Chernobyl - history. How did the biggest disaster of a nuclear power plant happen?

 It is still difficult to unequivocally answer the question of who is to blame for the Chernobyl disaster of April 26, 1986. Most often, the fault is the constructional faults of the reactor or the operating errors of the nuclear power plant. How did the event that changed the face of nuclear energy happens?

The construction of the Chernobyl nuclear power plant began in the 1970s. The first reactor was put into operation in 1977. In the following years, more reactors were put into operation, including the fourth one in 1983, in which the catastrophe later took place. There were supposed to be 6 reactors in total, but after the accident, further expansion of the power plant was stopped.

RBMK-1000 reactors were used in Soviet power plants from the 1960s. They never met the safety standards of Western countries. Cooling with light water and graphite moderation made it possible to use uranium as fuel, which did not require additional enrichment. As a result, the RBMK type reactors are very economical, but also easily cause their instability.

The instability of the reactor is influenced by the increase in the amount of water vapor in its core. The increased presence of steam causes an increase in reactor power which in turn causes a further increase in the amount of steam produced. Thus, the reactor power gets out of control. And it was this mechanism that was to be the direct cause of the Chernobyl catastrophe.

The catastrophe took place during an experiment that was supposed to increase the safety of the power plant in an emergency. The test was to show how long, after a possible failure, the power plant would be able to produce energy for its own operation. The duration of the experiment was planned only for a minute.

Due to the planned experiment, many of the normally functioning security systems have been disabled. It was originally supposed to be carried out during the day, but due to the failure of another power plant, the authorities ordered the reactor shutdown delay to be delayed to compensate for electricity production. Power plant workers who came to work for the night shift were not sufficiently prepared for the night shift.

The consent to shut down the reactor did not come from Kyiv until 23:04. The power plant workers probably cut the reactor's power too much, which dropped to 10 MW. This caused an excessive release of xenon-135, which further reduced power, causing the so-called "Xenon poisoning". In such a situation, the reactor should be shut down for 24 hours. However, the plant operators were unaware of the "xenon poisoning" and began to ramp up the reactor power to a test level.

At 01:23:04 an unfinished experiment began. Due to many errors and flaws in the design itself, it got out of hand. The reactor became unstable, and the emergency systems that had been partially disabled earlier did not work. The operators pressed the safety button that was supposed to turn off the reactor in an emergency. However, by constructing the safety bars, which accelerated the reactions for a moment before the reactor died out, the system led to the release of even more energy. At 1:24 am, the pressure of the water vapor triggered the first explosion.

As a result of subsequent chemical reactions, a second explosion took place, after which several tons of graphite used in the power plant ignited. It was the fire that released the most radioactive dust into the atmosphere. According to the most popular theory (questioned by many scientists), an explosion in a power plant blew up a 1,200-tonne reactor shell.

It is still not clear whether the catastrophe is more to blame for human error or the design defects of the reactor itself. Soviet authorities and the court blamed the plant operator, including Anatoly Dyatlov, who supervised the experiment, for the disaster. He was sentenced to 10 years in prison, but due to ill health caused by radiation sickness, he was released from prison before the end of his sentence.

The research carried out in the 21st century indicates that the RBMK-1000 reactor had huge design flaws. Contemporary analyzes and simulations show that they are largely responsible for the catastrophe. This issue will probably never be finally clarified again. Some researchers believe that the seismic instability in the vicinity of the power plant may have contributed to the catastrophe. There are also theories that the Chernobyl disaster was a deliberate act by the Americans to weaken the Soviet Union

The USSR authorities initially denied the catastrophe and then provided meager and unverifiable data. This sparked speculation in Europe about thousands of casualties and a deadly threat to the people of Europe.- In Poland, on April 28, there was a marked increase in radioactive radiation. In a non-sovereign Poland, subordinated to Soviet interests, the censorship survived the information about the catastrophe for several dozen hours - said, prof. Jerzy Eisler in the "Chronicle of two millennia" broadcast. The official cause of the disaster, disclosed to the public by Soviet experts and the court, was gross violations of safety rules by the reactor's personnel. The power plant management and Anatoly Dyatlov, who supervised the experiment, were found guilty. He was the only one who lived to see the end of the trial. He was sentenced to 10 years in prison but was released early due to radiation sickness. He defended the operation all the time, citing design defects of the reactor as the cause of the disaster, which should never have been approved for operation.

Soon after the graphite fire broke out, the fire brigade arrived at the crash site. The firefighters were convinced that they were putting out an ordinary fire on the roof of the power plant. Nobody warned them of the dangers of exposure to radioactive smoke. Soon they got radiation sickness, which manifested itself through burns, bloody vomiting, and loss of consciousness. All the firefighters who first arrived at the crash site died in agony. Only their commander survived, who later underwent extensive treatment. The fire was suppressed for some time, but it broke out again with greater force.

On April 27, in the morning, Professor Borys Legasov arrived at the crash site. It was he who ordered the immediate evacuation of the 10-kilometer death zone, which included the nearby city of Pripyat. It was mainly inhabited by power plant workers and their families. On behalf of Legasov, several thousand tons of sand, boron, dolomite, clay, and lead were dropped from military helicopters onto the burning reactor. The material melted and formed a compact lump surrounding the reactor, which allowed the fire to be contained.

Water was also pumped out of tanks under the reactor to prevent an explosion that could contaminate another area. Then, with the help of miners from Tula, the reactor was secured from below with a "concrete pillow". As it turned out later, these actions were right, because after a few days the radioactive remains of the reactor burned through the original base and fell into the tank secured with a "concrete pillow". When the crash site was later investigated, a new highly radioactive crystalline substance was found, which was called Chernobylite.

The first message for residents living within a radius of 10 km from the crash site was issued on the order of Legasov only 36 hours after the explosion. In the following days, the evacuation zone was first expanded to 20 and then to 30 km around the plant. The compulsory evacuation involved a total of approx. 350 thousand. people. The army deported the inhabitants by force, making it impossible to take any items from them, which were then destroyed.

As a result of their injuries and as a result of irradiation, 31 power plant workers and firefighters trying to extinguish the fire died. More and more soldiers were needed to work at the crash site, and they were mobilized from the farthest parts of the country. They were called liquidators. 650 thousand people who participated in the work to clean up the disaster area were exposed to radiation. The authorities did not provide the liquidators with adequate protection against radiation. Many of the soldiers working at the crash site sooner or later felt the effects of radiation on their health.

According to official data, as a result of cancer diseases, 60 thousand. liquidators of the consequences of the disaster, approx. 5 thousand died people. And the Doctors Against Nuclear War report estimates the number of cases of thyroid cancer due to the catastrophe at 10,000. Doctors from this organization believe that there is still a possibility of another 50,000 cases of thyroid cancer. In addition, according to their report, the catastrophe resulted in 10,000 fetal deformities and the death of 5,000 infants. In 2005, one million children and 2 million adults had the status of disaster victims in Ukraine.

The highest authorities of the USSR in the first days after the catastrophe decided to withhold information about it. A brief statement was issued which was very sparse on the matter. The inhabitants of Belarus and Ukraine, most at risk from radiation, were officially ordered to participate in the May Day parades. It was only on May 14 that the first secretary of the CPSU, Mikhail Gorbachev, officially announced the accident and assured him in a speech that the Soviet authorities were in control of the situation.

In the West, however, a radioactive cloud spreading over Europe was immediately detected. The threat was taken very seriously and measures were put in place to counter any possible effects of irradiation.

The catastrophe certainly weakened the Soviet Union. Ukraine and Belarus, whose border lies near the power plant, suffered the most of the Soviet republics. According to Mikhail Gorbachev, the USSR spent the equivalent of $ 18 billion on plant shutdown and decontamination activities.

Although the remaining reactors at the Chernobyl plant returned to operation shortly after, construction of other Soviet power plants based on this technology was halted. Excluding 784,320 ha of agricultural land and 694,200 ha of forests from production had a significant impact on the country's economy. And we are talking about one of the most fertile areas of the USSR.

Politically, the catastrophe contributed to the collapse of the Soviet Union in 1991. It showed the weakness of the state and undermined the credibility of the communist system. Ukrainian researchers also emphasize its importance in the pursuit of Ukraine's independence. Another consequence of the disaster, which is still felt today, is the prevailing fear of nuclear energy, which leads to the decommissioning of nuclear power plants and the fear of opening more such facilities.

The last working reactor of the power plant was not closed until December 2000. In November 2016, new protection was slung over the crash site to protect the area from radiation. The Ark was financed with the help of Western countries, including Poland. The cover is to last for another 100 years.

The zone around the Chernobyl power plant is closed to this day. However, in the surrounding houses, you can meet people living in the wild, earning their living from agriculture, and the Chernobyl power plant itself and the deserted Pripyat have become a world-famous tourist attraction, visited by thousands of tourists every year.

The International Nuclear and Radiological Event Scale (INES), developed in 1990, classifies incidents and accidents at nuclear facilities into seven levels. Both the Chernobyl reactor accident and the Fukushima nuclear disaster are classified in level 7 as a "major accident" involving the release of large amounts of radioactive radiation and having serious consequences for people and the environment.

If the term "nuclear disaster" is understood as not only accidents at nuclear facilities but also any man-made radioactive emissions, some events caused much more nuclear contamination than the Chernobyl accident, says Kate Brown, professor of science, technology, and society at the Massachusetts Institute of Technology in an interview with DW.

- Take, for example, the radioactive fallout after the detonation of nuclear bombs during the times of ground-based nuclear weapons tests in regions around the world. And let's take just one isotope, radioactive iodine, which is harmful to human health because it is absorbed by the human thyroid gland and causes thyroid cancer and other diseases. It is estimated that Chernobyl released 45 million Ci (Ci-kiur - a unit of measure for radioactivity). The Soviets and Americans released 20 billion of you of radioactive iodine in just two test years in 1961 and 1962. And it did not happen as a result of an accident or as a result of human error - emphasizes the researcher.

Denis Wiszniewski, a biologist from the Chernobyl Biosphere Reserve, has been observing the nature around the crash site for twenty years. He had never seen two-headed wolves or five-legged rodents. 'The influence of ionizing radiation can with some probability cause changes in the body, but in most cases, it simply reduces the lifespan of the body,' he explained in an interview with DW.

For example, offspring of rodents with the mutations would still die during pregnancy. Errors in the genome or its disruptions lead to the fact that the body is unable to function, and animals born with disabilities would not be able to survive long in the wild, says Wiszniewski. He and his colleagues have studied thousands of animals in the Exclusion Zone over the past decades and found no strange morphological changes.

However, 35 years after the nuclear disaster, the land in the shutdown zone is still radioactively contaminated. One-third of the area is contaminated with transuranic elements with a half-life of over 24,000 years.

The restricted zone around Chernobyl has become a magnet for tourists from all over the world just 25 years after the nuclear disaster. The success of the HBO miniseries "Chernobyl" increased the number of visitors to 124,000 in 2019 - twice as many as in the previous year.

The State Exclusion Zone Management Agency reports that it is currently establishing more than 20 land, water, and air routes to facilitate visits. Strict security measures are in place during the visit to protect people. During the tour, it is obligatory to wear a dress that covers the body as much as possible, to navigate on official routes, and it is forbidden to eat and drink outdoors. According to official data, the potential radiation dose for a one-day visit is up to 0.1 millisieverts.

If such rules are followed, a visit to the Chernobyl Exclusion Zone is harmless to health, says Sven Dokter, spokesman for the German Society for the Safety of Nuclear Equipment and Reactors (GRS) in an interview for DW. - We are far from the dose ranges, which should be advised against in order to protect health. For comparison, on average, a person in Germany receives a radiation dose of just over 4 millisieverts per year. Half of it comes from natural radiation, to which we are always exposed, the other half comes mainly from medical applications and air travel, Dokter explains.

A dose of up to 0.1 millisievert can be obtained by cosmic rays, for example during a flight from Munich to Japan. And in some medical applications, the radiation dose is even much higher, says Dokter. The typical dose for a pelvic x-ray is 0.3-0.7 millisieverts and for a chest CT scan 4-7 millisieverts.

Chernobyl and Pripyat, a city built for nuclear power plant workers, are officially uninhabited. However, after the reactor crash in 1986, they were never completely abandoned. Since then, several thousand people have found employment in both cities. Most of them are men who work two-week shifts and ensure the functioning of the critical infrastructure in both cities - incl. because reactors 1-3, which survived the accident in reactor 4, were still in operation until 1991, 1996, and 2000, respectively.

Among the unofficial residents, there are people returning voluntarily. They settled on their own mainly in the years following the nuclear disaster in villages that have remained empty since the evacuation of more than 115,000 inhabitants. The exact number of returnees is unknown.

Despite the bans still in force, it is estimated that in 2016 there were still about 180 people living in the entire Exclusion Zone. As these are mainly elderly people, this number is trending downwards. The settlers are only tolerated by the authorities, yet they receive support from the state in everyday life. Postmen provide them with pensions once a month, and a door-to-door shop provides them with food every two or three months. There are also grocery stores in Chernobyl and even at least two hotels, although they are mainly intended for business travelers.

In May, measurements at the Chernobyl reactor are worrying. There are warnings that if this is not met with an appropriate response, another catastrophe may occur, wrote the New Scientist portal.

For over 35 years, that is, since the explosion of the Chernobyl nuclear reactor, scientists have been conducting measurements under the containment dome. According to the New Scientist portal, they have recently observed a sharp increase in nuclear reactions in the inaccessible chamber of the destroyed complex. They are now investigating whether the problem will stabilize or will require a dangerous and difficult intervention. Suspected sub-reactor 305/2 may be at fault. One of its chambers is most likely full of radioactive material. It has been unavailable since the disaster. One suggestion as to why this is so is that a new structure placed above a dilapidated reactor in 2016 is causing the power plant to dry up. As New Scientist writes, when uranium or plutonium fuel decays radioactively, it emits neutrons that can promote the fission reaction. Large amounts of water slow down this process.

The emission of neutrons from the 305/2 sub-reactor has increased by 40% since 2016. They are emitted by plutonium or uranium. There may be other uncontrolled reactions with dire consequences. Huge amounts of water are needed to slow down the processes. Unfortunately, the concrete structure above the reactor is drying up this place.