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April 10 - April 13, 2023
In the bureaucratic upheaval that followed the fall of Khrushchev, in 1966 responsibility for operating new atomic stations throughout the USSR was transferred from Sredmash to the civilian Ministry of Energy and Electrification.
As one of the twelve founding members of the International Atomic Energy Agency, since 1957 the USSR had been obliged to report any nuclear accident that took place within its borders. But of the dozens of dangerous incidents that occurred inside Soviet nuclear facilities over the decades that followed, not one was ever mentioned to the IAEA. For almost thirty years, both the Soviet public and the world at large were encouraged to believe that the USSR operated the safest nuclear industry in the world.
Although it would be decades before the truth finally emerged, the Mayak disaster remained, for many years, the worst nuclear accident in history.
The RBMK was a triumph of Soviet gigantomania, a testament to its creators’ unrelenting pursuit of economies of scale: twenty times the size of Western reactors by volume, it was capable of producing 3,200 megawatts of thermal energy, or 1,000 megawatts of electricity, enough to keep the lights on for half the population of Kiev.
Serious design faults dogged the RBMK from the outset.
To make it more competitive with fossil energy power stations, the RBMK had been deliberately designed to maximize the electricity output of the uranium fuel it burned up. But it was only when they started up Leningrad Unit One that the designers discovered that the effects of the positive void coefficient grew worse as more of the fuel was burned; the longer it was in operation, the harder the reactor became to control.
The results of the experiments in Leningrad made it obvious that there were important differences between the way they had predicted the reactor would perform in theory and how it worked in practice. But the designers decided not to examine these results too closely. Even as it went into full-scale commercial operation, nobody knew how the RBMK would behave during a major accident.
The RBMK was so large that reactivity in one area of the core often had only a loose relationship to that in another. The operators had to control it as if it were not a single unit but several separate reactors in one.
Starting from their fully withdrawn position above the reactor, it would take between eighteen and twenty-one seconds for the AZ-5 rods to descend completely into the core; the designers hoped that the rods’ slow speed would be compensated for by their great number. But eighteen seconds is a long time in neutron physics—and an eternity in a nuclear reactor with a high positive void coefficient.
On the night of November 30, 1975, just over a year after it had first reached full operating capacity, Unit One of the Leningrad nuclear power plant was being brought back online after scheduled maintenance when it began to run out of control. The AZ-5 emergency protection system was tripped, but before the chain reaction could be stopped, a partial meltdown occurred, destroying or damaging thirty-two fuel assemblies and releasing radiation into the atmosphere over the Gulf of Finland.
Despite their apparent urgency, the reactor designers failed to act on a single one of these directives, and Moscow promptly ordered more of the reactors to be built.
On August 1, 1977, more than seven years after Viktor Brukhanov had watched the first stake being driven into the snow-covered ground beside the Pripyat, and two years later than planned, Reactor Number One of the Chernobyl nuclear power plant at last went critical.
At their first planned maintenance shutdown, the Chernobyl operators found that the serpentine plumbing of the reactor was riddled with faults: the water-steam coolant pipes were corroded, the zirconium-steel joints on the fuel channels had come loose, and the designers had failed to build any safety system to protect the reactor against a failure of its feed-water supply—eventually, the Chernobyl engineers had to design and fabricate their own.
In 1980 NIKIET completed a confidential study that listed nine major design failings and thermohydraulic instabilities which undermined the safety of the RBMK reactor. The report made it clear that accidents were not merely possible under rare and improbable conditions but also likely in the course of everyday operation.
Instead of engineering new safety systems, NIKIET simply revised the operating instructions for the RBMK-1000.
Meanwhile, every accident that did occur at a nuclear station in the Soviet Union continued to be regarded as a state secret, kept even from the specialists at the installations where they occurred.
In the years that followed, there would be even more serious accidents at nuclear plants elsewhere in the Soviet Union, and all of them would be covered up.
In 1983, on top of the myriad drawbacks of the reactor that had emerged since it went into operation, the reactor designers learned of one more: a curious design fault in the rods of the AZ-5 emergency protection system. The first conclusive evidence appeared at the end of the year, during the physical start-up of two of the newest RBMK reactors to be added to the Soviet grid: Unit One of the Ignalina nuclear power plant in Lithuania, and Unit Four in Chernobyl, the most advanced of the RBMK-1000 line.
It was an absurd and chilling inversion in the role of a safety device, as if the pedals of a car had been wired in reverse, so that hitting the brakes made it accelerate instead of slowing down.
The temperature inside the reactor rose to 4,650 degrees centigrade—not quite as hot as the surface of the sun.
The entire building shuddered as Reactor Number Four was torn apart by a catastrophic explosion, equivalent to as much as sixty tonnes of TNT.
Almost seven tonnes of uranium fuel, together with pieces of control rods, zirconium channels, and graphite blocks, were pulverized into tiny fragments and sucked high into the atmosphere, forming a mixture of gases and aerosols carrying radioisotopes, including iodine 131, neptunium 239, cesium 137, strontium 90, and plutonium 239—among the most dangerous substances known to man.
Lieutenant Pravik called in a number three alarm, the highest-level emergency alert, summoning every available fire brigade in the Kiev region.
This scenario was the maximum design-basis accident and an atomshchik’s worst nightmare: an active zone starved of thousands of gallons of vital coolant, raising the threat of a core meltdown.
Toptunov had released the rods from their electromagnetic clutches to let gravity take them all the way to their stops, but somehow they had halted before bringing the reactor to shutdown.
He gave orders to Shift Foreman Alexander Akimov to dismiss all nonessential personnel still at their posts, including Senior Reactor Control Engineer Leonid Toptunov, who had pressed the AZ-5 scram button. Then he told Akimov to activate the emergency cooling pumps and smoke exhaust fans, and gave instructions to open the gates of the coolant pipe valves. “Lads,” he said, “we’ve got to get water into the reactor.”
Standing no more than fifty meters away from the reactor, Tregub and Yuvchenko were among the first to comprehend what had happened to Unit Four. It was a terrifying, apocalyptic sight: the roof of the reactor hall was gone, and the right-hand wall had been almost completely demolished by the force of the explosion. Half of the cooling circuit had simply disappeared: on the left, the water tanks and pipework that had once fed the main circulation pumps dangled in midair. Yuvchenko knew at that moment that Valery Khodemchuk was certainly dead: the spot where he had been standing lay beneath a
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And from somewhere in the heart of the tangled mass of rebar and shattered concrete—from deep inside the ruins of Unit Four, where the reactor was supposed to be—Alexander Yuvchenko could see something more frightening still: a shimmering pillar of ethereal blue-white light, reaching straight up into the night sky, disappearing into infinity.
Then Tregub yanked him back around the corner and out of immediate danger: the phenomenon that had entranced the young engineer was created by the radioactive ionization of air and was an almost certain sign of an unshielded nuclear reactor open to the atmosphere.
“Lads, it’s the guts of the reactor,” he said. “If we survive until the morning, we’ll live forever.”
Its yellow beam caught the outlines of the gigantic steel disc of Elena tilted in the air, balanced on the edges of the reactor vault; the hundreds of narrow steam tubes that ran through it had been shorn away in ragged clumps, like the hair of a mutilated doll. The control rods were long gone. As they gazed at the molten crater beneath, the three men realized in horror that they were staring directly into the active zone: the blazing throat of the reactor.
But the operators gave little thought to radiation, and the panicked dosimetrists who dashed through the unit provided no useful information: the needles of all their monitoring equipment simply ran off the scale.
In the darkness around their feet were hundreds of sources of lethal ionizing radiation: lumps of graphite, fragments of fuel assemblies, and pellets of the reactor’s uranium dioxide fuel itself, scattered across the rooftops and emitting fields of gamma rays reaching thousands of roentgen an hour.
Even then, the handful of men on the roof struggled to extinguish even the smallest blazes, caused by materials which seemed to burn more savagely when they poured water on them. These were almost certainly pellets of uranium dioxide, which, superheated to more than 4,000 degrees Celsius before the explosion, had ignited on contact with the air; when hosed with water, the resulting reaction released oxygen, explosive hydrogen, and radioactive steam.
Some roof panels had collapsed completely into the hall beneath, while others dangled treacherously underfoot, leaving a patchwork of voids almost invisible in the darkness. The heat was so intense that the bitumen surface melted underfoot, tugging at the firemen’s boots, making walking difficult.
Many more hours would pass, and other men would sacrifice themselves to the delusion that Reactor Number Four survived intact, before Director Brukhanov and the men in the bunker acknowledged their terrible mistake.
Reactor Number Four was gone. In its place was a simmering volcano of uranium fuel and graphite—a radioactive blaze that would prove all but impossible to extinguish.
But when asked about the progress of emergency cooling of the core—the vital work that would ensure Reactor Number Four could soon be repaired and brought back online—the Chernobyl engineer’s composure snapped abruptly. “There’s nothing left to be cooled!” he shouted. Then the line went dead.
Sklyarov, who had almost no interest in seeing a blazing nuclear plant at close quarters, tried to object. “The station is under the supervision of Moscow. It doesn’t belong to us,” he said. “The station might not be Ukrainian,” Scherbitsky replied, “but the land and the people are.”
In the bunker beneath the power plant, Director Brukhanov sat at his desk in a bewildered stupor, apparently still unable to recognize the true scale of the catastrophe and refusing to accept the radiation readings reported by his plant’s own head of civil defense.
By eight in the morning, samples taken by technicians from the plant’s Department of Nuclear Safety revealed the presence of fission products and particles of nuclear fuel on the ground and in water around the station. This provided conclusive evidence that the core of the reactor had been destroyed and that radioactive substances had been released into the atmosphere.
There was one dead and dozens of injured; it was clear that they had been exposed to enormous levels of radioactivity and undeniably exhibited the symptoms of radiation sickness. Yet the chief of the station’s external dosimetry, tasked with measuring radiation beyond the plant’s limits, insisted there was no need to evacuate Pripyat.
The document stated that levels of radiation near Unit Four had reached 1,000 microroentgen per second—a tolerable 3.6 r/hr. But it failed to explain that this was the highest reading possible for the equipment used to take the measurements.
The energy minister’s report was bleak. He now believed things were far more serious than he’d first thought: this was not the usual kind of accident at all. There had been an explosion in one of the reactors; the damage was extensive; the consequences were hard to predict; urgent measures were necessary.
In the midst of his traditional hymn to the glories of the nuclear power industry, Slavsky paused, and then mentioned that, apparently, there had been some mishap at an atomic station in Ukraine. But he added quickly that this plant was run by their neighbors at the Ministry of Energy. Whatever the accident was, it wouldn’t halt the onward march of Soviet nuclear power.
At around 11:00 a.m., a little more than nine hours after the crisis had begun, the first of the planes from Moscow touched down on the tarmac in Kiev. Led by Boris Prushinsky, the Ministry of Energy’s nuclear accident emergency response team included scientists from Soyuzatomenergo and the institutes that designed the reactor and the plant itself, members of the KGB, and a quartet of specialists from Moscow’s Hospital Number Six—the State Institute of Biophysics’ clinic dedicated to treating radiological injuries.
Although the shell-shocked director would later continue to give his superiors contradictory information—and for several more hours tell others that Reactor Number Four remained intact—at this moment, Brukhanov acknowledged the truth. “There is no unit anymore,” he said.
As the helicopter banked away, Prushinsky forced himself to confront what his mind still refused to accept: Reactor Number Four had ceased to exist.
The map the breathless Logachev presented to Malomuzh showed the radiation reading just beside the plant cafeteria, scribbled hastily in pencil: 2,080 roentgen an hour. “You mean milliroentgen, son,” the Party chief said. “Roentgen,” Logachev said. Logachev’s commander studied the map. He finished one cigarette and then lit another. “We need to evacuate the city,” he said.
And as dense clouds of radionuclides continued to roil into the sky above Reactor Number Four, the experts assembled in the White House still could not agree on whether to evacuate Pripyat.
