Explosive truth about Chernobyl revealed in climax to hit TV drama

Explosive truth about Chernobyl: As the heart-stopping climax to the hit TV drama about the 1986 nuclear disaster reveals, a series of blunders triggered the impossible

  • The explosion in Reactor 4 at Chernobyl took place on the night of April 26, 1986
  • Last president of Soviet Union once said it was perhaps cause of state’s collapse
  • The blast emitted more than 400 times the amount of radiation than Hiroshima
  • Estimates of numbers who died in aftermath vary between 4,000 and 93,000 

Mikhail Gorbachev, the last president of the Soviet Union, once said that Chernobyl was ‘perhaps the real cause’ of the state’s collapse.

The attempted cover-up of the world’s worst nuclear disaster, the endless lies and obfuscation, and the risk to the lives of millions laid bare the failings of the communist regime as never before.

It proved to the Soviet people that the time had come for radical change and that Gorbachev’s policy of glasnost — openness — was the only option.

At the very least, the explosion in Reactor 4 on the night of April 26, 1986, hastened the end of the ‘Evil Empire’.

The blast emitted more than 400 times the amount of radiation into the atmosphere than the atomic bomb dropped on Hiroshima in 1945.

Dramatic scenes in Chernobyl when engineers try to stabilise the reactor by pressing the AZ-5 failsafe button

The emergency AZ-5 button was designed to stop the nuclear reactor running out of control (Z in the Cyrillic alphabet looks like 3)

There was an argument in the control room about which rules should be followed prior to the explosion and which should not

The radioactive clouds following the explosion reached as far as Western Europe. Thousands died a premature death as a result

Estimates of the numbers who died in the aftermath vary between 4,000 and 93,000, many of them children.

More than 300,000 people were evacuated from a contaminated area covering 1,000 square miles and much of the ‘dead zone’ is still a no-go area.

Three decades on and — given the exhaustive investigations by Soviet and Western scientists and nuclear authorities — you might imagine that there is little new to shock us.

But an acclaimed new TV dramatisation of the disaster and the months that followed has revealed the scarcely believable levels of incompetence, irresponsibility and cost-cutting that combined to create a perfect storm.

It would culminate in the last safety backstop — the emergency AZ-5 button designed to stop the nuclear reactor running out of control — acting as a catalyst for the explosion.

On Tuesday night, in the final episode of Sky Atlantic’s Chernobyl series, we saw a compelling re-enactment of the show trial of the three senior operatives blamed for the accident. The drama was all the more fascinating for asking and answering, with and terrible simplicity, the scientific questions which, until now, have left many of us bewildered as to how such an event could ever have taken place.

The Chernobyl reactor is pictured in a real-life image following the explosion on the night of April 26, 1986


As an expert trial witness in the programme painstakingly explained, in the Soviet-designed RBMK-1000 nuclear reactor’s core, there were more than 1,600 fuel rods of radioactive Uranium-235.

This form of uranium is unstable, meaning its atoms are constantly breaking down — a process called fission — to release sub-atomic particles called neutrons. It is a process that produces enormous heat and energy. And this has to be kept under careful control. So to keep the core cool, and not dangerously overheat, a series of pumps sends a constant flow of water through it, which heats up, producing steam which then powers turbines to produce electricity.

To control the amount of energy (heat) produced by the core, the operators can manage the level of reactivity, increasing it or decreasing it, by inserting or removing control rods made of boron which absorbs neutrons, slowing the nuclear reaction down.

In effect, the boron control rods act like the brakes on the car. There were 211 such rods within the Chernobyl reactor.

HBO’s Chernobyl has been a critical hit. Pictured are the show’s stars Emily Watson and Jared Harris as Soviet nuclear physicists Ulana Khomyuk and Valery Legasov

The V.I. Lenin Nuclear Power Station at Chernobyl, with its four RBMK nuclear reactors, was the pride of the Soviet Union (pictured: Chernobyl TV miniseries)


Located about 81 miles north of the city of Kiev in the Ukraine, the Chernobyl Nuclear Power Plant consisted of four reactors built in the Seventies and Eighties.

The cooling water was provided by a man-made reservoir fed by the Pripyat River.

The plant was an important contributor to the Soviet economy, powering 30million homes and businesses and provided 10 per cent of Ukraine’s electricity needs.

The accident happened in Reactor Four, which was completed at the end of 1983. The plant director, Viktor Bryukhanov, signed a certificate to say it had undergone all of its final safety tests.

In fact, Bryukhanov was rushing to meet a deadline — for which he was later rewarded with the prestigious title of ‘Hero of Socialist Labour’ — and the reactor still had to undergo one vital test.

This was to check whether in the event of a power blackout — caused by equipment failure or perhaps attack by a foreign enemy — the power in the slowing turbines would be enough to keep the water pumps going until back-up diesel generators could kick in.

To test the theory, the turbines would be switched off and, as they slowly wound down, their electrical output would be measured to see if indeed they did provide enough to power the water pumps.

It was an operating system the West had rejected because of concerns about design flaws and its safety, but the Soviets were confident it was secure (pictured: Five-part miniseries Chernobyl)

The series of events that led to the explosion in the reactor at Chernobyl

This test was due to take place on the afternoon of April 25, 1986. But at the last minute the officials running the power-grid demanded it be delayed until the end of that day’s production in local factories.

It was postponed until midnight, by which time the day staff had gone off duty. They were replaced by a far less experienced night shift, including 25-year-old Leonid Toptunov who was responsible for controlling the reactor. He had been in the job for just four months.

Toptunov was certainly no match for his bullying manager, deputy chief-engineer Anatoly Dyatlov, whose promotion depended on the test being performed successfully. Nobody in the control room had experience of such a procedure.


First, there was a hopeless lack of clear instructions. The rule book studied by shift foreman Alexander Akimov, contained a number of crossings-out.

There was an argument in the control room about which should be followed and which should not.

In particular, the team debated the power level at which it was safe to begin the test. The lower the power, the greater the chance of the reactor becoming unstable.

While the rules stipulated a minimum of 700 megawatts, Dyatlov insisted 200 megawatts were safe. He overruled Akimov. However, this proved academic when an error by Toptunov resulted in the power level being set to near zero.

As a major drama series, Chernobyl, sheds new light on the impact of one of the world’s worst nuclear incidents

At that level, the reactor was already showing signs of becoming increasingly unstable. The only safe option then was to increase the power again slowly, over a number of days. But Dyatlov was adamant the test went ahead. He gave the order to take the power level back up to 700 megawatts, a sudden and dangerous increase.

To achieve this, Akimov and Toptunov had to start pulling the boron control rods out completely, until only 6 of the 211 remained in place — the equivalent of taking the foot off the brakes.

This chain of decisions later led Dyatlov to be put on trial with other members of Chernobyl’s management. One of the prosecution witnesses was Valery Legasov, a prominent Soviet chemist played by Jared Harris in the Sky Atlantic drama.

Legasov initially toed the party line in putting the blame on the men, and Dyatlov in particular (the latter was sentenced to 10 years hard labour).

But he later incurred the wrath of the state by admitting that, while Dyatlov was very much culpable, he could not have known of a fatal flaw in the system which meant the system’s supposed fail-safe button actually acted as a detonator.


In the control room of every nuclear reactor, there is an emergency button which, when pressed, inserts all the boron control rods into the core in one go and brings the nuclear reaction to a dead halt. But at Chernobyl — and many other Soviet reactors — this fail-safe was fatally compromised, as highlighted by Legasov.

The Soviets had cut costs by making the tips out of the rods out of graphite, much cheaper than boron. But graphite, far from stopping the reaction, actually accelerates it. This would usually be counteracted by the boron in the rest of the rod — but in the extreme and unusual circumstances that night in Reactor Four the boron had no chance to kick in.

At 1.23am, the AZ-5 emergency button was activated. As the rods were inserted back into the core to slow the reactor, the presence of the graphite tips resulted in a skyrocketing of the reaction in the core.

This converted every last molecule of water into steam which expanded and ruptured the fuel-rod channels, fixing them in position so the boron rods could no longer be pushed into the core, and endlessly accelerating the nuclear reaction in an unstoppable chain reaction.

The temperature in the reactor reached 4,650c — almost as hot as the sun’s surface — and triggered a huge explosion as a build-up of steam blasted the 1,000-ton plate covering the reactor into the air.

This was the first of a series of explosions which ‘vaporised’ into the atmosphere some 50 tons of radioactive uranium which has a half-life (the time it takes for the radioactivity to fall to half of its original value) of 700 million years. A further 70 tons were scattered around the area.


We are horribly familiar with much of the story: the radioactive clouds which reached as far as Western Europe and the thousands who died a premature death.

All of which begs one final question: could such an accident happen again?

Valery Legasov did his best to ensure it could not. His criticisms of the Soviet state ensured he never worked in science again. He committed suicide on April 27, 1988, a day after the second anniversary of Chernobyl. But he recorded audio-tapes in which he reiterated the shortcomings in his country’s nuclear system.

Soviet reactors were then retro-fitted to prevent a repetition. But it is fair to say no system can be foolproof as long as the egotism, incompetence and dishonesty which led to the Chernobyl disaster remain part of human nature.

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