Almost 25 years have passed since the terrible event that shocked the whole world. The echoes of this catastrophe of the century will stir the souls of people for a long time, and its consequences will affect people more than once. The disaster at the Chernobyl nuclear power plant - why did it happen and what are its consequences for us?
Why did the Chernobyl disaster happen?
There is still no clear opinion about what caused the disaster at the Chernobyl nuclear power plant. Some argue that the reason is faulty equipment and gross mistakes during the construction of the nuclear power plant. Others see the cause of the explosion as a malfunction of the circulating water supply system, which provided cooling to the reactor. Still others are convinced that the permissible load experiments carried out at the station that ominous night were to blame, during which a gross violation of operating rules occurred. Still others are confident that if there had been a protective concrete cap over the reactor, the construction of which was neglected, such a spread of radiation that occurred as a result of the explosion would not have occurred.
Most likely, this terrible event occurred due to the combination of the listed factors - after all, each of them took place. Human irresponsibility, acting at random in matters relating to life and death, and the deliberate concealment of information about what happened on the part of the Soviet authorities led to consequences, the results of which will echo for a long time to more than one generation of people around the world.
Chernobyl disaster. Chronicle of events
The explosion at the Chernobyl nuclear power plant occurred in the dead of night on April 26, 1986. A fire brigade was called to the scene. Brave and courageous people, they were shocked by what they saw and, judging by the off-scale radiation meters, they immediately guessed what had happened. However, there was no time to think - and a team of 30 people rushed to fight the disaster. For protective clothing, they wore ordinary helmets and boots - of course, they in no way could protect the firefighters from huge doses of radiation. These people have been dead for a long time; they all died a painful death at different times from the cancer that struck them..
By morning the fire was extinguished. However, pieces of uranium and graphite emitting radiation were scattered throughout the territory of the nuclear power plant. The worst thing is that the Soviet people did not immediately learn about the disaster that occurred at the Chernobyl nuclear power plant. This made it possible to maintain calm and prevent panic - this is exactly what the authorities sought, turning a blind eye to the cost of their ignorance for people. The unaware population spent two whole days after the explosion calmly resting in the territory, which had become deadly dangerous, going out into nature, to the river; on a warm spring day, children spent a long time on the street. And everyone absorbed huge doses of radiation.
And on April 28, complete evacuation was announced. 1,100 buses in a convoy transported the population of Chernobyl, Pripyat and other nearby settlements. People abandoned their homes and everything in them - they were only allowed to take with them identity cards and food for a couple of days.
A zone with a radius of 30 km was recognized as an exclusion zone unsuitable for human life. The water, livestock and vegetation in this area were considered unfit for consumption and hazardous to health.
The temperature in the reactor in the first days reached 5000 degrees - it was impossible to approach it. A radioactive cloud hung over the nuclear power plant and circled the Earth three times. To nail it to the ground, the reactor was bombed from helicopters with sand and watered, but the effect of these actions was negligible. There was 77 kg of radiation in the air - as if a hundred atomic bombs had been dropped on Chernobyl at the same time.
A huge ditch was dug near the Chernobyl nuclear power plant. It was filled with the remains of the reactor, pieces of concrete walls, and the clothes of disaster relief workers. For a month and a half, the reactor was completely sealed with concrete (the so-called sarcophagus) to prevent radiation leakage.
In 2000, the Chernobyl nuclear power plant was closed. Work is still underway on the Shelter project. However, Ukraine, for which Chernobyl became a sad “inheritance” from the USSR, does not have the required money for it.
The tragedy of the century that they wanted to hide
Who knows how long the Soviet government would have hidden the “incident” if not for the weather. Strong winds and rains, which inappropriately passed through Europe, carried radiation throughout the world. Ukraine, Belarus and the southwestern regions of Russia, as well as Finland, Sweden, Germany, and Great Britain suffered the most.
For the first time, unprecedented numbers on radiation level meters were seen by employees of the nuclear power plant in Forsmark (Sweden). Unlike the Soviet government, they rushed to immediately evacuate all the people living in the surrounding area before determining that the problem was not their reactor, but the supposed source of the emanating threat was the USSR.
And exactly two days after Forsmark scientists declared a radioactive alert, US President Ronald Reagan held in his hands photographs of the Chernobyl nuclear power plant disaster site taken by a CIA artificial satellite. What was depicted on them would have horrified even a person with a very stable psyche.
While periodicals around the world trumpeted the dangers arising from the Chernobyl disaster, the Soviet press escaped with a modest statement that there had been an “accident” at the Chernobyl nuclear power plant.
Chernobyl disaster and its consequences
The consequences of the Chernobyl disaster made themselves felt in the very first months after the explosion. People living in the areas adjacent to the site of the tragedy died from hemorrhages and apoplexy.
The liquidators of the consequences of the accident suffered: out of a total number of liquidators of 600,000, about 100,000 people are no longer alive - they died from malignant tumors and destruction of the hematopoietic system. The existence of other liquidators cannot be called cloudless - they suffer from numerous diseases, including cancer, disorders of the nervous and endocrine systems. Many evacuees and affected populations in the surrounding areas have these same health problems.
The consequences of the Chernobyl disaster for children are terrible. Developmental delays, thyroid cancer, mental disorders and a decrease in the body's resistance to all types of diseases - this is what awaited children exposed to radiation.
However, the worst thing is that the consequences of the Chernobyl disaster affected not only people living at that time. Problems with pregnancy, frequent miscarriages, stillborn children, frequent births of children with genetic disorders (Down syndrome, etc.), weakened immunity, an astounding number of children with leukemia, an increase in the number of cancer patients - all these are echoes of the disaster at the Chernobyl nuclear power plant, the end of which will come yet not soon. If it comes...
Not only people suffered from the Chernobyl disaster - all life on Earth felt the deadly force of radiation. As a result of the Chernobyl disaster, mutants appeared - descendants of humans and animals born with various deformations. A foal with five legs, a calf with two heads, fish and birds of unnaturally huge sizes, giant mushrooms, newborns with deformities of the head and limbs - photos of the consequences of the Chernobyl disaster are terrifying evidence of human negligence.
The lesson taught to humanity by the Chernobyl disaster was not appreciated by people. We still treat our own lives with the same carelessness, we still strive to squeeze the maximum out of the riches given to us by nature, everything we need “here and now.” Who knows, maybe the disaster at the Chernobyl nuclear power plant became the beginning to which humanity is moving slowly but surely...
Film about the Chernobyl disaster
We advise everyone who is interested to watch the full-length documentary film “The Battle of Chernobyl”. This video can be watched right here online and for free. Enjoy watching!
Find another video on youtube.com
Chernobyl nuclear power plant during construction
The territory of the Polesie region has been inhabited and developed by people for several millennia. By creating new infrastructure, building cities, drying swamps and irrigating lands, people recorded their history.
Pripyat River near the Chernobyl Nuclear Power Plant
Chernobyl and Pripyat
Compared to the young Pripyat, the city of Chernobyl is already several centuries old. Pripyat's time stopped when she reached her 16th birthday. In turn, Chernobyl is considered one of the oldest settlements in Ukrainian Polesie.
A few centuries ago, this city united not only cultural and historical monuments. At the same time, Chernobyl also united different nationalities. Representatives of different nations lived in commonwealth with each other.
Moreover, the modern exclusion zone was previously a real historical place, because there were Tatar burial mounds and the ruins of old monasteries. Of course, there are also memorial sites here from the Great Patriotic War. However, the Chernobyl tragedy on April 26, 1986 made much of the above disappear, while the once historical lands remained mothballed for many centuries.
Cemetery of radioactive equipment in Chernobyl
In what year did the Chernobyl tragedy occur?
The Chernobyl tragedy occurred in a year when the Soviet energy industry was supposed to enter a new stage of development, because in addition to planned experiments, the Chernobyl nuclear power plant was preparing to launch new power units with the RBMK-1000 reactor. The successful use of nuclear resources has drowned out the most important thing that a specialist should have - responsibility. And this is not only responsibility for the safety of others. This is mindfulness while using the gigantic power of nuclear fuel.
The RBMK-1000 reactor and the nuclear fuel it contained turned out to be invincible opponents for the common man. Alluring with its potential, it succumbed and ended up in the hands of man, but in an unexpected moment, when everyone allowed themselves to relax, it brought great tragedy to Chernobyl and its surroundings.
Consequences of the Chernobyl accident
The Chernobyl tragedy of 1986 is considered the largest in human history. The moment the reactor of the fourth power unit exploded was accompanied by the formation of a column of fire that stretched several kilometers upward. This column contained radioactive particles and penetrated even those layers of the atmosphere that it seemed simply could not reach.
The Chernobyl disaster is gradually being forgotten, although it seemed that the most grandiose man-made disaster in the history of mankind in terms of its scale and consequences - the accident at the Chernobyl nuclear power plant - will forever be etched in human memory and will serve as a menacing warning to people living today and their descendants that the nucleus of an atom must always be dealt with talk to YOU about the frivolous, self-confident attitude towards nuclear energy,
The article examines the technical side of this huge tragedy. I tell specialists in advance that much is given here in an extremely simplified form, in some places even to the detriment of scientific accuracy. This was done so that even a person very far from physics and nuclear energy would understand what happened and why on the night of April 25-26, 1986.
Although this disaster is not directly related to military science and history, it was the “stupid and illiterate, rude and stupid” army that had to use the lives and health of its soldiers and officers to correct the mistakes of the “intelligent geniuses of science, the concentration of all the best that is in our society ".
It was highly educated and technically competent nuclear scientists, all these “Promstroykompleks”, “Atomstroy”, Dontekhenergo”, all the venerable academicians, doctors of sciences who managed to arrange this disaster, but were unable to either organize work to eliminate the consequences or manage all the material resources provided at their disposal.
It turned out that they simply did not know what to do now, they did not know the processes occurring in the reactor. You should have seen their shaking hands, confused faces, and pitiful babble of self-justification in those days.
Orders and decisions were either made or cancelled, but nothing was done. And radioactive dust rained down on the heads of Kiev residents.
And only when the head of the chemical forces of the Ministry of Defense got down to work and troops began to gather at the site of the tragedy; When at least some concrete work began, these “scientists” breathed a sigh of relief. Now you can again intelligently argue about the scientific aspects of the problem, give interviews, criticize the mistakes of the military, and tell tales about your scientific foresight.
Physical processes occurring in a nuclear reactor
A nuclear power plant is not much different from a thermal power plant. The whole difference is that in a thermal power plant, steam for turbines driving electric generators is obtained by heating water from the combustion of coal, fuel oil, gas in the furnaces of steam boilers, and in a nuclear power plant, steam is obtained in a nuclear reactor from the same water.
When the atomic nucleus of heavy elements decays, several neutrons are released from it. The absorption of such a free neutron by another atomic nucleus causes excitation and decay of this nucleus. At the same time, several neutrons are also released from it, which in turn... The so-called nuclear chain reaction begins, accompanied by the release of thermal energy.
Attention! First term! Multiplication factor - K. If at a given stage of the process the number of free neutrons formed is equal to the number of neutrons that caused nuclear fission, then K = 1 and each unit of time the same amount of energy is released, but if the number of free neutrons formed is greater than the number of neutrons that caused nuclear fission , then K>1 and at each subsequent moment of time the energy release will increase. And if the number of free neutrons produced is less than the number of neutrons that caused nuclear fission, then K<1 и в каждый следующий момент времени выделение энергии будет уменьшаться.
The task of the power plant duty shift personnel is precisely to keep K approximately equal to 1. If K<1, то реакция будет затухать, количество вырабатываемого пара уменьшаться, пока реактор не остановится. Если К>1 and it cannot be made equal to 1, then what happened at the Chernbyl nuclear power plant will happen.
It seems easy to come to the conclusion that the nuclear fission reaction will increase all the time, because One free neutron during the splitting of an atomic nucleus releases 2-3 neutrons and the number of free neutrons should increase all the time.
To prevent this from happening, tubes containing a substance that absorbs neutrons well (cadmium or boron) are placed between the tubes containing nuclear fuel. By moving such tubes out of the reactor core, or vice versa, introducing such tubes into the zone, they can be used to capture some of the free neutrons, thus regulating their number in the reactor core and maintaining the K coefficient close to unity.
When uranium nuclei fission, nuclei of lighter elements are formed from their fragments. Among them is tellurium-135, which turns into iodine-135, and iodine in turn quickly turns into xenon-135. This xenon is very active in capturing free neutrons. If the reactor operates in a stable mode, then the xenon-135 atoms burn out quite quickly and do not affect the operation of the reactor. However, if there is a sharp and rapid decrease in reactor power for some reason, xenon does not have time to burn out and begins to accumulate in the reactor, significantly reducing K, i.e. helping to reduce reactor power. The phenomenon of so-called (Attention! Second term!) xenon poisoning of the reactor is growing. At the same time, the iodine-135 accumulated in the reactor begins to turn into xenon even more actively. This phenomenon is called (Attention! Third term!) iodine pit.
Under such conditions, the reactor does not respond well to the extension of control rods (tubes with boron or cadmium), because neutrons are actively absorbed by xenon. However, in the end, with a sufficiently significant extension of the control rods from the core, the power of the reactor begins to increase, heat generation increases, and xenon begins to burn out very quickly. It no longer captures free neutrons and their number is rapidly increasing. The reactor gives a sharp jump in power. The control rods lowered at this moment do not have time to absorb the neutrons quickly enough. The reactor may escape the operator's control.
The instructions require that when there is a certain amount of xenon in the core, do not try to increase the power of the reactor, but by lowering the control rods, finally stop the reactor. But the natural removal of xenon from the reactor core takes up to several days. All this time, no electricity is generated by this energy unit.
There is another term - reactor reactivity, i.e. how the reactor responds to operator actions. This coefficient is determined by the formula p=(K-1)/K. At p>0 the reactor accelerates, at p=0 the reactor operates in a stable mode, at p< 0 идет затухание реактора.
Principles of reactor design
Nuclear fuel is black tablets with a diameter of about 1 cm and a height of about 1.5 cm. They contain 2% uranium dioxide 235, and 98% uranium 238, 236, 239. In all cases, with any amount of nuclear fuel, a nuclear explosion cannot develop , because for an avalanche-like rapid fission reaction characteristic of a nuclear explosion, a concentration of uranium 235 of more than 60% is required.
Two hundred nuclear fuel pellets are loaded into a tube made of zirconium metal. The length of this tube is 3.5m. diameter 1.35 cm. This tube is called (Attention! Fifth term!) Fuel element - fuel element.
36 fuel rods are assembled into a cassette (another name is “assembly”).
The RBMK-1000 brand reactor (high-power channel reactorchernob-5.jpg (7563 bytes) with an electric power of 1000 megawatts) is a cylinder with a diameter of 11.8 m and a height of 7 meters, made of graphite blocks (the size of each block is 25x25x60cm. Through each The block passes through a hole - a channel. There are a total of 1872 such holes - channels in this cylinder. 1661 channels are intended for cartridges with nuclear fuel, and 211 for control rods containing a neutron absorber (cadmium or boron).
This cylinder is surrounded by a 1 meter thick wall made of the same graphite blocks, but without holes. The whole thing is surrounded by a steel tank filled with water. This entire structure lies on a metal plate and is covered on top with another plate (lid). The total weight of the reactor is 1850 tons. The total mass of nuclear fuel in the reactor is 190 tons.
In the figure on the left is an assembly with fuel rods in the reactor channel, on the right is a control rod in the reactor channel.
Each reactor supplies steam to two turbines. Each turbine has an electrical power of 500 megawatts. The thermal power of the reactor is 3200 megawatts.
The operating principle of the reactor is as follows:
Water under pressure of 70 atmospheres by main circulation pumps
The main circulation pump is supplied through pipelines to the lower part of the reactor, from where it is pressed through the channels into the upper part of the reactor, washing the assemblies with fuel rods.
In fuel rods, under the influence of neutrons, a nuclear chain reaction occurs with the release of a large amount of heat. The water heats up to a temperature of 248 degrees and boils. A mixture of 14% steam and 86% water is supplied through pipelines to separator drums, where steam is separated from water. Steam is supplied through a pipeline to the turbine.
From the turbine, through a pipeline, steam, which has already turned into water with a temperature of 165 degrees, returns to the separator drum, where it mixes with hot water coming from the reactor and cools it to 270 degrees. This water is again supplied through the pipeline to the pumps. The cycle is complete. Additional water can be supplied to the separator from outside through the pipeline (6).
There are only eight main circulation pumps. Six of them are in operation, and two are in reserve. There are only four separator drums. The dimensions of each are 2.6 m in diameter, 30 meters long. They work simultaneously.
Prerequisites for disaster
The reactor is not only a source of electricity, but also its consumer. Until nuclear fuel is unloaded from the reactor core, water must be continuously pumped through it so that the fuel rods do not overheat.
Typically, part of the electrical power of turbines is selected for the reactor's own needs. If the reactor is shut down (fuel replacement, preventive maintenance, emergency shutdown), then the reactor is powered from neighboring units or an external power grid.
In case of extreme emergency, power is provided from backup diesel generators. However, in the best case scenario, they will be able to start producing electricity no sooner than in one to three minutes.
The question arises: how to power the pumps until the diesel generators reach operating mode? It was necessary to find out how long from the moment the steam supply to the turbines is turned off, they, rotating by inertia, will generate a current sufficient for emergency power supply to the main reactor systems. The first tests showed that the turbines cannot provide electricity to the main systems in the inertial rotation mode (coasting mode).
Dontekhenergo specialists proposed their own system for controlling the magnetic field of the turbine, which promised to solve the problem of power supply to the reactor in the event of an emergency shutdown of the steam supply to the turbine.
On April 25, it was planned to test this system in operation, because... The 4th power unit was still planned to be shut down for repair work that day.
However, it was necessary, firstly, to use something as a ballast load so that measurements could be taken on a running-out turbine. Secondly, it was known that if the thermal power of the reactor dropped to 700-1000 megawatts, the reactor emergency shutdown system (ERS) would be triggered, the reactor would be shut down and it would be impossible to repeat the experiment several times, because xenon poisoning will occur.
It was decided to block the ECCS system and use backup main circulation pumps as a ballast load.
(main central pump)
These were the FIRST and SECOND tragic mistakes that led to everything else.
Firstly, there was absolutely no need to block the ECCS.
Secondly, anything could be used as a ballast load, but not circulation pumps.
It was they who connected the completely distant electrical processes and processes occurring in the reactor.
Chronicle of the disaster
13.05. The reactor power was reduced from 3200 megawatts to 1600. Turbine No. 7 was stopped. Power supply to the reactor electrical systems was transferred to turbine No. 8.
14.00. The emergency shutdown system of the ECCS reactor is blocked. At this time, the Kievenergo dispatcher ordered to delay the shutdown of the unit (end of the week, afternoon, energy consumption is increasing). The reactor is operating at half power, and the ECCS has not been reconnected. This was a gross mistake by the staff, but it did not affect the development of events.
23.10. The dispatcher lifts the ban. The personnel begins to reduce the power of the reactor.
April 26, 1986 0.28. The reactor power has decreased to a level where the system for controlling the movement of the control rods must be transferred from local to general (in normal mode, groups of rods can be moved independently of each other - this is more convenient, but at low power all rods must be controlled from one place and move simultaneously).
This was not done. This was the THIRD tragic mistake. At the same time, the operator makes a FOURTH tragic mistake. It does not command the car to "hold power". As a result, the reactor power is rapidly reduced to 30 megawatts. Boiling in the channels decreased sharply, and xenon poisoning of the reactor began.
The shift staff makes the FIFTH tragic mistake (I would give a different assessment to the actions of the shift at this moment. This is no longer a mistake, but a crime. All instructions require shutting down the reactor in such a situation). The operator removes all control rods from the core.
1.00. The reactor power was raised to 200 megawatts against the 700-1000 prescribed by the test program. This was the second criminal act of the shift. Due to the growing xenon poisoning of the reactor, the power cannot be raised higher.
1.03. The experiment began. The seventh pump is connected to the six operating main circulation pumps as a ballast load.
1.07. The eighth pump is connected as a ballast load. The system is not designed to operate such a number of pumps. The cavitation failure of the main circulation pump began (they simply do not have enough water). They suck water out of the separator drums and its level in them drops dangerously. The huge flow of fairly cold water through the reactor reduced steam generation to a critical level. The machine completely removed the automatic control rods from the core.
1.19. Due to the dangerously low water level in the separator drums, the operator increases the supply of feed water (condensate) to them. At the same time, the staff makes the SIXTH tragic mistake (I would say the second criminal act). It blocks reactor shutdown systems based on signals of insufficient water level and steam pressure.
1.19.30 The water level in the separator drums began to rise, but due to a decrease in the temperature of the water entering the reactor core and its large quantity, boiling there stopped.
The last automatic control rods left the core. The operator makes his SEVENTH tragic mistake. He completely removes the last manual control rods from the core, thereby depriving himself of the ability to control the processes occurring in the reactor.
The fact is that the height of the reactor is 7 meters and it responds well to the movement of the control rods when they move in the middle part of the core, and as they move away from the center, controllability deteriorates. The speed of movement of the rods is 40 cm. per second
1.21.50 The water level in the separator drums has slightly exceeded the norm and the operator turns off some of the pumps.
1.22.10 The water level in the separator drums has stabilized. Much less water now enters the core than before. Boiling begins again in the core.
1.22.30 Due to the inaccuracy of the control systems, which were not designed for such an operating mode, it turned out that the water supply to the reactor was about 2/3 of what was required. At this moment, the station computer issues a printout of the reactor parameters indicating that the reactivity margin is dangerously low. However, the staff simply ignored this data (this was the third criminal act that day). The instructions prescribe in such a situation to immediately shut down the reactor in an emergency manner.
1.22.45 The water level in the separators has stabilized, and the amount of water entering the reactor has been brought back to normal.
The thermal power of the reactor slowly began to increase. The staff assumed that the operation of the reactor had been stabilized and it was decided to continue the experiment.
This was the EIGHTH tragic mistake. After all, practically all the control rods were in the raised position, the reactivity margin was unacceptably small, the ECCS was disabled, and the systems for automatically shutting down the reactor due to abnormal steam pressure and water level were blocked.
1.23.04 Personnel blocks the reactor emergency shutdown system, which is triggered in the event of a loss of steam supply to the second turbine, if the first one has already been turned off. Let me remind you that turbine No. 7 was turned off at 13.05 on 25.04 and now only turbine No. 8 was working.
This was the NINTH tragic mistake. (and the fourth criminal act this day). The instructions prohibit disabling this reactor emergency shutdown system in all cases. At the same time, the personnel shuts off the steam supply to turbine No. 8. This is an experiment to measure the electrical characteristics of the turbine in run-down mode. The turbine begins to lose speed, the voltage in the network decreases and the main circulation pump powered by this turbine begins to reduce speed.
The investigation established that if the emergency shutdown system of the reactor had not been turned off by a signal that the steam supply to the last turbine had been stopped, the disaster would not have occurred. Automation would have shut down the reactor.
But the staff intended to repeat the experiment several times using different parameters for controlling the magnetic field of the generator. Shutting down the reactor excluded this possibility.
1.23.30 The main circulation pumps significantly reduced their speed and the flow of water through the reactor core decreased significantly. Steam formation began to rapidly increase. Three groups of automatic control rods went down, but they could not stop the increase in the thermal power of the reactor, because there weren't enough of them anymore. Because The steam supply to the turbine was turned off, its speed continued to decrease, and the pumps supplied less and less water to the reactor.
1.23.40 The shift supervisor, realizing what is happening, orders to press the AZ-5 button. At this command, the control rods move down at maximum speed. Such a massive introduction of neutron absorbers into the reactor core is intended to completely stop nuclear fission processes in a short time.
This was the last TENTH tragic personnel error and the last direct cause of the disaster. Although it should be said that if this last mistake had not been made, then the catastrophe would have been inevitable.
And this is what happened - at a distance of 1.5 meters under each rod
the so-called “displacer” is suspended
This is an aluminum cylinder 4.5 m long, filled with graphite. Its task is to ensure that when the control rod is lowered, the increase in neutron absorption does not occur abruptly, but more smoothly. Graphite also absorbs neutrons, but somewhat weaker. than boron or cadmium.
When the control rods are raised to their maximum limit, the lower ends of the displacers are 1.25 m above the lower boundary of the core. In this space there is water that is not yet boiling. When all the rods sharply went down the AZ-5 singal, the rods themselves with boron and cadmium had not yet actually entered the active zone, and the displacer cylinders, acting like pistons, displaced this water from the active zone. The fuel rods were exposed.
There was a sharp jump in vaporization. The steam pressure in the reactor increased sharply and this pressure did not allow the rods to fall down. They hovered after walking only 2 meters. The operator turns off the power to the rod couplings.
Pressing this button turns off the electromagnets that keep the control rods attached to the valve. After such a signal is given, absolutely all the rods (both manual and automatic control) are disconnected from their reinforcement and freely fall down under the influence of their own weight. But they were already hanging, supported by steam, and did not move.
1.23.43 Self-acceleration of the reactor began. Thermal power reached 530 megawatts and continued to grow rapidly. The last two emergency protection systems were activated - by power level and by the rate of power growth. But both of these systems control the issuance of the AZ-5 signal, and it was given manually 3 seconds ago.
1.23.44 In a split second, the thermal power of the reactor increased 100 times and continued to increase. The fuel rods became hot, and the swelling fuel particles tore the shells of the fuel rods. The pressure in the core increased many times over. This pressure, overcoming the pressure of the pumps, forced the water back into the supply pipelines.
Further, the steam pressure destroyed part of the channels and steam pipelines above them.
This was the moment of the first explosion.
The reactor ceased to exist as a controlled system.
After the destruction of the channels and steam lines, the pressure in the reactor began to drop and water again flowed into the reactor core.
Chemical reactions of water with nuclear fuel, heated graphite, and zirconium began. During these reactions, rapid formation of hydrogen and carbon monoxide began. The gas pressure in the reactor rapidly increased. The reactor cover, weighing about 1,000 tons, lifted, breaking all the pipelines.
1.23.46 The gases in the reactor combined with atmospheric oxygen, forming an explosive gas, which instantly exploded due to the high temperature.
This was the second explosion.
The reactor lid flew up, turned 90 degrees and fell back down again. The walls and ceiling of the reactor hall collapsed. A quarter of the graphite located there and fragments of hot fuel rods flew out of the reactor. These debris fell on the roof of the turbine hall and other places, creating about 30 fires.
The fission chain reaction has stopped.
The station staff began leaving their jobs at approximately 1.23.40. But from the moment the AZ-5 signal was issued until the moment of the second explosion, only 6 seconds passed. It is impossible to figure out what is happening during this time, and even more so to have time to do something to save yourself. The employees who survived the explosion left the hall after the explosion.
At 1.30 a.m. the first fire brigade, Lieutenant Pravik, arrived at the scene of the fire.
What happened next, who behaved how and what was done correctly and what was wrong is no longer the topic of this article.
author Yuri Veremeev
Literature
1. Journal "Science and Life" No. 12-1989, No. 11-1980.
2.X. Kuhling. Handbook of Physics. ed. "World". Moscow. 1983
3. O.F.Kabardin. Physics. Reference materials. Education. Moscow. 1991
4.A.G.Alenitsin, E.I.Butikov, A.S.Kondratiev. Brief physical and mathematical reference book. The science. Moscow. 1990
5. Report of the IAEA expert group “On the causes of the accident of the RBMK-1000 nuclear reactor at the Chernobyl power plant on April 26, 1986.” Uralurizdat. Ekaterinburg. 1996
6. Atlas of the USSR. Main Directorate of Geodesy and Cartography under the Council of Ministers of the USSR. Moscow. 1986
The Chernobyl disaster occurred at 1 hour 23 minutes on April 26: a reactor explosion occurred at the 4th power unit with a partial collapse of the power unit building. A strong fire started in the premises and on the roof. A mixture of the remains of the reactor core, molten metal, sand, concrete and nuclear fuel spread throughout the premises of the power unit. The explosion released a huge amount of radioactive elements into the atmosphere.
Causes of the accident
A day earlier, on April 25, the 4th power unit was shut down for preventive maintenance. During this repair, the turbogenerator was tested for run-down. The fact is that if you stop supplying superheated steam to this generator, it will be able to generate energy for a long time before it stops. This energy could be used in case of emergencies at nuclear power plants.These were not the first tests. The previous 3 test programs were unsuccessful: the turbogenerator provided less energy than expected. Great hopes were placed on the results of the fourth tests. Omitting details, the activity of the reactor is controlled by the insertion and withdrawal of absorber rods. At the Chernobyl nuclear power plant, these rods had an unsuccessful design, due to which, when they were abruptly removed, an “end effect” occurred - the reactor power, instead of falling, increased sharply.
Unfortunately, such features of the rods were studied in detail only after the Chernobyl disaster, but operating personnel should know about the “end effect”. The personnel did not know about this, and when simulating an emergency shutdown, that same sharp increase in reactor activity occurred, leading to an explosion.
The power of the explosion is evidenced by the fact that the 3,000-ton concrete reactor cover came off, pierced the roof of the power unit, and took out a loading and unloading machine along the way.
Consequences of the accident
As a result of the Chernobyl disaster, 2 nuclear power plant employees died. 28 people died later from radiation sickness. Of the 600 thousand liquidators who took part in the work at the destroyed station, 10% died from radiation sickness and its consequences, 165 thousand became disabled.A huge amount of equipment used during the liquidation had to be written off and left in cemeteries, right on the contaminated territory. Subsequently, the equipment slowly began to go into scrap metal and...
Vast areas were contaminated with radioactive substances. An exclusion zone was created within a radius of 30 km from the nuclear power plant: 270 thousand were resettled to other areas.
The station area was decontaminated. A protective sarcophagus was built over the destroyed power unit. The station was closed, but due to a lack of electricity, it was reopened in 1987. In 2000, under pressure from Europe, the station was finally closed, although it still performs distribution functions. The protective sarcophagus has fallen into disrepair, but there are no funds to build a new one.
On the night of April 26, 1986, at the fourth power unit of the Chernobyl nuclear power plant (ChNPP), located on the territory of Ukraine (at that time the Ukrainian SSR) on the right bank of the Pripyat River, 12 kilometers from the city of Chernobyl, Kyiv region, the largest accident in the history of world nuclear energy occurred .
The fourth power unit of the Chernobyl Nuclear Power Plant was put into commercial operation in December 1983.
On April 25, 1986, the Chernobyl Nuclear Power Plant was scheduled to conduct design tests of one of the safety systems at the fourth power unit, after which the reactor was planned to be shut down for scheduled repair work. During the tests, it was supposed to de-energize the nuclear power plant equipment and use the mechanical energy of rotation of stopping turbogenerators (the so-called run-down) to ensure the operation of the power unit’s safety systems. Due to dispatch restrictions, the shutdown of the reactor was delayed several times, which caused certain difficulties in controlling the reactor's power.
On April 26, at 01:24 a.m., an uncontrolled increase in power occurred, which led to explosions and destruction of a significant part of the reactor facility. Due to the explosion of the reactor and the subsequent fire at the power unit, a significant amount of radioactive substances was released into the environment.
Measures taken in the following days to fill the reactor with inert materials led first to a decrease in the power of radioactive release, but then an increase in temperature inside the destroyed reactor shaft led to an increase in the amount of radioactive substances released into the atmosphere. Radionuclide emissions decreased significantly only by the end of the first ten days of May 1986.
At a meeting on May 16, the government commission decided on the long-term conservation of the destroyed power unit. On May 20, the Ministry of Medium Engineering issued an order “On the organization of construction management at the Chernobyl nuclear power plant,” in accordance with which work began on the creation of the “Shelter” structure. The construction of this facility, involving about 90 thousand builders, lasted 206 days from June to November 1986. On November 30, 1986, by decision of the state commission, the mothballed fourth power unit of the Chernobyl nuclear power plant was accepted for maintenance.
The fission products of nuclear fuel released from the destroyed reactor into the atmosphere were carried by air currents over large areas, causing their radioactive contamination not only near nuclear power plants within the borders of Ukraine, Russia and Belarus, but also hundreds and even thousands of kilometers from the accident site. The territories of many countries have been exposed to radioactive contamination.
As a result of the accident, the territories of 17 European countries with a total area of 207.5 thousand square kilometers were exposed to radioactive contamination with cesium-137 with levels above 1 Ci/km2 (37 kBq/m2). The territories of Ukraine (37.63 thousand square kilometers), Belarus (43.5 thousand square kilometers), and the European part of Russia (59.3 thousand square kilometers) were significantly contaminated with cesium-137.
In Russia, 19 subjects were exposed to radiation contamination with cesium-137. The most polluted regions are Bryansk (11.8 thousand square kilometers of contaminated areas), Kaluga (4.9 thousand square kilometers), Tula (11.6 thousand square kilometers) and Oryol (8.9 thousand square kilometers).
About 60 thousand square kilometers of territories contaminated with cesium-137 with levels above 1 Ci/km 2 are located outside the former USSR. The territories of Austria, Germany, Italy, Great Britain, Sweden, Finland, Norway and a number of other Western European countries were contaminated.
A significant part of the territory of Russia, Ukraine and Belarus was contaminated at a level exceeding 5 Ci/km 2 (185 kBq/m 2). Agricultural land covering an area of almost 52 thousand square kilometers was affected by cesium-137 and strontium-90, with half-lives of 30 and 28 years, respectively.
Immediately after the disaster, 31 people died, and 600 thousand liquidators who took part in firefighting and cleanup received high doses of radiation. Almost 8.4 million residents of Belarus, Ukraine and Russia were exposed to radioactive radiation, of which almost 404 thousand people were resettled.
Due to the very high radioactive background after the accident, the operation of the nuclear power plant was stopped. After work on the decontamination of the contaminated area and the construction of the Shelter facility, the first power unit of the Chernobyl NPP was launched on October 1, 1986, the second on November 5, and the third power unit of the station was put into operation on December 4, 1987.
In accordance with the Memorandum signed in 1995 between Ukraine, the G7 states and the European Union Commission, on November 30, 1996, a decision was made to permanently shut down the first power unit, and on March 15, 1999, the second power unit.
On December 11, 1998, the Law of Ukraine “On the general principles of subsequent operation and decommissioning of the Chernobyl nuclear power plant and the transformation of the destroyed fourth power unit of this nuclear power plant into an environmentally safe system” was adopted.
The Chernobyl nuclear power plant stopped generating electricity on December 15, 2000, when the third power unit was permanently shut down.
In December 2003, the UN General Assembly supported the decision of the Council of Heads of State of the CIS to proclaim April 26 as the International Day of Remembrance for Victims of Radiation Accidents and Disasters, and also called on all UN member states to celebrate this International Day and hold relevant events within its framework.
The material was prepared based on information from RIA Novosti and open sources
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