The April 26, 1986 One of the accidents that would mark the history of mankind occurred at the Vladimir Ilich Lenin nuclear power plant in Ukraine. Known as the chernobyl accident and together with Fukushima nuclear accident in 2011 is the most serious nuclear accident in history.
Since then there is no agreement on exactly what happened and why it happened., not even in the total deaths caused by this accident. But there is a common point that determines that the day before the accident a test was being carried out for which it was necessary to reduce the power. For this reason, reactor 4 began to experience certain imbalances that caused the core to overheat and the consequent explosions and fires that culminated in the lifting of the 1,200-ton reactor lid, exposing enormous amounts of radioactive materials that reached North America and most of Europe.
What happened in Chernobyl
According to a report signed by the International Atomic Energy Agency in August 1986, on April 26 of that same year, a test was planned to improve the safety of the reactor. To perform this test they needed to check how long the turbine would continue to generate power when disconnected from the power produced by the reactor. In this way, in the event of a stoppage, the emergency pumps would need a minimum of power to turn on and cover those 60-75 seconds that the diesel generators took to start up. But the technicians at the plant did not know if, by cutting off the power of the steam, the turbine would continue to work due to inertia during those seconds.
On April 25 it was agreed how the test would be carried out by the employees of the first shift in the morning and those who had been prepared for the exam. They also had a team of electrical engineers to check the new voltage regulation system. In this way, at one in the morning of April 26, the energy began to be reduced, in the way in which it had been programmed and reaching 50% when the employees of the morning shift were already in the plant.
But the entire test had to be stopped due to the failure of another power plant in the country, which had stopped and the controller of the kyiv power grid cut Chernobyl power reduction to be able to cope with demand from the other plant. The Chernobyl director stopped the test but certain changes were already taking place in the plant that would affect and endanger the personnel. Among them, the emergency core cooling system, which was prepared to supply water to the plant if there was a loss of coolant, had been deactivated.
As of 11 p.m., the kyiv grid controller had not given the order to resume the power-down test, so due to this delay, there were many mismatches they had no solution. We also have to take into account that by this time the morning employees, who were supposed to have carried out the test, had long left and the afternoon shift was also leaving while the night shift was not. It would arrive until 00h, which, according to what had been agreed, they would only have had to monitor the heat that had remained. In this way, the employees of the night shift hardly had time to carry out the experiment and at the change of shift the power was further reduced.
As established, the power of reactor 4 had to drop to 700-1000 MW which was achieved on April 26 at 00:05 but due to the production of xenon (a gas that works as a neutron absorber) the power continued to drop, generating what is known as xenon poisoning. When the power was already at 500MW, Toptunov who was in charge of the operation mistakenly inserted the control rods very quickly and the power plummeted to 30MW. The plant employees decided to increase the power manually and the power went back up to 160-200MW but due to xenon poisoning the power could not be increased any further. This caused the imbalance of the neutrons and the alarms were triggered but were disregarded in order to continue maintaining the power level. Finally, 200 MW of power was reached and everyone returned to prepare for the experiment. Additional water pumps were prepared to increase the flow of water, but this produced an increase in the temperature at the inlet of the reactor core and the safety margin was endangered, reaching the boiling point of the water. Employees cut off the water pumps to increase steam pressure and manually removed the control rods in order to maintain the required power. With all these measures carried out, a very unstable reactor configuration was produced. The control rods that were supposed to remain to check if the reactor was losing coolant were manually removed, as was the automatic emergency shutdown system. An enormous range of violations of the Nuclear Safety Regulations of the Soviet Union. If the reactor went into supercriticality, it could not recover automatically.
How did the Chernobyl explosion happen?
After 1:20 in the morning, the experiment began. Although for normal operation 6 of the eight pumps used to be on, only 4 were. The steam input to the turbines was cut off and they began to work by inertia. The diesel generators came on and should have covered the power demand in about 40 seconds. Until then, the energy had to be supplied by the turbine but as the turbine generator decreased so did the energy reaching the pumps and due to the reduction of the water steam voids formed in the core.
Due to low power levels, the reactor went into positive feedback and the steam voids formed caused the water to have less cooling capacity to absorb neutrons but increased the power of the reactor so more water was turning into steam and an extreme power increase was taking place that could not be controlled because the systems emergency were offline and employees could not detect it in time. A few seconds later, an emergency shutdown of the reactor was registered which, inadvertently, would end in an explosion. To date, it is not known why the button that carried out the emergency stop was pressed, if it was due to the increase in temperature or because, having finished the experiment, they had to press the button as a routine method. Likewise, most experts say that it was pressed by a quick order to see the increase in power, but there are no documents or evidence to prove it. What is recorded is that the emergency stoppage was not produced by an automatic system but by manual action.
After loud noises, the explosion produced a cloud of hydrogen in the nucleus that caused the flight of the reactor cover and the fire in the plant with a strong emission of toxic products.
Consequences of Chernobyl
What happened in this nuclear accident changed the world because radioactive materials polluted the air and soil so the health of all the inhabitants of the area was affected. Many operators were in charge of mitigating the effects of the accident, but the effects could not be controlled. Thousands of deaths were caused by exposure to these highly toxic materials.
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The problem was that it was very difficult to clarify deaths and illnesses had been caused by this nuclear accident and above all by the enormous spread of pollutants through the air. In addition, these toxic materials were distributed through food to areas that had not been contaminated.
The central employees they suffered the worst consequences, with deaths from intoxication but many of them were also left disabled and sick for life. Leukemia, cancer, psychological disorders, premature aging…were some of the problems in which they were involved. Being exposed to these materials also caused some of their descendants to suffer the consequences and be born with problems and diseases.
Besides, the infant mortality increased very significantly in all the affected countries, giving a figure of about 5,000 infant deaths due to the Chernobyl accident, and between 1,000 and 3,000 birth deformities for the same reason. As for abortions, more than 100,000 were caused by radiation.
The radiation did not affect only Ukraine, it also spread throughout Europe causing more diseases, different tumors and infant deaths in the Czech Republic, Germany, Belarus, Greece, Scotland or Romania.
Chernobyl today
Pripyat, the closest city to the nuclear power plant is currently a ghost town but that thousands of tourists continue to visit. We can see graffiti, posters and decorations in honor of all those who died in the catastrophe. During the 1990s, there were many robberies and looting in this area, which is why it is currently closely watched by the Police and the Army.
This area has known how to take advantage of the Chernobyl accident to attract tourism and today they carry out retro tours in which you can put on a suit like the ones worn by the employees of the plant, drive a car of the time and travel back in time to those years.
Despite the desolation and abandonment of the city, 30 years after the tragedy, there is still hope. The area has become a natural reserve in which different species of animals that cannot be seen in Europe coexist: wolves, deer, turtles, beavers, horses… and contrary to what we might think, they do not have mutations but have a longer life expectancy and a good index of birth
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