The Chernobyl Nuclear Power Plant is stationed near the city of Pripyat in Ukraine, which was formerly part of the Soviet Union. The nuclear power station is 14.5 km northwest of the city of Chernobyl, from which it gets its name. At the time of the disaster, the power plant had four RBMK-1000 reactors in service while two were under construction. Due to the flawed design of the RBMK-1000 reactors and negligence of plant operators, the Unit 4 reactor at the Chernobyl plant exploded on April 26, 1986 releasing large amounts of radioactive material into the atmosphere. The Chernobyl Disaster is regarded as the worst nuclear power plant accident in history, both in terms of cost and casualties. Though only two people died due to the explosion, thousands of deaths were caused by cancer developing in people due to exposure to the radiation. Here are 10 facts about the Chernobyl Disaster including its cause, its impact and its effect on humans as well as the environment.


#1 Positive void coefficient of the RBMK reactor was a major cause of the disaster

In nuclear engineering, the void coefficient is a number which estimates how much the reactivity of a nuclear reactor changes as voids (typically steam bubbles) form in the reactor coolant. A reactor with a positive void coefficient increases the core reactivity when voids increase in the coolant and the result is opposite in a reactor with a negative void coefficient. When the reactor operates at high power levels, there is a high flow of water which pushes the voids out quickly and thus voids don’t have much contribution to reactivity. However, at low power levels, steam voids take longer to get out of the reactor thus having a large impact on reactivity. The Chernobyl Nuclear Power Plant had four Soviet built RBMK-1000 (Reaktor Bolshoy Moshchnosti Kanalnyy) reactors in service while two were under construction. The RBMK reactors at Chernobyl had a large positive void coefficient, i.e. of 4.7 beta, which allowed to save costs. However, this large positive void coefficient was one of the primary causes leading to the disaster.

RBMK Nuclear Reactor diagram
Schematic Diagram of RBMK Nuclear Reactor


#2 Negligence of plant operators contributed to the Chernobyl Disaster

On 25th April 1986, a safety system test was planned to be carried out at Unit 4 reactor at Chernobyl before it was scheduled to be shut down for maintenance. During the test, in violation of safety regulations, the plant operators shut down the reactor’s power-regulating system and its emergency safety systems. Moreover, they allowed the reactor to run at 7% power. The RBMK reactor, with its high positive void coefficient, becomes very unstable at low power levels. As voids began to be produced in the coolant, the nuclear chain reaction increased. The reactor went into a positive feedback loop in which void formation increased the power output to dangerously high levels. This in turn led to the Chernobyl Disaster.

Chernobyl Reactor location
Location of Chernobyl Reactor No 4 on a map of Europe


#3 Thirty people died due to direct exposure to radiation emitted from the reactor

At 1:23 AM on April 26, 1986, the chain reaction in the Unit 4 RBMK reactor went out of control and the output rose to more than 200 megawatts. This resulted in a power surge that caused a powerful explosion that detached the 1,000-ton steel and concrete lid covering the reactor core. This in turn led to the reactor core releasing large amounts of radioactive material into the atmosphere. After a few seconds, a second even more powerful explosion blew the reactor building apart. Due to this, burning graphite and other parts of the reactor core were discharged leading to a number of intense fires around the reactor. 1 person died at the point of explosion while another succumbed to severe injuries at the hospital. Within three months of the incident, 28 others died as a result of Acute Radiation Syndrome (ARS).

Chernobyl reactor after the explosion
The Chernobyl reactor after the explosion on 26th April 1986


#4 The Soviet Union attempted a cover up of the disaster

In the immediate aftermath of the disaster, the Soviet Union went to extreme lengths to cover it up. They even kept their own citizens in the dark and did not alert the neighboring countries to keep the radiation from spreading. However, the cover started falling apart within a couple of days of the disaster as Swedish air monitors detected an abnormal amount of radiation in the atmosphere and determined its origin to be in the USSR. As a result, the Soviets were pressurized into accepting that the disaster did occur but they falsely reported that only two people had died at Chernobyl. They even went to the extent of proclaiming that the situation was now stable and completely under control. It was not until 6th May when the authorities realized the gravity of the situation and closed schools in Kiev, the capital of Ukraine which was located just 65 miles from the site of the incident. They ultimately warned the residents to stay inside their homes in order to protect themselves from the radiation. It took years before a full account of the incident could be unearthed.

Times report on the Chernobyl Disaster
Times report on the Chernobyl Disaster, April 29, 1986


#5 Chernobyl Nuclear Power Plant kept running for 14 years after the disaster

In response to the Chernobyl Disaster, the remaining three reactors at the nuclear power station were shut down. However, within the next year and a half, the units 1, 2, and 3 were restarted even through the move received widespread condemnation. The protest against the move was due to the alleged design flaws of the reactors and extensive contamination at the site which exposed thousands of plant operators to lethal risk. In 1991, a turbine hall fire led to the closure of Unit 2. After the Soviet Union dissolved and Ukraine became independent, the two additional units were closed in 1995 as the new nation agreed to shut them down in return for international financial assistance. Unit 1 stopped operating in 1996 and the year 2000 marked the official closing of the plant with the shutdown of Unit 3. Thus, even after such a major accident, authorities surprisingly kept the plant running until the year 2000.

Shutting down of the last Chernobyl reactor
New York Times report of Ukraine shutting down the last Chernobyl reactor


#6 Radioactive Contamination from the Disaster Was Detected all over Europe

The Chernobyl Disaster is estimated to have released about four hundred times more radioactive material then the atomic bombing of Hiroshima and Nagasaki. Approximately, 100,000 square km was significantly contaminated by the incident. Belarus, Ukraine and Russia were the worst hit regions followed by Sweden, Finland, Austria, Norway, Bulgaria, Switzerland and Greece. Sweden was the first nation to officially identify the effect of the disaster on 28th April after traces of radioactive particles were found on the clothes of the workers at the Forsmark Nuclear Power Plant (1100 km away from Chernobyl). Although Finland had already identified the rise in radiation levels before Sweden, their publication was delayed by a civil service strike.


#7 Thousands of cancer deaths were caused by the radioactive fallout

In the first five years after the Chernobyl Disaster, the cases of cancer among children in Ukraine increased by more than 90 percent. By the time 25 years had passed after the incident, around 5,000 cases of thyroid cancer were registered in Russia, Ukraine and Belarus among those people who were less than 18 at the time of the explosion. The World Health Organization estimates that approximately 5,000 cancer deaths were related to the Chernobyl accident. However, this figure is challenged by others. In 2005, The United Nations agencies estimated that the cancer deaths caused by Chernobyl Disaster were around 4,000 out of the 5 million people residing in the contaminated areas. However, the ultimate death toll as a result of the disaster may be significantly higher. Greenpeace International has suggested that around 90,000 may have died due to the Chernobyl Disaster.

Chernobyl Disaster death toll
Estimated Deaths due to the Chernobyl Disaster by various sources


#8 Millions of acres of farmland and forest area was contaminated

The radioactive release from the Chernobyl Disaster contaminated about 125,000 km sq of land in Belarus, Ukraine and Russia. Around 52,000 km sq of this was in agricultural use while the other was forest, water bodies and urban centers. A particularly effected site was a pine forest in which all the trees were killed due to exposure to radiation. This region came to be known as the “Red Forest” because the dead trees turned a bright ginger color. The top 10–15 cm of the soil of the severely contaminated area was removed while the dead trees were cut down. This waste was placed in trenches and covered with a layer of sand. A total volume of 100,000 meter cube was buried reducing soil contamination by at least a factor of 10. Also, around 350 animals were reported to be born with gross deformities within the first four years of the disaster. While some of them were missing certain organs such as eyes, heads or ribs; others were born with extra limbs. Birds with deformed beaks were also reported.

Chernobyl Disaster Red Forest
A portion of the Red Forest caused due to the Chernobyl Disaster


#9 Fear of birth abnormalities led to countless abortions throughout Europe

Due to the media frenzy following the Chernobyl Disaster, there was a dramatic increase in the cases of abortion filings throughout Europe, especially in countries where abortion was legal. Pregnant women feared that exposure to the radiation, however small, might effect the birth of otherwise normal babies. For instance, in Greece, doctors were unable to deny these requests from worried pregnant women, leading to a termination of in excess of 2,500 pregnancies. According to Dr. Robert Baker, due to misplaced fears of radiation from the disaster, an estimated 150,000 abortions may have been performed on pregnancies which were in fact otherwise healthy. This excludes the data of the most severely hit regions of Soviet Union, Ukraine and Belarus due to unavailability. Also, there was no increase in birth defects in Belarus or Ukraine, the two nations which had the highest exposure to fallout.

Chernobyl Power Plant sarcophagus
Chernobyl Power Plant in 2006 with the sarcophagus containment structure


#10 Chernobyl is the most disastrous nuclear power plant accident in history

The Chernobyl Disaster is regarded as the worst nuclear power plant accident in history, both in terms of cost and casualties. Along with the Fukushima Disaster in Japan in 2011, it is one of only two nuclear energy accidents classified as a level 7 event, the maximum classification on the International Nuclear Event Scale. The effort to minimize its damage along with decontamination of the surrounding area involved over 500,000 workers and cost an estimated 18 billion rubles. By May 14, within 20 days of the disaster, around 116,000 people who were living within a 30-kilometer radius of the reactor were evacuated and later relocated. In the years following the accident, a further 220,000 people were resettled into less contaminated areas. The 30 km radius or 2,800 km sq exclusion zone was later extended to 4,300 km sq. Today, a few hundred former residents of the area have returned back even though there is still a risk of radiation exposure. In fact, the immediate surrounding area of the plant won’t be safe for human habitation for at least 20,000 years.


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