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Facts, Timeline, and Aftermath of the 1986 Chernobyl Nuclear Disaster

Facts, Timeline, and Aftermath of the 1986 Chernobyl Nuclear Disaster
An abandoned city, rusting buildings, rise in cancer and thyroid cases, deformed children and animals... we all know about the Chernobyl Nuclear Disaster that took place in Ukraine more than 25 years ago. We present some of the most striking Chernobyl Nuclear Disaster facts, along with the timeline of its events, causes, casualties, summary, and long-term effects.
Gaurav Athavale
Last Updated: Dec 19, 2017
Did You Know?
Within the nuclear plant's 'exclusion zone', an area of 4 square miles consists of the Red Forest, which got the name because of the dark-brown colored pine tree trunks. This happened due to the absorption of extremely high radioactive particles that blasted out through the nuclear plant towards the surrounding areas. This location is one of the most radioactively contaminated regions on our planet.
On 26th April, 1986, an explosion took place at the Chernobyl nuclear plant located in Ukraine, releasing massive amounts of radioactive material into the atmosphere, which also spread to the neighboring countries like Belarus, Russia, and several other European regions. Apart from the recent Fukushima nuclear disaster, the catastrophe at Chernobyl is also rated at Level 7 on the International Nuclear Event Scale. This is the highest level that can be attributed to such a disaster.

This accident directly claimed about 32 lives when it occurred, and people died due to acute radiation syndrome as they were exposed to extremely high doses of radiation. Till date, numerous physical deformities and cancer cases are still reported, which are linked to radiation exposure from this incident in the neighboring areas of Chernobyl and Pripyat. Damages amounted to around USD 18 billion as a result of this event, along with evacuation of several people. At least 500,000 workers were recruited and assigned in the rescue and relief mission; many of them were called the 'liquidators'.
Location and Brief Overview of the Chernobyl Nuclear Disaster
Ukraine Political Map
On the incident day, some tests were going on at the nuclear station's reactor 4, which is in proximity to the city of Pripyat, situated near the Belarus border and the Dnieper River. Suddenly, a surge in electrical supply took place, which initiated an emergency shutdown of the reactor core. But, during this time, another large surge occurred, which was beyond the withstanding capacity of the reactor vessel.

The chamber exploded causing the neutron moderator to get exposed to air, resulting in a chain reaction. The graphite moderator also exploded causing a fire, and hence a large amount of radioactive material was released in the atmosphere, which spread to neighboring areas. More than half of the fallout was concentrated in Belarus. Russia, Ukraine, and Belarus were the three countries, which suffered most due to the radioactive fallout.
Causes and Timeline of the Chernobyl Nuclear Disaster
Before we go on to the timeline of this event, let us understand in brief the test that was carried out on that fateful day:

When a nuclear reactor does not receive coolant flow, much radioactive heat is released as reactions start immediately. In this case, the emergency cooling systems get switched on, but their diesel generators take some time to start (at least 1 minute for running on full power). This was the same situation considering Chernobyl reactor no. 4, and it was considered unsafe for radioactive reactions to take place without any emergency cooling effect. It was decided to use the rotational power of steam turbines to run the systems before the diesel generators took control.

Before 1986, several test were being carried out, though without much success. A decision was taken to alter the electrical power supply in the next test carried out on 26th April, 1986. The procedure began with an emergency power shutdown, but the entire program was not followed according to the prescribed regulations. The management had not taken prior approval of the relevant organizations who oversaw Soviet nuclear programs. Also, it was mandatory that the power produced by the plant should not go below 70 MW, but this factor was not considered while undertaking the test.

At 1 p.m., on 25th April, the day shift of workers and engineers start decreasing the power level to 50% of the usual level of 3200 MW. A nearby power station experiences a power level drop, and it is decided to postpone the test so that electricity demand will not be hampered.

Around 11 p.m., emergency core cooling systems are shut down, which are not supposed to affect the power output, to aid the postponed test. The day shift workers leave after their time is done, but are supposed to have finished the test on that day itself. The night shift workers do not arrive until midnight, and hence, the core shutdown continued as they do not have ample time to carry out the test.

The power continues to decrease, and the night-shift workers start the control rod movement. They are initially assigned only to decrease the decay heat from previous day's preparations. Just after midnight, the radioactive core power goes below 700 MW to about 500 MW, as officers insert the rods more than necessary. Thus, reactor core poisoning starts taking place, i.e., in this case, formation of a xenon isotope in an unstable manner.

Around 12.30 a.m., on 26th April, the output power is less than 5% as that of the total expected limit, leading to an increase in xenon poisoning. The power is so low that it cannot be used to take the rods out again, which had the probability of reduction in poisoning effect. The rod control system is forced to shut down. This results in a small increase in power but not enough to run the system.

Till now, the rods are near their original upper limits, but the situation is difficult due to unstable core temperature levels, low power levels, irregular supply of coolant liquid, etc. This set off several alarms in the power station. The operators decide not get bothered by the alarms, and till 12.45 a.m., the experiment and testing is continued.

At about 1 a.m., power is increased till 200 MW, and water pumps are started to help in maintaining the coolant temperatures. But, the cooling does not take place as less time is available to cool down the rods. Water heat up and reaches near its boiling temperature, but now, it is released in a large quantity in an uncontrollable way.

At 1.15 a.m., the water finally lowers down the rod temperatures, but the flow goes beyond the prescribed limit, and a loss of steam pressure is reported, triggering off more alarms. Water starts absorbing a lot of neutrons emitted by the rods. A couple of water-circulation pumps are turned off, and a few control rods that can be removed manually are taken out so that power can be kept stable.

On the contrary, all these steps lead to a very unstable situation, and hence officers begin the actual experiment at 1.20 a.m. Supply of steam to the turbines is stopped, and many steam voids are formed inside the core. The ability of water to absorb neutrons started deceasing, leading to a consequent increase of reactor power and increase in steam generation.

A chain reaction starts and power increase takes place continuously. The reactor undergoes emergency shutdown and the process to insert the rods is started, which generally takes place in about 20 seconds. But, one of the graphite rod cores has a faulty design, and coupled up with an unstable situation the reactor power does not stop decreasing.

A massive power surge occurs as the rods are inserted leading to a continuous production of steam. The reactor power is above 30,000 MW, which is more than the upper limit needed for nuclear operations. Steam starts leaking from the reactor ,and as the pressure builds up even more, the entire assembly explodes at around 1.23 a.m. This also leads to the fracturing of other fuel channels.

Just after a few seconds, a second explosion occurs, wherein few pieces of the graphite core with intact radioactive control rods are ejected outside, giving rise to the radioactive fallout spread. This explosion is attributed to the release of hydrogen as graphite starts reacting with the supplied water. The entire reactor is shut down but the damage has already been done.
Chernobyl Nuclear Disaster Pictures
The slide-show below shows various places that were immediately abandoned following the explosion, and also shows the new confinement construction.
Abandoned building in pripyat
Abandoned Building in Pripyat
Abandoned school beds in pripyat
Abandoned School Bunk Beds in Pripyat
Abandoned school classroom
Abandoned School Classroom
Building with ussr symbol
Building in Ruins with USSR Symbol
Derelict amusement park
Derelict Amusement Park
Destroyed cooling towers at chernobyl
Destroyed Cooling Towers at Chernobyl
Destroyed reactor at chernobyl
Destroyed Reactor No. 4
Destroyed sports hall
Destroyed Sports Hall
Swimming pool ruins
Swimming Pool Ruins
Nuclear plant
New Containment Structure
Short and Long-term Effects
Health Effects on Humans
Apart from the death toll of 32 people, which resulted from acute radiation syndrome, at least 30 more died from prolonged radiation sickness (ARS) till 2008. Several children lost their lives due to thyroid problems, and more than 130 cases of confirmed ARS have been recorded. It has been estimated that there might be at least 16,000 cases of thyroid cancer in the surrounding regions till the year 2065, due to radiation exposure from this disaster. Also, till the same year there might be at least 25,000 cases of other cancer types among people who lived in the Chernobyl-Pripyat region.

According to estimates, about 180 metric tons of nuclear material in the form of dioxides and fuel products was present in reactor no. 4, and at least 30% of the entire amount got released into the atmosphere. After the explosion, the city of Pripyat was not evacuated immediately, but consequently several people started to fall sick and at least 200 people (mostly from the rescue and relief crew) had to be admitted in hospitals immediately. At least a million people were evacuated from the surrounding regions including Pripyat. The government predicted that in the next few years, cancer rate would rise by at least 2%.

On of the worst and most horrifying health effects caused were the mutations; many children had deformed body parts, missing fingers and eyes, missing limbs, deformed skulls, etc. Several cases of dipygus (multiple limbs) were seen in both humans and animals. Apart from thyroid-related diseases, the Down's Syndrome also affected children after the radioactive fallout.
Effects on Plants and Animals
In addition to the Red Forest mentioned above, several patches of land became barren shortly after the incident as floral species absorbed the radiation particles. Several animals who were present in that area died and few experienced a halt in the reproduction process. Some animals suffered from thyroid problems and showed stunted growth. On the reactor walls and outer portions, a type of radiotrophic fungi started growing; they absorb the nuclear energy for their growth. Such fungi were collected by a robot, which was directed into the reactor for further analysis after the disaster.

In Germany, it was discovered that the radioactive content in hunted wild boars had increased, and hence it was banned to kill any wild animal for meat in this country. In Norway, the cattle and other livestock had to be given clean and decontaminated food for several months before they and their future generations could be used as meat. Cesium isotopes had the largest impact on the food chain in the United Kingdom region mainly regarding animal husbandry of sheep and their usage for wool and meat. Most of the restrictions were lifted in the last decade. Mutations in animals consisted of reduced brain size, albinism, uneven pair of body parts like limbs, eyes, deformed toes and fingers, etc.
After the incident, considering the aftermath, several concerns were raised about the safety and operations of nuclear power stations all over the world. The development of such stations decreased drastically in the Soviet Government. After many protests by anti-nuclear agencies, several precautions were undertaken at numerous nuclear stations and the secretive transparency of techniques used was reduced to avoid such incidents in the future.
A New Containment Structure (NSC) is currently being constructed, which will cover up the entire nuclear reactor no. 4, including the sarcophagus built by the liquidators after the accident took place. This sarcophagus consisted of reinforced steel and concrete, and the purpose was to decrease the amount of radiation spreading out from the reactor's core chambers. The NSC is being designed to completely stop any radioactive particles from being emitted, so that the interior parts would be preserved.