Translated material
Chernobyl: half -life. Explosion
Radio Liberty recalls the history of the Chernobyl disaster, the investigation of its causes and the elimination of the consequences
Exactly 30 years ago, on the night of April 26, 1986, the largest technogenic disaster in the history of mankind took place: an accident at the Chernobyl nuclear power plant. The explosion in the reactor zone of the fourth block of the station led to large -scale emissions of radioactive substances, infection of a territory of hundreds of thousands of square kilometers and tragically changed the fate of millions of people. The attitude to atomic energy has changed forever: the explosion at the Chernobyl station showed how grandiose and long -term the consequences of the accident at the atomic facility.
In the first part of a special project dedicated to the anniversary of the disaster, Radio Liberty tells what exactly happened on the Chernobyl nuclear power plant in the last day before the accident and directly after it.
On the main page of the project "Dates of half -life"
-Hello, is this HPV-2? What burns there?
-Explosion on the main building, between the 3rd and 4th block.
- Are there people there?
- Yes!
This dialogue between the dispatchers of the central fire department and the militarized fire department of the Chernobyl nuclear power plant occurred in half a night on April 26, 1986 - in the first minutes of the largest catastrophe in the history of atomic energy. The commanders of the first fire brigades, who arrived at the scene of the accident, Vladimir Krak and Viktor Kibelok extinguished a fire without any radiation protection, in tarpaulin robes. They did not allow the fire to spread from the emergency 4 block to the neighboring 3rd and became one of the first victims of the Chernobyl accident. Both died from the consequences of a serious radiation disease on one day - May 11, 1986. The rule and the kibenka was 23 years old.
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In essence, the nuclear power plant is arranged as a samovar. A vertical pipe passes through the tank of a conventional samovar, into which you throw cones and chips. They turn into coals, and the coals heat the water. The nuclear reactor, like that exploded into the Chernobyl nuclear power plant, is also similar to a tank, only large, 7 meters high and 12 meters with diameter, and inside, like a samovar, is permeated with vertical pipes, only there are 1683 pieces. The reactor tank, the so -called active zone, unlike the samovar, is filled not with water, but with graphite blocks, and water, on the contrary, is located just in the pipes. And already in these pipes with water, heat -eating elements are immersed - bundles of long and thin, thickness thickness, tubes. In these thin tubes, as in a package with aspirin or candies, there are coals of an atomic samovar - nuclear fuel tablets, as a rule, from enriched uranium dioxide. In them, a chain reaction of the division of nuclei occurs, heat is released from this, the water in the channel heats up, the steam turns the power generator turbine, condenses and enters the reactor channels again.
One tiny fuel tablet can distinguish energy comparable to the burning of a half -ton of coal
The task of the samovar is to boil water as soon as possible, so that they especially do not need to control them, throw more firewood, and nothing more. But the operation of the reactor needs to be controlled, and so that it is clear how this is done, it is worth saying a few words about the chain reaction. Nuclear fuel tablets contain the u-235 uranium isotope atoms-about 2 percent of the total mass. When a neutron hit the core of such an atom, the isotope breaks up into several other atoms and several new neutrons fly out of it. Some of the new neutrons are lost, but some encounter other U-235 nuclei, causing their division, and the chain reaction continues. Each breakdown occurs with the release of large energy, which heats water in the reactor. One tiny fuel tablet can distinguish energy comparable to the burning of a half -ton of coal.
Block control panel of the CHAS power unit
To control the chain reaction of division, it is necessary to regulate the share of neutrons leading to a new division of nuclei: the more neutrons are lost in the process, the less they will remain to be divided. In reactors of the RBMC type used by the Chernobyl nuclear power plant, this is done using rods made of well -absorbing neutrons. The more rods and the deeper they are immersed in the active zone, the less freely flying neutrons will remain, which means that the division reaction will slow down and the amount of heat released by fuel will decrease. We lower the rods into the reactor - slow down the reaction, remove the rods - accelerate. The main task of management is to hold the chain reaction in it in a more or less stable state, that is, so that the number of dividing nuclei in it is approximately constant.
Until April 26, 1986, this system seemed completely safe. Few could imagine that a chain reaction could get out of control, it seemed to be always stopped by completely dropping all absorbing rods into the active zone-for this it is enough to press only one emergency button with the AZ-5 inscription. This is exactly what one of the operators of the 4th power unit of the Chernobyl nuclear power plant at 1 hour 23 minutes 38 seconds of that fatal night. The reactor was supposed to stop, but instead, after a few moments there was an explosion that changed the fate of millions of people, the Soviet Union and all the atomic energy.
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In April 1986, tests were planned at the Chernobyl nuclear power plant. In the midst of the Cold War, the capture of the power plant was considered as one of the probable scenarios. The enemy surrounded the nuclear power plant may first cut off the station from external power supply, which needs pumps that drive water through the reactor tank. The pump stop even for a short time is very dangerous, and the reserve diesel generators will automatically turn on only after forty seconds. Can a reactor feed yourself with electricity into this gap?
It was a matter of bonuses, improvements and even possessing a transitional red banner
It seemed that yes: a huge turbine flywheel rotating by inertia would continue to produce electricity, it can be directly connected to the pumps until diesel generators turn on. In practice, they tried to put such an experience repeatedly, including the Chernobyl nuclear power plant, but every time something did not work out. Friday, April 25, seemed an ideal moment for the next tests: the weekend began, which means that reduction of energy generation by the station was not so critical for consumers. In addition, it was the last weekend before May Day, which could be approached with the next labor achievement - it was a matter of bonuses, increase and even possessing a transitional red banner.
Operational meeting of builders at the emergency 4 power unit
By the way, at that moment it belonged to the workshop, which served the unfortunate reactor of the 4th Chernobyl unit.
The Chernobyl unit that took place on the 4th block in the last day before the explosion is well known, almost permanently: according to testimony, according to the records of the operational magazine and at the risk of life from radioactive ruins, paper rolls with devices indicators. And this terrible chronicle is surprisingly similar to a chronicle of the distressing aircraft.
April 25 at 1 hour 5 minutes, that is, a day before the explosion, the preparation of tests and a gradual decrease in the thermal power of the reactor were started on the block. By morning, she fell in half - up to 1600 MW. At 14:00, according to the approved program, the emergency cooling system was disabled. Now the staff of the station was supposed to reduce the capacity to the level of 700-1000 MW - it was in this mode that they were going to conduct tests. However, Kyivenergo dispatcher demanded to suspend the program for several hours: the working day continued and the enterprises needed electricity. As a result, the further unloading of the reactor continued only after eleven in the evening of Friday. By 00:05 Saturday, its power reached 720 MW.
It was unpleasant, but such failures in similar situations happened before
Until this moment, the tests were held in the standard mode, except for the delay, and there was no reason to worry. The power continued to be reduced: by 00:28 it fell to 500 MW. At this moment, when moving from automatic to manual control, it suddenly fell to 30 MW (and according to some reports, to zero). It was unpleasant, but such failures in similar situations happened earlier. The deputy chief engineer of the station Anatoly Dyatlov, who led the tests on the remote control, ordered the reactor to begin to start, withdrawing the rods from it. Not everyone liked the idea: the senior engineer Leonid Toptunov, who was responsible for power control, noticed that this could make the reactor poorly controlled, suggested that the reactor drown out and stop the experiment. Woodpeckers, a great authority at the station, a man who did not like objections, demanded to continue acceleration.
Five minutes later, the testimony really grew to 160 mV - it seemed that the crisis was overcome. Over the next thirty -five minutes, the thermal power of the reactor was lifted a little higher, to 200 MW, and stabilize. Along the way, warning signals were triggered on the remote control: they reported that the so-called seizure drums (in them the steam is separated from the water and goes to the turbine) work abnormally, but they did not pay much attention to this. As the senior engineer Boris Stolyarchuk later recalled for water circulation in the reactor, "the level of seizure drums was always difficult to control at low power levels, any operator knew this and was ready for this. Therefore, I did not experience any special feelings."
In the machine room of the 1st power unit of the Chernobyl nuclear power plant, again launched after the accident
At 1 hour 23 minutes 4 seconds on April 26, the staff finally was ready to start testing. The supply of steam to the turbines was turned off. The main circulation pumps of the reactor responsible for circulation in the water system have now worked due to the inertia of the turbine. This mode had to be held for 40 seconds - until the reserve diesel generators are turned on. What happened in the next moments is unknown for certain. It seems that the stabilized reactor began to suddenly gain power, first slowly, then faster and faster. In any case, 34 seconds after the start of the test, one of the operators decided to urgently drown out the reactor and pressed the AZ-5 main emergency protection button, which immediately absorbing the rods in the active zone. The time of the full introduction of the rods into the active zone is 18 seconds, but the power was supposed to fall immediately. Instead, it grew up even more, almost all the malfunctions were lit on the remote control, and after another three seconds in the reactor zone there were either one or two powerful explosions - the evidence in this subject diverges. The light in the control room went out, smoke, steam and dust fell into the room. The reactor of the fourth Chernobyl unit was completely destroyed.
Small particles rose with streams of hot air high in the sky, larger fragments flew out like cannon fragments
The atomic samovar cover - the structure of metal and concrete weighing 3,000 tons - raised and turned, hanging out over the destroyed active zone. The five hundredth unloading-loading machine, with which the tubes with uranium tablets are replaced in the reactor, was thrown 15 meters and fell into the reactor mine. Everything that was in the active zone flew into the atmosphere: graphite, zirconium, nuclear fuel. Small particles rose with streams of hot air high in the sky, larger fragments flew out like cannon foxes-some of them were later found in a cooler pond more than a kilometer from the 4th block. The explosion power was later estimated at 100-250 tons in the TNT equivalent.
It was a very powerful and destructive explosion, but it is wrong to imagine it as something similar to an explosion of a nuclear bomb. The Chernobyl explosion was not nuclear, but thermal, and its power was almost a hundred times less than the power of the first Trinity in the history of the nuclear explosion. The engineers who were on the remote control during the accident did not even understand that the reactor was destroyed. Directly during the explosion, only one person died: the mechanic Valery Khodamchuk, who was on duty at the pumps at the pumps, was apparently littered with fragments, his body was never found. The next morning, the engineer-owner of the automation system Vladimir Schashhenok died from injuries.
The cover of the atomic reactor of the RBMC of the 1st power unit of the Chernobyl nuclear power plant
There were no more deaths from the consequences of the explosion itself, but in the next days, one after another, the victims of radiation began to die. The first to arrive at the place of disasters are firefighters and a kibeok, a young engineer Toptunov, who offered to drown out a reactor after a power failure that worked with him on the Akimov remote control. Mechanic Valery Pervachenko, who received the strongest radiation burns, while unsuccessfully wanted his friend Khodamchuk. Two fishermen who caught fish in the warm water of the cooler pond and with curiosity watched the fire on the roof of the 4th side. In total, in the first weeks after the accident, 31 people died, of which 29 from acute radiation illness.
He was a clear soldier's step to the explosion
Anatoly Dyatlov, who led the change in the operators of the 4th block at the night of the accident, received a fatal dose of 390 BAER, but survived. He will be sentenced to 10 years in prison, he will sit only 4 and will be released in connection with the disease after official letters, including signed by Andrei Sakharov. Woodpeckers will live up to the 10th anniversary of the disaster and in one of the last interviews will say: "The reactor was unwinded by purely due to the fault of the Institute of Atomic Energy and Nickyt. With such a bouquet of inconsistency, its explosion, its explosion was inevitable. He went to the explosion with a clear soldier's step."