The Chernobyl disaster: Five interesting facts about the worst nuclear accident in history

The Chernobyl disaster occurred on 26 April 1986 at the No. 4 reactor of the Chernobyl Nuclear Power Plant near the city of Pripyat, in the north of Ukraine, in what was then the Soviet Union. It occurred when an RBMK 1000 reactor overheated and exploded during a safety test, releasing at least 5% of the radioactive reactor core into the environment and depositing radioactive material across a wide swathe of Europe.

The explosion itself killed two engineers. Another 28 to 30 operators and firemen who helped fight the blaze died of acute radiation syndrome within a few weeks of the accident, and a number of workers later died of causes related to suspected radiation exposure.

Workers of the plant, firefighters, and residents of the nearby city of Pripyat received dangerous doses of ionizing radiation. 

The event also likely had a significant environmental impact. Radiation contaminated drinking water and fish over large distances, destroyed 1.5 square miles (4 square kilometers) of pine forest, and killed or induced mutations in other plants or animals. Large areas of Belarus, Ukraine, Russia, and parts of Europe were contaminated to varying degrees.

The Chernobyl nuclear accident was one of the worst to have occurred,  rating a seven on the International Nuclear Event Scale (INES), along with Fukushima nuclear disaster. It did, however, lead to major changes in safety and industry cooperation. Former Soviet President Gorbachev has said that the Chernobyl accident was one of the most important factors in the fall of the Soviet Union.

Here are some interesting facts about Chernobyl nuclear disaster.

1) The reactor had design flaws

The Chernobyl disaster is usually attributed to human error. Viktor Bryukhanov, the manager of construction and director of the nuclear plant, was held responsible for the accident and imprisoned for violation of safety regulations in 1987. He was released in 1991.

But now we know that the cause of the accident was most likely a combination of human error and design deficiencies in the Soviet-era RBMK 1000 reactors and that many of these faults were known by Soviet experts but kept secret from Bryukhanov.

Some of these flaws were:

• The reactor can possess a positive void coefficient, where an increase in steam bubbles ('voids') is accompanied by an increase in core reactivity. This can be produced by the usage of graphite as a moderator instead of water. The void coefficient is a number that calculates the reactivity of a nuclear reactor as the void content (steam bubbles) increases or decreases in the reactor’s moderator. As steam increases in the fuel channels, the neutrons that would have been absorbed by the denser water produce increased fission in the fuel. In the accident at Chernobyl 4, conditions resulted in a positive void coefficient that was large enough to overwhelm all other influences on the power coefficient. The reactivity of the reactor increased as the steam inside the core increased. The core then became more reactive and produced more steam and more power, until extreme temperature and pressure in the core led to the reactor’s failure — causing severe damage to a number of fuel assemblies, which eventually resulted in the explosion that destroyed the reactor.
• A lack of a sound containment structure or other enclosure around the reactor. The pressure in the core produced a blast that exposed it and leaked radioactive steam into the atmosphere. This could have been prevented with a reinforced gas-tight shell. 

Additionally, the power plant operators weren’t adequately trained to work with this type of reactor. Unaware of its weaknesses, the reactor crew disabled automatic shutdown mechanisms to prepare for a test on the reactor would perform following a loss of main electrical power supply.

As the reactor began overheating, a peculiarity of the design of the control rods caused a dramatic power surge as they were inserted into the reactor, leading to the rapid increase in core reactivity.

2) The real death toll of the disaster is unknown

It took almost two weeks after the explosion for firefighters to put out the graphite-fueled fire. 

But the fire wasn’t the only threat, as toxic fumes —composed mainly of fission products iodine-131, cesium-134, plutonium-239, and cesium-137— were still in the air. 

Apart from the two engineers killed at the blast, 28-31 emergency workers and plant operators died of acute radiation sickness in the first three months after the accident. 

According to the International Atomic Energy Agency (IAEA), there were also 1,800 documented cases of thyroid cancer in children living in the region who were between 0-14 years old at the time of the accident, which is “far higher than normal”. This is likely related to the release of iodine-131, which accumulates in the thyroid.  

A 2005 report by the United Nations estimated that up to 4,000 deaths might ultimately result from radiation exposure from the accident.

The Chernobyl nuclear disaster also increased unnecessary induced abortions due to fear of birth defects —an effect of the radiophobia that spread among the people in the affected areas. It has been estimated that more than 1 million abortions were performed in the Soviet Union and Europe as a result of incorrect advice on the effects of radiation exposure, but these numbers cannot be confirmed.

3) Evacuations started 36 hours after the accident

Many people in Pripyat —located around 2 miles (3 kilometers) from the Chernobyl Nuclear Power Plant— began suffering from symptoms like headaches and vomiting within a hours after the accident, but an evacuation wasn’t ordered until 36 hours after the accident. 

This was likely due to the fact that the Soviet authorities were reluctant to acknowledge first that an accident had occurred and then the full extent of the accident. On April 28, radiation levels set off alarms at the Forsmark Nuclear Power Plant in Sweden, around 620 mi (1,000 km) from Chernobyl. However, when the Swedish government contacted the Soviets, they initially denied an accident had taken place at all and only admitted it once the Swedish government said they were about to file a report with the International Atomic Energy Agency.

Although Pripyat inhabitants were initially told that they would only be away for three days, the Chernobyl Exclusion Zone (officially called the Chernobyl Nuclear Power Plant Zone of Alienation) was created about 10 days later with a radius of 30 kilometers (19 miles) of the nuclear plant. 

Residents never went back and Pripyat is a ghost city since then. 

The Chernobyl Exclusion Zone now measures approximately 1,000 square miles (2,600 square kilometers). Around 7,000 people live and work in and around the plant (or did until the beginning of the war with Russia), and around 150 have returned to the surrounding villages, despite the risks. 

4) The “liquidator” status

Civil and military personnel exposed to radiation while trying to mitigate the effects of the nuclear disaster were termed “liquidators”. Those who worked as liquidators have a similar status to veterans and are entitled to certain social benefits, although many have since complained of a deterioration in their compensation and medical support over time.

Around 600,000 people were granted the status of “liquidator.” They were mainly men and women who worked on the clean-up and decontamination of the area —such as those who removed contaminated debris from the nuclear plant, those who worked on the construction of the “sarcophagus” (a steel and concrete structure to cover the exploded reactor and prevent further contamination), those who helped build settlements for evacuees, etc. 

5) The contamination spread to several areas of Europe

The disaster took place around 59 miles (94 kilometers) from Kyiv, Ukraine’s capital city, at a time when it was a territory of the Soviet Union. But with winds and rainfalls, radioactive contamination quickly spread to Russia, Belarus, and some parts of Scandinavia and southeast Europe. 

Radionuclides settled in the soil and water, contaminating fish, plants, and the animals that ate them. Subsequently, animal products such as milk and meat were affected, too. Some forest food products and crops were also contaminated with levels of radiation deemed above safe consumption levels for a while. 

Fortunately, many radioactive elements released into the air are short-lived, but strontium-90 and cesium-137 each have around a 30-year half-life. These elements have been found in lakes, and they are also present in the water and fish of rivers of Ukraine, Russia, and Belarus, as well as in the air of the Chernobyl Exclusion Zone.