What is plutonium made from? Weapons-grade plutonium: application, production, disposal

He is truly precious.

Background and history

In the beginning there were protons - galactic hydrogen. As a result of its compression and subsequent nuclear reactions, the most incredible “ingots” of nucleons were formed. Among them, these “ingots,” there were apparently those containing 94 protons. Theorists' estimates suggest that about 100 nucleon formations, which include 94 protons and from 107 to 206 neutrons, are so stable that they can be considered the nuclei of isotopes of element No. 94.

But all these isotopes - hypothetical and real - are not so stable as to survive to this day since the formation of the elements of the solar system. The half-life of the longest-lived isotope of element No. 94 is 75 million years. The age of the Galaxy is measured in billions of years. Consequently, the “primordial” plutonium had no chance of surviving to this day. If it was formed during the great synthesis of the elements of the Universe, then those ancient atoms of it “extinct” long ago, just as dinosaurs and mammoths became extinct.

In the 20th century new era, AD, this element was recreated. Of the 100 possible isotopes of plutonium, 25 have been synthesized. The nuclear properties of 15 of them have been studied. Four have found practical application. And it was opened quite recently. In December 1940, when uranium was irradiated with heavy hydrogen nuclei, a group of American radiochemists led by Glenn T. Seaborg discovered a previously unknown alpha particle emitter with a half-life of 90 years. This emitter turned out to be the isotope of element No. 94 with a mass number of 238. In the same year, but a few months earlier, E.M. McMillan and F. Abelson obtained the first element heavier than uranium - element No. 93. This element was called neptunium, and the 94th was called plutonium. The historian will definitely say that these names originate in Roman mythology, but in essence the origin of these names is rather not mythological, but astronomical.

Elements No. 92 and 93 are named after the distant planets of the solar system - Uranus and Neptune, but Neptune is not the last in the solar system, even further lies the orbit of Pluto - a planet about which almost nothing is still known... A similar construction We also see on the “left flank” of the periodic table: uranium – neptunium – plutonium, however, humanity knows much more about plutonium than about Pluto. By the way, astronomers discovered Pluto just ten years before the synthesis of plutonium - almost the same period of time separated the discoveries of Uranus - the planet and uranium - the element.

Riddles for cryptographers

The first isotope of element No. 94, plutonium-238, has found practical application these days. But in the early 40s they didn’t even think about it. It is possible to obtain plutonium-238 in quantities of practical interest only by relying on the powerful nuclear industry. At that time it was just in its infancy. But it was already clear that by releasing the energy contained in the nuclei of heavy radioactive elements, it was possible to obtain weapons of unprecedented power. The Manhattan Project appeared, which had nothing more than a name in common with the famous New York area. This was the general name for all work related to the creation of the first atomic bombs in the United States. It was not a scientist, but a military man, General Groves, who was appointed head of the Manhattan Project, who “affectionately” called his highly educated charges “broken pots.”

The leaders of the “project” were not interested in plutonium-238. Its nuclei, like the nuclei of all isotopes of plutonium with even mass numbers, are not fissile by low-energy neutrons*, so it could not serve as a nuclear explosive. Nevertheless, the first not very clear reports about elements No. 93 and 94 appeared in print only in the spring of 1942.

* We call low-energy neutrons neutrons whose energy does not exceed 10 keV. Neutrons with energy measured in fractions of an electronvolt are called thermal, and the slowest neutrons, with energy less than 0.005 eV, are called cold. If the neutron energy is more than 100 keV, then such a neutron is considered fast.

How can we explain this? Physicists understood: the synthesis of plutonium isotopes with odd mass numbers was a matter of time, and not too long. Odd isotopes were expected to, like uranium-235, be able to support a nuclear chain reaction. Some people saw them as potential nuclear explosives, which had not yet been received. And plutonium, unfortunately, justified these hopes.

In encryption of that time, element No. 94 was called nothing more than... copper. And when the need arose for copper itself (as a structural material for some parts), then in the codes, along with “copper,” “genuine copper” appeared.

"The Tree of the Knowledge of Good and Evil"

In 1941, the most important isotope of plutonium was discovered - an isotope with a mass number of 239. And almost immediately the theorists' prediction was confirmed: the nuclei of plutonium-239 were fissioned by thermal neutrons. Moreover, during their fission, no less number of neutrons were produced than during the fission of uranium-235. Ways to obtain this isotope in large quantities were immediately outlined...

Years have passed. Now it’s no secret to anyone that the nuclear bombs stored in arsenals are filled with plutonium-239 and that these bombs are enough to cause irreparable damage to all life on Earth.

There is a widespread belief that humanity was clearly in a hurry with the discovery of the nuclear chain reaction (the inevitable consequence of which was the creation of a nuclear bomb). You can think differently or pretend to think differently - it’s more pleasant to be an optimist. But even optimists inevitably face the question of the responsibility of scientists. We remember the triumphant June day of 1954, the day when the first nuclear power plant in Obninsk turned on. But we cannot forget the morning of August 1945 - “the morning of Hiroshima”, “the black day of Albert Einstein”... We remember the first post-war years and the rampant atomic blackmail - the basis of American policy in those years. But hasn’t humanity experienced a lot of troubles in subsequent years? Moreover, these anxieties were intensified many times over by the consciousness that if a new world war broke out, nuclear weapons would be used.

Here you can try to prove that the discovery of plutonium did not add fear to humanity, that, on the contrary, it was only useful.

Let's say it happened that for some reason or, as they would say in the old days, by the will of God, plutonium was inaccessible to scientists. Would our fears and concerns then be reduced? Nothing happened. Nuclear bombs would be made from uranium-235 (and in no less quantity than from plutonium), and these bombs would “eat up” even larger parts of the budgets than now.

But without plutonium there would be no prospect of peaceful use of nuclear energy on a large scale. There simply would not be enough uranium-235 for a “peaceful atom”. The evil inflicted on humanity by the discovery of nuclear energy would not be balanced, even partially, by the achievements of the “good atom.”

How to measure, what to compare with

When a plutonium-239 nucleus is split by neutrons into two fragments of approximately equal mass, about 200 MeV of energy is released. This is 50 million times more energy released in the most famous exothermic reaction C + O 2 = CO 2. “Burning” in a nuclear reactor, a gram of plutonium gives 2·10 7 kcal. In order not to break traditions (and in popular articles, the energy of nuclear fuel is usually measured in non-systemic units - tons of coal, gasoline, trinitrotoluene, etc.), we also note: this is the energy contained in 4 tons of coal. And an ordinary thimble contains an amount of plutonium energetically equivalent to forty carloads of good birch firewood.

The same energy is released during the fission of uranium-235 nuclei by neutrons. But the bulk of natural uranium (99.3%!) is the isotope 238 U, which can only be used by turning uranium into plutonium...

Energy of stones

Let us evaluate the energy resources contained in natural uranium reserves.

Uranium is a trace element and is found almost everywhere. Anyone who has visited, for example, Karelia, will probably remember granite boulders and coastal cliffs. But few people know that a ton of granite contains up to 25 g of uranium. Granites make up almost 20% of the weight of the earth's crust. If we count only uranium-235, then a ton of granite contains 3.5·10 5 kcal of energy. It's a lot, but...

Processing granite and extracting uranium from it requires spending an even larger amount of energy - about 10 6 ...10 7 kcal/t. Now, if it were possible to use not only uranium-235, but also uranium-238 as an energy source, then granite could be considered at least as a potential energy raw material. Then the energy obtained from a ton of stone would already be from 8·10 7 to 5·10 8 kcal. This is equivalent to 16...100 tons of coal. And in this case, granite could provide people with almost a million times more energy than all the chemical fuel reserves on Earth.

But uranium-238 nuclei do not fission by neutrons. This isotope is useless for nuclear energy. More precisely, it would be useless if it could not be converted into plutonium-239. And what is especially important: practically no energy needs to be spent on this nuclear transformation - on the contrary, energy is produced in this process!

Let's try to figure out how this happens, but first a few words about natural plutonium.

400 thousand times less than radium

It has already been said that isotopes of plutonium have not been preserved since the synthesis of elements during the formation of our planet. But this does not mean that there is no plutonium in the Earth.

It is formed all the time in uranium ores. By capturing neutrons from cosmic radiation and neutrons produced by the spontaneous fission of uranium-238 nuclei, some - very few - atoms of this isotope turn into atoms of uranium-239. These nuclei are very unstable; they emit electrons and thereby increase their charge. Neptunium, the first transuranium element, is formed. Neptunium-239 is also highly unstable, and its nuclei emit electrons. In just 56 hours, half of the neptunium-239 turns into plutonium-239, the half-life of which is already quite long - 24 thousand years.

Why isn't plutonium extracted from uranium ores? Low, too low concentration. “A gram of production is a year of work” - this is about radium, and the ores contain 400 thousand times less plutonium than radium. Therefore, it is extremely difficult not only to mine, but even to detect “terrestrial” plutonium. This was done only after the physical and chemical properties of plutonium produced in nuclear reactors were studied.

When 2.70 >> 2.23

Plutonium is accumulated in nuclear reactors. In powerful neutron streams, the same reaction occurs as in uranium ores, but the rate of formation and accumulation of plutonium in the reactor is much higher - a billion billion times. For the reaction of converting ballast uranium-238 into energy-grade plutonium-239, optimal (within acceptable) conditions are created.

If the reactor operates on thermal neutrons (recall that their speed is about 2000 m per second, and their energy is a fraction of an electron volt), then from a natural mixture of uranium isotopes an amount of plutonium is obtained that is slightly less than the amount of “burnt out” uranium-235. A little, but less, plus the inevitable losses of plutonium during its chemical separation from irradiated uranium. In addition, the nuclear chain reaction is maintained in the natural mixture of uranium isotopes only until a small fraction of uranium-235 is consumed. Hence the logical conclusion: a “thermal” reactor using natural uranium - the main type of currently operating reactors - cannot ensure the expanded reproduction of nuclear fuel. But what is promising then? To answer this question, let’s compare the course of the nuclear chain reaction in uranium-235 and plutonium-239 and introduce another physical concept into our discussions.

The most important characteristic of any nuclear fuel is the average number of neutrons emitted after the nucleus has captured one neutron. Physicists call it the eta number and denote it by the Greek letter η. In “thermal” reactors on uranium, the following pattern is observed: each neutron generates an average of 2.08 neutrons (η = 2.08). Plutonium placed in such a reactor under the influence of thermal neutrons gives η = 2.03. But there are also reactors that operate on fast neutrons. It is useless to load a natural mixture of uranium isotopes into such a reactor: a chain reaction will not occur. But if the “raw material” is enriched with uranium-235, it can be developed in a “fast” reactor. In this case, η will already be equal to 2.23. And plutonium, exposed to fast neutron fire, will give η equal to 2.70. We will have “extra half a neutron” at our disposal. And this is not at all little.

Let's see what the resulting neutrons are spent on. In any reactor, one neutron is needed to maintain a nuclear chain reaction. 0.1 neutrons are absorbed by the structural materials of the installation. The “excess” is used to accumulate plutonium-239. In one case, the “excess” is 1.13, in the other – 1.60. After the “burning” of a kilogram of plutonium in a “fast” reactor, colossal energy is released and 1.6 kg of plutonium is accumulated. And uranium in a “fast” reactor will give the same energy and 1.1 kg of new nuclear fuel. In both cases, expanded reproduction is evident. But we must not forget about the economy.

Due to a number of technical reasons, the plutonium reproduction cycle takes several years. Let's say five years. This means that the amount of plutonium per year will increase by only 2% if η = 2.23, and by 12% if η = 2.7! Nuclear fuel is capital, and any capital should yield, say, 5% per annum. In the first case there are large losses, and in the second there are large profits. This primitive example illustrates the “weight” of every tenth of the number η in nuclear power.

Sum of many technologies

When, as a result of nuclear reactions, the required amount of plutonium has accumulated in uranium, it must be separated not only from the uranium itself, but also from fission fragments - both uranium and plutonium, burned up in the nuclear chain reaction. In addition, the uranium-plutonium mass also contains a certain amount of neptunium. The most difficult things to separate are plutonium from neptunium and rare earth elements (lanthanides). Plutonium, as a chemical element, has been unlucky to some extent. From a chemist's point of view, the main element of nuclear energy is just one of fourteen actinides. Like rare earth elements, all elements of the actinium series are very similar to each other in chemical properties; the structure of the outer electron shells of the atoms of all elements from actinium to 103 is the same. What’s even more unpleasant is that the chemical properties of actinides are similar to the properties of rare earth elements, and among the fission fragments of uranium and plutonium there are more than enough lanthanides. But then element 94 can be in five valence states, and this “sweets the pill” - it helps to separate plutonium from both uranium and fission fragments.

The valency of plutonium varies from three to seven. Chemically, the most stable (and therefore the most common and most studied) compounds are tetravalent plutonium.

The separation of actinides with similar chemical properties - uranium, neptunium and plutonium - can be based on the difference in the properties of their tetra- and hexavalent compounds.

There is no need to describe in detail all the stages of the chemical separation of plutonium and uranium. Usually, their separation begins with the dissolution of uranium bars in nitric acid, after which the uranium, neptunium, plutonium and fragmentation elements contained in the solution are “separated”, using traditional radiochemical methods for this - coprecipitation with carriers, extraction, ion exchange and others. The final plutonium-containing products of this multi-stage technology are its dioxide PuO 2 or fluorides - PuF 3 or PuF 4. They are reduced to metal with barium, calcium or lithium vapor. However, the plutonium obtained in these processes is not suitable for the role of a structural material - fuel elements of nuclear power reactors cannot be made from it, and the charge of an atomic bomb cannot be cast. Why? The melting point of plutonium – only 640°C – is quite achievable.

No matter what “ultra-gentle” conditions are used to cast parts from pure plutonium, cracks will always appear in the castings during solidification. At 640°C, solidifying plutonium forms a cubic crystal lattice. As the temperature decreases, the density of the metal gradually increases. But then the temperature reached 480°C, and then suddenly the density of plutonium dropped sharply. The reasons for this anomaly were discovered quite quickly: at this temperature, plutonium atoms are rearranged in the crystal lattice. It becomes tetragonal and very “loose”. Such plutonium can float in its own melt, like ice on water.

The temperature continues to drop, now it has reached 451°C, and the atoms again formed a cubic lattice, but located at a greater distance from each other than in the first case. With further cooling, the lattice first becomes orthorhombic, then monoclinic. In total, plutonium forms six different crystalline forms! Two of them are distinguished by a remarkable property - a negative coefficient of thermal expansion: with increasing temperature, the metal does not expand, but contracts.

When the temperature reaches 122°C and the plutonium atoms rearrange their rows for the sixth time, the density changes especially dramatically - from 17.77 to 19.82 g/cm 3 . More than 10%! Accordingly, the volume of the ingot decreases. If the metal could still resist the stresses that arose at other transitions, then at this moment destruction is inevitable.

How then to make parts from this amazing metal? Metallurgists alloy plutonium (adding small amounts of the required elements to it) and obtain castings without a single crack. They are used to make plutonium charges for nuclear bombs. The weight of the charge (it is determined primarily by the critical mass of the isotope) is 5...6 kg. It could easily fit into a cube with an edge size of 10 cm.

Heavy isotopes

Plutonium-239 also contains in small quantities higher isotopes of this element - with mass numbers 240 and 241. The 240 Pu isotope is practically useless - this is ballast in plutonium. From 241, americium is obtained - element No. 95. In their pure form, without admixture of other isotopes, dlutonium-240 and plutonium-241 can be obtained by electromagnetic separation of plutonium accumulated in a reactor. Before this, plutonium is additionally irradiated with neutron fluxes with strictly defined characteristics. Of course, all this is very complicated, especially since plutonium is not only radioactive, but also very toxic. Working with it requires extreme caution.

One of the most interesting isotopes of plutonium, 242 Pu, can be obtained by irradiating 239 Pu for a long time in neutron fluxes. 242 Pu very rarely captures neutrons and therefore “burns out” in the reactor more slowly than other isotopes; it persists even after the remaining isotopes of plutonium have almost completely turned into fragments or turned into plutonium-242.

Plutonium-242 is important as a “raw material” for the relatively rapid accumulation of higher transuranium elements in nuclear reactors. If plutonium-239 is irradiated in a conventional reactor, then it will take about 20 years to accumulate microgram amounts of, for example, California-251 from grams of plutonium.

It is possible to reduce the accumulation time of higher isotopes by increasing the intensity of the neutron flux in the reactor. This is what they do, but then you cannot irradiate large amounts of plutonium-239. After all, this isotope is divided by neutrons, and too much energy is released in intense flows. Additional difficulties arise with cooling the container and reactor. To avoid these difficulties, it would be necessary to reduce the amount of plutonium irradiated. Consequently, the yield of californium would again become scanty. Vicious circle!

Plutonium-242 is not fissile by thermal neutrons, it can be irradiated in large quantities in intense neutron fluxes... Therefore, in reactors, all elements from californium to einsteinium are “made” from this isotope and accumulated in weight quantities.

Not the heaviest, but the longest lived

Every time scientists managed to obtain a new isotope of plutonium, the half-life of its nuclei was measured. The half-lives of isotopes of heavy radioactive nuclei with even mass numbers change regularly. (This cannot be said for odd isotopes.)

Rice. 8.

Look at the graph showing the dependence of the half-life of even isotopes of plutonium on the mass number. As the mass increases, the “lifetime” of the isotope also increases. A few years ago, the high point of this graph was plutonium-242. And then how will this curve go - with a further increase in the mass number? Exactly 1 , which corresponds to a lifetime of 30 million years, or to the point 2 , which has been answering for 300 million years? The answer to this question was very important for geosciences. In the first case, if 5 billion years ago the Earth consisted entirely of 244 Pu, now only one atom of plutonium-244 would remain in the entire mass of the Earth. If the second assumption is true, then plutonium-244 may be in the Earth in concentrations that could already be detected. If we were lucky enough to find this isotope in the Earth, science would receive the most valuable information about the processes that took place during the formation of our planet.

A few years ago, scientists were faced with the question: is it worth trying to find heavy plutonium in the Earth? To answer it, it was necessary first of all to determine the half-life of plutonium-244. Theorists could not calculate this value with the required accuracy. All hope was only for experiment.

Plutonium-244 accumulated in a nuclear reactor. Element No. 95, americium (isotope 243 Am), was irradiated. Having captured a neutron, this isotope turned into americium-244; americium-244 in one out of 10 thousand cases turned into plutonium-244.

The preparation of plutonium-244 was isolated from a mixture of americium and curium. The sample weighed only a few millionths of a gram. But they were enough to determine the half-life of this interesting isotope. It turned out to be equal to 75 million years. Later, other researchers clarified the half-life of plutonium-244, but not by much - 82.8 million years. In 1971, traces of this isotope were found in the rare earth mineral bastnäsite.

Many attempts have been made by scientists to find an isotope of the transuranium element that lives longer than 244 Pu. But all attempts remained in vain. At one time, hopes were placed on curium-247, but after this isotope was accumulated in the reactor, it turned out that its half-life is only 14 million years. It was not possible to break the record of plutonium-244 - it is the longest-lived of all isotopes of transuranium elements.

Even heavier isotopes of plutonium undergo beta decay, and their lifetimes range from a few days to a few tenths of a second. We know for sure that all isotopes of plutonium are formed in thermonuclear explosions, up to 257 Pu. But their lifetime is tenths of a second, and many short-lived isotopes of plutonium have not yet been studied.

Possibilities of the first isotope

And finally - about plutonium-238 - the very first of the “man-made” isotopes of plutonium, an isotope that at first seemed unpromising. It is actually a very interesting isotope. It is subject to alpha decay, i.e. its nuclei spontaneously emit alpha particles - helium nuclei. Alpha particles generated by plutonium-238 nuclei carry high energy; dissipated in matter, this energy turns into heat. How big is this energy? Six million electron volts are released from the decay of one atomic nucleus of plutonium-238. In a chemical reaction, the same energy is released when several million atoms are oxidized. An electricity source containing one kilogram of plutonium-238 develops a thermal power of 560 watts. The maximum power of a chemical current source of the same mass is 5 watts.

There are many emitters with similar energy characteristics, but one feature of plutonium-238 makes this isotope indispensable. Alpha decay is usually accompanied by strong gamma radiation, penetrating through large layers of matter. 238 Pu is an exception. The energy of gamma rays accompanying the decay of its nuclei is low, and it is not difficult to protect against it: the radiation is absorbed by a thin-walled container. The probability of spontaneous fission of nuclei of this isotope is also low. Therefore, it has found application not only in current sources, but also in medicine. Batteries containing plutonium-238 serve as a source of energy in special cardiac stimulators.

But 238 Pu is not the lightest known isotope of element No. 94; isotopes of plutonium have been obtained with mass numbers from 232 to 237. The half-life of the lightest isotope is 36 minutes.

Plutonium is a big topic. The most important things are told here. After all, it has already become a standard phrase that the chemistry of plutonium has been studied much better than the chemistry of such “old” elements as iron. Whole books have been written about the nuclear properties of plutonium. The metallurgy of plutonium is another amazing section of human knowledge... Therefore, you should not think that after reading this story, you truly learned plutonium - the most important metal of the 20th century.

There are 15 known isotopes of plutonium. The most important of these is Pu-239 with a half-life of 24,360 years. The specific gravity of plutonium is 19.84 at a temperature of 25°C. The metal begins to melt at a temperature of 641°C and boils at 3232°C. Its valency is 3, 4, 5 or 6.

The metal has a silvery tint and turns yellow when exposed to oxygen. Plutonium is a chemical reactive metal and easily dissolves in concentrated hydrochloric acid, perchloric acid, and hydroiodic acid. During decay, the metal releases heat energy.

Plutonium is the second transuranic actinide discovered. In nature, this metal can be found in small quantities in uranium ores.

Plutonium is poisonous and requires careful handling. The most fissionable isotope of plutonium has been used as a nuclear weapon. In particular, it was used in a bomb that was dropped on the Japanese city of Nagasaki.

This is a radioactive poison that accumulates in the bone marrow. Several accidents, some fatal, occurred while experimenting on people to study plutonium. It is important that the plutonium does not reach critical mass. In solution, plutonium forms a critical mass faster than in the solid state.

Atomic number 94 means that all plutonium atoms are 94. In air, plutonium forms on the surface of the metal. This oxide is pyrophoric, so smoldering plutonium will flicker like ash.

There are six allotropic forms of plutonium. The seventh form appears at high .

In an aqueous solution, plutonium changes color. Various shades appear on the surface of the metal as it oxidizes. The oxidation process is unstable and the color of plutonium can change suddenly.

Unlike most substances, plutonium becomes denser when melted. In the molten state this element is more powerful than other metals.

The metal is used in radioactive isotopes in thermoelectric generators that power spacecraft. It is used in the production of electronic cardiac stimulators.

Inhaling plutonium vapor is hazardous to health. In some cases, this can cause lung cancer. Inhaled plutonium has a metallic taste.

Weapons-grade plutonium is plutonium in the form of a compact metal containing at least 93.5% of the 239Pu isotope. Intended for the creation of nuclear weapons.

1.Name and features

They call it “weapon-grade” to distinguish it from “reactor-grade”. Plutonium is formed in any nuclear reactor operating on natural or low-enriched uranium, containing mainly the 238U isotope, when it captures excess neutrons. But as the reactor operates, the weapons-grade isotope of plutonium quickly burns up, and as a result, a large number of isotopes 240Pu, 241Pu and 242Pu accumulate in the reactor, formed by the successive capture of several neutrons - since the burnup depth is usually determined by economic factors. The lower the burnup depth, the fewer isotopes 240Pu, 241Pu and 242Pu will contain plutonium separated from irradiated nuclear fuel, but the less plutonium is formed in the fuel.

Special production of plutonium for weapons containing almost exclusively 239Pu is required mainly because isotopes with mass numbers 240 and 242 create a high neutron background, making it difficult to design effective nuclear weapons, in addition, 240Pu and 241Pu have a significantly shorter half-life than 239Pu, due to which the plutonium parts heat up, and it is necessary to additionally introduce heat removal elements into the design of the nuclear weapon. Even pure 239Pu is warmer than the human body. Additionally, the decay products of heavy isotopes spoil the crystal lattice of the metal, which can lead to a change in the shape of plutonium parts, which can lead to the failure of a nuclear explosive device.

In principle, all these difficulties can be overcome, and nuclear explosive devices made from “reactor” plutonium have been successfully tested, however, in ammunition, where compactness, light weight, reliability and durability play an important role, exclusively specially produced weapons-grade plutonium is used. The critical mass of metallic 240Pu and 242Pu is very large, 241Pu is slightly larger than that of 239Pu.

2.Production

In the USSR, the production of weapons-grade plutonium was carried out first at the Mayak plant in Ozersk (formerly Chelyabinsk-40, Chelyabinsk-65), then at the Siberian Chemical Plant in Seversk (formerly Tomsk-7), and later the Krasnoyarsk Mining Plant was put into operation -chemical plant in Zheleznogorsk (also known as Sotsgorod and Krasnoyarsk-26). Production of weapons-grade plutonium in Russia ceased in 1994. In 1999, the reactors in Ozyorsk and Seversk were shut down, and in 2010 the last reactor in Zheleznogorsk was shut down.

In the United States, weapons-grade plutonium was produced in several places, such as the Hanford complex in Washington state. Production was closed in 1988.

3.Synthesis of new elements

The transformation of some atoms into others occurs through the interaction of atomic or subatomic particles. Of these, only neutrons are available in large quantities. A gigawatt nuclear reactor produces about 3.75 kg (or 4 * 1030) neutrons over the course of a year.

4.Plutonium production

Plutonium atoms are formed as a result of a chain of atomic reactions beginning with the capture of a neutron by a uranium-238 atom:

U238 + n -> U239 -> Np239 -> Pu239

or, more precisely:

0n1 + 92U238 -> 92U239 -> -1e0 + 93Np239 -> -1e0 + 94Pu239

With continued irradiation, some atoms of plutonium-239 are able, in turn, to capture a neutron and turn into the heavier isotope plutonium-240:

Pu239 + n -> Pu240

To obtain plutonium in sufficient quantities, strong neutron fluxes are needed. These are exactly what are created in nuclear reactors. In principle, any reactor is a source of neutrons, but for the industrial production of plutonium it is natural to use one specially designed for this purpose.

The world's very first commercial plutonium production reactor was the B-reactor at Hanford. Worked on September 26, 1944, power - 250 MW, productivity - 6 kg of plutonium per month. It contained about 200 tons of uranium metal, 1200 tons of graphite and was cooled with water at a rate of 5 cubic meters/min.

Loading panel of the Hanford reactor with uranium cassettes:

Scheme of its work. In a reactor for irradiating uranium-238, neutrons are created as a result of a stationary chain reaction of fission of uranium-235 nuclei. On average, 2.5 neutrons are produced per fission of U-235. To maintain the reaction and simultaneously produce plutonium, it is necessary that on average one or two neutrons be absorbed by U-238, and one would cause the fission of the next U-235 atom.

Neutrons produced during the fission of uranium have very high speeds. Uranium atoms are arranged in such a way that the capture of fast neutrons by the nuclei of both U-238 and U-235 is unlikely. Therefore, fast neutrons, having experienced several collisions with surrounding atoms, gradually slow down. In this case, U-238 nuclei absorb such neutrons (intermediate velocities) so strongly that nothing is left to fission U-235 and maintain the chain reaction (U-235 is divided from slow, thermal neutrons).

This is counteracted by a moderator, some light substance surrounding the uranium blocks. In it, neutrons are decelerated without absorption, experiencing elastic collisions, in each of which a small part of the energy is lost. Good moderators are water and carbon. Thus, neutrons slowed down to thermal speeds travel through the reactor until they cause fission of U-235 (U-238 absorbs them very weakly). With a certain configuration of the moderator and uranium rods, conditions will be created for the absorption of neutrons by both U-238 and U-235.

The isotopic composition of the resulting plutonium depends on the length of time the uranium rods are in the reactor. A significant accumulation of Pu-240 occurs as a result of prolonged irradiation of a cassette with uranium. With a short residence time of uranium in the reactor, Pu-239 is obtained with an insignificant content of Pu-240.

Pu-240 is harmful to weapons production for the following reasons:

1. It is less fissile than Pu-239, so slightly more plutonium is required to make weapons.

2. Second, much more important reason. The level of spontaneous fission in Pu-240 is much higher, which creates a strong neutron background.

In the very early years of atomic weapon development, neutron emission (high neutron background) was a problem in achieving a reliable and effective charge due to premature detonation. Strong neutron fluxes made it difficult or impossible to compress a bomb core containing several kilograms of plutonium into a supercritical state - before this it was destroyed by the strongest, but still not the maximum possible energy output. The advent of mixed nuclei - containing highly enriched U-235 and plutonium (in the late 1940s) - overcame this difficulty when it became possible to use relatively small amounts of plutonium in mostly uranium nuclei. The next generation of charges, fusion amplified devices (in the mid-1950s), completely eliminated this difficulty, guaranteeing high energy release even with low-power initial fission charges.

Plutonium produced in special reactors contains a relatively small percentage of Pu-240 (<7%), плутоний "оружейного качества"; в реакторах АЭС отработанное ядерное топливо имеет концентрацию Pu-240 более 20%, плутоний "реакторного качества".

In special-purpose reactors, uranium is present for a relatively short period of time, during which not all U-235 burns out and not all U-238 turns into plutonium, but a smaller amount of Pu-240 is formed.

There are two reasons for producing plutonium with low Pu-240 content:

Economic: the only reason for the existence of plutonium special reactors. Decaying plutonium by fission or converting it into less fissile Pu-240 reduces returns and increases production costs (to the point where its price balances with the cost of processing irradiated fuel with low plutonium concentrations).

Handling Difficulty: While neutron emission is not a major concern for weapon designers, it can create manufacturing and handling challenges for such a charge. Neutrons create an additional contribution to occupational exposure to those who assemble or maintain weapons (neutrons themselves do not ionize, but they create protons that can). In fact, charges that involve direct contact with people, such as the Davy Crocket, may require ultra-pure, low-neutron-emitting plutonium for this reason.

The actual casting and processing of plutonium is done by hand in sealed chambers with operator gloves. Like these:

This implies very little protection for humans from neutron-emitting plutonium. Therefore, plutonium with a high content of Pu-240 is processed only by manipulators, or the time each worker works with it is strictly limited.

For all these reasons (radioactivity, worse properties of Pu-240) it is explained why reactor-quality plutonium is not used for the manufacture of weapons - it is cheaper to produce weapons-grade plutonium in special. reactors. Although, apparently, it is also possible to make a nuclear explosive device from a reactor one.

Plutonium ring

This ring is made of electrolytically purified plutonium metal (over 99.96% pure). Typical of the rings prepared at Los Alamos and sent to Rocky Flats for weapon making until production was recently suspended. The mass of the ring is 5.3 kg, sufficient for the manufacture of a modern strategic charge, the diameter is approximately 11 cm. The ring shape is important for ensuring critical safety.

Casting of plutonium-gallium alloy recovered from a weapons core:

Plutonium during the Manhattan Project

Historically, the first 520 milligrams of plutonium metal produced by Ted Magel and Nick Dallas at Los Alamos on March 23, 1944:

Press for hot pressing of plutonium-gallium alloy in the form of hemispheres. This press was used at Los Alamos to make plutonium cores for the charges detonated at Nagasaki and Operation Trinity.

Products cast on it:

Additional by-product isotopes of plutonium

Neutron capture, not accompanied by fission, creates new isotopes of plutonium: Pu-240, Pu-241 and Pu-242. The last two accumulate in small quantities.

Pu239 + n -> Pu240

Pu240 + n -> Pu241

Pu241 + n -> Pu242

A side chain of reactions is also possible:

U238 + n -> U237 + 2n

U237 -> (6.75 days, beta decay) -> Np237

Np237 + n -> Np238

Np238 -> (2.1 days, beta decay) -> Pu238

The overall measure of irradiation (waste) of a fuel cell can be expressed in megawatt days/ton (MW-day/t). Weapons grade plutonium quality is obtained from elements with a small amount of MW-day/t, it produces fewer by-product isotopes. Fuel cells in modern pressurized water reactors reach levels of 33,000 MW-day/t. Typical exposure in a weapons breeder (with expanded breeding of nuclear fuel) reactor is 1000 MW-day/t. Plutonium in the Hanford graphite-moderated reactors is irradiated up to 600 MW-day/t, in Savannah the heavy water reactor produces plutonium of the same quality at 1000 MW-day/t (possibly due to the fact that some of the neutrons are spent on the formation of tritium) . During the Manhattan Project, natural uranium fuel received only 100 MW-day/t, thus producing very high quality plutonium-239 (only 0.9-1% Pu-240, other isotopes in even smaller quantities).

Related information.

Plutonium (plutonium) Pu, - artificially obtained radioactive chemical element, Z=94, atomic mass 244.0642; belongs to actinides. Currently, 19 isotopes of plutonium are known. The lightest of them is 228 Ri (71/2=1.1 s), the heaviest is ^Pu (7i/ 2 =2.27 days), 8 nuclear isomers. The most stable isotope is 2A- 236, 238, 239, 240, 242 and 244: 21013, 6.29-11,2.33-10,8.51109, 3.7-12,1.48-8 and 6.66-uz Bq/g, respectively. The average energy of a-radiation of isotopes with A = 236, 238, 239, 240, 242 and 244 is 5.8, 5.5, 5.1, 5.2, 4.9 and 4.6 MeV, respectively. Light isotopes of plutonium (2 3 2 Pu, 2 34 Pu, 235 Pu, 2 3 7 Pu) undergo electron capture. 2 4 "Pi - p-emitter (Ep = 0.0052 MeV). Practically the most important is 2 39Ru (7|/ 2 =2.44-104 years, a-decay, spontaneous fission (z, my %)) is divided under the influence of slow neutrons and is used in nuclear reactors as fuel, and in atomic bombs as a charge substance.

Plutonium-236 (7i/ 2 =2.85i years), a-emitter: 5.72 MeV (30.56%) and 5.77 MeV (69.26%), daughter nuclide 2 3 2 U, specific activity 540 Ci/ G. Probability of spontaneous fission kg 6. The spontaneous fission rate of 5.8-7 divisions per 1 g/hour corresponds to a half-life for this process of 3.5-109 years.

Can be obtained by reactions:

This isotope is also formed during the decay of the a-emitter 2 4оСш (7i/ 2 =27 days) and the p-emitter 23 6m Np (7i/ 2 =22 h). 2 h 6 Ri decays in the following directions: a-decay, probability 100% and spontaneous fission (probability

Plutopium-237 (7!/ 2 =45> 2 days), daughter product 2 37Np. Can be obtained by bombarding natural uranium with helium ions with an energy of 40 MeV through nuclear reactions:

It is also formed in small quantities when uranium is irradiated with reactor neutrons. The main type of decay is electron capture

(99%, characteristic X-ray emission, daughter product ^Np), but there is a-decay to form 2 zi and weak y-emission, half-life 45.2 days. 2 z7Rts is used in systems for monitoring the chemical yield of plutonium during its isolation from samples of environmental components, as well as for studying the metabolism of plutonium in the human body

Plutonium-238, 7*1/2=87.74 years, a-emitter (energies 5.495(76%), 5.453(24%) and 5.351(0.15%) MeV, weak y-emitter (energies from 0.044 to 0.149 MeV). The activity of 1 g of this nuclide is ~633.7 GBq (specific activity 17 Ci/g); every second in the same amount of substance -1200 acts of spontaneous fission occur. The rate of spontaneous fission is 5.1-6 fissions per 1 g /hour correspond to a half-life for this process of 3.8-10 10 years. In this case, a very high thermal power develops: 567 W / kg. G D el = 3.8-10 10 years. Cross section of thermal neutron capture a = 500 barn , fission cross section under the influence of thermal neutrons is 18 barn. It has a very high specific α-radioactivity (283 times stronger than ^Pu), which makes it much more serious source of neutrons from reactions (a, n).

• 2 h 8Pu is formed as a result of the following decays:
  • (3 -decay of nuclide 2 3 8 Np:

2 h 8 Ru is formed in any nuclear reactor operating on natural or low-enriched uranium, containing mainly the 2 h 8 u isotope. In this case, the following nuclear reactions occur:

It is also formed when uranium is bombarded with helium ions with an energy of 40 MeV:

decay occurs in the following directions: a-decay in 2 34U (probability 10%, decay energy 5.593 MeV):

the energy of the emitted alpha particles is 5.450 Mei (in 2.9% of cases; and 5.499 Mei (in 70.91% of cases). The probability of spontaneous fission is 1.9-7%.

During the a-decay of 2 3 8 Pu, 5.5 MeV of energy is released. In a source of electricity containing one kilogram of 2-3 8 Ri, a thermal power of ~50 watts develops. The maximum power of a chemical current source of the same mass is 5 watts. There are many emitters with similar energy characteristics, but one feature of 2 3Ri makes this isotope irreplaceable. Usually a decay is accompanied by strong y emission. 2 z 8 Ri is an exception. The energy of y-quanta accompanying the decay of its nuclei is low. The probability of spontaneous fission of nuclei of this isotope is also low. 288 Ri is used for the manufacture of nuclear electric batteries and neutron sources, as power sources for pacemakers, for generating thermal energy in spacecraft, as part of radioisotope smoke detectors, etc.

Plutonium-239, 71/2=2.44th 4 years, a-decay 00%, total decay energy 5.867 MeV, emits a-particles with energies of 5.15 (69%), 5.453 (24%) and 5.351(0, 15%) and weak y-radiation, thermal neutron capture cross section st = 271 barn. Specific activity 2.33109 Bq/g. The rate of spontaneous division of 36 divisions/g/hour corresponds to 7” divisions = 5.5-10*5 years. 1 kg 2 39Ri is equivalent to 2.2-107 kilowatt-hours of thermal energy. The explosion of 1 kg of plutonium is equal to the explosion of 20,000 tons of TNT. The only isotope of plutonium used in atomic weapons. 2 39Pu is part of the 2P+3 family. Its decay product is 2 35U. This isotope is fissioned by thermal neutrons and is used in nuclear reactors as a fuel. 2 39Ri is obtained in jalopy paktops according to pakpiya:

Reaction cross section -455 barn. *39Pu is also formed when

bombardment of uranium with deuterons with energies above 8 MeV by nuclear reactions:

as well as when uranium is bombarded with helium ions with an energy of 40 MeV
spontaneous division, probability 1.36-10*7%.

Chemical separation of plutonium from uranium is a relatively simpler task than separation of uranium isotopes. As a result, the cost of plutonium is several times lower than the cost of 2 zzi. When a 2 39Pu nucleus is split by neutrons into two fragments of approximately equal mass, about 200 MeV of energy is released. Capable of maintaining a fission chain reaction. The relatively short half-life of 2 39Pu (compared to ^u) implies a significant release of energy during radioactive decay. 2 39Rc produces 1.92 W/kg. A well-insulated block of plutonium heats up to a temperature of over 100° in two hours and soon to the a-p transition point, which poses a problem for weapons design due to volume changes during phase transitions of plutonium. Specific activity 2 39Pu 2.28-12 Bq/g. 2 39Pu is easily fissile by thermal neutrons. The fissile isotope 239 Pu upon complete decay provides thermal energy equivalent to 25,000,000 kWh/kg. 2 39Pi has a fission cross section for slow neutrons of 748 barn, and a radiation capture cross section of 315 barn. 2 39Pu has larger scattering and absorption cross sections than uranium and a larger number of neutrons during fission (3.03 neutrons per fission event compared to 2.47 for 2 zzi), and, accordingly, a lower critical mass. Pure 2 39Pu has an average neutron emission from spontaneous fission of -30 neutrons/s-kg (-10 fissions/s).-

Plutonium-240, 71/2=6564 l, a-decay, specific activity 8.51-109 Bq/g. Spontaneous fission rate 1.6-6 divisions/g/hour, Ti/2=i.2-io u l. 24°Pu has a three times smaller effective neutron capture cross section than 239 Pu and in most cases turns into 2 4*Pu.

24op and is formed during the decay of certain radionuclides:

Decay energy 5.255 MeV, a-particles with energies 5.168 (72.8%), 5.123 (27.10%) MeV;

Spontaneous division, probability 5.7-6.

In uranium fuel, the content of ^Pu increases during reactor operation. In the spent fuel of a nuclear reactor there is 70% *39Pu and 26% 2 4°Pu, which makes it difficult to manufacture atomic weapons, so weapons-grade plutonium is obtained in reactors specially designed for this by processing uranium after several tens of days of irradiation. *4°Pu is the main isotope that pollutes weapons-grade 2 39Pu. The level of its content is important because of the intensity of spontaneous fission - 415,000 fission/s-kg, 1000 neutrons/s-kg are emitted, since each fission produces 2.26 neutrons - 30,000 times more than an equal mass of 2 39Ri. The presence of just 1% of this isotope produces so many neutrons that the cannon charge circuit is inoperable - early initiation of the explosion will begin and the charge will be atomized before the bulk of the explosive explodes. The cannon scheme is possible only with a content of *39Pu, which is practically impossible to achieve. Therefore, plutonium bombs are assembled using an implosion scheme, which allows the use of plutonium that is quite heavily contaminated with the isotope IgPu. Weapons-grade plutonium contains 2 4°Pu

Due to the higher specific activity (1/4 of 2 39Pi), the thermal output is higher, 7.1 W/kg, which exacerbates the problem of overheating. The specific activity of ^Pu is 8.4109 Bq/g. The content of IgPu in weapons-grade plutonium (0.7%) and in reactor-grade plutonium (>19%). The presence of 24 °Pu in fuel for thermal reactors is undesirable, but this isotope serves as fuel in fast reactors.

Plutonium-241, G,/2=14 l, daughter product 241 Am, p- (99%, ?рmax=0.014 MeV), a (1%, two lines: 4.893 (75%) and 4.848 (25%) MeV ) and y-emitter, specific activity of ^Pu 3.92-12 Ci/g. It is obtained by strong irradiation of plutonium with neutrons, as well as in a cyclotron by the reaction 2 3 8 U(a,n) 241 Pu. This isotope is fissile by neutrons of any energy (the neutron absorption cross section of ^'Pu is 1/3 greater than that of ^Phi, the fission cross section of thermal neutrons is about 100 barn, the probability of fission upon absorption of a neutron is 73%), has a low neutron background and moderate thermal power and therefore does not directly affect the ease of use of plutonium. It decays into 241 Am, which fissions very poorly and creates a lot of heat: 10 6 W/kg. ^‘Pu has a large fission cross section for reactor neutrons (poo barn), which allows it to be used as fuel. If a weapon initially contains 241 Ri, then after a few years its reactivity decreases, and this should be taken into account to prevent a decrease in charge power and an increase in self-heating. 24 'Ru itself does not heat up much (only 3.4 W/kg) despite its very short half-life due to very weak P radiation. When a neutron is absorbed by a 24 * Pu nucleus, if it does not fission, it turns into 242 Pu. 241 Pu is the main source of ^‘As.

Plutonium-242 (^/2=373300 years),

Plutonium-243 No/2=4-956 hours), p"- (energy 0.56 MeV) and y-emitter (several lines in the range 0.09-0.16 MeV) Cross section of the reaction 242 Pu(n ,y) 243 Pu on slow neutrons 00 barn. Formed during the p-decay of "^sPu 24 zAsh, can be obtained by irradiation with neutrons 2 4 2 Pu. Due to its short half-life, it is present in irradiated reactor fuel in small quantities.

Plutonium-244 (Ti/ 2 =8.o*io 7 years), a-emitter, E a = 4.6 MeV, capable of spontaneous fission, specific activity 6.66-105 Bq/g, thermal neutron capture cross section 0=19 barn. It is not only the longest-lived isotope of plutonium, but also the longest-lived of all isotopes of transuranium elements. Specific activity 2

Even heavier isotopes of plutonium are subject to p-decay, and their lifetimes range from several days to several tenths of a second. In thermonuclear explosions, all isotopes of plutonium are formed, up to 2 57Pu. But their lifetime is tenths of a second, and many short-lived isotopes of plutonium have not yet been studied.

Plutonium is a very heavy, silvery-white metal that shines like nickel when freshly refined. Atomic mass 244.0642 amu. (g/mol), atomic radius 151 pm, ionization energy (first electron) 491.9(5.10) kJ/mol (eV), electronic configuration 5f 6 7s 2. Ion radius: (+4e) 93, (+3e) 08 pm, electronegativity (Pauling) 1.28, T P l = 639.5°, G K ip = 3235°, plutonium density 19.84 (a-phase ), the heat of evaporation of plutonium is 80.46 kcal/mol. The vapor pressure of plutonium is significantly higher than the vapor pressure of uranium (at 1540 0 300 times). Plutonium can be distilled from molten uranium. Six allotropic modifications of metallic plutonium are known. At temperatures

In laboratory conditions, metallic plutonium can be obtained by the reduction reactions of plutonium halides with lithium, calcium, barium or magnesium at 1200°:

Metallic plutonium is also obtained by reducing plutonium trifluoride in the vapor phase at 1300 0 using calcium silicide according to the reaction

or thermal decomposition of plutonium halides in a vacuum.

Plutonium has many specific properties. It has the lowest thermal conductivity of all metals, the lowest electrical conductivity, with the exception of manganese. In its liquid phase it is the most viscous metal. When temperature changes, plutonium undergoes the most severe and unnatural changes in density.

Plutonium has six different phases (crystal structures) in solid form (Table 3), more than any other element. Some transitions between phases are accompanied by dramatic changes in volume. In two of these phases - delta and delta prime - plutonium has the unique property of contracting as the temperature increases, and in the others it has an extremely high temperature coefficient of expansion. When melted, the plutonium contracts, allowing the unmelted plutonium to float. In its densest form, the a-phase, plutonium is the sixth densest element (only osmium, iridium, platinum, rhenium and neptunium are heavier). In the a-phase, pure plutonium is brittle. A large number of alloys and intermetallic compounds of plutonium with Al, Be, Co, Fe, Mg, Ni, Ag are known. The compound PuBe, 3 is a source of neutrons with an intensity of 6.7 * 107 neutrons/skg.

Rice. 5.

Due to its radioactivity, plutonium is warm to the touch. A large piece of plutonium in a thermally insulated shell is heated to a temperature exceeding the boiling point of water. Finely ground plutonium is pyromorphic and spontaneously ignites at 300 0. It reacts with halogens and hydrogen halides, forming halides, with hydrogen - hydrides, with carbon - carbide, with nitrogen it reacts at 250 0 to form nitride, and when exposed to ammonia it also forms nitrides. Reduces CO2 to CO or C, and carbide is formed. Interacts with gaseous sulfur compounds. Plutonium is easily soluble in hydrochloric, 85% phosphoric, hydroiodic, perchloric and concentrated chloroacetic acids. Dilute H2SO4 dissolves plutonium slowly, but concentrated H2S04 and HN03 passivate it and do not react with it. Alkalis have no effect on metallic plutonium. Plutonium salts readily hydrolyze upon contact with neutral or alkaline solutions, creating insoluble plutonium hydroxide. Concentrated solutions of plutonium are unstable due to radiolytic decomposition leading to precipitation.

Table 3. Densities and temperature range of plutonium phases:

The main valency of plutonium is 4+. It is an electronegative, chemically reactive element (by 0.2 V), much more so than uranium. It quickly fades, forming an iridescent film, initially light yellow, eventually turning into dark purple. If the oxidation is quite rapid, an olive green oxide powder (PuO 2) appears on its surface.

Plutonium oxidizes easily and corrodes quickly even in the presence of slight moisture. It becomes rusty in an atmosphere of inert gas with water vapor much faster than in dry air or pure oxygen. When plutonium is heated in the presence of hydrogen, carbon, nitrogen, oxygen, phosphorus, arsenic, fluorine, silicon, and tellurium, it forms solid insoluble compounds with these elements.

Among the plutonium oxides, Pu 2 0 3 and Pu 0 2 are known.

Pu02 plutonium dioxide is an olive-green powder, black shiny crystals or balls from red-brown to amber-yellow. The crystal structure is of the fluorite type (Pu-* + form a face-centered cubic system, and O 2- form a tetrahedron). Density 11.46, Gpl=2400°. It is formed from almost all salts (for example, oxalate, peroxide) of plutonium when heated in air or in an atmosphere of 0 2, at temperatures of 700-1000 0, regardless of the oxidation state of plutonium in these salts. For example, it can be obtained by calcination of Pu(IV) Pu(C 2 0 4) 2 -6H 2 0 oxalate hexahydrate (formed during spent fuel reprocessing):

Pu0 2, midday at low temperatures, easily dissolves in concentrated hydrochloric and nitric acids. On the contrary, calcined Pu0 2 is difficult to dissolve and can only be brought into solution as a result of special treatment. It is insoluble in water and organic solvents. Slowly reacts with a hot mixture of concentrated HN0 3 with HF. This stable compound is used as a gravimetric form in the determination of plutonium. It is also used to prepare fuel in nuclear power.

Particularly reactive Pu0 2, but containing small amounts of oxalate, is obtained by the decomposition of Pu(C 2 0 4) 2 -6H 2 0 at 130-^-300°.

Hydride R11H3 obtained from elements at 150-5-200°.

Plutonium forms halides and oxyhalides, disilicide PuSi 2 and sesquisulfide PuSi,33^b5, which are of interest due to their low fusibility, as well as carbides of various stoichiometries: from PuS to Pu2C3. RiS - black crystals, G 11L = 1664 0. Together with UC it can be used as fuel for nuclear reactors.

Plutonium nitride, PuN - crystals of gray (to black) color with a face-centered cubic lattice of the NaCl type (0 = 0.4905 nm, z = 4, space group Ptzt; the lattice parameter increases with time under the influence of its own a-radiation); T pl.=2589° (with decomposition); density 14350 kg/m3. Has high thermal conductivity. At high temperatures (~1boo°) it is volatile (with decomposition). It is obtained by reacting plutonium with nitrogen at 6oo° or with a mixture of hydrogen and ammonia (pressure 4 kPa). Powdered plutonium PuN oxidizes in air at room temperature, completely transforming into Pu0 2 after 3 days, dense plutonium oxidizes slowly (0.3% in 30 days). It hydrolyzes slowly with cold water and quickly when heated, forming Pu0 2; easily dissolves in dilute hydrochloric and sulfuric acids to form the corresponding Pu(III) salts; According to the force of action on plutonium nitride, acids can be arranged in the series HN0 3 >HC1>H 3 P0 4 >>H 2 S04>HF. Can be used as reactor fuel.

There are several plutonium fluorides: PuF 3, PuF 4, PuF6.

Plutonium tetrafluoride PuF 4 is a pink substance or brown crystals, monoclinic system. Isomorphous with Zr, Hf, Th, U, Np and Ce tetrafluoride. Г pl = 1037 0, Г к, «1 = 1277°. It is poorly soluble in water and organic solvents, but easily dissolves in aqueous solutions in the presence of Ce(IV), Fe(III), Al(III) salts or ions that form stable complexes with fluorine ions. The pink precipitate PuF 4 -2.5H 2 0 is obtained by precipitation with hydrofluoric acid from aqueous solutions of Pu(III) salts. This compound dehydrates when heated to 350 m in a current of HF.

PuF 4 is formed by the action of hydrogen fluoride on plutonium dioxide in the presence of oxygen at 550° according to the reaction:

PuF 4 can also be obtained by treating PuF 3 with fluorine at 300 0 or by heating Pu(III) or Pu(IV) salts and a flow of hydrogen fluoride. From aqueous solutions of Pu(IV), PuF 4 is precipitated with hydrofluoric acid in the form of a pink precipitate with the composition 2PuF 4 H 2 0. PuF 4 almost completely coprecipitates with LaF 3. When heated in air to 400 0 PuF 4 turns into Pu0 2.

Plutonium hexafluoride, PuFe - volatile crystals at room temperature of a yellowish-brown color (at low temperatures - colorless) of an orthorhombic structure, Gpl = 52°, T knp =b2° at atmospheric pressure, density 5060 kgm-z, heat of sublimation 12.1 kcal/mol, heat of evaporation = 7.4 kcal mol * 1, heat of fusion = 4.71 kcal/mol, very prone to corrosion and sensitive to autoradiolysis. PuFe is a low-boiling liquid, thermally much less stable and less volatile than UF6. PuFe vapor is colored like NO 2, the liquid is dark brown. Strong fluorinating agent and oxidizing agent; reacts violently with water. Extremely sensitive to moisture; c H 2 0 in daylight can react very vigorously with a flash to form Pu0 2 and PuF 4 . PuFe, condensed at -195 0 on ice, when heated, slowly hydrolyzes to Pu0 2 Fo. Compact PuFe spontaneously decomposes due to the a-radiation of plutonium.

UF6 is obtained by treating PuF 4 or Pu0 2 with fluorine at 6004-700°.

Fluorination of PuF 4 with fluorine at 7004-800° occurs very quickly and is an exothermic reaction. To avoid decomposition, the resulting PuF6 is quickly removed from the hot zone - frozen or synthesis is carried out in a fluorine flow, which quickly removes the product from the reaction volume.

PuFa can also receive by payback:

There are Pu(III), Pu(IV) and Pu(VII) nitrates: Pu(N0 3) 3, Pu(N0 3) 4 and Pu0 2 (N0 3) 2, respectively.

Plutonium nitrate, Pu(N0 3) 4 *5H 2 0 is obtained by slow (over several months) evaporation of a concentrated Pu(IV) nitrate solution at room temperature. Well soluble in HN0 3 and water (nitric acid solution is dark green, brown). Soluble in acetone, ether and tributyl phosphate. Solutions of plutonium nitrate and alkali metal nitrates in concentrated nitric acid upon evaporation release double nitrates Me 2 [Pu(N0 3)b], where Me + =Cs +, Rb +, K +, Th +, C 9 H 7 NH +, C 5 H 5 NH + , NH 4 + .

Plutonium (IV) oxalate, Pu(C 2 0 4) 2 -6H 2 0, is a sandy (sometimes yellow-green) powder. Isomorphous with U(C 2 0 4)-6H 2 0. Plutonium oxalate hexahydrate is poorly soluble in mineral acids and well in solutions of oxalates and ammonium or alkali metal carbonates with the formation of complex compounds. Precipitated with oxalic acid from nitrate (i.5*4.5M HNO.0 solutions of Pu(IV):

It dehydrates when heated in air to 0°, above 400 0 it decomposes:

In compounds, plutonium exhibits oxidation states from +2 to +7. In aqueous solutions it forms ions corresponding to oxidation states from +3 to +7. In this case, ions of all oxidation states, except Pu(VII), can be in solution simultaneously in equilibrium. Plutonium ions in solution undergo hydrolysis and easily form complex compounds. The ability to form complex compounds increases in the Pu5 + series

Pu(IV) ions are the most stable in solution. Pu(V) is disproportioned into Pu(lV) and Pu(Vl). The valence state of Pu(VI) is characteristic of strongly oxidizing aqueous solutions, and it corresponds to the plutonyl ion Pu0 2 2+. Plutonium ions with charges 3 + and 4 + exist in aqueous solutions in the absence of hydrolysis and complex formation in the form of highly hydrated cations. Pu(V) and Pu(VI) in acidic solutions are oxygen-containing cations of the M0 2 + and M0 2 2+ type.

The oxidation states of plutonium (III, IV, V and VI) correspond to the following ionic states in acidic solutions: Pu 3+, Pu4 +, Pu0 2 2+ and Pu0 5 3 Due to the "closeness of the oxidation potentials of plutonium ions to each other" in solutions they can simultaneously plutonium ions with different oxidation states exist in equilibrium. In addition, disproportionation of Pu(IV) and Pu(V) is observed:

The rate of disproportionation increases with increasing plutonium concentration and temperature.

Reese+ solutions have a blue-violet color. In its properties, Rts + is close to rare earth elements. Its hydroxide, fluoride, phosphate and oxalate are insoluble. Pu(IV) is the most stable state of plutonium in aqueous solutions. Pu(IV) is prone to complex formation with nitric, sulfuric, hydrochloric, acetic and other acids. Thus, in concentrated nitric acid, Pu(IV) forms complexes Pu(N0 3)5- and Pu(G) 3)6 2". In aqueous solutions, Pu(IV) is easily hydrolyzed. Plutonium hydroxide (green) is prone to polymerization. Insoluble fluoride, hydroxide, oxalate, iodate Pu(IV).Pu(IV) coprecipitates well with insoluble hydroxides, lanthanum fluoride, Zr, Th, Ce iodates, Zr and Bi phosphates, Th, U(IV), Bi, La oxalates. Pu(IV) form double fluorides and sulfates with Na, K, Rb, Cs and NH 4 +. Pu(obtained in about.2 M solution of HN0 3 by mixing solutions of Pu(III) and Pu(VI). From salts of Pu( VI) Of interest are sodium plutonylacetate NaPu0 2 (C 2 H 3 0 2) 3 and ammonium plutonylacetate NH 4 Pu0 2 (C 2 H 3 0 2), which are similar in structure to the corresponding compounds U, Np and At.

Formal oxidation potentials of plutonium (in V) in lM solution of HC10 4:

The stability of the complex formed with this anion for actinide ions decreases in the following order: M4 + >M0 2+ >M3 + >M0 2 2+ > M0 2+, i.e. in order of decreasing ionic potential. The ability of anions to form complexes with actinide ions decreases for singly charged anions - fluoride > nitrate > chloride > perchlorate; for doubly charged anions carbonate>oxalate>sulfate. A large number of complex ions are formed with organic substances.

Both Pu(IV) and Pu(VI) are well extracted from acidic solutions with ethyl ether, TBP, diisopropyl ketone, etc. Claw-shaped complexes, for example, with a-thenoyltrifluoroacetone, p-diketone, cupferone, are well extracted with non-polar organic solvents . Extraction of Pu(IV) complexes with a-thenoyltrifluoroacetone (TTA) makes it possible to purify plutonium from most impurities, including actinide and rare earth elements.

Aqueous solutions of plutonium ions in different states have the following colors: Pu(III), as Pcs + (blue or lavender); Pu(IV), as Pc4* (yellow-brown); Pu(VI), as Pu0 2 2+ (pink-orange). Pu(V), like Pu0 2+, is initially pink, but being unstable in solution, this ion disproportionates into Pu 4+ and Pu0 2 2+; Pu 4+ is then oxidized, moving from Pu0 2 + to Pu0 2 2+, and reduced to Pu 3+. Thus, an aqueous solution of plutonium over time becomes a mixture of Pcs + and Pu0 2 2+. Pu(VII), as Pu0 5 2 - (dark blue).

To detect plutonium, a radiometric method is used, based on measuring the a-radiation of plutonium and its energy. This method is characterized by fairly high sensitivity: it allows discover 0.0001 µg 2 39Pi. If there are other α-emitters in the analyzed sample, identification of plutonium can be performed by measuring the energy of α-particles using α-spectrometers.

A number of chemical and physicochemical methods for the qualitative determination of plutonium use the difference in the properties of the valence forms of plutonium. The Pu(III) ion in fairly concentrated aqueous solutions can be detected by its bright blue color, which differs sharply from the yellow-brown color of aqueous solutions containing Pu(IV) ions.

The light absorption spectra of solutions of plutonium salts in various oxidation states have specific and narrow absorption bands, which makes it possible to identify valence forms and detect one of them in the presence of others. The most characteristic light absorption maxima of Pu(III) lie in the region of 600 and 900 mmk, Pu(IV) - 480 and 66 mmk, Pu(V) - 569 mmk and Pu(VI) 830+835 mmk.

Although plutonium is chemically toxic, like any heavy metal, this effect is weak compared to its radiotoxicity. The toxic properties of plutonium appear as a consequence of a-radioactivity.

For 2 s 8 Pu, 2 39Pu, 24op U) 242p u> 244Pu radiation hazard group A, MZA=z,7-uz Bq; for 2 4>Pu and 2 43Pu radiation hazard group B, MZA = 3.7-104 Bq. If the radiological toxicity is 2 3 and taken as unity, the same indicator for plutonium and some other elements forms the series: 235U 1.6 - 2 39Pu 5.0 - 2 4 1 As 3.2 - 9"Sr 4.8 - ^Ra 3.0. It can be seen that plutonium is not the most dangerous among radionuclides.

Let us briefly discuss the industrial production of plutonium.

Plutonium isotopes are produced in powerful uranium reactors using slow neutrons using the (p, y) reaction and in breeder reactors using fast neutrons. Plutonium isotopes are also produced in power reactors. By the end of the 20th century, the world had produced a total of -1300 tons of plutonium, of which ~300 tons were for weapons use, the rest was a by-product of nuclear power plants (reactor plutonium).

Weapons-grade plutonium is distinguished from reactor-grade plutonium not so much by the degree of enrichment and chemical composition, but by its isotopic composition, which depends in a complex way on both the time of irradiation of uranium with neutrons and the storage time after irradiation. The content of the isotopes 24°Pu and 2 4‘Pu is especially important. Although an atomic bomb can be created with any content of these isotopes in plutonium, nevertheless, the presence of 2 4 «p u in 239r determines the quality of the weapon, because the neutron background and such phenomena as the growth of critical mass and thermal output depend on it. The neutron background affects the explosive device by limiting the total mass of plutonium and the need to achieve high implosion speeds. Therefore, bombs of the old designs required a low content of 2 4or and. But “high” design projects use plutonium of any purity. Therefore, the term “weapon-grade plutonium” has no military meaning; this is an economic parameter: a “high” bomb design is significantly more expensive than a “low” one.

As the share of 24op U) increases, the cost of plutonium falls and the critical mass increases. The 7% 24°Pu content makes the overall cost of plutonium minimal. Average composition of weapons-grade plutonium: 93.4% 239 Ri, 6.o%

24°Pu and 0.6% 241 Pu. The thermal power of such plutonium is 2.2 W/kg, the level of spontaneous fission is 27100 fissions/s. This level allows 4 kg of plutonium to be used in a weapon with a very low probability of pre-detonation in a good implosion system. After 20 years, most of the 24, Pu will turn into ^'At, significantly increasing the heat release - up to 2.8 W/kg. Since 241 Pu is highly fissile, but 241 At is not, this will lead to a decrease in the reactivity margin of plutonium. Neutron radiation from 5 kg of weapons-grade plutonium of 300,000 neutrons/s creates a radiation level of 0.003 rad/hour at a distance of 1 m. The background is reduced by a factor of 10 by the reflector and the explosive surrounding it. However, prolonged contact of maintenance personnel with a nuclear explosive device during its maintenance can result in a radiation dose equal to the annual limit.

Due to the small difference in the masses of 2 - "* 9 Pu and 24 °Pu, these isotopes are not separated by industrial enrichment methods. Although they can be separated using an electromagnetic separator. It is easier, however, to obtain a purer 2 zeRi by reducing the residence time in the reactor *3 *i There is no reason to reduce the content of 24 °Pi to less than 6%, since this concentration does not interfere with the creation of effective triggers of thermonuclear charges.

In addition to weapons-grade plutonium, there is also reactor-grade plutonium. Plutonium from spent nuclear fuel consists of many isotopes. The composition depends on the type of reactor and operating mode. Typical values ​​for a light water reactor: 2 × 8 Pu - 2%, 239Pu - 61%, 24 °Pll - 24%, 24iPu - 10%, 242 Pll - 3%. It is difficult to make a bomb from such plutonium (virtually impossible for terrorists), but in countries with developed technology, reactor plutonium can be used to produce nuclear charges.

Table 4. Characteristics of plutonium types.

The isotopic composition of plutonium accumulated in the reactor depends on the degree of fuel burnup. Of the five main isotopes formed, two are with odd Z- 2 39Pi and 24,Pi are fissionable, i.e. capable of fission under the influence of thermal neutrons, and can be used as reactor fuel. In the case of using plutonium as reactor fuel, the amount of accumulated 2 39 Ri and 241 Ri is important. If plutonium recovered from spent fuel is reused in fast neutron reactors, its isotopic composition gradually becomes less suitable for weapons use. After several fuel cycles, the accumulation of 2 × 8 Pu, #2 4″ Pu and ^ 2 Pu makes it unsuitable for this purpose. Mixing in such material is a convenient method to "denature" the plutonium, ensuring that fissile materials do not proliferate.

Both weapons-grade and reactor-grade plutonium contain some amount of ^Pu. ^'Pu decays into 24 'Am by emission of a p-particle. Since the daughter 241 At has a significantly longer half-life (432 l) than the parent 241 Pu (14.4 l), its amount in the charge (or in the NFC waste) increases as ^'Pu decays. y-Radiation generated in as a result of the decay of 241 Am, much stronger than that of 241 Pu, therefore, it also increases over time. The concentration of ®4phi and the period of its storage directly correlate with the level of y-radiation resulting from an increase in the content of 24 'As. Plutonium cannot be stored for a long time - Once it has been used, it must be used, otherwise it will have to be subjected to time-consuming and expensive recycling again.

Table 5. Some characteristics of weapons-grade and reactor-grade plutonium

The most practically important isotope 2 39Pu is produced in nuclear reactors during long-term neutron irradiation of natural or enriched uranium:

Unfortunately, other nuclear reactions are also taking place, leading to the emergence of other isotopes of plutonium: 2 - 38 Pu, a4or u, 24 Phi and 242 Pu, the separation of which from 2 39Rc, although solvable, is a very difficult task:

When uranium is irradiated by reactor neutrons, both light and heavy isotopes of plutonium are formed. Let us first consider the formation of plutonium isotopes with a mass less than 239.

A small portion of the neutrons emitted during fission have energy sufficient to excite the reaction 2 3 8 U(n,2n) 2 3?u. 237 U is a p-emitter and with T’,/ 2 =6.8 days it turns into long-lived 2 37Np. This isotope in a graphite reactor on natural uranium is formed in an amount of 0.1% of the total amount of simultaneously formed 2 39Pu. The capture of slow neutrons by 2 3?Np leads to the formation of 2 3 8 Np. The cross section of this reaction is 170 barn. The chain of reactions looks like:

Since two neutrons are involved here, the yield is proportional to the square of the radiation dose and the ratio of the amounts of 238 Pu to 2 39Pu is proportional to the ratio of 2 39Pu to 238 U. The proportionality is not strictly observed due to the lag in the formation of 23?Np associated with the 6.8 day period half-life of ^U. A less important source of the formation of 238 Pu in 2 39Pu is the decay of 242 St, formed in uranium reactors. 238 Pu is also formed by the reactions:

Since this is a third-order neutron reaction, the ratio of the amount of 2 3 8 Pu formed in this way to 2 39 Pu is proportional to the square of the ratio * 3 8 Pu to 2 3 8 U. However, this chain of reactions becomes relatively more significant when working with uranium enriched in ^u.

The concentration of 2 × 8 Pu in a sample containing 5.6% 24 °Pu is 0.0115%. This value makes a fairly significant contribution to the total a-activity of the drugs, since ^Pu Ti/2= 86.4 l.

The presence of 2 6 Pu in plutonium produced in the reactor is associated with a number of reactions:

The yield of 2 3 6 Pu during the irradiation of uranium is ~ω-9-io" 8%.

From the point of view of the accumulation of plutonium in uranium, the main transformations are associated with the formation of the isotope 2 39Pu. But other side reactions are also important, since they determine the yield and purity of the target product. The relative content of the heavy isotopes 240 Pu, ^Phi, 242 Pu, as well as 23Pu, 2 37Np and ^"Ash depends on the dose of neutron irradiation of uranium (the residence time of uranium in the reactor). The cross sections for neutron capture by plutonium isotopes are large enough to cause successive reactions (n, y) even at low concentrations of 2 39Pu in uranium.

Table 6. Isotopic composition of plutonium isolated from irradiated it thrones of natural uranium. _

The 241 Pu formed during the irradiation of uranium with neutrons turns into 241 As, which is discharged during the chemical-technological processing of uranium blocks (241 At, however, gradually accumulates again in purified plutonium). For example, the a-activity of metallic plutonium, containing 7.5% 24 °Pu, increases by 2% after a year (due to the formation of 24, At). 24, Pu has a large fission cross section for reactor neutrons, amounting to - poo barn, which is important when using plutonium as reactor fuel.

If uranium or plutonium is subjected to strong neutron irradiation, the synthesis of minor actinides begins:

Formed from 2 4*Pu, 2 4*Am in turn reacts with neutrons, forming 2 3 8 Pu and 2 4 2 Pu:

This process opens up the possibility of obtaining plutonium preparations with relatively low y-radiation.

Rice. 6. Change in the ratio of plutonium isotopes during long-term irradiation of 2 39Pu with a neutron flux of 3*10*4 n/cm 2 s.

Thus, the long-lived isotopes of plutonium - ^Pu and 2 44Pu are formed during long-term (about a hundred days or more) irradiation with 2 39Pu neutrons. In this case, the yield of 2 4 2 Pu reaches several tens of percent, while the amount of 2 44 Pu formed is a fraction of a percent of ^Pu. At the same time, Am, Cm and other transplutonium, as well as fragmentation elements are obtained.

In the production of plutonium, uranium (in the form of metal) is irradiated in an industrial reactor (thermal or fast), the advantages of which are high neutron density, low temperature, and the possibility of irradiation for a time much shorter than the reactor campaign.

The main problem that arose during the production of weapons-grade plutonium in a reactor was choosing the optimal time for irradiation of uranium. The fact is that the isotope 238, which makes up the bulk of natural uranium, captures neutrons, forming 239Pu, while 2333 supports the fission chain reaction. Since the formation of heavy isotopes of plutonium requires additional neutron capture, the amount of such isotopes in uranium grows more slowly than the amount of 2 39Pu. Uranium irradiated in a reactor for a short time contains a small amount of 2 39Pu, but it is purer than with long exposures, since harmful heavy isotopes have not had time to accumulate. However, 2 39Рц itself is subject to fission and with an increase in its concentration in the reactor, the rate of its transmutation increases. Therefore, uranium must be removed from the reactor several weeks after the start of irradiation.

Rice. 7- Accumulation of plutonium isotopes in the reactor: l - ^Pu; 2 - 240 Pu (at short times, weapons-grade plutonium is formed, and at long times, reactor-grade plutonium is formed, i.e., unsuitable for weapons use).

The overall irradiation rate of a fuel cell is expressed in megawatt days/ton. Weapons-grade plutonium is produced from elements with a small amount of MW-day/t and produces fewer by-product isotopes. Fuel cells in modern pressurized water reactors reach levels of 33,000 MW-day/t. Typical exposure in a breeder reactor is 100 MW-day/t. During the Manhattan Project, natural uranium fuel received only 100 MW-day/t, so it produced a very high quality 239 Ri (total 1 % 2 4°Pll).

Chemistry

Plutonium Pu - element No. 94 is associated with very great hopes and very great fears of humanity. These days it is one of the most important, strategically important elements. It is the most expensive of the technically important metals - it is much more expensive than silver, gold and platinum. He is truly precious.

Background and history

In the beginning there were protons - galactic hydrogen. As a result of its compression and subsequent nuclear reactions, the most incredible “ingots” of nucleons were formed. Among them, these “ingots,” there were apparently those containing 94 protons. Theorists' estimates suggest that about 100 nucleon formations, which include 94 protons and from 107 to 206 neutrons, are so stable that they can be considered the nuclei of isotopes of element No. 94.
But all these isotopes - hypothetical and real - are not so stable as to survive to this day since the formation of the elements of the solar system. The half-life of the longest-lived isotope of element No. 94 is 81 million years. The age of the Galaxy is measured in billions of years. Consequently, the “primordial” plutonium had no chance of surviving to this day. If it was formed during the great synthesis of the elements of the Universe, then those ancient atoms of it “extinct” long ago, just as dinosaurs and mammoths became extinct.
In the 20th century new era, AD, this element was recreated. Of the 100 possible isotopes of plutonium, 25 have been synthesized. The nuclear properties of 15 of them have been studied. Four have found practical application. And it was opened quite recently. In December 1940, when uranium was irradiated with heavy hydrogen nuclei, a group of American radiochemists led by Glenn T. Seaborg discovered a previously unknown alpha particle emitter with a half-life of 90 years. This emitter turned out to be the isotope of element No. 94 with a mass number of 238. In the same year, but a few months earlier, E.M. McMillan and F. Abelson obtained the first element heavier than uranium, element number 93. This element was called neptunium, and element 94 was called plutonium. The historian will definitely say that these names originate in Roman mythology, but in essence the origin of these names is rather not mythological, but astronomical.
Elements No. 92 and 93 are named after the distant planets of the solar system - Uranus and Neptune, but Neptune is not the last in the solar system, even further lies the orbit of Pluto - a planet about which almost nothing is still known... A similar construction We also see on the “left flank” of the periodic table: uranium - neptunium - plutonium, however, humanity knows much more about plutonium than about Pluto. By the way, astronomers discovered Pluto just ten years before the synthesis of plutonium - almost the same period of time separated the discoveries of Uranus - the planet and uranium - the element.

Riddles for cryptographers

The first isotope of element No. 94, plutonium-238, has found practical application these days. But in the early 40s they didn’t even think about it. It is possible to obtain plutonium-238 in quantities of practical interest only by relying on the powerful nuclear industry. At that time it was just in its infancy. But it was already clear that by releasing the energy contained in the nuclei of heavy radioactive elements, it was possible to obtain weapons of unprecedented power. The Manhattan Project appeared, which had nothing more than a name in common with the famous New York area. This was the general name for all work related to the creation of the first atomic bombs in the United States. It was not a scientist, but a military man, General Groves, who was appointed head of the Manhattan Project, who “affectionately” called his highly educated charges “broken pots.”
The leaders of the “project” were not interested in plutonium-238. Its nuclei, like the nuclei of all plutonium isotopes with even mass numbers, are not fissile by low-energy neutrons, so it could not serve as a nuclear explosive. Nevertheless, the first not very clear reports about elements No. 93 and 94 appeared in print only in the spring of 1942.
How can we explain this? Physicists understood: the synthesis of plutonium isotopes with odd mass numbers was a matter of time, and not too long. Odd isotopes were expected to, like uranium-235, be able to support a nuclear chain reaction. Some people saw them as potential nuclear explosives, which had not yet been received. And these hopes plutonium, unfortunately, he justified it.
In encryption of that time, element No. 94 was called nothing more than... copper. And when the need arose for copper itself (as a structural material for some parts), then in the codes, along with “copper,” “genuine copper” appeared.

"The Tree of the Knowledge of Good and Evil"

In 1941, the most important isotope of plutonium was discovered - an isotope with mass number 239. And almost immediately the theorists' prediction was confirmed: plutonium-239 nuclei were fissioned by thermal neutrons. Moreover, during their fission, no less number of neutrons were produced than during the fission of uranium-235. Ways to obtain this isotope in large quantities were immediately outlined...
Years have passed. Now it’s no secret to anyone that the nuclear bombs stored in arsenals are filled with plutonium-239 and that these bombs are enough to cause irreparable damage to all life on Earth.
There is a widespread belief that humanity was clearly in a hurry with the discovery of the nuclear chain reaction (the inevitable consequence of which was the creation of a nuclear bomb). You can think differently or pretend to think differently - it’s more pleasant to be an optimist. But even optimists inevitably face the question of the responsibility of scientists. We remember the triumphant June day of 1954, the day when the first nuclear power plant in Obninsk turned on. But we cannot forget the morning of August 1945 - “the morning of Hiroshima”, “the black day of Albert Einstein”... We remember the first post-war years and the rampant atomic blackmail - the basis of American policy in those years. But hasn’t humanity experienced a lot of troubles in subsequent years? Moreover, these anxieties were intensified many times over by the consciousness that if a new world war broke out, nuclear weapons would be used.
Here you can try to prove that the discovery of plutonium did not add fear to humanity, that, on the contrary, it was only useful.
Let's say it happened that for some reason or, as they would say in the old days, by the will of God, plutonium was inaccessible to scientists. Would our fears and concerns then be reduced? Nothing happened. Nuclear bombs would be made from uranium-235 (and in no less quantity than from plutonium), and these bombs would “eat up” even larger parts of the budgets than now.
But without plutonium there would be no prospects for the peaceful use of nuclear energy on a large scale. There simply would not be enough uranium-235 for a “peaceful atom”. The evil inflicted on humanity by the discovery of nuclear energy would not be balanced, even partially, by the achievements of the “good atom.”

How to measure, what to compare with

When a plutonium-239 nucleus is split by neutrons into two fragments of approximately equal mass, about 200 MeV of energy is released. This is 50 million times more energy released in the most famous exothermic reaction C + O 2 = CO 2. “Burning” in a nuclear reactor, a gram of plutonium gives 2,107 kcal. In order not to break tradition (and in popular articles, the energy of nuclear fuel is usually measured in non-systemic units - tons of coal, gasoline, trinitrotoluene, etc.), we also note: this is the energy contained in 4 tons of coal. And an ordinary thimble contains an amount of plutonium energetically equivalent to forty carloads of good birch firewood.
The same energy is released during the fission of uranium-235 nuclei by neutrons. But the bulk of natural uranium (99.3%!) is the isotope 238 U, which can only be used by turning uranium into plutonium...

Energy of stones

Let us evaluate the energy resources contained in natural uranium reserves.
Uranium is a trace element and is found almost everywhere. Anyone who has visited, for example, Karelia, will probably remember granite boulders and coastal cliffs. But few people know that a ton of granite contains up to 25 g of uranium. Granites make up almost 20% of the weight of the earth's crust. If we count only uranium-235, then a ton of granite contains 3.5-105 kcal of energy. It's a lot, but...
Processing granite and extracting uranium from it requires spending an even larger amount of energy - about 106-107 kcal/t. Now, if it were possible to use not only uranium-235, but also uranium-238 as an energy source, then granite could be considered at least as a potential energy raw material. Then the energy obtained from a ton of stone would be from 8-107 to 5-108 kcal. This is equivalent to 16-100 tons of coal. And in this case, granite could provide people with almost a million times more energy than all the chemical fuel reserves on Earth.
But uranium-238 nuclei do not fission by neutrons. This isotope is useless for nuclear energy. More precisely, it would be useless if it could not be converted into plutonium-239. And what is especially important: practically no energy needs to be spent on this nuclear transformation - on the contrary, energy is produced in this process!
Let's try to figure out how this happens, but first a few words about natural plutonium.

400 thousand times less than radium

It has already been said that isotopes of plutonium have not been preserved since the synthesis of elements during the formation of our planet. But this does not mean that there is no plutonium in the Earth.
It is formed all the time in uranium ores. By capturing neutrons from cosmic radiation and neutrons produced by the spontaneous fission of uranium-238 nuclei, some - very few - atoms of this isotope turn into atoms of uranium-239. These nuclei are very unstable; they emit electrons and thereby increase their charge. Neptunium, the first transuranium element, is formed. Neptunium-239 is also highly unstable, and its nuclei emit electrons. In just 56 hours, half of the neptunium-239 turns into plutonium-239, the half-life of which is already quite long - 24 thousand years.
Why is plutonium not extracted from uranium ores?? Low, too low concentration. “Production per gram - labor per year” - this is about radium, and plutonium in ores is 400 thousand times less than radium. Therefore, it is extremely difficult not only to mine, but even to detect “terrestrial” plutonium. This was done only after the physical and chemical properties of plutonium produced in nuclear reactors were studied.
Plutonium is accumulated in nuclear reactors. In powerful neutron streams, the same reaction occurs as in uranium ores, but the rate of formation and accumulation of plutonium in the reactor is much higher - a billion billion times. For the reaction of converting ballast uranium-238 into energy-grade plutonium-239, optimal (within acceptable) conditions are created.
If the reactor operates on thermal neutrons (recall that their speed is about 2000 m per second, and their energy is a fraction of an electronvolt), then from a natural mixture of uranium isotopes an amount of plutonium is obtained that is slightly less than the amount of “burnt out” uranium-235. A little, but less, plus the inevitable losses of plutonium during its chemical separation from irradiated uranium. In addition, the nuclear chain reaction is maintained in the natural mixture of uranium isotopes only until a small fraction of uranium-235 is consumed. Hence the logical conclusion: a “thermal” reactor using natural uranium - the main type of currently operating reactors - cannot ensure the expanded reproduction of nuclear fuel. But what is promising then? To answer this question, let’s compare the course of the nuclear chain reaction in uranium-235 and plutonium-239 and introduce another physical concept into our discussions.
The most important characteristic of any nuclear fuel is the average number of neutrons emitted after the nucleus has captured one neutron. Physicists call it the eta number and denote it by the Greek letter q. In “thermal” reactors on uranium, the following pattern is observed: each neutron generates an average of 2.08 neutrons (η = 2.08). Plutonium placed in such a reactor under the influence of thermal neutrons gives η = 2.03. But there are also reactors that operate on fast neutrons. It is useless to load a natural mixture of uranium isotopes into such a reactor: a chain reaction will not occur. But if the “raw material” is enriched with uranium-235, it can be developed in a “fast” reactor. In this case, c will already be equal to 2.23. And plutonium, exposed to fast neutron fire, will give η equal to 2.70. We will have “extra half a neutron” at our disposal. And this is not at all little.

Let's see what the resulting neutrons are spent on. In any reactor, one neutron is needed to maintain a nuclear chain reaction. 0.1 neutrons are absorbed by the construction materials of the installation. The “excess” is used to accumulate plutonium-239. In one case the “excess” is 1.13, in the other it is 1.60. After the “burning” of a kilogram of plutonium in a “fast” reactor, colossal energy is released and 1.6 kg of plutonium is accumulated. And uranium in a “fast” reactor will provide the same energy and 1.1 kg of new nuclear fuel. In both cases, expanded reproduction is evident. But we must not forget about the economy.
Due to a number of technical reasons, the plutonium reproduction cycle takes several years. Let's say five years. This means that the amount of plutonium per year will increase by only 2% if η=2.23, and by 12% if η=2.7! Nuclear fuel is capital, and any capital should yield, say, 5% per annum. In the first case there are large losses, and in the second there are large profits. This primitive example illustrates the “weight” of every tenth of a number in nuclear energy.
Something else is also important. Nuclear power must keep pace with growing energy demand. Calculations show that his condition is fulfilled in the future only when η approaches three. If the development of nuclear energy sources lags behind society’s energy needs, then there will be two options left: either “slow down progress” or take energy from some other sources. They are known: thermonuclear fusion, annihilation energy of matter and antimatter, but are not yet technically accessible. And it is not known when they will become real sources of energy for humanity. And the energy of heavy nuclei has long become a reality for us, and today plutonium, as the main “supplier” of atomic energy, has no serious competitors, except, perhaps, uranium-233.

Sum of many technologies

When, as a result of nuclear reactions, the required amount of plutonium has accumulated in uranium, it must be separated not only from the uranium itself, but also from fission fragments - both uranium and plutonium, burned up in the nuclear chain reaction. In addition, the uranium-plutonium mass also contains a certain amount of neptunium. The most difficult things to separate are plutonium from neptunium and rare earth elements (lanthanides). Plutonium, as a chemical element, has been unlucky to some extent. From a chemist's point of view, the main element of nuclear energy is just one of fourteen actinides. Like rare earth elements, all elements of the actinium series are very similar to each other in chemical properties; the structure of the outer electron shells of the atoms of all elements from actinium to 103 is the same. What’s even more unpleasant is that the chemical properties of actinides are similar to the properties of rare earth elements, and among the fission fragments of uranium and plutonium there are more than enough lanthanides. But then element 94 can be in five valence states, and this “sweets the pill” - it helps to separate plutonium from both uranium and fission fragments.
The valency of plutonium varies from three to seven. Chemically, the most stable (and therefore the most common and most studied) compounds are tetravalent plutonium.
The separation of actinides with similar chemical properties - uranium, neptunium and plutonium - can be based on the difference in the properties of their tetra- and hexavalent compounds.

There is no need to describe in detail all the stages of the chemical separation of plutonium and uranium. Usually, their separation begins with the dissolution of uranium bars in nitric acid, after which the uranium, neptunium, plutonium and fragmentation elements contained in the solution are “separated”, using traditional radiochemical methods for this - precipitation, extraction, ion exchange and others. The final plutonium-containing products of this multi-stage technology are its dioxide PuO 2 or fluorides - PuF 3 or PuF 4. They are reduced to metal with barium, calcium or lithium vapor. However, the plutonium obtained in these processes is not suitable for the role of a structural material - fuel elements of nuclear power reactors cannot be made from it, and the charge of an atomic bomb cannot be cast. Why? The melting point of plutonium - only 640°C - is quite achievable.
No matter what “ultra-gentle” conditions are used to cast parts from pure plutonium, cracks will always appear in the castings during solidification. At 640°C, solidifying plutonium forms a cubic crystal lattice. As the temperature decreases, the density of the metal gradually increases. But then the temperature reached 480°C, and then suddenly the density of plutonium drops sharply. The reasons for this anomaly were discovered quite quickly: at this temperature, plutonium atoms are rearranged in the crystal lattice. It becomes tetragonal and very “loose”. Such plutonium can float in its own melt, like ice on water.
The temperature continues to fall, now it has reached 451°C, and the atoms again formed a cubic lattice, but located at a greater distance from each other than in the first case. With further cooling, the lattice first becomes orthorhombic, then monoclinic. In total, plutonium forms six different crystalline forms! Two of them are distinguished by a remarkable property - a negative coefficient of thermal expansion: with increasing temperature, the metal does not expand, but contracts.
When the temperature reaches 122°C and the plutonium atoms rearrange their rows for the sixth time, the density changes especially dramatically - from 17.77 to 19.82 g/cm 3 . More than 10%!
Accordingly, the volume of the ingot decreases. If the metal could still resist the stresses that arose at other transitions, then at this moment destruction is inevitable.
How then to make parts from this amazing metal? Metallurgists alloy plutonium (adding small amounts of the required elements to it) and obtain castings without a single crack. They are used to make plutonium charges for nuclear bombs. The weight of the charge (it is determined primarily by the critical mass of the isotope) is 5-6 kg. It could easily fit into a cube with an edge size of 10 cm.

Heavy isotopes of plutonium

Plutonium-239 also contains in small quantities higher isotopes of this element - with mass numbers 240 and 241. The 240 Pu isotope is practically useless - it is ballast in plutonium. From 241, americium is obtained - element No. 95. In its pure form, without admixture of other isotopes, plutonium-240 and plutonium-241 can be obtained by electromagnetic separation of plutonium accumulated in the reactor. Before this, plutonium is additionally irradiated with neutron fluxes with strictly defined characteristics. Of course, all this is very complicated, especially since plutonium is not only radioactive, but also very toxic. Working with it requires extreme caution.
One of the most interesting isotopes of plutonium, 242 Pu, can be obtained by irradiating 239 Pu for a long time in neutron fluxes. 242 Pu very rarely captures neutrons and therefore “burns out” in the reactor more slowly than other isotopes; it persists even after the remaining isotopes of plutonium have almost completely turned into fragments or turned into plutonium-242.
Plutonium-242 is important as a “raw material” for the relatively rapid accumulation of higher transuranium elements in nuclear reactors. If plutonium-239 is irradiated in a conventional reactor, then it will take about 20 years to accumulate microgram amounts of, for example, California-252 from grams of plutonium.
It is possible to reduce the accumulation time of higher isotopes by increasing the intensity of the neutron flux in the reactor. This is what they do, but then you cannot irradiate large amounts of plutonium-239. After all, this isotope is divided by neutrons, and too much energy is released in intense flows. Additional difficulties arise with reactor cooling. To avoid these difficulties, it would be necessary to reduce the amount of plutonium irradiated. Consequently, the yield of californium would again become scanty. Vicious circle!
Plutonium-242 is not fissile by thermal neutrons, it can be irradiated in large quantities in intense neutron fluxes... Therefore, in reactors, all elements from americium to fermium are “made” from this isotope and accumulated in weight quantities.
Every time scientists managed to obtain a new isotope of plutonium, the half-life of its nuclei was measured. The half-lives of isotopes of heavy radioactive nuclei with even mass numbers change regularly. (This cannot be said for odd isotopes.)
As the mass increases, the “lifetime” of the isotope also increases. Several years ago, the high point of this graph was plutonium-242. And then how will this curve go - with a further increase in the mass number? To point 1, which corresponds to a lifetime of 30 million years, or to point 2, which corresponds to 300 million years? The answer to this question was very important for geosciences. In the first case, if 5 billion years ago the Earth consisted entirely of 244 Pu, now only one atom of plutonium-244 would remain in the entire mass of the Earth. If the second assumption is true, then plutonium-244 may be in the Earth in concentrations that could already be detected. If we were lucky enough to find this isotope in the Earth, science would receive the most valuable information about the processes that took place during the formation of our planet.

Half-lives of some isotopes of plutonium

A few years ago, scientists were faced with the question: is it worth trying to find heavy plutonium in the Earth? To answer it, it was necessary first of all to determine the half-life of plutonium-244. Theorists could not calculate this value with the required accuracy. All hope was only for experiment.
Plutonium-244 accumulated in a nuclear reactor. Element No. 95 - americium (isotope 243 Am) was irradiated. Having captured a neutron, this isotope turned into americium-244; americium-244 in one out of 10 thousand cases turned into plutonium-244.
The preparation of plutonium-244 was isolated from a mixture of americium and curium. The sample weighed only a few millionths of a gram. But they were enough to determine the half-life of this interesting isotope. It turned out to be equal to 75 million years. Later, other researchers clarified the half-life of plutonium-244, but not by much - 81 million years. In 1971, traces of this isotope were found in the rare earth mineral bastnäsite.
Many attempts have been made by scientists to find an isotope of the transuranium element that lives longer than 244 Pu. But all attempts remained in vain. At one time, hopes were placed on curium-247, but after this isotope was accumulated in the reactor, it turned out that its half-life is only 16 million years. It was not possible to break the record of plutonium-244 - it is the longest-lived of all isotopes of transuranium elements.
Even heavier isotopes of plutonium undergo beta decay, and their lifetimes range from a few days to a few tenths of a second. We know for sure that all isotopes of plutonium are formed in thermonuclear explosions, up to 257 Pu. But their lifetime is tenths of a second, and many short-lived isotopes of plutonium have not yet been studied.

Possibilities of the first plutonium isotope

And finally - about plutonium-238 - the very first of the “man-made” isotopes of plutonium, an isotope that at first seemed unpromising. It is actually a very interesting isotope. It is subject to alpha decay, that is, its nuclei spontaneously emit alpha particles - helium nuclei. Alpha particles generated by plutonium-238 nuclei carry high energy; dissipated in matter, this energy turns into heat. How big is this energy? Six million electron volts are released from the decay of one atomic nucleus of plutonium-238. In a chemical reaction, the same energy is released when several million atoms are oxidized. An electricity source containing one kilogram of plutonium-238 develops a thermal power of 560 watts. The maximum power of a chemical current source of the same mass is 5 watts.
There are many emitters with similar energy characteristics, but one feature of plutonium-238 makes this isotope indispensable. Alpha decay is usually accompanied by strong gamma radiation, penetrating through large layers of matter. 238 Pu is an exception. The energy of gamma rays accompanying the decay of its nuclei is low, and it is not difficult to protect against it: the radiation is absorbed by a thin-walled container. The probability of spontaneous fission of nuclei of this isotope is also low. Therefore, it has found application not only in current sources, but also in medicine. Batteries containing plutonium-238 serve as a source of energy in special cardiac stimulators.
But 238 Pu is not the lightest known isotope of element No. 94; isotopes of plutonium have been obtained with mass numbers from 232 to 237. The half-life of the lightest isotope is 36 minutes.

Plutonium is a big topic. The most important things are told here. After all, it has already become a standard phrase that the chemistry of plutonium has been studied much better than the chemistry of such “old” elements as iron. Whole books have been written about the nuclear properties of plutonium. The metallurgy of plutonium is another amazing section of human knowledge... Therefore, you should not think that after reading this story, you truly learned plutonium - the most important metal of the 20th century.

• HOW TO CARRY PLUTONIUM. Radioactive and toxic plutonium requires special care during transportation. A container was designed specifically for its transportation - a container that is not destroyed even in aircraft accidents. It is made quite simply: it is a thick-walled stainless steel vessel surrounded by a mahogany shell. Obviously, plutonium is worth it, but imagine how thick the walls must be if you know that a container for transporting only two kilograms of plutonium weighs 225 kg!
• POISON AND ANTIDOTE. On October 20, 1977, Agence France-Presse reported that a chemical compound had been found that can remove plutonium from the human body. A few years later, quite a lot became known about this compound. This complex compound is a linear carboxylase catechinamide, a substance of the chelate class (from the Greek “chela” - claw). The plutonium atom, free or bound, is captured in this chemical claw. In laboratory mice, this substance was used to remove up to 70% of absorbed plutonium from the body. It is believed that in the future this compound will help extract plutonium from both production waste and nuclear fuel.