Chernobyl Nuclear Disaster

INDEX

Summary
Introduction
The disaster
Emergency response
Third Explosion
Clean-up and after-effects
Conclusion

1. Summary

On 26th April 1986 at 1:23 AM, the lid on top of Reactor Number 4 of the Chernobyl Nuclear Power Plant in the Soviet Union starts shaking. The shockwaves are felt all throughout the building. The workers present realized that the nuclear reaction in the reactor was completely out of control by then, and that reactor had to be stopped quickly. So one of those workers pressed the Emergency Shut Down button. By pressing the button, the control rods were designed to enter the reactors and prevent the reactions. But they didn't work as designed. After the button was pressed, the control rods entered the reactor, but as soon as they went in, there was a huge blast. A huge explosion. After this blast, the reactor was engulfed in flames. The harmful radioactive material present there rose up into the air with the flames. The amount of harmful radioactive material released in this disaster was equal to 400 Hiroshima atomic bombs. This disaster is still considered to be the World's Worst Nuclear Disaster. The radiation spreading through the air had an effect on not only Ukraine but all over Europe from Spain to Sweden also. There was radioactive rain in the United Kingdom. The radioactive dust which settled on the grass in the hills was consumed by cows and the amount of radiation in the milk of those cows spiked. Due to this, thousands of children got Thyroid Cancer.

2. Introduction

After World War II, the Soviet Union invested a lot of money in nuclear power plants.
Chernobyl Nuclear Power Plant Its official name was ‘Vladimir lenin nuclear power plant’.
Chernobyl Nuclear Power Plant was built approx 16 km away from the Chernobyl city
It consisted of 4 reactors of RBMK 1000 design. The purpose of power plants is to generate electricity.
In this case, each reactor could produce 1,000 Megawatts of electricity. The four reactors could together supply electricity to meet 10% of Ukraine's electricity demand.
This disaster took place in Reactor Number 4, during a routine safety test.
In this case, the control rods were made of boron carbide, which absorbs the neutrons and slows down the chain reaction, and reduce the power output.
Moderators were made up of graphite which would slow down the neutrons and increase the chances of the neutron hitting another atom of uranium isotope thus increasing the speed of reaction and the power output.

3. The Disaster

On that ill-fated night, the 26th of April. The workers were testing the unit. Workers were tasked with reducing the output of the nuclear power plant from 1,600 MW of electricity to 700 MW.
But as soon as the workers inserted the control rods, the power dropped even more. It fell below their expectations. And reached 30 MW. The workers working there couldn't comprehend why it happened.
The reason behind this was xenon poisoning.
Seeing that very little electricity was produced, the shift supervisor, Anatoly, ordered the workers to take out some of the control rods.
There are normally 211 control rods in a reactor, All but 8 of them were taken out.
Only 8 control rods remained in the reaction chamber. This was a violation of the safety protocols because it was clearly written in the rule book that under any circumstances, there should not be fewer than 15 control rods in the reactor.
At 01:19 AM, because the control rods were abruptly taken out, the reaction spiked suddenly. The power output increased rapidly, and whatever little water was present in the core, turned into steam.
It also meant that the amount of water in the reactor core kept decreasing. Remember, water was supposed to work as the coolant. A positive feedback loop was created here. As the water turned into steam.
Resulting in the reaction gaining more speed.
The Xenon present in the reactor till then which was working to slow down the reaction, burned out when the reaction sped up. This was the point of the Extreme Power Surge.
A lot of steam was being produced here, and the lid of the containment structure started shaking. Shockwaves were felt throughout the building, and power output reached 33000 MW
Workers realized that they have to execute an emergency stop. So they pressed the Emergency Stop button. It was at 01:23 AM. Pressing this button meant that the control rods would be reinserted into the reactor, to slow down the reaction. At a glance, it would feel like a logical step, but this reactor had a design flaw.
A control rod is actually made up of two parts. The main part of the control rod is made of Boron, it slows down the reaction by absorbing the Neutrons. But the tip of the control rods was made of graphite. The same graphite was used as a moderator in the reaction. That worked by speeding up the reaction.
As soon as the button was pressed, and the remaining control rods were inserted into the reactor, the control rods with their graphite tips. This caused a blast.
The graphite infinitely sped up the already speeding reaction. The power generation of the reactor reached 33,000 MW.
The first blast was 6 to 8 seconds after the emergency button was pressed. Because of this blast, the core of the reactor started melting. After 2-3 seconds, there was an even more powerful blast.
The radioactive material started spreading through the atmosphere. The reason behind the second blast is said to be the graphite present in the reactor started burning. It combusted as well.
But with more than 100 radioactive elements and 5% Uranium fuel, there were 192 tonnes of Uranium fuel in the reactor.

4. Emergency response

At 01:26 AM the fire alarm began ringing. Firefighters reached the spot. this fire was caused due to graphite. It wasn't about to die down easily. It took more than 10 days to put out this fire.
Helicopters were called in to drop thousands of tonnes of clay, sand, Boron, and lead from the sky. As These elements can reduce the spread of radiation.
But it was a truly dangerous task, one of the helicopters crashed and due to this four people died.
The firefighters who had reached to put out the fire, experienced fatigue and nauseous after they went home. Symptoms of Radiation Sickness.
When you are exposed to an extremely high dose of radiation, these symptoms begin appearing indicating that you will die in a few months.
About 28 of these firefighters passed away within a few months. People who were exposed to comparatively less radiation died in a couple of years, and those who were exposed to even less developed diseases like cancer within 10 years.

5. Third Explosion

This reactor was producing high levels of heat even after the fire died down. It couldn't be controlled. Due to this heat, the base of the reactor started cracking. It was highly problematic. Because there was a water tank under the reactor. Filled with radioactive water. If the reactor producing high levels of heat came in contact with the water, the water would have instantly converted into steam. this leads to an explosion. it leads to an explosion.
There was only one way to prevent this from happening. A person had to dive into the radioactive water tank, and drain the radioactive water out of the reactor. To do this, a real-life hero was needed. The water was radioactive. would be in a danger throughout their remaining life.
We had three such heroes. ‘Alexel ananenko’, ‘valeri bezpalov’, ‘boris baranov’. On 4th May 1986, they dived into the water tank. They swam in the dark guided by only one lamp. They located the valves that had to be opened to drain the water. The good news is that all three divers survived.

6. Clean-Up and After-Effects

The next step was to clean up the radioactive waste lying there. Initially, the officers of the Soviet Union used remote-controlled robots to do this.
But the robots started breaking down near the radioactive waste. Thousands of people had to be sent in to clean up. They were known as the
liquidators.
During 1986-1987, 200,000 liquidators were dispatched to actively clean up this area.
When the fire caused by the blast was being put out, The Soviet Union government tried to cover up the whole incident because The Cold War was underway. On 28th April 1986, the Soviet Union admitted that a disaster had indeed taken place.
By 2nd May 1986, a 30 km radius was set up all around this nuclear power plant, It was declared an exclusion zone. This became a restricted area where no one could enter except for scientists and government officials.

To contain the radioactive waste, another structure was built on top of it, known as the Sarcophagus, a concrete and metal structure to control the radiation coming off of it. But this structure wasn't built for the long term. About 28 years after it was constructed, rust and cracks started forming.
This is why in 2010, the construction of the new safe confinement began. This new structure was fit atop the existing sarcophagus. 3 billion dollars were spent on building this new structure. It took 9 years to build it. But since it was built with a plan for the long term, it is said that this can keep the reactor closed off for the next 100 years.
In 2018, the United Nations Scientific Community reported that 20,000 cases of thyroid cancer were seen in children below the age of 18 years. Who lived through the disaster.
The main reason for this is said to be the radioactive dust settling on the grass on the pastures where cattle were fed.
their milk contained a high level of Iodine 131. leading to thyroid cancer in children.

7. Conclusion

The cost of the disaster to the Soviet Union $235 billion.
Emergency response, cleaning up, relocating people, paying the expenses of the survivors, carrying out evacuations, and decontamination of the environment, they had to bear all expenses. Politically, it is said to be a major reason for the breakdown of the Soviet Union.

Scientists all around the world started conducting research on preventing such future nuclear disasters. As a direct result of this disaster, the World Association of Nuclear Operators was founded in 1989. The aim of this international organization was to conduct safety checks of all the nuclear power plants in the world. And to conduct research into how their safety can be further increased.

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