nm, density 19.12 kg/dm3. From 669°C to 776°C, the b-modification with a tetragonal lattice is stable (parameters A= 1.0758 nm, With= 0.5656 nm). The g-modification with a cubic body-centered lattice is stable up to a melting temperature of 1135°C ( A= 0.3525 nm). Boiling point 4200°C.
The chemical activity of uranium metal is high. In air it becomes covered with a film of oxide. Powdered uranium is pyrophoric; upon combustion of uranium and 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, when decomposing, it forms uranium trioxide UO 3. In addition to uranium oxides of the stoichiometric composition UO 2 , UO 3 and U 3 O 8 , uranium oxide of 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. HALOGEN), uranium produces uranium halides. Among them, UF 6 hexafluoride is a yellow crystalline substance that easily sublimes even with low heating (40-60°C) and is equally easily hydrolyzed by water. Uranium hexafluoride UF 6 is of the greatest practical importance. It is obtained by reacting uranium metal, uranium oxides or UF 4 with fluorine or fluorinating agents BrF 3, CCl 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, as well as uranium iodides UI 3 and UI 4 were obtained. 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, producing hydrogen and powdered uranium. When uranium is sintered with boron, depending on the molar ratio of the reagents and the process conditions, borides UB 2, UB 4 and UB 12 appear.
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 sulfur (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 and reacts slowly with H 2 SO 4 and H 3 PO 4. Salts appear containing the uranyl cation UO 2 2+.
In aqueous solutions, uranium compounds exist in oxidation states from +3 to +6. Standard oxidation potential of U(IV)/U(III) pair - 0.52 V, U(V)/U(IV) pair 0.38 V, U(VI)/U(V) pair 0.17 V, 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 into U 4+ and UO 2 2+. U 3+ ions have a characteristic red color, U 4+ ions have a green color, and UO 2 2+ ions have a yellow color.
In solutions, uranium compounds are most stable in the oxidation state +6. All uranium compounds in solutions are prone to hydrolysis and complex formation, most strongly the U 4+ and UO 2 2+ cations.
Application
Uranium metal and its compounds are used primarily 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
It is found in microquantities (10 -5 -10 -8%) in the tissues of plants, animals and humans. It accumulates to the greatest extent 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 bronchopulmonary lymph nodes. The content in organs and tissues of humans and animals does not exceed 10 -7 g.
Uranium and its compounds are highly toxic. Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds, the MPC in air is 0.015 mg/m 3 , for insoluble forms of uranium the MPC is 0.075 mg/m 3 . When uranium enters the body, it affects all organs, being a general cellular poison. The molecular mechanism of action of uranium is associated with its ability to suppress enzyme activity. The kidneys are primarily affected (protein and sugar appear in the urine, oliguria). With chronic intoxication, disorders of hematopoiesis and the nervous system are possible.

Encyclopedic Dictionary. 2009 .

See what "URANIUM (chemical element)" is in other dictionaries:

U (Uran, uranium; at O = 16 atomic weight U = 240) the element with the highest atomic weight; All elements, in atomic weight, fall between hydrogen and uranium. This is the heaviest member of the metallic subgroup of group VI of the periodic table (see Chromium, ... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

Uranium (U) Atomic number 92 Appearance of a simple substance Properties of the atom Atomic mass (molar mass) 238.0289 a. e.m. (g/mol) ... Wikipedia

Uranium (lat. Uranium), U, a radioactive chemical element of group III of the periodic system of Mendeleev, belongs to the actinide family, atomic number 92, atomic mass 238.029; metal. Natural U. consists of a mixture of three isotopes: 238U √ 99.2739%... ... Great Soviet Encyclopedia

Uranium (chemical element)- URANIUM, U, radioactive chemical element of group III of the periodic table, atomic number 92, atomic mass 238.0289; belongs to actinides; metal, melting point 1135°C. Uranium is the main element of nuclear energy (nuclear fuel), used in... ... Illustrated Encyclopedic Dictionary Wikipedia

- (Greek uranos sky). 1) god of the sky, father of Saturn, the oldest of the gods, in Greek. mythol. 2) a rare metal that 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) 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, radioactive chemical element of group III of the periodic table, atomic number 92, atomic mass 238.0289; belongs to actinides; metal, melting point 1135shC. Uranium is the main element of nuclear energy (nuclear fuel), used in... ... Modern encyclopedia

DEFINITION

Uranus- ninety-second element of the Periodic Table. Designation - U from the Latin “uranium”. Located in the seventh period, IIIB group. Refers to metals. The nuclear charge is 92.

Uranium is a silver-colored metal with a glossy surface (Fig. 1). Heavy. Malleable, flexible and soft. Inherent properties of paramagnets. Uranium is characterized by the presence of three modifications: α-uranium (orthorhombic system), β-uranium (tetragonal system) and γ-uranium (cubic system), each of which exists in a certain temperature range.

Rice. 1. Uranium. Appearance.

Atomic and molecular mass of uranium

Relative molecular weight of the substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 the mass of a carbon atom.

Since in the free state uranium exists in the form of monatomic U molecules, the values of its atomic and molecular masses coincide. They are equal to 238.0289.

Isotopes of uranium

It is known that uranium does not have stable isotopes, but natural uranium consists of a mixture of those isotopes 238 U (99.27%), 235 U and 234 U, which are radioactive.

There are unstable isotopes of uranium with mass numbers from 217 to 242.

Uranium ions

At the outer energy level of the uranium atom there are three electrons, which are valence:

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 5f 3 6s 2 6p 6 6d 1 7s 2 .

As a result of chemical interaction, uranium gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:

U 0 -3e → U 3+ .

Molecule and atom of uranium

In the free state, uranium exists in the form of monatomic U molecules. Here are some properties characterizing the uranium atom and molecule:

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Exercise

In the series of radioactive transformation of uranium there are the following stages:

238 92 U → 234 90 Th → 234 91 Pa → X.

What particles are emitted in the first two stages? What isotope X is formed in the third stage if it is accompanied by the emission of a β-particle?

Answer

We determine how the mass number and charge of the radionuclide nucleus change at the first stage. The mass number will decrease by 4 units, and the charge number by 2 units, therefore, at the first stage, α-decay occurs.

We determine how the mass number and charge of the radionuclide nucleus change at the second stage. The mass number does not change, but the nuclear charge increases by one, indicating β-decay.

(according to Pauling) 1.38 U←U 4+ -1.38V
U←U 3+ -1.66V
U←U 2+ -0.1V 6, 5, 4, 3 Thermodynamic properties 19.05/³ 0.115 /( ·) 27.5 /( ·) 1405.5 12.6 / 4018 417 / 12.5 ³/ Crystal lattice orthorhombic 2.850 c/a ratio n/a n/a

Story

Even in ancient times (1st century BC), natural uranium was used to make yellow glaze for.

Uranium was discovered in 1789 by the German chemist Martin Heinrich Klaproth while studying the mineral (“uranium tar”). He was named in honor of uranium, discovered in 1781. In the metallic state, uranium was obtained in 1841 by the French chemist Eugene Peligot during the reduction of UCl 4 with potassium metal. Uranium was discovered in 1896 by a Frenchman. Initially, uranium was assigned 116, but in 1871 he 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 came to the conclusion that these elements () are more correctly placed in the periodic table in the same cell with element number 89. This arrangement is due to the fact that in actinides the 5f electron sublevel is completed.

Being in nature

Uranium is a characteristic element for the granite layer and sedimentary shell of the earth's crust. The content in the earth's crust is 2.5 10 -4% by weight. In sea water, the concentration of uranium is less than 10 -9 g/l; in total, sea water contains from 10 9 to 10 10 tons of uranium. Uranium is not found in free form in the earth's crust. About 100 uranium minerals are known, the most important of which are U 3 O 8, 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.

Isotopes

Natural Uranium consists of a mixture of three isotopes: 238 U - 99.2739%, half-life T 1 / 2 = 4.51 Ї 10 9 years, 235 U - 0.7024% (T 1 / 2 = 7.13 Ї 10 8 years) and 234 U - 0.0057% (T 1 / 2 = 2.48Ї10 5 years).

There are 11 known artificial radioactive isotopes with mass numbers from 227 to 240.

The longest-lived - 233 U (T 1 / 2 = 1.62/10 5 years) is obtained by irradiating thorium with neutrons.

The uranium isotopes 238 U and 235 U are the ancestors of two radioactive series.

Receipt

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, they precipitate quickly: these are heavy minerals. Secondary minerals of element No. 92 are lighter, in which case the heavy gangue settles out earlier. (However, it is not always truly empty; it may contain many useful elements, including uranium).

The next stage is leaching of concentrates, transferring element No. 92 into solution. Acid and alkaline leaching are used. The first is cheaper, since they use uranium to extract uranium. But if in the feedstock, such as uranium tar, uranium is in the tetravalent state, then this method is not applicable: tetravalent uranium is practically insoluble in sulfuric acid. And either you need to resort to alkaline leaching, or first oxidize the uranium to a hexavalent state.

Acid leaching is also not used in cases where the uranium concentrate contains or. Too much acid has to be spent on dissolving them, and in these cases it is better to use ().

The problem of uranium leaching from oxygen is solved by oxygen purge. A stream is fed into a mixture of uranium ore and minerals heated to 150 °C. At the same time, sulfur minerals are formed, which washes away uranium.

At the next stage, uranium must be selectively isolated from the resulting solution. Modern methods - and - allow us to solve this problem.

The solution contains not only uranium, but also others. Some of them, under certain conditions, behave in the same way as uranium: they are extracted with the same solvents, deposited on the same ion exchange resins, and precipitate under the same conditions. Therefore, to selectively isolate uranium, it is necessary to use many redox reactions in order to get rid of one or another unwanted companion at each stage. On modern ion exchange resins, uranium is released very selectively.

Methods ion exchange and extraction They are also good because they make it possible to quite completely extract uranium from poor solutions, in a liter of which there are only tenths of a gram of element No. 92.

After these operations, the uranium is converted into a solid state - into one of the oxides or into UF 4 tetrafluoride. But this uranium still needs to be purified from impurities with a large thermal neutron capture cross section - , . Their content in the final product should not exceed hundred thousandths and millionths of a percent. So we have to dissolve the already obtained technically pure product again - this time in . Uranyl nitrate UO 2 (NO 3) 2 during extraction with tributyl phosphate and some other substances is further purified to the required standards. Then this substance is crystallized (or peroxide UO 4 ·2H 2 O is precipitated) and carefully calcined. As a result of this operation, uranium trioxide UO 3 is formed, which is reduced to UO 2.

This substance is the penultimate one on the way from ore to metal. At temperatures from 430 to 600 °C it reacts with dry hydrogen fluoride and turns into UF 4 tetrafluoride. It is from this compound that uranium metal is usually obtained. Obtained with the help or usual.

Physical properties

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. Uranium has three allotropic forms: alpha (prismatic, stable up to 667.7 °C), beta (tetragonal, stable from 667.7 to 774.8 °C), gamma (with a body-centered cubic structure, existing from 774.8 °C to the melting point).

Chemical properties

The chemical activity of uranium metal is high. In air it becomes covered with a rainbow film. Powdered uranium, it spontaneously ignites at a temperature of 150-175 °C. 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 an atmosphere above 500 °C, UO 2 is formed. 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).

Application

Nuclear fuel

The greatest use is for uranium 235 U, in which self-sustaining is possible. Therefore, this isotope is used as fuel in, as well as in (critical mass about 48 kg). Isolation of the U 235 isotope from natural uranium is a complex technological problem (see). The U 238 isotope is capable of fission under the influence of bombardment with high-energy neutrons; this feature is used to increase power (neutrons generated by a thermonuclear reaction are used). As a result of neutron capture followed by β-decay, 238 U can be converted into 239, which is then used as nuclear fuel.

Uranium-233, produced artificially in reactors (by irradiation with neutrons and turning into and then into uranium-233) is a nuclear fuel for nuclear power plants and the production of atomic bombs (critical mass of about 16 kg). Uranium-233 is also the most promising fuel for gas-phase nuclear rocket engines.

Other Applications

A small addition of uranium gives the glass a beautiful greenish-yellow tint.
Uranium-235 carbide alloyed with niobium carbide and zirconium carbide is used as fuel for nuclear jet engines (working fluid - hydrogen + hexane).
Alloys of iron and depleted uranium (uranium-238) are used as powerful magnetostrictive materials.
At the beginning of the twentieth century uranyl nitrate was widely used as a virilating agent for producing tinted photographic prints.

Depleted uranium

After U-235 is extracted from natural uranium, the remaining material is called "depleted uranium" because it is depleted of the 235 isotope. According to some estimates, about 560,000 tons of depleted uranium hexafluoride (UF 6) are stored in the United States. Depleted uranium is half as radioactive as natural uranium, mainly due to the removal of U-234 from it. Because the primary use of uranium is energy production, depleted uranium is a useless product with little economic value.

Its main use is due to the high density of uranium and its relatively low cost: its use for radiation protection (oddly enough) and as ballast in aerospace applications such as control surfaces of aircraft. Each aircraft contains 1,500 kg of depleted uranium for these purposes. This material is also used in high-speed gyroscope rotors, large flywheels, as ballast in space landers and racing yachts, and when drilling oil wells.

Armor-piercing projectile cores

The most famous use of uranium is as cores for American . When alloyed with 2% or 0.75% 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 (tensile strength is more than 1600 MPa, while , 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 effectiveness to the more expensive . The process of armor destruction is accompanied by the grinding of a uranium pig into dust and its ignition in air on the other side of the armor. About 300 tons of depleted uranium remained on the battlefield during Operation Desert Storm (mostly the remains of shells from the 30 mm GAU-8 cannon of A-10 attack aircraft, each shell containing 272 g of uranium alloy).

Such shells were used by NATO troops in combat operations on the territory of Yugoslavia. After their application, the environmental problem of radiation contamination of the country's territory was discussed.

Depleted uranium is used in modern tank armor, such as the tank.

Physiological action

It is found in microquantities (10 -5 -10 -8%) in the tissues of plants, animals and humans. It accumulates to the greatest extent 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, and bronchopulmonary. The content in organs and tissues of humans and animals does not exceed 10 -7 g.

Uranium and its compounds toxic. Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds, the MPC in air is 0.015 mg/m 3 , for insoluble forms of uranium 0.075 mg/m 3 . When uranium enters the body, it affects all organs, being a general cellular poison. The molecular mechanism of action of uranium is related to its ability to suppress activity. First of all, they are affected (protein and sugar appear in the urine,). In chronic cases, disorders of hematopoiesis and the nervous system are possible.

Uranium mining in the world

According to the “Red Book on Uranium”, released in 2005, 41,250 tons of uranium were mined (in 2003 - 35,492 tons). According to OECD data, there are 440 commercial enterprises operating in the world, which consume 67 thousand tons of uranium per year. This means that its production provides only 60% of its consumption (the rest is recovered from old nuclear warheads).

Production by country in tons by U content for 2005-2006.

Production in Russia

The remaining 7% is obtained by underground leaching by JSC Dalur () and JSC Khiagda ().

The resulting ores and uranium concentrate are processed at the Chepetsk Mechanical Plant.