- Valery, Boris and Ulana risk their lives and reputations to expose the truth about Chernobyl.
- On April 25th 1986, twelve hours before the accident, Dyatlov meets Bryukhanov and Fomin. Bryukhanov has been waiting for this safety test to be completed for 3 yrs and this means a promotion for him to a plum position in Moscow. Dyatlov has been prepping for the test and has reduced reactor output to 1600 megawatts. Bryukhanov asks him to delay the further reduction of output by 10 hrs as its the end of the month and orders from the top are to keep producing power as the factories need to meet production quotas. Dyatlov agrees to this, even though he knows reactor becomes unstable by working in reduced power output conditions for long periods of time.
Legasov's testimony to the IAEA in Vienna, in which he lies (Legasov tells the IAEA that Chernobyl was purely due to operator error and there was no design flaw in the reactor itself). Khomyuk now wants Legasov to tell the truth at the Dyatlov hearing. She wants the world to know about the design flaw in RBMK reactors and force the central committee to take action.
In Jul 1987, Dyatlov, Bryukhanov, and Fomin are put on trial in the abandoned city of Chernobyl. Shcherbina is called first to give testimony, explaining the general workings of a nuclear power plant. Shcherbina also says that the reactor 4 was completed and went into production on Dec 20th 1983. Bryukhanov signed a certificate of completion on Dec 31st 1983, but did not complete the backup generator safety test, one that was required for completion.
Shcherbina explains that an inherent problem with nuclear reactors is that they need coolant (water) to be pumped through it as a heat exchanger. This water is pumped into the reactor through the power generated by the turbine (which relies on nuclear power). But if the reactor output declines, the turbines would stop spinning and the water would stop going into the reactor leading to a meltdown. As such, an RBMK has backup diesel generators which need 60 seconds to power up if the power output decreased or failed. The premise of the safety test was to use the output of the dying turbine to power the pumps for those crucial 60 secs before the generators came online. Apr 26th, 1986 was the 4th attempt at this safety test, with 3 previous attempts resulting in failure.
Khomyuk and Legasov testify on the events leading up to the accident, based on interviews with people in the control room. Khomyuk says that by 2 pm on Apr 25th, the reactor was running at 50% output, half the output of 3200 MW and ready to be taken down to final test output of 700 MW. At midnight there is a shift change and Akimov and Toptunov are not aware of the purpose of the safety test and are not trained on the instructions for carrying it out.
Flashbacks show that due to a ten-hour delay in a safety test and Dyatlov's impatience to carry it out, the reactor stalled, then experienced a power spike. Akimov activated the emergency shutdown, but a design flaw in the control rods spiked the power to ten times the reactor's limit before it exploded.
Legasov explains that nuclear fuel increases reactivity and Boron control rods reduce it. But heat generates steam, which creates a positive void coefficient, which increases reactivity. As heat rises, the reactivity reduces, which caused negative temperature coefficient. Now in reactor 4, the addition factor was that Xenon is created by fission, which is burned away in normal conditions. But since reactor 4 was running at 50% power for 10 hrs, the Xenon did not burn away and reduced reactivity.
As Akimov and Toptunov reduced power, the built up Xenon stalled the reactor and the output went to 30 MW. Dyatlov threatens them to bring the reactor back on, but Akimov is adamant that protocol should be followed and reactor shut down for 24 hrs. Dyaltov prevails and Akimov assists Toptunov as he very slowly pulls 205 of the 211 reactor control rods out to bring the output back up. But the fuel is now cold, and the negative temp coefficient doesn't exist, but the core is still contaminated with xenon. The output goes back up to 200 MW. Dyatlov orders the test to proceed with 200 MW, even though prescribed output minimum is 700 MW. The water pumps are shut down to simulate loss of power from the reactor. The reactor now has no checks on it at all.
Legasov pauses for a few moments and then reveals the suppressed information about the Leningrad plant, admitting he lied in his previous testimony in Vienna. The presiding judge and prosecutor try to stop him but Shcherbina, the ranking official in the room, orders them to let Legasov continue. Legasov states that the only reason the USSR built graphite moderated reactor, with boron rods with graphite tips and no lead shielding, is because it is considerably less costly. Realizing what's about to occur, Akimov tries to scram the reactor with the AZ-5 button, the sole function of which is to drop all control rods into their containment channels and neutralize the core. As the rods with the graphite tips are dropped into their channels, reactivity skyrockets and every molecule of water converts to steam and ruptures the rod channels. The control rods are not fixed in place and can't move any further. The reaction accelerates endlessly and reactor 4 at this point is a nuclear bomb. Legasov states that the last power level reading recorded was 33,000 megawatts.
He is detained by the KGB and informed that his testimony will be suppressed in the state media; furthermore, he is forbidden to speak to anyone about Chernobyl, he will receive no credit for his role in containing the disaster, and he will never work again.
The ending shows pictures and video of the real Legasov and other major players, revealing their fates, as well as the ongoing aftermath of the accident. After Legasov's death, the communist party accepted the design flaws of the RBMK reactor and retrofitted them to prevent another catastrophe like Chernobyl. Shcherbina died Aug 22, 1990, 4 yrs and 4 months after Chernobyl. Dyatlov, Bryukhanov and Fomin are sentenced to 10 yrs in prison. Dyatlov dies from radiation in 1995. Fomin returns to work at another nuclear plant.
Of the 400 miners, 100 died before the age of 40. 600,000 people served in the contaminated zone and yet no records were kept of their fate. In 2017 a new shield, the New Safe Confinement, was erected over Chernobyl reactor 4 at a cost of $2 billion. It will last over a 100 yrs. According to official Soviet records 31 people died in the disaster.
An epilogue is then given regarding the aftermath of the events:- Valery Legasov took his own life on April 26, 1988. The audio tapes he left behind regarding Chernobyl, were circulated among the Soviet scientific community. After his suicide, the government finally acknowledged the AZ-5 issue, and steps were taken to rectify it.
- Ulana Khomyuk was a fictional and composite character created for the mini-series and meant to represent the various scientists who helped in the clean-up, investigation and understanding of what had happened at Chernobyl.
- Boris Shcherbina died on August 22, 1990.
- For their roles in the Chernobyl disaster, Viktor Bryukhanov, Anatoly Dyatlov and Nikolai Fomin were sentenced to ten years hard labor. After his release, Nikolai Fomin returned to work at a nuclear power plant in Kalinin, Russia. Anatoly Dyatlov died from radiation-related illness in 1995.
- The body of Chernobyl's pump operator Valery Khodemchuk was never recovered, and is permanently entombed under Reactor 4.
- The clothes removed from the firefighters still remain in the basement of Pripyat Hospital and are still dangerously radioactive.
- Following the death of her husband and daughter, Lyudmilla Ignatenko suffered multiple strokes. Doctors said she would never have children, but she eventually had a son, whom she now lives with in Kiev.
- Of the people who looked upon the open core from a railway bridge not far from the explosion, it has been reported that none survived. It is now known as "The Bridge of Death."
- Over 400 miners worked around the clock for one month to prevent a total nuclear meltdown. It is estimated that at least 100 of them died before the age of 40.
- The divers who drained the bubbler tanks did not perish after their task. All three survived after hospitalization, and two are still alive today.
- Over 600,000 people were conscripted as liquidators to serve in the Exclusion Zone. Despite widespread accounts of sickness and death as a result of radiation, the Soviet government kept no official records of their fate.
- The contaminated region of Ukraine and Belarus, known as the Exclusion Zone, ultimately encompassed 2,600 square kilometers.
- Approximately 300,000 people were displaced from their homes in Pripyat. They were told this was only temporary, but people are still forbidden from returning.
-Mikhail Gorbachev presided over the Soviet Union until its dissolution in 1991. In 2006, he wrote, "The nuclear meltdown at Chernobyl... was perhaps the true cause of the collapse of the Soviet Union."- In 2017, work was completed on the New Safe Confinement at Chernobyl at a cost of nearly two billion dollars. It is designed to last 100 years.
-Following the explosion, there was a dramatic spike in cancer rates across Ukraine and Belarus. The highest increase was among children.- The final number of how many people died due to Chernobyl is not know. While estimates put the range between 4,000 to 93,000 deaths, the official death toll, unchanged since 1987, is 31.
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