Nuclear energy consists of large quantity enterprises for various purposes. The raw materials for this industry are mined from uranium mines. It is then delivered to fuel production plants.

The fuel is then transported to nuclear power plants, where it enters the reactor core. When nuclear fuel reaches the end of its useful life, it is subject to disposal. It is worth noting that hazardous waste appears not only after fuel reprocessing, but also at any stage - from uranium mining to work in the reactor.

Nuclear fuel

There are two types of fuel. The first is uranium mined in mines, which is of natural origin. It contains raw materials that are capable of forming plutonium. The second is fuel that is created artificially (secondary).

Nuclear fuel is also divided according to its chemical composition: metallic, oxide, carbide, nitride and mixed.

Uranium mining and fuel production

A large share of uranium production comes from just a few countries: Russia, France, Australia, the USA, Canada and South Africa.

Uranium is the main element for fuel in nuclear power plants. To get into the reactor, it goes through several stages of processing. Most often, uranium deposits are located next to gold and copper, so its extraction is carried out with the extraction of precious metals.

During mining, human health is at great risk because uranium is a toxic material, and the gases that appear during its mining cause various forms of cancer. Although the ore itself contains a very small amount of uranium - from 0.1 to 1 percent. The population living near uranium mines is also at great risk.

Enriched uranium is the main fuel for nuclear power plants, but after its use remains great amount radioactive waste. Despite all its dangers, uranium enrichment is an integral process of creating nuclear fuel.

In its natural form, uranium practically cannot be used anywhere. In order to be used, it must be enriched. Gas centrifuges are used for enrichment.

Enriched uranium is used not only in nuclear energy, but also in weapons production.

Transportation

At any stage of the fuel cycle there is transportation. It is carried out by everyone accessible ways: by land, sea, air. This is a big risk and a big danger not only for the environment, but also for humans.

During the transportation of nuclear fuel or its elements, many accidents occur, resulting in the release of radioactive elements. This is one of the many reasons why it is considered unsafe.

Decommissioning of reactors

None of the reactors have been dismantled. Even the infamous Chernobyl The whole point is that, according to experts, the cost of dismantling is equal to, or even exceeds, the cost of building a new reactor. But no one can say exactly how much money will be needed: the cost was calculated based on the experience of dismantling small stations for research. Experts offer two options:

1. Place reactors and spent nuclear fuel in repositories.
2. Build sarcophagi over decommissioned reactors.

In the next ten years, about 350 reactors around the world will reach their end of life and must be taken out of service. But since the most suitable method in terms of safety and price has not been invented, this issue is still being resolved.

There are currently 436 reactors operating around the world. Of course, this is a big contribution to the energy system, but it is very unsafe. Research shows that in 15-20 years, nuclear power plants will be able to be replaced by stations that run on wind energy and solar panels.

Nuclear waste

A huge amount of nuclear waste is generated as a result of the activities of nuclear power plants. Reprocessing nuclear fuel also leaves behind hazardous waste. However, none of the countries found a solution to the problem.

Today, nuclear waste is kept in temporary storage facilities, in pools of water, or buried shallowly underground.

The safest method is storage in special storage facilities, but radiation leakage is also possible here, as with other methods.

In fact, nuclear waste has some value, but requires strict compliance with the rules for its storage. And this is the most pressing problem.

An important factor is the time during which the waste is hazardous. Each has its own decay period during which it is toxic.

Types of nuclear waste

During the operation of any nuclear power plant, its waste enters the environment. This is water for cooling turbines and gaseous waste.

Nuclear waste is divided into three categories:

1. Low level - clothing of nuclear power plant employees, laboratory equipment. Such waste can also come from medical institutions and scientific laboratories. They do not pose a great danger, but require compliance with safety measures.
2. Intermediate level - metal containers in which fuel is transported. Their radiation level is quite high, and those who are close to them must be protected.
3. The high level is spent nuclear fuel and its reprocessing products. The level of radioactivity is rapidly decreasing. High level waste is very small, about 3 percent, but it contains 95 percent of all radioactivity.

The life cycle of nuclear fuel based on uranium or plutonium begins at mining enterprises, chemical plants, in gas centrifuges, and does not end at the moment the fuel assembly is unloaded from the reactor, since each fuel assembly has to go through a long path of disposal and then reprocessing.

Extraction of raw materials for nuclear fuel

Uranium is the heaviest metal on earth. About 99.4% of the earth's uranium is uranium-238, and only 0.6% is uranium-235. The International Atomic Energy Agency's Red Book report shows that uranium production and demand are rising despite the Fukushima nuclear accident, which has left many wondering about the prospects for nuclear power. Over the past few years alone, proven uranium reserves have increased by 7%, which is associated with the discovery of new deposits. The largest producers remain Kazakhstan, Canada and Australia; they mine up to 63% of the world's uranium. In addition, metal reserves are available in Australia, Brazil, China, Malawi, Russia, Niger, USA, Ukraine, China and other countries. Previously, Pronedra wrote that in 2016, 7.9 thousand tons of uranium were mined in the Russian Federation.

Today, uranium is mined in three different ways. The open method does not lose its relevance. It is used in cases where deposits are close to the surface of the earth. With the open method, bulldozers create a quarry, then the ore with impurities is loaded into dump trucks for transportation to processing complexes.

Often the ore body lies at great depth, in which case the underground mining method is used. A mine is dug up to two kilometers deep, the rock is extracted by drilling in horizontal drifts, and transported upward in freight elevators.

The mixture that is transported upward in this way has many components. The rock must be crushed, diluted with water and the excess removed. Next, sulfuric acid is added to the mixture to carry out the leaching process. During this reaction, chemists obtain a yellow precipitate of uranium salts. Finally, uranium with impurities is purified in a refining facility. Only after this is uranium oxide produced, which is traded on the stock exchange.

There is a much safer, environmentally friendly and cost-effective method called borehole in situ leaching (ISL).

With this method of mining, the territory remains safe for personnel, and the radiation background corresponds to the background in large cities. To mine uranium using leaching, you need to drill 6 holes at the corners of the hexagon. Through these wells, sulfuric acid is pumped into uranium deposits and mixed with its salts. This solution is extracted, namely, pumped through a well in the center of the hexagon. To achieve the required concentration of uranium salts, the mixture is passed through sorption columns several times.

Nuclear fuel production

It is impossible to imagine the production of nuclear fuel without gas centrifuges, which are used to produce enriched uranium. After reaching the required concentration, the uranium dioxide is pressed into so-called tablets. They are created using lubricants that are removed during firing in kilns. The firing temperature reaches 1000 degrees. After this, the tablets are checked to ensure they meet the stated requirements. Surface quality, moisture content, and the ratio of oxygen and uranium are important.

At the same time, tubular shells for fuel elements are being prepared in another workshop. The above processes, including subsequent dosing and packaging of tablets in shell tubes, sealing, decontamination, are called fuel fabrication. In Russia, the creation of fuel assemblies (FA) is carried out by the Mashinostroitelny Zavod in the Moscow region, the Novosibirsk Chemical Concentrates Plant in Novosibirsk, the Moscow Polymetals Plant and others.

Each batch of fuel assemblies is created for a specific type of reactor. European fuel assemblies are made in the shape of a square, while Russian ones have a hexagonal cross-section. Reactors of the VVER-440 and VVER-1000 types are widely used in the Russian Federation. The first fuel elements for VVER-440 began to be developed in 1963, and for VVER-1000 - in 1978. Despite the fact that new reactors with post-Fukushima safety technologies are being actively introduced in Russia, there are many old-style nuclear installations operating throughout the country and abroad, so fuel assemblies remain equally relevant for different types reactors.

For example, to provide fuel assemblies for one core of the RBMK-1000 reactor, over 200 thousand components made of zirconium alloys, as well as 14 million sintered uranium dioxide pellets, are needed. Sometimes the cost of manufacturing a fuel assembly can exceed the cost of the fuel contained in the elements, which is why it is so important to ensure high energy efficiency per kilogram of uranium.

Costs for production processes V %

Separately, it is worth mentioning fuel assemblies for research reactors. They are designed in such a way as to make observation and study of the neutron generation process as comfortable as possible. Such fuel rods for experiments in the fields of nuclear physics, isotope production, and radiation medicine are produced in Russia by the Novosibirsk Chemical Concentrates Plant. FAs are created on the basis of seamless elements with uranium and aluminum.

The production of nuclear fuel in the Russian Federation is carried out by the fuel company TVEL (a division of Rosatom). The company works on enriching raw materials, assembling fuel elements, and also provides fuel licensing services. "Kovrov Mechanical Plant" in the Vladimir region and "Ural Gas Centrifuge Plant" in Sverdlovsk region create equipment for Russian fuel assemblies.

Features of transportation of fuel rods

Natural uranium is characterized by a low level of radioactivity, however, before the production of fuel assemblies, the metal undergoes an enrichment procedure. The content of uranium-235 in natural ore does not exceed 0.7%, and the radioactivity is 25 becquerels per 1 milligram of uranium.

Uranium pellets, which are placed in fuel assemblies, contain uranium with a uranium-235 concentration of 5%. Finished fuel assemblies with nuclear fuel are transported in special metal containers high strength. For transportation, rail, road, sea and even air transport are used. Each container contains two assemblies. Transportation of non-irradiated (fresh) fuel does not pose a radiation hazard, since the radiation does not extend beyond the zirconium tubes into which the pressed uranium pellets are placed.

A special route is developed for the fuel shipment; the cargo is transported accompanied by security personnel from the manufacturer or the customer (more often), which is primarily due to the high cost of the equipment. In the entire history of nuclear fuel production, not a single transport accident involving fuel assemblies has been recorded that would have affected the radiation background environment or led to casualties.

Fuel in the reactor core

A unit of nuclear fuel - a TVEL - is capable of releasing enormous amounts of energy over a long period of time. Neither coal nor gas can compare with such volumes. The fuel life cycle at any nuclear power plant begins with the unloading, removal and storage of fresh fuel in the fuel assembly warehouse. When the previous batch of fuel in the reactor burns out, personnel assemble the fuel assemblies for loading into the core (the working area of ​​the reactor where the decay reaction occurs). As a rule, the fuel is partially reloaded.

Full fuel is added to the core only at the time of the first startup of the reactor. This is due to the fact that the fuel rods in the reactor burn out unevenly, since the neutron flux varies in intensity in different zones of the reactor. Thanks to metering devices, station personnel have the opportunity to monitor the degree of burnout of each unit of fuel in real time and make replacements. Sometimes, instead of loading new fuel assemblies, assemblies are moved among themselves. In the center of the active zone, burnout occurs most intensely.

FA after a nuclear power plant

Uranium that has been spent in a nuclear reactor is called irradiated or burnt up. And such fuel assemblies are used as spent nuclear fuel. SNF is positioned separately from radioactive waste, since it has at least 2 useful components - unburned uranium (the burnup depth of the metal never reaches 100%) and transuranium radionuclides.

IN Lately physicists began to use radioactive isotopes accumulated in spent nuclear fuel in industry and medicine. After the fuel has completed its campaign (the time the assembly is in the reactor core under operating conditions at rated power), it is sent to the cooling pool, then to storage directly in the reactor compartment, and after that for reprocessing or disposal. The cooling pool is designed to remove heat and protect against ionizing radiation, since the fuel assembly remains dangerous after removal from the reactor.

In the USA, Canada or Sweden, spent fuel is not sent for reprocessing. Other countries, including Russia, are working on a closed fuel cycle. It allows you to significantly reduce the cost of producing nuclear fuel, since part of the spent fuel is reused.

The fuel rods are dissolved in acid, after which researchers separate the plutonium and unused uranium from the waste. About 3% of raw materials cannot be reused; these are high-level wastes that undergo bituminization or vitrification procedures.

1% plutonium can be recovered from spent nuclear fuel. This metal does not need to be enriched; Russia uses it in the process of producing innovative MOX fuel. A closed fuel cycle makes it possible to make one fuel assembly approximately 3% cheaper, but this technology requires large investments in the construction of industrial units, so it has not yet become widespread in the world. However, the Rosatom fuel company does not stop research in this direction. Pronedra recently wrote that in Russian Federation are working on fuel capable of recycling isotopes of americium, curium and neptunium in the reactor core, which are included in the same 3% of highly radioactive waste.

Nuclear fuel producers: rating

1. The French company Areva until recently provided 31% of the global market for fuel assemblies. The company produces nuclear fuel and assembles components for nuclear power plants. In 2017, Areva underwent a qualitative renovation, new investors came to the company, and the colossal loss of 2015 was reduced by 3 times.
2. Westinghouse is the American division of the Japanese company Toshiba. It is actively developing the market in Eastern Europe, supplying fuel assemblies to Ukrainian nuclear power plants. Together with Toshiba, it provides 26% of the global nuclear fuel production market.
3. The fuel company TVEL of the state corporation Rosatom (Russia) is in third place. TVEL provides 17% of the global market, has a ten-year contract portfolio worth $30 billion and supplies fuel to more than 70 reactors. TVEL develops fuel assemblies for VVER reactors, and also enters the market of nuclear plants of Western design.
4. Japan Nuclear Fuel Limited, according to the latest data, provides 16% of the world market and supplies fuel assemblies to most nuclear reactors in Japan itself.
5. Mitsubishi Heavy Industries is a Japanese giant that produces turbines, tankers, air conditioners, and, more recently, nuclear fuel for Western-style reactors. Mitsubishi Heavy Industries (a division of the parent company) is engaged in the construction of APWR nuclear reactors, research activities together with Areva. This company was chosen by the Japanese government to develop new reactors.

A modern car can run on gasoline with an octane rating of 72 - but it will be a sad and slow ride. A nuclear power plant is capable of operating on fuel developed 50 years ago - but it will work in an unprofitable mode; the reactor will not be able to realize the new capabilities incorporated into it by its designers. Since the creation of the very first nuclear power plant, nuclear scientists have been constantly working hard work to improve the quality of nuclear fuel, increasing the benefits nuclear energy.

We have all seen and are already accustomed to what nuclear power plants look like - gigantic structures that can and should be considered one of the symbols modern stage development of human civilization. Huge turbines, the rotating rotor of which creates enormous force electricity, powerful pumps that drive water under high pressure through the reactor core, durable reactor vessels, additional sealed shells that can withstand earthquakes and airplanes falling on them. Pipelines of the primary and secondary circuits, giant cooling towers in which the water of the secondary circuit cools - everything here is large, sometimes colossal. But the heart of any nuclear reactor is very tiny, because the controlled nuclear fission reaction occurs inside very small fuel pellets containing uranium enriched in the isotope-235. It is here, in small tablets, that the most important thing happens - the release of a huge amount of heat, for the beneficial use of which everything that we see at nuclear power plants is created. This is all, big and beautiful, complex equipment that requires enormous effort in production and operation - just “service” for fuel pellets.

Nuclear energy without formulas

It is quite difficult to talk about what nuclear fuel from a nuclear power plant is - in ordinary cases, the description requires multi-level mathematical formulas, atomic physics and other quantum mechanics. Let's try to do without all this in order to understand how our nuclear scientists tamed uranium, making it a reliable source of the much-needed energy we need. electrical energy. It seems to us that logic and simple everyday common sense will be quite enough for this, and Starting point will be a school description of a fission chain reaction. Remember?

“A neutron strikes a uranium nucleus, knocks out two neutrons from it at once, which now strike a couple of nuclei, knocking out four at once...”

Nuclear chain reaction

In mathematical terms, with a neutron multiplication factor equal to two, a controlled chain reaction is impossible. The number of free neutrons and decay events of uranium nuclei is growing so avalanche-like that there can only be one result - an atomic explosion. In order for the reaction to proceed smoothly, so that it can be controlled and regulated, it is necessary to achieve a multiplication factor of 1.02 - one hundred free “initial” neutrons should give rise to the appearance of 102 free neutrons of the “second generation”, all the rest must be eliminated, absorbed, neutralized – call this process whatever you want, but it must happen. This threshold value was calculated theoretically, for which a special “thank you” to our scientists. They found that the natural content of the isotope-235 is not enough for the multiplication factor to exceed one. In other words, if we want the fission reaction to continue, we need to learn how to increase the content of this isotope to 3-4%, that is, 5-6 times higher than what Mother Nature provides us. The theorists did the calculations, but practical engineers did the rest of the work, coming up with ways to use materials that absorb excess neutrons in the reactor core, and invented “neutron neutralizers.”

Chemistry is life

How uranium is enriched based on the isotope-235 content, Analytical online journal Geoenergetics.ru I already told you that first uranium needs to be turned into gas, into uranium fluoride, then using gas centrifuges to “weed out” the heavy atoms, due to which the number of light atoms will increase (the nucleus of the main isotope of uranium contains 238 protons and neutrons, such an atom weighs three atomic units larger than the uranium-235 atom). Great - fluoride has become richer in uranium-235, everything is fine. And then – what and how? The path of nuclear fuel into nuclear power plant reactors begins in the caring hands of chemists who perform extremely important work- they transform gas into a solid substance, and into the kind that the nuclear scientists “ordered” them. What makes nuclear energy so surprising is that it is not limited only to atomic physics; it uses dozens of scientific disciplines at once, including Rosatom There is always a place for chemists, materials scientists, metallurgists and many, many other specialists.

And physicists “order” chemists uranium dioxide - a powder of molecules containing one uranium atom and two oxygen atoms. Why him? Yes, many of the properties of these molecules are painfully good. The melting point of uranium dioxide is 2,840 degrees; it is very difficult to make it melt; in the history of nuclear energy, there have been only three accidents involving the melting of nuclear fuel. Uranium dioxide is little susceptible to the so-called gas swelling - an interesting phenomenon, but harmful for nuclear energy. What happens in the reactor core is the embodiment of the dream of medieval alchemists, transformations of some take place there chemical elements in others, completely different from them. A free neutron that hits a uranium-235 nucleus not only knocks additional free neutrons out of it - it causes the nucleus itself to split into different parts. Exactly how fission occurs and what new nuclei are formed is a matter of chance, but statistics show that among other fission fragments there are also gases. They accumulate inside the fuel pellet and behave as gases should - they try to occupy as much volume as possible, they try to literally tear the fuel pellet to shreds. Agree, there is nothing useful in this - we need the fuel pellet to be intact and healthy, so that it can remain in the core for as long as possible in order to transfer to us all the energy contained in the nuclei of uranium atoms. So only hardcore, only uranium dioxide - it allows you to use higher temperatures, which increases the efficiency of a nuclear power plant, it allows you to increase the fuel burnup.

“Nuclear fuel burn-up” is a completely scientific and technical term, but to understand what it is, the highest physical education not required. Fuel burnup is the fraction of uranium nuclei that have undergone nuclear transformation when exposed to neutrons. Expressed as a percentage, the higher the percentage, the greater the number of uranium nuclei we were able to use for the purposes we needed, receiving heat from them that was used to generate electricity. Fuel burnup is thus one of the main economic parameters of a nuclear power plant. If we placed 100 kilograms of uranium-235 into the core, and at the end of the fuel campaign we removed 99 kg of it from it - such a design of the core, reactor and nuclear power plant is worthless. But if it turns out that there is no uranium-235 left in the fuel pellet removed from the core, then the designers have done well and it’s time to urgently give each of them a Nobel Prize, better – two.

In fact, a burnout rate of 100% is unattainable in principle, but this does not mean that they are not fighting for it - there are serious battles for every percentage. The greater the burnup depth, the lower the cost of the resulting electricity, and competition with energy based on the combustion of hydrocarbons has not been canceled. Moreover, the longer the tablet “burns”, the less often the reactor needs to recharge the fuel. The design of the VVER (water-cooled water-cooled power reactor) is such that the fuel is changed when the reactor is completely stopped and cooled down - it’s safer. The fewer such shutdowns, the higher the installed capacity utilization factor; capacity factor is the second most important economic indicator of a nuclear power plant. The technical data sheet of your vacuum cleaner states its power - say, 1,200 Wh. But you will get 1,200 watts if the vacuum cleaner works for exactly an hour, in the half-hour operation mode - half an hour “something grabbed your lower back” you will get only 600 watts, or, in other words, the capacity of the vacuum cleaner will be only 50%. As in the case of fuel burnup, the cherished goal is 100%, and again, every percent counts, because the economics of a nuclear reactor must be more profitable than the economics of a thermal power plant and even the economics of a hydroelectric power station.

It would seem - how can you show more profitable economic results than a hydroelectric power station, which does not require fuel at all, where only the energy of falling water is used? Yes, it’s very simple - water does not fall on hydraulic units 24 hours a day, 365 days a year; this requires a very specific volume of water in the reservoir. Until this volume is reached, the hydroelectric power station will “rest”, and the nuclear power plant, which knows nothing about such pauses, will have time to catch up and overtake its rival. Here is a short summary - the efficiency, burnup, and capacity factor of any nuclear power plant critically depend on the fuel pellet and its material. A chemist turning uranium fluoride gas into uranium dioxide powder, remember - the future of nuclear energy depends on your skill!

Fuel tablets – step by step

Explain in simple words you can do a lot, but doing such an exercise in order to describe the work of chemists is impossible from the word “in general,” so get ready. Uranium fluoride gas is first passed through an aqueous solution to obtain uranyl fluoride, which is mixed with ammonia and the acid residue of carbonic acid. The result is ammonium uranyl carbonate, which precipitates - consider that half the battle is already done, we have at least something solid, not gaseous. The suspension is passed through a filter, washed and sent to a fluidized bed furnace, where due to the high temperature, all unnecessary impurities disintegrate, leaving a dry residue of uranium trioxide powder (for every 1 atom of uranium in this molecule there are three atoms of oxygen). That's it, now he's almost ours!

Area for the production of uranium dioxide powder using high-temperature pyrohydrolysis

The temperature is high again - 500 degrees, but this time with the passage of hydrogen, which takes over the extra oxygen atom, and the chemists calmly go on a lunch break, allowing the physicists to take the uranium dioxide they covet. However, they rejoice early - they are immediately slapped on the outstretched raking hands ... by metallurgists, since fuel tablets are produced by powder metallurgy. The powder resulting from the work of chemists is crushed, sifted and a fine powder is obtained - crushed to the point of almost dust. After adding binders and lubricants, the tablets are pressed and annealed again to remove unnecessary impurities. After this, the temperature rises to 1,750 degrees, the tablets become denser, heavier - now they can be processed using mechanical methods. The cylindrical grinder comes into play to get the required dimensions - that's all.

Uranium pellet production area

No, well, not quite “all”, because immediately after this inspectors come to the workshop to check the geometric dimensions, surface quality, moisture content, and the ratio of oxygen and uranium atoms. Please note that it is not necessary to check the ratio of uranium-235 and uranium-238 atoms - no matter what manipulations chemists perform, their actions do not affect the composition of atomic nuclei. The result of all this work is fuel tablets weighing only 4.5 grams, but these tiny pellets contain the same amount of energy as 400 kg of coal, in 360 cubic meters natural gas or 350 kg of oil.

Production and technical control of nuclear ceramic fuel pellets

The range of tablets produced at Russian nuclear enterprises that are part of TVEL Fuel Company– more than 40 varieties, different sizes, different degrees of enrichment of uranium-235. But one thing remains unchanged - nuclear energy continues to use uranium dioxide as fuel, which in itself is one of the barriers to the spread of radioactivity. At operating temperatures, this material retains 98% of decomposition products inside itself, reducing the sealing load to a minimum. In order for the fuel to perform its “barrier” functions, it is important that the interaction of the fuel with the coolant is minimal - otherwise radioactive decay products have a chance to escape into the atmosphere. external environment with all the ensuing unpleasant consequences.

A fuel rod is not just a “long tube”

Okay, the tablets have been made, what next? The idea of ​​a nuclear reactor is simple - the coolant must “remove” all the heat released as a result of nuclear reactions. This is not a one-time removal; this removal must occur throughout the entire fuel session - the time the fuel is in the reactor core. In VVER reactors, this work is performed by water passing through the core under high pressure. Throw fuel tablets into the core like dumplings into boiling water? This is not an option; it is much more reasonable to ensure that the fuel pellets are in a stationary position, along which a stream of water passes under pressure, taking away the water formed during nuclear reactions. thermal energy. Consequently, some kind of “clamp” is needed, which is designed to ensure a stationary location of the fuel - this is a hollow thin-walled tube, inside of which the fuel pellets are contained - the fuel rod, the fuel element.

Fuel elements (fuel elements), Photo: wikimedia.org

Why thin-walled? So that the heat generated in the fuel pellets can be “removed” almost unhindered by water, that is, the first requirement for the material of the fuel rod walls is the highest possible thermal conductivity. Took - gave, took - gave. The second requirement is also quite obvious - the outer side of the fuel element walls is constantly in water, therefore its material should not be afraid of corrosion. The third condition is also obvious - the material must withstand constant high radioactivity, without causing harm to basic nuclear processes. It must absorb as few neutrons as possible so as not to interrupt the nuclear reaction, so as not to force the production of uranium with a higher degree of enrichment in the isotope-235. The diameter of the tube, as well as the diameter of the fuel pellets, should be as small as possible - otherwise the heat that is generated in the central segments will not reach the coolant. This is the set of requirements that such a “simple” thing as a thin wall of a fuel rod must meet.

At the stage of development of nuclear energy, stainless steel became such a material, but this did not last long - it turned out that steel takes up too many free neutrons, something less voracious is needed. By this time, nuclear scientists had worked thoroughly and found a metal with a minimum neutron capture cross section - zirconium. In this case, the word “section” replaces the word “probability”. The probability that a passing neutron will be captured in its snare by the nucleus of a zirconium atom is minimal, while zirconium has an excellent heat transfer coefficient, it does not interact with water, it melts only at temperatures above 1'855 degrees, it has a very low coefficient of thermal expansion - instead In order to “swell” when heated, it simply “discharges” heat into the external environment. Agree - it’s simply an ideal material for nuclear energy, if you can achieve it in ideal chemical purity, since any impurity tends to actively “eat up” free neutrons.

Fuel rod and fuel assembly production workshop

As soon as metallurgists announced that they had learned to cope with this task, nuclear energy switched to zirconium. The only enterprise in Russia and one of three in the world that has a full cycle of production of zirconium and its alloys is the Chepetsk Mechanical Plant (Glazov, Udmurtia), which is part of the TVEL fuel company. Since 1986, ChMP switched to manufacturing fuel element casings from E-110 alloy - one percent of niobium is added to zirconium, and this small increase significantly increases the corrosion resistance of the material. The mechanical properties of the currently used alloy E-365, which, in addition to zirconium and niobium, contain iron and tin, have even better mechanical properties. Each step in the production of fuel rods is extremely important; the presence of these elements makes it possible to better cope with welding and other joining methods different materials. Fuel elements produced in Russia meet all IAEA requirements, show excellent performance properties, and make it possible to improve the economic indicators of nuclear energy.

What may seem like a “simple mechanical part”, of course, is not.

Fuel rod in section, Fig.: heuristic.su

Here short description fuel rod with contents inside. Length – 3.8 meters, outer diameter – 9.1 mm. Inside are uranium dioxide tablets with an outer diameter of 7.57 mm and a height of 20 mm; in the center of each tablet there is a hole with a diameter of 1.2 mm. The pellet does not touch the walls of the fuel rod; the gap and hole inside the pellets are designed so that the fuel rod can retain radioactive gases formed during nuclear decay. The pellets are fixed inside the fuel element with bushings, the total length of the column of pellets is 3.53 meters, during the fuel session the length increases by 30 mm. Yes, everything is measured in millimeters and even in their fractions - after all, nuclear energy deals with the smallest particles of matter.

Here is a tablet with a diameter of less than 8 mm - it would seem that there could be something interesting in it? But during nuclear reactions, the temperature in the central part of the tablet reaches 1'500-1'600 degrees, and on the outer surface - only 470. A difference of a thousand degrees at a distance of 3-4 millimeters, metal becoming gas - such are the miracles inside the tiny pills.

From fuel rod to fuel assembly

They made the tablets, placed them in the fuel rod - that’s it? Of course not - the tube together with fuel weighs only 2.1 kg, which is the mass of uranium on long work will not be enough. The next stage in the formation of nuclear fuel is the formation of fuel assemblies and fuel assemblies. For the most widespread reactor in Russia, VVER-1000, 312 fuel rods are assembled into one fuel assembly, and gaps are left between them for the entry of control and protection system rods filled with such an effective neutron absorber as boron. At the bottom of the fuel assembly there is a so-called shank - the place to which the fuel rods are attached.

Frame manufacturing - welding of channels and spacer grids

In the upper part, the fuel rods are attached to the head through a spring block - it protects the fuel rods from floating during reactor operation. Yes, uranium - heavy element, zirconium cannot be called light either, but it is worth remembering that the nominal flow rate of water through the fuel assembly is 500 cubic meters per hour, water moves along the fuel rods at a speed of 200 km/h in the direction from bottom to top - such a flow will make anything float up. The fuel rods are separated from each other using spacer grids, which hold these tubes in their regular places, ensuring the most efficient heat removal. There are from 12 to 15 spacer grids on fuel assemblies of different designs, only this number allows the water to do the job of removing useful heat.

Channels and spacer grids, quality control

And, nevertheless, even this did not completely save us from the problem of bending of fuel rods and fuel assemblies. Our assemblies could not withstand mechanical axial loads - almost four meters in length with a shell thickness of 0.65 mm, a powerful flow of water, and high temperatures did their job. In 1993, it became finally clear that something needed to be done about this problem, to find ways to get rid of it. Minatom made a corresponding request to the IAEA - what is the situation with this problem in Western countries. The IAGTE conducted a corresponding survey with operating organizations, and did not find any sensation - Western nuclear scientists also have this problem, they are also looking for ways to cope with it.

Now, excuse me, but once again we will have to touch on the main myth of liberal economics - the efficiency of the private owner in comparison with the clumsy, inertial state sector of the economy. There are a considerable number of private owners of nuclear power plants in the West, and especially in the USA, but they could not solve the problem. Minatom acted in accordance with the traditions of the Ministry of Medium Machine Building - it entrusted the solution of the problem to two design bureaus at once, so that as a result of the struggle of two good projects the victory went to the best. Participants in the capitalist competition were the Podolsk OKB (experimental design bureau) "Gidropress" and the Nizhny Novgorod OKBM (OKB Mashinostroeniya) named after. Afrikantova. Both design bureaus are currently part of the Atomenergomash machine-building holding, but this does not reduce the intensity of competition.

Competition is the engine of progress

Nizhny Novgorod residents developed a TVS design, which received the abbreviation TVSA; as development progressed, modifications of TVSA-12, TVSA-PLUS, TVSA-T appeared one after another. Its main characteristic feature is that corners began to be welded to the spacer grids to increase the rigidity of the structure, but Gidropress did not accept this concept - the excess amount of zirconium, from which the corners are made, in the core, according to experts, can negatively affect the neutron characteristics of the core reactor zones. The modification created at Gidropress with the abbreviation UTVS (Advanced TVS) does not use rigid welding of spacer grids and guide channels. UTVS began to be used at nuclear power plants with increased requirements for seismic resistance - at the Chinese Tianwan, at the Iranian Bushehr, at the Indian Kudankulam." However, to say that this development was made only by employees of the Gidropress Design Bureau is incorrect; the Kurchatov Institute, the Obninsk Physics and Energy Institute, the Novosibirsk Chemical Concentrates Plant, the Research Institute named after. Bochvara. But the result is important - the pilot test at the Rostov NPP showed excellent results, foreign customers were extremely pleased with the increased reliability of the UTVS.

Beam assembly

Watching the details of the battle between two design bureaus is a fascinating spectacle, but there are so many technical details that it will take some effort professional translators. Wide and narrow gratings, sparse gratings, turbulators and deflectors, gratings with oblique channels, heat transfer intensifiers, the speed of loading cassettes into the core, combination with the operation of reloading machines, terminology from hydrodynamics and thermomechanics - this is really a completely separate language... Important for nuclear energy the result achieved by both design bureaus, the scientific and creative dispute of which continues to this day. Improvements and modifications allow the use of fuel with higher enrichment in uranium-235 content - this figure for VVER-1000 increased from 3.77% to 4.95%. It would seem that the difference is completely insignificant, but as a result, the fuel burnup increased from 40 MW per day per kilogram of uranium to 58 MW per kilogram, almost 50%. But this result is already very significant; it allows us to compete on an equal footing with hydrocarbon energy in terms of the cost of electricity produced, and makes the prospects for the development of nuclear energy more and more encouraging. One of the achievements - increasing the power of existing VVER reactors by 4-7% without changing their design is based precisely on the optimization of nuclear fuel and fuel assemblies has become another competitive advantage on the international market.

Finished fuel assembly

Of course, UTVS did not become a kind of “final” for the improvement of fuel assemblies. The main advantage of UTVS compared to the previous generation fuel was provided by the transition from stainless steel to zirconium, to the E-110 alloy. The developers were able to increase the rigidity of the structure without the use of corners - they strengthened the spacer grids and began to use spot welding to increase resistance to deformation during operation. They managed to increase the length of the fuel column - now more uranium is placed in the reactor core, fuel sessions have become longer, fuel refueling can be carried out less frequently, which means an increase in capacity.

New fuel for Iran

Since the beginning of 2014, the negotiation process began between TVEL and the Iranian customer represented by Atomic Energy Organization of Iran (AEOI) And Iran Nuclear Power Production and Development Company (NPPD) on the transition of the Bushehr NPP to new fuel cassettes - TVS-2M. To ensure the negotiation process TVEL developed a “Feasibility study for the implementation of TVS-2M at the Bushehr NPP,” in which the customer was provided with a full amount of information for analysis and decision-making on such a transition. Most The best way Convincing a potential customer is not intrusive marketing; in nuclear energy, this approach almost never brings results. The Russian fuel company simply brought together an analysis of the results of the implementation of TVS-2M at the Russian VVER-1000 and at the Tianwan NPP in China - reactors of the same type as those operating as part of the power unit at the Bushehr NPP. In China, the first two units of the Tianwan NPP operate on TVS-2M in an 18-month fuel cycle. And Iranian nuclear scientists were able to verify that the fuel burn-up increased, the duration of fuel campaigns increased, and the capacity factor increased.

After analyzing the results obtained and checking them on site, the Iranian customers made a response - they developed a list of works by Russian enterprises, which is necessary to ensure licensing of the new fuel by nuclear regulatory authorities. Further work was already joint - our and Iranian specialists together compiled a list of necessary upgrades to the equipment of the power unit at the Bushehr NPP, which needed to be carried out so that the reactor could accept TVS-2M into the core. As a matter of fact, the operation of our VVER-1000 on the new fuel showed such results that a complete transition to TVS-2M became simply inevitable - fuel burnup increased by 20%, and the fuel component of the cost of electricity production decreased by almost 9%.

The outcome of the negotiations with the Iranian customer is quite natural. In April this year TVEL signed with AEOI And NPPD additional agreement to the current contract for fuel supply to the Bushehr NPP - from 2020 TVEL will begin supplies of TVS-2M to Iran. There is no rush, no fuss - simply both ours and the Iranian nuclear projects we support continue to develop consistently, providing consumers with electricity in the volumes they need. We will probably find out what customers in India and China think about this in the near future. Height economic indicators power units due to the use of new fuel without significant changes in the equipment set is so indicative that there is confidence that reflection will not take long. We just have to keep an eye on further development events and congratulate you again TVEL, OKB Gidropress and the entire development team with the fact that their new fuel has now received international recognition.

Of course, today's story about the development of nuclear fuel is far from complete - changes in this part are constantly taking place. Fuel for VVER-1200 has been developed, development of fuel for other types of reactors is underway, TVEL continues to produce fuel for Western-design reactors together with French partners, TVEL independently developed TVS-Kvadrat fuel, which is being tested at the Swedish Ringhals nuclear power plant and licensed for the American market. Enterprises TVEL are producing fuel for the BN-800, a pilot batch of REMIX fuel has been produced, and the development of nitride fuel is nearing completion for a promising lead-cooled reactor - Rosatom and doesn't think he can afford to rest on his laurels.

Nuclear fuel is the “heart” of nuclear energy; monitoring how new types of it are created and what results they give when using them is useful in that it allows you to compare the cost of generating electricity at nuclear power plants and at thermal power plants. In addition, this time we did not touch upon what results the developers of new types of fuel at OKBM im. Afrikantova – and their ideas are also very actively used Rosatom. In a word, today’s story about nuclear fuel is unlikely to remain the only one.

Photo: zaochnik.ru, kak-eto-sdelano.livejournal.com

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Nuclear fuel is a material used in nuclear reactors to carry out a controlled chain reaction. It is extremely energy-intensive and unsafe for humans, which imposes a number of restrictions on its use. Today we will learn what nuclear reactor fuel is, how it is classified and produced, and where it is used.

Progress of the chain reaction

During a nuclear chain reaction, the nucleus splits into two parts, which are called fission fragments. At the same time, several (2-3) neutrons are released, which subsequently cause the fission of subsequent nuclei. The process occurs when a neutron hits the nucleus of the original substance. Fission fragments have high kinetic energy. Their inhibition in matter is accompanied by the release of a huge amount of heat.

Fission fragments, together with their decay products, are called fission products. Nuclei that share neutrons of any energy are called nuclear fuel. As a rule, they are substances with an odd number of atoms. Some nuclei are fissioned purely by neutrons whose energy is above a certain threshold value. These are predominantly elements with an even number of atoms. Such nuclei are called raw material, since at the moment of capture of a neutron by a threshold nucleus, fuel nuclei are formed. The combination of combustible material and raw material is called nuclear fuel.

Classification

Nuclear fuel is divided into two classes:

1. Natural uranium. It contains fissile uranium-235 nuclei and uranium-238 feedstock, which is capable of forming plutonium-239 upon neutron capture.
2. A secondary fuel not found in nature. This includes, among other things, plutonium-239, which is obtained from fuel of the first type, as well as uranium-233, which is formed when neutrons are captured by thorium-232 nuclei.

From point of view chemical composition, there are the following types of nuclear fuel:

1. Metal (including alloys);
2. Oxide (for example, UO 2);
3. Carbide (for example PuC 1-x);
4. Mixed;
5. Nitride.

TVEL and TVS

Fuel for nuclear reactors is used in the form of small pellets. They are placed in hermetically sealed fuel elements (fuel elements), which, in turn, are combined into several hundred fuel assemblies (FA). Nuclear fuel is subject to high requirements for compatibility with fuel rod claddings. It must have a sufficient melting and evaporation temperature, good thermal conductivity, and not greatly increase in volume under neutron irradiation. The manufacturability of production is also taken into account.

Application

To nuclear power plants and others nuclear installations fuel comes in the form of fuel assemblies. They can be loaded into the reactor both during its operation (in place of burnt-out fuel assemblies) and during a repair campaign. In the latter case, fuel assemblies are replaced in large groups. In this case, only a third of the fuel is completely replaced. The most burned-out assemblies are unloaded from the central part of the reactor, and in their place are placed partially burned-out assemblies that were previously located in less active areas. Consequently, new fuel assemblies are installed in place of the latter. This simple rearrangement scheme is considered traditional and has a number of advantages, the main one of which is ensuring uniform energy release. Of course, this is a schematic diagram that gives only a general idea of ​​the process.

Excerpt

After spent nuclear fuel is removed from the reactor core, it is sent to a cooling pool, which is usually located nearby. The fact is that spent fuel assemblies contain a huge amount of uranium fission fragments. After unloading from the reactor, each fuel rod contains about 300 thousand Curies of radioactive substances, releasing 100 kW/hour of energy. Due to this, the fuel self-heats and becomes highly radioactive.

The temperature of newly unloaded fuel can reach 300°C. Therefore, it is kept for 3-4 years under a layer of water, the temperature of which is maintained in the established range. As it is stored under water, the radioactivity of the fuel and the power of its residual emissions decreases. After about three years, self-heating of the fuel assembly reaches 50-60°C. Then the fuel is removed from the pools and sent for processing or disposal.

Uranium metal

Uranium metal is used relatively rarely as fuel for nuclear reactors. When a substance reaches a temperature of 660°C, a phase transition occurs, accompanied by a change in its structure. Simply put, uranium increases in volume, which can lead to the destruction of fuel rods. In the case of prolonged irradiation at a temperature of 200-500°C, the substance undergoes radiation growth. The essence of this phenomenon is the elongation of the irradiated uranium rod by 2-3 times.

The use of uranium metal at temperatures above 500°C is difficult due to its swelling. After nuclear fission, two fragments are formed, the total volume of which exceeds the volume of that very nucleus. Some fission fragments are represented by gas atoms (xenon, krypton, etc.). Gas accumulates in the pores of the uranium and forms internal pressure, which increases as the temperature increases. Due to an increase in the volume of atoms and an increase in gas pressure, nuclear fuel begins to swell. Thus, this refers to the relative change in volume associated with nuclear fission.

The strength of swelling depends on the temperature of the fuel rods and burnout. With increasing burnup, the number of fission fragments increases, and with increasing temperature and burnup, the internal gas pressure increases. If the fuel has higher mechanical properties, then it is less susceptible to swelling. Uranium metal is not one of these materials. Therefore, its use as fuel for nuclear reactors limits the burnup, which is one of the main characteristics of such fuel.

The mechanical properties of uranium and its radiation resistance are improved by alloying the material. This process involves adding aluminum, molybdenum and other metals to it. Thanks to doping additives, the number of fission neutrons required per capture is reduced. Therefore, materials that weakly absorb neutrons are used for these purposes.

Refractory compounds

Some refractory uranium compounds are considered good nuclear fuel: carbides, oxides and intermetallic compounds. The most common of these is uranium dioxide (ceramics). Its melting point is 2800°C, and its density is 10.2 g/cm 3 .

Since this material does not undergo phase transitions, it is less susceptible to swelling than uranium alloys. Thanks to this feature, the burnout temperature can be increased by several percent. At high temperatures, ceramics do not interact with niobium, zirconium, stainless steel and other materials. Her main drawback lies in the low thermal conductivity - 4.5 kJ (m*K), which limits the specific power of the reactor. In addition, hot ceramics are prone to cracking.

Plutonium

Plutonium is considered a low-melting metal. It melts at a temperature of 640°C. Due to its poor plastic properties, it is practically impossible to machine. The toxicity of the substance complicates the manufacturing technology of fuel rods. The nuclear industry has repeatedly attempted to use plutonium and its compounds, but they have not been successful. It is not advisable to use fuel for nuclear power plants containing plutonium due to an approximately 2-fold reduction in the acceleration period, which standard reactor control systems are not designed for.

For the manufacture of nuclear fuel, as a rule, plutonium dioxide, alloys of plutonium with minerals, and a mixture of plutonium carbides and uranium carbides are used. Dispersion fuels, in which particles of uranium and plutonium compounds are placed in a metal matrix of molybdenum, aluminum, stainless steel and other metals, have high mechanical properties and thermal conductivity. The radiation resistance and thermal conductivity of the dispersion fuel depend on the matrix material. For example, at the first nuclear power plant, the dispersed fuel consisted of particles of a uranium alloy with 9% molybdenum, which were filled with molybdenum.

As for thorium fuel, it is not used today due to difficulties in the production and processing of fuel rods.

Production

Significant volumes of the main raw material for nuclear fuel - uranium - are concentrated in several countries: Russia, the USA, France, Canada and South Africa. Its deposits are usually located near gold and copper, so all these materials are mined at the same time.

The health of people working in mining is at great risk. The fact is that uranium is a toxic material, and the gases released during its mining can cause cancer. And this despite the fact that the ore contains no more than 1% of this substance.

Receipt

The production of nuclear fuel from uranium ore includes the following stages:

1. Hydrometallurgical processing. Includes leaching, crushing and extraction or sorption recovery. The result of hydrometallurgical processing is a purified suspension of oxyuranium oxide, sodium diuranate or ammonium diuranate.
2. Conversion of a substance from oxide to tetrafluoride or hexafluoride, used to enrich uranium-235.
3. Enrichment of a substance by centrifugation or gas thermal diffusion.
4. Conversion of enriched material into dioxide, from which fuel rod “pellets” are produced.

Regeneration

During operation of a nuclear reactor, fuel cannot be completely burned out, so free isotopes are reproduced. In this regard, spent fuel rods are subject to regeneration for the purpose of reuse.

Today, this problem is solved through the Purex process, consisting of the following stages:

1. Cutting fuel rods into two parts and dissolving them in nitric acid;
2. Cleaning the solution from fission products and shell parts;
3. Isolation of pure compounds of uranium and plutonium.

After this, the resulting plutonium dioxide is used for the production of new cores, and the uranium is used for enrichment or also for the production of cores. Reprocessing nuclear fuel is a complex and expensive process. Its cost has a significant impact on the economic feasibility of using nuclear power plants. The same can be said about the disposal of nuclear fuel waste that is not suitable for regeneration.

Operating principle and design of TURD

Currently, 2 design options for TURD are proposed:

TNR based on a thermonuclear reactor with magnetic plasma confinement

In the first case, the principle of operation and design of the TNRE are as follows: the main part of the engine is the reactor in which a controlled thermonuclear fusion reaction occurs. The reactor is a hollow cylindrical “chamber”, open on one side, the so-called. an “open trap” thermonuclear fusion installation (also called a “magnetic bottle” or a mirror chamber). The reactor “chamber” does not necessarily (and even undesirably) need to be completely sealed; most likely, it will be a lightweight, size-stable truss that carries the coils of the magnetic system. Currently, the so-called scheme is considered the most promising. "ambipolar confinement" or "magnetic mirrors" (eng. tandem mirrors), although other confinement schemes are possible: gas-dynamic traps, centrifugal confinement, reversed magnetic field (FRC). By modern estimates, the length of the reaction “chamber” will be from 100 to 300 m with a diameter of 1-3 m. Conditions are created in the reactor chamber sufficient to begin the thermonuclear fusion of the components of the selected fuel pair (temperatures of the order of hundreds of millions of degrees, Lawson criterion factors). Thermonuclear fuel - preheated plasma from a mixture of fuel components - is fed into the reactor chamber, where a constant fusion reaction occurs. Magnetic field generators (magnetic coils of one design or another) surrounding the core create fields of high intensity and complex configuration in the reactor chamber, which keep high-temperature thermonuclear plasma from contact with the reactor structure and stabilize the processes occurring in it. The thermonuclear “burning” zone (plasma torch) is formed along the longitudinal axis of the reactor. The resulting plasma, guided by magnetic control systems, flows out of the reactor through a nozzle, creating jet thrust.

It should be noted the possibility of “multi-mode” operation of the TURD. By injecting a relatively cold substance into the plasma plume jet, the overall thrust of the engine can be sharply increased (by reducing the specific impulse), which will allow a ship with a turboprop engine to effectively maneuver in the gravitational fields of massive celestial bodies, such as large planets, where a large total thrust of the engine is often required. According to general estimates, a nuclear-powered engine of such a design can develop thrust from several kilograms up to tens of tons with a specific impulse from 10,000 sec to 4 million sec. For comparison, the specific impulse of the most advanced chemical rocket engines is about 450 seconds.

TURD based on inertial fusion systems (pulse thermonuclear reactor)

The engine of the second type is an inertial pulsed thermonuclear engine. In such a reactor, a controlled thermonuclear reaction occurs in a pulsed mode (fractions of a microsecond with a frequency of 1-10 Hz), with periodic compression and heating of microtargets containing thermonuclear fuel. Initially, it was planned to use a laser fusion engine (LTYARD). Such a LTE was proposed, in particular, for an interstellar automatic probe in the Daedalus project. Its main part is a reactor operating in pulsed mode. Thermonuclear fuel (for example, deuterium and tritium) is supplied into the spherical chamber of the reactor in the form of targets - a complex design of spheres from a mixture of frozen fuel components in a shell with a diameter of several millimeters. On the outer part of the chamber there are powerful - on the order of hundreds of terawatt - lasers, a nanosecond pulse of radiation from which hits the target through optically transparent windows in the walls of the chamber. In this case, a temperature of more than 100 million degrees is instantly created on the surface of the target at a pressure of about a million atmospheres - conditions sufficient for the start of a thermonuclear reaction. A thermonuclear micro-explosion with a power of several hundred kilograms of TNT occurs. The frequency of such explosions in the chamber in the Daedalus project is about 250 per second, which required feeding fuel targets at a speed of more than 10 km/s using an EM gun. Expanding plasma flows from the open part of the reactor chamber through a nozzle of a suitable design, creating jet thrust. It has now been theoretically and practically proven that laser method compression/heating of microtargets is a dead end - including it is almost impossible to build lasers of such power with a sufficient resource. Therefore, the option with ion-beam compression/heating of microtargets is currently being considered for inertial synthesis, as it is more efficient, compact and with a much longer resource.

And yet, there is an opinion that a TURE based on the inertial-pulse principle is too bulky due to the very large powers circulating in it, with a worse specific impulse and thrust than a TURE with magnetic confinement, which is caused by the pulse-periodic type of its action . Ideologically, explosive rockets based on thermonuclear charges such as the Orion project are adjacent to TUREs based on the inertial-pulse principle.

Types of reactions and fusion fuel

TJARD can use different kinds thermonuclear reactions depending on the type of fuel used. In particular, the following types of reactions are currently fundamentally feasible:

Deuterium + tritium reaction (D-T fuel)

2 H + 3 H = 4 He + n at an energy output of 17.6 MeV

This reaction is most easily feasible from the point of view modern technologies, provides a significant energy output, fuel components are relatively cheap. Its disadvantage is a very large output of unwanted (and useless for direct generation of thrust) neutron radiation, which carries away most of the reaction power and sharply reduces the efficiency of the engine. Tritium is radioactive, its half-life is about 12 years, that is, its long-term storage is impossible. At the same time, it is possible to surround a deuterium-tritium reactor with a shell containing lithium: the latter, irradiated by a neutron flux, turns into tritium, which to a certain extent closes the fuel cycle, since the reactor operates in breeder mode. Thus, the fuel for a D-T reactor is actually deuterium and lithium.

Reaction deuterium + helium-3

2 H + 3 He = 4 He + p. with an energy output of 18.3 MeV

The conditions for achieving it are much more complicated. Helium-3 is also a rare and extremely expensive isotope. IN industrial scale not currently produced. Although the energy output D-T reactions above, the D-3He reaction has the following advantages:

Reduced neutron flux, the reaction can be classified as “neutronless”,

Less radiation protection mass,

Less weight of the reactor magnetic coils.

During the D-3 He reaction, only about 5% of the power is released in the form of neutrons (versus 80% for the D-T reaction). About 20% is released in the form of x-rays. All remaining energy can be directly used to create jet thrust. Thus, the D-3He reaction is much more promising for use in a nuclear power reactor.

Other types of reactions

Reaction between deuterium nuclei (D-D, monopropellant) D + D -> 3 He + n with an energy yield of 3.3 MeV, and

D + D -> T + p+ with an energy output of 4 MeV. The neutron yield in this reaction is quite significant.

Some other types of reactions are possible:

P + 6 Li → 4 He (1.7 MeV) + 3 He (2.3 MeV) 3 He + 6 Li → 2 4 He + p + 16.9 MeV p + 11 B → 3 4 He + 8.7 MeV

There is no neutron yield in the above reactions.

The choice of fuel depends on many factors - its availability and low cost, energy output, ease of achieving the conditions required for the thermonuclear fusion reaction (primarily temperature), the necessary design characteristics of the reactor, etc. The most promising for the implementation of nuclear powered rocket engines are the so-called. “neutronless” reactions, since the neutron flux generated by thermonuclear fusion (for example, in the deuterium-tritium reaction) carries away a significant part of the power and cannot be used to create thrust. In addition, neutron radiation generates induced radioactivity in the structure of the reactor and ship, creating a danger for the crew. The deuterium-helium-3 reaction is promising due to the lack of neutron yield. Currently, another concept of TNRE has been proposed - using small amounts of antimatter as a catalyst for a thermonuclear reaction.

History, current state and prospects for TURD development

The idea of ​​creating a TNRE appeared almost immediately after the first thermonuclear reactions (testing of thermonuclear charges). One of the first publications on the topic of TURD development was an article by J. Ross published in 1958. Currently, theoretical developments of such types of engines are underway (in particular, based on laser thermonuclear fusion) and, in general, extensive practical research in the field of controlled thermonuclear fusion. There are solid theoretical and engineering prerequisites for the implementation of this type of engine in the foreseeable future. Based on the calculated characteristics of TNREs, such engines will be able to ensure the creation of high-speed and efficient interplanetary transport for the exploration of the Solar system. However, real samples of TNRE have not yet been created at the moment (2012).

see also

Links

• Cosmonautics of the XXI century: thermonuclear engines // newspaper “For Science”, 2003
• New Scientist Space (01/23/2003): Nuclear fusion could power NASA spacecraft (English)
• Physical Encyclopedia, vol. 4, article “thermonuclear reactions”, on page 102, Moscow, “Big Russian Encyclopedia”, 1994, 704 p.