The nuclear reactor works smoothly and accurately. Otherwise, as you know, there will be trouble. But what's going on inside? Let us try to formulate the principle of operation of a nuclear (atomic) reactor briefly, clearly, with stops.

In fact, the same process is going on there as in a nuclear explosion. Only now the explosion occurs very quickly, but in the reactor all this is stretched out for a long time. As a result, everything remains safe and sound, and we receive energy. Not so much that everything around was immediately blown up, but quite enough to provide the city with electricity.

Before you understand how a controlled nuclear reaction is going, you need to know what is nuclear reaction generally.

Nuclear reaction Is the process of transformation (fission) of atomic nuclei during their interaction with elementary particles and gamma quanta.

Nuclear reactions can take place with both absorption and release of energy. Second reactions are used in the reactor.

Nuclear reactor Is a device whose purpose is to maintain a controlled nuclear reaction with the release of energy.

Often a nuclear reactor is also called atomic. Note that there is no fundamental difference here, but from the point of view of science, it is more correct to use the word "nuclear". There are many types of nuclear reactors now. These are huge industrial reactors designed to generate energy at power plants, nuclear reactors in submarines, small experimental reactors used in scientific experiments. There are even reactors used for desalination of seawater.

The history of the creation of a nuclear reactor

The first nuclear reactor was launched in the not so distant 1942. It happened in the USA under the leadership of Fermi. This reactor was called the "Chicago Woodpile".

In 1946, the first Soviet reactor started up under the leadership of Kurchatov. The body of this reactor was a ball of seven meters in diameter. The first reactors did not have a cooling system, and their power was minimal. By the way, the Soviet reactor had an average power of 20 watts, while the American one had only 1 watt. For comparison: the average power of modern power reactors is 5 Gigawatts. Less than ten years after the launch of the first reactor, the world's first industrial nuclear power plant was opened in the city of Obninsk.

The principle of operation of a nuclear (atomic) reactor

Any nuclear reactor has several parts: active zone with fuel and moderator , neutron reflector , coolant , control and protection system ... Isotopes are most often used as fuel in reactors uranium (235, 238, 233), plutonium (239) and thorium (232). The active zone is a boiler through which ordinary water (heat carrier) flows. Among other coolants, "heavy water" and liquid graphite are less commonly used. If we talk about the operation of a nuclear power plant, then a nuclear reactor is used to generate heat. Electricity itself is generated by the same method as in other types of power plants - steam rotates a turbine, and the energy of motion is converted into electrical energy.

Below is a diagram of the operation of a nuclear reactor.

As we have already said, during the decay of a heavy uranium nucleus, lighter elements and several neutrons are formed. The resulting neutrons collide with other nuclei, also causing their fission. In this case, the number of neutrons grows like an avalanche.

It needs to be mentioned here neutron multiplication factor ... So, if this coefficient exceeds a value equal to one, a nuclear explosion occurs. If the value is less than one, there are too few neutrons and the reaction is extinguished. But if you maintain the value of the coefficient equal to one, the reaction will proceed for a long time and stably.

The question is how to do this? In the reactor, the fuel is in the so-called fuel elements (TVELakh). These are rods in which, in the form of small tablets, there is nuclear fuel ... The fuel rods are connected in hexagonal cassettes, of which there can be hundreds in the reactor. Cassettes with fuel rods are located vertically, with each fuel rod having a system that allows you to adjust the depth of its immersion in the core. In addition to the cassettes themselves, among them there are control rods and emergency protection rods ... The rods are made of a material that absorbs neutrons well. Thus, the control rods can be lowered to different depths in the core, thereby adjusting the neutron multiplication factor. The emergency rods are designed to shut down the reactor in case of an emergency.

How is a nuclear reactor started?

We figured out the very principle of operation, but how to start and make the reactor work? Roughly speaking, here it is - a piece of uranium, but a chain reaction does not start in it by itself. The fact is that in nuclear physics there is a concept critical mass .

The critical mass is the mass of fissile matter necessary for the start of a nuclear chain reaction.

With the help of fuel rods and control rods, a critical mass of nuclear fuel is first created in the reactor, and then the reactor is brought to the optimal power level in several stages.

In this article, we have tried to give you a general idea of ​​the structure and principle of operation of a nuclear (atomic) reactor. If you have any questions on the topic or at the university asked a problem in nuclear physics, please contact specialists of our company... We, as usual, are ready to help you solve any pressing issue in your studies. In the meantime, we are doing this, your attention is another educational video!

To understand the principle of operation and design of a nuclear reactor, you need to take a short excursion into the past. A nuclear reactor is a centuries-old embodied, albeit not completely, the dream of mankind about an inexhaustible source of energy. Its ancient "progenitor" is a fire made of dry branches that once lit up and warmed the vaults of the cave, where our distant ancestors found salvation from the cold. Later, people mastered hydrocarbons - coal, shale, oil and natural gas.

A stormy, but short-lived era of steam followed, followed by an even more fantastic era of electricity. Cities were filled with light, and workshops were filled with the roar of hitherto unseen machines, driven by electric motors. Then it seemed that progress had reached its climax.

Everything changed at the end of the 19th century, when the French chemist Antoine Henri Becquerel accidentally discovered that uranium salts are radioactive. Two years later, his compatriots Pierre Curie and his wife Maria Sklodowska-Curie obtained radium and polonium from them, and the level of their radioactivity was millions of times higher than those of thorium and uranium.

The baton was picked up by Ernest Rutherford, who studied in detail the nature of radioactive rays. Thus began the age of the atom, which gave birth to its beloved child - the atomic reactor.

First nuclear reactor

"Firstborn" is from the USA. In December 1942, the reactor gave the first current, which got the name of its creator - one of the greatest physicists of the century, E. Fermi. Three years later, the ZEEP nuclear facility came to life in Canada. "Bronze" went to the first Soviet F-1 reactor, launched at the end of 1946. IV Kurchatov became the head of the domestic nuclear project. More than 400 nuclear power units are successfully operating in the world today.

Types of nuclear reactors

Their main purpose is to support a controlled nuclear reaction that produces electricity. Some reactors produce isotopes. In short, they are devices in the depths of which some substances are converted into others with the release of a large amount of thermal energy. This is a kind of "furnace", where instead of traditional types of fuel, uranium isotopes - U-235, U-238 and plutonium (Pu) - are "burned".

Unlike, for example, a car designed for several types of gasoline, each type of radioactive fuel corresponds to its own type of reactor. There are two of them - on slow (with U-235) and fast (with U-238 and Pu) neutrons. Most nuclear power plants have slow neutron reactors. In addition to nuclear power plants, installations "work" in research centers, on nuclear submarines, etc.

How the reactor works

All reactors have approximately the same scheme. Its "heart" is an active zone. It can be roughly compared to the firebox of an ordinary stove. Only instead of firewood there is nuclear fuel in the form of fuel elements with a moderator - TVELs. The active zone is located inside a kind of capsule - a neutron reflector. Fuel rods are "washed" by a coolant - water. Since the "heart" has a very high level of radioactivity, it is surrounded by reliable radiation protection.

Operators control the operation of the plant using two critical systems - chain reaction control and a remote control system. If an abnormal situation arises, the emergency protection is instantly triggered.

How the reactor works

The atomic "flame" is invisible, since the processes take place at the level of nuclear fission. In the course of a chain reaction, heavy nuclei disintegrate into smaller fragments, which, when excited, become sources of neutrons and other subatomic particles. But the process does not end there. Neutrons continue to "split", as a result of which a lot of energy is released, that is, what happens for the sake of which nuclear power plants are being built.

The main task of the personnel is to maintain the chain reaction with the help of control rods at a constant, adjustable level. This is its main difference from the atomic bomb, where the process of nuclear decay is uncontrollable and proceeds rapidly, in the form of a powerful explosion.

What happened at the Chernobyl nuclear power plant

One of the main reasons for the disaster at the Chernobyl nuclear power plant in April 1986 was the gross violation of operational safety rules during routine maintenance at the 4th power unit. Then 203 graphite rods were removed from the core at the same time instead of 15 allowed by the regulations. As a result, the uncontrolled chain reaction that began ended in a thermal explosion and complete destruction of the power unit.

New generation reactors

Over the past decade, Russia has become one of the leaders in the world nuclear power industry. At the moment, the state corporation "Rosatom" is building nuclear power plants in 12 countries, where 34 power units are being built. Such a high demand is evidence of the high level of modern Russian nuclear technology. Next in line are reactors of the new 4th generation.

"Brest"

One of them is Brest, which is being developed as part of the Breakthrough project. Current open-cycle systems run on low-enriched uranium, leaving a large amount of spent fuel to be disposed of, which is costly. "Brest" is a fast neutron reactor, a unique closed cycle.

In it, the spent fuel, after appropriate processing in a fast neutron reactor, again becomes a full-fledged fuel that can be loaded back into the same installation.

Brest is distinguished by a high level of security. It will never "explode" even in the most serious accident, it is very economical and environmentally friendly, since it reuses its "renewed" uranium. It also cannot be used to produce weapons-grade plutonium, which opens up the broadest prospects for its export.

VVER-1200

VVER-1200 is an innovative 3+ generation reactor with a capacity of 1150 MW. Thanks to its unique technical capabilities, it has almost absolute operational safety. The reactor is abundantly equipped with passive safety systems that will work even in the absence of power supply in automatic mode.

One of them is a passive heat removal system, which is automatically activated when the reactor is completely de-energized. In this case, emergency hydraulic tanks are provided. With an abnormal pressure drop in the primary circuit, a large amount of water containing boron is fed into the reactor, which quenches the nuclear reaction and absorbs neutrons.

Another know-how is found at the bottom of the containment - the melt trap. If, nevertheless, as a result of the accident, the core "flows", the "trap" will not allow the containment to collapse and prevent the ingress of radioactive products into the ground.

The fission chain reaction is always accompanied by the release of enormous energy. The practical use of this energy is the main task of a nuclear reactor.

A nuclear reactor is a device in which a controlled, or controlled, nuclear fission reaction is carried out.

According to the principle of operation, nuclear reactors are divided into two groups: thermal reactors and fast reactors.

How a nuclear thermal reactor works

A typical nuclear reactor contains:

• Active zone and moderator;
• Reflector of neutrons;
• Heat carrier;
• Chain reaction control system, emergency protection;
• Monitoring and radiation protection system;
• Remote control system.

1 - active zone; 2 - reflector; 3 - protection; 4 - control rods; 5 - coolant; 6 - pumps; 7 - heat exchanger; 8 - turbine; 9 - generator; 10 - capacitor.

Active zone and retarder

It is in the core that the controlled fission chain reaction takes place.

Most nuclear reactors use the heavy isotopes of uranium-235. But in natural samples of uranium ore, its content is only 0.72%. This concentration is not enough for a chain reaction to develop. Therefore, the ore is artificially enriched, bringing the content of this isotope to 3%.

Fissile material, or nuclear fuel, in the form of pellets is placed in hermetically sealed rods called fuel rods (fuel rods). They permeate the entire core filled with moderator neutrons.

Why do you need a neutron moderator in a nuclear reactor?

The fact is that the neutrons born after the decay of uranium-235 nuclei have a very high speed. The probability of their capture by other uranium nuclei is hundreds of times less than the probability of the capture of slow neutrons. And if their speed is not reduced, the nuclear reaction can die out over time. The moderator also solves the problem of reducing the speed of neutrons. If water or graphite is placed in the path of fast neutrons, their speed can be artificially reduced and thus the number of particles captured by atoms can be increased. At the same time, for a chain reaction in the reactor, less nuclear fuel is needed.

As a result of the deceleration process, thermal neutrons, the speed of which is practically equal to the speed of thermal motion of gas molecules at room temperature.

As a moderator in nuclear reactors, water, heavy water (deuterium oxide D 2 O), beryllium, and graphite are used. But the best moderator is heavy water D 2 O.

Neutron reflector

To avoid leakage of neutrons into the environment, the core of a nuclear reactor is surrounded by neutron reflector... The materials used for reflectors are often the same as those used for retarders.

Heat carrier

The heat released during a nuclear reaction is removed using a coolant. As a coolant in nuclear reactors, ordinary natural water, previously purified from various impurities and gases, is often used. But since water boils already at a temperature of 100 0 C and a pressure of 1 atm, in order to increase the boiling point, the pressure in the primary coolant circuit is increased. The water in the primary circuit, circulating through the reactor core, washes the fuel rods, heating up to a temperature of 320 0 C. Then, inside the heat exchanger, it gives off heat to the water in the secondary circuit. The exchange passes through heat exchange tubes, so there is no contact with the water of the second circuit. This excludes the ingress of radioactive substances into the second loop of the heat exchanger.

And then everything happens as in a thermal power plant. The water in the second circuit turns into steam. The steam turns a turbine, which drives an electric generator, which generates an electric current.

In heavy water reactors, heavy water D 2 O serves as the coolant, and molten metal is used in reactors with liquid metal coolants.

Chain reaction control system

The current state of the reactor is characterized by a quantity called reactivity.

ρ = ( k -1) / k ,

k = n i / n i -1 ,

where k - neutron multiplication factor,

n i - the number of next generation neutrons in a nuclear fission reaction,

n i -1 , - the number of neutrons of the previous generation in the same reaction.

If k ˃ 1 , the chain reaction grows, the system is called supercritically th. If k< 1 , the chain reaction dies out, and the system is called subcritical... At k = 1 the reactor is in stable critical condition, since the number of fissile nuclei does not change. In this state, reactivity ρ = 0 .

The critical state of the reactor (the required neutron multiplication factor in a nuclear reactor) is maintained by moving control rods... The material from which they are made includes substances that absorb neutrons. By extending or sliding these rods into the core, the rate of the nuclear fission reaction is controlled.

The control system provides control of the reactor during its start-up, scheduled shutdown, operation at power, as well as emergency protection of the nuclear reactor. This is achieved by changing the position of the control rods.

If any of the reactor parameters (temperature, pressure, rate of power rise, fuel consumption, etc.) deviates from the norm, and this can lead to an accident, special emergency rods and there is a rapid cessation of the nuclear reaction.

To ensure that the parameters of the reactor comply with the standards, they are monitored monitoring and radiation protection systems.

To protect the environment from radioactive radiation, the reactor is placed in a thick concrete case.

Remote control systems

All signals about the state of the nuclear reactor (coolant temperature, radiation level in different parts of the reactor, etc.) are sent to the reactor control panel and processed in computer systems. The operator receives all the necessary information and recommendations for eliminating certain deviations.

Fast Reactors

The difference between reactors of this type and reactors on thermal neutrons is that fast neutrons arising after the decay of uranium-235 are not slowed down, but are absorbed by uranium-238, followed by its transformation into plutonium-239. Therefore, fast reactors are used to obtain weapons-grade plutonium-239 and thermal energy, which the generators of the nuclear power plant convert into electrical energy.

The nuclear fuel in such reactors is uranium-238, and the raw material is uranium-235.

In natural uranium ore, 99.2745% is accounted for by uranium-238. When a thermal neutron is absorbed, it does not divide, but becomes an isotope of uranium-239.

Some time after β-decay, uranium-239 turns into the nucleus of neptunium-239:

239 92 U → 239 93 Np + 0 -1 e

After the second β-decay, fissile plutonium-239 is formed:

239 9 3 Np → 239 94 Pu + 0 -1 e

And finally, after the alpha decay of plutonium-239 nuclei, uranium-235 is obtained:

239 94 Pu → 235 92 U + 4 2 He

Fuel rods with raw materials (enriched with uranium-235) are located in the reactor core. This zone is surrounded by a breeding zone, which consists of fuel rods with fuel (depleted uranium-238). Fast neutrons emitted from the core after the decay of uranium-235 are captured by the nuclei of uranium-238. The result is plutonium-239. Thus, new nuclear fuel is produced in fast reactors.

Liquid metals or their mixtures are used as coolants in fast-neutron nuclear reactors.

Classification and application of nuclear reactors

The main application of nuclear reactors is found in nuclear power plants. With their help, electric and thermal energy is obtained on an industrial scale. Such reactors are called energy .

Nuclear reactors are widely used in propulsion systems of modern nuclear submarines, surface ships, and in space technology. They supply electrical energy to motors and are called transport reactors .

For scientific research in the field of nuclear physics and radiation chemistry, fluxes of neutrons, gamma quanta, which are obtained in the core, are used. research reactors. The energy generated by them does not exceed 100 MW and is not used for industrial purposes.

Power experimental reactors even less. It reaches only a few kW. Various physical quantities are studied at these reactors, the importance of which is important in the design of nuclear reactions.

TO industrial reactors include reactors for producing radioactive isotopes used for medical purposes, as well as in various fields of industry and technology. Reactors for seawater desalination are also classified as industrial reactors.

Nuclear reactor core- the concentration of the most concentrated type of energy of all that is currently used - is located in a steel shell with 15-centimeter walls. The core contains uranium-235 in pellets loaded into hundreds of stainless steel tubes, each about three meters long.

Atoms of uranium-235 undergo a chain reaction of nuclear fission, during which they split into pieces with the release of a huge amount of energy. Fission of 1 gram (0.35 ounce) of uranium-235 releases as much energy as is released from the combustion of about 2,000 liters of oil.Water passing through the reactor core heats the secondary circuit feed water, converting it into steam fed to the turbine blades.

In addition to releasing energy, the fissioning atoms of uranium-235 release neutrons, one of the two main types of particles in the atomic nucleus. These neutrons collide with other atoms of uranium-235, splitting them and releasing the additional amount of neutrons needed to sustain the chain reaction and thereby create a long-term source of energy. The chain reaction is controlled by introducing boron or cadmium rods into the core - materials that absorb neutrons well.

Chain reaction in uranium-235

When it collides with a neutron, the uranium-235 atom becomes unstable and splits into two smaller atoms. This process is called nuclear fission. When uranium-235 fissions, it releases two or three neutrons, which can collide with other atoms of uranium-235 and start a self-sustaining chain reaction.

Nuclear power

Nuclear fission releases a tremendous amount of energy inside the reactor core. The water passing through the hot core heats the secondary circuit feed water and turns it into steam, which is then fed to the turbine.

Nuclear power plant at the Japan Institute for Atomic Energy Research.

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Industrial nuclear reactors were originally developed only in countries with nuclear weapons. USA, USSR, Great Britain and France were actively investigating different versions of nuclear reactors. However, later in the nuclear power industry, three main types of reactors began to dominate, differing mainly in fuel, coolant used to maintain the required core temperature, and a moderator used to reduce the speed of neutrons released during the decay process and needed to maintain the chain reaction.

Among them, the first (and most widespread) type is an enriched uranium reactor, in which both the coolant and the moderator is ordinary, or "light" water (light water reactor). There are two main types of light-water reactors: a reactor in which steam rotating turbines is formed directly in the core (boiling-water reactor), and a reactor in which steam is formed in an external, or second, circuit connected to a heat exchanger , see below). The development of a light water reactor began under the programs of the US armed forces. For example, in the 1950s, General Electric and Westinghouse developed light water reactors for submarines and aircraft carriers of the US Navy. These firms were also involved in the implementation of military programs for the development of technologies for the regeneration and enrichment of nuclear fuel. In the same decade, a boiling graphite-moderated reactor was developed in the Soviet Union.

The second type of reactor, which has found practical application, is a gas-cooled reactor (with graphite moderator). Its creation was also closely related to early nuclear weapons development programs. In the late 1940s - early 1950s, Great Britain and France, striving to create their own atomic bombs, focused on the development of gas-cooled reactors, which quite efficiently produce weapons-grade plutonium and, moreover, can work on natural uranium.

The third type of reactor that has had commercial success is a reactor in which both the coolant and the moderator are heavy water, and the fuel is also natural uranium. In the early nuclear age, the potential benefits of a heavy water reactor were explored in a number of countries. However, then the production of such reactors was concentrated mainly in Canada, in part because of its vast reserves of uranium.

There are currently five types of nuclear reactors in the world. These are VVER (Water-Water Power Reactor), RBMK (High Power Channel Reactor), heavy water reactor, ball-bed reactor and gas circuit, fast neutron reactor. Each type of reactor has design features that distinguish it from others, although, of course, individual structural elements can be borrowed from other types. VVERs were built mainly on the territory of the former USSR and in Eastern Europe, there are many RBMK reactors in Russia, Western Europe and Southeast Asia, heavy water reactors were mainly built in America.

VVER. VVER reactors are the most common type of reactor in Russia. The cheapness of the coolant-moderator used in them and the relative safety in operation are very attractive, despite the need to use enriched uranium in these reactors. From the very name of the VVER reactor, it follows that both the moderator and the coolant are ordinary light water. Uranium enriched to 4.5% is used as fuel.

RBMK. RBMK is built on a slightly different principle than VVER. First of all, boiling occurs in its core - a steam-water mixture enters from the reactor, which, passing through the separators, is divided into water returning to the reactor inlet and steam, which goes directly to the turbine. The electricity generated by the turbine is spent, as in the VVER reactor, also for the operation of circulation pumps. Its schematic diagram is shown in Fig. 4.

The electrical capacity of RBMK is 1000 MW. NPPs with RBMK reactors make up a significant share in the nuclear power industry. So, they are equipped with Leningrad, Kursk, Chernobyl, Smolensk, Ignalina nuclear power plants.

Comparing various types of nuclear reactors, it is worth dwelling on the two most common types of these devices in our country and in the world: VVER and RBMK. The most fundamental differences: VVER - pressure vessel (pressure is kept by the reactor vessel); RBMK - channel reactor (pressure is maintained independently in each channel); in VVER the coolant and moderator are the same water (no additional moderator is introduced), in RBMK the moderator is graphite, and the coolant is water; in VVER steam is generated in the second vessel of the steam generator, in RBMK steam is generated directly in the reactor core (boiling reactor) and goes directly to the turbine - there is no secondary circuit. Due to the different structure of the cores, the operating parameters of these reactors are also different. For the safety of the reactor, a parameter such as coefficient of reactivity- it can be figuratively represented as a value that shows how changes in one or another parameter of the reactor will affect the intensity of the chain reaction in it. If this coefficient is positive, then with an increase in the parameter by which the coefficient is given, the chain reaction in the reactor in the absence of any other influences will grow and at the end it will become possible to transform it into an uncontrolled and cascade-increasing one - the reactor will accelerate. During the acceleration of the reactor, intense heat release occurs, leading to the melting of heat separators, their melt flowing into the lower part of the core, which can lead to the destruction of the reactor vessel and the release of radioactive substances into the environment.

Table 13 shows the reactivity indices for RBMK and VVER reactors.

In a VVER reactor, when steam appears in the core or when the coolant temperature rises, leading to a decrease in its density, the number of collisions of neutrons with atoms of coolant molecules decreases, the moderation of neutrons decreases, as a result of which they all leave the core without reacting with other nuclei. The reactor stops.

To summarize, the RBMK reactor requires less fuel enrichment, has better capabilities for the production of fissile material (plutonium), has a continuous operating cycle, but is more potentially dangerous in operation. The degree of this hazard depends on the quality of the emergency protection systems and the qualifications of the operating personnel. In addition, due to the absence of a secondary circuit, RBMK has more radiation emissions into the atmosphere during operation.

Heavy water reactor. In Canada and America, the developers of nuclear reactors, when solving the problem of maintaining a chain reaction in the reactor, preferred to use heavy water as a moderator. Heavy water has a very low neutron absorption and very high moderating properties, exceeding those of graphite. As a result, heavy water reactors operate on unenriched fuel, which makes it possible not to build complex and dangerous uranium enrichment facilities.

Ball-packed reactor. In a spherical-filled reactor, the core has the shape of a ball, into which fuel elements, also spherical, are filled. Each element is a graphite sphere in which uranium oxide particles are interspersed. Gas is pumped through the reactor - most often carbon dioxide CO2 is used. The gas is supplied to the core under pressure and subsequently enters the heat exchanger. The reactor is controlled by absorber rods inserted into the core.

Fast neutron reactor. A fast reactor is very different from all other types of reactors. Its main purpose is to ensure the expanded breeding of fissile plutonium from uranium-238 in order to burn all or a significant part of natural uranium, as well as the available reserves of depleted uranium. With the development of the power of fast reactors, the problem of self-sufficiency of nuclear power with fuel can be solved.

There is no moderator in a fast reactor. In this regard, not uranium-235 is used as fuel, but plutonium and uranium-238, which can be fissioned from fast neutrons. Plutonium is needed to provide a sufficient neutron flux density that uranium-238 alone cannot provide. The heat release of a fast neutron reactor is ten to fifteen times higher than the heat release of slow neutron reactors, and therefore, instead of water (which simply cannot cope with such a volume of energy for transfer), sodium melt is used (its inlet temperature is 370 degrees, and at the outlet - 550, Currently, fast neutron reactors are not widely used, mainly due to the complexity of the design and the problem of obtaining sufficiently stable materials for structural parts. There is only one reactor of this type in Russia (at the Beloyarsk NPP). reactors have a great future.

To summarize, the following should be said. VVER reactors are quite safe to operate, but require highly enriched uranium. RBMK reactors are safe only with proper operation and well-developed protection systems, but they are capable of using low-enriched fuel or even spent fuel from VVERs. Heavy water reactors are good for everyone, but it's too expensive to get heavy water. The technology for the production of spherical-packed reactors is still not well developed, although this type of reactors should be recognized as the most acceptable for widespread use, in particular, due to the absence of catastrophic consequences in an accident with reactor acceleration. Fast neutron reactors are the future of the production of fuel for nuclear power, these reactors use nuclear fuel most efficiently, but their design is very complex and still unreliable.