Firstly I will explain a few phrases:
- Nuclear fission: it is a process in which atoms are split. In this process excessive neutrons are thrown, they hit other atoms and split them too. A split of an atom emits a huge amount of energy, this energy can be used to heat water in the reactor.
- Nuclear reactor: it is a place where the whole process of an atom splitting, water warming, and other stuff happens. It is a heart of nuclear power plant.
- Nuclear fuel: in this case, Uranium-235 is a radioactive substance used for nuclear fission.
- Meltdown: it is a process in which nuclear core melts by overheating. This overheating happens when nuclear reactor can’t be efficiently cooled, as it must be cooled faster than the reactor is heating. This overheating can be so huge that it starts to melt everything around.
- Control rods: these rods were made of boron in Chernobyl, they are used to slow down nuclear fission.
- Dosimeter: a device for measuring radiation levels.
HBO miniseries “Chernobyl”
After HBO miniseries “Chernobyl” many people are looking for information about Chernobyl disaster. I watched these miniseries myself and can tell that it was an outstanding documentary to watch. If you will do a little research you will find that there was a lot of truth. It was even more interesting to watch knowing that it was filmed in my country Lithuania. In spite of it being very accurate about disaster one thing I did not like is actors hadn’t Russian accent. But this article is not about miniseries or actors accent, I want to talk about what really happened in Chernobyl and how it could have been prevented.
How nuclear reactors work?
So how nuclear reactors work? The simplest answer would be: nuclear fission which happens in reactors, produces an enormous amount of energy which heats water. Water turns to steam and steam spins turbo-generators which generates electricity. Well, the whole process is not so simple. Nuclear fission must be controlled, otherwise, it can become an uncontrollable chain reaction which could meltdown core and a huge catastrophe could happen. That is what happened in Chernobyl. So when atoms split they produce another 2 radioactive atoms and few neutrons are shot out. These neutrons can hit other atoms and split them. This process continues until neutrons are slowed down or stopped, this is what is called a chain reaction.
Now to slow down these neutrons engineers are using control rods, which are absorbing these fast neutrons and are reducing a number of wandering neutrons and moderators, which are slowing down neutrons. As this process generates an enormous amount of heat, the nuclear reactor must be cooled and that is done by pumping water through the reactor.
The heat from the nuclear reactor turns water into steam, which travels to turbines. While turbines spin it generates electricity, which travels to the power grid. But this is not the only destination where generated electricity goes, water pump and control room gets it too. Now that’s where another problem sits, what if nuclear reactor stopped and it doesn’t spin turbine? Without a turbine generating electricity, water pump won’t work and the nuclear reactor would overheat. This is why near every nuclear power plant a diesel generator stands, they are started if turbines fail to generate electricity for water pumps.
About Chernobyl Nuclear Power Plant
Chernobyl Nuclear Power Plant or how it is officially called Vladimir Ilyich Lenin Nuclear Power Plant. This nuclear power plant started to generate electricity in 1977. This nuclear power plant had 4 RBMK reactors each able to withstand 3,200MW of thermal energy, 2 additional were building but they weren’t finished. These reactors were used in another 16 nuclear power plants. I must mention that just before a moment of explosion, nuclear reactor No. 4 was working over 10 times larger power than it was designed to hold. Nuclear reactor worked at 33,000 MW in the last moments.
What happened in Chernobyl?
1986, April 26 Nuclear Reactor No. 4 is under a backup test. Operators of the nuclear power plant had to reduce the power of the nuclear reactor. But they reduced it too much, to about 30MW, under this power they weren’t available to continue a test. So they tried to bring back power by dragging almost all control rods after a little time power has increased significantly. Operators tried to shut down the reactor by pushing an emergency button (АЗ-5, spelled AZ-5).
This is a photo of A3-5 Chernobyl nuclear reactor No. 1 emergency button (in a red square) :
This button had to drop all control rods into the reactor to stop the reactor, but RBMK reactors had one huge disadvantage. Control rods had tips of graphite which increases radioactivity and speeds up the reactor. So when they pushed the emergency button they increased nuclear reactor speed even more.
Heat in the nuclear reactor was so huge, that every molecule of water has been vaporized. Soon steam pressure built up in reactor, this pressure was so big that rods in the reactor have started jumping even though they weighted about 350kg each. After seconds the reactor exploded because steam had nowhere to escape. This explosion was so huge that a 1000 ton lid was lifted up. Zirconium mixed with water and produced hydrogen which is super explosive. As the lid was off, oxygen mixed with hydrogen and it got caught on fire. This led to a second even more powerful explosion. These explosions threw a lot of radioactive material into the air. The radioactive leak was so immense that even air was ionized and started to glow like a blue beam.
Right after the explosion a lot of people were sent to the reactor to extinguish a fire. Over 28 firefighters died in the following weeks by the cause of immense radiation. They were already sick in the morning after the explosion. A lot of people in Pripyat didn’t knew what really happened. Until 2 days after explosion, they were evacuated from the city. People thought that this was a temporary evacuation, but Pripyat will be uninhabitable for many centuries. There was a lot of tries to stop radiation from spreading, but most of them were unsuccessful. Wind spread radioactive clouds over East Europe up to Sweden. Cancer and birth defections rates have grown up significantly. Forests near Chernobyl turned red, many animals and birds died from radiation.
How Chernobyl disaster could have been prevented?
Well, there are few ways how it could have been prevented:
First of all and the most obvious probably, everything would be good if everyone would have taken all safety precautions before a backup test. After reactor power had dropped to only 1% of its thermal capacity operators should have increased power just bit by bit to burn xenon which poisoned reactor. (Xenon slows radioactivity of nuclear reactor)
Secondly, when they lifted control rods and power started rising, operators should have dropped control rods back one by one, not all at once. This would have gradually stopped reactor without increasing radioactivity so significantly.
And the last and most arguably actually, operators shouldn’t have pressed A3-5 button and somehow pumped water into the reactor to cool it down. Of course, they didn’t know about A3-5 weak spot. As water is one of the best radioactivity “slowers”. Even though if they didn’t pump water and didn’t press A3-5 the result would have been only a meltdown probably, the reactor wouldn’t have exploded and radioactive material leak out would be significantly smaller.
In spite of big radiation levels, Chernobyl exclusion zone now is a shelter for wild animals, as hunters are not coming into this zone. Even though Pripyat is uninhabitable you can actually book a tour in Chernobyl and Pripyat. You won’t get acute radiation syndrome as dangerous radiation levels are kept in reactor shelter, however, you will be exposed to a bit more radiation than background radiation levels. Tour guides have dosimeters with them to measure radiation levels through a trip.
To prevent radioactive particles escaping from the nuclear reactor, scientists have decided to build a containment building which would cover the whole nuclear reactor and its old sarcophagus which had to do the same job. A new containment building is massive and huge in dimensions, its height is over 108 meters, length 260 meters and it weighs about 31 000 tones. The total cost of it was 2.1 billion euros and as it was an international problem, it was funded by people and companies from all around the world. It’s function actually not just to prevent radioactive particles from escaping, but to deconstruct what is left from the reactor and to remove radioactive material. That is why robotic arms have been attached to the shelter roof. To build this shelter, engineers had to take a lot of safety precautions, as the building is enormous it had to be built in site, so workers got a pretty big radioactive dose.
If you would like to walk in Chernobyl
Here is a list of Chernobyl tour websites if you would like to explore a ghost town: