Nuclear reactor reaction speed. Nuclear reactor, principle of operation, operation of a nuclear reactor

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

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

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

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

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

The inner shell, 1 meter 20 cm thick, has special steel cables that increase the strength of concrete almost three times and will prevent the structure from crumbling. 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, not to release the contents of the reactor outside the containment zone.

This design of the nuclear power plant allows it to withstand an airplane crash weighing up to 200 tons, a magnitude 8 earthquake, a tornado and a tsunami.

The first sealed shell was built at the American Connecticut Yankee nuclear power plant in 1968.

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

What does a nuclear reactor consist of?

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

  • Active zone. This is the area where the nuclear fuel (fuel generator) and moderator are placed. Fuel atoms (most often uranium is the fuel) undergo a chain fission reaction. The moderator is designed to control the fission process and allows for the required reaction in terms of speed and strength.
  • Neutron reflector. A reflector surrounds the core. It consists of the same material as the moderator. In essence, this is a box, the main purpose of which is to prevent neutrons from leaving the core and entering the environment.
  • Coolant. The coolant must absorb the heat 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 power a nuclear power plant reactor.

Fuel for nuclear power plants

What does a nuclear power plant operate on? Fuel for nuclear power plants are chemical elements with radioactive properties. At all nuclear power plants, this element is uranium.

The design of the 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, it is necessary to carry out many 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 ore, because... it was easier to decompose and transform. It turned out that such uranium in nature is only 0.7% (the remaining percentage goes to the 238th isotope).

What to do in this case? They decided to enrich uranium. Uranium enrichment is a process in which a lot of the necessary 235x isotopes remain in it and few unnecessary 238x isotopes. The task of uranium enrichers is to turn 0.7% into almost 100% uranium-235.

Uranium can be enriched using two technologies: gas diffusion or gas centrifuge. To use them, uranium extracted from ore is converted into a gaseous state. It is enriched in the form of gas.

Uranium powder

Enriched uranium gas is converted into a solid state - uranium dioxide. This pure solid uranium 235 appears as large white crystals, which are later crushed into uranium powder.

Uranium tablets

Uranium tablets are solid metal discs, a couple of centimeters long. To form such tablets from uranium powder, it is mixed with a substance - a plasticizer; it improves the quality of pressing the tablets.

The pressed pucks 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. How a nuclear power plant operates directly depends on how well the uranium fuel is compressed and baked.

The tablets are baked in molybdenum boxes, because only this metal is capable of not melting at “hellish” temperatures of over one and a half thousand degrees. After this, uranium fuel for nuclear power plants is considered ready.

What are TVEL and FA?

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 the human body. These holes contain uranium fuel, the atoms of which carry out the desired reaction.

It’s impossible to just throw fuel into the reactor, well, unless you want to cause 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 is a fuel element (not to be confused with the same name of the Russian company that produces them). It is essentially a thin and long zirconium tube made from zirconium alloys into which uranium tablets 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 rods 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 are working simultaneously in the reactor.
FA – fuel assembly. NPP workers call fuel assemblies bundles.

Essentially, these are several fuel rods fastened together. FA is finished nuclear fuel, what a nuclear power plant operates on. It is the fuel assemblies that are loaded into the nuclear reactor. About 150 – 400 fuel assemblies are placed in one reactor.
Depending on the reactor in which the fuel assemblies will operate, 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 over 4 years of operation produces the same amount of energy as when burning 670 cars of coal, 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.

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

Nuclear fuel for nuclear power plants weighs prohibitively much, because... uranium is one of the heaviest metals on the planet. Its specific gravity is 2.5 times greater than that of steel.

Nuclear power plant: operating principle

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

IT IS IMPORTANT TO KNOW:

Without going into the intricacies of nuclear physics, the operating principle of a nuclear power plant looks like this:
After the start-up of a nuclear reactor, absorber rods are removed from the fuel rods, which prevent the uranium from reacting.

Once 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 generates heat.

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 actually generates the electric current.

If you do not monitor the process, uranium neutrons can collide with each other until they explode the reactor and smash the entire nuclear power plant to smithereens. The process is controlled by computer sensors. They detect an increase in temperature or change in pressure in the reactor and can automatically stop reactions.

How does the operating principle of nuclear power plants differ from thermal power plants (thermal power plants)?

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

Types of nuclear reactors

How a nuclear power plant operates depends on exactly how its nuclear reactor operates. 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, uranium 235 is used, which goes through the stages of enrichment, creation of uranium pellets, etc. Today, the vast majority of reactors use slow neutrons.
Fast neutron reactor.

These reactors are the future, because... They work on uranium-238, which is a dime a dozen in nature and there is no need to enrich this element. The only downside of such reactors is the very high costs of design, construction and startup. Today, fast neutron reactors operate only in Russia.

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

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

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


From a chemical point of view, deuterium oxide is an ideal moderator and coolant, because its atoms interact most effectively with 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 ordinary “light” and familiar water is much easier to use.

A few facts about nuclear reactors...

It’s interesting that one nuclear power plant reactor takes at least 3 years to build!
To build a reactor, you need equipment that operates on an electric current of 210 kiloamperes, which is a million times higher than 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 a nuclear power plant works in general; to put everything into perspective, let’s look at how the most popular pressurized water 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, have already accumulated more than 1000 years of trouble-free operation and have never given serious deviations.

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

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

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

NPP operational safety

Having learned the principle of operation of nuclear power plants, we must understand how safety works. The construction of nuclear power plants today requires increased attention to safety rules.
NPP safety costs account for approximately 40% of the total cost of the plant itself.

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

  • The first barrier is the strength of uranium pellets. It is important that they are not destroyed by high temperatures in a nuclear reactor. Much of how a nuclear power plant operates depends on how the uranium pellets are “baked” during the initial manufacturing stage. If the uranium fuel pellets are not baked correctly, 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 seal is broken, then at best the reactor will be damaged and work will stop; at worst, everything will fly up into the air.
  • The third barrier is a durable steel reactor vessel a, (that same large tower - hermetic zone) which “holds” all radioactive processes. If the housing is damaged, radiation will escape into the atmosphere.
  • The fourth barrier is emergency protection rods. Rods with moderators are suspended above the core by magnets, which can absorb all neutrons in 2 seconds and stop the chain reaction.

If, despite the design 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 this temperature the bottom of the reactor vessel will melt, and all the remains of nuclear fuel and molten structures will flow into a special “glass” suspended above the reactor core.

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

Thus, the nuclear power plant design implies several degrees of protection, which almost completely eliminate any possibility of an accident.

The device and principle of operation are based on the initialization and control of a self-sustaining nuclear reaction. It is used as a research tool, to produce radioactive isotopes, and as an energy source for nuclear power plants.

operating principle (briefly)

This uses a process in which a heavy nucleus breaks up into two smaller fragments. These fragments are in a highly excited state and emit neutrons, other subatomic particles and photons. Neutrons can cause new fissions, resulting in more of them being emitted, and so on. Such a continuous self-sustaining series of splittings is called a chain reaction. This releases a large amount of energy, the production of which is the purpose of using nuclear power plants.

The operating principle of a nuclear reactor is such that about 85% of the fission energy is released within a very short period of time after the start of the reaction. The rest is produced by the radioactive decay of fission products after they have emitted neutrons. Radioactive decay is a process in which an atom reaches a more stable state. It continues after division is completed.

In an atomic bomb, the chain reaction increases in intensity until most of the material is fissioned. This happens very quickly, producing the extremely powerful explosions typical of such bombs. The design and operating principle of a nuclear reactor are based on maintaining a chain reaction at a controlled, almost constant level. It is designed in such a way that it cannot explode like an atomic bomb.

Chain reaction and criticality

The physics of a nuclear fission reactor is that the chain reaction is determined by the probability of the nucleus splitting after neutrons are emitted. If the population of the latter decreases, then the rate of division will eventually drop to zero. In this case, the reactor will be in a subcritical state. If the neutron population is maintained at a constant level, then the fission rate will remain stable. The reactor will be in critical condition. Finally, if the population of neutrons grows over time, the fission rate and power will increase. The state of the core will become supercritical.

The operating principle of a nuclear reactor is as follows. Before its launch, the neutron population is close to zero. Operators then remove control rods from the core, increasing nuclear fission, which temporarily pushes the reactor into a supercritical state. After reaching rated power, operators partially return the control rods, adjusting the number of neutrons. Subsequently, the reactor is maintained in a critical condition. When it needs to be stopped, operators insert the rods all the way. This suppresses fission and transfers the core to a subcritical state.

Reactor types

Most of the world's nuclear power plants are power plants, generating the heat needed to spin turbines that drive electrical power generators. There are also many research reactors, and some countries have submarines or surface ships powered by atomic energy.

Energy installations

There are several types of reactors of this type, but the light water design is widely used. In turn, it can use pressurized water or boiling water. In the first case, the high-pressure liquid is heated by the heat of the core and enters the steam generator. There, heat from the primary circuit is transferred to the secondary circuit, which also contains water. The ultimately generated steam serves as the working fluid in the steam turbine cycle.

The boiling-water reactor operates on the principle of a direct energy cycle. Water passing through the core is brought to a boil at medium pressure. The saturated steam passes through a series of separators and dryers located in the reactor vessel, which causes it to become superheated. The superheated water vapor is then used as the working fluid to turn the turbine.

High temperature gas cooled

A high-temperature gas-cooled reactor (HTGR) is a nuclear reactor whose operating principle is based on the use of a mixture of graphite and fuel microspheres as fuel. There are two competing designs:

  • a German "fill" system that uses spherical fuel elements with a diameter of 60 mm, which are a mixture of graphite and fuel in a graphite shell;
  • the American version in the form of graphite hexagonal prisms that interlock to create a core.

In both cases, the coolant consists of helium under a pressure of about 100 atmospheres. In the German system, helium passes through gaps in the layer of spherical fuel elements, and in the American system, helium passes through holes in graphite prisms located along the axis of the central zone of the reactor. Both options can operate at very high temperatures, since graphite has an extremely high sublimation temperature and helium is completely chemically inert. Hot helium can be applied directly as a working fluid in a gas turbine at high temperature, or its heat can be used to generate water cycle steam.

Liquid metal and working principle

Sodium-cooled fast reactors received much attention in the 1960s and 1970s. It seemed then that their breeding capabilities would soon be needed to produce fuel for the rapidly expanding nuclear industry. When it became clear in the 1980s that this expectation was unrealistic, enthusiasm waned. However, a number of reactors of this type have been built in the USA, Russia, France, Great Britain, Japan and Germany. Most of them run on uranium dioxide or its mixture with plutonium dioxide. In the United States, however, the greatest success has been achieved with metallic fuels.

CANDU

Canada is focusing its efforts on reactors that use natural uranium. This eliminates the need to resort to the services of other countries to enrich it. The result of this policy was the deuterium-uranium reactor (CANDU). It is controlled and cooled with heavy water. The design and operating principle of a nuclear reactor consists of using a reservoir of cold D 2 O at atmospheric pressure. The core is pierced by pipes made of zirconium alloy containing natural uranium fuel, through which heavy water that cools it circulates. Electricity is produced by transferring fission heat in heavy water to a coolant that circulates through a steam generator. The steam in the secondary circuit then passes through a conventional turbine cycle.

Research facilities

For scientific research, a nuclear reactor is most often used, the operating principle of which is to use water cooling and plate-shaped uranium fuel elements in the form of assemblies. Capable of operating over a wide range of power levels, from several kilowatts to hundreds of megawatts. Since power generation is not the primary purpose of research reactors, they are characterized by the thermal energy produced, the density and the nominal energy of the core neutrons. It is these parameters that help quantify the ability of a research reactor to conduct specific research. Low power systems are typically found in universities and used for teaching, while high power systems are needed in research laboratories for materials and performance testing and general research.

The most common is a research nuclear reactor, the structure and operating principle of which is as follows. Its core is located at the bottom of a large, deep pool of water. This simplifies the observation and placement of channels through which neutron beams can be directed. At low power levels there is no need to pump coolant as natural convection of the coolant provides sufficient heat removal to maintain safe operating conditions. The heat exchanger is usually located on the surface or at the top of the pool where hot water accumulates.

Ship installations

The original and main application of nuclear reactors is their use in submarines. Their main advantage is that, unlike fossil fuel combustion systems, they do not require air to generate electricity. Therefore, a nuclear submarine can remain submerged for long periods of time, while a conventional diesel-electric submarine must periodically rise to the surface to fire its engines in mid-air. gives a strategic advantage to naval ships. Thanks to it, there is no need to refuel at foreign ports or from easily vulnerable tankers.

The operating principle of a nuclear reactor on a submarine is classified. However, it is known that in the USA it uses highly enriched uranium, and is slowed down and cooled by light water. The design of the first nuclear submarine reactor, USS Nautilus, was heavily influenced by powerful research facilities. Its unique features are a very large reactivity reserve, ensuring a long period of operation without refueling and the ability to restart after a stop. The power plant in submarines must be very quiet to avoid detection. To meet the specific needs of different classes of submarines, different models of power plants were created.

US Navy aircraft carriers use a nuclear reactor, the operating principle of which is believed to be borrowed from the largest submarines. Details of their design have also not been published.

In addition to the United States, Great Britain, France, Russia, China and India have nuclear submarines. In each case, the design was not disclosed, but it is believed that they are all very similar - this is a consequence of the same requirements for their technical characteristics. Russia also has a small fleet that uses the same reactors as Soviet submarines.

Industrial installations

For production purposes, a nuclear reactor is used, the operating principle of which is high productivity with a low level of energy production. This is due to the fact that a long stay of plutonium in the core leads to the accumulation of unwanted 240 Pu.

Tritium production

Currently, the main material produced by such systems is tritium (3H or T) - the charge for Plutonium-239 has a long half-life of 24,100 years, so countries with nuclear weapons arsenals using this element tend to have there is more of it than necessary. Unlike 239 Pu, tritium has a half-life of approximately 12 years. Thus, to maintain the necessary supplies, this radioactive isotope of hydrogen must be produced continuously. In the United States, Savannah River (South Carolina), for example, operates several heavy water reactors that produce tritium.

Floating power units

Nuclear reactors have been created that can provide electricity and steam heating to remote isolated areas. In Russia, for example, small power plants specifically designed to serve Arctic settlements have found use. In China, the 10 MW HTR-10 provides heat and power to the research institute where it is located. Development of small automatically controlled reactors with similar capabilities is underway in Sweden and Canada. Between 1960 and 1972, the US Army used compact water reactors to power remote bases in Greenland and Antarctica. They were replaced by oil-fired power plants.

Conquest of space

In addition, reactors were developed for power supply and movement in outer space. Between 1967 and 1988, the Soviet Union installed small nuclear units on its Cosmos series satellites to power equipment and telemetry, but the policy became a target of criticism. At least one of these satellites entered the Earth's atmosphere, causing radioactive contamination in remote areas of Canada. The United States has launched only one nuclear-powered satellite, in 1965. However, projects for their use in long-distance space flights, manned exploration of other planets, or on a permanent lunar base continue to be developed. This will necessarily be a gas-cooled or liquid metal nuclear reactor, the physical principles of which will provide the highest possible temperature necessary to minimize the size of the radiator. In addition, a reactor for space technology must be as compact as possible to minimize the amount of material used for shielding and to reduce weight during launch and spaceflight. The fuel supply will ensure the operation of the reactor for the entire period of the space flight.

I. Design of a nuclear reactor

A nuclear reactor consists of the following five main elements:

1) nuclear fuel;

2) neutron moderator;

3) regulatory systems;

4) cooling systems;

5) protective screen.

1. Nuclear fuel.

Nuclear fuel is a source of energy. There are currently three known types of fissile materials:

a) uranium 235, which makes up 0.7%, or 1/140 of natural uranium;

6) plutonium 239, which is formed in some reactors based on uranium 238, which makes up almost the entire mass of natural uranium (99.3%, or 139/140 parts).

Capturing neutrons, uranium 238 nuclei turn into neptunium nuclei - the 93rd element of the Mendeleev periodic system; the latter, in turn, turn into plutonium nuclei - the 94th element of the periodic table. Plutonium is easily extracted from irradiated uranium by chemical means and can be used as nuclear fuel;

c) uranium 233, which is an artificial isotope of uranium obtained from thorium.

Unlike uranium 235, which is found in natural uranium, plutonium 239 and uranium 233 are obtained only artificially. That's why they are called secondary nuclear fuel; The source of such fuel is uranium 238 and thorium 232.

Thus, among all the types of nuclear fuel listed above, uranium is the main one. This explains the enormous scope that searches and exploration of uranium deposits are taking in all countries.

The energy released in a nuclear reactor is sometimes compared with that released during a chemical combustion reaction. However, there is a fundamental difference between them.

The amount of heat obtained during the fission of uranium is immeasurably greater than the amount of heat obtained during combustion, for example, of coal: 1 kg of uranium 235, equal in volume to a pack of cigarettes, could theoretically provide as much energy as 2600 tons of coal.

However, these energy opportunities are not fully exploited, since not all uranium 235 can be separated from natural uranium. As a result, 1 kg of uranium, depending on the degree of its enrichment with uranium 235, is currently equivalent to approximately 10 tons of coal. But it should be taken into account that the use of nuclear fuel facilitates transportation and, therefore, significantly reduces the cost of fuel. British experts have calculated that by enriching uranium they will be able to increase the heat produced in reactors by 10 times, which would equate 1 ton of uranium to 100 thousand tons of coal.

The second difference between the process of nuclear fission, which occurs with the release of heat, and chemical combustion is that the combustion reaction requires oxygen, while to initiate a chain reaction only a few neutrons and a certain mass of nuclear fuel is required, equal to the critical mass, which we define already given in the section on the atomic bomb.

And finally, the invisible process of nuclear fission is accompanied by the emission of extremely harmful radiation, from which protection must be provided.

2. Neutron moderator.

In order to avoid the spread of fission products in the reactor, nuclear fuel must be placed in special shells. To make such shells, you can use aluminum (the coolant temperature should not exceed 200°), or even better, beryllium or zirconium - new metals, the production of which in their pure form is fraught with great difficulties.

The neutrons produced during nuclear fission (on average 2–3 neutrons during the fission of one nucleus of a heavy element) have a certain energy. In order for the probability of neutrons to split other nuclei to be greatest, without which the reaction will not be self-sustaining, it is necessary that these neutrons lose part of their speed. This is achieved by placing a moderator in the reactor, in which fast neutrons are converted into slow ones as a result of numerous successive collisions. Since the substance used as a moderator must have nuclei with a mass approximately equal to the mass of neutrons, that is, the nuclei of light elements, heavy water was used as a moderator from the very beginning (D 2 0, where D is deuterium, which replaced light hydrogen in ordinary water N 2 0). However, now they are trying to use graphite more and more - it is cheaper and gives almost the same effect.

A ton of heavy water purchased in Sweden costs 70–80 million francs. At the Geneva Conference on the Peaceful Uses of Atomic Energy, the Americans announced that they would soon be able to sell heavy water at a price of 22 million francs per ton.

A ton of graphite costs 400 thousand francs, and a ton of beryllium oxide costs 20 million francs.

The substance used as a moderator must be pure to avoid loss of neutrons as they pass through the moderator. At the end of the run, the neutrons have an average speed of about 2200 m/sec, while their initial speed was about 20 thousand km/sec. In reactors, the release of heat occurs gradually and can be controlled, unlike an atomic bomb, where it occurs instantly and takes on the character of an explosion.

Some types of fast reactors do not require a moderator.

3. Regulatory system.

A person should be able to cause, regulate and stop a nuclear reaction at will. This is achieved using control rods made of boron steel or cadmium - materials that have the ability to absorb neutrons. Depending on the depth to which the control rods are lowered into the reactor, the number of neutrons in the core increases or decreases, which ultimately makes it possible to regulate the process. The control rods are controlled automatically using servomechanisms; Some of these rods can instantly fall into the core in case of danger.

At first there were concerns that a reactor explosion would cause the same damage as an atomic bomb. In order to prove that a reactor explosion occurs only under conditions different from normal ones and does not pose a serious danger to the population living in the vicinity of the nuclear plant, the Americans deliberately blew up one so-called “boiling” reactor. Indeed, there was an explosion that we can characterize as “classical,” that is, non-nuclear; this once again proves that nuclear reactors can be built near populated areas without any particular danger to the latter.

4. Cooling system.

During nuclear fission, a certain energy is released, which is transferred to the decay products and the resulting neutrons. This energy, as a result of numerous collisions of neutrons, is converted into thermal energy, therefore, in order to prevent rapid failure of the reactor, heat must be removed. In reactors designed to produce radioactive isotopes, this heat is not used, but in reactors designed to produce energy, it becomes, on the contrary, the main product. Cooling can be carried out using gas or water, which circulates in the reactor under pressure through special tubes and is then cooled in a heat exchanger. The heat released can be used to heat the steam that rotates a turbine connected to the generator; such a device would be a nuclear power plant.

5. Protective screen.

In order to avoid the harmful effects of neutrons that can fly outside the reactor, and to protect yourself from the gamma radiation emitted during the reaction, reliable protection is necessary. Scientists have calculated that a reactor with a power of 100 thousand kW emits such an amount of radioactive radiation that a person located at a distance of 100 m from it would receive it in 2 minutes. lethal dose. To ensure the protection of personnel servicing the reactor, two-meter walls are built from special concrete with lead slabs.

The first reactor was built in December 1942 by the Italian Fermi. By the end of 1955, there were about 50 nuclear reactors in the world (USA - 2 1, England - 4, Canada - 2, France - 2). It should be added that by the beginning of 1956, about 50 more reactors were designed for research and industrial purposes (USA - 23, France - 4, England - 3, Canada - 1).

The types of these reactors are very diverse, ranging from slow neutron reactors with graphite moderators and natural uranium as fuel to fast neutron reactors using uranium enriched with plutonium or uranium 233, produced artificially from thorium, as fuel.

In addition to these two opposing types, there is a whole series of reactors that differ from each other either in the composition of the nuclear fuel, or in the type of moderator, or in the coolant.

It is very important to note that, although the theoretical side of the issue is now well studied by specialists in all countries, in the practical field different countries have not yet reached the same level. The USA and Russia are ahead of other countries. It can be argued that the future of nuclear energy will depend mainly on the progress of technology.

From the book The Wonderful World Inside the Atomic Nucleus [lecture for schoolchildren] author Ivanov Igor Pierovich

The structure of the LHC collider Now a few pictures. A collider is an accelerator of colliding particles. There, particles accelerate along two rings and collide with each other. This is the largest experimental installation in the world, because the length of this ring - the tunnel -

From the book The Newest Book of Facts. Volume 3 [Physics, chemistry and technology. History and archaeology. Miscellaneous] author Kondrashov Anatoly Pavlovich

From the book The Atomic Problem by Ran Philip

From book 5b. Electricity and magnetism author Feynman Richard Phillips

From the author's book

Chapter VIII Principle of operation and capabilities of a nuclear reactor I. Design of a nuclear reactor A nuclear reactor consists of the following five main elements: 1) nuclear fuel; 2) neutron moderator; 3) control system; 4) cooling system; 5) protective

From the author's book

Chapter 11 INTERNAL STRUCTURE OF DIELECTRICS §1. Molecular dipoles§2. Electronic polarization §3. Polar molecules; orientation polarization§4. Electric fields in dielectric voids§5. Dielectric constant of liquids; Clausius-Mossotti formula§6.

This nondescript gray cylinder is the key link in the Russian nuclear industry. It doesn’t look very presentable, of course, but once you understand its purpose and look at the technical characteristics, you begin to understand why the secret of its creation and structure is protected by the state like the apple of its eye.

Yes, I forgot to introduce: here is a gas centrifuge for separating uranium isotopes VT-3F (nth generation). The principle of operation is elementary, like a milk separator; the heavy is separated from the light by the influence of centrifugal force. So what is the significance and uniqueness?

First, let's answer another question - in general, why separate uranium?

Natural uranium, which lies right in the ground, is a cocktail of two isotopes: uranium-238 And uranium-235(and 0.0054% U-234).
Uran-238, it's just heavy, gray metal. You can use it to make an artillery shell, or... a keychain. Here's what you can do from uranium-235? Well, firstly, an atomic bomb, and secondly, fuel for nuclear power plants. And here we come to the key question - how to separate these two, almost identical atoms, from each other? No, really HOW?!

By the way: The radius of the nucleus of a uranium atom is 1.5 10 -8 cm.

In order for uranium atoms to be driven into the technological chain, it (uranium) must be converted into a gaseous state. There is no point in boiling, it is enough to combine uranium with fluorine and get uranium hexafluoride HFC. The technology for its production is not very complicated and expensive, and therefore HFC they get it right where this uranium is mined. UF6 is the only highly volatile uranium compound (when heated to 53°C, the hexafluoride (pictured) directly transforms from a solid to a gaseous state). Then it is pumped into special containers and sent for enrichment.

A little history

At the very beginning of the nuclear race, the greatest scientific minds of both the USSR and the USA mastered the idea of ​​diffusion separation - passing uranium through a sieve. Small 235th the isotope will slip through, and the “fat” 238th will get stuck. Moreover, making a sieve with nano-holes for Soviet industry in 1946 was not the most difficult task.

From the report of Isaac Konstantinovich Kikoin at the scientific and technical council under the Council of People's Commissars (presented in a collection of declassified materials on the USSR atomic project (Ed. Ryabev)): Currently, we have learned to make meshes with holes of about 5/1,000 mm, i.e. 50 times greater than the free path of molecules at atmospheric pressure. Consequently, the gas pressure at which the separation of isotopes on such grids will occur must be less than 1/50 of atmospheric pressure. In practice, we assume to work at a pressure of about 0.01 atmospheres, i.e. under good vacuum conditions. Calculations show that to obtain a product enriched to a concentration of 90% with a light isotope (this concentration is sufficient to produce an explosive), it is necessary to combine about 2,000 such stages in a cascade. In the machine we are designing and partially manufacturing, it is expected to produce 75-100 g of uranium-235 per day. The installation will consist of approximately 80-100 “columns”, each of which will have 20-25 stages installed.”

Below is a document - Beria’s report to Stalin on the preparation of the first atomic bomb explosion. Below is a short information about the nuclear materials produced by the beginning of the summer of 1949.

And now imagine for yourself - 2000 hefty installations, for the sake of just 100 grams! Well, what to do with it, we need bombs. And they began to build factories, and not just factories, but entire cities. And okay, only the cities, these diffusion plants required so much electricity that they had to build separate power plants nearby.

In the USSR, the first stage D-1 of plant No. 813 was designed for a total output of 140 grams of 92-93% uranium-235 per day at 2 cascades of 3100 separation stages identical in power. An unfinished aircraft plant in the village of Verkh-Neyvinsk, 60 km from Sverdlovsk, was allocated for production. Later it turned into Sverdlovsk-44, and plant 813 (pictured) into the Ural Electrochemical Plant - the world's largest separation plant.

And although the technology of diffusion separation, albeit with great technological difficulties, was debugged, the idea of ​​​​developing a more economical centrifuge process did not leave the agenda. After all, if we manage to create a centrifuge, then energy consumption will be reduced from 20 to 50 times!

How does a centrifuge work?

Its structure is more than elementary and looks like an old washing machine operating in the “spin/dry” mode. The rotating rotor is located in a sealed casing. Gas is supplied to this rotor (UF6). Due to the centrifugal force, hundreds of thousands of times greater than the Earth’s gravitational field, the gas begins to separate into “heavy” and “light” fractions. Light and heavy molecules begin to group in different zones of the rotor, but not in the center and along the perimeter, but at the top and bottom.

This occurs due to convection currents - the rotor cover is heated and a counterflow of gas occurs. There are two small intake tubes installed at the top and bottom of the cylinder. A lean mixture enters the lower tube, and a mixture with a higher concentration of atoms enters the upper tube. 235U. This mixture goes into the next centrifuge, and so on, until the concentration 235th uranium will not reach the desired value. A chain of centrifuges is called a cascade.

Technical features.

Well, firstly, the rotation speed - in the modern generation of centrifuges it reaches 2000 rps (I don’t even know what to compare it with... 10 times faster than the turbine in an aircraft engine)! And it has been working non-stop for THREE DECADES! Those. Now centrifuges, turned on under Brezhnev, are rotating in cascades! The USSR no longer exists, but they keep spinning and spinning. It is not difficult to calculate that during its working cycle the rotor makes 2,000,000,000,000 (two trillion) revolutions. And what bearing will withstand this? Yes, none! There are no bearings there.

The rotor itself is an ordinary top; at the bottom it has a strong needle resting on a corundum bearing, and the upper end hangs in a vacuum, held by an electromagnetic field. The needle is also not simple, made from ordinary wire for piano strings, it is tempered in a very cunning way (like GT). It is not difficult to imagine that with such a frantic rotation speed, the centrifuge itself must be not just durable, but extremely durable.

Academician Joseph Friedlander recalls: “They could have shot me three times. Once, when we had already received the Lenin Prize, there was a major accident, the lid of the centrifuge flew off. The pieces scattered and destroyed other centrifuges. A radioactive cloud rose. We had to stop the entire line - a kilometer of installations! At Sredmash, General Zverev commanded the centrifuges; before the atomic project, he worked in Beria’s department. The general at the meeting said: “The situation is critical. The country's defense is at risk. If we don’t quickly rectify the situation, ’37 will repeat for you.” And immediately closed the meeting. We then came up with a completely new technology with a completely isotropic uniform structure of the lids, but very complex installations were required. Since then, these types of lids have been produced. There were no more troubles. In Russia there are 3 enrichment plants, many hundreds of thousands of centrifuges.”
In the photo: tests of the first generation of centrifuges

The rotor housings were also initially made of metal, until they were replaced by... carbon fiber. Lightweight and highly tensile, it is an ideal material for a rotating cylinder.

UEIP General Director (2009-2012) Alexander Kurkin recalls: “It was getting ridiculous. When they were testing and checking a new, more “resourceful” generation of centrifuges, one of the employees did not wait for the rotor to stop completely, disconnected it from the cascade and decided to carry it by hand to the stand. But instead of moving forward, no matter how he resisted, he embraced this cylinder and began to move backward. So we saw with our own eyes that the earth rotates, and the gyroscope is a great force.”

Who invented it?

Oh, it's a mystery, wrapped in mystery and shrouded in suspense. Here you will find captured German physicists, the CIA, SMERSH officers and even the downed spy pilot Powers. In general, the principle of a gas centrifuge was described at the end of the 19th century.

Even at the dawn of the Atomic Project, Viktor Sergeev, an engineer at the Special Design Bureau of the Kirov Plant, proposed a centrifuge separation method, but at first his colleagues did not approve of his idea. In parallel, scientists from defeated Germany struggled to create a separation centrifuge at a special research institute-5 in Sukhumi: Dr. Max Steenbeck, who worked as a leading Siemens engineer under Hitler, and former Luftwaffe mechanic, graduate of the University of Vienna, Gernot Zippe. In total, the group included about 300 “exported” physicists.

Alexey Kaliteevsky, General Director of Centrotech-SPb CJSC, Rosatom State Corporation, recalls: “Our experts came to the conclusion that the German centrifuge is absolutely unsuitable for industrial production. Steenbeck's apparatus did not have a system for transferring the partially enriched product to the next stage. It was proposed to cool the ends of the lid and freeze the gas, and then defrost it, collect it and put it into the next centrifuge. That is, the scheme is inoperative. However, the project had several very interesting and unusual technical solutions. These “interesting and unusual solutions” were combined with the results obtained by Soviet scientists, in particular with the proposals of Viktor Sergeev. Relatively speaking, our compact centrifuge is one-third the fruit of German thought, and two-thirds Soviet.” By the way, when Sergeev came to Abkhazia and expressed his thoughts about the selection of uranium to the same Steenbeck and Zippe, Steenbeck and Zippe dismissed them as unrealizable.

So what did Sergeev come up with?

And Sergeev’s proposal was to create gas selectors in the form of pitot tubes. But Dr. Steenbeck, who, as he believed, had eaten his teeth on this topic, was categorical: “They will slow down the flow, cause turbulence, and there will be no separation!” Years later, while working on his memoirs, he would regret it: “An idea worthy of coming from us! But it never occurred to me...”

Later, once outside the USSR, Steenbeck no longer worked with centrifuges. But before leaving for Germany, Geront Zippe had the opportunity to get acquainted with a prototype of Sergeev’s centrifuge and the ingeniously simple principle of its operation. Once in the West, “the cunning Zippe,” as he was often called, patented the centrifuge design under his own name (patent No. 1071597 of 1957, declared in 13 countries). In 1957, having moved to the USA, Zippe built a working installation there, reproducing Sergeev’s prototype from memory. And he called it, let’s pay tribute, “Russian centrifuge” (pictured).

By the way, Russian engineering has shown itself in many other cases. An example is a simple emergency shut-off valve. There are no sensors, detectors or electronic circuits. There is only a samovar faucet, which touches the cascade frame with its petal. If something goes wrong and the centrifuge changes its position in space, it simply turns and closes the inlet line. It's like the joke about an American pen and a Russian pencil in space.

Our days

This week the author of these lines attended a significant event - the closure of the Russian office of US Department of Energy observers under a contract HEU-LEU. This deal (highly enriched uranium - low enriched uranium) was, and remains, the largest agreement in the field of nuclear energy between Russia and America. Under the terms of the contract, Russian nuclear scientists processed 500 tons of our weapons-grade (90%) uranium into fuel (4%) HFCs for American nuclear power plants. Revenues for 1993-2009 amounted to 8.8 billion US dollars. This was the logical outcome of the technological breakthrough of our nuclear scientists in the field of isotope separation made in the post-war years.
In the photo: cascades of gas centrifuges in one of the UEIP workshops. There are about 100,000 of them here.

Thanks to centrifuges, we have obtained thousands of tons of relatively cheap, both military and commercial product. The nuclear industry is one of the few remaining (military aviation, space) where Russia holds undisputed primacy. Foreign orders alone for ten years in advance (from 2013 to 2022), Rosatom’s portfolio excluding the contract HEU-LEU is 69.3 billion dollars. In 2011 it exceeded 50 billion...
The photo shows a warehouse of containers with HFCs at the UEIP.

On September 28, 1942, Resolution of the State Defense Committee No. 2352ss “On the organization of work on uranium” was adopted. This date is considered the official beginning of the history of the Russian nuclear industry.

A 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 occurs.

Based on the principle of operation, nuclear reactors are divided into two groups: thermal neutron reactors and fast neutron reactors.

How does a thermal neutron nuclear reactor work?

A typical nuclear reactor has:

  • Core and moderator;
  • Neutron reflector;
  • Coolant;
  • Chain reaction control system, emergency protection;
  • Control 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.

Core and moderator

It is in the core that a controlled fission chain reaction occurs.

Most nuclear reactors operate on 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 tablets is placed in hermetically sealed rods, which are called fuel rods (fuel elements). They permeate the entire active zone filled with moderator neutrons.

Why is a neutron moderator needed 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 capture of slow neutrons. And if their speed is not reduced, the nuclear reaction may die out over time. The moderator 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, a chain reaction in the reactor will require less nuclear fuel.

As a result of the slowdown process, thermal neutrons, the speed of which is almost equal to the speed of thermal movement of gas molecules at room temperature.

Water, heavy water (deuterium oxide D 2 O), beryllium, and graphite are used as a moderator in nuclear reactors. But the best moderator is heavy water D2O.

Neutron reflector

To avoid neutron leakage into the environment, the core of a nuclear reactor is surrounded by neutron reflector. The material used for reflectors is often the same as in moderators.

Coolant

The heat released during a nuclear reaction is removed using a coolant. Ordinary natural water, previously purified from various impurities and gases, is often used as a coolant in nuclear reactors. 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 primary circuit water 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 secondary circuit water. The exchange takes place through heat exchange tubes, so there is no contact with the secondary circuit water. This prevents radioactive substances from entering the second circuit of the heat exchanger.

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

In heavy water reactors, the coolant is heavy water D2O, and in reactors with liquid metal coolants it is molten metal.

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 neutrons of the next generation in the 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 supercritical y. 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 neutron absorbent substances. By extending or pushing these rods into the core, the rate of the nuclear fission reaction is controlled.

The control system provides control of the reactor during its startup, 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 the nuclear reaction quickly stops.

Ensure that the reactor parameters comply with the standards control and radiation protection systems.

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

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 thermal neutron reactors is that fast neutrons arising after the decay of uranium-235 are not slowed down, but are absorbed by uranium-238 with its subsequent conversion into plutonium-239. Therefore, fast neutron reactors are used to produce weapons-grade plutonium-239 and thermal energy, which nuclear power plant generators 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 uranium-238. When a thermal neutron is absorbed, it does not fission, but becomes an isotope of uranium-239.

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

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 the plutonium-239 nucleus, uranium-235 is obtained:

239 94 Pu → 235 92 U + 4 2 He

Fuel rods with raw materials (enriched 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 uranium-238 nuclei. As a result, plutonium-239 is formed. Thus, new nuclear fuel is produced in fast neutron reactors.

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

Classification and application of nuclear reactors

Nuclear reactors are mainly used in nuclear power plants. With their help, electrical and thermal energy is produced on an industrial scale. Such reactors are called energy .

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

For scientific research in the field of nuclear physics and radiation chemistry, fluxes of neutrons and gamma quanta are used, which are obtained in the core 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 a value of only a few kW. These reactors study various physical quantities, the meaning of which is important in the design of nuclear reactions.

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