What caused the catastrophic Chernobyl nuclear accident?
Paraphrased from Wikipedia articles
The Chernobyl accident is considered the most disastrous nuclear power plant accident in history, both in terms of cost and casualties. It has been approximated that about four hundred times more radioactive material was released from Chernobyl than by the atomic bombing of Hiroshima and Nagasaki.
How does a nuclear reactor work?
As explained in the HBO mini-series Chernobyl by the character playing Valery Legasov, Chief of the commission investigating the Chernobyl disaster who later exposed the design flaws -
On 26 April 1986, at 01:23:40, Reactor no. 4 at Chernobyl suffered a catastrophic power increase, leading to explosions in its core & a subsequent nuclear meltdown
The accident occurred during a safety test on a common Soviet reactor type - the RBMK nuclear power reactor. The test supervisor (Anatoly Dyatlov) failed to follow the test procedure, creating unstable operating conditions which, combined with inherent RBMK reactor design flaws and the intentional disabling of several emergency safety systems, resulted in an uncontrolled nuclear chain reaction.
The struggle to safeguard against scenarios that were perceived as having the potential for greater catastrophe, together with later decontamination efforts of the surroundings, ultimately involved over 500,000 liquidators (civil and military personnel who were conscripted to deal with consequences) and cost an estimated 18 billion rubles (roughly $30 billion USD in 1986, or $68 billion USD in 2019 adjusted for inflation)
The clean up operations are the disaster area are the largest civil engineering task in history, involving a quarter of a million construction workers who all reached their official lifetime limits of radiation.
Only 10% of the debris cleared from the roof of what was left of the reactor was performed by robots with the other 90% removed by approximately 5,000 "bio-robots" who absorbed, on average, an estimated dose of 25 rem (250 mSv) of radiation each.
"..robots are not the great remedy for everything. Where there was very high radiation, the robot ceased to be a robot—the electronics quit working" - Valery Legasov
The accident prompted safety upgrades on all remaining Soviet-designed RBMK reactors, of which 10 continue to power electric grids as of 2019.
The policy of openness (glasnost) and 'uncompromising criticism' of outmoded arrangements had been proclaimed at the 27th Congress (of the Communist Party of Soviet Union), but it was only in the tragic days following the Chernobyl disaster that glasnost began to change from an official slogan into an everyday practice.
"The lesson of Chernobyl isn't that modern nuclear power is dangerous. The lesson is that lying, arrogance, and suppression of criticism are dangerous" - Craig Mazin
The four most harmful radionuclides spread from Chernobyl were iodine-131, caesium-134, caesium-137 and strontium-90, with half-lives of 8.02 days, 2.07 years, 30.2 years and 28.8 years respectively. Radiation is most damaging to cells that are actively dividing. In adult mammals cell division is slow, except in hair follicles, skin, bone marrow and the gastrointestinal tract, which is why vomiting and hair loss are common symptoms of acute radiation sickness.
According to the IAEA the "designation of the affected population as "victims" rather than "survivors" has led them to perceive themselves as helpless, weak and lacking control over their future".
The Chernobyl accident is considered the most disastrous nuclear power plant accident in history, both in terms of cost and casualties. It has been approximated that about four hundred times more radioactive material was released from Chernobyl than by the atomic bombing of Hiroshima and Nagasaki.
How does a nuclear reactor work?
As explained in the HBO mini-series Chernobyl by the character playing Valery Legasov, Chief of the commission investigating the Chernobyl disaster who later exposed the design flaws -
A nuclear reactor makes electricity with steam. The steam turns a turbine which generates electricity.
Where a typical power plant makes steam by burning coal, in a nuclear plant, we use something called fission.
We take an unstable element like Uranium 235, which has too many neutrons.
A neutron is, (like a) bullet.
So, bullets are flying off of the uranium. Now...if we put enough uranium atoms close together, the bullets from one atom will eventually strike another atom.
The force of this impact splits that atom apart, releasing a tremendous amount of energy, fission.
The neutrons are actually traveling so fast... we call this "flux"...it's relatively unlikely that the uranium atoms will ever hit one another.
In RBMK reactors, we surround the fuel rods with graphite to moderate, slow down, the neutron flux.
On 26 April 1986, at 01:23:40, Reactor no. 4 at Chernobyl suffered a catastrophic power increase, leading to explosions in its core & a subsequent nuclear meltdown
The accident occurred during a safety test on a common Soviet reactor type - the RBMK nuclear power reactor. The test supervisor (Anatoly Dyatlov) failed to follow the test procedure, creating unstable operating conditions which, combined with inherent RBMK reactor design flaws and the intentional disabling of several emergency safety systems, resulted in an uncontrolled nuclear chain reaction.
The struggle to safeguard against scenarios that were perceived as having the potential for greater catastrophe, together with later decontamination efforts of the surroundings, ultimately involved over 500,000 liquidators (civil and military personnel who were conscripted to deal with consequences) and cost an estimated 18 billion rubles (roughly $30 billion USD in 1986, or $68 billion USD in 2019 adjusted for inflation)
The clean up operations are the disaster area are the largest civil engineering task in history, involving a quarter of a million construction workers who all reached their official lifetime limits of radiation.
Only 10% of the debris cleared from the roof of what was left of the reactor was performed by robots with the other 90% removed by approximately 5,000 "bio-robots" who absorbed, on average, an estimated dose of 25 rem (250 mSv) of radiation each.
"..robots are not the great remedy for everything. Where there was very high radiation, the robot ceased to be a robot—the electronics quit working" - Valery Legasov
The accident prompted safety upgrades on all remaining Soviet-designed RBMK reactors, of which 10 continue to power electric grids as of 2019.
The policy of openness (glasnost) and 'uncompromising criticism' of outmoded arrangements had been proclaimed at the 27th Congress (of the Communist Party of Soviet Union), but it was only in the tragic days following the Chernobyl disaster that glasnost began to change from an official slogan into an everyday practice.
"The lesson of Chernobyl isn't that modern nuclear power is dangerous. The lesson is that lying, arrogance, and suppression of criticism are dangerous" - Craig Mazin
The four most harmful radionuclides spread from Chernobyl were iodine-131, caesium-134, caesium-137 and strontium-90, with half-lives of 8.02 days, 2.07 years, 30.2 years and 28.8 years respectively. Radiation is most damaging to cells that are actively dividing. In adult mammals cell division is slow, except in hair follicles, skin, bone marrow and the gastrointestinal tract, which is why vomiting and hair loss are common symptoms of acute radiation sickness.
According to the IAEA the "designation of the affected population as "victims" rather than "survivors" has led them to perceive themselves as helpless, weak and lacking control over their future".
Radiation levels in 1996 (10 years after the disaster) around Chernobyl
Source: Wikipedia
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