Written by in section: Health > Catastrophe
Medically Reviewed by Dr. Aj Thomas MS, MBA & Updated on Apr 27, 2016
Chernobyl - quick facts about world’s worst nuclear disaster
Chernobyl: Abandoned city of Pripyat

Three decades ago on April 26, 1986 at 1 hour past midnight a series of operational errors were unfolding at a nuclear reactor inside the Soviet Union which ultimately lead to the worst nuclear accident in human history.

The number 4 reactor at Chernobyl Nuclear Power Plant exploded at 01:23 saturday morning releasing huge quantities of radioactive dust, radioactive gases and radioactive aerosols high into the sky and surrounding areas.

The reactor core was exposed and burning for nine days and during this time it was continuously ejecting radioactive materials into the sky.

All these ejected materials quickly formed a radioactive cloud and started moving in the direction wind was blowing and came down wherever it rained, contaminating the area where it landed.

Unfortunately, the wind changed direct many times during this period and this localized accident quickly became a global issue.

On the whole more than 190 tons of highly radioactive materials were released into the atmosphere and surrounding areas.


The location of the disaster

The accident took place at Chernobyl Nuclear Power Plant located 14.5 km from the city of Chernobyl which is located 95 km north of the capital of Ukraine, Kyiv.

The closest city to the reactor was the city of Pripyat at a distance of 3 km which had a population of 50,000 people at the time of the disaster. The city was built to house the power plant workers and their families.

The reactor was built in this area due to its close proximity yet safe distance from the city of Kyiv. It also had sufficient water supply for cooling and railway line passing through for logistics.

The disaster sent a plume of radiation to countries as far as the United Kingdom. However, the countries that were most affected by the disaster were Ukraine, Belarus and Russia due to the location of the reactor in close proximities to these countries.


How does a nuclear power plant like Chernobyl work?

The working principles behind a nuclear reactor is very simple, however, to build a working nuclear power plant requires very high levels of technical expertise.

Most nuclear power plants use Uranium-235 which is an unstable isotope of Uranium. A neutron is used to split the Uranium-235 into smaller isotopes while it releases large amounts of heat energy.

Using this heat energy water is heated to produce steam and the steam is used to rotate a turbine that can generate electricity.

A moderator like graphite is used to slow down the neutrons in order for the chain reaction to be sustained.

A control rod made of boron carbide is used to absorb excess neutrons to prevent an uncontrolled chain reaction which could lead to a nuclear catastrophe. It is also used to fully shut down the reactor by fully inserting the control rods into the core of the reactor.

Water is circulated through the reactor core to cool and prevent overheating of the reactor.


Why did the Chernobyl Nuclear Power Plant explode?

The operators of the power plant decided to test the emergency cooling system that should prevent the reactor core from overheating in case of power loss to the reactor main cooling systems.

To simulate a multiple system failure, various redundancy backup systems were deliberately disabled.

During the test a sudden surge of power followed by series of operational errors, lack of experience, flouted safety procedures, hidden reactor design flaws and sheer bad luck lead to the world’s worst nuclear disaster.

Senior engineers and management working at the plant tried to convince Moscow that it was only a minor incident and this misinformation greatly delayed evacuation and disaster management.

In whole, total disregard for safety protocols and mismanagement lead to the disaster.


The following is a list of surprising facts behind the tragedy.


Reactor Design flaw

The reactor used at the power plant was known as RBMK 1000 which is a pressurized water-cooled reactor. It had a design flaw (positive void coefficient) that the operating crew were not aware.

However, under normal testing and operating procedures this hidden design flaw should never have been a problem

Unfortunately, on that day during the testing phase the reactor was set in a configuration that was well outside the allowed safe operating configuration for the reactor and this design flaw just contributed to the ultimate failure of the reactor.


Containment building

It is a shield made out of thick steel or other durable materials that covers the entire reactor like a protective casing.

The RBMK 1000 designs did not have a containment building designed to prevent radioactive steam from leaking outside in case of reactor breach.

Containment building also prevents outside atmosphere to come in contact with flammable materials inside the reactor in case of a reactor breach.

This safety feature could have drastically limited the extend of radiation contamination after the breach of reactor core after the initial steam explosion and may have also prevented the following graphite fire.


Inexperienced operators and bad timing

Operators worked in three shifts at the power plant. The day shift had the most experienced engineers and operators. All major tests were usually conducted during this period.

On the previous day leading to the accident, the test was started during the day shift and had to unexpectedly be paused because of a power shortage occurring due a nearby power station going offline without any warning.

The electricity grid operators requested Chernobyl power plant operators not to reduce power as it would be the case during the testing and the permission to reduce power was granted later into the night when power requirements for the city of Kyiv was at its lowest and the evening shift was getting ready to leave.

The Chernobyl power plant management was under hurry to complete the test and asked the third shift to continue the test. The third shift operators were trained to operate the reactor safely, handle emergencies and conduct standard tests.

However, they were not well trained to test and simulate multiple system failures with all backup systems disabled which almost never happens in normal operational emergencies. Such tests required very deep understanding about every design aspects and knowledge about the limitation of the reactor.


Slow reaction and evacuation

After the accident, it was not possible to immediately estimate the seriousness of the accident.

Most local Ukrainian experts underestimated the extent of contamination and believed that many of the radiation detectors that were showing unbelievably high readings were simply not working properly.

There were many conflicting reports and readings immediately after the accident. Due to this chaos the city of Pripyat beside the reactor was evacuated only on sunday afternoon the 27th of April, 36 hours after the tragedy.

One of the main reason the evacuation was delayed was due to the Chernobyl management trying to downplay the accident.

They initially reported to Moscow that it was just a minor incident and there was no danger to the surrounding areas.

However, Moscow sent in their own experts and they were shocked to learn that all their measuring instruments were showing readings off the chart.

At the time of the evacuation, the radiation reading in the vicinity was 60,000 times above the normal levels.

Many of the residents received fatal radiation doses and would die in the coming days due to illnesses related to the radiation fallout.

The evacuation of the entire city of 50,000 people and surrounding areas were completed in less than 4 hours.

They were instructed to abandon all personal belongings and were promised that they could return soon.

This was done with the intention to reduce panic, chaos and make way for very quick evacuation. They also wanted to avoid the risk of people transporting contaminated personal belongings to other parts of the country.

After the evacuation was completed, the entire city was sealed off. All pets and wild animals in the nearby forests were neutralized. All personal belongings left behind was removed and buried to prevent contamination.


Shrouded in Secrecy

After the disaster the Soviets initially tried to cover it up. However, the news about the disaster came out when alarm bells started ringing in a nuclear power plant’s radiation detector in Sweden almost 1,000 kilometers away on monday morning the 28th of April.

The radioactive cloud had traveled to Northern Europe and radiation detectors picked up contamination from the cloth surface of the employees arriving for work at the Swedish power plant.

Later that day the Soviets made an official announcement about the accident but did not mention how serious it was due to lack of reliable information.


Safe Confinement building

Left: A photo taken immediately after the accident showing the exposed reactor core. Right: Temporary safe confinement building build to last 20 years.
Left: A photo taken immediately after the accident showing the exposed reactor core.
Right: Temporary safe confinement building build to last 20 years.

In the months following the accident a safe confinement building was built around the destroyed reactor to prevent any further radiation fallout.

Beneath this structure lays more than 200 tons of radioactive materials and they produce more than 10,000 roentgens per hour inside the containment building. Anything above 500 roentgens over 5 hours is fatal for human beings.

A new safe confinement building is being built to replace the old one. It is estimated that it would take 100 years to completely dismantled and remove the remaining radioactive materials from the destroyed reactor.


The show must go on

There were four functional RBMK 1000 reactors at the time of accident at Chernobyl. Reactor 1 was commissioned in 1977, Reactor 2 in 1978, Reactor 3 in 1981 and Reactor 4 in 1983. Reactor 5 and 6 was under construction when the explosion took place in Reactor 4 in 1986.

The entire area was so contaminated that the authorities decided to cancel the construction of the reactor 5 and 6.

The remaining 3 functional reactors however continued to be exploited till it was completely shutdown and decommissioned in 2000. Workers were brought to the site from the nearby cities by train.

Today it is possible to visit these places using guided tours and is very popular among people looking for extreme adventures.


Disaster management and clean up

Lightweight robots from Soviet space program (moon explorer) used to clean the highly radioactive rooftops of reactor 3 and 4.
Lightweight robots from Soviet space program were used to clean the highly radioactive rooftops of reactor 3 and 4.

The rooftops of the adjacent reactor number 3 and the undamaged rooftop of reactor 4 were covered with highly radioactive materials from the reactor core.

They had to be cleared and use of heavy bulldozers were not possible because of the delicate rooftops.

Many remote controlled robots from Soviet Union, Germany and Japan were brought in to do the job. The all stopped working almost immediately due to the high levels of radiation on the rooftops.

Only specialized radiation shielded robots designed for exploring the moon surface could work in these conditions. Due to their delicate nature, they often got stuck in the large debris with some debris weighing up to 60 kgs.

Finally, human beings with shielded costumes were used to complete the job. They were called “Bio-robots” and could only work for 40 seconds before they received their maximum lifetime permissible radiation dose.

Left: People is radiation shielded costumes on the reactor rooftop for their 40 second mission. Right: It is believed that radiation coming from the reactor below damaged the film in this photo.
Left: People is radiation shielded costumes on the reactor rooftop for their 40 second mission.
Right: It is believed that radiation coming from the reactor below damaged the film in this photo.

More than 5000 so called “Bio-robots” were used to complete the task. On the whole they did 90% of the cleaning job left after what machines could do. A large majority of people who died from radiation related causes were from this group.

More than 600,000 firefighters and emergency workers (Chernobyl liquidators) participated in managing the disaster and the cleanup process of the surrounding areas.

Left: A very rare photo of Chernobyl reactor 4 before the accident. Right: Reactor 4 with confinement building taken from the most popular angle view.
Left: A very rare photo of Chernobyl reactor 4 before the accident.
Right: Reactor 4 with confinement building taken from the most popular tourist angle.

An area of 30 km radius around the damaged reactor was marked as the Chernobyl Exclusion Zone and all people living in this area were evacuated.

Many highly contaminated houses had to be buried and all the equipment used for the cleanup process were abandoned inside the zone.

The entire zone was decontaminated using various methods like binding chemicals, topsoil removal and chemical washing.

Decontamination efforts in the abandoned city of Pripyat
Decontamination efforts in the abandoned city of Pripyat, 1986

The radiation spread unevenly across the region and now includes many countries with areas deemed uninhabitable.

On the whole more than 350,000 people have been relocated due to Chernobyl accident. Over 7 million people were indirectly affected by the disaster. Over 100,000 square kilometers of land has been contaminated.

Currently more than 150,000 people still lives in highly contaminated area in Belarus, Russia and Ukraine.


Radiation sources in Chernobyl contaminated areas

The Chernobyl accident exposed people to 90 times more radiation than Hiroshima atomic bomb.

Many of the radioactive materials that originated from the reactor core had a very short half-life and they have completely disappeared from the environment since.

One of the most problematic radioactive isotopes in the early days was iodine 131.

Iodine-131 (131I) is a radioactive isotope of Iodine and has a half-life of 8 days. During the early days immediately after the accident this iodine isotope was quickly absorbed by the thyroid glands in children resulting in many cases of thyroid cancers.


Other sources of ionizing radiation that continue to haunt the contaminated territories are:

Caesium-137 (137Cs) is a radioactive isotope of cesium with a half-life of about 30.17 years.

Biochemically it is very similar to potassium and our bodies can mistake it for potassium and therefore actively absorb it and ends up in the entire body with higher concentrations in soft tissues. It increases the risk of developing blood cancer (leukemia).


Strontium-90 (90Sr) is a radioactive isotope of strontium with a half-life of 28.8 years. Biochemically it is similar to calcium and can be mistaken for calcium by our bodies which actively absorb it and ends up in the bones. It increases the risk of developing blood cancer (leukemia) and bone cancers.


Plutonium-241 (241Pu) is an isotope of plutonium with a half-life of 14 years. The problem with 241Pu is that it can decay into americium-241 which is a radioactive element with a half-life of 432 years!


Chernobyl Death Toll

As per International Atomic Energy Agency (IAEA), United Nations (UN) and World Health Organization (WHO) reports, the Chernobyl accident is directly responsible for 4000 deaths. These were individuals who received very high doses of ionizing radiation.

The same report says that an additional 5000 people died due to medium to low doses of ionizing radiation.

A large percentage of these deaths were linked to cancers associated with radiation exposure and consuming contaminated food.

The first nine days were the most dangerous period as the core was exposed and burning. It was continuously ejecting radioactive materials high into the sky to form radioactive clouds.

More than 5000 tons of different materials were dropped into the reactor core during this period using helicopters to seal it temporarily.

Around this time the radioactive clouds moved in every direction wind was blowing and came down with rain on numerous locations hundreds and thousands of kilometers away from the reactor.

Chernobyl radiation fallout map
Chernobyl radiation fallout map

More than 5 million people continue to live in territories that have been contaminated by the radiation fallout in Ukraine, Belarus and Russia.

Based on research done by scientist like Dr. Alexey Yablokov, Dr. Alexey Nesterenko and Dr. Vassili Nesterenko it is estimated that more than 1,000,000 people may have died across Europe as a result of Chernobyl accident in the following two decades alone. They also believe the numbers will continue to increase in the coming years.

However, it is important to note that these numbers are speculative in nature and points more in the direction of worst-case scenarios.

Numerous studies based on Linear No Threshold (LNT) model estimates the death toll to be in the area of 10,000 to 100,000 across Europe.

The large discrepancies among various studies is due to the nature of problem we are dealing with. In many cases of cancers, it is difficult to exactly pinpoint what may have been the contributing factors.

Usually there is a lag of 5 to 30 years before cancer develops in individuals that have received high to medium doses of ionizing radiation. This huge timeframe gives enough window for large discrepancies and speculation.

It is very convenient and easy to convince the general public that all cancers in the affected areas are due to ionizing radiation, when in fact any number of other factors could have been the reason.


Psychological consequences

It is believed that more than 20% of deaths linked to Chernobyl is directly related to psychological consequences of the fear among the people who received minor doses.

The stress of abandoning everything and permanent relocation combined with fear of the unknown lead many into severe depression, alcoholism and suicide in the following years.

All these people were otherwise healthy and never experienced any illness like cancer with is associated with radiation exposure.


Chernobyl abortions

After the Chernobyl accident journalists around the world started engaging in creating speculative sensational news reports on a topic very popular at the time.

They disregarded basic ethics of journalism and also disregarded expert advices from scientist in the field and started speculating on the outcomes of the tragedy.

The end result was widespread fear and panic in many countries in Europe.

Due to the atmosphere of fear and panic created by mass media, many couples resorted to aborting their pregnancies due to the fear of birth defects in their unborn child.

We will never know for sure how many unborn babies were unnecessarily aborted by the direct actions of these news reports.

Research has shown that extremely low radiation doses received by the population outside the contaminated areas does not pose any significant health hazard that justifies an extreme step like abortion.

New reports immediately after the Chernobyl accident. Reports claiming 2000 deaths when in fact only 2 people had died by then.
News reports immediately after the Chernobyl accident.
Reports claiming 2000 deaths when in fact only 2 people had died by then.

Mass media has an undeniably strong influence in shaping public opinion and actions. Therefore, in times of tragedies like this, it is very important to coordinate their news efforts with experts from the field to make sure that whatever information is passed on to the public is reliable, not speculative in nature and answers more questions than it creates.


The big question: Are nuclear power plants safe?

The fear about nuclear energy comes from highly publicized tragedies like Chernobyl and Fukushima. We need to stop relying on our emotions and look at the issues in an objective way

Nuclear power plants are safe and have a lot of failsafe mechanisms and backups built into their designs to make sure that an accident does not happen.

A single failure of a safety protocol does not cause a nuclear accident because of the build in multiple redundancy safety mechanisms.

For an accident to occur, a combination of multiple failures combined with operation errors and sheer bad luck should occur.

Modern civilization depends on cheap energy like never before and in order for our civilization to continue developing quickly we need access to cheap and reliable sources of energy.

Nuclear power plants when operated properly, causes no air pollutions and is one of the cheapest form of energy available today.

From a health perspective, a nuclear power plant is much safer than conventional fossil fuel power plants.

A lesser know fact is that air pollutions caused by fossil fuel use is directly responsible for the death of millions of people around the world every year as per WHO reports, yet many people turn a blind eye towards these facts.


The Paradox

Most Nuclear fission reactors around the world were designed for 30-35 years of exploitation. It was believed by the designers that by then these reactors could be replaced with newer and safer designs.

However, thanks to mass protest against nuclear energy, radiophobia and miss information among the general public, support for nuclear energy is very slim.

Therefor many countries are not able to upgrade their already outdated reactors by building new ones and are forced to continue exploiting the aging reactor by modifying and upgrading them on the older design and framework.

From the Chernobyl and Fukushima accidents we know that radioactive clouds know no boundaries and no amount of political pressure can stop it. If an old reactor explodes, it will take a lot of surrounding countries with it.

At this point you might be thinking this is only a third world issue, if so, then think again. You will be surprised to know how old and leaky are the reactors in many developed countries that are situated next to major cities.

Of course, if all the people around the world united and forced their politicians to shut down all nuclear reactors we could theoretically solve this issue.

Let’s be practical and we know that this is never going to happen. Every industrialized nation depends on cheap energy to keep their competitive edge over other countries.

So our only hope is to make sure whatever nuclear reactor our country is using is the latest, safest and well managed reactor.


Future of nuclear energy

The cleanest sources of energy are from sources that are renewable like solar, wind and water. However, the current technology does not allow us to have a cost effective solutions to harvest these sources. Another problem is the limited availability of these sources in areas that need them the most.

Without any doubt we will need to slowly phase out fossil fuel based power plants in the coming future. This leaves us with just one practical approach, that is nuclear energy.

Harnessing the power inside the atoms is the key to nuclear energy and there two ways to do this with very different outcomes:


Nuclear fission reactors

We have mastered the art of splitting unstable atoms to harness the power inside the atom and this approach is called nuclear fission.

Unfortunately, this process requires the use of dangerous radioactive elements like uranium isotopes. They are unstable elements and the resulting elements are also radioactive and are dangerous for human beings and our environment.

Of course modern nuclear fission reactors are very safe and the continuing technological developments are making it even more safer.

The problem is that we have not yet figured out how exactly to safely dispose of the waste products from these reactors. For now, all what we could do is store them in specialized containers in secure and isolated locations.


Nuclear fusion reactors

In a fusion reactor, lighter atoms (hydrogen isotopes) are combined to create a larger atom (helium) while it releases large amounts of energy. The raw materials for this reaction is hydrogen element which is the most abundant element found in our universe. This approach is called nuclear fusion.

It is the same kind of nuclear reaction taking place inside the sun without which life would have been impossible on earth.

However, scientists have been struggling to master this technology since 1970s. So far it requires more energy to create this reaction than it can generate.

Scientists will eventually crack this puzzle one day. When that happens, human beings can be totally liberated from all other harmful sources of energy and will have access to the holy grails of clean energy available in unlimited quantities.

So in short, nuclear energy is the future! We have not yet harnessed the right type of nuclear energy.

×Hi :-) If you found this article interesting, please share the gift of knowledge.

Share this article


  • Last Reviewed on:Apr 27, 2016
  • Medically Reviewed by:Dr. Aj Thomas MSMBA
  • References:


    1. Nuclear Energy Agency. Assessment of Radiological and Health Impacts 2002 Update of Chernobyl : Ten Years On. Chernobyl, Assess Radiol Heal Impacts. 2002:157.
  • External Reviewer: 

Please share!