Biology
Toxins produced by sea cucumbers are of pharmacological interest. Fishermen on the Pacific Islands use poisonous Cuvier's tubules of some species when fishing.
see also
Literature
- Dolmatov I.Yu., Mashanov V.S. Regeneration in holothurians. - Vladivostok: Dalnauka, 2007. - 208 p.
Links
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See what "Holothurians" are in other dictionaries:
Neg. worm-like echinoderm marine animals, found in the Southern Ocean. This includes sea cucumber. Dictionary of foreign words included in the Russian language. Pavlenkov F., 1907. HOLOTHURIA or SEA EGGERS (Greek holothuriae). Order of echinoderms... ... Dictionary of foreign words of the Russian language
sea cucumbers- ii, pl. holothurie f. gr. holothurion 1. A marine animal with a worm-like body. BAS 2. And over there to the side, stacked in rows in long woodpiles are some small, thick sulfur sticks, like sausages. These are all sea cucumbers, sea animals, like... ... Historical Dictionary of Gallicisms of the Russian Language
Sea cucumbers (Holothuroidea), class of echinoderms. Fossil skeletal plates of G. are known from the Devonian. Body b. h. barrel-shaped or worm-shaped (length from several mm to 2 m), many with external. appendages (tentacles, legs, papillae, sail, etc.), ... ... Biological encyclopedic dictionary
- (Holotburioidea), a class of the echinoderm type, differ from other representatives of the same type by a worm-shaped body, leathery skin and outer integument containing calcareous bodies, the absence of an external madrepous plate, a crown for the most part... ... Encyclopedia of Brockhaus and Efron
- (sea cucumbers), a class of animals such as echinoderms. The body is usually worm-shaped, from a few mm to 2 m. About 1100 species, found throughout the seas and oceans. Bottom, crawling forms. Many, when irritated, are able to throw out their insides or... ... Modern encyclopedia
- (sea cucumbers, sea capsules), a class of marine invertebrate animals such as echinoderms. The body is usually worm-shaped, from a few mm to 2 m. Approx. 1100 species, almost everywhere in the seas and oceans. Bottom crawling forms. Some are capable of... Big Encyclopedic Dictionary
- (Holothuroidea) a class of echinoderms with a highly reduced skeleton, consisting of numerous microscopic calcareous needles, decomposed. forms. Marine animals belonging to nekton. Rare in fossil form, found in the form of imprints or... ... Geological encyclopedia
Sea cucumbers, sea capsules (Holothuroidea) HOLOTHURIA Cucumeria planci one of the types of edible sea cucumbers. class of marine invertebrates such as echinoderms (Echinodermata). They live on the bottom, mainly in shallow water areas, where they usually lie like... ... Collier's Encyclopedia
- (Holothurioidea) class of the echinodermata type (Echinodermata, see), differ from other representatives of the same type by a worm-shaped body, leathery outer integuments containing calcareous bodies, the absence of an external madrepore plate, ... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Ephron
Yi; pl. (unit holothuria, i; g.). [Greek holothurion] Class of marine invertebrate animals such as echinoderms; sea cucumbers. * * * holothurians (sea cucumbers, sea capsules), a class of marine invertebrate animals such as echinoderms. The body is usually... encyclopedic Dictionary
Crayfish, crabs in the sea. They can be explored and described for an infinite amount of time. Oceanologists never cease to be amazed by their new discoveries.
Some inhabitants live right before our eyes, even under our feet. They hunt, feed, reproduce. And there are species that go far into the depths, where there is no light and, it would seem, no life.
The most incredible creature we are about to meet is the sea cucumber, aka sea cucumber, aka nautical cucumber. Outwardly it looks like a very lazy, overfed, huge worm.
This is a creature that has lived for many millions of years in the expanses of water and has survived more than one historical period. It got its name - sea cucumber - from the philosopher from Rome, Pliny. And, for the first time, several of its types have already been described by Aristotle.
Sea cucumber meat is beneficial for health, so it is very popular in cooking that you even have to breed them in swimming pools. Cooks fry them, dry them, can them, and freeze them.
Marinate and add to salads. When preparing sea cucumber meat, culinary specialists advise adding a lot of spices; it has the ability to absorb all the smells and tastes as much as possible.
Interestingly, the nutritional value of meat does not deteriorate during heat treatment. The Japanese generally eat sea cucumber - cucumaria, exclusively raw, after marinating for five minutes in soy sauce with the addition of garlic.
Considering the flesh of sea cucumbers to be a panacea for all diseases. Sea cucumbers are filled with macro and microelements, vitamins, minerals and amino acids. More than thirty chemical elements from Mindileev’s table.
Its meat contains the largest number of useful components, like no other inhabitant of the deep sea, and it is completely disinfected; viruses, bacteria and microbes are not familiar to it.
Also, in the sixteenth century, information came to us about unique healing properties of sea cucumber. Now it is used in the pharmaceutical industry. For medical purposes, especially in Japan and China.
Residents of these countries call sea cucumber - ginseng obtained from the sea. This is a natural component for the complete restoration of the human body after serious illnesses and complex surgical interventions.
Helps regenerate human tissue. Improves heart function, normalizes blood pressure. Stimulates the functioning of the gastrointestinal tract. Sea cucumber also has certain components that help in treating joints.
Also, incredibly, but true, this animal has the ability to regenerate. This is a similarity to the Phoenix bird, only from the sea. Even if he has less than half of his body left, after a while, it will already be a full-fledged animal. But such recovery will take a lot of time, up to half a year or more.
ABOUT description and characteristics of sea cucumber
Who is he? nautical cucumber? This echinoderm, an invertebrate mollusk that lives only in sea waters. Its closest relatives are the starfish and the sea urchin.
In appearance, he is a natural silkworm caterpillar, slowly and voluntarily crawling along the bottom of the sea. Dark marsh, brown, almost black, sometimes scarlet. Depending on where they live, their colors change.
For example, on a sandy river bottom you can even find blue sea cucumbers. Body sizes are different. Some species are half a centimeter long. And there are also fifty centimeter individuals. The average size of a mollusk is like a matchbox - five, six centimeters wide, and up to twenty cm long. It weighs almost one kilogram.
When awake and calm, the sea cucumber almost always lies on its side. On its lower part of the body, called the belly, there is a mouth covered with suckers all around its circumference. With the help of them the animal feeds.
It’s like vacuuming everything from the bottom that you can profit from. There can be up to thirty of these suckers. The entire skin of the sea cucumber is tightly covered with limescale. On the back there are pimply formations with small light spines. They have legs that grow along the entire length of the body, in rows.
The body of a sea cucumber has another unique ability to change its density. He becomes rock hard in case he feels his life is in danger. And it can be very elastic if it needs to crawl under some rock for shelter.
Lifestyle and habitat
They call sea cucumbers types of sea cucumbers, living in the northern part of the Kuril Islands, central territories in China and Japan, in southern Sakhalin. There are more than a hundred varieties of them on the territory of Russia.
Sea cucumbers are animals living at a depth of no more than twenty meters. They spend all their time lying at the bottom. They move very little in their lives.
Sea cucumbers live only in salt water. Fresh waters are destructive for them. They love calm water and muddy bottoms. So that in case of danger you can bury yourself in it. Or stick to some stone.
When an echinoderm is attacked by an enemy, the animal may split into several parts while fleeing. Over time, these parts will, of course, recover.
Since these animals do not have lungs, they breathe through the anus. Pumping water into yourself, sifting out oxygen. Some specimens can pump up to seven hundred liters of water through themselves in one hour. Also, sea cucumbers use the anus as a second mouth.
They tolerate temperature changes calmly, and minor minuses do not affect their livelihoods in any way. They also have a positive attitude towards high temperatures in reservoirs.
Even if some mollusk freezes in the ice, and it is gradually warmed up, it will move away and continue to live. These animals live in large schools, forming entire canvases of individuals on the bottom.
Sea cucumber nutrition
Sea cucumbers are those animals that collect and eat all the decaying carrion found at the bottom. Sea cucumber in hunting for plankton, along the way it collects all the silt and sand that comes along the way. Then he passes it all through himself. Therefore, half of its interior consists of soil.
The over-poisoned, so-called food, comes out through the anus. Considering the fact that you won’t be full of sand, a sea cucumber has to absorb a huge amount of land in a day. In just one year of their life, these mollusks pass through themselves up to forty kilograms of sand and silt. Moreover, in the spring their appetite doubles.
Holothurians have sensitive receptors, with the help of which they accurately determine the amount of food located on the seabed. And if the prey is hidden deep in the sand, the sea cucumber will sense this and will bury itself in the ground until it catches the food. And when he feels that there is not enough food, he quickly runs along the tops and collects dead remains.
Sea cucumber reproduction and lifespan
By the third year of their life, sea cucumbers are already sexually mature and ready to reproduce. Based on their appearance, it is difficult to understand which of them is male and which is female. But they are heterosexual animals.
The mating season begins in late spring and lasts throughout the summer. But there are also species for which the spawning period can occur at any time of the year. Having broken up into pairs, the mollusks get closer to the shore on a hill, or crawl onto stones or onto lying mussels.
When mating has already occurred, they attach their hind legs to some surface with suction cups and raise their heads up. In this bent position they begin to spawn.
This procedure lasts up to three days. And what’s remarkable is in the dark. In one year, a female sea cucumber can lay more than fifty million eggs. These individuals are very prolific.
At the end, the exhausted animals crawl into their chosen shelter and hibernate for almost two months. Having slept and rested, sea cucumbers develop a voracious appetite, and they begin to eat everything.
In the third week of life, in fry, something like suction cups appear around the mouth opening. With their help, they attach themselves to marine vegetation and then grow and develop on it.
And many types of sea cucumbers, females, carry their young on their backs, throwing them towards them with their tail. The cubs also begin to grow pimples on their backs, and small legs on their bellies.
The fry grows up, its body increases, the number of legs is added. He is already becoming like his parents, a mini worm. In the first year they reach small sizes, up to five centimeters. By the end of the second year they grow twice as large and already look like a young adult. Holothurians live eight to ten years.
Currently you can buy sea cucumber no problem. There are entire aquarium farms dedicated to their cultivation. Expensive fish restaurants order whole batches to their kitchens. And by rummaging around on the Internet, you can easily get what you want.
Scientists at the Princeton Plasma Physics Laboratory have proposed the idea of the longest-lasting nuclear fusion device that can operate for more than 60 years. At the moment, this is a difficult task: scientists are struggling to make a thermonuclear reactor work for a few minutes - and then years. Despite the complexity, the construction of a thermonuclear reactor is one of the most promising tasks in science, which can bring enormous benefits. We tell you what you need to know about thermonuclear fusion.
1. What is thermonuclear fusion?
Don't be intimidated by this cumbersome phrase, it's actually quite simple. Fusion is a type of nuclear reaction.
During a nuclear reaction, the nucleus of an atom interacts either with an elementary particle or with the nucleus of another atom, due to which the composition and structure of the nucleus changes. A heavy atomic nucleus can decay into two or three lighter ones - this is a fission reaction. There is also a fusion reaction: this is when two light atomic nuclei merge into one heavy one.
Unlike nuclear fission, which can occur either spontaneously or forcedly, nuclear fusion is impossible without the supply of external energy. As you know, opposites attract, but atomic nuclei are positively charged - so they repel each other. This situation is called the Coulomb barrier. To overcome repulsion, these particles must be accelerated to crazy speeds. This can be done at very high temperatures - on the order of several million Kelvin. It is these reactions that are called thermonuclear.
2. Why do we need thermonuclear fusion?
During nuclear and thermonuclear reactions, a huge amount of energy is released, which can be used for various purposes - you can create powerful weapons, or you can convert nuclear energy into electricity and supply it to the whole world. Nuclear decay energy has long been used in nuclear power plants. But thermonuclear energy looks more promising. In a thermonuclear reaction, much more energy is released for each nucleon (the so-called constituent nuclei, protons and neutrons) than in a nuclear reaction. For example, when fission of a uranium nucleus into one nucleon produces 0.9 MeV (megaelectronvolt), and whenDuring the fusion of helium nuclei, energy equal to 6 MeV is released from hydrogen nuclei. Therefore, scientists are learning to carry out thermonuclear reactions.
Thermonuclear fusion research and reactor construction make it possible to expand high-tech production, which is useful in other areas of science and high-tech.
3. What are thermonuclear reactions?
Thermonuclear reactions are divided into self-sustaining, uncontrolled (used in hydrogen bombs) and controlled (suitable for peaceful purposes).
Self-sustaining reactions take place in the interior of stars. However, there are no conditions on Earth for such reactions to take place.
People have been conducting uncontrolled or explosive thermonuclear fusion for a long time. In 1952, during Operation Ivy Mike, the Americans detonated the world's first thermonuclear explosive device, which had no practical value as a weapon. And in October 1961, the world's first thermonuclear (hydrogen) bomb ("Tsar Bomba", "Kuzka's Mother"), developed by Soviet scientists under the leadership of Igor Kurchatov, was tested. It was the most powerful explosive device in the entire history of mankind: the total energy of the explosion, according to various sources, ranged from 57 to 58.6 megatons of TNT. To detonate a hydrogen bomb, it is necessary to first obtain a high temperature during a conventional nuclear explosion - only then will the atomic nuclei begin to react.
The power of an explosion during an uncontrolled nuclear reaction is very high, and in addition, the proportion of radioactive contamination is high. Therefore, in order to use thermonuclear energy for peaceful purposes, it is necessary to learn how to control it.
4. What is needed for a controlled thermonuclear reaction?
Hold the plasma!
Unclear? Let's explain now.
First, atomic nuclei. In nuclear energy, isotopes are used - atoms that differ from each other in the number of neutrons and, accordingly, in atomic mass. The hydrogen isotope deuterium (D) is obtained from water. Superheavy hydrogen or tritium (T) is a radioactive isotope of hydrogen that is a byproduct of decay reactions carried out in conventional nuclear reactors. Also in thermonuclear reactions, a light isotope of hydrogen is used - protium: this is the only stable element that does not have neutrons in the nucleus. Helium-3 is found on Earth in negligible quantities, but there is a lot of it in the lunar soil (regolith): in the 80s, NASA developed a plan for hypothetical installations for processing regolith and releasing a valuable isotope. But another isotope is widespread on our planet - boron-11. 80% of boron on Earth is an isotope necessary for nuclear scientists.
Secondly, the temperature is very high. The substance participating in the thermonuclear reaction must be an almost completely ionized plasma - this is a gas in which free electrons and ions of different charges float separately. To turn a substance into plasma, a temperature of 10 7 –10 8 K is required - that’s hundreds of millions of degrees Celsius! Such ultra-high temperatures can be achieved by creating high-power electrical discharges in the plasma.
However, you cannot simply heat the necessary chemical elements. Any reactor will instantly evaporate at such temperatures. This requires a completely different approach. Today it is possible to contain plasma in a limited area using ultra-powerful electric magnets. But it has not yet been possible to fully use the energy obtained as a result of a thermonuclear reaction: even under the influence of a magnetic field, the plasma spreads in space.
5. Which reactions are most promising?
The main nuclear reactions planned to be used for controlled fusion will use deuterium (2H) and tritium (3H), and in the longer term helium-3 (3He) and boron-11 (11B).
Here's what the most interesting reactions look like.
1) 2 D+ 3 T -> 4 He (3.5 MeV) + n (14.1 MeV) - deuterium-tritium reaction.
2) 2 D+ 2 D -> 3 T (1.01 MeV) + p (3.02 MeV) 50%
2 D+ 2 D -> 3 He (0.82 MeV) + n (2.45 MeV) 50% - this is the so-called deuterium monopropellant.
Reactions 1 and 2 are fraught with neutron radioactive contamination. Therefore, “neutron-free” reactions are the most promising.
3) 2 D+ 3 He -> 4 He (3.6 MeV) + p (14.7 MeV) - deuterium reacts with helium-3. The problem is that helium-3 is extremely rare. However, the neutron-free yield makes this reaction promising.
4) p+ 11 B -> 3 4 He + 8.7 MeV - boron-11 reacts with protium, resulting in alpha particles that can be absorbed by aluminum foil.
6. Where to carry out such a reaction?
A natural thermonuclear reactor is a star. In it, the plasma is held under the influence of gravity, and radiation is absorbed - thus, the core does not cool down.
On Earth, thermonuclear reactions can only be carried out in special installations.
Pulse systems. In such systems, deuterium and tritium are irradiated with ultra-powerful laser beams or electron/ion beams. Such irradiation causes a sequence of thermonuclear microexplosions. However, such systems are unprofitable to use on an industrial scale: much more energy is spent on accelerating atoms than is obtained as a result of fusion, since not all accelerated atoms react. Therefore, many countries are building quasi-stationary systems.
Quasi-stationary systems. In such reactors, plasma is contained by a magnetic field at low pressure and high temperature. There are three types of reactors based on different magnetic field configurations. These are tokamaks, stellarators (torsatrons) and mirror traps.
Tokamak stands for "toroidal chamber with magnetic coils". This is a “donut” (torus)-shaped chamber on which coils are wound. The main feature of a tokamak is the use of alternating electric current, which flows through the plasma, heats it and, creating a magnetic field around itself, holds it.
IN stellarator (torsatron) the magnetic field is completely contained by magnetic coils and, unlike a tokamak, can be operated continuously.
In z mirror (open) traps The principle of reflection is used. The chamber is closed on both sides by magnetic “plugs” that reflect the plasma, keeping it in the reactor.
For a long time, mirror traps and tokamaks fought for primacy. Initially, the trap concept seemed simpler and therefore cheaper. In the early 60s, open traps were abundantly funded, but the instability of the plasma and unsuccessful attempts to contain it with a magnetic field forced these installations to become more complicated - seemingly simple structures turned into infernal machines, and it was impossible to achieve a stable result. Therefore, in the 80s, tokamaks came to the fore. In 1984, the European JET tokamak was launched, which cost only $180 million and whose parameters allowed for a thermonuclear reaction. In the USSR and France, superconducting tokamaks were designed, which spent almost no energy on the operation of the magnetic system.
7. Who is now learning to carry out thermonuclear reactions?
Many countries are building their own thermonuclear reactors. Kazakhstan, China, the USA and Japan have their own experimental reactors. The Kurchatov Institute is working on the IGNITOR reactor. Germany launched the Wendelstein 7-X fusion stellarator reactor.
The most famous is the international tokamak project ITER (ITER, International Thermonuclear Experimental Reactor) at the Cadarache research center (France). Its construction was supposed to be completed in 2016, but the amount of necessary financial support has increased, and the timing of the experiments has moved to 2025. The European Union, USA, China, India, Japan, South Korea and Russia participate in ITER activities. The EU plays the main share in financing (45%), while the remaining participants supply high-tech equipment. In particular, Russia produces superconducting materials and cables, radio tubes for heating plasma (gyrotrons) and fuses for superconducting coils, as well as components for the most complex part of the reactor - the first wall, which must withstand electromagnetic forces, neutron radiation and plasma radiation.
8. Why don't we still use fusion reactors?
Modern tokamak installations are not thermonuclear reactors, but research installations in which the existence and preservation of plasma is possible only for a while. The fact is that scientists have not yet learned how to retain plasma in a reactor for a long time.
At the moment, one of the greatest achievements in the field of nuclear fusion is the success of German scientists who managed to heat hydrogen gas to 80 million degrees Celsius and maintain a cloud of hydrogen plasma for a quarter of a second. And in China, hydrogen plasma was heated to 49.999 million degrees and held for 102 seconds. Russian scientists from the G.I. Budker Institute of Nuclear Physics, Novosibirsk, managed to achieve stable heating of the plasma to ten million degrees Celsius. However, the Americans recently proposed a way to retain plasma for 60 years - and this is encouraging.
In addition, there is debate regarding the profitability of nuclear fusion in industry. It is unknown whether the benefits of generating electricity will cover the costs of nuclear fusion. It is proposed to experiment with reactions (for example, abandon the traditional deuterium-tritium reaction or monopropellant in favor of other reactions), construction materials - or even abandon the idea of industrial thermonuclear fusion, using only it for individual reactions in fission reactions. However, scientists still continue experiments.
9. Are fusion reactors safe?
Relatively. Tritium, which is used in fusion reactions, is radioactive. In addition, neurons released as a result of synthesis irradiate the reactor structure. The reactor elements themselves become covered with radioactive dust due to exposure to plasma.
However, a fusion reactor is much safer than a nuclear reactor in terms of radiation. There are relatively few radioactive substances in the reactor. In addition, the design of the reactor itself assumes that there are no “holes” through which radiation can leak. The vacuum chamber of the reactor must be sealed, otherwise the reactor simply will not be able to operate. During the construction of thermonuclear reactors, materials tested by nuclear energy are used, and reduced pressure is maintained in the premises.
When will thermonuclear power plants appear?
Scientists most often say something like “in 20 years we will solve all fundamental issues.” Engineers from the nuclear industry are talking about the second half of the 21st century. Politicians talk about a sea of clean energy for pennies, without bothering with dates.
How scientists search for dark matter in the depths of the Earth
Hundreds of millions of years ago, minerals beneath the earth's surface may have retained traces of a mysterious substance. All that remains is to get to them. More than two dozen underground laboratories scattered around the world are busy searching for dark matter.
How Siberian scientists helped man fly to the stars
On April 12, 1961, Yuri Gagarin made the first flight into space - the pilot’s good-natured smile and his cheerful “Let’s go!” became a triumph of Soviet cosmonautics. For this flight to take place, scientists all over the country were racking their brains about how to make a rocket that would withstand all the dangers of unknown space - this was not without the ideas of scientists from the Siberian Branch of the Academy of Sciences.
The second half of the 20th century was a period of rapid development of nuclear physics. It became clear that nuclear reactions could be used to produce enormous energy from tiny amounts of fuel. Only nine years passed from the explosion of the first nuclear bomb to the first nuclear power plant, and when a hydrogen bomb was tested in 1952, there were predictions that thermonuclear power plants would come into operation in the 1960s. Alas, these hopes were not justified.
Thermonuclear reactions Of all the thermonuclear reactions, only four are of interest in the near future: deuterium + deuterium (products - tritium and proton, released energy 4.0 MeV), deuterium + deuterium (helium-3 and neutron, 3.3 MeV), deuterium + tritium (helium-4 and neutron, 17.6 MeV) and deuterium + helium-3 (helium-4 and proton, 18.2 MeV). The first and second reactions occur in parallel with equal probability. The resulting tritium and helium-3 “burn” in the third and fourth reactions
Igor Egorov
The main source of energy for humanity today is the combustion of coal, oil and gas. But their supplies are limited, and combustion products pollute the environment. A coal power plant produces more radioactive emissions than a nuclear power plant of the same power! So why haven't we switched to nuclear energy sources yet? There are many reasons for this, but the main one recently has been radiophobia. Despite the fact that a coal-fired power plant, even during normal operation, harms the health of many more people than emergency emissions at a nuclear power plant, it does so quietly and unnoticed by the public. Accidents at nuclear power plants immediately become the main news in the media, causing general panic (often completely unfounded). However, this does not mean that nuclear energy does not have objective problems. Radioactive waste causes a lot of trouble: technologies for working with it are still extremely expensive, and the ideal situation when all of it will be completely recycled and used is still far away.
Of all the thermonuclear reactions, only four are of interest in the near future: deuterium + deuterium (products - tritium and proton, released energy 4.0 MeV), deuterium + deuterium (helium-3 and neutron, 3.3 MeV), deuterium + tritium (helium -4 and neutron, 17.6 MeV) and deuterium + helium-3 (helium-4 and proton, 18.2 MeV). The first and second reactions occur in parallel with equal probability. The resulting tritium and helium-3 “burn” in the third and fourth reactions.
From fission to fusion
A potential solution to these problems is the transition from fission reactors to fusion reactors. While a typical fission reactor contains tens of tons of radioactive fuel, which is converted into tens of tons of radioactive waste containing a wide variety of radioactive isotopes, a fusion reactor uses only hundreds of grams, maximum kilograms, of one radioactive isotope of hydrogen, tritium. In addition to the fact that the reaction requires an insignificant amount of this least dangerous radioactive isotope, its production is also planned to be carried out directly at the power plant in order to minimize the risks associated with transportation. The synthesis products are stable (non-radioactive) and non-toxic hydrogen and helium. In addition, unlike a fission reaction, a thermonuclear reaction immediately stops when the installation is destroyed, without creating the danger of a thermal explosion. So why has not a single operational thermonuclear power plant been built yet? The reason is that the listed advantages inevitably entail disadvantages: creating the conditions for synthesis turned out to be much more difficult than initially expected.
Lawson criterion
For a thermonuclear reaction to be energetically favorable, it is necessary to ensure a sufficiently high temperature of the thermonuclear fuel, a sufficiently high density and sufficiently low energy losses. The latter are numerically characterized by the so-called “retention time”, which is equal to the ratio of the thermal energy stored in the plasma to the energy loss power (many people mistakenly believe that the “retention time” is the time during which hot plasma is maintained in the installation, but this is not so) . At a temperature of a mixture of deuterium and tritium equal to 10 keV (approximately 110,000,000 degrees), we need to obtain the product of the number of fuel particles in 1 cm 3 (i.e., plasma concentration) and the retention time (in seconds) of at least 10 14. It does not matter whether we have a plasma with a concentration of 1014 cm -3 and a retention time of 1 s, or a plasma with a concentration of 10 23 and a retention time of 1 ns. This criterion is called the Lawson criterion.
In addition to the Lawson criterion, which is responsible for obtaining an energetically favorable reaction, there is also a plasma ignition criterion, which for the deuterium-tritium reaction is approximately three times greater than the Lawson criterion. “Ignition” means that the fraction of thermonuclear energy that remains in the plasma will be enough to maintain the required temperature, and additional heating of the plasma will no longer be required.
Z-pinch
The first device in which it was planned to obtain a controlled thermonuclear reaction was the so-called Z-pinch. In the simplest case, this installation consists of only two electrodes located in a deuterium (hydrogen-2) environment or a mixture of deuterium and tritium, and a battery of high-voltage pulse capacitors. At first glance, it seems that it makes it possible to obtain compressed plasma heated to enormous temperatures: exactly what is needed for a thermonuclear reaction! However, in life, everything turned out, alas, to be far from so rosy. The plasma rope turned out to be unstable: the slightest bend leads to a strengthening of the magnetic field on one side and a weakening on the other; the resulting forces further increase the bending of the rope - and all the plasma “falls out” onto the side wall of the chamber. The rope is not only unstable to bending, the slightest thinning of it leads to an increase in the magnetic field in this part, which compresses the plasma even more, squeezing it into the remaining volume of the rope until the rope is finally “squeezed out.” The compressed part has a high electrical resistance, so the current is interrupted, the magnetic field disappears, and all the plasma dissipates.
The principle of operation of the Z-pinch is simple: an electric current generates an annular magnetic field, which interacts with the same current and compresses it. As a result, the density and temperature of the plasma through which the current flows increases.
It was possible to stabilize the plasma bundle by applying a powerful external magnetic field to it, parallel to the current, and placing it in a thick conductive casing (as the plasma moves, the magnetic field also moves, which induces an electric current in the casing, tending to return the plasma to its place). The plasma stopped bending and pinching, but it was still far from a thermonuclear reaction on any serious scale: the plasma touches the electrodes and gives off its heat to them.
Modern work in the field of Z-pinch fusion suggests another principle for creating fusion plasma: a current flows through a tungsten plasma tube, which creates powerful X-rays that compress and heat the capsule with fusion fuel located inside the plasma tube, just as it does in a thermonuclear bomb. However, these works are purely research in nature (the mechanisms of operation of nuclear weapons are studied), and the energy release in this process is still millions of times less than consumption.
The smaller the ratio of the large radius of the tokamak torus (the distance from the center of the entire torus to the center of the cross-section of its pipe) to the small one (the cross-section radius of the pipe), the greater the plasma pressure can be under the same magnetic field. By reducing this ratio, scientists moved from a circular cross-section of the plasma and vacuum chamber to a D-shaped one (in this case, the role of the small radius is played by half the height of the cross-section). All modern tokamaks have exactly this cross-sectional shape. The limiting case was the so-called “spherical tokamak”. In such tokamaks, the vacuum chamber and plasma are almost spherical in shape, with the exception of a narrow channel connecting the poles of the sphere. The conductors of magnetic coils pass through the channel. The first spherical tokamak, START, appeared only in 1991, so this is a fairly young direction, but it has already shown the possibility of obtaining the same plasma pressure with a three times lower magnetic field.
Cork chamber, stellarator, tokamak
Another option for creating the conditions necessary for the reaction is the so-called open magnetic traps. The most famous of them is the “cork cell”: a pipe with a longitudinal magnetic field that strengthens at its ends and weakens in the middle. The field increased at the ends creates a “magnetic plug” (hence the Russian name), or “magnetic mirror” (English - mirror machine), which keeps the plasma from leaving the installation through the ends. However, such retention is incomplete; some charged particles moving along certain trajectories are able to pass through these jams. And as a result of collisions, any particle will sooner or later fall on such a trajectory. In addition, the plasma in the mirror chamber also turned out to be unstable: if in some place a small section of the plasma moves away from the axis of the installation, forces arise that eject the plasma onto the chamber wall. Although the basic idea of the mirror cell was significantly improved (which made it possible to reduce both the instability of the plasma and the permeability of the mirrors), in practice it was not even possible to approach the parameters necessary for energetically favorable synthesis.
Is it possible to make sure that the plasma does not escape through the “plugs”? It would seem that the obvious solution is to roll the plasma into a ring. However, then the magnetic field inside the ring is stronger than outside, and the plasma again tends to go to the chamber wall. The way out of this difficult situation also seemed quite obvious: instead of a ring, make a “figure eight”, then in one section the particle will move away from the axis of the installation, and in another it will return back. This is how scientists came up with the idea of the first stellarator. But such a “figure eight” cannot be made in one plane, so we had to use the third dimension, bending the magnetic field in the second direction, which also led to a gradual movement of the particles from the axis to the chamber wall.
The situation changed dramatically with the creation of tokamak-type installations. The results obtained at the T-3 tokamak in the second half of the 1960s were so stunning for that time that Western scientists came to the USSR with their measuring equipment to verify the plasma parameters themselves. The reality even exceeded their expectations.
These fantastically intertwined tubes are not an art project, but a stellarator chamber bent into a complex three-dimensional curve.
In the hands of inertia
In addition to magnetic confinement, there is a fundamentally different approach to thermonuclear fusion - inertial confinement. If in the first case we try to keep the plasma at a very low concentration for a long time (the concentration of molecules in the air around you is hundreds of thousands of times higher), then in the second case we compress the plasma to a huge density, an order of magnitude higher than the density of the heaviest metals, in the expectation that the reaction will have time to pass in that short time before the plasma has time to scatter to the sides.
Originally, in the 1960s, the plan was to use a small ball of frozen fusion fuel, uniformly irradiated from all sides by multiple laser beams. The surface of the ball should have instantly evaporated and, expanding evenly in all directions, compressed and heated the remaining part of the fuel. However, in practice, the irradiation turned out to be insufficiently uniform. In addition, part of the radiation energy was transferred to the inner layers, causing them to heat up, which made compression more difficult. As a result, the ball compressed unevenly and weakly.
There are a number of modern stellarator configurations, all of which are close to a torus. One of the most common configurations involves the use of coils similar to the poloidal field coils of tokamaks, and four to six conductors twisted around a vacuum chamber with multidirectional current. The complex magnetic field created in this way allows the plasma to be reliably contained without requiring a ring electric current to flow through it. In addition, stellarators can also use toroidal field coils, like tokamaks. And there may be no helical conductors, but then the “toroidal” field coils are installed along a complex three-dimensional curve. Recent developments in the field of stellarators involve the use of magnetic coils and a vacuum chamber of a very complex shape (a very “crumpled” torus), calculated on a computer.
The problem of unevenness was solved by significantly changing the design of the target. Now the ball is placed inside a special small metal chamber (it is called “holraum”, from the German hohlraum - cavity) with holes through which laser beams enter inside. In addition, crystals are used that convert IR laser radiation into ultraviolet. This UV radiation is absorbed by a thin layer of hohlraum material, which is heated to enormous temperatures and emits soft X-rays. In turn, X-ray radiation is absorbed by a thin layer on the surface of the fuel capsule (ball with fuel). This also made it possible to solve the problem of premature heating of the internal layers.
However, the power of the lasers turned out to be insufficient for a noticeable portion of the fuel to react. In addition, the efficiency of the lasers was very low, only about 1%. For fusion to be energetically beneficial at such a low laser efficiency, almost all of the compressed fuel had to react. When trying to replace lasers with beams of light or heavy ions, which can be generated with much greater efficiency, scientists also encountered a lot of problems: light ions repel each other, which prevents them from focusing, and are slowed down when colliding with residual gas in the chamber, and accelerators It was not possible to create heavy ions with the required parameters.
Magnetic prospects
Most of the hope in the field of fusion energy now lies in tokamaks. Especially after they opened a mode with improved retention. A tokamak is both a Z-pinch rolled into a ring (a ring electric current flows through the plasma, creating a magnetic field necessary to contain it), and a sequence of mirror cells assembled into a ring and creating a “corrugated” toroidal magnetic field. In addition, a field perpendicular to the torus plane, created by several individual coils, is superimposed on the toroidal field of the coils and the plasma current field. This additional field, called poloidal, strengthens the magnetic field of the plasma current (also poloidal) on the outside of the torus and weakens it on the inside. Thus, the total magnetic field on all sides of the plasma rope turns out to be the same, and its position remains stable. By changing this additional field, it is possible to move the plasma bundle inside the vacuum chamber within certain limits.
A fundamentally different approach to synthesis is offered by the concept of muon catalysis. A muon is an unstable elementary particle that has the same charge as an electron, but 207 times more mass. A muon can replace an electron in a hydrogen atom, and the size of the atom decreases by a factor of 207. This allows one hydrogen nucleus to move closer to another without expending energy. But to produce one muon, about 10 GeV of energy is spent, which means it is necessary to perform several thousand fusion reactions per muon to obtain energy benefits. Due to the possibility of a muon “sticking” to the helium formed in the reaction, more than several hundred reactions have not yet been achieved. The photo shows the assembly of the Wendelstein z-x stellarator at the Max Planck Institute for Plasma Physics.
An important problem of tokamaks for a long time was the need to create a ring current in the plasma. To do this, a magnetic circuit was passed through the central hole of the tokamak torus, the magnetic flux in which was continuously changed. The change in magnetic flux generates a vortex electric field, which ionizes the gas in the vacuum chamber and maintains current in the resulting plasma. However, the current in the plasma must be maintained continuously, which means that the magnetic flux must continuously change in one direction. This, of course, is impossible, so the current in tokamaks could only be maintained for a limited time (from a fraction of a second to several seconds). Fortunately, the so-called bootstrap current was discovered, which occurs in a plasma without an external vortex field. In addition, methods have been developed to heat the plasma, simultaneously inducing the necessary ring current in it. Together, this provided the potential for maintaining hot plasma for as long as desired. In practice, the record currently belongs to the Tore Supra tokamak, where the plasma continuously “burned” for more than six minutes.
The second type of plasma confinement installation, which has great promise, is stellarators. Over the past decades, the design of stellarators has changed dramatically. Almost nothing remained of the original “eight”, and these installations became much closer to tokamaks. Although the confinement time of stellarators is shorter than that of tokamaks (due to the less efficient H-mode), and the cost of their construction is higher, the behavior of the plasma in them is calmer, which means a longer life of the first inner wall of the vacuum chamber. For the commercial development of thermonuclear fusion, this factor is of great importance.
Selecting a reaction
At first glance, it is most logical to use pure deuterium as a thermonuclear fuel: it is relatively cheap and safe. However, deuterium reacts with deuterium a hundred times less readily than with tritium. This means that to operate a reactor on a mixture of deuterium and tritium, a temperature of 10 keV is sufficient, and to operate on pure deuterium, a temperature of more than 50 keV is required. And the higher the temperature, the higher the energy loss. Therefore, at least for the first time, thermonuclear energy is planned to be built on deuterium-tritium fuel. Tritium will be produced in the reactor itself due to irradiation with the fast lithium neutrons produced in it.
"Wrong" neutrons. In the cult film “9 Days of One Year,” the main character, while working at a thermonuclear installation, received a serious dose of neutron radiation. However, it later turned out that these neutrons were not produced as a result of a fusion reaction. This is not the director’s invention, but a real effect observed in Z-pinches. At the moment of interruption of the electric current, the inductance of the plasma leads to the generation of a huge voltage - millions of volts. Individual hydrogen ions, accelerated in this field, are capable of literally knocking neutrons out of the electrodes. At first, this phenomenon was indeed taken as a sure sign of a thermonuclear reaction, but subsequent analysis of the neutron energy spectrum showed that they had a different origin.
Improved retention mode. The H-mode of a tokamak is a mode of its operation when, with a high power of additional heating, plasma energy losses sharply decrease. The accidental discovery of the enhanced confinement mode in 1982 is as significant as the invention of the tokamak itself. There is no generally accepted theory of this phenomenon yet, but this does not prevent it from being used in practice. All modern tokamaks operate in this mode, as it reduces losses by more than half. Subsequently, a similar regime was discovered in stellarators, indicating that this is a general property of toroidal systems, but confinement is only improved by about 30% in them.
Plasma heating. There are three main methods of heating plasma to thermonuclear temperatures. Ohmic heating is the heating of plasma due to the flow of electric current through it. This method is most effective in the first stages, since as the temperature increases, the electrical resistance of the plasma decreases. Electromagnetic heating uses electromagnetic waves with a frequency that matches the frequency of rotation around the magnetic field lines of electrons or ions. By injecting fast neutral atoms, a stream of negative ions is created, which are then neutralized, turning into neutral atoms that can pass through the magnetic field to the center of the plasma to transfer their energy there.
Are these reactors? Tritium is radioactive, and powerful neutron irradiation from the D-T reaction creates induced radioactivity in the reactor design elements. We have to use robots, which complicates the work. At the same time, the behavior of a plasma of ordinary hydrogen or deuterium is very close to the behavior of a plasma from a mixture of deuterium and tritium. This led to the fact that throughout history, only two thermonuclear installations fully operated on a mixture of deuterium and tritium: the TFTR and JET tokamaks. At other installations, even deuterium is not always used. So the name “thermonuclear” in the definition of a facility does not mean at all that thermonuclear reactions have ever actually occurred in it (and in those that do occur, pure deuterium is almost always used).
Hybrid reactor. The D-T reaction produces 14 MeV neutrons, which can even fission depleted uranium. The fission of one uranium nucleus is accompanied by the release of approximately 200 MeV of energy, which is more than ten times the energy released during fusion. So existing tokamaks could become energetically beneficial if they were surrounded by a uranium shell. Compared to fission reactors, such hybrid reactors would have the advantage of preventing an uncontrolled chain reaction from developing in them. In addition, extremely intense neutron fluxes should convert long-lived uranium fission products into short-lived ones, which significantly reduces the problem of waste disposal.
Inertial hopes
Inertial fusion is also not standing still. Over the decades of development of laser technology, prospects have emerged to increase the efficiency of lasers by approximately ten times. And in practice, their power has been increased hundreds and thousands of times. Work is also underway on heavy ion accelerators with parameters suitable for thermonuclear use. In addition, the concept of “fast ignition” has been a critical factor in the progress of inertial fusion. It involves the use of two pulses: one compresses the thermonuclear fuel, and the other heats up a small part of it. It is assumed that the reaction that begins in a small part of the fuel will subsequently spread further and cover the entire fuel. This approach makes it possible to significantly reduce energy costs, and therefore make the reaction profitable with a smaller fraction of reacted fuel.
Tokamak problems
Despite the progress of installations of other types, tokamaks at the moment still remain out of competition: if two tokamaks (TFTR and JET) back in the 1990s actually produced a release of thermonuclear energy approximately equal to the energy consumption for heating the plasma (even though such a mode lasted only about a second), then nothing similar could be achieved with other types of installations. Even a simple increase in the size of tokamaks will lead to the feasibility of energetically favorable fusion in them. The international reactor ITER is currently being built in France, which will have to demonstrate this in practice.
However, tokamaks also have problems. ITER costs billions of dollars, which is unacceptable for future commercial reactors. No reactor has operated continuously for even a few hours, let alone for weeks and months, which again is necessary for industrial applications. There is no certainty yet that the materials of the inner wall of the vacuum chamber will be able to withstand prolonged exposure to plasma.
The concept of a tokamak with a strong field can make the project less expensive. By increasing the field by two to three times, it is planned to obtain the required plasma parameters in a relatively small installation. This concept, in particular, is the basis for the Ignitor reactor, which, together with Italian colleagues, is now beginning to be built at TRINIT (Trinity Institute for Innovation and Thermonuclear Research) near Moscow. If the engineers’ calculations come true, then at a cost many times lower than ITER, it will be possible to ignite plasma in this reactor.
Forward to the stars!
The products of a thermonuclear reaction fly away in different directions at speeds of thousands of kilometers per second. This makes it possible to create ultra-efficient rocket engines. Their specific impulse will be higher than that of the best electric jet engines, and their energy consumption may even be negative (theoretically, it is possible to generate, rather than consume, energy). Moreover, there is every reason to believe that making a thermonuclear rocket engine will be even easier than a ground-based reactor: there is no problem with creating a vacuum, with thermal insulation of superconducting magnets, there are no restrictions on dimensions, etc. In addition, the generation of electricity by the engine is desirable, but It’s not at all necessary, it’s enough that he doesn’t consume too much of it.
Electrostatic confinement
The concept of electrostatic ion confinement is most easily understood through a setup called a fusor. It is based on a spherical mesh electrode, to which a negative potential is applied. Ions accelerated in a separate accelerator or by the field of the central electrode itself fall inside it and are held there by an electrostatic field: if an ion tends to fly out, the electrode field turns it back. Unfortunately, the probability of an ion colliding with a network is many orders of magnitude higher than the probability of entering into a fusion reaction, which makes an energetically favorable reaction impossible. Such installations have found application only as neutron sources.
In an effort to make a sensational discovery, many scientists strive to see synthesis wherever possible. There have been numerous reports in the press regarding various options for so-called “cold fusion.” Synthesis was discovered in metals “impregnated” with deuterium when an electric current flows through them, during the electrolysis of deuterium-saturated liquids, during the formation of cavitation bubbles in them, as well as in other cases. However, most of these experiments have not had satisfactory reproducibility in other laboratories, and their results can almost always be explained without the use of synthesis.
Continuing the “glorious tradition” that began with the “philosopher’s stone” and then turned into a “perpetual motion machine”, many modern scammers are now offering to buy from them a “cold fusion generator”, “cavitation reactor” and other “fuel-free generators”: about the philosophical Everyone has already forgotten the stone, they don’t believe in perpetual motion, but nuclear fusion now sounds quite convincing. But, alas, in reality such energy sources do not exist yet (and when they can be created, it will be in all news releases). So be aware: if you are offered to buy a device that generates energy through cold nuclear fusion, then they are simply trying to “cheat” you!
According to preliminary estimates, even with the current level of technology, it is possible to create a thermonuclear rocket engine for flight to the planets of the Solar System (with appropriate funding). Mastering the technology of such engines will increase the speed of manned flights tenfold and will make it possible to have large reserve fuel reserves on board, which will make flying to Mars no more difficult than working on the ISS now. Speeds of 10% of the speed of light will potentially become available for automatic stations, which means it will be possible to send research probes to nearby stars and obtain scientific data during the lifetime of their creators.
The concept of a thermonuclear rocket engine based on inertial fusion is currently considered the most developed. The difference between an engine and a reactor lies in the magnetic field, which directs the charged reaction products in one direction. The second option involves using an open trap, in which one of the plugs is deliberately weakened. The plasma flowing from it will create a reactive force.
Thermonuclear future
Mastering thermonuclear fusion turned out to be many orders of magnitude more difficult than it seemed at first. And although many problems have already been solved, the remaining ones will be enough for the next few decades of hard work of thousands of scientists and engineers. But the prospects that the transformations of hydrogen and helium isotopes open up for us are so great, and the path taken is already so significant that it makes no sense to stop halfway. No matter what numerous skeptics say, the future undoubtedly lies in synthesis.
1. Nuclear power is a field of science and industrial technology in which methods and means of converting nuclear energy into thermal and electrical energy are developed and used in practice. The foundations of nuclear energy are nuclear power plants (NPPs). The source of energy at nuclear power plants is nuclear reactors, in which a controlled chain reaction of fission of nuclei of heavy elements occurs, mainly U-235 and Pu-239.
Nuclear reactors are of two types: slow neutron reactors and fast neutron reactors. Most nuclear power plants in the world are built on the basis of slow neutron reactors. The first reactors built in the USA (1942), the USSR (1946) and other developed countries were intended to produce weapons-grade plutonium Pu-239. The heat released in them was a by-product. This heat was removed from the reactor using a cooling system and simply released into the environment.
The mechanism of heat release in the reactor is as follows. The two fragments that arise during the fission of a uranium nucleus carry away enormous kinetic energy of about 200 MeV. Their initial speed reaches 5000 km/s. Moving among uranium, moderator or structural elements, these fragments, colliding with atoms, transfer their energy to them and gradually slow down to thermal speeds. The reactor core is heating up. By increasing the intensity of the nuclear reaction, it is possible to achieve greater thermal powers.
The heat generated in the reactor is removed using a liquid or gaseous coolant. In general, a coolant reactor resembles a steam tube boiler (water flows through pipes inside the furnace and heats up). Therefore, along with the concept of “nuclear reactor”, the synonym “nuclear boiler” is often used.
In Fig. Figure 144 shows a diagram of a nuclear power plant in reactor 1. The neutron flux density inside the operating reactor reaches 10 14 particles every 1 cm 2 per second.
A distinction is made between thermal and electrical power of the reactor. Electrical power is no more than 30% of thermal power. The world's first nuclear power plant was built in 1954 in the USSR in Obninsk. Its thermal power is 30 MW, electrical power is 5 MW. The active zone of a uranium-graphite slow neutron reactor has the shape of a cylinder with a diameter of 1.5 m and a height of 1.7 m. The coolant is water. Water temperature at the reactor inlet is + 190°C, at the outlet + 280°C, pressure 100 atm.
The reactor load is 550 kg of uranium enriched to 5%. Duration of operation at rated power is 100 days. The design burnup of U-235 is 15%. The reactor contains 128 fuel elements (fuel elements). The Obninsk NPP was built with the aim of developing technological solutions for nuclear energy. In later serial nuclear power plants, the load and power of reactors increases hundreds of times.
2. Slow neutron nuclear reactor. As already mentioned in §21, the main task in the development of nuclear reactors was that the reactor could operate on natural uranium, i.e. extracted chemically from ores and containing a natural mixture of isotopes: U-238 (99.282%), U-235 (0.712%), U-234 (0.006%), or on relatively cheap low-enriched uranium, in which the isotope content is U-235 or Pu-239 increased to 2-5%.
To do this, three conditions must be met: firstly, the mass of fissile material in the reactor (U-235 or Pu-239) must be no less than critical for its given configuration. This means that, on average, one neutron from the number produced in each nuclear fission event could cause the next fission event. Secondly, neutrons need to be slowed down to thermal speeds, and this must be done in such a way as to minimize their losses due to radiation capture by the nuclei of non-fissile materials. Third, develop principles and create means of controlling a nuclear chain reaction. Although all these conditions are interrelated, for each of them it is possible to identify the main ways of their implementation.
A. Achieving a critical mass of fissile material is possible in two ways: simply increasing the mass of uranium and enriching uranium. Due to the low concentration of fissile material, its critical mass in the reactor is much greater than in an atomic bomb. For example, in the Obninsk NPP /m cr U-235 is about 25 kg. In more modern high-power reactors, m cr reaches several tons. To reduce losses due to neutron leakage from the reactor, its core is surrounded by a neutron reflector. This is a substance with light nuclei that weakly absorbs neutrons (graphite, beryllium).
b. Neutron moderation. Figure 145 shows the energy spectrum of neutrons emitted by fissile nuclei of U-235. The abscissa axis shows the kinetic energy E of neutrons, and the ordinate axis shows the relative frequency ΔN/N of repetition of such energy in conventional units. The curve has a maximum at E = 0.645 MeV. The figure shows that the fission of U-235 nuclei produces predominantly fast neutrons with energy E > 1 MeV.
As mentioned earlier, the effective cross section for neutron capture by U-235 nuclei is maximum for thermal neutrons, when their energy E< 1 Мэв. Поэтому для наиболее эффективного использования нейтронов их надо замедлять до тепловых скоростей. Казалось бы, это можно сделать простым наращиванием массы естественного урана. В этом случае нейтроны, последовательно сталкиваясь с ядрами урана, должны постепенно уменьшать свою энергию и приходить к тепловому равновесию с массой урана. Но в естественном уране на 1 ядро U-235 приходиться 140 ядер U-238. Сечение радиационного захвата быстрых нейтронов ядрами U-238 невелико (σ=0,3 барна), и этот путь был бы возможен, если бы не резонансная область (см. рис.139), где σ возрастает в тысячи раз. Например, при энергии нейтронов E=7эВ σ достигает 5000 барн. Нейтроны этот диапазон энергий в уране не пройдут. Они почти все будут захвачены ядрами U-238
To prevent such absorption from occurring, neutrons must be removed from the uranium mass, slowed down in a moderator that weakly absorbs neutrons (graphite, heavy water, beryllium) and returned back to the uranium mass (diffuse). This is achieved by loading uranium into thin tubes of fuel elements (fuel rods) . And the fuel rods are immersed in the moderator channels.
Typically, fuel rods are thin-walled tubes with a diameter of 15-20 mm made of zirconium alloy. Nuclear fuel is placed inside the fuel rods in the form of tablets compressed from uranium oxide U0 2. The oxide does not sinter at high temperatures and is easily removed when recharging fuel rods. Depending on the size of the reactor core, the length of the fuel rods can reach 7-8 m. Several fuel rods are mounted in containers, which are pipes with a diameter of 10-20 cm or prisms. When reactors are recharged, these containers are replaced, and their disassembly and replacement of fuel rods is carried out at the plant.
The reactor itself is most often a cylinder, through the upper base of which vertical channels are made in a checkerboard pattern. Containers with fuel rods and absorber control rods are placed in these channels.
V. Nuclear chain reaction control carried out using rods made of materials that strongly absorb neutrons - cadmium 48 113 Cd and boron 5 10 V. The latter is often in the form of carbide B 4 C (melting point for cadmium 321 ° C, for boron 2075 ° C). Their absorption cross sections are σ = 20,000 and 4,000 barn, respectively. The parameters of the absorber rods are calculated so that when the rods are fully inserted, a nuclear reaction certainly does not occur in the reactor. With the gradual removal of the rods, the multiplication factor K in the core increases and at a certain position of the rod reaches unity. At this moment the reactor begins to operate. During operation, the K coefficient gradually decreases due to contamination of the reactor with fission fragments. This decrease in K is compensated by the extension of the rods. In case of a sudden increase in the intensity of the reaction, there are additional rods. Their rapid release into the core immediately stops the reaction.
Reactor control is made easier by the presence of delayed neutrons. Their share for different isotopes ranges from 0.6 to 0.8%; for U-235 it is approximately 0.64%. The average half-life of fission fragments producing delayed neutrons is T = 9 s, the average lifetime of one generation of delayed neutrons is τ = T/ln2 = 13 s.
During stationary operation of the reactor, the multiplication factor of fast neutrons is K b = 1. The total coefficient K = K b + K differs from unity by the fraction of delayed neutrons and can reach K = 1 + 0.006. In the second generation, after 13 seconds, the number of neutrons is N = N 0 K 2 = N 0 (1.006)2 = 1.012MN 0. In the tenth generation, after 130 s, their number will be N 0 K 10 = 1.062 MN 0, which is still far from an emergency situation. Therefore, the automatic control system, based on monitoring the neutron flux density in the core, is quite capable of monitoring the slightest nuances in the operation of the reactor and responding to them by moving the control rods.
3. Reactor poisoning- this is the accumulation of radioactive products in it. The accumulation of stable products in it is called slagging of the reactor. In both cases, nuclei accumulate, intensively absorbing neutrons. The capture cross section of the most powerful xenon-135 poisoner reaches 2.6 * 10 6 barn.
The mechanism of Xe-135 formation is as follows. When U-235 or Pu-239 is fissioned by slow neutrons, with a probability of 6%, a fragment is obtained - a tellurium nucleus of 52,135 Te. With a period of 0.5 minutes, Te-135 undergoes β - decay, turning into the nucleus of the iodine isotope I. This isotope is also β - active with a period of 6.7 hours. The decay product of I-135 is the xenon isotope 54 135 Xe. With a period of T = 9.2 hours, Xe-135 undergoes β - decay, turning into a practically stable cesium isotope 55 135 Cz. (/T= 3*10 6 years).
Other decay patterns produce other harmful nuclei, such as samarium 62,139 Sm. Poisoning occurs especially quickly during the initial period of reactor operation. Over time, radioactive equilibrium is established between the decay products. From this moment, the slagging of the reactor begins to increase.
A reactor in which the fissile material (uranium), moderator (graphite) and absorber (cadmium) are separate phases and have interfaces is called heterogeneous. If all these elements in a liquid or gaseous state represent one common phase, the reactor is called homogeneous. For energy chains, exclusively heterogeneous reactors are built.
5. Fast neutron reactors. The nuclei of U-235, Pu-239 and U-233 are fissioned by all neutrons. Therefore, if you increase the enrichment of uranium, for example, with the U-235 isotope, then due to the increase in the concentration of fissile nuclei, an increasingly larger proportion of neutrons will fission the U-235 nuclei without leaving the uranium mass. At a certain concentration of fissile nuclei and with a sufficient mass of uranium in the core, the neutron multiplication factor reaches unity even without moderating them. The reactor will operate on fast neutrons (abbreviated as fast reaction).
The advantage of a fast reaction over a slow reaction (that is, over a reaction with slow neutrons) is that neutrons are used more efficiently. As a result, the reproduction of nuclear fuel increases. In a slow reaction of 2.5 neutrons, 1 also goes to the U-235 nucleus, maintaining the reaction, approximately 1 goes to the U-238 nucleus, then forming Pu-239 (nuclear fuel), and 0.5 neutrons are lost. One core of “burnt” U-235 produces approximately 1 core of Pu-239. In a fast reaction, out of 2.5 neutrons, 1 is also used to maintain the reaction. But less than 0.5 neutrons are lost. Therefore, more neutrons enter the U-238 nuclei. As a result, more than 1 Pu-239 nucleus is formed per one core of “burnt” U-235. Expanded reproduction of nuclear fuel is taking place. The creation and operation of fast neutron reactors is more difficult than slow neutron reactors. Firstly, the volume of the active zone decreases sharply. This increases the energy density, which leads to an increase in temperature and tightens the requirements for structural materials and coolant. Secondly, the requirements for the reactor control system are increasing, that is, for the speed of operations performed by the control system.
6. Prospects for nuclear energy. Today, normally operating nuclear power plants are the cleanest of all energy sources. They do not emit C0 2 and S0 2, like thermal plants, and therefore do not aggravate the greenhouse effect and do not flood arable land with water, like hydroelectric power plants. Taking into account the possibility of processing U-238 into Pu-239 and Th-232 into U-233, the reserves of readily available nuclear fuel will last for hundreds of years. The use of nuclear power plants will save oil, gas and coal for the chemical industry. There are two difficulties with expanding the nuclear power plant fleet. One is objective, its essence is that the problems associated with the disposal and disposal of waste nuclear fuel and structural elements that have spent their reactor life have not been fully resolved.
The second difficulty is subjective. Compared to thermal and hydropower plants, servicing nuclear power plants requires a higher technical culture and imposes enormous responsibility on a person. The slightest deviation from technological discipline can result in tragedy for thousands of people.
7. Fusion. From the distribution curve of the specific binding energy it follows that the fusion of light nuclei into one nucleus, like the fission of heavy nuclei, must be accompanied by the release of a huge amount of energy. All nuclei carry the same positive charge. To bring them closer to the distance at which fusion begins, two interacting nuclei need to be accelerated towards each other. This can be done in two ways. Firstly, with the help of accelerators. This path is cumbersome and ineffective. Secondly, simply heating the gas to the required temperature. Therefore, fusion reactions of light nuclei initiated by heating a gas are called thermonuclear reactions. Let us estimate the temperature of deuterium gas at which thermonuclear fusion of deuterium + deuterium begins. 1 2 H+ 1 2 H→ 2 3 He + 0 1 n + 3.27 MeV.
To merge nuclei, they need to be brought together at a distance of r = 2*10 -15 m. The potential energy during such a rapprochement should be equal to the kinetic energy of both nuclei in the system
center of mass (1/4πε 0)*(e 2 /r) = 2*(mυ 2 /2) = 2*(3/2)* kT. Gas temperature T=(1/3K)*(1/4πε 0)*(e 2 /r)=3*10 9 K. The energy distribution of particles is close to Maxwellian. Therefore, there are always “hotter” particles, and also due to the tunnel effect, the fusion reaction begins at lower temperatures T ≈ 10 7 K.
In addition to the reaction, two more are of particular interest: deuterium + deuterium and deuterium + tritium. 2 1 H + 1 2 H+ 1 2 p + 4.03 MeV. (22.3) and 1 2 H + 1 3 H → 2 4 He + 0 1 n +17.59 MeV. (22.4)
The latter reaction releases approximately 5 times more energy per unit mass than the fission of U-235. This energy is the kinetic energy of the movement of neutrons and the resulting helium nuclei. Under terrestrial conditions, it was possible to realize a nuclear fusion reaction in the form of an uncontrolled explosion of a thermonuclear hydrogen bomb.
8. Hydrogen bomb is a conventional atomic bomb, the nuclear charge of which (U-235 or Pu-239) is surrounded by a blanket of a substance containing light atoms. For example, lithium deuteride LiD. The high temperature that occurs when an atomic charge is detonated initiates thermonuclear fusion of light atoms. This releases additional energy, increasing the power of the bomb. In addition to reactions (22.1) and (22.3), another one can occur in a bomb with a lithium deuteride blanket. 3 6 Li+ 1 1 p→ 2 4 He + 2 3 He + 4 MeV. (22.5). (22.4). But tritium is β - an active element. With a period of 12 years it turns into He-3. Therefore, hydrogen charges with tritium have a limited shelf life and must be tested regularly. The substances involved in thermonuclear fusion do not produce radioactive products. But thanks to the intense neutron flux, radioactivity is induced in the nuclei of structural materials and surrounding bodies. Therefore, it is impossible to implement a “clean” fusion reaction without radioactive waste.
9. The problem of controlled thermonuclear fusion (U HS) has not yet been resolved. Its solution is very promising for the energy sector. The water of the seas and oceans contains approximately 0.015% deuterium (by the number of atoms). There is about 10-20 kg of water on earth. If you extract deuterium from this water, then the energy that can be obtained from it is equivalent to 6 * 10 18 K)" tons of coal, this is a gigantic amount (about 0.001 Earth masses). Therefore, deuterium in the seas and oceans is a practically inexhaustible source of energy.
The problem of CTS comes down to two tasks. Firstly, you need to learn how to create a high temperature T>10 7 K in a limited volume. Secondly, maintain the volume of plasma dressed to this temperature for a time sufficient for the nuclear fusion reaction to occur. Both of these problems are far from being solved.
10. Thermonuclear reactions in stars. According to modern concepts, a star is born from extended gas and dust clouds, consisting mainly of hydrogen. As a result of gravitational compression, the cloud becomes denser and begins to undress, turning into a protostar. When the temperature in the center of a protostar reaches 10 7 K, thermonuclear reactions of synthesis of light elements, mainly hydrogen, are excited in it. Gravitational compression is suspended by increased gas-kinetic and optical pressure. A protostar turns into a star. There are two possible cycles of converting hydrogen into helium. The main reactions that make up each cycle are listed below. In parentheses next to the reaction equations, the average reaction time τ is indicated, calculated using the effective reaction cross section for the pressures and temperatures that exist inside the star.
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