by Daniil Pelymov
[REGNUM] Saturday, April 26, 1986, was a legal day off for all Soviet citizens—almost everyone, except those on shift, was preparing for rest and dacha work. The latter included the Chernobyl Nuclear Power Plant staff. At 1:23:04 a.m., the plant's deputy chief engineer, Anatoly Dyatlov, ordered the start of the planned experiment in Unit 4.
Within seconds, the situation spiraled out of control. The clock at the Chernobyl Nuclear Power Plant showed 1:23:47 AM when two explosions occurred. The first blew off the reactor's 2,000-ton biological containment plate. The second destroyed the building and released the reactor's molten interior into the atmosphere.
Two days later, a radioactive cloud of nuclear fuel particles and gases reached Sweden, and 10 days later, Japan and North America. By this time, Chernobyl Nuclear Power Plant workers—the first victims of the disaster—were dying of acute radiation sickness in Pripyat's Medical Unit No. 126. A mass evacuation from Pripyat would not begin until 36 hours after the explosion.
The event, which the whole world knows by the name of the nearest large city of Chernobyl, went down in history asThe largest nuclear power plant accident and one of the most devastating man-made disasters of the 20th century. Its consequences are still felt 40 years later.
“It never occurred to me then that we were moving towards an event of planetary scale, an event that would likely go down in human history as… the destruction of Pompeii or something close to it,” recalled Academician Valery Legasov, who in 1986 was a member of the government commission investigating the causes and eliminating the consequences.
TECHNICAL FLAWS OR THE "DYATLOV FACTOR"?
The Chernobyl Nuclear Power Plant operated RBMK-1000 reactors (a high-power pressure-tube reactor, later better known as the Chernobyl-type reactor). The press often claims that, until April 1986, RBMKs were considered perfectly reliable, and that only the disaster revealed their shortcomings.
The RBMK reactor did have many advantages over a different reactor design, the VVER (pressurized water reactor). For example, the VVER had to be shut down periodically for fuel loading, while the RBMK reactor was continuously fueled using a special device.
But specialists were also aware of the RBMK-1000's weaknesses. Fortunately, the practice had been relatively long—the first "Chernobyl reactor" was built at the Leningrad Nuclear Power Plant back in 1973.
The first point is the positive void coefficient of reactivity. This means that when the steam content of the reactor coolant, such as water, increases, the chain reaction in the RBMK does not slow down, as in other reactor types, but rather accelerates.
Chernobyl-type RBMK reactors became extremely unstable when power levels dropped sharply. Operators were unable to anticipate or anticipate the spontaneous acceleration of the reaction.
The second problematic issue was the design of the reactor's control and protection system (CPS) rods.
These rods are needed to regulate the reactor's operation: they are inserted into the core, absorbing active neutrons, suppressing the chain reaction, and reducing the reactor's power. The more rods inserted into the core, the greater the suppression.
The 12-meter rods consisted of two parts. The main part, 7 meters long, contained a neutron absorber—boron carbide. Beneath the absorber was a graphite displacer approximately 5 meters long. It was this graphite part that caused the problem, known as the "end effect."
When the rod insertion rate is high (for example, when an emergency requires an urgent shutdown of the reactor) and there are only a few rods (fewer than 15), the power suddenly increases instead of the desired reduction. As a result, the reactor slows down 5–6 seconds later, and these seconds can be critical. This is what happened at the Chernobyl Nuclear Power Plant.
Technical details are needed to clarify: a combination of all these flaws played a role in Chernobyl. But human error is to blame. It was also already known that the RBMK reactor's safety systems weren't perfect.
The first RBMK reactor units were developed and delivered not to the Ministry of Energy (which was responsible for "peaceful atoms" at nuclear power plants), but to an entity with a very vague name: the USSR Ministry of Medium Machine Building. In reality, the ministry was connected to the military-industrial complex; the reactors were installed on nuclear submarines and for other "non-peaceful" purposes.
The first Chernobyl reactors lacked the safety systems required for nuclear power plant operation. For example, when the first units at the Leningrad Nuclear Power Plant were installed, it turned out there were insufficient emergency pumps and no hydraulic cylinders at all for the emergency cooling system (ECCS).
Ministry of Energy specialists were fine-tuning the safety systems while the plants were still in operation—Chernobyl Deputy Chief Engineer Dyatlov should have taken this into account. But he didn't.
And he committed criminal negligence, which cost him his life, among others.
Dyatlov scheduled an experiment for April 25, 1986, to test the "turbine generator rotor coastdown" mode. This meant testing whether, if the turbine were de-energized, its rotational inertia would be sufficient to continue powering the pumps.
At 1:23:04 AM, the experiment began. The turbine was shut down. And then the first bullet went off—the positive steam reactivity effect: instead of the reactor's power declining, it began to rise.
At 1:23:40 AM, shift supervisor Alexander Akimov pressed the emergency shutdown button. This was supposed to be a lifesaver, but instead, it acted as a detonator. "The second gun went off"—the end effect: due to the graphite tips, the rods, upon entering the core for 5-6 seconds, did not shut down the reactor, but rather sharply increased its power.
During those fateful "extra seconds," the first explosion occurred, blowing off the reactor's roof. Human underestimation of the technical shortcomings had a cumulative effect.
HEROISM, NEGLIGENCE AND MISUNDERSTANDING
Those who investigators would later call the first wave of victims arrived at the scene: the fire crews of Lieutenants Vladimir Pravik and Viktor Kibenok. They were unaware they were heading not to a fire, but to the epicenter of a nuclear explosion. Lyudmila, the widow of one of the firefighters, Vasily Ignatenko, recalled:
"Vasya... said, 'Close the windows and go to bed. There's a fire at the station. I'll be there soon.' I didn't hear the explosion itself. I only saw flames. It was as if the whole sky was glowing. The firefighters went there in their canvas jackets. They weren't told there was radiation. They thought they were putting out a regular fire on the roof. Vasya later said the graphite under their feet was hot, like coals in a fire. Their boots were melting. They kicked it away with their feet, this graphite... They weren't told. They didn't know."
Meanwhile, the Chernobyl Nuclear Power Plant's chief engineer, Nikolai Fomin, was "sitting on the phone"—connected with the control panel of Unit 4. The plant's director, Viktor Bryukhanov, was reporting to Kyiv—to the Ukrainian SSR Ministry of Energy and the regional committee secretary—and to Moscow—to the Central Committee and the All-Union Ministry of Energy. In all cases, the situation was described as follows:
"The reactor is intact. We're refilling the apparatus. The emergency control and safety system tank in the central hall exploded. The explosion blew down the tent. Radiation levels are within normal limits."
Fomin and Bryukhanov reported the death of one employee, senior operator of the main circulation pumps of the reactor shop, Valery Khodemchuk, and the severe burns of the adjuster, Vladimir Shashenok.
Director Bryukhanov, Chief Engineer Fomin (who personally participated in the cleanup in the first hours), and Deputy Chief Engineer Dyatlov will be arrested and tried under Article 220 of the Criminal Code of the Ukrainian SSR—violation of safety regulations at explosive facilities. They were accused of concealing the scale of the accident.
But did they realize the scale of what was happening? Dyatlov recalled:
"I climbed up onto the overpass between the units... There were chunks of graphite under my feet. I knew it was graphite from the core, but my brain refused to accept it. I went to the control room to see Akimov. His face was already brown. I asked, 'What's wrong with the reactor?' He replied, 'We did everything right, pressed the AZ-5 [emergency protection button], but it exploded.'"
The deputy chief engineer assured:
"I still couldn't believe the reactor was gone. I ordered water to be pumped into the core. We poured water into nothing, it evaporated, and carried the contaminants into the city. It was a terrible mistake, but we followed instructions written for a living reactor, not a corpse."
Regardless, following the instructions worsened the consequences of the accident. This water injection—hundreds of tons per hour—became an additional factor in contamination. Instead of containment, management facilitated the spread of nuclides.
HOT, TERRIBLE DAY
As Chernobyl Nuclear Power Plant employees with lethal doses of radiation began arriving at Medical Unit No. 126, the city of Pripyat was enjoying a peaceful Saturday—and preparing for the May Day holiday. People were strolling with their children and fishing in a pond where the water was filling with radioactive isotopes.
Residents of the former city recall that the weather that weekend was unseasonably hot. People poured out onto the streets.
Radiation levels on the bridge at the entrance to the city (later called the Bridge of Death) were already measured in hundreds of roentgens, but no one set up a cordon.
The government commission arrived only in the evening. And only on April 27, 36 hours later, was the decision made to evacuate. From the diaries of liquidator Sergei Gazin, an eyewitness to the evacuation:
"The worst was on the 27th. A column of buses—no end in sight. People were told, 'We're leaving for three days, take only valuables and documents.' It was a white lie, so we were told, to prevent panic. But this lie was criminal. People left their pets, their windows open... I remember an old woman who didn't want to leave her apartment: 'Darling, I survived the Germans, and I'll survive this atomic bomb of yours.' They led her out by the arms. She cried because she hadn't milked the cow in the barn. She didn't realize that the cow was already glowing in the dark."
REAL PEOPLE WHO WERE CALLED "BIOROBOTS"
While there were and are legitimate questions about the plant's management and the party and economic leadership (from the bosses in Pripyat to the Central Committee of the CPSU and the Council of Ministers of the USSR), the heroism of the Chernobyl Nuclear Power Plant engineers and workers and the liquidators is undeniable.
These included firefighters fighting the blaze on the roof and helicopter pilots hovering just 200 meters above the burning Unit 4, dumping sand, boron, and lead into the crater. The lead sheets they placed under their seats to shield themselves from the radiation from below were of little help; the radiation permeated the cockpits.
Miners from Tula and the Donbass performed equally terrifying work. They dug a 136-meter tunnel under the reactor's foundation to install a cooling plate. In a confined space, in temperatures exceeding 50 degrees Celsius, the miners worked practically without clothing or respirators. In the Donetsk and Aleksin mines, people were accustomed to the dust, but here it was deadly.
A special place in this chronicle is occupied by those semi-officially called "biorobots." When German "Joker" technology and Japanese radio-controlled robots malfunctioned, losing control due to ultra-high gamma radiation, people came out onto the roof.
Conscripts and reservists wearing homemade lead aprons ran to a direct line of sight to the reactor. They had just 45 seconds to scoop up a piece of graphite or a fuel rod fragment with a shovel and throw it into the hole.
For one such exit, a person received a lifelong dose of radiation, essentially trading their health for seconds of safety for the rest of the world. This massive feat helped curb the elements.
A PAINFUL LESSON
After Chernobyl, work was done to correct the mistakes. RBMK reactors were now supplied with 2.8% enriched fuel, eliminating the first Chernobyl hazard—the void coefficient of reactivity. A new design of emergency control rods was installed—they entered the core in no more than 2.5 seconds, eliminating the second hazard—the terminal effect.
But it was practically impossible to “roll back” the main effect.
The Chernobyl disaster sparked a phobia against nuclear energy. In Western Europe, it gave carte blanche to the green movement (including its political wing)—the complete closure of nuclear power plants in Italy and Germany was essentially an "echo of Chernobyl."
In the USSR, the tragedy became one of the main themes of perestroika journalism. During the "half-life" of the Soviet Union, opposition and separatist movements played the environmental card, among other things.
But one can hardly blame the average citizen for opposing nuclear power plants—after all, the scale and consequences of the disaster were obvious. For the nuclear industry, the experience of Chernobyl's "man-made hell" was a painful lesson, remembered even by today's specialists. Failure to account for design defects and the inability of people to react promptly turn a source of "clean" electricity (a properly operating nuclear power plant has minimal impact on the environment) into a weapon of mass destruction.