Nuclear fuel for nuclear power plants. Nuclear power plants

The use of nuclear fuel in reactors for the production of thermal energy has a number of important features due to the physical properties and the nuclear nature of the processes. These features determine the specifics of nuclear energy, the nature of its technology, special operating conditions, economic indicators and impact on environment. They also determine the main scientific, technical and engineering problems that must be solved with the widespread development of reliable, economical and safe nuclear technology.

The most important features of nuclear fuel, manifested in its energy use:

1. high calorific value, i.e. heat release per unit mass of separated nuclides;

2. the impossibility of complete "burning" (fission) of all fissile nuclides for a one-time stay of fuel in the reactor, since in the reactor core, it is always necessary to have a critical mass of fuel and it is possible to “burn” only that part of it that exceeds the critical mass;

3. the ability to have partial, under certain conditions, complete and even extended reproduction (conversion) of fissile nuclides, i.e. obtaining secondary nuclear fuel from reproducing nuclear materials (238 U and 232 Th);

4. “burning” of nuclear fuel in a reactor does not require an oxidizing agent and is not accompanied by continuous discharge of “combustion” products into the environment;

5. the fission process is simultaneously accompanied by the accumulation of radioactive short-lived and long-lived fission products, as well as decay products, long time preserving high level radioactivity. Thus, the fuel irradiated in the reactor and spent in it has an extremely high radioactivity and, as a result, decay heat, which creates special difficulties in handling irradiated nuclear fuel;

6. chain reaction of fission of nuclear fuel is accompanied by the release of huge fluxes of neutrons. Under the influence of high-energy neutrons (E>0.1 MeV) in the irradiated structural materials of the reactor (fuel cladding, fuel assembly parts, in-reactor devices, vessel), as well as in the coolant and biological protection materials, in the gaseous atmosphere filling the space between the reactor and its biological protection, many chemically stable (non-radioactive) elements are converted into radioactive ones. There is a so-called induced activity.

The high heat generating capacity of nuclear fuel is due to the significant intranuclear energy released during each act of fission of a heavy atom of uranium or plutonium. During the combustion of fossil fuels, chemical oxidative processes take place, accompanied by a relatively low energy release.

During the combustion (oxidation) of a carbon atom, in accordance with the reaction C + O 2 → CO 2, about 4 eV of energy is released for each act of interaction, while during the fission of the nucleus of the uranium atom 235 U + n → X 1 + X 2, about 200 MeV of energy per fission event. Such a highly concentrated release of energy per unit mass leads to huge thermal stresses. The temperature difference along the radius of the fuel element reaches several hundred degrees.

In addition, the core materials experience enormous dynamic and radiation loads due to the coolant flow and the powerful radiation effect on the fuel and structural materials of high-density ionizing radiation flows. In particular, the radiation action of fast neutrons causes significant radiation damage in the structural materials of the reactor (embrittlement, swelling, increased creep). Therefore, the materials used in reactors are subject to special requirements. One of them is the highest degree of purity from impurities (the so-called nuclear-grade materials). Due to this, the cross section of interaction and absorption (which is important for maintaining a fission chain reaction) of neutrons by materials is minimal.

The level of requirements for the composition and properties of materials used in reactor construction turned out to be so high that it initiated the development of a number of new and advanced technologies for the production of special materials and semi-finished products, as well as special methods and means for controlling their quality. At present, a technology has been developed and mastered for the industrial production of such materials as beryllium, graphite of nuclear purity, heavy water, zirconium and niobium alloys, calcium metal, boron and heat-resistant stainless steels, boron enriched with the 10 V isotope, and rare earth elements.

The high caloric content causes a sharp reduction in both the mass and physical volumes of nuclear fuel required to produce a given amount of energy. Thus, the storage and transportation of the feedstock (chemical concentrate of natural uranium) and finished fuel require relatively low costs. The consequence of this is the independence of the location of nuclear power plants from the area of production and manufacture of nuclear fuel, which significantly affects the choice of an economically advantageous geographical location of productive forces. In this sense, one can speak of the universal character of nuclear fuel. Its nuclear-physical properties are the same everywhere, and the economy of use practically does not depend on the distance to the consumer. The ability not to link the location of nuclear power plants with the place of production and manufacture of nuclear fuel makes it possible to economically optimally locate them throughout the country, bringing them as close as possible to consumers of electrical and thermal energy. Compared to fossil fuel power plants, nuclear power plants do not experience difficulties associated with seasonal climatic conditions for the delivery and supply of fuel. Nuclear materials extracted from the subsoil and undergoing processing can be stored for any number of years at very low cost, without requiring large and expensive storage facilities.

The need for repeated circulation of nuclear fuel in the fuel cycle and the impossibility of its complete combustion during a one-time stay in the reactor is due to the need to maintain a fission chain reaction. A self-sustaining chain reaction in the core is possible only if there is a critical mass of fissile material in it in a given configuration and under certain conditions for slowing down and absorbing neutrons. Therefore, in order to obtain thermal energy in the reactor, when operating at the design power for a given time, it is necessary to have some excess of fissile nuclides in the core in excess of the critical mass. This excess creates a reactivity margin of the reactor core, which is necessary to achieve the specified or calculated fuel burnup. Burnup of nuclear fuel in the reactor core is called the process of spending fissile nuclides, primary and secondary, as a result of fission during their interaction with neutrons. Burnup is usually determined by the amount of released thermal energy or the amount (mass) of separated nuclides per unit mass of fuel loaded into the reactor. Therefore, in order to burn a certain amount of uranium in a reactor, it is necessary to load it with fuel having a significantly larger mass than the critical one. In this case, after reaching the specified burnup depth, when the reactivity margin is exhausted, it is necessary to replace the spent fuel with fresh fuel in order to maintain the fission chain reaction. The requirement to constantly keep in the reactor core a large mass of nuclear fuel, designed for a long period of operation to ensure a given power output, causes significant one-time costs for paying for the first fuel load and subsequent batches prepared for refueling. This is one of the essential and fundamental differences between the conditions for the use of nuclear fuel in power plants in comparison with organic fuel.

However, the spent fuel removed from the core will contain significant amounts of fissile materials and fertile nuclides of significant value. This fuel, after chemical purification from fission products, can be returned to the fuel cycle for reuse. The amount of fissile nuclides in the spent fuel, which remains unused during its one-time stay in the reactor, depends on the type of reactor and on the type of fuel and can be up to 50% of those initially loaded. Naturally, such valuable "waste" must be used. For this purpose, special technical means and facilities for the storage, transportation and chemical recovery of spent fuel (SFA). Fissile materials extracted from SFAs can be returned and repeatedly circulated through reactors and fuel plants nuclear industry: radiochemical plants that ensure the regeneration (purification of fission products and impurities) of the fuel unloaded from the reactor and its return to the fuel cycle after the necessary additional enrichment with fissile nuclides; steel plants for the production of new fuel elements, in which regenerated fuel is added to fresh, not irradiated in reactors. Thus, characteristic feature fuel supply in nuclear power is the technical possibility and the need to return to the cycle (recycle) not used in the conditions of a single stay in the reactor fissile and fertile isotopes of uranium and plutonium. To ensure uninterrupted fuel supply, the necessary capacities of fuel cycle enterprises are being created. They can be considered as enterprises that satisfy the "own needs" of nuclear energy as an industry. The concept of development of nuclear power engineering based on nuclear fuel breeder reactors is based on the possibility of recycling uranium and plutonium. In addition, the recycling of uranium and plutonium significantly reduces the need for natural uranium and for uranium enrichment capacity for thermal neutron reactors, which currently dominate the developing nuclear power industry. As long as there is no reprocessing of spent fuel, there is no recycling of uranium and plutonium. This means that thermal reactors can only be powered by fresh fuel derived from mined and processed uranium, while the spent fuel will be stored.

Breeding of nuclear fuel takes place in almost any reactor designed for energy production, which, along with fissile materials, contains fertile raw materials (238 U and 232 Th). If we do not consider the hypothetical case of using super-enriched (~ 90%) uranium fuel for some special reactors, then in all nuclear reactors used in the power industry, there will be a partial, and under certain conditions, complete and even expanded reproduction of nuclear fuel - plutonium isotopes, having the same high calorific value as 235 U. Plutonium can be separated from spent fuel in chemical processing plants in its pure form and used to make mixed uranium-plutonium fuel. The possibility of producing plutonium in any thermal neutron reactor makes it possible to qualify any nuclear power plant as a dual-purpose enterprise: generating not only thermal and electrical energy, but also producing new nuclear fuel- plutonium. However, the role of plutonium is manifested not only in its accumulation in spent fuel. A significant part of the resulting fissile isotopes of plutonium undergoes fission in the reactor, improving the fuel balance and contributing to an increase in the burnup of the fuel loaded into the core. The most expedient, according to today's ideas, is the use of plutonium in fast neutron reactors, where it makes it possible to provide a gain in critical mass, and, consequently, in loading compared to 235 U by 20-30% and to obtain very high coefficients exceeding unity. reproduction. The use of plutonium in the fuel load of thermal neutron reactors, although it does not make it possible to obtain a significant gain in critical mass and such high breeding rates as in fast neutron reactors, however, creates a great effect by increasing nuclear fuel resources.

In nuclear energy, in addition to uranium, there are opportunities for the development of thorium fuel cycles. At the same time, the natural isotope 232 Th is used to produce 233 U, which is similar in its nuclear properties to 235 U. However, at present it is difficult to expect any significant use of the uranium-thorium cycle in nuclear power engineering. This is explained by the fact that 232 Th, like 238 U, is only a fertile, but not fissile material, and the thorium processing technology has a number of specific features and has not yet been developed on an industrial scale. At the same time, there is no shortage of natural uranium yet. Moreover, there is a continuous accumulation in warehouses of waste uranium ready for use as a fertile material in breeder reactors.

The absence of the need for an oxidizer to generate energy is one of the key environmental benefits of using nuclear power compared to hydrocarbons. Gas emissions from nuclear power plants are mainly due to the needs of the station's ventilation systems. Unlike nuclear power plants, millions of cubic meters of combustion gases are released into the air every year. These include, first of all, oxides of carbon, nitrogen and sulfur, which destroy the ozone layer of the planet and create a great burden on the biosphere of adjacent territories.

Unfortunately, in addition to the advantages of nuclear energy, there are also disadvantages. These include, in particular, the formation of fission and activation products during the operation of a nuclear reactor. Such substances interfere with the operation of the reactor itself and are radioactive. However, the volume of generated radioactive waste is limited (much orders of magnitude less than waste from thermal plants). In addition, there are proven technologies for their purification, extraction, conditioning, safe storage and disposal. A number of radioactive isotopes extracted from spent fuel are actively used in industrial and other technologies. At further development technologies for reprocessing SFAs, there are also prospects for the extraction of fission products from it - rare earth elements of great value.

Selection from the book: "Nuclear energy. Did you ask? We answer!"

Akatov A. A., Koryakovsky Yu. S. 2012

Why does Russia need a nuclear industry?

Historically, the main reason for the emergence of the nuclear industry in our country was the creation of nuclear weapons. Was there a significant need for this? In 1945, by dropping nuclear warheads on Hiroshima and Nagasaki, the United States made it clear who was "in charge" on the world stage. The cities of the USSR could well have shared the fate of the Japanese, although now this may seem like an exaggeration. IN as soon as possible our scientists were able to create their own nuclear weapons and restore the balance of power, but almost in parallel with the nuclear defense sphere, nuclear energy began to develop, nuclear power plants began to be built, designed to generate electricity through a fission chain reaction. Gradually, the “peaceful” atom replaced the “military” atom, and at the moment our country does not need to develop nuclear charges for weapons. So now the most important task industry is to provide Russian consumers with electricity in the face of a growing energy shortage.

When did the first nuclear power plant in the history of mankind give industrial current?

In the field of peaceful use atomic energy we were ahead of the Americans: the first nuclear power plant gave industrial current on June 27, 1954. This event took place not far from Moscow - in the city of Obninsk, on the territory of the Physico-Energy Institute. A.I. Leipunsky. The first nuclear power plant, the “old lady”, as it was called in the last years of operation, worked successfully for 48 years, and was stopped relatively recently, in 2002. The Institute of Physics and Power Engineering exists to this day, being one of the largest scientific centers our country.

Is nuclear fuel just uranium?

Of course not. Almost all over the world, nuclear fuel is used based on uranium enriched in the so-called fissile isotope - uranium-235. The content of uranium-235 in uranium, from which the fuel is made, is 3-5%, and the remaining 95-97% is non-fissile uranium-238. But metal uranium is not loaded into the reactors, it is converted into the form of dioxide (UO2), from which pellets are stamped. Tablets are placed in metal tubes, which are called fuel elements, or fuel rods. The fuel elements are combined into fuel assemblies (FA). The fuel assemblies are the modules that are loaded into or unloaded from the reactor when the fuel is changed.

What is the "nuclear fuel cycle"?

In this case we are talking not about the mathematical or physical concept of a cycle. In industry, a cycle is commonly referred to as a group of enterprises that are closely related to each other. For example, like this: a product produced by one of the enterprises is a raw material for another. In the nuclear industry, a group of industries has been formed that solves problems related to the manufacture and use of nuclear fuel. The work of nuclear fuel cycle enterprises is organized as follows. First, uranium ore is extracted from the bowels, uranium is cleaned of unnecessary impurities, enriched in the desired isotope (uranium-235) and converted into a form suitable for "burning" in a nuclear reactor - into the form of nuclear fuel. For several years, the fuel "works" in the reactor, due to which nuclear power plant electricity is generated, nuclear icebreakers and submarines sail the seas and oceans, and scientists make new discoveries. After being in the reactor, the fuel (now called spent nuclear fuel) is highly radioactive and contains valuable components that were formed during the nuclear reaction. It must be safely processed, valuable materials isolated, and the resulting radioactive waste converted into a safe form and buried. These tasks are also solved by enterprises that are part of the nuclear fuel cycle. Russian Federation the corresponding production facilities are merged into the Atomenergo holding.

Why people get rich, we know. Why is uranium enriched?

In a nuclear reactor, a self-sustaining nuclear fission chain reaction takes place. It happens like this: a neutron enters the uranium-235 nucleus, it is divided into two parts and emits 2-3 neutrons that fall into the neighboring uranium-235 nuclei, they also divide - and the reaction supports itself. But if there are few such nuclei nearby, then neutrons may not get into them - and the reaction will not go. Thus, the performance of a nuclear reactor is determined by the concentration of uranium-235 nuclei in the core. Natural uranium contains 99.3% non-fissile uranium-238 and only 0.7% fissile uranium-235. And if fuel from natural uranium is loaded into the reactor, then the nuclear reaction will not proceed. Therefore, natural uranium is enriched, the content of uranium-235 is adjusted to 3-5%. (Uranium itself, of course, cannot be enriched, the help of specialists is needed). For the sake of justice, it must be said that there are reactors operating on fuel with a natural content of uranium-235. But they use heavy water, the production of which also requires certain costs.

How many nuclear power units are there in Russia and in the world?

Our country has 10 nuclear power plants with 33 nuclear power units. The share of electricity generated at Russian nuclear power plants is about 17% of the total, and almost coincides with the world average - 15%. All our nuclear power plants, with the exception of Bilibino, are located in the European part of the country. The reactors of the earliest nuclear power plants are periodically upgraded to bring them into line with ever-tightening safety requirements. In July 2012, 433 nuclear power units were in operation around the world.

Are the same reactors installed at Russian nuclear power plants, or not?

The nuclear power industry of our country is mainly represented by three types of reactors:

RBMK (high power channel reactor)

VVER (pressure-cooled power reactor)

BN (Fast Neutron Reactor) RBMK type reactors are installed at single-loop nuclear power plants with water coolant. They use graphite as a neutron moderator, which is why these reactors are also called uranium-graphite reactors. At the Bilibino nuclear power plant younger brothers RBMK - EGP reactors with a similar principle of operation. VVER-type reactors operate at double-circuit nuclear power plants; water circulates in both the first and second circuits. These reactors are called water-cooled reactors, since water is both a coolant and a neutron moderator at the same time. Newly built units will be equipped with next-generation VVER reactors, more powerful and safer. And we still have only one BN reactor, although a second large fast neutron reactor will be launched in the coming years. But these types of reactors are the future, as they allow more complete use of uranium reserves.

How long does nuclear fuel "work" in a reactor?

The uranium fuel loaded into the reactor works for 3-4 years. For the annual operation of a large nuclear power unit, only a few tens of tons of low-enriched uranium are required. For comparison, a coal-fired station that generates an equivalent amount of electricity consumes five trains of coal, but not per year, but ... per day.

Why not replace nuclear power plants with "windmills"?

Wind energy is too scattered and difficult to collect. It makes sense to install "windmills" in those regions where steady strong winds blow. These are deserts, sea coasts, and in our country they occupy only 10% of the country's area. And we are talking, as a rule, about remote territories, from where it is very far to the nearest consumer of electricity. Of course, this type of energy is not "forbidden". There are areas on the map of Russia where it is really advisable to install wind farms. But they are not yet able to solve the problem of energy supply throughout the country, and especially on the scale of large metropolitan areas.

Let's stop all nuclear power plants!

After Chernobyl accident and the recent accident at the Fukushima-I nuclear power plant in Japan, the opinion circulated in society that if the reactors at all nuclear power plants were shut down, this would significantly reduce the risks. However, people who think so forget about important role Nuclear power plants in the power supply of large regions. For example, the Leningrad NPP produces a third of the electricity consumed in the Northwestern Federal District. What to replace it with? Still increase the combustion of gas, fuel oil, coal? This will entail additional environmental, economic and transport risks. And one more thing: by shutting down all nuclear power plants, we will not reduce, but, on the contrary, increase radiation risks. The problem of spent nuclear fuel and accumulated radioactive waste will not disappear anywhere, but will only grow, since a shutdown nuclear power unit cannot be left to fate. It will be necessary to simultaneously launch several complex and costly programs for the decommissioning of nuclear power units, including the cleaning of objects from radioactive contamination and the dismantling of equipment that is a powerful source of radiation. And the resulting radioactive waste cannot be thrown into a landfill - the question of where to place it will also require a solution.

How many specialists manage the operation of the power unit?

If we compare a nuclear power unit and a person, then the reactor can be called the heart, and the unit control panel (BCR) can be called the brain. From here, the operators - high-class professionals - control the processes occurring in the reactor, the operation of the steam turbine and the power unit as a whole. There are three of them, and each sits at his own remote control. In addition, the head of the block shift or his deputy is located in the control room, but they do not take a direct part in the management, rather performing the function of observers with the right to intervene, for example, when an error is detected in the actions of the operator. Only 4-5 people. It seems that this is not enough for such a responsible task? But at Western nuclear power plants, only two employees perform similar functions, while a number of tasks are shifted to automation.

How quickly can a nuclear reactor be shut down?

Literally in two seconds. In the design of any reactor, there are so-called emergency rods. During normal operation, they are removed from the reactor core and suspended above it. When an alarm comes, the rods literally fall down under their own weight, instantly stopping the chain reaction in the nuclear fuel. By the way, at the time of the Chernobyl accident, the system worked an order of magnitude slower. It took 14 seconds to shut down the reactor in 1986, which was one of the reasons why the accident could not be prevented. Lessons learned have been learned and a lot of work has been done to improve emergency protection to avoid a similar situation in the future.

Is it true that nuclear fuel glows after being used in a reactor?

Yes, this mesmerizing sight can be observed if the spent fuel is in the water. Externally, it looks like a blue halo surrounding the fuel assemblies, vertically installed under a layer of dark water at a depth of several meters. It seems that the fuel is illuminated by searchlights, but in fact it is not. Fast electrons emitted by nuclear fuel move at a speed exceeding the speed of light in water and radiate in the blue region of the spectrum. This phenomenon is called Cherenkov-Vavilov radiation, and it occurs even in solid transparent media. Nuclear fuel does not glow in air.

How much waste is generated at nuclear power plants?

Not very much: for a year of operation of a large power unit, we receive 100-200 cubic meters of solid radioactive waste (SRW) and about the same amount of liquid radioactive waste (LRW). Sources solid waste- contaminated parts and materials, used equipment of the reactor circuit, contaminated clothing, tools, rags used for wiping, etc. Source of liquid waste - small leaks of radioactive water used as a coolant, as well as aqueous solutions used to clean radioactively contaminated equipment, wastewater special laundry and so on. Moreover, the primary volume of liquid waste is quite high - about 10,000 cubic meters per year. Therefore, they are evaporated, as a result of which the initial amount is reduced by tens and even hundreds of times.

And what is the situation with waste at other enterprises of the nuclear fuel cycle?

The largest amount of radioactive waste is generated in the process of uranium mining. They are waste rock dumps and radiometric sorting waste. There is almost no uranium in them. And although the amount of such waste is large - more than fifty thousand cubic meters, provided annual work one thousand megawatt reactor - we should not forget that these wastes are low-level, that is, they are practically safe. If their storage is organized correctly, then such tailings do not pose a threat to the population and the environment. In addition, in our country they are only in Krasnokamensk (Trans-Baikal Territory).

What stage of the nuclear fuel cycle generates the most hazardous waste?

At the stage of spent nuclear fuel reprocessing. It should be noted that fresh fuel does not pose a radiation threat: uranium fuel tablets can be held in your hands. But when uranium is fissioned in a reactor, fission products are produced, and many of them pose a serious radiation threat. However, the danger emanating from them is significantly reduced over time. So, 40 years after being removed from the reactor, the amount of radioactive products decreases by a thousand times compared to the original. In addition, the volume of high-level waste generated during the reprocessing of spent fuel is a very small fraction (less than 1%) of the total amount of radioactive waste generated at all stages of the nuclear fuel cycle. If tailings are also taken into account, then the share of high-level waste will not exceed 0.01%. High-level waste is vitrified, and its volume in the entire history of spent nuclear fuel reprocessing in Russia per one inhabitant of our country is comparable to the volume of a golf ball.

How is waste from nuclear power plants handled?

The first stage is their strict accounting and collection. Accounting is necessary to ensure safety, given the inadmissibility of radioactive substances getting into the environment, and even into the hands of terrorists. Therefore, the system of accounting and control of radioactive substances and radioactive waste in Russia has been brought to the national level. The second stage is compactification, the maximum reduction in the volume of waste. Liquid waste is evaporated, solid waste is compressed and incinerated. This reduces the cost of their storage and final isolation. The third stage is conditioning, where the waste is transferred to a chemically stable, environmentally safe state. Waste with low radioactivity may be stored in drums and containers, for more hazardous materials more reliable matrices are provided: blocks of cement, bitumen or glass. The final stage is the shipment of radioactive waste to specialized storage facilities, and then to the final isolation facility.

Should we be afraid of the import of radioactive waste into our country from other states?

In accordance with existing laws, the import of radioactive waste into the territory of our country is prohibited. It is allowed to import into Russia only spent sources of ionizing radiation and spent nuclear fuel produced in our country and returned under an intergovernmental agreement. But it is wrong to call spent fuel waste for one simple reason: waste is those materials that have completely exhausted their useful resource, in which there is nothing valuable. To spent fuel, which contains unburned uranium, plutonium, a set of other isotopes that can be used in geology, medicine, agriculture, space, etc., this does not apply. It is a source of valuable products and can be reused.

Why are radioactive substances dangerous?

Radionuclides (radioactive nuclei), both natural and technogenic, differ from stable nuclei in that they can spontaneously transform into the nuclei of other elements. In this case, the nucleus emits radiation, or, as experts call it, ionizing radiation. Radiation causes some damage to cells, causing deviations in their work. True, cells successfully fight this effect if the doses of radiation are small. Moreover, in the absence of the usual radiation background, the body is oppressed, immunity is reduced. But if the radiation flow is powerful, the cells die, which leads to disruption of the functions of organs and tissues. It should be noted that in our ordinary life the probability of falling under such a strong radiation effect that it affects health is extremely small. In ordinary life, the average Russian receives from all sources a dose of radiation 25-50 times lower than the minimum dose for which at least minor harmful effects are noted.

Tell us about working conditions in uranium mines. Is it dangerous?

Let us first give a historical example relating to the era before the discovery of the phenomenon of radioactivity. Medieval miners from southern Saxony often fell ill and died early from lung pathology, but suffered less often from joint diseases because they drank mine-origin water containing uranium. Of course, no one knew about this. Therefore, it is not surprising that in the past, working in uranium mines was a dangerous business, and the incidence of disease in uranium mines was quite high. They began to figure out what was the matter, and came to the conclusion: the reason is the high concentration of natural radioactive gas - radon, which is an indispensable companion of uranium deposits. Having understood the problem, they wrote out a "recipe" - to ensure good ventilation of the mines. This had a positive effect, and now, according to statistics, the death rate of workers in uranium mining is no higher than in mining enterprises in other industries.

Are only nuclear workers irradiated? Or not?

And in other industries, workers can receive an increased dose of radiation. The oil and gas complex “distinguished itself” here to the greatest extent. The essence of the problem is that, along with oil and gas, natural radioactive substances, such as radium, are extracted from the ground. These isotopes are deposited on the internal surfaces of pipelines, pumps, tanks and lead to a significant increase in the radiation background. When this problem was dealt with closely, it was found out that the doses received by employees of oil producing enterprises in some places exceed the maximum doses for NPP personnel, and millions of tons of oil sludge, in accordance with domestic standards, should be considered as radioactive waste.

How much does the nuclear power plant contribute to my annual dose?

Experts have carefully studied this issue and were surprised. The contribution of all enterprises in the nuclear industry, the consequences of radiation accidents and nuclear weapons tests to the dose of the average Russian is about 0.3%. Moreover, this figure remains fair for the regions where nuclear power plants are located. The rest is natural sources and medical research. The exception is the areas contaminated as a result of radiation accidents, but even there the "atomic" contribution is lower than the medical component.

The probability of an accident at a nuclear power plant is small, but still not zero. How to "null" it?

The probability of an accident at any large industrial facility will never be equal to zero - everyone who is familiar with the subject of mathematical statistics knows this. In accordance with the canons of this discipline, any event can occur with one probability or another: there is even a probability (though very small) of death from a meteorite. In other words, it is not in our power to "nullify" the possibility of an accident, but we can make it negligible. At NPPs under construction, the probability of a major radiation accident is 10–7 per reactor per year. This is comparable to the probability of a plane falling on our house, if not a meteorite. You are not afraid to live in your own house? modern projects They are also safe because they are equipped with innovative technical solutions to prevent the release of radioactive substances outside the station even in the event of a severe accident.

How to behave in case of a radiation accident?

Firstly, it would be nice to make sure that the accident with the release of radiation really happened, and the information about it is not a "duck", since such provocations have taken place more than once. Their number dropped sharply after the opening of the russianatom.ru website, which displays information online from the sensors of the radiation monitoring system of Rosatom enterprises. If an accident does occur, it is necessary to carefully close windows and doors, make a supply of water, wear respirators or gauze bandages to protect against radioactive aerosols, listen to the radio, take iodine-containing drugs in accordance with the instructions and wait for the end of the alarm or, if the situation develops unfavorably, evacuation .

Why do we need "iodine prophylaxis"?

One of the dangerous radioactive isotopes produced during the operation of a nuclear reactor is iodine-131. It is able to selectively accumulate in the thyroid gland, an organ responsible for the production of two important hormones, and a malfunction of the thyroid gland affects the functioning of the body as a whole. Iodine prophylaxis is as follows: people who have fallen into the zone of radioactive contamination take ordinary iodine: a stable contained in the drug, displaces radioactive iodine from the thyroid gland, and its exposure is significantly reduced. You can take a pharmacy alcohol solution of iodine by diluting a few drops in water or milk, but it is better to use iodine-containing preparations. For example, potassium iodide tablets. Fortunately, the threat from iodine-131 is not long-term. The half-life of this isotope is about 8 days, which means that a few tens of days after the release, its concentration decreases to safe values. Finally, advice. In case of provocation, do not drink iodine! Cases have been recorded when, as a result of groundless rumors about an accident at a nuclear power plant, people drank so much alcohol solution of iodine that there was a need for medical care.

I heard that alcohol removes radioactive substances from the body. Is it so?

This popular opinion could have been eradicated long ago, but, unfortunately, it is actively supported by the nuclear scientists themselves. However, behind this lies nothing more than a convenient excuse to "think for three." In the same way, some people look hopefully at the calendar to see if there is any holiday today? The story about the benefits of alcohol is based on real facts: alcohol really interacts with free radicals - dangerous compounds that are formed in cells when exposed to radiation and when radioactive substances enter the body. The problem is that in order to achieve a more or less significant effect on their neutralization, it is necessary to drink so much alcohol that this will lead to severe poisoning of the body. We must not forget that alcohol is a poison. To reduce the effects of irradiation and remove radioactive substances from the body, special drugs have been developed - radioprotectors. Not delivering such pleasure as drinking alcoholic beverages, they nevertheless have a much stronger effect.

Tell me about the red forest. Is he still red?

During the accident at the Chernobyl nuclear power plant, a cloud of radioactive substances covered the nearby forest. Coniferous trees were especially affected. Deciduous species shed their leaves every year and thus are cleared of radionuclides, while this “option” is not available for spruces and pines. As a result, the trees died, and the needles turned red. Photos of the "red forest" are actively used as an argument that testifies to the dangers of nuclear energy. But let's compare the facts: due to the most serious radiation accident in the history of mankind, 560 hectares of forest died, while the "normal" work of the Norilsk plant led to the destruction of trees on a thousand-fold larger area - 600,000 hectares! By the way, now a grove is turning green in place of the “red forest”, and birds are singing, although the radiation background there is significantly increased.

Nuclear fuel is the 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 find out what a nuclear reactor fuel is, how it is classified and produced, where it is used.

The course of the chain reaction

During a nuclear chain reaction, the nucleus is divided into two parts, which are called fission fragments. At the same time, several (2-3) neutrons are released, which subsequently cause the fission of the following nuclei. The process occurs when a neutron enters the nucleus of the original substance. Fission fragments have high kinetic energy. Their deceleration 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 fission with neutrons of any energy are called nuclear fuel. As a rule, they are substances with an odd number of atoms. Some nuclei fission purely by neutrons whose energy is above a certain threshold. These are predominantly elements with an even number of atoms. Such nuclei are called raw materials, since at the moment of neutron capture by the threshold nucleus, fuel nuclei are formed. The combination of fuel and raw material is thus called nuclear fuel.

Classification

Nuclear fuel is divided into two classes:

natural uranium. It contains fissile uranium-235 nuclei and raw material uranium-238, which is capable of forming plutonium-239 upon neutron capture.
Secondary fuel not found in nature. Among other things, it includes plutonium-239, which is obtained from the fuel of the first type, as well as uranium-233, which is formed during the capture of neutrons by thorium-232 nuclei.

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

Metal (including alloys);
Oxide (for example, UO 2);
Carbide (for example PuC 1-x);
mixed;
Nitride.

TVEL and TVS

Fuel for nuclear reactors is used in the form of small pellets. They are placed in hermetically sealed fuel elements (TVELs), which, in turn, are combined into several hundred fuel assemblies (FAs). Nuclear fuel is subject to high requirements for compatibility with fuel rod cladding. It should 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

For 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 burned-out fuel assemblies) and during the repair campaign. In the latter case, the fuel assemblies are changed in large groups. In this case, only a third of the fuel is completely replaced. The most burnt-out assemblies are unloaded from the central part of the reactor, and partially burnt-out assemblies that were previously located in less active areas are put in their place. 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 of which is to ensure uniform energy release. Of course, this is a conditional scheme, which gives only general ideas about the process.

Excerpt

After removal of the spent nuclear fuel from the reactor core, it is sent to the spent fuel pool, which, as a rule, is located nearby. The fact is that spent fuel assemblies contain great amount fission fragments of uranium. After unloading from the reactor, each fuel element contains about 300 thousand Curies of radioactive substances, releasing 100 kWh of energy. Due to it, the fuel self-heats and becomes highly radioactive.

The temperature of recently 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 within the established range. As the fuel is stored under water, the radioactivity of the fuel and the power of its residual emissions decreases. Approximately three years later, self-heating of fuel assemblies already reaches 50–60°C. Then the fuel is removed from the pools and sent for processing or disposal.

Metallic uranium

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

The force of swelling depends on the temperature of the fuel rods and burnup. With an increase in burnup, the number of fission fragments increases, and with an increase in temperature and burnup, the internal pressure of gases increases. If the fuel has higher mechanical properties, then it is less prone to swelling. Metallic uranium is not one of these materials. Therefore, its use as a fuel for nuclear reactors limits the burnup depth, which is one of the main characteristics of such fuel.

The mechanical properties of uranium and its radiation resistance are improved by doping the material. This process involves the addition of aluminum, molybdenum and other metals to it. Thanks to dopants, 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 compounds of uranium are considered good nuclear fuel: carbides, oxides and intermetallic compounds. The most common of these is uranium dioxide (ceramic). Its melting point is 2800°C and its density is 10.2 g/cm 3 .

Since this material has no phase transitions, it is less prone to swelling than uranium alloys. Thanks to this feature, the burnout temperature can be increased by several percent. On high temperatures ah ceramics does not interact with niobium, zirconium, stainless steel and other materials. Its main drawback is its 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 640°C. Due to poor plastic properties, it is practically not amenable to machining. The toxicity of the substance complicates the fuel rod manufacturing technology. In the nuclear industry, attempts have been repeatedly made to use plutonium and its compounds, but they have not been successful. It is impractical to use fuel for nuclear power plants containing plutonium because of the approximately 2-fold decrease in the acceleration period, which is not designed for standard reactor control systems.

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

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

Mining

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 found 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 such stages as:

Hydrometallurgical processing. Includes leaching, crushing and extraction or sorption extraction. The result of hydrometallurgical processing is a purified suspension of oxyuranium oxide, sodium diuranate or ammonium diuranate.
Conversion of a substance from oxide to tetrafluoride or hexafluoride used to enrich uranium-235.
Enrichment of a substance by centrifugation or gaseous thermal diffusion.
Conversion of the enriched material into dioxide, from which the "pills" of fuel rods are produced.

Regeneration

During the operation of a nuclear reactor, the fuel cannot completely burn 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 by the Purex process, which consists of the following steps:

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

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

Nuclear power is a modern and rapidly developing way of generating electricity. Do you know how nuclear power plants are arranged? What is the principle of operation of a nuclear power plant? What types of nuclear reactors exist today? We will try to consider in detail the scheme of operation of a nuclear power plant, delve into the structure of a nuclear reactor and find out how safe the atomic method of generating electricity is.

How is a nuclear power plant organized?

Any station is a closed area far from the residential area. There are several buildings on its territory. The most important building is the reactor building, next to it is the turbine hall from which the reactor is controlled, and the safety building.

The scheme is impossible without a nuclear reactor. An atomic (nuclear) reactor is a device of a nuclear power plant, which is designed to organize a chain reaction of neutron fission with the obligatory release of energy in this process. But what is the principle of operation of a nuclear power plant?

The entire reactor plant is placed in the reactor building, a large concrete tower that hides the reactor and, in the event of an accident, will contain all the products of a nuclear reaction. This large tower is called containment, hermetic shell or containment.

The containment zone in the new reactors has 2 thick concrete walls - shells.
An 80 cm thick outer shell protects the containment area from external influences.

The inner shell with a thickness of 1 meter 20 cm has special steel cables in its device, which increase the strength of concrete by almost three times and will not allow the structure to crumble. On the inside, it is lined with a thin sheet of special steel, which is designed to serve as additional protection for the containment and, in the event of an accident, prevent the contents of the reactor from being released outside the containment area.

Such a device of a nuclear power plant can withstand the fall of an aircraft weighing up to 200 tons, an 8-magnitude earthquake, tornado and tsunami.

The first pressurized enclosure was built at the American nuclear power plant Connecticut Yankee in 1968.

The total height of the containment area is 50-60 meters.

What is a nuclear reactor made of?

To understand the principle of operation of a nuclear reactor, and hence the principle of operation of a nuclear power plant, you need to understand the components of the reactor.

active zone. This is the area where the nuclear fuel (heat releaser) and the moderator are placed. Atoms of fuel (most often uranium is the fuel) perform a fission chain reaction. The moderator is designed to control the fission process, and allows you to carry out the reaction required in terms of speed and strength.
Neutron reflector. The reflector surrounds the active zone. It consists of the same material as the moderator. In fact, this is a box, the main purpose of which is to prevent neutrons from leaving the core and getting into the environment.
Coolant. The coolant must absorb the heat that was released during the fission of fuel atoms and transfer it to other substances. The coolant largely determines how a nuclear power plant is designed. The most popular coolant today is water.
Reactor control system. Sensors and mechanisms that bring the nuclear power plant reactor into action.

Fuel for nuclear power plants

What does a nuclear power plant do? Fuel for nuclear power plants are chemical elements with radioactive properties. For everyone nuclear power plants uranium is such an element.

The design of stations implies that nuclear power plants operate on complex composite fuel, and not on a pure chemical element. And in order to extract uranium fuel from natural uranium, which is loaded into a nuclear reactor, you need to carry out a lot of manipulations.

Enriched uranium

Uranium consists of two isotopes, that is, it contains nuclei with different masses. They were named by the number of protons and neutrons isotope -235 and isotope-238. Researchers of the 20th century began to extract uranium 235 from the ore, because. it was easier to decompose and transform. It turned out that there is only 0.7% of such uranium in nature (the remaining percentages went to the 238th isotope).

What to do in this case? They decided to enrich uranium. Enrichment of uranium is a process when there are many necessary 235x isotopes and few unnecessary 238x isotopes left in it. The task of uranium enrichers is to make almost 100% uranium-235 from 0.7%.

Uranium can be enriched using two technologies - gas diffusion or gas centrifuge. For their use, uranium extracted from ore is converted into a gaseous state. In the form of gas, it is enriched.

uranium powder

Enriched uranium gas is converted into a solid state - uranium dioxide. This pure solid uranium 235 looks like large white crystals that are later crushed into uranium powder.

Uranium tablets

Uranium pellets are solid metal washers, a couple of centimeters long. In order to mold such tablets from uranium powder, it is mixed with a substance - a plasticizer, it improves the quality of tablet pressing.

Pressed washers are baked at a temperature of 1200 degrees Celsius for more than a day to give the tablets special strength and resistance to high temperatures. The way a nuclear power plant works directly depends on how well the uranium fuel is compressed and baked.

Tablets are baked in molybdenum boxes, because. only this metal is able not to melt at "hellish" temperatures over one and a half thousand degrees. After that, uranium fuel for nuclear power plants is considered ready.

What is TVEL and TVS?

The reactor core looks like a huge disk or pipe with holes in the walls (depending on the type of reactor), 5 times larger than a human body. These holes contain uranium fuel, the atoms of which carry out the desired reaction.

It’s impossible to simply throw fuel into a reactor, well, if you don’t want to get an explosion of the entire station and an accident with consequences for a couple of nearby states. Therefore, uranium fuel is placed in fuel rods, and then collected in fuel assemblies. What do these abbreviations mean?

TVEL - fuel element (not to be confused with the same name Russian company that produces them). In fact, this is a thin and long zirconium tube made of zirconium alloys, into which uranium pellets are placed. It is in fuel rods that uranium atoms begin to interact with each other, releasing heat during the reaction.

Zirconium was chosen as a material for the production of fuel rods due to its refractoriness and anti-corrosion properties.

The type of fuel elements depends on the type and structure of the reactor. As a rule, the structure and purpose of fuel rods does not change; the length and width of the tube can be different.

The machine loads more than 200 uranium pellets into one zirconium tube. In total, about 10 million uranium pellets work simultaneously in the reactor.
FA - fuel assembly. NPP workers call fuel assemblies bundles.

In fact, these are several TVELs fastened together. TVS is ready nuclear fuel, what the nuclear power plant works on. It is fuel assemblies that are loaded into a nuclear reactor. About 150 - 400 fuel assemblies are placed in one reactor.
Depending on which reactor the fuel assembly will operate in, they come in different shapes. Sometimes the bundles are folded into a cubic, sometimes into a cylindrical, sometimes into a hexagonal shape.

One fuel assembly for 4 years of operation generates the same amount of energy as when burning 670 coal cars, 730 tanks with natural gas or 900 tanks loaded with oil.
Today, fuel assemblies are produced mainly at factories in Russia, France, the USA and Japan.

In order to deliver fuel for nuclear power plants to other countries, fuel assemblies are sealed in long and wide metal pipes, air is pumped out of the pipes and delivered on board cargo aircraft by special machines.

Nuclear fuel for nuclear power plants weighs prohibitively much, tk. uranium is one of the most heavy metals on the planet. His specific gravity 2.5 times more than steel.

Nuclear power plant: principle of operation

What is the principle of operation of a nuclear power plant? The principle of operation of nuclear power plants is based on a chain reaction of fission of atoms of a radioactive substance - uranium. This reaction takes place in the core of a nuclear reactor.

If you don't go into details nuclear physics, the principle of operation of a nuclear power plant looks like this:
After the nuclear reactor is started, absorbing rods are removed from the fuel rods, which prevent the uranium from reacting.

As soon as the rods are removed, the uranium neutrons begin to interact with each other.

When neutrons collide, a mini-explosion occurs at the atomic level, energy is released and new neutrons are born, a chain reaction begins to occur. This process releases heat.

The heat is transferred to the coolant. Depending on the type of coolant, it turns into steam or gas, which rotates the turbine.

The turbine drives an electric generator. It is he who, in fact, generates electricity.

If you do not follow the process, uranium neutrons can collide with each other until the reactor is blown up and the entire nuclear power plant is blown to smithereens. Computer sensors control the process. They detect an increase in temperature or a change in pressure in the reactor and can automatically stop the reactions.

What is the difference between the principle of operation of nuclear power plants and thermal power plants (thermal power plants)?

Differences in work are only at the first stages. In nuclear power plants, the coolant receives heat from the fission of atoms of uranium fuel, in thermal power plants, the coolant receives heat from the combustion of organic fuel (coal, gas or oil). After either the atoms of uranium or the gas with coal have released heat, the schemes of operation of nuclear power plants and thermal power plants are the same.

Types of nuclear reactors

How a nuclear power plant works depends on how its nuclear reactor works. Today there are two main types of reactors, which are classified according to the spectrum of neurons:
A slow neutron reactor, also called a thermal reactor.

For its operation, 235 uranium is used, which goes through the stages of enrichment, the creation of uranium tablets, etc. Today, slow neutron reactors are in the vast majority.
Fast neutron reactor.

These reactors are the future, because they work on uranium-238, which is a dime a dozen in nature and it is not necessary to enrich this element. The disadvantage of such reactors is only in very high costs for design, construction and launch. Today, fast neutron reactors operate only in Russia.

The coolant in fast neutron reactors is mercury, gas, sodium or lead.

Slow neutron reactors, which are used today by all nuclear power plants in the world, also come in several types.

The IAEA organization (International Atomic Energy Agency) has created its own classification, which is used most often in the world nuclear industry. Since the principle of operation of a nuclear power plant largely depends on the choice of coolant and moderator, the IAEA has based its classification on these differences.

From a chemical point of view, deuterium oxide is an ideal moderator and coolant, because its atoms most effectively interact with the neutrons of uranium compared to other substances. Simply put, heavy water performs its task with minimal losses and maximum results. However, its production costs money, while it is much easier to use the usual “light” and familiar water for us.

A few facts about nuclear reactors...

It is interesting that one nuclear power plant reactor is built for at least 3 years!
To build a reactor, you need equipment that runs on an electric current of 210 kilo amperes, which is a million times the current that can kill a person.

One shell (structural element) of a nuclear reactor weighs 150 tons. There are 6 such elements in one reactor.

Pressurized water reactor

We have already found out how the nuclear power plant works in general, in order to “sort it out” let's see how the most popular pressurized nuclear reactor works.
All over the world today, generation 3+ pressurized water reactors are used. They are considered the most reliable and safe.

All pressurized water reactors in the world over all the years of their operation in total have already managed to gain more than 1000 years of trouble-free operation and have never given serious deviations.

The structure of nuclear power plants based on pressurized water reactors implies that distilled water circulates between the fuel rods, heated to 320 degrees. To prevent it from going into a vapor state, it is kept under a pressure of 160 atmospheres. The NPP scheme calls it primary water.

The heated water enters the steam generator and gives off its heat to the water of the secondary circuit, after which it “returns” to the reactor again. Outwardly, it looks like the pipes of the primary water circuit are in contact with other pipes - the water of the second circuit, they transfer heat to each other, but the waters do not contact. Tubes are in contact.

Thus, the possibility of radiation getting into the water of the secondary circuit, which will further participate in the process of generating electricity, is excluded.

Nuclear power plant safety

Having learned the principle of operation of nuclear power plants, we must understand how safety is arranged. The design of nuclear power plants today requires increased attention to safety rules.
The cost of nuclear power plant safety is approximately 40% of the total cost of the plant itself.

The NPP scheme includes 4 physical barriers that prevent the release of radioactive substances. What are these barriers supposed to do? At the right time, be able to stop the nuclear reaction, ensure constant heat removal from the core and the reactor itself, and prevent the release of radionuclides from the containment (containment zone).

The first barrier is the strength of uranium pellets. It is important that they do not collapse under the influence of high temperatures in a nuclear reactor. In many ways, how a nuclear power plant works depends on how the uranium pellets were "baked" at the initial stage of production. If the uranium fuel pellets are baked incorrectly, the reactions of the uranium atoms in the reactor will be unpredictable.
The second barrier is the tightness of fuel rods. Zirconium tubes must be tightly sealed, if the tightness is broken, then at best the reactor will be damaged and work stopped, at worst everything will fly into the air.
The third barrier is a strong steel reactor vessel a, (that same large tower - a containment area) which "holds" all radioactive processes in itself. The hull is damaged - radiation will be released into the atmosphere.
The fourth barrier is emergency protection rods. Above the active zone, rods with moderators are suspended on magnets, which can absorb all neutrons in 2 seconds and stop the chain reaction.

If, despite the construction of a nuclear power plant with many degrees of protection, it is not possible to cool the reactor core at the right time, and the fuel temperature rises to 2600 degrees, then the last hope of the safety system comes into play - the so-called melt trap.

The fact is that at such a temperature the bottom of the reactor vessel will melt, and all the remnants of nuclear fuel and molten structures will flow into a special “glass” suspended above the reactor core.

The melt trap is refrigerated and refractory. It is filled with the so-called "sacrificial material", which gradually stops the fission chain reaction.

Thus, the NPP scheme implies several degrees of protection, which almost completely exclude any possibility of an accident.

A nuclear power plant is a complex of necessary systems, devices, equipment and structures intended for the production electrical energy. The station uses uranium-235 as fuel. The presence of a nuclear reactor distinguishes nuclear power plants from other power plants.

There are three mutual transformations of forms of energy at nuclear power plants

Nuclear power

goes into heat

Thermal energy

goes into mechanical

mechanical energy

converted to electrical

1. Nuclear energy turns into heat

The basis of the station is the reactor - a structurally allocated volume where nuclear fuel is loaded and where a controlled chain reaction takes place. Uranium-235 is fissile with slow (thermal) neutrons. As a result, a huge amount of heat is released.

STEAM GENERATOR

2. Thermal energy is converted into mechanical

Heat is removed from the reactor core by a coolant - a liquid or gaseous substance passing through its volume. This thermal energy used to produce water vapor in a steam generator.

POWER GENERATOR

3. Mechanical energy is converted into electrical energy

The mechanical energy of the steam is sent to the turbogenerator, where it is converted into electrical energy and then goes to the consumers through the wires.

What is a nuclear power plant made of?

A nuclear power plant is a complex of buildings that house technological equipment. The main building is the main building where the reactor hall is located. It houses the reactor itself, the nuclear fuel holding pool, the refueling machine (for fuel refueling), all this is monitored by operators from the block control room (BCR).

The main element of the reactor is the active zone (1) . It is located in a concrete shaft. Mandatory components of any reactor are the control and protection system, which allows to carry out the selected mode of the controlled fission chain reaction, as well as the emergency protection system - to quickly stop the reaction in the event of emergency. All this is mounted in the main building.

There is also a second building where the turbine hall (2) is located: steam generators, the turbine itself. Next along the technological chain are capacitors and high-voltage power lines that go beyond the station site.

On the territory there is a building for reloading and storage of spent nuclear fuel in special pools. In addition, the stations are equipped with elements circulation system Cooling towers (3) (concrete tower tapering at the top), cooling pond (natural or artificial) and spray pools.

What are nuclear power plants?

Depending on the type of reactor, nuclear power plants can have 1, 2 or 3 coolant operation circuits. In Russia, bypass NPPs with VVER-type reactors (pressure-cooled power reactor) are most widely used.

NPP WITH 1-LOOP REACTORS

The single-circuit scheme is used at nuclear power plants with RBMK-1000 type reactors. The reactor operates in a block with two condensing turbines and two generators. In this case, the boiling reactor itself is a steam generator, which makes it possible to use a single-loop scheme. The single-loop scheme is relatively simple, but the radioactivity in this case extends to all elements of the block, which complicates biological protection.

Currently, there are 4 nuclear power plants with single-loop reactors operating in Russia

NPP WITH 2-LOOP REACTORS

The double-circuit scheme is used at nuclear power plants with water-cooled reactors of the VVER type. Pressurized water is supplied to the reactor core, which is heated. The energy of the coolant is used in the steam generator to form saturated steam. The second circuit is non-radioactive. The unit consists of one 1000 MW condensing turbine or two 500 MW turbines with associated generators.

Currently, Russia has 5 nuclear power plants with double-loop reactors

NPP WITH 3-LOOP REACTORS

The three-loop scheme is used at nuclear power plants with fast neutron reactors with a sodium coolant of the BN type. To exclude the contact of radioactive sodium with water, a second circuit is constructed with non-radioactive sodium. Thus, the circuit turns out to be three-circuit.