thermonuclear fusion, the reaction of fusion of light atomic nuclei into heavier nuclei, occurring at superhigh temperatures and accompanied by the release of huge amounts of energy. Nuclear fusion is the reverse reaction of atomic fission: in the latter, energy is released due to the splitting of heavy nuclei into lighter ones. see also NUCLEAR FISSION; NUCLEAR POWER.
According to modern astrophysical concepts, the main source of energy for the Sun and other stars is thermonuclear fusion occurring in their depths. Under terrestrial conditions, it is carried out during the explosion of a hydrogen bomb. Thermonuclear fusion is accompanied by a colossal energy release per unit mass of reacting substances (about 10 million times greater than in chemical reactions). Therefore, it is of great interest to master this process and, on its basis, create a cheap and environmentally friendly source of energy. However, despite the fact that large scientific and technical teams in many developed countries are engaged in research on controlled thermonuclear fusion (CTF), there are still many complex problems to be solved before the industrial production of thermonuclear energy becomes a reality.
Modern nuclear power plants using the fission process only partially satisfy the world's electricity needs. The fuel for them is the natural radioactive elements uranium and thorium, the prevalence and reserves of which in nature are very limited; therefore, for many countries there is a problem of their import. The main component of thermonuclear fuel is the hydrogen isotope deuterium, which is found in sea water. Its reserves are publicly available and very large (the oceans cover ~ 71% of the Earth's surface area, and deuterium accounts for about 0.016% of the total number of hydrogen atoms that make up water). In addition to the availability of fuel, thermonuclear energy sources have the following important advantages over nuclear power plants: 1) the UTS reactor contains much less radioactive materials than a nuclear fission reactor, and therefore the consequences of an accidental release of radioactive products are less dangerous; 2) thermonuclear reactions produce less long-lived radioactive waste; 3) TCB allows direct electricity generation.
Artsimovich L.A. Controlled thermonuclear reactions. M., 1963
Thermal and nuclear power plants(book 1, section 6; book 3, section 8). M., 1989
Find "NUCLEAR FUSION" on
For the first time, the problem of controlled thermonuclear fusion in the Soviet Union was formulated and offered some constructive solution for it by the Soviet physicist O. A. Lavrentiev. In addition to him, such outstanding physicists as A. D. Sakharov and I. E. Tamm, as well as L. A. Artsimovich, who headed the Soviet program on controlled thermonuclear fusion since 1951, made an important contribution to solving the problem.
Historically, the issue of controlled thermonuclear fusion at the global level arose in the middle of the 20th century. It is known that I. V. Kurchatov in 1956 made a proposal for the cooperation of atomic scientists from different countries in solving this scientific problem. This happened during a visit to the British nuclear center "Harwell" ( English) .
Reaction types
The fusion reaction is as follows: two or more atomic nuclei, as a result of the application of a certain force, approach so much that the forces acting at such distances prevail over the Coulomb repulsion forces between equally charged nuclei, as a result of which a new nucleus is formed. When creating a new nucleus, a large energy of strong interaction will be released. According to the well-known formula E=mc² , having released energy, the system of nucleons will lose part of its mass. Atomic nuclei, which have a small electric charge, are easier to bring to the right distance, so heavy hydrogen isotopes are one of the best fuels for a fusion reaction.
It has been found that a mixture of two isotopes, deuterium and tritium, requires the least energy for a fusion reaction compared to the energy released during the reaction. However, although a mixture of deuterium and tritium (D-T) is the subject of most fusion research, it is by no means the only potential fuel. Other mixtures may be easier to manufacture; their reaction can be better controlled, or more importantly, produce fewer neutrons. Of particular interest are the so-called "neutronless" reactions, since the successful industrial use of such fuel will mean the absence of long-term radioactive contamination of materials and reactor design, which, in turn, could positively affect public opinion and the overall cost of operating the reactor, significantly reducing costs. for decommissioning and disposal. The problem remains that the fusion reaction using alternative fuels is much more difficult to maintain, so the D-T reaction is considered only a necessary first step.
Controlled thermonuclear fusion can use various types of thermonuclear reactions depending on the type of fuel used.
Deuterium + Tritium Reaction (D-T Fuel)
The most easily implemented reaction is deuterium + tritium:
2 H + 3 H = 4 He + n for an energy output of 17.6 MeV (MeV).
Such a reaction is most easily implemented from the point of view of modern technologies, gives a significant yield of energy, and fuel components are cheap. The disadvantage is the release of unwanted neutron radiation.
Two nuclei: deuterium and tritium fuse to form a helium nucleus (alpha particle) and a high-energy neutron:
Tokamak (TOroidal Chamber with Magnetic Coils) is a toroidal facility for magnetic plasma confinement. The plasma is held not by the walls of the chamber, which are not able to withstand its temperature, but by a specially created magnetic field. A feature of the tokamak is the use of an electric current flowing through the plasma to create a toroidal field necessary for plasma equilibrium.
Reaction deuterium + helium-3
It is much more difficult, at the limit of what is possible, to carry out the reaction deuterium + helium-3
2 H + 3 He = 4 He + at an energy output of 18.4 MeV.The conditions for achieving it are much more complicated. Helium-3 is also a rare and extremely expensive isotope. It is not currently produced on an industrial scale. However, it can be obtained from tritium, obtained in turn at nuclear power plants; or mined on the moon.
The complexity of conducting a thermonuclear reaction can be characterized by the triple product ntτ (density per temperature per hold time). According to this parameter, the reaction D- 3 He is about 100 times more difficult than D-T.
Reaction between deuterium nuclei (D-D, monopropellant)
In addition to the main reaction in DD-plasma, the following also occur:
These reactions slowly proceed in parallel with the deuterium + helium-3 reaction, and the tritium and helium-3 formed during them are very likely to immediately react with deuterium.
Other types of reactions
Several other types of reactions are also possible. The choice of fuel depends on many factors - its availability and low cost, energy yield, ease of achieving the conditions required for the fusion reaction (primarily temperature), the necessary design characteristics of the reactor, etc.
"Neutronless" reactions
The most promising are the so-called "neutronless" reactions, since the neutron flux generated by thermonuclear fusion (for example, in the deuterium-tritium reaction) carries away a significant part of the power and generates induced radioactivity in the reactor design. The deuterium + helium-3 reaction is promising, also due to the lack of a neutron yield.
Reactions on light hydrogen
D + T → 4 He (3.5 MeV) + n (14.1 MeV).
However, in this case, most (more than 80%) of the released kinetic energy falls precisely on the neutron. As a result of collisions of fragments with other atoms, this energy is converted into thermal energy. In addition, fast neutrons create a significant amount of radioactive waste. In contrast, the fusion of deuterium and helium-3 produces almost no radioactive products:
D + 3 He → 4 He (3.7 MeV) + p (14.7 MeV), where p is a proton.
This allows for simpler and more efficient fusion kinetic reaction conversion systems such as the magnetohydrodynamic generator.
Reactor designs
There are two principal schemes for the implementation of controlled thermonuclear fusion, the development of which is currently ongoing (2012):
The first type of thermonuclear reactor is much better developed and studied than the second.
Radiation safety
A thermonuclear reactor is much safer than a nuclear reactor in terms of radiation. First of all, the amount of radioactive substances in it is relatively small. The energy that can be released as a result of any accident is also small and cannot lead to the destruction of the reactor. At the same time, there are several natural barriers in the design of the reactor that prevent the spread of radioactive substances. For example, the vacuum chamber and the shell of the cryostat must be sealed, otherwise the reactor simply cannot work. However, during the design of ITER, great attention was paid to radiation safety both during normal operation and during possible accidents.
There are several sources of possible radioactive contamination:
- the radioactive isotope of hydrogen is tritium;
- induced radioactivity in the materials of the installation as a result of neutron irradiation;
- radioactive dust generated as a result of plasma impact on the first wall;
- radioactive corrosion products that can form in the cooling system.
In order to prevent the spread of tritium and dust if they go beyond the vacuum chamber and the cryostat, a special ventilation system is needed to maintain a reduced pressure in the reactor building. Therefore, there will be no air leakage from the building, except through ventilation filters.
In the construction of a reactor, ITER for example, where possible, materials already tested in nuclear power will be used. Due to this, the induced radioactivity will be relatively small. In particular, even in the event of failure of the cooling systems, natural convection will be sufficient to cool the vacuum chamber and other structural elements.
Estimates show that even in the event of an accident, radioactive releases will not pose a danger to the public and will not necessitate evacuation.
Fuel cycle
The first generation reactors will most likely run on a mixture of deuterium and tritium. The neutrons that appear during the reaction will be absorbed by the reactor shield, and the heat released will be used to heat the coolant in the heat exchanger, and this energy, in turn, will be used to rotate the generator.
. .Fusion reaction as an industrial power source
Fusion energy is considered by many researchers (in particular, Christopher Llewellyn-Smith) as a "natural" source of energy in the long term. Proponents of the commercial use of fusion reactors for power generation make the following arguments in their favor:
The cost of electricity compared to traditional sources
Critics point out that the question of the cost-effectiveness of nuclear fusion in the production of electricity for general use remains open. The same study, commissioned by the Bureau of Science and Technology of the British Parliament, indicates that the cost of generating electricity using a fusion reactor is likely to be at the top of the cost spectrum for traditional energy sources. Much will depend on the technology available in the future, the structure and regulation of the market. The cost of electricity directly depends on the efficiency of use, the duration of operation and the cost of disposing of the reactor.
There is also the question of the cost of research. EU countries spend about 200 million euros annually on research, and it is predicted that it will take several more decades before the industrial use of nuclear fusion becomes possible. Supporters of alternative non-nuclear sources of electricity believe that it would be more appropriate to direct these funds to the introduction of renewable sources of electricity.
Availability of commercial fusion energy
Despite widespread optimism (since the early studies of the 1950s), significant obstacles between today's understanding of nuclear fusion processes, technological possibilities and the practical use of nuclear fusion have not yet been overcome. It is not even clear how cost-effective the production of electricity using thermonuclear fusion can be. While there has been constant progress in research, researchers are constantly confronted with new challenges. For example, the challenge is to develop a material that can withstand neutron bombardment, which is estimated to be 100 times more intense than conventional nuclear reactors. The severity of the problem is exacerbated by the fact that the interaction cross section of neutrons with nuclei ceases to depend on the number of protons and neutrons with increasing energy and tends to the cross section of the atomic nucleus - and for 14 MeV neutrons there is simply no isotope with a sufficiently small interaction cross section. This necessitates very frequent replacement of D-T and D-D reactor designs and reduces its profitability to such an extent that the cost of reactor designs made of modern materials for these two types turns out to be more than the cost of the energy produced on them. Three types of solutions are possible:
- Rejection of pure nuclear fusion and its use as a source of neutrons for the fission of uranium or thorium.
- Rejection of D-T and D-D synthesis in favor of other synthesis reactions (for example, D-He).
- A sharp reduction in the cost of structural materials or the development of processes for their recovery after irradiation. Huge investments in materials science are also required, but the prospects are uncertain.
Side reactions D-D (3%) during the synthesis of D-He complicate the production of cost-effective designs for the reactor, but are not impossible at the current technological level.
There are the following research phases:
1. Equilibrium or "pass" mode(Break-even): when the total energy released during the fusion process is equal to the total energy expended to start and maintain the reaction. This ratio is marked with the symbol Q.
2. Blazing Plasma(Burning Plasma): An intermediate stage in which the reaction will be supported mainly by alpha particles that are produced during the reaction, and not by external heating. Q ≈ 5. So far (2012) has not been reached.
3. Ignition(Ignition): stable self-sustaining reaction. Must be achieved at high values Q. So far not achieved.
The next step in research should be the International Thermonuclear Experimental Reactor (ITER). At this reactor, it is planned to study the behavior of high-temperature plasma (flaming plasma with Q~ 30) and structural materials for an industrial reactor.
The final phase of the research will be DEMO: a prototype industrial reactor that will achieve ignition and demonstrate the practical suitability of new materials. The most optimistic forecasts for the completion of the DEMO phase: 30 years. Taking into account the approximate time for the construction and commissioning of an industrial reactor, we are separated by ~40 years from the industrial use of thermonuclear energy.
Existing tokamaks
In total, about 300 tokamaks were built in the world. The largest of them are listed below.
- USSR and Russia
- T-3 is the first functional apparatus.
- T-4 - an enlarged version of the T-3
- T-7 is a unique installation, in which for the first time in the world a relatively large magnetic system with a superconducting solenoid based on tin niobate, cooled by liquid helium, was implemented. The main task of the T-7 was completed: the prospect for the next generation of superconducting solenoids of thermonuclear power engineering was prepared.
- T-10 and PLT are the next step in the world of fusion research, they are almost the same size, equal power, with the same confinement factor. And the results obtained are identical: the coveted temperature of thermonuclear fusion has been reached at both reactors, and the lag according to the Lawson criterion is only two hundred times.
- T-15 is today's reactor with a superconducting solenoid that gives a field of 3.6 T.
- Libya
- TM-4A
Links
- E.P. Velikhov; S.V. Mirnov Controlled thermonuclear fusion enters the finish line (PDF). Troitsk Institute for Innovation and Thermonuclear Research. Russian Research Center "Kurchatov Institute".. ac.ru. - Popular Statement of the Problem. Archived from the original on February 5, 2012. Retrieved August 8, 2007.
- C. Llewellyn-Smith. On the way to thermonuclear energy. Materials of a lecture given on May 17, 2009 at FIAN.
- A grandiose experiment on thermonuclear fusion will be held in the United States.
see also
Notes
- Bondarenko B. D. "The role of O. A. Lavrentiev in posing the question and initiating research on controlled thermonuclear fusion in the USSR" // UFN 171 , 886 (2001).
- Review by A. D. Sakharov, published in the section “From the Archive of the President of the Russian Federation”. UFN 171 , 902 (2001), p. 908.
- Scientific community of physicists of the USSR. 1950s-1960s. Documents, memoirs, research/ Compiled and edited by P. V. Vizgin and A. V. Kessenikh. - St. Petersburg. : RGHA, 2005. - T. I. - S. 23. - 720 p. - 1000 copies.
- Early US thermonuclear munitions also used natural lithium deuteride, which contains mainly a lithium isotope with a mass number of 7. It also serves as a source of tritium, but for this, the neutrons participating in the reaction must have an energy of 10 MeV and higher.
- Thermonuclear power plants of a neutronless cycle (for example, D + 3 He → p + 4 He + 18.353 MeV) with an MHD generator on high-temperature plasma;
- E. P. Velikhov, S. V. Putvinsky Thermonuclear reactor. Fornit (October 22, 1999). - Report dated 10/22/1999, made within the framework of the Energy Center of the World Federation of Scientists. Archived from the original on 5 February 2012. Retrieved 16 January 2011.
- (English) Postnote: Nuclear Fusion, 2003
- EFDA | European Fusion Development Agreement
- Tore Supra
- Tokamak Fusion Test Reactor
- Princeton Plasma Physics Laboratory Overview
- MIT Plasma Science & Fusion Center: research>alcator>
- Home - Fusion Website
- Fusion Plasma Research
- The Artificial Sun
- Thermonuclear came out of zero - Newspaper. Ru
- Information about the movie "Spider-Man 2" ("Spider-Man 2") - Cinema "Cosmos"
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All stars, including our Sun, produce energy using thermonuclear fusion. The scientific world is in trouble. Scientists do not know all the ways in which such fusion (thermonuclear) can be obtained. The fusion of light atomic nuclei and their transformation into heavier ones indicates that energy has been obtained, which can be either controlled or explosive. The latter is used in thermonuclear explosive structures. A controlled thermonuclear process differs from the rest of nuclear energy in that it uses a decay reaction when heavy nuclei are split into lighter ones, but nuclear reactions using deuterium (2 N) and tritium (3 N) - fusion, that is, controlled thermonuclear fusion. In the future, it is planned to use helium-3 (3 He) and boron-11 (11 V).
Dream
One should not confuse the traditional and well-known thermonuclear fusion with what is the dream of today's physicists, in the embodiment of which no one yet believes. This refers to a nuclear reaction at any, even room temperature. Also, this is the absence of radiation and cold thermonuclear fusion. Encyclopedias tell us that a nuclear fusion reaction in atomic-molecular (chemical) systems is a process that does not require significant heating of a substance, but humanity has not yet produced such energy. This is despite the fact that absolutely all nuclear reactions in which fusion occurs are in the state of plasma, and its temperature is millions of degrees.
At the moment, this is not even a dream of physicists, but science fiction writers, but nevertheless, developments have been ongoing for a long time and persistently. Thermonuclear fusion without the constantly accompanying danger of the level of Chernobyl and Fukushima - is this not a great goal for the benefit of mankind? Foreign scientific literature has given different names to this phenomenon. For example, LENR stands for low-energy nuclear reactions, and CANR stands for chemically induced (assisted) nuclear reactions. Successful implementation of such experiments was declared quite often, representing the most extensive databases. But either the media gave out another "duck", or the results spoke of incorrectly staged experiments. Cold thermonuclear fusion has not yet received truly convincing evidence of its existence.
star element
Hydrogen is the most abundant element in space. Approximately half of the mass of the Sun and most of the other stars falls on its share. Hydrogen is not only in their composition - there is a lot of it in interstellar gas and in gas nebulae. And in the depths of stars, including the Sun, the conditions for thermonuclear fusion are created: there the nuclei of hydrogen atoms are converted into helium atoms, through which huge energy is generated. Hydrogen is its main source. Every second, our Sun radiates energy equivalent to four million tons of matter into space.
This is what the fusion of four hydrogen nuclei into one helium nucleus gives. When one gram of protons burns, the energy of thermonuclear fusion is released twenty million times more than when the same amount of coal is burned. Under terrestrial conditions, the power of thermonuclear fusion is impossible, since such temperatures and pressures as exist in the depths of stars have not yet been mastered by man. Calculations show that for at least another thirty billion years, our Sun will not die out or weaken due to the presence of hydrogen. And on Earth, people are just beginning to understand what hydrogen energy is and what the reaction of thermonuclear fusion is, since working with this gas is very risky, and it is extremely difficult to store it. So far, humanity can only split the atom. And every reactor (nuclear) is built on this principle.
Thermonuclear fusion
Nuclear energy is a product of the splitting of atoms. Synthesis, on the other hand, receives energy in a different way - by combining them with each other, when deadly radioactive waste is not formed, and a small amount of sea water would be enough to produce the same amount of energy as is obtained from burning two tons of coal. In the laboratories of the world it has already been proven that controlled thermonuclear fusion is quite possible. However, power plants that would use this energy have not yet been built, even their construction is not foreseen. But two hundred and fifty million dollars were spent by the United States alone to investigate the phenomenon of controlled thermonuclear fusion.
Then these studies were literally discredited. In 1989, chemists S. Pons (USA) and M. Fleshman (Great Britain) announced to the whole world that they had achieved a positive result and launched thermonuclear fusion. The problems were that scientists were too hasty, not subjecting their discovery to review by the scientific world. The media immediately seized the sensation and filed this claim as the discovery of the century. The verification was carried out later, and not just errors in the experiment were discovered - it was a failure. And then not only journalists succumbed to disappointment, but also many highly respected world-class physicists. The reputable laboratories at Princeton University spent more than fifty million dollars to test the experiment. Thus, cold thermonuclear fusion, the principle of its production, were declared pseudoscience. Only small and scattered groups of enthusiasts continued these studies.
essence
Now the term is proposed to be replaced, and instead of cold nuclear fusion, the following definition will sound: a nuclear process induced by a crystal lattice. This phenomenon is understood as anomalous low-temperature processes, which are simply impossible from the point of view of nuclear collisions in a vacuum - the release of neutrons through the fusion of nuclei. These processes can exist in non-equilibrium solids stimulated by transformations of elastic energy in the crystal lattice under mechanical influences, phase transitions, sorption or desorption of deuterium (hydrogen). This is an analogue of the already well-known hot thermonuclear reaction, when hydrogen nuclei merge and turn into helium nuclei, releasing colossal energy, but this happens at room temperature.
Cold fusion is more precisely defined as chemically induced photonuclear reactions. Direct cold thermonuclear fusion was never achieved, but completely different strategies were suggested by searches. A thermonuclear reaction is triggered by the generation of neutrons. Mechanical stimulation by chemical reactions leads to the excitation of deep electron shells, giving rise to gamma or X-ray radiation, which is intercepted by the nuclei. That is, a photonuclear reaction occurs. Nuclei decay, and thus generate neutrons and, quite possibly, gamma rays. What can excite internal electrons? Probably a shock wave. From the explosion of conventional explosives.
Reactor
For more than forty years, the world thermonuclear lobby has been spending about a million dollars annually on research into thermonuclear fusion, which is supposed to be obtained with the help of TOKAMAK. However, almost all progressive scientists are against such research, since a positive result is most likely impossible. Western Europe and the United States disappointedly began to dismantle all their TOKAMAKS. And only in Russia they still believe in miracles. Although many scientists consider this idea an ideal brake alternative to nuclear fusion. What is TOKAMAK? This is one of two projects for a fusion reactor, which is a toroidal chamber with magnetic coils. And there is also a stellarator, in which the plasma is kept in a magnetic field, but the coils that induce the magnetic field are external, in contrast to the TOKAMAK.
This is a very complex design. TOKAMAK is quite worthy of the Large Hadron Collider in terms of complexity: more than ten million elements, and the total costs, together with construction and project costs, significantly exceed twenty billion euros. The collider was much cheaper, and maintaining the ISS also costs no more. Toroidal magnets require eighty thousand kilometers of superconducting filament, their total weight exceeds four hundred tons, and the entire reactor weighs about twenty-three thousand tons. The Eiffel Tower, for example, weighs just over seven thousand. The TOKAMAK plasma is eight hundred and forty cubic meters. Height - seventy-three meters, sixty of them - underground. For comparison: the Spasskaya Tower is only seventy-one meters high. The area of the reactor platform is forty-two hectares, like sixty football fields. The plasma temperature is one hundred and fifty million degrees Celsius. At the center of the Sun, it is ten times lower. And all this for the sake of controlled thermonuclear fusion (hot).
Physicists and chemists
But let's get back to the "rejected" discovery of Fleshman and Pons. All of their colleagues claim that they still managed to create conditions where deuterium atoms obey wave effects, nuclear energy is released in the form of heat in accordance with the theory of quantum fields. The latter, by the way, is perfectly developed, but hellishly complex and hardly applicable to the description of some specific phenomena of physics. That is probably why people do not want to prove it. Flashman demonstrates a cut in the laboratory's concrete floor from an explosion he claims was caused by a cold fusion. However, physicists do not believe chemists. I wonder why?
After all, how many opportunities for humanity are closed with the cessation of research in this direction! The problems are simply global, and there are many of them. And they all require a solution. This is an environmentally friendly source of energy, through which it would be possible to decontaminate huge volumes of radioactive waste after the operation of nuclear power plants, desalinate sea water and much more. If we could master the production of energy by turning some elements of the periodic table into completely different ones without using neutron fluxes for this purpose, which create induced radioactivity. But science officially and now considers it impossible to transform any chemical elements into completely different ones.
Rossi-Parkhomov
In 2009, the inventor A. Rossi patented an apparatus called the Rossi Energy Catalyst, which implements cold thermonuclear fusion. This device has been repeatedly demonstrated to the public, but has not been independently verified. Physicist Mark Gibbs on the pages of the journal morally destroyed both the author and his discovery: without an objective analysis, they say, confirming the coincidence of the results obtained with the declared ones, this cannot be news of science.
But in 2015, Alexander Parkhomov successfully repeated Rossi's experiment with his low-energy (cold) nuclear reactor (LENR) and proved that the latter has great prospects, although its commercial significance is questionable. The experiments, the results of which were presented at a seminar at the All-Russian Research Institute for the Operation of Nuclear Power Plants, show that the most primitive copy of Rossi's brainchild, his nuclear reactor, can produce two and a half times more energy than it consumes.
Energoniva
The legendary scientist from Magnitogorsk, A. V. Vachaev, created the Energoniva installation, with the help of which he discovered a certain effect of transmutation of elements and the generation of electricity in this process. It was hard to believe. Attempts to draw the attention of fundamental science to this discovery were futile. Criticism came from everywhere. Probably, the authors did not need to independently build theoretical calculations regarding the observed phenomena, or the physicists of the higher classical school should have been more attentive to experiments with high-voltage electrolysis.
But on the other hand, such a relationship was noted: not a single detector registered a single radiation, but it was impossible to be near the operating installation. The research team consisted of six people. Five of them soon died between the ages of forty-five and fifty-five, and the sixth became disabled. Death came for completely different reasons after some time (for about seven to eight years). Nevertheless, at the Energoniva installation, the followers of the third generation and the student of Vachaev carried out experiments and made the assumption that a low-energy nuclear reaction took place in the experiments of the deceased scientist.
I. S. Filimonenko
Cold thermonuclear fusion was studied in the USSR already in the late fifties of the last century. The reactor was designed by Ivan Stepanovich Filimonenko. However, no one managed to understand the principles of operation of this unit. That is why, instead of the position of an undisputed leader in the field of nuclear energy technologies, our country has taken the place of a raw material appendage that sells its own natural resources, depriving entire generations of the future. But the pilot plant had already been created, and it produced a warm fusion reaction. The author of the most breakthrough energy structures that suppress radiation was a native of the Irkutsk region, who went through the entire war from his sixteen to twenty years as a scout, an order bearer, an energetic and talented physicist I. S. Filimonenko.
Cold-type thermonuclear fusion was closer than ever. Warm fusion took place at a temperature of only 1150 degrees Celsius, and heavy water was the basis. Filimonenko was denied a patent: supposedly a nuclear reaction is impossible at such a low temperature. But the synthesis was on! Heavy water was decomposed by electrolysis into deuterium and oxygen, deuterium was dissolved in the palladium of the cathode, where the nuclear fusion reaction took place. The production is waste-free, that is, without radiation, and neutron radiation was also absent. Only in 1957, having enlisted the support of academicians Keldysh, Kurchatov and Korolev, whose authority was indisputable, Filimonenko managed to get things off the ground.
Decay
In 1960, in connection with a secret decree of the Council of Ministers of the USSR and the Central Committee of the CPSU, work began on the invention of Filimonenko under the control of the Ministry of Defense. During the experiments, the researcher found that during the operation of the reactor, some kind of radiation appears, which reduces the half-life of isotopes very quickly. It took half a century to understand the nature of this radiation. Now we know what it is - neutronium with dineutronium. And then, in 1968, the work practically stopped. Filimonenko was accused of political disloyalty.
In 1989, the scientist was rehabilitated. His installations began to be recreated in the NPO Luch. But the matter did not go further than the experiments - they did not have time. The country perished, and the new Russian had no time for fundamental science. One of the best engineers of the twentieth century died in 2013 without seeing the happiness of mankind. The world will remember Ivan Stepanovich Filimonenko. Cold thermonuclear fusion will someday be established by his followers.
Scientists at the Princeton Plasma Physics Laboratory have proposed the idea of the most durable nuclear fusion device that can operate for more than 60 years. At the moment, this is a daunting task: scientists are struggling to get a fusion reactor to work for a few minutes - and then years. Despite the complexity, the construction of a fusion reactor is one of the most promising tasks of science, which can bring great benefits. We tell you what you need to know about thermonuclear fusion.
1. What is thermonuclear fusion?
Do not be afraid of this cumbersome phrase, in fact, everything is quite simple. Thermonuclear 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 change. 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 take place both spontaneously and 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, it is necessary to disperse these particles to crazy speeds. This can be done at very high temperatures, on the order of several million kelvins. 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 that can be used for various purposes - you can create the most powerful weapon, 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, for each nucleon (the so-called constituent nuclei, protons and neutrons), much more energy is released than in a nuclear reaction. For example, when fission of a uranium nucleus per nucleon accounts for 0.9 MeV (megaelectronvolt), and whenIn the synthesis of a helium nucleus, an energy equal to 6 MeV is released from hydrogen nuclei. Therefore, scientists are learning to carry out thermonuclear reactions.
Fusion research and the construction of reactors allow for the expansion of 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 interiors 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 Evie 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, Kuzkin's Mother), developed by Soviet scientists under the leadership of Igor Kurchatov, was tested. It was the most powerful explosive device in the history of mankind: the total energy of the explosion, according to various sources, ranged from 57 to 58.6 megatons of TNT. In order to detonate a hydrogen bomb, it is first necessary to obtain a high temperature during a conventional nuclear explosion - only then will the atomic nuclei begin to react.
The power of the explosion in an uncontrolled nuclear reaction is very high, 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 manage it.
4. What is needed for a controlled thermonuclear reaction?
Hold the plasma!
Unclear? Now let's explain.
First, atomic nuclei. Nuclear energy uses isotopes - atoms that differ from each other in the number of neutrons and, accordingly, in atomic mass. The hydrogen isotope deuterium (D) is extracted from water. Superheavy hydrogen or tritium (T) is a radioactive isotope of hydrogen that is a by-product of decay reactions carried out in conventional nuclear reactors. Also in thermonuclear reactions, a light isotope of hydrogen, protium, is used: this is the only stable element that does not have neutrons in the nucleus. Helium-3 is contained on Earth in negligible amounts, but it is very abundant in the lunar soil (regolith): in the 80s, NASA developed a plan for hypothetical installations for processing regolith and isotope extraction. On the other hand, another isotope, boron-11, is widespread on our planet. 80% of the boron on Earth is an isotope necessary for nuclear scientists.
Second, the temperature is very high. The substance participating in a thermonuclear reaction should be an almost completely ionized plasma - it is a gas in which free electrons and ions of various charges float separately. To turn a substance into a plasma, a temperature of 10 7 -10 8 K is required - these are hundreds of millions of degrees Celsius! Such ultra-high temperatures can be obtained by creating high-power electric discharges in the plasma.
However, it is impossible to simply heat the necessary chemical elements. Any reactor will instantly vaporize at these temperatures. A completely different approach is required here. To date, it is possible to keep the plasma in a limited area with the help of heavy-duty 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. What reactions are most promising?
The main nuclear reactions that are planned to be used for controlled thermonuclear fusion will use deuterium (2H) and tritium (3H), and in the more distant future, helium-3 (3He) and boron-11 (11B).
Here are the most interesting reactions.
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% is the so-called deuterium monopropellant.
Reactions 1 and 2 are fraught with neutron radioactive contamination. Therefore, "neutronless" 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 conduct such a reaction?
The natural fusion reactor is the star. In it, the plasma is held under the influence of gravity, and the radiation is absorbed - thus, the core does not cool down.
On Earth, thermonuclear reactions can only be carried out in special facilities.
impulse systems. In such systems, deuterium and tritium are irradiated with ultra high power laser beams or electron/ion beams. Such irradiation causes a sequence of thermonuclear microexplosions. However, it is unprofitable to use such systems on an industrial scale: much more energy is spent on the acceleration of atoms than is obtained as a result of fusion, since not all accelerated atoms enter into a reaction. Therefore, many countries are building quasi-stationary systems.
Quasi-stationary systems. In such reactors, the plasma is held 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 camera in the form of a "donut" (torus), on which coils are wound. The main feature of the tokamak is the use of an alternating electric current that flows through the plasma, heats it up 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.
W 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 supremacy. Initially, the concept of a trap seemed simpler and therefore cheaper. In the early 60s, open traps were heavily funded, but the instability of the plasma and unsuccessful attempts to contain it with a magnetic field forced these installations to complicate - simple-looking designs turned into hellish machines, and it did not work out to achieve a stable result. Therefore, tokamaks came to the fore in the 1980s. In 1984, the European JET tokamak was launched, the cost of which was only 180 million dollars and the parameters of which made it possible to carry out 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 fusion reactors. There are experimental reactors in Kazakhstan, China, the USA and Japan. The Kurchatov Institute is working on the IGNITOR reactor. Germany launched the Wendelstein 7-X stellarator fusion reactor.
The most famous international project is the ITER tokamak (ITER, International Thermonuclear Experimental Reactor) at the Cadarache Research Center (France). Its construction was supposed to be completed in 2016, but the size of the necessary financial support has increased, and the timing of the experiments has shifted to 2025. The European Union, the USA, China, India, Japan, South Korea and Russia participate in the activities of ITER. The main share in financing is played by the EU (45%), the rest of the participants supply high-tech equipment. In particular, Russia produces superconducting materials and cables, radio tubes for plasma heating (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 do we still not use thermonuclear 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 keep the plasma in the reactor for a long time.
At the moment, one of the biggest 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 plasma heating up to ten million degrees Celsius. However, the Americans have recently proposed a method for confining plasma for 60 years - and this inspires optimism.
In addition, there is controversy regarding the profitability of fusion in industry. It is not known whether the benefits of electricity generation will offset the costs of fusion. It is proposed to experiment with reactions (for example, abandon the traditional deuterium-tritium or monopropellant reaction in favor of other reactions), structural materials - or even abandon the idea of industrial thermonuclear fusion, using it only for individual reactions in fission reactions. However, scientists still continue to experiment.
9. Are fusion reactors safe?
Relatively. Tritium, which is used in thermonuclear reactions, is radioactive. In addition, neurons released as a result of fusion irradiate the reactor structure. The elements of the reactor themselves are 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 the absence of "holes" through which radiation can leak. The vacuum chamber of the reactor must be sealed, otherwise the reactor simply cannot work. During the construction of thermonuclear reactors, materials tested by nuclear power are used, and reduced pressure is maintained in the rooms.
When will fusion power plants appear?
Scientists most often say something like “in 20 years we will solve all the fundamental issues”. Nuclear engineers are talking about the second half of the 21st century. Politicians talk about a sea of clean energy for a penny, without bothering with dates.
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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 the Soviet cosmonautics. In order for this flight to take place, scientists all over the country were racking their brains on how to make such a rocket that would withstand all the dangers of unexplored space - here the ideas of scientists from the Siberian Branch of the Academy of Sciences could not have done without.
Of the four main sources of nuclear energy, only two have now been brought to industrial implementation: the energy of radioactive decay is utilized in current sources, and the fission chain reaction is utilized in nuclear reactors. The third source of nuclear energy - the annihilation of elementary particles has not yet left the realm of fantasy. The fourth source controlled thermonuclear fusion, UTS, is on the agenda. Although this source is less than the third one in its potential, it significantly exceeds the second one.
Thermonuclear fusion in laboratory conditions is quite simple to implement, but so far it has not been possible to achieve the reproduction of energy. However, work in this direction is being carried out, and radiochemical methods are being developed, in the first place, technologies for producing tritium fuel for UTS installations.
This chapter considers some radiochemical aspects of thermonuclear fusion and discusses the prospects for the use of facilities for CTS in the nuclear power industry.
Controlled thermonuclear fusion- the reaction of the fusion of light atomic nuclei into heavier nuclei, occurring at superhigh temperatures and accompanied by the release of huge amounts of energy. Unlike explosive thermonuclear fusion (used in the hydrogen bomb), it is controlled. In the main nuclear reactions that are planned to be used for the implementation of controlled thermonuclear fusion, -H and 3 H will be used, and in the more distant future, 3 He and “B”.
Hopes for controlled thermonuclear fusion are associated with two circumstances: i) it is believed that stars exist due to a stationary thermonuclear reaction, and 2) an uncontrolled thermonuclear process was quite simply implemented in the explosion of a hydrogen bomb. It seems that there are no fundamental obstacles to maintaining a controlled nuclear fusion reaction. However, intensive attempts to implement CTS in laboratory conditions with energy gain ended in complete failure.
However, TCF is now seen as an important technological solution to replace fossil fuels in energy production. The worldwide need for energy requiring an increase in electricity production and the exhaustibility of non-renewable raw materials stimulate the search for new solutions.
Thermonuclear reactors use the energy released during the fusion of light atomic nuclei. Reminiscent of:
The fusion reaction of tritium and deuterium nuclei is promising for the implementation of controlled thermonuclear fusion, since its cross section is quite large even at low energies. This reaction provides a specific calorific value of 3.5-11 J/g. The main reaction D+T=n+a has the largest cross section o t ah=5 barn at resonance at deuteron energy E pSh x= 0.108 MeV, compared with the reactions D+D=n+3He a,„ a *=0.i05 barn; E max = 1.9 MeV, D+D=p+T o tah = 0.09 barn; E max = 2.0 MeV, as well as with the reaction 3He+D=p+a a m ax=0.7 barn; Eotax= 0.4 MeV. In the last reaction, 18.4 MeV is released. In reaction (3), the sum of energies n+a is equal to 17.6 MeV, the energy of the resulting neutrons? n = 14.1 MeV; and the energy of the resulting a-particles is 3.5 MeV. If in the reactions T(d,n)a and:) He(d,p)a the resonances are rather narrow, then in the reactions D(d,n)3He and D(d,p)T there are very broad resonances with large values cross sections in the region from 1 to 10 MeV and linear growth from 0.1 MeV to 1 MeV.
Comment. The problems with easily ignitable DT fuel are that tritium is not found in nature and must be obtained from lithium in the breeder blanket of a fusion reactor; tritium is radioactive (Ti/ 2 =12.6 years), the DT-reactor system contains from 10 to 10 kg of tritium; 80% of the energy in the DT reaction is released with 14-MeV neutrons, which induce artificial radioactivity in the reactor structures and produce radiation damage.
On fig. 1 shows the energy dependences of the reaction cross sections (1 - h). The graphs for the cross sections of reactions (1) and (2) are practically the same - with increasing energy, the cross section increases and at high energies the probability of the reaction tends to a constant value. The cross section for reaction (3) first increases, reaches a maximum of 10 barn at energies of the order of 90 MeV, and then decreases with increasing energy.
Rice. 1. Cross sections of some thermonuclear reactions as a function of particle energy in the center of mass system: 1 - nuclear reaction (3); 2 - reactions (1) and (2).
Due to the large scattering cross section during the bombardment of tritium nuclei by accelerated deuterons, the energy balance of the thermonuclear fusion process according to the D - T reaction can be negative, because more energy is spent on accelerating deuterons than is released during fusion. A positive energy balance is possible if the bombarding particles, after an elastic collision, are able to participate in the reaction again. To overcome the electrical repulsion, the nuclei must have a large kinetic energy. These conditions can be created in a high-temperature plasma, in which atoms or molecules are in a completely ionized state. For example, the DT - reaction begins to proceed only at temperatures above 10 8 K. Only at such temperatures is more energy released per unit volume and per unit "time than it is spent. CTS consists in solving two problems: heating the substance to the required temperatures and holding it for a time sufficient to “burn” a significant part of the thermonuclear fuel.
It is believed that controlled thermonuclear fusion can be realized if the Lawson criterion is fulfilled (lt>10‘4 s cm-z, where P - density of high-temperature plasma, t - time of its retention in the system).
When this criterion is met, the energy released during CTS exceeds the energy introduced into the system.
Plasma must be kept inside a given volume, because in free space, the plasma instantly expands. Due to the high temperatures, the plasma cannot be placed into a tank from any
material. To contain the plasma, it is necessary to use a high-strength magnetic field, which is created using superconducting magnets.
Rice. 2. Schematic diagram of a tokamak.
If you do not set the goal of obtaining an energy gain, then in laboratory conditions it is quite simple to implement the CTS. To do this, it is enough to lower an ampoule with lithium deuteride into the channel of any slow reactor operating on the uranium fission reaction (you can use lithium with a natural isotope composition (7% 6 Li), but it is better if it is enriched with a stable isotope 6 Li). Under the action of thermal neutrons, the following nuclear reaction occurs:
As a result of this reaction, there are "hot" tritium atoms. The energy of the recoil atom of tritium (~3 MeV) is sufficient for the reaction of interaction of tritium with deuterium located in LiD:
For energy purposes, this method is not suitable: the energy costs of the process exceed the energy released. Therefore, one has to look for other options for implementing the CTS, options that provide a large energy gain.
They try to implement CTS with energy gain either in quasi-stationary (t > 1 s, tg>yu see "Oh, or in impulse systems (t * io -8 s, n>u 22 cm*h). In the former (tokamak, stellarator, mirror trap, etc.), plasma is confined and thermally isolated in magnetic fields of various configurations. In pulsed systems, plasma is created by irradiating a solid target (grains of a mixture of deuterium and tritium) with focused radiation from a powerful laser or electron beams: when a beam of small solid targets hits the focus, a successive series of thermonuclear microexplosions occurs.
Among various chambers for confining plasma, a chamber with a toroidal configuration is promising. In this case, the plasma is created inside the toroidal chamber using an electrodeless ring discharge. In a tokamak, the current induced in the plasma is, as it were, the secondary winding of the transformer. The magnetic field, while holding the plasma, is created both by the current flowing through the coil around the chamber and by the current induced in the plasma. To obtain a stable plasma, an external longitudinal magnetic field is used.
A thermonuclear reactor is a device for generating energy due to fusion reactions of light atomic nuclei occurring in plasma at very high temperatures (> 0 8 K). The main requirement that a thermonuclear reactor must satisfy is that the energy release as a result of
thermonuclear reactions more than compensated for the energy costs from external sources to maintain the reaction.
Rice. h. The main components of the reactor for controlled thermonuclear fusion.
A thermonuclear reactor of the TOKAMAK type (Toroidal Chamber with Magnetic Coils) consists of a vacuum chamber forming a channel where the plasma circulates, magnets that create a field and plasma heating systems. This is accompanied by vacuum pumps that constantly pump out gases from the channel, a fuel delivery system as it burns out, and a diverter - a system through which the energy obtained as a result of a thermonuclear reaction is removed from the reactor. The toroidal plasma is in a vacuum shell. a-Particles formed in the plasma as a result of thermonuclear fusion and located in it, increase its temperature. Neutrons penetrate the wall of the vacuum chamber into the zone of a blanket containing liquid lithium, or a lithium compound enriched in 6 Li. When interacting with lithium, the kinetic energy of neutrons is converted into heat, and tritium is simultaneously generated. The blanket is placed in a special shell that protects the magnet from emitted neutrons, y-radiation, and heat fluxes.
In tokamak-type devices, plasma is created inside a toroidal chamber using an electrodeless ring discharge. For this purpose, an electric current is created in the plasma bunch, and at the same time it has its own magnetic field - the plasma bunch itself becomes a magnet. Now, using an external magnetic field of a certain configuration, it is possible to suspend a plasma cloud in the center of the chamber, preventing it from touching the walls.
Divertor - a set of devices (special poloidal magnetic coils; panels in contact with plasma - plasma neutralizers), with the help of which the area of direct contact of the wall with the plasma is maximally removed from the main hot plasma. It serves to remove heat from the plasma in the form of a stream of charged particles and to pump out the reaction products neutralized on the divertor plates: helium and protium. Purifies plasma from contaminants that interfere with the fusion reaction.
A thermonuclear reactor is characterized by a power amplification factor equal to the ratio of the thermal power of the reactor to the power of the cost of its production. The thermal power of the reactor is added up:
- - from the power released during a thermonuclear reaction in plasma;
- - from the power that is introduced into the plasma to maintain the combustion temperature of a thermonuclear reaction or a stationary current in the plasma;
- - from the power released in the blanket - a shell surrounding the plasma, in which the energy of thermonuclear neutrons is utilized and which serves to protect the magnetic coils from radiation exposure. Blanket fusion reactor - one of the main parts of a thermonuclear reactor, a special shell surrounding the plasma, in which thermonuclear reactions occur and which serves to utilize the energy of thermonuclear neutrons.
The blanket covers the plasma ring from all sides, and the main energy carriers born during D-T fusion - 14-MeV neutrons - give it to the blanket), heating it. The blanket contains heat exchangers through which water is passed. Power plant steam rotates the steam turbine, and she - the rotor of the generator.
The main task of the blanket is to harvest energy, transform it into heat and transfer it to power generating systems, as well as protect operators and the environment from ionizing radiation generated by a thermonuclear reactor. Behind the blanket in a thermonuclear reactor there is a layer of radiation protection, the functions of which are to further weaken the neutron flux and the y-quanta formed during reactions with matter to ensure the operability of the electromagnetic system. This is followed by biological protection, for which station personnel can work.
"Active" blanket - breeder, designed to produce one of the components of thermonuclear fuel. In reactors that consume tritium, the blanket includes breeder materials (lithium compounds) designed to ensure efficient production of tritium.
When operating a thermonuclear reactor on deuterium-tritium fuel, it is necessary to replenish the amount of fuel (D + T) in the reactor and remove 4He from the plasma. As a result of reactions in the plasma, tritium burns out, and the main part of the fusion energy is transferred to neutrons, for which the plasma is transparent. This leads to the need to place a special zone between the plasma and the electromagnetic system, in which the burnable tritium is reproduced and the main part of the neutron energies is absorbed. This area is called the breeder blanket. It reproduces tritium burnt in plasma.
Tritium in a blanket can be produced by irradiating lithium with neutron fluxes according to nuclear reactions: 6 Li (n, a) T + 4.8 MeV and 7 Li (n, n'a) - 2.4 MeV.
When producing tritium from lithium, it should be taken into account that natural lithium consists of two isotopes: 6 Li (7.52%) and 7 Li (92.48%). The absorption cross section of thermal neutrons with pure 6 Li 0 = 945 barn, and the activation cross section for the reaction (p, p) is 0.028 barn. In natural lithium, the cross section for the removal of neutrons produced during the fission of uranium is 1.01 barn, and the cross section for the absorption of thermal neutrons is about a = 70.4 barn.
The energy spectra of y-radiation during radiative capture of thermal neutrons 6 Li are characterized by the following values: .94 MeV. total energy
In a thermonuclear reactor operating on D-T fuel, as a result of the reaction:
y-radiation per neutron capture is equal to 1.45 MeV. For 7 Li, the absorption cross section is 0.047 barn and the activation cross section is 0.033 barn (at neutron energies above 2.8 MeV). The cross section for the extraction of fission neutrons LiH of natural composition = 1.34 barn, metallic Li - 1.57 barn, LiF - 2.43 barn.
thermonuclear neutrons are formed, which, leaving the plasma volume, fall into the blanket region containing lithium and beryllium, where the following reactions occur:
Thus, the fusion reactor will burn deuterium and lithium, and as a result of the reactions, the inert gas helium will be formed.
During the D-T reaction in plasma, tritium burns out and a neutron with an energy of 14.1 MeV is formed. In a blanket, this neutron must generate at least one tritium atom to cover its losses in the plasma. Tritium reproduction rate to("the amount of tritium formed in the blanket per one incident thermonuclear neutron") depends on the neutron spectrum in the blanket, the magnitude of neutron absorption and leakage. k> 1,05.
Rice. Fig. 4. Dependences of the cross section of nuclear reactions of tritium formation on the neutron energy: 1 - reaction 6 Li (n, t) ‘» He, 2 – reaction 7 Li (n, n’, 0 4 He.
For the 6 Li nucleus, the absorption cross section of thermal neutrons with the formation of tritium is very large (953 barn at 0.025 eV). At low energies, the neutron absorption cross section in Li follows the law (l/u) and, in the case of natural lithium, reaches 71 barn for thermal neutrons. For 7 Li, the cross section for interaction with neutrons is only 0.045 barn. Therefore, to increase the performance of the breeder, natural lithium should be enriched in the 6 Li isotope. However, an increase in the content of 6 Li in a mixture of isotopes has little effect on the breeding ratio of tritium: there is an increase by 5% with an increase in the enrichment in the isotope 6 Li to 50% in the mixture. In the reaction 6 Li(n, T)» Not all slowed down neutrons are absorbed. In addition to strong absorption in the thermal region, there is a small absorption (
The dependence of the cross section for the reaction 6 Li(n,T) 4 He on the neutron energy is shown in Fig. . 7. As is typical for many other nuclear reactions, the cross section for the 6 Li(n,f) 4 He reaction decreases as the neutron energy increases (with the exception of the resonance at 0.25 MeV).
The reaction with the formation of tritium on the ?Li isotope proceeds with fast neutrons at an energy of ?n>2.8 MeV. In this reaction
tritium is produced and there is no loss of a neutron.
A nuclear reaction for 6 Li cannot give an extended reproduction of tritium and only compensates for the burnt out tritium
The reaction to ?1l results in the appearance of one tritium nucleus for each absorbed neutron and the regeneration of this neutron, which is then absorbed during slowing down and gives one more tritium nucleus.
Comment. In natural Li, the tritium reproduction coefficient to"2. For Li, LiFBeF 2 , Li 2 0, LiF, Y^Pbz k= 2.0; 0.95; 1.1; 1.05 and i.6, respectively. Molten salt LiF (66%) + BeF 2 (34%) is called flyb ( FLiBe), its use is preferable in terms of safety and reduction of tritium losses.
Since not every neutron of the DT reaction participates in the formation of a tritium atom, it is necessary to multiply the primary neutrons (14.1 MeV) using the (n, 2n) or (n, cn) reaction, on elements that have a sufficiently large cross section during the interaction of fast neutrons , for example, on y Be, Pb, Mo, Nb and many other materials with Z> 25. For beryllium, the threshold (n, 2 P) reactions 2.5 MeV; at 14 MeV 0=0.45 barn. As a result, in versions of the blanket with liquid or ceramic lithium (LiA10 2), it is possible to achieve to* 1.1+1.2. If the reactor chamber is surrounded by a uranium blanket, neutron multiplication can be significantly increased due to fission reactions and (n, 2n), (n, zl) reactions.
Remark 1. The induced activity of lithium upon irradiation with neutrons is practically absent, since the resulting radioactive isotope 8Li (cr-radiation with an energy of 12.7 MeV and /?-radiation with an energy of ~6 MeV) has a very short half-life - 0.875 s. The low activation of lithium and the short half-life facilitate the biological protection of the plant.
Remark 2. The activity of tritium contained in the blanket of a thermonuclear DT-reactor is ~*10 6 Ci; therefore, the use of DT-fuel does not exclude the theoretical possibility of an accident on a scale of several percent of the Chernobyl one (the release was 510 7 Ci). The release of tritium with the formation of T 2 0 can lead to radioactive fallout, the ingress of tritium into groundwater, water bodies, living organisms, plants with accumulation, ultimately, in food.
The choice of material and aggregate state of the breeder is a serious problem. The material of the breeder should provide a high percentage of conversion of lithium into tritium and easy extraction of the latter for subsequent transfer to the fuel preparation system.
The main functions of the breeder blanket include: formation of a plasma chamber; tritium production with coefficient k>i; conversion of the kinetic energy of the neutron into heat; utilization of heat generated in the blanket during the operation of a thermonuclear reactor; radiation protection of the electromagnetic system; biological radiation protection.
A thermonuclear reactor on D-T-fuel, depending on the material of the blanket, can be "clean" or hybrid. The blanket of a "clean" thermonuclear reactor contains Li, in which, under the action of neutrons, tritium is obtained and the thermonuclear reaction is enhanced from 17.6 MeV to 22.4
MeV. In the blanket of a hybrid ("active") thermonuclear reactor, not only is tritium produced, but there are also zones in which waste 2 s 8 is placed to obtain 2 39Pu. In this case, an energy equal to 140 MeV per neutron is released in the blanket. The energy efficiency of a hybrid fusion reactor is six times higher than that of a clean one. At the same time, better absorption of thermonuclear neutrons is achieved, which increases the safety of the facility. However, the presence of fissile radioactive substances creates a radiation environment similar to that in nuclear fission reactors.
Rice. five.
There are two pure breeder blanket concepts, based on the use of liquid tritium-fertile materials, or on the use of solid lithium-containing materials. Blanket design options are associated with the type of coolants chosen (liquid metal, liquid salt, gas, organic, water) and the class of possible structural materials.
In the liquid version of the blanket, lithium is the coolant, and tritium is the fertile material. The blanket section consists of the first wall, a breeder zone (molten lithium salt, a reflector (steel or tungsten) and a light shielding component (for example, titanium hydride). The main feature of a self-cooled lithium blanket is the absence of an additional neutron moderator and neutron breeder. use the following salts: Li 2 BeF 4 ( T pl = 459°), LiBeF 3 (T wx .=380°), FLiNaBe (7^=305-320°). Among the given salts, Li 2 BeF 4 has the lowest viscosity, but the highest Twl. Perspective is the Pb-Li eutectic and the FLiNaBe melt, which also acts as a self-cooler. The neutron breeders in such a breeder are spherical Be granules 2 mm in diameter.
In a blanket with a solid breeder, lithium-containing ceramics are used as the breeder material, and beryllium serves as a neutron breeder. The composition of such a blanket includes such elements as the first wall with coolant collectors; neutron breeding zone; tritium breeding zone; channels for cooling the breeding and reproduction zones of tritium; iron protection; blanket fastening elements; lines for inlet and outlet of coolant and tritium carrier gas. Structural materials - vanadium alloys and steel of ferritic or ferritic-martensitic class. Radiation protection is made of steel sheets. The coolant used is gaseous helium under UMPa pressure with an inlet temperature of 300 0 , and an outlet temperature of the coolant of 650 0 .
The radiochemical task is to isolate, purify and return tritium to the fuel cycle. At the same time, the choice of functional materials for regeneration systems of fuel components (breeder materials) is important. The material of the breeder (breeder) must ensure the removal of thermonuclear fusion energy, the generation of tritium and its efficient extraction for subsequent purification and transformation into reactor fuel. For this purpose, a material with high temperature, radiation and mechanical resistance is required. Equally important are the diffusion characteristics of the material, which ensure high tritium mobility and, as a consequence, good efficiency of tritium extraction from the breeder material at relatively low temperatures.
The working substances of the blanket can be: ceramics Li 4 Si0 4 (or Li 2 Ti0 3) - a reproducing material and beryllium - a neutron breeder. Both breeder and beryllium are used in the form of a layer of monodisperse pebbles (granules with a shape close to spherical). The diameters of Li 4 Si0 4 and Li 2 Ti0 3 granules vary in the ranges of 0.2–10.6 mm and 0.8 mm, respectively, while beryllium granules have a diameter of 1 mm. The share of the effective volume of the layer of granules is 63%. To breed tritium, the ceramic breeder is enriched with the 6 Li isotope. Typical enrichment level for 6 Li: 40% for Li 4 Si0 4 and 70% for Li 2 Ti0 3 .
At present, lithium metatitanate 1l 2 TiO 3 is considered the most promising because of the relatively high rate of tritium release at relatively low temperatures (from 200 to 400 0), radiation and chemical resistance. It was demonstrated that lithium titanate granules enriched up to 96% 6 Li under conditions of intense neutron irradiation and thermal effects make it possible to generate lithium at a practically constant rate for two years. The extraction of tritium from neutron-irradiated ceramics is carried out by programmed heating of the breeder material in the continuous pumping mode.
It is assumed that in the nuclear industry, thermonuclear fusion facilities can be used in three areas:
- - hybrid reactors, in which the blanket contains fissile nuclides (uranium, plutonium), the fission of which is controlled by a powerful flux of high-energy (14 MeV) neutrons;
- - combustion initiators in electronuclear subcritical reactors;
- - transmutation of long-lived environmentally hazardous radionuclides in order to neutralize radioactive waste.
The high energy of thermonuclear neutrons provides great opportunities for separating the energy groups of neutrons for burning a specific radionuclide in the resonant region of the cross sections.