1. Nuclear power - This is the field of science and industrial technology, in which methods and means of transformation of nuclear energy into thermal and electrical are being developed and used in practice. The foundations of nuclear power make up nuclear power plants (NPP). The source of energy at nuclear power plants are served by nuclear reactors, in which a controlled chain reaction of dividing the cores of heavy elements is located, mainly U-235 and RU-239.
Nuclear reactors are of two types: reactors on slow neutrons and reactors on fast neutrons. Most NPPs in the world are based on reactors on slow neutrons. The first reactors built in the United States (1942), in the USSR (1946) and in other developed countries, were intended for the operation of weapons plutonium RU-239. The heat released in them was a by-product. This heat was removed from the reactor using the cooling system and simply reset into the environment.
The mechanism of heat isolation in the reactor is as follows. The two fragments that arise when dividing the core of uranium, carry out huge kinetic energy about 200 MeV. Their initial speed reaches 5000 km / s. Moving among uranium, a moderator or structural elements, these fragments, facing atoms, transmit their energy to them and gradually slow down to heat velocities. The active zone of the reactor is heated. By increasing the intensity of the nuclear reaction, you can reach large thermal capacities.
The heat released in the reactor is carried out using a liquid or gaseous coolant. In general, the coolant reactor resembles a pair-tube boiler (water flows through the pipes inside the furnace and heats up). Therefore, along with the concept of "nuclear reactor", the "nuclear boiler" synonym is often used.
In fig. 144 shows the NPP scheme, in the reactor 1. The density of the neutron flux inside the operating reactor reaches 10 14 particles after 1 cm 2 per second.
The thermal and electrical power of the reactor is distinguished. Electrical power is no more than 30% of thermal. The first NPP in the world was built in 1954 in the USSR in Obninsk. Its thermal capacity is 30 MW, electric 5 MW. The active zone of uranium-graphite reactor on slow neutrons has the form of a cylinder with a diameter of 1.5 m and a height of 1.7 m. Coolant-suppl. The temperature of water at the entrance to the reactor + 190 ° C, at the output of + 280 ° C, pressure of 100 atm.
The reactor load is 550 kg of uranium enriched to 5%. Duration of work on the rated power of 100 days. The design depth of the U-235 burnout is 15%. The reactor contains 128 fuel elements (fuelists). The Obninsk NPP was built in order to work out technological solutions for nuclear power. In later serial NPP, the loading and power of the reactors increase hundreds of times.
2. Nuclear reactor on slow neutrons. As mentioned in §21, the main task in the development of nuclear reactors was to ensure that the reactor could work on natural uranium, i.e. produced by chemical method from ore and containing a natural mixture of isotopes: U-238 (99.282%), U-235 (0.712%), U-234 (0.006%), or at a relatively low low-income uranium, in which the content of U-235 isotope or Ru-239 increased to 2-5%.
For this, it is necessary to perform three conditions: first, the mass of the fissile substance in the reactor (U-235 or RU-239) must be at its configuration that is not less critical. This means that, on average, one neutron from among the nuclear division obtained in each act could cause the next division act. Secondly, neutrons need to be slowed down to heat velocities, and to do so to minimize their losses on the radiation seizure of the nucleus of non-declarative materials. Thirdly, develop principles and create chain nuclear reaction controls. Although all these conditions are interconnected, for each of them you can allocate the main ways to implement them.
but. The achievement of the critical mass of the dividing substance is possible in two ways: a simple increase in uranium mass and uranium enrichment. Due to the low concentration of the dividing substance, its critical mass in the reactor is much more than in an atomic bomb. For example, in the Obnin NPP / M KR, the U-235 is about 25 kg. In more modern powerful Ma reactors, Ma reaches several tons. To reduce the losses for neutron leakage from the reactor, its active zone is surrounded by neutron reflector. This is a substance with light nuclei, weakly absorbing neutrons (graphite, beryllium).
b. Slow Neutron. In fig.145, the energy spectrum of neutrons emitted by the U-235 cores is shared. In the abscissa axis, the kinetic energy of neutrons is postponed, along the ordinate axis, the relative frequency Δn / n is repetition of such energy in conventional units. The curve has a maximum at e \u003d 0.645 MeV. It can be seen from the figure that when dividing the U-235 nuclei is predominantly fast neutrons with Energy E\u003e 1 MeV.
As mentioned earlier, the effective cross section of the neutron capture of the 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
So that this absorption does not happen, neutrons should be derived from the mass of uranium, slow down in a weakly absorbing neutron moderator (graphite, heavy water, beryllium) and return to the mass of uranium (diffundated) This is achieved by the fact that uranium is loaded into thin pipes of fuel elements (fuelles) . And Twists plunge V.Kanala Speeder.
Typically, the two-wing tubes with a diameter of 15-20 mm from a zirconium alloy. The core fuel is laid in the form of tablets compressed from uranium oxide U0 2. The oxide does not squeeze at high temperature and is easily removed when the fuel is recharged. Depending on the size of the active zone of the reactor, the length of the fuelists can reach 7-8 m. Mounted two pieces in containers, which are pipes with a diameter of 10-20 cm or prism. When recharging the reactors, these containers are replaced, and their disassembly and replacement of fuelists are produced at the factory.
The reactor itself represents most often a cylinder, through the top base of which vertical channels are done in checkers. In these channels there are containers with fuelheels and control rods of the absorber.
in. Chain Nuclear Reaction Management It is carried out using rods from materials that absorb neutrons - cadmium 48 113 Cd and boron 5 10 V. The latter is often in the form of carbide in 4 C (melting point in cadmium 321 ° C, at boron 2075 ° C). Their absorption cross sections, respectively, σ \u003d 20,000 and 4000 barn. The parameters of the absorbing rods are calculated so that with fully inserted rods, the nuclear reaction in the reactor is not known. With gradual removal of the rods, the coefficient of reproduction to the active zone increases and at a certain position of the rod comes to one. At this point, the reactor starts working. In the process of operation, the coefficient k gradually decreases due to the contamination of the reactor by fragments of division. This reduction is compensated by nodes. In case of sudden growth in the intensity of the reaction, there are additional rods. Their fast reset to the active zone immediately stops the reaction.
The reactor control is facilitated by the presence of delayed neutrons. Their proportion in different isotopes ranges from 0.6 to 0.8%, in U-235 approximately 0.64%. The average half-life of the fragments of the division boring the delayed neutrons, T \u003d 9 s, the average lifetime of one generation of delayed neutrons τ \u003d t / ln2 \u003d 13 s.
With the stationary operation of the reactor, the coefficient of reproduction of rapid neutrons K b \u003d 1. The total coefficient K \u003d to b + K is different from the unit to the proportion of delay neutrons and can reach K \u003d 1 + 0.006. In the second generation, after 13 seconds, the number of neutrons n \u003d n 0 k 2 \u003d n 0 (1.006) 2 \u003d 1.012mn 0. In the tenth generation after 130s their number will be N 0 k 10 \u003d 1.062mn 0, which is far from the emergency. Therefore, the automatic control system based on controlling the neutron flux density in the active zone quite has time to track the slightest nuances in the operation of the reactor and respond to the movement of regulating rods.
3. Reactor poisoning - This is the accumulation of radioactive products in it. The accumulation of stable products is called the reactor slapping. In both cases, the kernels are accumulated, intensively absorbing neutrons. The seizure cross section at the most powerful xenon-135 statement reaches 2.6 * 10 6 barn.
He-135 formation mechanism Next. When dividing U-235 or RU-239 slow neutrons with a probability of 6%, a fragment is obtained - the kernel of Telllur 52 135 TE. With a period of 0.5 min TE-135, the β - -enspad is experiencing, turning into the iodine Iodine isotope core. This isotope is also β - active with a period of 6.7 hours. The product of the decay I-135 is the xenon isotope 54 135 x. With a period t \u003d 9.2 h x-135, β is experiencing β - decay, turning into a practically stable cesium isotope 55 135 cz. (/ T \u003d 3 * 10 6 years).
As a result of other decay schemes, other harmful kernels are formed, for example, SAMARIA 62 139 SM. Especially quickly poisoning goes to the initial period of operation of the reactor. Over time, a radioactive equilibrium is established between the decay products. From this point on, the growth of the reactor shares begins.
The reactor in which the fideling substance (uranium), the retarder (graphite) and the absorber (cadmium) are individual phases and have the boundaries of the partition, is called heterogeneous. All these elements in a liquid or gaseous state are one common phase, the reactor is called homogeneous. For energy chains, exclusively heterogeneous reactors are built.
5. Fast neutron reactors. The kernel U-235, RU-239 and U-233 are divided into all neutrons. Therefore, if you increase uranium enrichment, for example, the U-235 isotope, then, due to an increase in the concentration of the dividing nuclei, the entire majority of neutrons will divide the U-235 kernel without leaving the mass of uranium. At some concentration of the dividing nuclei and with a sufficient mass of uranium in the active zone, the coefficient of neutron reproduction reaches a unit and without a slowdown. The reactor will work on rapid neutrons (abbreviated - fast reaction).
The advantage of a quick reaction before slow (that is, before the reaction to slow neutrons) is that neutrons are more efficiently used. As a result, the reproduction of nuclear fuel is increasing. In the slow reaction of 2.5 neutrons, also 1 goes to the U-235 kernel, maintaining the reaction, approximately 1 in the U-238 kernel, forming the RU-239 (nuclear fuel), and 0.5 neutron is lost. PA One core of the "burnt" U-235 is obtained about 1 nucleus RU-239. In a fast reaction of 2.5 neutrons, also 1 is on maintaining the reaction. But neutrons are lost less than 0.5. Therefore, the Y-238 nucleus falls more neutrons. As a result, the "burnt" core of the "burnt" U-235 is formed more than 1 Ru-239. There is an extended reproduction of nuclear fuel. The creation and operation of reactors on fast neutrons is more complicated than on slow. First, the volume of the active zone sharply decreases. This increases the density of the energy release, which leads to an increase in temperature and tightens the requirements for structural materials and the coolant. Secondly, the requirements for the reactor control system increase, that is, to the speed of operations by the control system.
6. Prospects for nuclear power.To date, normally working NPPs are environmentally friendly of all energy sources. They do not emit C0 2 and S0 2, like thermal stations, and therefore do not exacerbate the greenhouse effect and no arable lands are poured with water as hydropower plants. Given the possibility of recycling U-238 in the RU-239 and TH-232 in U-233, the reserves of easily affordable nuclear fuel will have enough for hundreds of years. The use of nuclear power plants will preserve oil, gas and coal for the chemical industry. Difficulties with the expansion of the NPP Park Two. One objective, the essence of it is that the problems associated with the disposal and disposal of the waste of nuclear fuel and elements of the design, which have developed a resource of reactors are not fully resolved.
The second difficulty is subjective. Compared to thermal and hydraulic stations, the maintenance of the NPP requires a higher technical culture and imposes a huge responsibility on humans. The slightest retreat from technological discipline can turn into a tragedy for thousands of people.
7. Thermonuclear synthesis. From the curve of the distribution of specific communication, it follows that the merger of the lung nuclei into one core, as well as the division of heavy nuclei, must be accompanied by the allocation of a huge amount of energy. All nuclei bear the same positive charge. To bring them closer to the distance on which synthesis begins, the two interacting kernels should be dispersed towards each other. This can be done in two ways. First, with the help of accelerators. This path is cumbersome and inffective. Secondly, just heating the gas to the required temperature. Therefore, the fusion of light nuclei, initiated by heat heating, is called thermonuclear reactions. We estimate the temperature of the deuterium gas at which the thermonuclear synthesis of deuterium + deuterium begins. 1 2 H + 1 2 N → 2 3 not + 0 1 n + 3.27 MeV.
To merge nuclei, they need to bring them closer to the distance R \u003d 2 * 10 -15 m. Potential energy with such a convergence should be equal to the kinetic energy of both nuclei in the system
center of mass. (1 / 4πε 0) * (E 2 / R) \u003d 2 * (Mυ 2/2) \u003d 2 * (3/2) * CT. Gas temperature T \u003d (1 / 3K) * (1 / 4πε 0) * (E 2 / R) \u003d 3 * 10 9 K. Distribution of particles by energies close to Maxwelovsky. Therefore, there are always more "hot" particles, as well as thanks to the tunnel effect, the synthesis reaction begins at smaller temperatures T ≈ 10 7 K.
In addition to the reaction, two more are more interesting: 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 N → 2 4 not + 0 1 N +17.59 MeV. (22.4)
In the last reaction, the mass of the mass is released approximately 5 times more energy than when dividing U-235. This energy is the kinetic energy of neutron movement and the generated helium nuclei. In earthly conditions, it was possible to realize the reaction of nuclear synthesis in the form of an unmanaged explosion of the thermonuclear hydrogen bomb.
8. Hydrogen bomb It is a conventional atomic bomb whose nuclear charge (U-235 or Ri-239) is surrounded by a blanket from a substance containing light atoms. For example, deuteride lithium lid. The high temperature resulting when undermining atomic charge initiates thermonuclear synthesis of light atoms. Due to this, additional energy is distinguished, increasing the capacity of the bomb. In addition to reactions (22.1) and (22.3), another one can go in a bomb with a blanket of lithium. 3 6 Li + 1 1 P → 2 4 NE + 2 3 NOT + 4MEV. (22.5). (22.4). But tritium - β - - an active element. With a period of 12 years, it turns into non-3. Therefore, hydrogen charges with tritium have a limited shelf life and should be regularly tested. From the substances involved in thermonuclear synthesis, radioactive products are not formed. But due to the intense neutron flow, radioactivity is guided in the kernels of structural materials and the surrounding bodies. Therefore, it is impossible to implement a "clean" reaction of the synthesis without radioactive waste.
9. The problem of controlled thermonuclear synthesis (UH) Not solved so far. Its solution is very promising for energy. In the water of the seas and oceans, it contains approximately 0.015% of the deuterium (by the number of atoms). Water on earth about 10 20 kg. 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 stone coal, this is a gigantic value (about 0.001 mass of the Earth), therefore, the deuterium of the seas and oceans is a practically an inexhaustible source of energy.
The TCB problem comes down to two tasks, firstly, it is necessary to learn how to create a high temperature of T\u003e 10 7 K. Secondly, to hold the volume to this plasma temperature over time sufficient to flow the reaction of the core synthesis. Both of these tasks are far from solving.
10. Thermonuclear reactions in the stars.According to modern ideas, the star is born from extended gas-pepped clouds consisting mainly of hydrogen. As a result of gravitational compression, the cloud is compacted and begins to refuse, turning into the protozozer. When the temperature in the center of the protozer reaches 10 7 K, the thermalide reactions of the synthesis of light elements are excited in it, mainly hydrogen gravitational compression is suspended with increased gas-systemic and optical pressure. The protocol turns into a star. Two cycles of the conversion of hydrogen in helium are possible. Below are the main reactions that constitute each cycle. In brackets next to the reaction equations, the average reaction time τ, calculated by the effective cross section of the reaction for those pressures and temperatures that are inside the star are indicated.
According to modern astrophysical ideas, the main source of energy of the Sun and other stars is the thermalide synthesis in their depths. On earthly conditions, it is carried out in the explosion of a hydrogen bomb. Thermonuclear synthesis is accompanied by colossal energy release per unit mass of reactant substances (about 10 million times large than in chemical reactions). Therefore, it is of great interest to master this process and based on it to create a cheap and environmentally friendly source of energy. However, despite the fact that the studies of the controlled thermonuclear synthesis (TCC) are engaged in large scientific and technical groups in many developed countries, there are still many complex problems before the industrial production of thermonuclear energy will become a reality.
Modern nuclear power plants using the division process only partly satisfy the global electricity needs. The fuel for them is the natural radioactive elements of uranium and thorium, the prevalence and reserves of which are very limited in nature; Therefore, for many countries, the problem of their imports arise. The main component of thermonuclear fuel is a deuterium hydrogen isotope, which is contained in sea water. Its reserves are publicly available and very high (the world ocean covers ~ 71% of the surface area of \u200b\u200bthe Earth, and the share of deuterium accounts for approx. 0.016% of the total number of hydrogen atoms included in the water). In addition to the availability of fuel, thermonuclear energy sources have the following important advantages over nuclear power plants: 1) The TCT reactor contains much less radioactive materials than the division atomic reactor, and therefore the consequences of random emission of radioactive products are less dangerous; 2) with thermonuclear reactions, fewer long-lived radioactive waste is formed; 3) TTS allows direct electricity to obtain.
Physical foundations of nuclear synthesis
The successful implementation of the synthesis reaction depends on the properties of the atomic nuclei used and the possibility of obtaining a dense high-temperature plasma, which is necessary for initiating the reaction.
Nuclear forces and reactions.
The energy release in nuclear synthesis is due to the extremely intense attraction forces acting inside the nucleus; These forces hold together the protons and neutrons included in the core. They are very intense at distances ~ 10 -13 cm and extremely quickly weaken with increasing distance. In addition to these forces, positively charged protons create electrostatic repulsion forces. The radius of the electrostatic forces is much larger than that of nuclear, so they begin to prevail when the core is removed from each other.
As shown by G. Gama, the probability of the reaction between two convergent light nuclei is proportional, where e. – the basis of natural logarithms, Z. 1 and Z. 2 - the number of protons in the interacting nuclei, W. - the energy of their relative rapprochement, and K. - Permanent multiplier. The energy required to carry out the reaction depends on the number of protons in each nucleus. If it is more than three, this energy is too large and the reaction is practically impracticable. Thus, with increasing Z. 1 I. Z. 2 The probability of the reaction decreases.
The likelihood that two nuclei will enter into interaction, characterized by the "reaction cross section", measured in Barns (1 B \u003d 10 -24 cm 2). The reaction cross section is the area of \u200b\u200ban effective cross section of the nucleus, in which the other kernel should "get" so that their interaction occurred. The deuterium reaction section with tritium reaches the maximum value (~ 5 b), when the interacting particles have the energy of the relative convergence of about 200 keV. At the energy of 20 keV, the cross section becomes less than 0.1 b.
Of the millions of accelerated particles entering the target, no more than one enters the nuclear interaction. The rest scatter their energy on electrons of the target atoms and slow down to speeds, in which the reaction becomes impossible. Consequently, the method of bombing of a solid target by accelerated nuclei (as it was in the Crookft - Walton experiment) for the TCB, since the energy obtained is much less spent.
Thermonuclear fuel.
Reactions with participation p.Playing a major role in the processes of nuclear synthesis in the sun and other homogeneous stars, on earthly conditions are not practical interest, since they have too small. To implement thermonuclear synthesis on Earth, a more suitable fuel type, as mentioned above, is deuterium.
But the most likely reaction is implemented in an equilicular mixture of deuterium and tritium (DT-mixture). Unfortunately, tritium radioactive and, due to the short period of half a life (T 1/2 ~ 12.3 years), is practically not found in nature. It is obtained artificially in fission reactors, as well as as a by-product in respondents with deuterium. However, the absence of tritium in nature is not an obstacle to the use of DT - the synthesis reaction, because Trithium can be produced, irradiating isotope 6 Li formed by neutron synthesis: n. + 6 Li ® 4 He + t..
If you surround the thermonuclear chamber with a layer of 6 Li (in natural lithium it contains 7%), then you can fully reproduce the tritium spent. And although in practice, some neutrons are inevitably lost, their loss is easy to fill, entering such an element into the shell, like beryllium, the kernel of which, if one rapid neutron appears, eats two.
The principle of the action of the thermonuclear reactor.
The merge response of the lung nuclei, the purpose of which is to obtain useful energy - is called controlled thermonuclear synthesis. It is carried out at temperatures of the order of hundreds of millions of Kelvinov. Such a process is implemented so far only in laboratories.
Tempered and temperature conditions.
Obtaining useful thermonuclear energy is possible only when performing two conditions. First, the mixture intended for synthesis should be heated to a temperature at which the kinetic energy of the nuclei provides a high probability of their confluence during collision. Secondly, the reactive mixture should be very well thermally insulated (i.e., high temperature should be maintained sufficiently long, so that the required number of reactions occurred and the energy elected due to this energy exceeded the energy spent on the heating of the fuel).
In quantitative form, this condition is expressed as follows. To heat the thermonuclear mixture, one cubic centimeter of its volume must be informant P. 1 = knt.where k. - numerical coefficient n. - the mixture density (number of cores in 1 cm 3), T. - Required temperature. To maintain the reaction, the informed thermonuclear power mixture should be maintained over time t. In order for the reactor to be energetically beneficial, it is necessary that during this time thermonuclear energy has been released in it more than it was spent on heating. The separated energy (also 1 cm 3) is expressed as follows:
where f.(T.) - coefficient depending on the temperature of the mixture and its composition, R. - Energy released in one elementary act of synthesis. Then the condition of energy profitability P. 2 > P. 1 will appear
The last inequality, known as the criterion of Louuson, is a quantitative expression of the requirements for the perfection of thermal insulation. The right side is "the number of Louuson" - depends on the temperature and composition of the mixture, and the more stronger the thermal insulation requirements, i.e. the harder it is to create a reactor. In the area of \u200b\u200bacceptable temperatures, the number of Louuson for pure deuterium is 10 16 C / cm 3, and for an equil-component DT mixture - 2h10 14 C / cm 3. Thus, the DT mixture is a more preferred thermonuclear fuel.
In accordance with the criterion of Louuson, which determines the energy density of the density at the time of deduction, in the thermonuclear reactor should be used as large n. or t. . Therefore, the Research of the TCC was partitioned by two different areas: in the first researchers they tried to hold relatively rarefied plasma using a magnetic field for quite a long time; In the second - with the help of lasers for a short time, create a plasma with a very high density. The first approach was devoted much more work than the second.
Magnetic retention of plasma.
During the synthesis reaction, the density of the hot reagent should remain at a level that would ensure a sufficiently high yield of useful energy per unit volume at a pressure that is able to withstand the camera with plasma. For example, for a mixture of deuterium - triytium at a temperature of 10 8 to the output is determined by the expression
If taken P. equal to 100 W / cm 3 (which roughly corresponds to the energy secreted by fuel cells in the nuclear fission reactors), then the density n. must be approx. 10 15 nuclei / cm 3, and corresponding pressure nt. - Approximately 3 MPa. The time of hold, according to the criterion of Louuson, should be at least 0.1 s. For deuterium deuterium plasma at a temperature of 10 9 to
In this case, when P. \u003d 100 W / cm 3, n. »3h10 15 nuclei / cm 3 and a pressure of about 100 MPa required retention time will be more than 1 s. Note that these densities constitute only 0.0001 from the density of atmospheric air, so that the reactor chamber must pump up to a high vacuum.
The above estimates of the deduction time, temperature and density are typical minimum parameters necessary for the operation of the thermonuclear reactor, and they are easier to achieve in the case of a deuterium-tritium mixture. As for thermonuclear reactions occurring during the explosion of the hydrogen bomb and in the depths of stars, it should be borne in mind that by virtue of completely different conditions in the first case, they proceed very quickly, and in the second - extremely slow compared to the processes in the thermonuclear reactor.
Plasma.
With a strong heating of the gas, its atoms are partially or completely losing electrons, as a result of which positively charged particles are formed, called ions, and free electrons. At temperatures of more than a million degrees, the gas consisting of light elements is completely ionized, i.e. Each atom loses all its electrons. The gas in the ionized state is called plasma (the term is introduced by I.NongMyur). Plasma properties differ significantly from the properties of neutral gas. Since there are free electrons in the plasma, the plasma performs electric current very well, and its conductivity is proportional to T. 3/2. The plasma can be heated, passing an electric current through it. The conductivity of the hydrogen plasma at 10 8 to the same as in copper at room temperature. Very large and thermal conductivity of the plasma.
To keep the plasma, for example, at a temperature of 10 8 K, it needs to be securely insulated. In principle, it is possible to isolate a plasma from the camera walls by placing it into a strong magnetic field. This is provided by the forces that occur when the interaction of currents with a magnetic field in plasma.
Under the action of the magnetic field, ions and electrons move along the spirals along its power lines. The transition from one power line to another is possible in particle collisions and when the transverse electric field is applied. In the absence of electric fields, high-temperature sparse plasma, in which collisions rarely occur, will only slowly diffuse across magnetic power lines. If the power lines of the magnetic field closure, giving them the shape of the loop, then the plasma particles will move along these lines while holding in the loop area. In addition to such a closed magnetic configuration, open systems were also proposed for the retention of the plasma (with the power lines of the field coming from the ends of the camera to the outside), in which the particles remain inside the chamber due to the velocity of the particles of magnetic "traffic jams". Magnetic plugs are created in the ends of the camera, where, as a result of a gradual increase in the field strength, a tapering beam of power lines is formed.
In practice, the magnetic retention of the plasma is quite large density turned out to be far from simple: it often arises magnetohydrodynamic and kinetic instability.
Magnitohydrodynamic instability are associated with bends and flexibility of magnetic power lines. In this case, the plasma can begin to move across the magnetic field in the form of clots, for several million dollars will leave the retention zone and will give heat to the walls of the chamber. Such instability can be suppressed by giving a certain configuration to a magnetic field.
Kinetic instability is very diverse and they have learned less detail. Among them, there are those that break up ordered processes, such as flowing through the plasma of a constant electric current or a particle stream. Other kinetic instability causes a higher transverse diffusion rate of plasma in a magnetic field than predicted collision theory for relaxable plasma.
Systems with a closed magnetic configuration.
If a strong electric field is applied to the ionized gas-conductive gas, then there will be a discharge current, simultaneously with which the magnetic field surrounds will appear. The interaction of the magnetic field with a current will lead to the appearance of compressive forces acting on charged particles. If the current flows along the axis of the conductive plasma cord, then the emerging radial forces is like rubber harness squeezed the cord, pushing the plasma boundary from the walls containing its camera. This phenomenon that is theoretically predicted by U. Bennett in 1934 and for the first time experimentally demonstrated by A.Weer in 1951, called a pinch effect. Pinch method is used to hold plasma; Its remarkable feature is that the gas is heated to high temperatures by the electric current (ohmic heating). The principal simplicity of the method led to its use in the first attempts to hold hot plasma, and the study of a simple pinch effect, despite the fact that it was subsequently supplanted by more than perfect methods, it was better to understand the problems with which experimenters are faced today.
In addition to the diffusion of plasma in the radial direction, there is still a longitudinal drift and its output through the ends of the plasma cord. Losses through the ends can be eliminated if you give a plasma chamber for a bagel (torus). In this case, it turns out a toroidal pinch.
For the simple pinch described above, the magnetohydrodynamic instability inherent in it is a serious problem. If a low bend occurs at the plasma cord, then the density of the power lines of the magnetic field from the inside of the bend increases (Fig. 1). Magnetic power lines that behave like a squeezing compression of harness will begin to "release" quickly, so that the bend will increase up to the destruction of the entire structure of the plasma cord. As a result of the plasma, come into contact with the walls of the camera and cooled. To exclude this destructive phenomenon, until the main axial current is transmitted in the chamber, a longitudinal magnetic field is created, which, together with the generated bending of the plasma cord (Fig. 2), create a longitudinal magnetic field. The principle of stabilization of the plasma cord by an axial field is based on two promising projects of thermonuclear reactors - tokamak and pinch with a converted magnetic field.
Open magnetic configurations.
Inertial retention.
Theoretical calculations show that thermonuclear synthesis is possible and without the use of magnetic traps. To do this, the rapid compression of a specially cooked target is carried out (the ball from the deuterium by the radius is approx. 1 mm) to such high densities that the thermonuclear reaction has time to complete before evaporation of the fuel target occurs. Compression and heating to thermonuclear temperatures can be produced with heavy duty laser pulses, from all sides evenly and at the same time irradiating the fuel ball (Fig. 4). With instant evaporation of its surface layers, carved particles acquire very high speeds, and the ball is under the action of large compressive forces. They are similar to the moving rocket with reactive forces, with the only difference that these forces are directed inside, to the center of the target. This method can create pressure of about 10 11 MPa and density, 10,000 times higher than the density of water. With such a density, almost all thermonuclear energy will be released as a small explosion in the time of ~ 10 -12 p. Toring microvalets, each of which is equivalent to 1-2 kg of trotyl, will not cause damage to the reactor, and the sequence of such microcruises through short periods of time would allow to implement the almost continuous production of useful energy. For inertial retention, the fuel target device is very important. The target in the form of concentric spheres from severe and lightweight materials will make it possible to achieve the most effective evaporation of particles and, therefore, the greatest compression.
Calculations show that at the energy of laser radiation about Meghadzhoule (10 6 J) and the laser efficiency of at least 10%, the produced thermonuclear energy should exceed the energy consumed for pumping the laser. Thermonuclear laser installations are available in Russian research laboratories, USA, Western Europe and Japan. Currently, the possibility of use instead of a laser beam of heavy ions or combinations of such a beam with a light beam is studied. Thanks to modern technology, this method of initiation of the reaction has an advantage over laser, since it allows you to get more useful energy. The disadvantage is the difficulty of focusing the beam on the target.
Magnetic Hold Installations
Magnetic plasma retention methods are investigated in Russia, USA, Japan and a number of European countries. The main attention is paid to the settings of toroidal type, such as Tokamak and Pinch with a converted magnetic field, which appeared as a result of the development of simpler pinches with a stabilizing longitudinal magnetic field.
For retention of plasma with a toroidal magnetic field B J. It is necessary to create conditions under which the plasma would not shift to the walls of the torus. This is achieved by the "twist" of the power lines of the magnetic field (so-called "rotational transformation"). Such twisting is carried out in two ways. In the first method, the current is passed through the plasma, leading to the configuration of the already considered sustainable pinch. Tok magnetic field B. Q ј - B. q together S. B. j Creates a summary field with the required twisting. If a B. J. B. q, then a configuration is known as the Tokamak (abbreviation of the expression "toroidal chamber with magnetic coils"). Tokamak (Fig. 5) was designed under the direction of L.A.Arzimovich at the Institute of Atomic Energy. I.V. Kurchatova in Moscow. For B. J. ~ B. q It turns out a pinch configuration with a converted magnetic field.
In the second way, special screw windings around the toroidal plasma chamber are used to ensure equilibrium plasma. Currents in these windings create a complex magnetic field, leading to twisting the power lines of the total field inside the thorah. This installation, called the stellarator, was developed at Princeton University (USA) L. Westzer with employees.
Tokamak.
An important parameter on which the holding of a toroidal plasma depends is "sustainability margin" q.equal rB. J / RB. q, where r. and R. - respectively small and large radii of toroidal plasma. At small q. A screw instability can develop - an analogue of the bending of direct pinch. Scientists in Moscow experimentally showed that q. \u003e 1 (i.e. B. J. B. q) The possibility of screw instability is greatly reduced. This makes it possible to effectively use the heat released heat to heat the plasma. As a result of perennial studies, the characteristics of the tokamaks have improved significantly, in particular by increasing the homogeneity of the field and the effective cleaning of the vacuum chamber.
The encouraging results obtained in Russia stimulated the creation of tokamaks in many laboratories of the world, and their configuration became the subject of intensive research.
Ohmic plasma heating in the tokamak is insufficient for the implementation of the reaction of thermonuclear synthesis. This is due to the fact that when the plasma is heated, its electrical resistance is highly reduced, and the resulting heat release during current is sharply reduced. Increase the current in the tokamak above some limit it is impossible, since the plasma cord may lose stability and transfer to the walls of the chamber. Therefore, various additional methods use for plasma heating. The most effective of them is the injection of the beams of neutral atoms with high energy and microwave irradiation. In the first case, the ions accelerated to energies 50-200 are neutralized (in order to avoid "reflections" of them back with a magnetic field when entering the chamber) and injected into plasma. Here they are again ionized and in the process of clashes give plasma their energy. In the second case, microwave radiation is used, the frequency of which is equal to the ion cyclotron frequency (the frequency of rotation of ions in the magnetic field). At this frequency, dense plasma behaves like an absolutely black body, i.e. Fully absorbs falling energy. On the Tokamak JET countries of the European Union by the injection of neutral particles was obtained by plasma with ion temperatures of 280 million Kelvinov and the retention time 0.85 s. On deuterium-tritium plasma, thermonuclear power obtained, reaching 2 MW. The duration of maintenance of the reaction is limited by the appearance of impurities due to spraying of the chamber walls: impurities penetrate the plasma and, ionaging, significantly increase energy losses due to radiation. Now work on the JET program is focused on research on the possibility of controlling impurities and their deletion of the so-called. "Magnetic Diverter."
Big Tokamaki also created in the USA - TFTR, in Russia - T15 and in Japan - JT60. Studies made on these and other installations laid the foundation for the further phase of work in the area of \u200b\u200bcontrolled thermonuclear fusion: the launch of a large reactor for technical testing is planned for 2010. It is assumed that this will be the joint work of the United States, Russia, the countries of the European Union and Japan. see also Tokamak.
Pinch with reversed field (pop).
Pop configuration differs from tokamak by what in it B. Q ~ B. j, but at the same time the direction of the toroidal field outside the plasma is opposite to its direction inside the plasma cord. J.Teallor showed that such a system is in a state with minimal energy and despite q.
The advantage of the configuration pop is that there is a ratio of the volumetric densities of the plasma energy and the magnetic field (value B) more than in the tokamak. It is fundamentally important that B was as much as possible as it will reduce the toroidal field, and therefore, it will reduce the cost of creating coils and the entire supporting structure. The weak side of the pop is that thermal insulation from these systems is worse than that of the tokamaks, and the problem of maintaining a reversed field has not been solved.
Stellarator.
In the stellarator on a closed toroidal magnetic field, a field created by a special screw winding, scum on the chamber body. The total magnetic field prevents the plasma drift towards the center and suppresses certain types of magnetohydrodynamic instability. Plasma itself can be created and heated by any of the methods used in the tokamak.
The main advantage of the stellarator is that the method applied in it is not associated with the presence of a current in the plasma (both in the tokamaks or in the base-effect installations), and therefore the stellarator can work in a stationary mode. In addition, the screw winding can have a "divertore" action, i.e. Clean the plasma from impurities and remove the reaction products.
Plasma holding in rallarators is comprehensively examined at the installations of the European Union, Russia, Japan and the United States. On the Stellarator "Weddelshtein VII" in Germany, it was possible to maintain a plasma-carrying plasma with a temperature of more than 5h10 6 Kelvin, heating it by injection of a high-energy atomic beam.
Last theoretical and experimental studies have shown that in most of the settings described, and especially in closed toroidal systems, the plasma retention time can be increased by increasing its radial dimensions and the retaining magnetic field. For example, for the tokamak it is estimated that the Louuson criterion will be performed (and even with some reserve) at the magnetic field tension of ~ 50 × 100 kgf and the small radius of the toroidal chamber OK. 2 m. These are the installation parameters per 1000 MW of electricity.
When creating such large plasma-retention plasma settings arise completely new technological problems. To create a magnetic field of about 50 kgf in a volume of several cubic meters with copper cooled cooled coils, a power source of several hundred megawatts will be required. Therefore, it is obvious that the windings of the coils must be made from superconducting materials, such as niobium alloys with titanium or with tin. The resistance of these materials electric current in the superconducting state is zero, and, therefore, the minimum amount of electricity will be spent on maintaining the magnetic field.
Reactive technology.
Prospects for thermonuclear research.
Experiments made on the Tokamak type installations showed that this system is very promising as a possible base of the TCC reactor. The best results are obtained on top today, and there is hope that with the appropriate increase in the scale of installations they will be able to implement industrial TCs. However, Tokamak is not economical enough. To eliminate this disadvantage, it is necessary that it does not work in a pulse, as now, but in continuous mode. But the physical aspects of this problem are still little investigated. It is also necessary to develop technical means that would improve plasma parameters and eliminate its instability. Given all this, you should not forget about other possible, albeit less developed variants of the thermonuclear reactor, such as a stellarator or pinch with a reversed field. The status of studies in this area has reached the stage when there are conceptual reactor projects for most of the high-temperature plasma-retention systems and for some systems with inertial retention. An example of the industrial development of the Tokamak can be the project "Arises" (USA).
The second half of the XX century was a period of rapid development of nuclear physics. It became clear that nuclear reactions can be used to obtain a huge energy from a meager amount of fuel. Total nine years have passed from the explosion of the first nuclear bomb to the first nuclear power plant, and when a hydrogen bomb was tested in 1952, predictions appeared, which in the 1960s thermonuclear power plants will come into account. Alas, these hopes were not justified.
Thermonuclear reactions of all thermonuclear reactions in the near future are interesting only four: deuterium + deuterium (products - tritium and proton, energies 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 reaction goes 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 is currently burning coal, oil and gas. But their reserves are limited, and combustion products pollute the environment. The coal power station gives more radioactive emissions than the NPP of the same power! So why have we still not switched to nuclear energy sources? There are many reasons for this, but the main one has recently become radio fleaphobia. Despite the fact that the coal power station even at regular work harms the health of a much larger number of people than emergency emissions at nuclear power plants, it makes it quiet and unnoticed to the public. Accidents at the NPP immediately become the main news in the media, causing a common panic (often completely unreasonable). However, this does not mean that nuclear power has no objective problems. Many hassle deliver radioactive waste: technologies for working with them are still extremely expensive, and before the ideal situation, when they all be fully recycled and used, far away.
Of all thermonuclear reactions in the near future, only four are interesting: deuterium + deuterium (products - tritium and proton, energic 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 reaction goes in parallel with equal probability. The three and fourth reactions formed tritium and helium-3 are "burned" in the third and fourth reactions.
From division to synthesis
Potentially solve these problems allows the transition from fission reactors to synthesis reactors. If a typical division reactor contains dozens of tons of radioactive fuel, which is converted to dozens of tons of radioactive waste containing a wide variety of radioactive isotopes, the synthesis reactor uses only hundreds of grams, a maximum of a kilogram, one radioactive hydrogen isotope - tritium. In addition, the reaction requires an insignificant amount of this least dangerous radioactive isotope, its production is also planned directly on the power plant to minimize the risks associated with transportation. Products of synthesis are stable (non-radioactive) and non-toxic hydrogen and helium. In addition, in contrast to the fission reaction, the thermonuclear reaction during the destruction of the installation instantly stops, without creating the hazards of the thermal explosion. So why is not a single acting thermonuclear power plant still not built? The reason is that deficiencies inevitably flow out of the listed advantages: the creation of the conditions of the synthesis turned out to be much more difficult than expected at the beginning.
Criteria Louuson
In order for the thermonuclear reaction to be energetically advantageous, it is necessary to provide a sufficiently high temperature of thermonuclear fuel, its high density and sufficiently small energy loss. The latter are numerically characterized by the so-called "retention time", which is equal to the ratio of the heat energy plasma to the power of energy losses (many mistakenly believe that the "deduction time" is the time during which hot plasma is maintained in the installation) . At the temperature of a mixture of deuterium and tritium, equal to 10 keV (approximately 110,000,000 degrees), we need to obtain a product of the number of fuel particles in 1 cm 3 (i.e. plasma concentrations) at the time of hold (in seconds) at least 10 14. At the same time, it does not matter whether we have a plasma with a concentration of 1014 cm -3 and the deduction time 1 C, or a plasma with a concentration of 10 23 and the holding time of 1 ns. This criterion is called the "Louuson criterion".
In addition to the criterion of Louuson, which is responsible for obtaining an energetically advantageous reaction, there is another plasma ignition criterion, which for the deuterium-tritium reaction is approximately three times more of the Louuson criterion. "Ignition" means that the share of thermonuclear energy, which remains in the plasma, will be enough to maintain the required temperature, and the additional heating of the plasma is no longer required.
Z-Pinch
The first device in which it was planned to obtain a controlled thermonuclear reaction was the so-called Z-Pinch. This setting in the simplest case consists of all of the two electrodes that have a deuterium (hydrogen-2) environment or a mixture of deuterium and tritium, and the batteries of high-voltage pulse capacitors. At first glance it seems that it allows you to get a compressed plasma, heated to a huge temperature: exactly what is needed for thermonuclear reaction! However, everything turned out in life, alas, far from so rosy. The plasma harness turned out to be unstable: its slightest bending leads to an increase in the magnetic field on one side and loosening on the other, the emerging forces increase the bending of the harness - and the entire plasma "falls out" on the side wall of the chamber. The harness is unstable not only to the bend, the slightest thinner will lead to an increase in this part of the magnetic field, which further compresses the plasma, squeezing it into the remaining volume of the harness until the harness is finally "transmitted". The transmitted part has a high electrical resistance, so that the current is broken, the magnetic field disappears, and the entire plasma is dissipated.
The principle of the Z-Pinch operation is simple: the electric current generates an annular magnetic field that interacts with the same current and compresses it. As a result, the density and plasma temperature, through which the current flows are increasing.
Stabilize the plasma harness was able to impose a powerful external magnetic field on it, parallel to it, and placing in a thick conductive casing (when the plasma is moved, the magnetic field is moved, which induces an electric current in the casing, striving to return the plasma to the place). The plasma ceased to be curled and challenged, but before the thermonuclear reaction in any serious scale was still far: the plasma concerns the electrodes and gives them their heat.
Modern work in the field of synthesis on Z-Pince suggest another principle of creating thermonuclear plasma: the current flows through the tungsten plasma tube, which creates powerful X-ray, compressing and warming capsule with thermonuclear fuel inside the plasma tube, just as happens in thermonuclear bomb. However, these works have a purely research nature (the mechanisms of the operation of nuclear weapons are studied), and the release of energy in this process is still millions of times less than consumption.
The less the ratio of the large radius of the tormaque torus (distances from the center of all the torus to the center of the cross section of its pipe) to the small (pipe cross section), the greater the plasma pressure at the same magnetic field. Reduced this ratio, scientists moved from the round cross section of the plasma and the vacuum chamber to the D-shaped (in this case, the role of a small radius performs half the height of the section). All modern tokamaks have the form of section that is. The ultimate case was the so-called "spherical tokamak". In such tokamaks, the vacuum chamber and plasma have almost spherical shape, with the exception of a narrow channel connecting the poles of the sphere. Conducts are conducted by magnetic coils. The first spherical Tokamak, Start, appeared only in 1991, so this is a fairly young direction, but it has already shown the opportunity to get the same plasma pressure with a smaller magnetic field.
ProCoscotron, Stellarator, Tokamak
Another option to create the conditions necessary for the reaction is the so-called open magnetic traps. The most famous of them is "proboscotron": a pipe with a longitudinal magnetic field, which is enhanced at its ends and weakens in the middle. The field enlarged at the ends creates a "magnetic cork" (from where the Russian name), or "magnetic mirror" (English - Mirror Machine), which keeps the plasma from the outlet of the installation through the ends. However, such a deduction is incomplete, some of the charged particles moving according to certain trajectories, it turns out to be able to go through these traffic jams. And as a result of the clashes, any particle will sooner or later fall on such a trajectory. In addition, the plasma in the proboscotron was also unstable: if in some place a small plasma section is removed from the installation axis, there are forces emitting a plasma on the chamber wall. Although the basic idea of \u200b\u200bproboscotron was significantly improved (which made it possible to reduce both the plasma instability and the permeability of the plugs), to the parameters necessary for energetically advantageous synthesis, in practice it was not even approached.
Is it possible so that the plasma does not leave through "traffic jams"? It would seem, an obvious decision - to collapse the plasma in the ring. However, then the magnetic field inside the ring is stronger than outside, and the plasma again tends to leave the camera wall. The way out of this difficult situation also seemed quite obvious: instead of the ring to make an "eight", then on one piece of the particle will be removed from the installation axis, and on the other it is to return backwards. That is how scientists came to the idea of \u200b\u200bthe first rallar. But such "eight" cannot be made in the same plane, so I had to use the third dimension, bending the magnetic field in the second direction, which also led to the gradual care of the particles from the axis to the chamber wall.
The situation has changed dramatically with the creation of Tokamak type settings. The results obtained on the T-3 tokamak in the second half of the 1960s were so staggering for the time that Western scientists came to the USSR with their measuring equipment to make sure the plasma parameters on their own. Reality even surpassed their expectations.
These fantastically twisted pipes are not an art project, but the chamber of the stellarator is curved in the form of a complex three-dimensional curve.
In the hands of inertia
In addition to magnetic retention, there is a fundamentally different approach to thermonuclear synthesis - inertial retention. If in the first case we try to hold a very low concentration plasma for a long time (the concentration of molecules in the air around you is hundreds of thousands of times more), then in the second - compress the plasma to a huge density, an order of magnitude higher than the density of the most heavy metals, calculating that the reaction It will be time to go through the short time until the plasma has time to fly apart.
Initially, in the 1960s, it was planned to use a small ball of frozen thermonuclear fuel, evenly irradiated from all sides by a plurality of laser rays. The surface of the ball was to instantly evaporate and, evenly expanding in all directions, squeeze and heat the remaining part of the fuel. However, in practice, the irradiation was not uniform enough. In addition, part of the radiation energy was transmitted to the internal layers, causing them to be heated, which complicated compression. As a result, the ball clenched unevenly and weakly.
There are a number of modern configurations of rallar, and they are all close to Torah. One of the most common configurations involves the use of coils similar to the coils of the poloidal field of tokamaks, and four-six-twisted screws around the vacuum chamber of conductors with a multidirectional current. The complex magnetic field created with this allows reliably to hold the plasma without requiring the flow of the annular electric current. In addition, the coils of a toroidal field can be used in the rallarators, like the tokamaks. And the screw conduits may be absent, but then the coils of the "toroidal" field are installed along a complex three-dimensional curve. Recent developments in the field of rallarators involve the use of magnetic coils and a vacuum chamber of a very complex form (strongly "crumpled" torus) calculated on the computer.
The problem of unevenness was solved by substantially changing the construction of the target. Now the ball is placed inside a special small metal chamber (it is called "Holraum", from it. Hohlraum - cavity) with holes through which laser rays fall inside. In addition, crystals are used, which convert laser radiation of the IR range in ultraviolet. This UV radiation is absorbed by the finest layer of the Holraum material, which at the same time heats up to a huge temperature and radiates in the field of soft x-ray. In turn, X-ray radiation is absorbed by the finest layer on the surface of the fuel capsule (fuel bulb). It made it possible to solve the problem of premature heating of the internal layers.
However, the power of lasers was insufficient to ensure that a noticeable part of the fuel can come to the reaction. In addition, the effectiveness of lasers was quite small, only about 1%. In order for the synthesis to be energetically advantageous with such a low DGD lasers, almost all compressed fuel should react. When trying to replace lasers for light or heavy ions, which can be generated from much more efficiency, scientists also encountered a lot of problems: light ions are repelled from each other, which prevents them from focusing, and are inhibited in collisions with residual gas in the chamber, and accelerators Heavy ions with the desired parameters could not be created.
Magnetic perspectives
Most of the hopes in the field of thermonuclear energy are now associated with tokamaks. Especially after the opening of them with improved retention. The tokamak is simultaneously and folded into the Z-pin ring (plasma flows the ring electric current that creates the magnetic field required for its retention), and the sequence of samplers collected in the ring and creating a "corrugated" toroidal magnetic field. In addition, the toroidal field of coils and the plasma current field is superimposed by the perpendicular plane of the Torah field created by several separate coils. This is an additional field called poloidal, enhances the magnetic field of plasma current (also poloidal) from the outer side of the Torah and weakens it from the inside. Thus, the total magnetic field from all sides of the plasma harness is equal, and its position remains stable. Changing this additional field, you can move the plasma zip in the vacuum chamber within certain limits.
A fundamentally different approach to synthesis offers a concept of muon catalysis. Muon is an unstable elementary particle having the same charge as an electron, but 207 times a large mass. Muon can replace the electron in the hydrogen atom, while the size of the atom decreases 207 times. This allows one hydrogen kernel to approach another without spending energy. But about 10 GeV of energy is spent on receiving one muon, which means the need to produce several thousand synthesis reactions to one muison to obtain energy beneficial. Because of the possibility of "sticking" of the muon to the helium formed in the reaction, it was not yet possible to achieve more than a few hundred reactions. In the photo - Assembling the WeddleStein Z-X Plasma Plasma Institute of Plasma Plasma Institute.
An important problem of Tokamakov for a long time was to create an annular current in the plasma. To do this, the magnetic circuit in which the magnetic flow in which was continuously changed through the central hole of the Tokamak Tokamak. The change in the magnetic flux creates a vortex electric field that ionizes gas in a vacuum chamber and supports current in the resulting plasma. However, the plasma current must be maintained continuously, which means that the magnetic flow should be continuously changed in one direction. This, of course, is impossible, so that the current in the tokamaks managed to maintain only a limited time (from the fraction of a second to several seconds). Fortunately, the so-called bootstart-current was discovered, which occurs in a plasma without an external vortex field. In addition, plasma heating methods were developed, simultaneously causing the required annular current. Together, this gave a potential opportunity for how much long-term maintenance of hot plasma. In practice, the record at the moment belongs to the Tore Supra tokamak, where the plasma continuously "burned" for more than six minutes.
The second type of plasma retention facilities with which high hopes are associated are rallarators. Over the past decades, the design of rallar has changed dramatically. From the initial "eight" almost nothing left, and these installations became much closer to the tokamaks. Although while the time of holding the rallarators is less than that of the tokamaks (due to less efficient H-fashion), and the cost of their construction is higher, the plasma behavior in them is more relaxed, which means a higher resource of the first inner wall of the vacuum chamber. For commercial development of thermonuclear synthesis, this factor is very important.
Select reaction
At first glance, it is the most logical to use pure deuterium in the most logical to use: it is relatively cheap and safe. However, deuterium with deuterium responds to a hundred times less eager than with tritium. This means that for the operation of the reactor on the mixture of deuterium and tritium, there is a temperature of 10 keV for operation, and more than 50 keV temperatures are needed in pure deuterium. And the higher the temperature - the higher the loss of energy. Therefore, at least the first time thermonuclear energy is planned to be built on deuterium-tritium fuel. Tritium will be developed in the reactor itself due to irradiation of lithium rapid neutrons formed in it.
"Wrong" neutrons. In the cult film "9 days of one year", the main character, working on thermonuclear plant, received a serious dose of neutron irradiation. However, it turned out that neutrons were born not as a result of the synthesis reaction. This is not a director's fiction, but a real effect observed in Z-Pinch. At the time of the electric current break, the inductance of the plasma leads to the generation of huge tension - millions of volts. Separate hydrogen ions, accelerating in this field, are able to literally knock out neutrons from the electrodes. At first, this phenomenon was indeed taken for the right sign of the flow of thermonuclear reaction, but the subsequent analysis of the neutron energy spectrum showed that they have different origins.
Improved retention mode. H-Fashion Tokamaka is such a mode of its work when with a high power of additional heating the loss of energy plasma decrease sharply. Random discovery in 1982 the regime with improved retention is not inferior to the invention of the tokamak itself. There is no generally accepted theory of this phenomenon yet, but this does not prevent this in practice in practice. All modern tokamaks work in this mode, as it reduces the loss of more than twice. Subsequently, a similar mode was found on rallarators, which indicates that this is the overall property of toroidal systems, but the retention is improved only by about 30%.
Plasma heating. There are three basic plasma heating method to thermonuclear temperature. Ohmic heating is plasma heating due to electric current through it. This method is most effective in the first stages, since with the increasing temperature of the plasma, electrical resistance is reduced. Electromagnetic heating uses electromagnetic waves with a frequency that coincides with the frequency of rotation around the magnetic power lines of electrons or ions. In the injection of rapid 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 plasma center in order to transmit its energy there.
Does this reactor? Trithium radioactive, and powerful neutron irradiation from D-T reaction creates induced radioactivity in the elements of the reactor design. You have to use robots, which complicates work. At the same time, the behavior of plasma of ordinary hydrogen or deuterium is very close to the plasma behavior from a mixture of deuterium and tritium. This led to the fact that in the entire history, only two thermonuclear installations were fully worked on a mixture of deuterium and tritium: TFTR and JET Tokamaki. On the other installations, even deuterium is not always used. So the name "Thermonuclear" in the definition of the installation does not mean that thermonuclear reactions ever actually occurred in it (and in those where they occur almost always use pure deuterium).
Hybrid reactor. D-T Reaction gives rise to 14 MeV neutrons that even depleted uranium can share. The division of one core of uranium is accompanied by the allocation of approximately 200 MeV of the energy, which is ten times more than once exceeds the energy released during synthesis. So already existing tokamaks could become energetically beneficial if they were surrounded by a uranium shell. Before fission reactors, such hybrid reactors would have an advantage in the impossibility of developing an unmanaged chain reaction in them. In addition, extremely intensive neutron fluxes should process long-lived uranium division products in short-lived, which significantly reduces the problem of waste disposal.
Inertial hopes
Inertial synthesis also does not stand still. For dozens of years of development of laser technology, prospects have emerged to increase the efficiency of lasers about ten times. And their power in practice managed to increase hundreds and thousands of times. Work is underway over heavy ion accelerators with parameters suitable for thermonuclear use. In addition, the concept of "rapid ignition" was the most important factor in progress in the field of inertial synthesis. It involves the use of two pulses: one squeezes thermonuclear fuel, and the other heats it with a small part. It is assumed that the reaction started in a small part of the fuel will subsequently spread further and covers all fuel. This approach allows to significantly reduce energy costs, and therefore make a reaction favorable with a smaller share of reacted fuel.
Tokamakov problems
Despite the progress of the installations of other types, the tokamaks are currently still out of competition: if on two tokamaks (TFTR and JET) in the 1990s, the release of thermonuclear energy was actually obtained, approximately equal to the cost of energy to heating plasma (let such a mode and It lasted only about a second), then at the installations of other types, nothing like that did not succeed. Even a simple increase in the size of the tokamaks will take into the feasibility of energetically advantageous synthesis. Now in France, the International ITER reactor is being built, which will have to demonstrate it in practice.
However, there are enough problems in Tokamakov. Iter worth billions of dollars, which is unacceptable for future commercial reactors. No reactor worked continuously during even several hours, not to mention weeks and months that again it is necessary for industrial use. So far there is no confidence that the materials of the inner wall of the vacuum chamber will be able to withstand the long-term effects of the plasma.
Make a project less costly can the concept of tokamak with a strong field. By increasing the field, two to three times it is planned to obtain the desired plasma parameters in a relatively small installation. On such a concept, in particular, the Ignitor reactor was founded, which, together with Italian colleagues, is now beginning to build in the Trinity near Moscow (Trinity Institute of Innovative and Thermonuclear Studies). If the calculations of the engineers are justified, then with many times less compared to ITER prices in this reactor will be able to get the ignition of the plasma.
Forward, to the stars!
The products of thermonuclear reaction are spilled in different directions with rates that make up thousand kilometers per second. This makes it possible to create super-efficient rocket engines. The specific impulse will be higher than that of the best electrical proactive engines, and the energy consumption may even be negative (theoretically, production is possible, rather than energy consumption). Moreover, there is every reason to believe that the thermonuclear missile engine will even easier than the ground reactor: there is no problem with the creation of a vacuum, with thermal insulation of superconducting magnets, there are no limitations on dimensions, etc. In addition, the production of the electricity engine is desirable, but It is not necessarily necessary, enough so that it does not consume it too much.
Electrostatic retention
The concept of electrostatic deduction of ions is easiest to understand on an example of an installation called "Fuss". Its base is a spherical mesh electrode, to which negative potential is supplied. Accelerated in a separate accelerator or the field of the most central electrode ions fall inside it and hold there with an electrostatic field: if the ion seeks to fly out, the field of the electrode turns it back. Alas, the probability of the collision of ion with a grid for many orders is higher than the likelihood to enter the reaction of the synthesis, which makes an energetically advantageous reaction impossible. Such installations were used only as sources of neutrons.
In an effort to make a sensational discovery, many scientists seek to see the synthesis everywhere where only you can. In the press, messages have repeatedly arose about various options for the so-called "cold synthesis". The synthesis was found in the "impregnated" by the deuterium of metals when the electric current flows through them, with the electrolysis of the deuterium-saturated liquids, during the formation of cavitation bubbles, as well as in other cases. However, most of these experiments did not have satisfactory reproducibility in other laboratories, and their results can almost always be explained without the use of synthesis.
Continuing the "glorious tradition", which began with the "Philosophical Stone", and then turning into the "Eternal Engine", many modern fraudsters offer them now to buy "Cold Synthesis Generator", "Cavitational Reactor" and other "best-demanding generators": about philosophical The stone was all already forgotten, they don't believe in the eternal engine, but nuclear synthesis now sounds quite convincing. But, alas, in fact, such sources of energy do not yet exist (and when they are able to create, it will be in all news releases). So know: if you are offered to buy a device generating energy at the expense of cold nuclear synthesis, then you are trying to simply "inflate"!
According to preliminary estimates, even at the modern level of technology it is possible to create a thermonuclear missile engine for flight to the planets of the solar system (with appropriate financing). Mastering the technology of such engines in tens of times will increase the speed of manned flights and will provide an opportunity to have large backup fuel reserves on board, which will allow you to fly to Mars not more difficult, than now work on the ISS. For automatic stations, the velocity will potentially become an affordable speed of 10% of the light speed, which means the possibility of sending research probes to the nearest stars and receiving scientific data during their creators.
The most worked currently considered the concept of the thermonuclear missile engine based on inertial synthesis. At the same time, the difference between the engine from the reactor lies in the magnetic field, which directs the charged reaction products in one direction. The second option involves the use of an open trap, which is intentionally weakened by one of the traffic jams. The plasma expiring from it will create reactive force.
Thermonuclear Future
The development of thermonuclear synthesis turned out to be more difficult for many orders of magnitude than it seemed at the beginning. And although many problems have already been solved, the remaining is enough for the next few decades of the intense labor of thousands of scientists and engineers. But the prospects that are opening up before us to transform the isotopes of hydrogen and helium, so great, and the path made is already so significant that it does not make sense to stop halfway. Whatever numerous skeptics speak, the future is definitely behind the synthesis.
Atom is a building element of the universe. There are only about a hundred atoms of various types. Most elements are stable (for example, oxygen and nitrogen atmosphere; carbon, oxygen and hydrogen are the main components of our body and all other living organisms). Other elements are mainly very heavy, unstable, and this means that they spontaneously disintegrate by generating other elements. This transformation is called a nuclear reaction.
Nuclear reactions - transformations of atomic nuclei when interacting with elementary particles, g-quanta or with each other.
Nuclear reactions are divided into two types: nuclear division and thermonuclear synthesis.
The nuclear fission reaction is the process of splitting the atomic nucleus by two (less often three) nuclei with close masses called fragments of division. As a result of division, other reaction products may occur: light nuclei (mainly alpha particles), neutrons and gamma quanta. The division is spontaneous (spontaneous) and forced.
Spontaneous (spontaneous) is the division of nuclei, in the process of which some sufficiently heavy nuclei disintegrated into two fragments with approximately equal masses.
Spontaneous division was first discovered for natural uranium. Like any other type of radioactive decay, spontaneous division is characterized by a half-life (division period). The half-life for spontaneous division changes for different nuclei in very wide limits (from 1018 years for 93NP237 to several tenths of a second for transuranone elements).
The forced division of the nuclei can be caused by any particles: photons, neutrons, protons, deuterons, b-particles, etc., if the energy that they contribute into the core is sufficient to overcome the division barrier. For atomic energy, the division caused by neutron is greater importance. The fission reaction of heavy nuclei was made for the first time in uranium U235. In order for the uranium core to fit into two fragments, the activation energy is reported to it. This energy of uranium core receives, capturing neutron. The kernel comes to the excited state, deformed, the "jumper" occurs between the parts of the kernel and under the action of the Coulomb of the repulsion, the nucleus is divided into two fragments of the unequal mass. Both fragments of radioactive and emit 2 or 3 secondary neutron.
Fig. four
Secondary neutrons are absorbed by the neighboring uranium cores, which causes their division. Under appropriate conditions, a self-developing process of mass division of nuclei may occur, called a chain nuclear reaction. This reaction is accompanied by excretion of colossal energy. For example, with full combustion of 1 g of uranium, 8.28 · 1010 J Energy is allocated. The nuclear reaction is characterized by a thermal effect, which represents the difference in masses of resting the nuclear reaction and formed as a result of the reaction of the nuclei, i.e. The energy effect of a nuclear reaction is determined mainly by the difference of the masses of the final and source nuclei. Based on the equivalence of energy and mass, it is possible to calculate the energy that is emitted or spent during the flow of a nuclear reaction, if you know exactly the mass of all nuclei and particles involved in the reaction. According to Einstein's law:
- ? E \u003d? MC2
- ? E \u003d (MA + MX - MB - MY) C2
where MA and MX are mass, respectively, the target kernel and the bombarding nucleus (particles);
mB and My - Masses and formed as a result of the reaction of the nuclei.
The more energy is released during the formation of the nucleus, the more stronger. The core communication energy is called the amount of energy required for the decomposition of the atomic nucleus to the components - nucleons (protons and neutrons).
An example of an unmanaged chain reaction of division may be an explosion of an atomic bomb, a controlled nuclear reaction is carried out in nuclear reactors.
Thermonuclear synthesis is the reaction, the reverse division of atoms, the fusion reaction of the lungs of atomic nuclei into heavier kernels occurring at ultra-high temperature and accompanied by the release of huge amounts of energy. The implementation of the controlled thermonuclear synthesis will give humanity a new environmentally friendly and almost inexhaustible source of energy, which is based on the collision of hydrogen isotopes nuclei, and hydrogen is the most common substance in the universe.
The synthesis process comes with a noticeable intensity only between light nuclei with a small positive charge and only at high temperatures when the kinetic energy of the encountered nuclei is sufficient to overcome the Coulomb potential barrier. With an incomparably, the reaction between heavy hydrogen isotopes (deuterium 2H and TIRITY 3H) go to the formation of strongly connected kernels of helium.
2D + 3T\u003e 4He (3.5 MeV) + 1N (14.1,1 MeV)
These reactions are of the greatest interest for the problem of controlled thermonuclear synthesis. Deuterium is contained in sea water. Its reserves are publicly available and very high: the share of deuterium accounts for about 0.016% of the total number of hydrogen atoms included in the water, while the world ocean covers 71% of the ground surface area. The response involving tritium is more attractive, since it is accompanied by a large energy release and flows at considerable speed. Trithium radioactive (half-life of 12.5 years) and does not occur in nature. Consequently, to ensure the work of the intended thermalide reactor, which uses as a nuclear fuel tritium, the possibility of reproduction of tritium should be provided.
The reaction with the so-called lunar isotope 3NE has a number of advantages compared to the most reachable deuterium-tritium reaction on earthly conditions.
2D + 3He\u003e 4He (3.7 MeV) + 1p (14.7 MeV)
Benefits:
- 1. 3He is not radioactive.
- 2. Tens of times the lower stream of neutrons from the reaction zone, which sharply reduces the induced radioactivity and the degradation of the reactor structural materials;
- 3. The resulting protons, in contrast to neutrons, are easily captured and can be used for additional generation of electricity.
Natural isotopic prevalence in the 3He atmosphere is 0.000137%. Most of the 3He on Earth remained since its formation. It is dissolved in the mantle and gradually enters the atmosphere. On earth it is mined in very small quantities calculated by several dozens of grams per year.
Helium-3 is a by-product of reactions flowing into the sun. As a result, on the moon, which has no atmosphere, this valuable substance is up to 10 million tons (at minimal estimates - 500 thousand tons). With thermonuclear synthesis, when 1 ton of helium-3 with 0.67 tons of deuterium comes into the reaction, the energy equivalent to the combustion of 15 million tons of oil is released (however, the technical possibility of this reaction is not studied). Consequently, the population of our planet of the lunar resource helium-3 should be enough for at least the next millennium. The main problem remains the reality of helium production from the lunar soil. The content of helium-3 in the regolite is ~ 1 g per 100 tons. Therefore, at least 100 million tons of soil should be recycled to produce tons of this isotope. The temperature at which the reaction of the thermonuclear synthesis is possible reaches the value of about 108 - 109 K. At this temperature, the substance is in a completely ionized state, which is called plasma. Thus, the construction of the reactor suggests: obtaining a plasma heated to temperatures in hundreds of millions of degrees; Saving a plasma configuration over time for nuclear reactions.
Thermonuclear energy has important advantages over nuclear stations: it uses absolutely neradoactive deuterium and helen-3 isotope and radioactive tritium, but in volumes of thousands of times smaller than in nuclear power. And in possible emergency situations, a radioactive background near the thermonuclear power plant will not exceed natural indicators. At the same time, the unit of the weight of thermonuclear fuel is obtained about 10 million times more energy than when combustion of organic fuel, and about 100 times more than when the uranium nuclei splitting. In natural conditions, thermonuclear reactions flow in the depths of the stars, in particular in the inner regions of the Sun, and serve as a constant source of energy that determines their radiation. The combustion of hydrogen in the stars is at low speed, but the giant sizes and density of the stars ensure the continuous emission of huge streams of energy for billions of years.
All chemical elements of our planet and the universe were generally formed as a result of thermonuclear reactions that occur in the stars nuclei. Thermonuclear reactions in the stars lead to a gradual change in the chemical composition of the star substance, which causes the stars restructuring and its promotion along the evolutionary path. The first stage of evolution ends with the depletion of hydrogen in the central areas of the stars. Then, after an increase in the temperature caused by the compression of the central layers of the star, devoid of energy sources, the thermal-sickening reactions of the combustion of helium are effective, which are replaced by burning C, O, Si and subsequent elements - up to Fe and Ni. Each stage of star evolution corresponds to certain thermonuclear reactions. The first in the chain of such nuclear reactions cost hydrogen thermonuclear reactions. They leak in two ways depending on the initial temperature in the center of the star. The first way is the hydrogen cycle, the second path is CNO-cycle.
Hydrogen cycle:
- 1H + 1H \u003d 2D + E + + V +1.44 MeV
- 2D + 1H \u003d 3He + g +5.49 MeV
I: 3He + 3He \u003d 4He + 21h + 12.86 MeV
or 3He + 4He \u003d 7Be + g + 1.59 MeV
7Be + E- \u003d 7Li + V + 0,862 MeV or 7BE + 1H \u003d 8B + g +0.137 MeV
II: 7Li + 1H \u003d 2 4He + 17,348 MeV 8B \u003d 8BE * + E + + V + 15.08MEV
III. 8Be * \u003d 2 4He + 2.99 MeV
The hydrogen cycle begins the reaction of the collision of two protons (1H, or p) to form the deuterium kernel (2D). Deuterium reacts with a proton, forming a light (lunar) isotope helium 3NE with the emission of gamma photon (g). The lunar isotope 3 can react two different ways: two cores 3 do with a collision form 4 with the cleavage of two protons or 3NE connected from 4TU and gives 7W. The latter, in turn, captures either an electron (E-), or a proton and another branching arises proton - proton chain of reactions. As a result, the hydrogen cycle may end three different ways I, II and III. To implement the branch of the first two reactions of V. C. Must be done twice, because in this case two cores 3 do not disappear. In branches III, especially energetic neutrinos are emitted in the decay of the boron 8B core with the formation of an unstable beryllium kernel in an excited state (8W *), which almost instantly disintegrates into two cores 4. CNO-cycle is a combination of three clips with each other or, more precisely, partially overlapping cycles: CN, NO I, NO II. The synthesis of helium from hydrogen in the reactions of this cycle proceeds with the participation of catalysts, the role of which is played by small impurities of the isotopes C, N and O in the stellar substance.
The main way of reaction CN-cycle:
- 12c + p \u003d 13n + g +1.95 MeV
- 13n \u003d 13c + E + + H +1.37 MeV
- 13c + p \u003d 14n + g +7.54 MeV (2.7 · 106 years)
- 14n + p \u003d 15o + g +7.29 MeV (3.2 · 108 years)
- 15O \u003d 15N + E + + N +2.76 MeV (82 seconds)
- 15N + P \u003d 12C + 4He +4.96 MeV (1,12 · 105 years)
The essence of this cycle consists in an indirect synthesis of b-particles of four protons in their consecutive centers, starting with 12c.
In the reaction with the proton capture, the nucleus 15N is another outcome - the formation of the nucleus 16o and the new NO I-cycle cycle is born.
It has exactly the same structure as CN-cycle:
- 14N + 1H \u003d 15O + g +7.29 MeV
- 15O \u003d 15N + E + + N +2.76 MeV
- 15N + 1H \u003d 16O + g +12.13 MeV
- 16O + 1H \u003d 17F + g +0.60 MeV
- 17F \u003d 17O + E + + N +2.76 MeV
- 17O + 1H \u003d 14N + 4He +1.19 MeV
NO I-cycle increases the rate of energy release in the CN-cycle, increasing the number of CN-cycle catalysts.
The last reaction of this cycle may also have a different outcome, generating another NO II-cycle:
- 15N + 1H \u003d 16O + g +12.13 MeV
- 16O + 1H \u003d 17F + g +0.60 MeV
- 17F \u003d 17O + E + + N +2.76 MeV
- 17O + 1H \u003d 18F + g +5.61 MeV
- 18O + 1H \u003d 15N + 4He +3, 98 MeV
Thus, CN, NO I and NO II cycles form a triple CNO cycle.
There is another very slow fourth cycle, of-cycle, but its role in the development of energy is negligible. However, this cycle is very important when explaining 19F origin.
- 17O + 1H \u003d 18F + g + 5.61 MeV
- 18F \u003d 18O + E + + H + 1.656 MeV
- 18o + 1h \u003d 19f + g + 7.994 MeV
- 19F + 1H \u003d 16O + 4He + 8.114 MeV
- 16O + 1H \u003d 17f + g + 0.60 MeV
- 17F \u003d 17O + E + + H + 2.76 MeV
With the explosive burning of hydrogen in surface layers of stars, for example, with outbreaks of supernovae, very high temperatures can develop, and the character of the CNO-cycle changes dramatically. It turns into the so-called hot CNO cycle, in which the reactions go very quickly and confusing.
Chemical elements are heavier than 4He begin to synthesize only after the total burnout of hydrogen in the central area of \u200b\u200bthe star:
4He + 4He + 4He\u003e 12c + g + 7,367 MeV
Carbon burning reactions:
- 12C + 12C \u003d 20NE + 4He +4,617 MeV
- 12C + 12C \u003d 23NA + 1H -2,241 MeV
- 12c + 12c \u003d 23mg + 1N +2,599 MeV
- 23mg \u003d 23NA + E + + H + 8, 51 MeV
- 12c + 12c \u003d 24mg + g +13,933 MeV
- 12C + 12C \u003d 16O + 24He -0,113 MeV
- 24mg + 1H \u003d 25Al + g
When a temperature is reached 5 · 109 K in the stars under conditions of thermodynamic equilibrium, a large amount of various reactions flows, as a result of which the atomic nuclei is formed up to Fe and Ni.
The synthesis reaction is as follows: two or more atomic nuclei are taken and with the use of some power come closer so much that the forces acting at such distances prevail over the forces of the Coulomb repulsion between the same charged nuclei, as a result of which a new kernel is formed. It will have a slightly smaller mass than the sum of the mass of the source nuclei, and the difference becomes energy which is distinguished during the reaction process. The amount of energy released describes the known formula E \u003d Mc². Lighter atomic nuclei is easier to reduce the desired distance, so hydrogen is the most common element in the universe - is the best combustible for the synthesis reaction.
It has been established that a mixture of two hydrogen isotopes, deuterium and tritium requires less than the energy for the synthesis reaction compared to the energy allocated during the reaction. However, although a mixture of deuterium and tritium (D-T) is the subject of most synthesis studies, it is in any case the only type of potential fuel. Other mixes can be easier in production; Their response can be more reliable to be monitored, or more importantly, produce less neutrons. Special interest is caused by the so-called "imminent" reactions, since the successful industrial use of such a fuel will mean the absence of long-term radioactive contamination of materials and the design of the reactor, which, in turn, could have a positive effect on public opinion and on the total cost of the reactor, significantly reduced Costs for its decommission. The problem remains that the synthesis reaction using alternative fuel species is much more difficult to maintain, because the D-T reaction is considered only the necessary first step.
Deuterium-Tritium Reaction Scheme
Controlled thermonuclear synthesis can use various types of thermonuclear reactions depending on the type of fuel used.
Reaction of deuterium + tritium (fuel D-T)
The easiest reaction is the deuterium + tritium:
2 H + 3 H \u003d 4 HE + N at an energy output of 17.6 MeV (megaelectronvolt)
This reaction is most easily feasible from the point of view of modern technologies, gives a significant energy output, fuel components are cheap. The lack of its release of undesirable neutron radiation.
Two nuclei: deuterium and tritium merge, with the formation of the helium nucleus (alpha particle) and high-energy neutron.
² + ³He \u003d 4 He +. At energy output 18.4 MeV
The conditions for its achievement is much more complicated. Helium-3, in addition, is a rare and extremely expensive isotope. On an industrial scale is currently not produced. However, it can be obtained from tritium obtained in turn on nuclear power plants.
The complexity of the implementation of the thermonuclear reaction can be characterized by the triplery of NTT (temperature density at the time of deduction). According to this parameter, the D-3He reaction is more complicated than D-T.
Reaction between deuterium nuclei (D-D, monotocol)
The reactions between the deuterium nuclei are also possible, they are a little more difficult reaction with Helium-3:
As a result, in addition to the main reaction in DD Plasma, it is also happening:
These reactions slowly flow in parallel with the deuterium + helium-3 reaction, and the tritium and helium-3 formed during them are highly likely to respond immediately with deuterium.
Other types of reactions
Some other types of reactions are possible. The choice of fuel depends on many factors - its availability and low cost, energy output, ease of achieving the conditions required for the reaction of the thermalide synthesis (primarily temperatures), the necessary design characteristics of the reactor and so on.
"Immunity" reactions
The most promising t. N. "Immunuted" reactions, as the neutron flux generated by thermonuclear synthesis (for example, in the deuterium-tritium reaction) takes a significant portion of the power and generates induced radioactivity in the design of the reactor. The deuterium-3 reaction is promising, including due to the lack of neutron output.
Conditions
Lithium-6 nuclear reaction with deuterium 6 Li (D, α) α
TCB is possible with the simultaneous execution of two criteria:
- Plasma temperature:
- Compliance with the Louuson Criteria:
where - the density of high-temperature plasma, is the time of retention of plasma in the system.
It is from the meaning of these two criteria, the rate of flowing a particular thermonuclear reaction is mainly dependent.
Currently, the controlled thermonuclear synthesis is not yet carried out on an industrial scale. The construction of an ITER international research reactor is in the initial stage.
Thermonuclear power and helium-3
Gely-3 reserves on Earth range from 500 kg to 1 ton, but on the moon it is in significant quantity: up to 10 million tons (at minimal estimates - 500 thousand tons). Currently, the controlled thermonuclear reaction is carried out by synthesizing the deuterium ² and tritium ³H with the release of helium-4 4 HE and the "fast" neutron N:
However, the large part (more than 80%) of the highlighted kinetic energy accounts for the neutron. As a result of collisions of fragments with other atoms, this energy is converted to thermal. In addition, rapid neutrons create a significant amount of radioactive waste. In contrast, the synthesis of deuterium and helium-3 ³He does not produce (almost) radioactive products:
Where p - proton
This allows you to use simpler and efficient synthesis kinetic conversion systems, such as a magnetohydrodynamic generator.
Reactor designs
Two fundamental schemes of carrying out controlled thermonuclear synthesis are considered.
Studies of the first type of thermonuclear reactors are significantly more developed than the second. In nuclear physics, with research of thermonuclear synthesis, a magnetic trap is used to hold plasma in some volume. The magnetic trap is designed to hold the plasma from contact with the elements of the thermonuclear reactor, i.e. Used primarily as the heat insulator. The default principle is based on the interaction of charged particles with a magnetic field, namely on the rotation of the charged particles around the magnetic field lines. Unfortunately, the magnetized plasma is not very stable and seeks to leave the magnetic field. Therefore, to create an effective magnetic trap, the highest duty electromagnet is used that consumes a huge amount of energy.
It is possible to reduce the size of the thermonuclear reactor if it is used simultaneously three ways to create armonuclear reaction.
A. Inertial synthesis. Lower the tiny capsules of deuterium-tritium fuel with a laser with a capacity of 500 trillion watts: 5. 10 ^ 14 W. This giant, a very short-term laser pulse 10 ^ -8 C leads to an explosion of fuel capsules, as a result of which a mini star is born at the fraction of a second. But thermonuclear reaction does not reach it.
B. At the same time use Z-Machine with tokamac.
The z-machine acts otherwise than the laser. It passes through the web of the finest wires surrounding the fuel capsule, the charge of the power in the Otrillion Watt 5. 10 ^ 11 W.
Next occurs approximately the same thing as with a laser: As a result of the Z-impact it turns out a star. During the tests on the Z machine, the synthesis reaction was already managed. http://www.sandia.gov/media/z290.htm.Capsules cover silver and connect the thread of silver or graphite. The ignition process looks like this: shoot the thread (attached to the group of silver balls, inside which a mixture of deuterium and tritium) into a vacuum chamber. To form with a breakdown (discharge) of a zipper channel for them, supply a plasma current. At the same time, irradiate capsules and plasma with laser radiation. And at the same time or earlier turn on the tokamak. Use three plasma heating processes simultaneously. That is, put the z machine and laser heating together inside the tokamak. You can create a oscillating circuit from the coils of the tokamak and organize the resonance. Then he would work in economical oscillatory mode.
Fuel cycle
The first generation reactors will most likely work on a mixture of deuterium and tritium. Neutrons that appear in the reaction process will absorb the protection of the reactor, 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.
. .The reaction with Li6 is exothermic, providing a small energy for the reactor. The reaction with Li7 is endothermic - but does not consume neutrons. At least some Li7 reactions are necessary to replace neutrons lost in reaction with other elements. Most of the reactor designs use the natural mixtures of lithium isotopes.
This fuel has a number of shortcomings:
The reaction produces a significant amount of neutrons that activate (radioactively infect) reactor and heat exchanger. Events are also required to protect against the possible source of radioactive tritium.
Only about 20% of the synthesis energy is in the form of charged particles (remaining neutrons), which limits the possibility of direct transformation of the energy of synthesis into electricity. The use of D-T reaction depends on the existing lithium reserves, which are significantly less than the reserves of deuterium. Neutron irradiation During the D-T reaction is so significant that after the first series of tests on the JET, the largest reactor today that uses this fuel, the reactor has become so radioactive that it was necessary to add a robotic remote service system to complete the annual test cycle.
There are, in theory, alternative fuel, which are deprived of these shortcomings. But their use hinders the fundamental physical limitation. To obtain a sufficient amount of energy from the synthesis reaction, it is necessary to retain a sufficiently dense plasma at a synthesis temperature (10 8 K) for a certain time. This fundamental aspect of the synthesis is described by the production of plasma denotation, N, at the time of heated plasma τ, which is required to achieve an equilibrium point. The product, Nτ, depends on the type of fuel and is the function of plasma temperature. Of all the fuel species, the deuterium-tritium mixture requires the lowest value of Nτ at least an order of magnitude, and the lowest reaction temperature is at least 5 times. Thus, the D-T reaction is the necessary first step, but the use of other fuel species remains an important goal of research.
Reaction of synthesis as an industrial source of electricity
The synthesis energy is considered by many researchers as a "natural" energy source in the long run. Supporters of the commercial use of thermonuclear reactors for the production of electricity lead the following arguments in their favor:
- Practically inexhaustible fuel reserves (hydrogen)
- Fuel can be extracted from sea water on any coast of the world, which makes it impossible to monopolize a fuel one or group of countries
- Impossibility of uncontrollable synthesis reaction
- Lack of combustion products
- No need to use materials that can be used to produce nuclear weapons, thus eliminated cases of sabotage and terrorism
- Compared to nuclear reactors, a slight amount of radioactive waste with a short half-life is produced.
- It is estimated that thimble, filled with deuterium, produces energy equivalent to 20 tons of coal. The lake of the medium size is able to provide any country of energy for hundreds of years. However, it should be noted that existing research reactors are designed to achieve a direct deuterium-tritium (DT) reaction, the fuel cycle of which requires the use of lithium for the production of tritium, while the statements about the inexhaustibility of energy concern the use of deuterium-deuterium (DD) reaction in the second generation of reactors.
- Just like the division reaction, the synthesis reaction does not produce atmospheric emissions of carbon dioxide, which is the main contribution to global warming. This is a significant advantage, since the use of combustible fossils for the production of electricity has its consequence that, for example, 29 kg of CO 2 (one of the main gases can be considered to be the cause of global warming) per resident of the United States a day.
Cost of electricity in comparison with traditional sources
Critics indicate that the question of the economic feasibility of using nuclear synthesis for the production of electricity remains open. In the same study commissioned in the right of the science and technology of the British Parliament, it is indicated that the cost of electricity production using the thermonuclear reactor will probably be at the top of the spectrum of the cost of traditional energy sources. A lot will depend on future technology, market structure and regulation. The cost of electricity directly depends on the efficiency of use, the duration of the exploitation and the cost of decomission of the reactor. Critics for commercial use of nuclear synthesis energy deny that hydrocarbon fuel is significantly subsidized by the government, both directly and indirectly, for example, the use of armed forces to ensure their uninterrupted supply, the war in Iraq is often given as an ambiguous example of such a subsidization method. Accounting for such indirect subsidies is very difficult, and makes an accurate comparison of the cost almost impossible.
Separately there is a matter of research cost. The countries of the European Community spend about 200 million € annually on research, and it is predicted that it takes for several more decades while the industrial use of nuclear synthesis will become possible. Supporters of alternative sources of electricity believe that it would be more expedient to send these funds to the introduction of renewable sources of electricity.
Availability of commercial energy of nuclear synthesis
Unfortunately, despite the common optimism (common since the 1950s, when the first studies began), substantial obstacles between today's understanding of nuclear synthesis processes, technological capabilities and practical use of nuclear synthesis are still not overcome, is unclear even how much may be Economically advantageous electricity production using thermonuclear synthesis. Although progress in research is constant, researchers are still faced with new problems. For example, the problem is the development of a material capable of withstanding neutron bombing, which is estimated to be 100 times more intense than in traditional nuclear reactors.
Distinguish the following stages in studies:
1.Equilibrium or "Pass" mode (Break-Even): When the total energy that stands out in the synthesis process equals the total energy of spending on starting and supporting the reaction. This ratio is marked with a symbol Q. The reaction equilibrium has been demonstrated on Jet (Joint European Torus) in the UK in 1997. (Having spent on its heating 52 MW of electricity, at the output, scientists received power by 0.2 MW above the spent.)
2.Burning plasma (Burning Plasma): Intermediate stage, on which the reaction will be maintained mainly by alpha particles, which are produced during the reaction process, and not external heated. Q ≈ 5. Until now is not achieved.
3. Ignition (Ignition): Stable response that supports itself. It must be achieved at large values \u200b\u200bof Q. So far not achieved.
The next step in research should be ITER (International ThermonuClear Experimental Reactor), an international thermonuclear experimental reactor. In 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 research will be Demo: the prototype of the industrial reactor, which will be reached with ignition, and the practical suitability of new materials is demonstrated. The most optimistic forecasts for the termination of the phase DEMO: 30 years. Given the approximate time on the construction and commissioning of the industrial reactor, it separates ~ 40 years from the industrial use of thermonuclear energy.
Existing tokamaki
In total, about 300 tokamaks were built in the world. Below are the largest of them.
- USSR and Russia
- T-3 is the first functional apparatus.
- T-4 - an enlarged T-3 version
- T-7 is a unique installation in which for the first time in the world is a relatively large magnetic system with a superconducting solenoid based on the niobata of tin cooled by liquid helium. The main task of the T-7 was completed: a prospect for the next generation of superconducting solenoids of thermonuclear energy was prepared.
- T-10 and PLT - the next step in world thermonuclear studies, they are almost the same size equal to power, with the same detection factor. And the results obtained are identical: on both reactors, the cherished temperature of thermonuclear synthesis was achieved, and the lag according to the criterion of Louuson - just two hundred times.
- T-15 - today's reactor with a superconducting solenoid, giving a field of 3.6 T. voltage.
- Libya
- TM-4A
- Europe and United Kingdom
- JET (eng.) (Joint Europeus Tor) is the largest toocamak in the world, created by the Euratom organization in the UK. It uses a combined heating: 20 MW - neutral injection, 32 MW - ion-cyclotron resonance. As a result, Louuson's criterion is only 4-5 times lower than the ignition level.
- Tore Supra (Fr.) (Eng.) - Tokamak with superconducting coils, one of the largest in the world. Located in the Research Center Kadarash (France).
- USA
- TFTR (eng.) (Test Fusion Tokamak Reactor) is the largest Tokamak USA (in Princeton University) with additional heating by fast neutral particles. A high result is achieved: the Louuson criterion with a true thermonuclear temperature is only 5.5 times lower than the ignition threshold. Closed in 1997
- NSTX (English) (National Spherical Torus Experiment) is spherical tokamak (sponamecha) currently working at Princeton University. The first plasma in the reactor was obtained in 1999, two years after the closure of TFTR.
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