What Really Happened at Chernobyl?
This is the first of a two part series of blog posts, where we take a look at the fascinating story surrounding the Chernobyl disaster and the physical, cultural and scientific effects it had on humanity.
“The nuclear meltdown at Chernobyl … was perhaps the real cause of the collapse of the Soviet Union.” — Mikhail Gorbachev (Last leader of the USSR)
The Chernobyl accident has been known and recognised as one of the most significant events in human history since it occurred in 1986, but many of the most important details were actually unknown to most people. This changed, however, as a result of the extremely popular 2019 HBO series, “Chernobyl”, which has revived the story: reminding the generations that lived through it of its impact and exposing a younger generation to the way it has shaped the world. It has actually been dubbed by many as “the greatest series ever”. I believe there is just something intriguing about the mysterious and dangerous nature of radiation, given that it can do so much damage whilst being invisible to the eye.
Nuclear physics 101
Radiation has an extremely negative stigma surrounding it, probably largely due to the Chernobyl incident. As a result, radiation is highly misunderstood. Many believe “all radiation is bad radiation”, but this is not the case. In fact, everyone is literally bathing in radiation every day, everywhere. Radiation is essentially just another word for emission. People worry about the word “radiation”, and yet they have radiators in their homes. Radiators in a domestic sense are obviously not something to worry about, all they do is “radiate” heat via various methods.
Everything emits radiation… yes, everything. “Banana equivalent dose” is actually a somewhat respected means of measuring ionising radiation exposure.
The belief that all radiation is dangerous has led to many ridiculous theories and conspiracies in the modern world, such as the idea that 5G is killing us, and that our phones are increasing cancer rates. These are simply not true in any regard whatsoever. Yes, these devices do emit radiation on an order which may be perceived as “high”, however it is only “high” relative to everything else in a regular environment (which can be deemed as “extremely low”).
Radiation is commonly measured in sieverts, and about 2 or more sieverts at once is required to kill a person. We measure everyday things in microsieverts: when you eat a banana, the naturally radioactive potassium inside it causes you to be exposed to about 0.1 microsieverts. That’s 1/10,000,000 sieverts.
The natural background radiation on Earth is about 0.15 microsieverts per hour. Uranium is the fuel primarily used in nuclear power plants, and a uranium mine has a background radiation of about 1.7 microsieverts per hour (ten times the natural exposure, but still not dangerous at all).
99% of the time, you needn’t worry about radiation levels. In the words of Elon Musk, you can strap a helmet made out of phones to your head permanently and not need to have any concerns (although I can’t guarantee it will be particularly comfortable). The most radiation you will likely ever be exposed to is on airplane: with the high altitude, there is less atmosphere protecting you from cosmic rays, and so the radiation can reach 3 microsieverts per hour. Still harmless, but as a precaution long serving commercial pilots are restricted from donating blood due to the amount of time spent with limited radiation protection.
However, there are certain cases where the radiation is at such a level that it can cause death within minutes. And in the case of Chernobyl, there was potential for radiation, and its effects, to wipe out millions (I will explore this later).
The not-so-calm before the storm
The Union of Soviet Socialist Republics (Soviet Union or U.S.S.R.) was established in 1922, and existed in eastern Europe and northern Asia, inheriting its territory from the Russian Empire — consisting of Russia, Ukraine, Belorussia, Latvia and many more. After the Allies victory over Germany and Japan in 1945, the Soviet Union became a global superpower, and thus a rival to the United States. As the two nations competed to be number one, The Cold War began. This was a period of geopolitical tension between the two nations and their respective allies. It is known as “cold” because it lasted for such a long time (1945 to 1989) and neither the Soviets or the US officially declared war on the other. As with almost any war, this period accelerated technological growth in a huge number of areas: military build-ups, the “Space Race” and nuclear power. And so as a direct result of the Soviets trying to leap ahead with nuclear power race, Chernobyl was formed (and as I will explain later, this attempted “leap” to get ahead may be the very reason that millions were nearly killed).
The Chernobyl Power Complex was built by the Soviet Union in the 1970s: construction began in 1970 and reactor №1 was commissioned in 1977. Reactors 1 and 2 were “first-generation” units, 3 and 4 were “second-generation”, and if it weren’t for the catastrophe of №4, the Soviets aimed to have 12 up and running by 2010. The power plant was built 10 miles from the city of Chernobyl, also being about 10 miles from the Belarus-Ukraine border. As a result of the plant being built, a brand-new city, Pripyat, was constructed just under 2 miles away. Its purpose was to act as an “atomgrad”, a type of closed city with the sole purpose of housing the workers and families of the Chernobyl power plant. Being the Soviet’s ninth “nuclear city”, it can be described as a “walled garden” — on the inside it was somewhat of a haven with numerous kindergardens, secondary schools, gyms, swimming pools, playgrounds, cafes, a now iconic amusement park, and so on. However, in true Soviet fashion it’s all well and good if you stayed within the city, but it was not easy to leave. By the time it was evacuated in 1986 it had a population of 49,360.
The Soviets believed the nuclear power plant to be extremely safe, far more so than any other type of power plant. It was only due to some concerned Ukrainian scientists that the plant was not built extremely close to Kyiv to house the workers. Thus, Pripyat was born and was seen as a successful, booming city, and the power plant was being expanded at a pleasing rate. All seemed to be on track…
The lead up
In the process of constructing Chernobyl Reactor 4, the Soviets offered those in charge of the power plant a reward if they were to complete and commission the 4th reactor before the end of 1983. The commissioning process of a nuclear reactor is important for a reason: it verifies the reactor’s integrity, and therefore safety. It is not something that can be done half-heartedly. And yet, that was the case with Reactor 4.
These three men can be described as “those in charge” when the Chernobyl accident occurred. They are the ones who would make the most out of the 1983 deadline reward, and therefore the ones who encouraged the rapid commissioning of Reactor 4. Towards the end of 1983, they were just inches away from completing the process, however the deadline was getting closer and closer and it seemed they wouldn’t be able to get it done in time. However, in December, a conscious decision was made to skip the last test, and get the reward. We can’t be sure, but the Soviet justice system places the above three men as the principle causes of that decision. If it is true, which the HBO series certainly portrays, these men are a showcase of how untamed greed can have consequences beyond comprehension.
So that was it, Chernobyl Reactor 4 was officially “commissioned”, and on December 20th 1983 it was operational; all whilst one test hadn’t been completed. For the next three years, the reactor functioned as intended.
26th April 1986 — The day that almost killed millions
After three years of functional operation, it was decided that Reactor 4’s skipped test was to be carried out. Put very simply, a nuclear reactor works as follows: the radioactive isotope (fuel) which emits the radiation (uranium-235 in this case), can be found in the reactor core. Cooling pumps are used to pump water around the reactor core. As the core emits radiation, the water is heated up and turned to steam. The released steam is used to turn turbines and power a generator, producing electricity. Control rods are used to moderate the rate at which the radioactive decay (alpha particles) are reaching the water, thus controlling the power output.
The experiment was to see that if there was to be a power outage and therefore a loss of electricity to the cooling pumps, would the turbines be able to spin sufficiently to power the cooling pumps and thus keep the reactor core from melting down for 30 seconds (the time taken for backup generators to start working). On April 25th, this test was to be carried out.
From the get go, things were not being done correctly. The test was meant to be performed during day time and yet it began at 1 AM. Later in the day, they were told that a reactor from another power plant in Ukraine, Mykolav, had gone offline, and so a large source of electricity was cut from the national grid. The grid operator at Mykolav requested that the test going on at Chernobyl be postponed for a few hours, and that they must not shutdown the reactor until after 11 PM. By this point, they had already slowed down the reactor to 50%. And so it was left in this low power state for another 9 hours.
The test extended to the post-midnight shift, commencing on the 26th April. Due to it being such an early shift, the staff present were not the most experienced. Consequently, they accidentally brought the power level too low, to a point where it was unstable enough that the actions made in the control room did not necessarily execute as intended. Aleksandr Akimov, the unit shift chief, wanted to abort the test but he was overruled by Anatoly Dyatlov who demanded the test was continued. Dyatlov, overriding objections and making threats, intimidated the staff into lifting the control rods in order to increase the reactor power so the test could progress. However, lifting the control rods did not cause the reactor to respond as intended, but rather, the power surged. To counter this, Dyatlov ordered the rods to be lowered, and yet the power did not drop. The temperature of the core was rising rapidly and the power eventually reached 120 times its maximum, they had a serious problem on their hands.
Dyaltov’s next move was to pump water through the reactor to cool it down, however by this point the control rods were already so hot that when water hit them, rather than cooling them down, it rapidly turned into steam. The pressure of all this excess steam broke every one of the pressure tubes: the first explosion erupted…
The 1000 tonne lid above the reactor fuel flew off and the release of radiation began, killing two workers instantly. Then, if that wasn’t enough, the air reached the reactor and the oxygen resulted in a dangerously large graphite fire. Consequently, the local firefighters were dispatched (every single one of whom died within a few weeks as a result of the radiation).
Following this, the water from the cooling pumps reacted with the metal of the fuel tubes, in a reaction which released hydrogen. This hydrogen exploded, the second explosion. In total, 400 times as much radioactive fallout was released as the bomb the US dropped on Hiroshima in 1945.
“Call everybody, everybody.” — Chernobyl Firefighter Dispatch
End of part 1
Hopefully you’re finding this account of the remarkable story of Chernobyl interesting! To prevent this blog post from getting too long, I’m going to stop this one here. If you want to find out what happens next, watch out for part 2 on Sunday!
Originally published at http://thephysicsfootprint.com on February 10, 2022.
