[Sciences] Chernobyl Catastrophe – Anatomy from a 30 year-old nuclear disaster

Today we marked the 30th anniversary of the Chernobyl catastrophe. I was seven when that catastrophic event happened. A lot of speculation, discussion, fears and also completely botched public relations mired the catastrophe. But also some of the most unexpected things happened.
As I am now 37 years old, I thought it would be a great time to go back to this, discussing about what exactly happened that night, the next days that saw a huge rush to reduce the impact of the catastrophe, the dreaded nuclear cloud that swayed through Europe and the disastrous PR of the French government, the closure of Pripyat and the unexpected rebound of the wildlife, but also the kind of impact the term of “radiation” had on my inner psyche that maybe raised my interest about the “post-nuke” genre in science-fiction.
First, I would say, the best would be to read this blog with the track “Radioactivity” by Kraftwerk, the German pioneers in electronic music that were capable to transform binary electronic sound into some nice of porto-electronic music.

1. The Chernobyl Central:
The nuclear site of Chernobyl is located at the vicinity of Pripyat, a small town that was primarily set for the engineers and staff working at the nuclear station. Pripyat is located near the Belarussian border and about 100 miles north from Kiev (Ukraine).

Nuclear central generate electricity using the energy produced by plutonium-239 decay into uranium-235 and by emitting an alpha particle (helium) with the release of an important thermal energy. This thermal energy allows the conversion of water from a liquid form into a gas (vapor) form that will allow the propelling of turbines that will transform this chemical energy into electrical energy. The process of nuclear fission is perpetuated by the decay of plutonium until the fuel rods have been completely burned up. Such fission process is perpetuated by the presence of neutrons generated that can bombard nearby uranium-238 and enrich them to become plutonium-239. However, such reaction can be modulated by the insertion of graphite rods that can absorb neutrons produced and reduce the reaction.
In the case of Chernobyl, the reactor in use was the RBMK type (more can be found about on the respective Wikipedia page (https://en.wikipedia.org/wiki/RBMK). RBMK nuclear reactors were cheap, efficient but suffered from several technical flaws in particular in its high propensity to become unstable if used in the level exceeding the nominal utilization.

2. The events that lead to Chernobyl catastrophe:
A series of events with little consequences by themselves indeed lead to the most catastrophic event in civil nuclear.
Chernobyl plant had a series design flaw that was fatal that day: a cooling system based on light (regular) water and the lag time between the time of an emergency shutdown and the activation of diesel engines (60-120 seconds) to allow the flow of water cooling inside the reactor to cool down the core).  This testing was planned to be done overnight, at the time the average consumption would be low enough to not generate a shortage in electricity supply. However, an unexpected failure in a regional power plant forced Chernobyl to produce more energy than its nominal usage and had the day team postponing the testing to the evening team.
As the evening team came to the central around midnight, they started the procedure by reducing the reactor power to 700MW (the minimum considered safe to avoid a shutdown of the central). However, an unexpected event happened as the reactor started to build-up Xenon-135, a byproduct that is normally disintegrated during a normal functioning of the central. Xenon-135 is also an excellent neutron absorber and can further decrease the amount of energy produced in a reaction named “reactor poisoning”. However, none of the operators were aware that the energy levels were already below the safety levels and inserted the graphite rods too deep, brining the energy production below 5% of the safety level. The reactor was running on unstable conditions, safety alarms went between 00:30-00:45 on but the operator decided to keep on with the procedure and delayed their maneuver to restore power to higher level. At 01:05, the operator were around 30% of the safety level but already doomed the reactor, as the coolant was not fast enough to contain the neutron production and the subsequent overheating.  At 01:19, the operators bypassed safety protocol and removed fail-safe rods below the minimum number required.
At 01:23, the emergency shutdown procedure was initiated and as a matter of series of poor design and decision-making triggered the reactor to unstoppable chain reaction. This procedure resulted in the insertion of all graphite rods that should have reduced the activity. However due to the flawed design of the rods, the poor neutron buffer properties of light water and the overheating of the coolant, it resulted in a positive feedback loop that further pushed the reactor to overheat (reaching a energy production from 200MW to 30’000MW in few minutes), pushing the coolant to vaporize and explode the roof of the reactor to a massive vapor pressure. A second explosion occurred after the explosion of the rooftop, estimated about the equivalent of ten tons of TNT the ejection of highly radioactive material from the reactor core to the surroundings, especially to reactor 3, as bitumen (a flammable material) was used in the conception of the roofings of the different reactors.

3. The Chernobyl catastrophe and the rapid response:
The radioactivity on site was disastrous with reports of 30’000 roentgens (R)/hour at the vicinity of the reactor core and 1’000 R/hour near the unit. A dose of 100R/hour is considered lethal to human beings. The two operators died on May 10 and 14 following the explosion. Although the report of the accident, staff in the reactor 3 were mentioned to continue their work, after ingestion of potassium iodine and gas mask. At 5:00, Yuri Bagdasarov (chief of the nightshift team) decided to go against the order and shutdown the reactor 3.
The radiation were so high that dosimeters designed to a maximal threshold value of 3.6R/h were literally outpaced within seconds of exposure, leaving workers with no realistic estimate of their exposure to radiation and obviously a blatant lack of personal protective equipment. The first emergency team was trying to tame the fire with no PPEs and for an exposure way beyond the safety level, leading these first responders to a certain death by radiation poisoning.
In the morning of the 26th and the following days, the emergency plan is set with one goal: to tame the fire inside the reactor and bring the reaction into control by dropping boron, lead and sand over the crater. 5000 tons will be dropped. The town of Pripyat was evacuated as well as the surroundings only by the beginning of the afternoon. Declassified KGB documents later indicated that the Soviet politburo in Moscow maintained the Ukrainian governor in the black during the first day of the accident, downsizing the gravity of the situation by pretexting that a fire occurred in the Chernobyl reactor 4 but it was under control and was extinguished. Pripyat residents started to develop some signs of radiation sickness as they described a metallic taste in their mouth, headaches and nausea. One witness of the event, Yuri Andreyev recalled his experience of that day to a recent BBC report:

Hundreds of reservists came to the site to help control the fire with a bare equipment against a lethal radiation. Some nicknamed them “liquidators”, some nicknamed them “bio-robots”. We estimate about 4’000 of the 200’000 workers were exposed to lethal levels of radiation.
Yet another danger was lurking that would have razed half of Europe. A danger that was equivalent to 10 times the strength of the Hiroshima bomb. The RBMK reactor design has two pools of coolant underneath the reactor. With the excessive heat, the melting of the concrete basement would have exposed the water that in contact would have further damaged the reactor (as light water is very poor neutron absorbent) and set the reaction further into a global catastrophe. The only way for avoiding such catastrophe was by manually opening the purging valves that would empty these coolant reservoirs. The only access was by swimming across the pool with a certain death by very high radiation exposure. Alexei Ananenko, Valeri Bezpalov and Boris Baranov, acclaimed as heroes as they exited the reactor after the valve opening, died from intense radiation sickness days after the exposure.
The combination of combustible fuel still burning, blended with molten graphite and concrete created a particular state of matter called corium that shows similarities with lava. As such corium started to pour into the pools, an emergency taskforce designed to dig a mine tunnel to pour an additional concrete slab was set, with miners digging 24/7 against the clock. In december 1986, a scientific team with the help of robots entered the reactor area and discovered that some of this corium has formed a particular feature in the pool that is referred as the “elephant foot”. Such matter was so radioactive that it was enough to sublime the camera and created inadvertently the first case of “selfie”.


Days after the explosion, radioactive particles carried by a nuclear cloud moved over West towards Europe. By the detection of higher atmospheric radiation levels recorded by Finland, Sweden and Austria, USSR could not anymore cover up the disaster and had to publicly announce after the inquiry of the IAEA of the catastrophe.
Another disaster was just started to fester, this time a PR disaster. Germany rapidly informed his citizens from Southern Germany (including Baden-Wurttemberg and Bayern) to not each any fresh fruits and vegetables from homegrown gardens and from hunting catch.
In France, on April 30th 1986, the French government tried to downplay the exposure to the radioactive cloud by using weather forecast that was comforting that anti-cyclone coming from the Azura Islands would bounce the cloud from the Eastern side of France as depicted in this archive footages:

However, in the following days after the passing of the radioactive cloud, journalists manually detect an increased radiation from fresh fruits and vegetables in Alsace (my birth region), labelling the region as the one hit the hardest by the radiation.

4. Aftermath of Chernobyl on the local fauna and flora:
Chernobyl accident had direct fallout on the Ukrainian and Belarussian population with increased cases of thyroid cancer among the population and increased congenital deformities during the first five years following the accident. In the vicinity of the central, a pine forest got a amount of radiation high enough to see changes in the colors of the trees from a emerald green into a red color, indicative of a major stress and death process. Such forest is classically referred as the “Red Forest”.
The area is now a ghost town with an important security exclusion zone of around 20 miles around the central. Surprisingly enough the reactors 1,2 and 3 were maintained operational and were still in function up to 15 years after the accident and only closed in 2001. Wildlife has kicked back and have been surprisingly capable to adapt to the irradiated environment. There are no blatant sign of mutations but in an uncanny outcome, Chernobyl site has become an interesting biological experiment to study the effect of accelerated evolution within an ecosystem.
Mutations are the key element of evolution. Under normal condition, mutations occur at very low frequency. However, due to the presence of alpha and gamma particles that are also known as ionizing agents, these particles can damage the DNA present in living organism of the ecosystem. Under normal circumstance, we have a DNA repair toolkit that can fix DNA damage in a fairly high fidelity level. However, the extent of DNA damage can significantly impairs a proper repair mechanism and increase mutation rates.
Some surprising reports are the ability of the ecosystem to have repopulated the whole area within 30 years of absence of human activity in the area. Another recent study also highlighted the persistence of falling leaves that are not undergoing any degradation, suggesting the presence of a high radioactivity on the soil surface. There are even reports of a particular fungi growing in the Unit 4 of the central that may have developed some evolutionary traits to sustain radiation damage by presence of melanin pigments. The area though remains highly radioactive.
Currently, there is an active project ongoing to build an extra sarcophagi layer over the existing but decaying first sarcophagi.  A current concern is the constant monitoring of the “elephant foot” that is still highly radioactive and that will take centuries to decay if not millennia.
A recent BBC footage went inside the reactor 4 few years ago:

For more information:
The BBC has done a remarkable work on reporting on Chernobyl disaster and even produced a docudrama retracing the catastrophe that can be watched here below.

Among different academic institutions that have a dedicated page on the effects of Chernobyl on wildlife, the department of Biology at Texas Tech University has an interesting website that worth being visited.






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