General, Research, Technology

How does a nuclear power plant work? Are nuclear plants dangerous?

Many people at the very beginning of the conversation about nuclearthe stations immediately begin to say that it is very dangerous and should be abandoned. Partly they are right, but their fears are greatly exaggerated. In order to get rid of such a stereotype, you just need to understand how the station works and make sure that the ingress of radioactive elements into the environment is simply impossible. Of course, if the station is functioning normally. The only question is how exactly it functions and where are the borders of this regular regime. Today we’ll talk about the design of a nuclear power plant, their types and how they produce electricity through the fission of uranium atoms. I’ll specially speak in plain language.

Even the picture is a little scary, but not everything is so scary.

Content

  • 1 When did the first nuclear power plant appear
  • 2 How much energy does a nuclear power plant produce?
  • 3 Are nuclear plants dangerous
  • 4 What does a nuclear power plant work on
  • 5 What are nuclear plants
  • 6 How a nuclear power plant works
  • 7 Accidents with radioactive releases

When did the first nuclear power station appear

The first serious step towards usingproperties of atomic fission, including atomic weapons and peaceful atoms, was the test of the first atomic bomb in 1945. It happened July 16 at a training ground in the state of New Mexico. During those trials, many realized that the horrors of World War II had faded a bit against what could have happened, such weapons appeared a little earlier.

The first nuclear tests in the USSR in the USSRoccurred only after 4 years - on August 29, 1949. Since then, the two largest powers have had technologies that allowed them not only to intimidate each other with their strength, but also to work for the benefit of a peaceful atom and the use of this destructive force in order to bring light and heat to every home.

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The first nuclear power plant was launched in1954 in the area of ​​the city of Obninsk, Moscow Region. The ideological inspirer and leader of the project was the famous Soviet physicist, academician of the USSR Academy of Sciences and part-time “father” of the Soviet atomic bomb Igor Kurchatov.

Igor Kurchatov at work.

How much energy does a nuclear power plant produce?

Of course, that first nuclear power plant is difficultto compare with modern ones, but it was she who laid the foundation for a new way of generating energy, as the first iPhone launched the smartphone building process, and Ford T launched mass production of cars.

Since then the number of nuclear power plants in the worldgreatly increased and reached 192 units (a total of 438 power units) in 31 countries of the world. 10 nuclear power plants are located in Russia (a total of 33 power units). According to this indicator, our country is in eighth place in the world, and in fourth place in energy production.

Total energy production is approximately392 MW. Among the leaders are the United States (103 MW), France (66 MW), Japan (46 MW), Russia (25 MW) and South Korea (21 MW). This is quite a lot, and according to statistics, nuclear plants provide 16 percent of the world's electricity consumption.

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High interest in nuclear power plants and theirwidespread use is due to the fact that their efficiency is 40-45 percent or more, and the risks are significantly less, despite all the terrible accidents that occurred. On the one hand, it seems that if it explodes, it won’t seem to be enough, but on the other hand, according to statistics, NPPs have 43 times less victims per kilowatt received than thermal power plants.

A thermal power plant is also a construction.

Are nuclear plants dangerous

As a result, we get a situation in which atomicenergy resembles the situation with airplanes. Many are afraid of them, but in reality, the risk of simply dying on the street is hundreds of times higher than crashing on an airplane. It’s just that accidents cause a lot of resonance and more people die at one time, but such accidents rarely occur.

In addition to the systems of the nuclear power plant itself, about which wetalk below, they are accompanied by serious precautions. Frankly, when I was near the Voronezh NPP I was a little uneasy, but when I gathered more information, I realized that I was overestimating the situation.

Around any nuclear power station there is at least30-kilometer zone, in which the situation and environmental situation are constantly monitored. This is not an exclusion zone, since people can live in it and even engage in agriculture. The restrictions apply only to the three-kilometer zone in the immediate vicinity of the station. But this, again, was done only with the aim of providing additional security, and not because it was dangerous to be there.

This is the safety zone around Balakovo NPP.

Probably the most dangerous period for the stationis the fuel loading moment. It is at this point that the reactor opens and there is a small risk of radioactive waste entering the air. True, this is not done often (on average once a year) and the emission will be very small.

What does a nuclear power plant work on

The main element on which atomicstation, is uranium-235, which is loaded into the reactor in special cartridges, which are called fuel elements (TVEL). In one reactor there can be several tens or even hundreds of them.

The fuel elements are delivered to the reactor on special platforms, and they are loaded into it with a crane. The same crane participated in the construction of the station and immersed the reactor itself in a special capsule.

By the way, the name TVEL was given to a company that produces nuclear fuel.

The average reactor uses about ten per year.kilogram of fuel. It is such a small volume that releases the amount of energy that the station produces. If we talk about the productivity of nuclear fuel, we can say that one gram of uranium-235 allows you to get as much energy as from burning fuel produced from two tons of oil. As a result, only ten kilograms of fuel are the equivalent of about seven hundred oil tanks.

These are only 15 tanks, and almost 700 tanks are equivalent to 10 kg of nuclear fuel.

What are nuclear plants

Many people think that it is radioactive fuel that produces electrical energy, but this is not entirely true. More precisely, this is not so at all.

The operation of a nuclear power plant can be divided intothree main steps. At the first stage, the atomic fission energy is converted into thermal energy. At the next stage, thermal energy is converted into mechanical energy. After this, the conversion of mechanical energy into electricity becomes a matter of technology.

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Reactors are divided into three main types: single-circuit, double-circuit, three-circuit. In the beginning, we will understand how the two-circuit circuit works, and a little later on its example we will see how the other types work.

How a nuclear plant works

The initial stage of energy release is howI said above, the reactor. It is placed in a special closed circuit called the first. It is, in fact, a large pan, or rather a pressure cooker, since the liquids inside it are under great pressure. So it turns out to increase the boiling point and increase the temperature of the entire primary circuit.

The capsule in which the reactor is located is called a pressurized chamber and has thick walls (at least 15 centimeters). This allows you to keep a lot of pressure inside and does not allow radiation to go outside.

Simplified scheme of nuclear power plants looks like this.

The main task of the rector is heat generationto heat the fluid inside the circuit. This happens due to a chain reaction. The basis of such a reaction is the fission of atoms by neutrons. In this case, after the fission of one atom, new neutrons are released, which continue to divide the atoms. Thus, the number of neutrons is constantly growing and atoms are being divided more and more. It turns out that very chain reaction that supports itself, but if this process is not stopped, the division will get out of control, too much energy will be released and an explosion will occur. Actually, this is what happens in the atomic bomb.

To prevent this from happening, inside the rector there isspecial rods with boron, which absorb neutrons very well and inhibit the reaction. The rods are several meters long and constantly either enter the reactor or exit it, thereby regulating the neutron fission coefficient and, as a consequence, the reaction rate. If this coefficient is less than one, the reaction is slowed down, if it is more, it accelerates, and if it is equal to one, then the system itself maintains its work. This unit must be achieved for the stable operation of the reactor.

After the reactor has heated the water insideof the primary circuit to a temperature of about 450 degrees, it passes through the heat exchanger tube and instantly heats the water of the secondary circuit. That, in turn, enters the evaporator and already water vapor with a temperature of about 350-400 degrees spins a huge turbine up to 3000 rpm. It is this turbine that produces electricity, which goes through wires to the power grid.

Complete isolation of the primary circuit from the secondaryallows to protect the working fluid and wastewater from radioactive contamination. This makes it easy to cool the liquid to further its work, because the promotion of the turbine at the last stage of the second loop.

After the water steam spins the turbine blades, it enters special condensers, which are large chambers. In them, the steam cools and turns into water.

It looks like Mitsubishi turbine manufacturing plant.

While the water temperature is still very high andit must still be cooled. To do this, she either directly or through a special channel enters the tower. This is a pipe that can be seen on the territory of thermal power plants. It has a height of about 70 meters, a large diameter and tapers to the top. Usually knocked out of her clouds of white vapor. Many people think that it is smoke, but it is steam. Water with a temperature close to the boiling point is sprayed at the base of this pipe and, mixed with air coming from the street, soars and cools. An average cooling tower can cool up to 20,000 cubic meters of water per hour or about 450,000 cubic meters per day

After cooling, water with special pumpsfed back into the system for heating and evaporation. Since a lot of water is required, nuclear power plants are accompanied by fairly large reservoirs and sometimes an extensive system of canals. This allows the station to operate without interruption.

Now you can return to single-circuit andthree-loop plant. The first ones have a simpler design, since they do not have a second circuit and the turbine spins directly with water heated by the reactor. The difficulty lies in the fact that the water must somehow be cleaned and are less environmentally friendly station.

The three-circuit scheme is applied on atomicstations equipped with fast neutron reactors. They are considered more promising, but should be equipped with an additional circuit in order to exclude contact of radioactive sodium with water. In an additional circuit is non-radioactive sodium.

Of course, the above diagram is approximate andsimplified. In addition, the station has various technical structures, a command console, a large number of protective systems that are duplicated many times, and other auxiliary systems. In addition, at the same station there are several power units, which also complicates the process of its control.

There are a lot of different structures on the territory of the nuclear power plant. Balakovo NPP.

In fact, a modern station can not justwork in automatic mode, but also do it without a person at all. At least, this applies to the power unit management. A person is needed to control and make adjustments to the work in case of an emergency. The risk of its occurrence is very low, but just in case, experts are on duty at the console.

Radioactive accident

If we are already talking about accidents at nuclear power plants, let's discuss how they are classified and which of them were the largest.

To classify accidents by severity and severityimpact on humans and nature, they are divided into 7 degrees on the International Nuclear Event Scale, gaining a certain level of INES. Based on this level, one can judge whether people were harmed and how damaged the equipment of the station itself was. Not all levels are considered dangerous.

For example, incidents at the Chernobyl nuclear power plant (26April 1986) and at the Fukushima-1 nuclear power plant (March 11, 2011) corresponded to the maximum seventh level, and some accidents, which almost no one knew about, corresponded to the fourth level. For example, an explosion at the Siberian Chemical Plant (Russia, 1993), an accident at the Tokaymura nuclear facility (Japan, 1999), and an accident at the Radio Element Institute in Fleurus (Belgium, 2006).

This is the Chock River.

Since we are talking about accidents, it is worth mentioning the first accident with radioactive contamination. It happened at the Chock River Laboratory on December 12, 1952.

It happened due to a number of operator errors andfailures in the emergency stop system. The reactor in the laboratory went into supercritical operation. The chain reaction supported itself and the release of energy was several times higher than normal. As a result, the core was damaged and radioactive fission products with a long half-life, together with a mass of cooling water, spilled into the basement. For a year of operation, the reactor was completely restored.

As you can see, accidents happen and sometimes their magnitudethey are frightening, but all the same, according to statistics, the operation of nuclear power plants is much safer and does less harm than burning fuel. The difference in environmental friendliness is already reaching three to four times. On the approach thermonuclear reactors, which should make the process even more environmentally friendly. So far, by and large, the only problem is spent fuel. It must somehow be deactivated and disposed of. Scientists are working on it. Let's hope they solve this problem.

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