O Chernobyl accident, that happened on April 26, 1986, was the biggest nuclear accident in history. This tragedy occurred at Plant V. I. Lenin, located in the city of Pripyat, about 20 km from the city of Chernobyl, in the extinct Soviet Union (present-day Ukrainian territory). It killed thousands of people and helped to speed up the end of the Soviet Union.
What happened in Chernobyl?
The Chernobyl accident happened at 1:23:47, therefore, in the early morning hours of April 26, 1986. This accident happened in reactor 4 of the Chernobyl plant and was the result of failurehuman, since the reactor operators did not comply with several items of safety protocols. Furthermore, it was later pointed out that the RBMK reactors (used at Chernobyl and other Soviet plants) had a serious error in your project, which allowed the accident to happen.
It all happened during a security test that was ongoing and resulted in the reactor 4 explosion. With the explosion, two workers at the plant were killed and, as a result, a fire in reactor 4 started and continued for days. The explosion left the nuclear reactor exposed, and the fire was responsible for throwing a large amount of radioactive material into the atmosphere.
Panel of a typical Soviet nuclear power plant from the 1980s.*
The wind took the radioactive material released into the atmosphere, mainly to the west and north of Pripyat, and the radiation spread around the world. Quickly, high levels of radiation were identified in places like Poland, Austria, Sweden, Belarus and even very distant places like the United Kingdom, United States and Canada.
The first to alert the international community that something had happened in the Soviet Union were the Swedes. Questions made to the Soviet government led him to admit that the accident had taken place on 28 April. Until then, the Soviets tried to hide what had happened, fearing the impact it would have on the country's reputation.
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How did the Chernobyl plant work?
The basic working principle of power plantinChernobyl it was similar to the others nuclear power plants: the reactor, where the fissile fuels are stored, causes the energy emitted by the fission of unstable elements, such as uranium or plutonium, heat and evaporate pure water at around 270°C. This water is kept under high pressures and, therefore, when released, it has enough power to move a set of turbines connected to a generator. Generators, in turn, are like big magnets and are wrapped in a huge number of conducting coils. The production of electric energy takes place according to the phenomenon called inductionelectromagnetic: while the generator is rotating, there will be generation of chainelectric.
THE Chernobyl power plant it was equipped with four RBMK-1000 nuclear reactors, capable of generating around 1000 MW of electrical energy each. At the time of the disaster, the Chernobyl plant was producing approximately 10% of all electricity consumed byUkraine. In addition, Chernobyl was the third nuclear power plant produced by the Soviet Union to use the RBMK reactors, produced by an outdated technology, created about 30 years before the date of accident.
Inside the nuclear reactors, there were hundreds of pellets. uranium-235. These pellets were arranged on long metallic rods, which were immersed in a tank of pure (distilled) water, used to regulate the nuclear fission process. The entire reactor was covered with a large, thick graphite armor.
The four reactors used at the Chernobyl plant were built between 1970 and 1977 and used the graphite as moderator of nuclear reactions. The moderation consisted of slowing down the neutrons emitted by the fissionsnuclear, making them thermal neutrons, so that the energy emitted by them was transferred to the graphite in the form of heat. When coming into contact with graphite walls, water also absorbs heat and evaporates in a controlled manner.
Today, however, we know of a serious problem related to this type of reactor: they are not very safe when operating at low power. In low power regimes, graphite ends up moderating an excessive amount of neutrons, releasing a lot of heat. With this, the fraction of water vapor inside the reactor increases significantly, as well as its internal pressure. As water vapor is not as efficient as liquid water in cooling fuel cells, the chain reaction is accelerated until it is no longer possible to moderate it.
In addition to the peculiarities of reactors that use graphite as a moderator, the Chernobyl reactors lacked a Crucial safety device to prevent the leakage of nuclear material: a steel containment dome and concrete.
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Causes of Disaster
The Chernobyl disaster was brought about by a succession of human errors and breaches of security procedures. On April 25, 1986, during a routine shutdown, plant technicians performed a test on the Chernobyl 4 reactor. The test consisted of determining how long the turbines were able to turn after an abrupt power outage. The test in question had already been carried out in the previous year, when it was noticed that the turbines had stopped very quickly. To solve this, new devices were installed throughout the year and needed testing.
The plant operator committed some crucial mistakes during the experiment, such as the deactivation of the reactor's automatic shutdown mechanism and the shutdown of four of the eight water pumps that cooled it. When the operator realized the state the reactor was in, it was too late. THE nuclear reaction was already extremely unstable, and the amount of energy it produced already exceeded 100 times its usual potency.
Plant technicians decided that it was necessary to pump gas xenon into the rods that contained the tablets with about 210 tons of uranium-235, as this gas has the ability to absorb the neutrons emitted by the nuclear fission. The reactor's installability made it impossible to control the fission solely through the use of the xenon. Thus, rods containing the element boron were inserted manually to curb neutron emission, however, when inserted, the rods expelled a certain volume of reactor water, consequently, the remaining water overheated and evaporated, expanding violently.
Inside the reactor of nuclear power plants, there are hundreds of rods, like the ones in the photo, filled with radioactive material.
The pressure produced by the water was large enough to loosen the reactor cover plate, which weighed no less than 1000 tons. At that time, a large amount of steam was responsible for releasing nuclear fission products, such as iodine-131, cesium-137 and isstrontium-90 for the atmosphere.
Two or three seconds after the first explosion, a second explosion ejected fragments from the fuel pellets as well as heated graphite (about 300 kg of carbon fragments). the reactor core merged thanks to the extremely high temperatures and became incandescent, starting a great fire. With that, a huge cloud of gases highly contaminated with different types of radioisotopes escaped into the atmosphere.
Lookalso: Cherenkov Effect and its relationship with nuclear reactors
After the second explosion occurred, half of reactor 4 was compromised. About 300 tons of water were used per hour to lower the reactor temperature. Between the second and the tenth day, with the help of helicopters, about 5000 tons of boron, dolomite, sand, clay and lead were dumped onto the glowing reactor, as an attempt to cease emission of radioactive particles.
The Chernobyl accident released about 100 MCi (megaCuries), or 4.1018 becquerels, of which about 2.5 Mci were from Cesium-137 – humanity's biggest radioactive accident. The becquerel quantity refers to the nuclear decay rate, that is, it measures the number of decays that take place every second. In other words, in the vicinity of reactor 4, there were 4,000,000,000,000,000,000 disintegrations nuclear per second, giving rise to dangerous nuclides like that of Cesium, whose half-life is about 30 years old.
What was done to contain the accident?
Containment structure built to prevent further leakage of radioactive material into Chernobyl.**
Shortly after the explosion of reactor 4, the Pripyat firefighters were summoned to put out the fire. As the work of the firefighters did not bring results, it was decided to throw materials, such as sand and boron, to contain the fire and decrease the dispersion of radioactive material.
Despite the seriousness of the accident, the Pripyat population just started to be evacuated 36 hours after the explosion. The city, located in the north of the current Ukraine, had at the time about 50,000 inhabitants, who were evacuated in 1200 buses sent by the Soviet government. The population of the city was instructed not to take their belongings and was informed that it was a temporary evacuation. The inhabitants of Pripyat were forced to abandon food and livestock.
In addition to carrying out the evacuation of the region's inhabitants, the Soviet government created a exclusion zone, which included sites that were at high risk for human presence. With that, everything within a 30 km radius of the Chernobyl plant was evacuated.
Due to the accident, a commission was created by the Soviet government with the objective of containing the dispersion of radioactive material. Belarusian writer Svetlana Aleksievitch pointed out that they were 800 thousand people mobilized in damage containment in the Chernobyl region|1|. Soldiers, scientists, firefighters, miners, workers, among others, were rushed to the region.
The so-called “liquidators” carried out different types of work in the Chernobyl region. Some worked by monitoring the radiation levels, but there were also those responsible for containing the emission of more radioactivity, clean up the city, bury contaminated objects, kill animals, evacuate the population, turn over the soil, etc.
Many of the liquidators sent to Chernobyl They did not knowof risk who ran with the work they did, but were encouraged by patriotism and the benefits offered by the Soviet government (such as salaries above the standard at the time). One of the most dangerous jobs was cleaning the roof of the plant, filled with radioactive materials that were part of the interior of reactor 4.
Those who worked on cleaning the roof of the plant became known as "biorobots”. Finally, the containment work included the construction of a structure that would contain the radioactive material. This structure was known as Chernobyl sarcophagus and was built between June and November 1986.
In November 2016, a new metallic containment structure for reactor 4 was built by the Ukrainian government. The new sarcophagus, which cost more than two billion euros, was built to withstand low-intensity earthquakes and designed to function until the end of the 21st century. It has about 7,300 tons of metal and 1000 cubic meters of cement.|2|.
Consequences
Panel in Pripyat, a city built in 1970 and abandoned after the nuclear accident.
The consequences of the Chernobyl accident were profound, especially for three countries: Ukraine, Belarus and Russia, all three former republics of the Soviet Union. On political issues, the Chernobyl accident reinforced the government's measures. Mikhail Gorbachev (then president of the USSR) to carry out the nuclear disarmament of the Soviet Union.
In addition, the accident also contributed to the end of the Soviet Union. This happened because there was very heavy economic impacts for the Soviet Union, a nation that had dragged itself into economic crisis since the 1970s and which saw its situation worsen in the 1980s with the afghan war (1979-1989) and the nuclear accident.
In environmental matters, the Chernobyl accident was unprecedented since man began to manipulate radioactive materials. It is believed that of 13% to 30% of the radioactive material from reactor 4 has been released into the atmosphere and, of this material, about 60% of it was concentrated in the territory of Belarus|3|.
Belarus, by the way, was the country most affected by the Chernobyl accident. About 23% of Belarusian territory has been contaminated and, as a result, the country lost around 264,000 hectares of arable land due to radiation. Furthermore, ¼ Belarusian forests have been contaminated and currently between one and two million people live in contaminated territory.
The Belarusian government even estimated that between 1986 and 2016 the economic loss caused by the Chernobyl accident was approximately 235 billion dollars. The Belarusian government alone has spent around 18 billion on emergency measures caused by the spread of radioactivity|4|.
In the case of Ukraine, 7% of its territory was affected; in the case of Russian territory, 1.5% was reached. The impact of the accident on the economy of these countries was gigantic. Until 2006, the Ukrainian government spent 5% to 7% of the country's budget on Chernobyl-related expenses. Belarus, in 1991 alone, spent about 22.3% of the country's budget on the consequences of Chernobyl. This number was reduced to 6.1% of the annual budget in 2002|5|.
Estimates made by scientists indicate that the Chernobyl region should remain inhabited for up to 20 thousand years until it becomes safe for human habitation. Despite this, there is evidence that some people have returned to live in the so-called “exclusion zone”.
The city of Pripyat, where the installation was located, was abandoned and today is a ghost town. Thirty years after the accident, the images show that nature has taken its place in the abandoned city. There is evidence that the number of animals present in the exclusion zone has increased considerably because of the small human presence.
Within the exclusion zone, natural life reemerged due to the limited human presence.
Another important consequence of the Chernobyl accident was the increase of the amount of cancer in the Ukrainian and Belarusian population, mainly. There are studies that show that, by 2005, around 6,000 children developed cancer of the thyroid as a result of exposure to radiation. There is also evidence that indicates the growth in the rate of patients per leukemia|6|.
New studies in this regard also pointed out that the cancer incidence thyroid activity in children has increased 40-fold since the explosion; in adults, the rate increased up to 7 times|7|. In addition to illnesses, the psychological impact of the accident was huge on thousands of people who suddenly lost everything and were forced to abandon their lives.
Studies suggest that among those who have gone through traumatic events (like the Chernobyl accident), the anxiety index is higher. The psychological consequences caused by the Chernobyl accident have been identified as similar to those who have gone through extremely traumatic events such as the atomic bombing of Hiroshima and Nagasaki.
Thousands of people who have been in contact with radiation have benefited from compensation provided by governments from affected countries and now receive a special pension, or have been retired due to disability, or receive special medical treatment etc. The beneficiaries were:
Infected people who got sick from radiation;
Liquidators;
People who worked in the Chernobyl region in subsequent years;
People who remained in contaminated areas;
People who have been evacuated from contaminated areas.
Until today the number of people who died is unknown because of the Chernobyl accident, and this is one of the most controversial issues when talking about the accident. Among the statistics raised, it is pointed out that two workers died during the explosion, 29 died in days after the accident due to exposure to radiation and another 18 died from diseases caused by contact with the radiation.
In any case, there are studies that suggest that, until 2006, around 4,000 people had died as a result of the accident, but there are studies that suggest higher numbers of deaths. Some studies suggest 9,000, 16,000, 60,000, and there are studies that indicate that up to 90,000 people may have died as a result of the accident. The truth is you'll never know for sure how many people died.
Also access: Discover the history of the accident with cesium-137 that happened in Goiânia
Responsible for the accident
Shortly after the explosion, the Soviet government organized a commission to discover the causes of the accident. A trial was held in the city of Chernobyl (also a ghost town like Pripyat), and six people were tried for the accident. Of these, three were sentenced to ten years in prison: viktorBryukhanov, Nikolaifomin and AnatolyDyatlov.
Bryukhanov and Dyatlov served five years in prison and received amnesty. Bryukhanov currently resides in Kiev, and Dyatlov died in 1994 as a result of radiation exposure. Fomin had a mental breakdown and tried to kill himself, after which he was transferred to a psychiatric clinic.
Radiation Hazards
THE radiation it is a way of transmitting energy through space. It exists in two forms: electromagnetic radiation and corpuscular radiation. Some heavy atoms, like the uranium, have nuclear installability, that is, their core cannot remain cohesive and, therefore, tends to decay into smaller and more stable cores.
During decay, some very energetic particles, such as protons, neutrons, coresinhelium,electrons and also electromagnetic waves, all of high energy, are emitted to all directions in space. The ionizing ability of these forms of radiation makes them potentially lethal.
THE radiation ionizing is any form of radiation, corpuscular or electromagnetic, that is capable of causing damage to the genetic code of cells due to the ionization process, which consists of stripping electrons from atoms. Ionizing radiation is able to kill cells or induce them to mutate so that their functioning or replication is affected. Among the various complications related to exposure to radiation sources (irradiation), cancer, genetic mutations, burns and death stand out.
The intensity of an ionizing radiation, such as gamma or x-rays, can be determined by the magnitude roentgen (R), which relates the amount of ionized charge in a given volume of matter. An adult human being can support a maximum dose of 500 roentgens. In the vicinity of the Chernobyl radioactive accident, radiation levels reached 20,000 roentgens per hour. Thus, some workers who were unprotected in the most critical areas of the accident received lethal doses of radiation in less than a minute.
The Chernobyl exclusion zone is over 2600 km² and will be uninhabitable for at least 3000 years.
In addition to the direct exposure, which took place in the vicinity of reactor 4, a large cloud charged with Radioactive particles and gases escaped from the Chernobyl complex because of the fire caused by the fusion of the reactor. Gaseous elements such as xenon-133, were immediately released into the atmosphere, however, their short half-life, of approximately five days, reduced the impacts of these gases on the health of employees and residents of the region. Other radioactive elements, such as iodine-131 or the tellurium-132, short half-life (8 days and 78 hours) were also suspended in the air, but soon lost their effects.
The biggest problem was the cesium-137, whose half-life takes more than 30 years. The precipitation of cesium-137 dust in the atmosphere made the Chernobyl region uninhabitable for a time that varies between 3,000 and 20,000 years.
|1| ALEKSIEVITCH, Svetlana. Voices of Chernobyl: the oral history of the nuclear disaster.
|2| New safety dome for Chernobyl reactor opens. To access, click on here.
|3| Chernobyl accident and its consequences. To access, click on here [in English].
|4| Chernobyl disaster: why are the consequences still observed and why is the international assistance still critical? To access, click on here [in English].
|5| Chernobyl Nuclear Accident. To access, click on here [in English].
|6| The Chernobyl accident. To access, click on here [in English].
|7| Same as note 4.
*Image credit: Krysja and Shutterstock
**Image credit: Olga Vladimirova and Shutterstock
By Rafael Helerbrock - Master in Physics and Daniel Neves - Graduated in History