CHAPTER 26

SECRETS OF CHERNOBYL

To appreciate the Chernobyl cataclysm, one must first understand its RBMK reactor—a crude design that was original to the Soviet Union and not merely a copy of Western ideas. As everyone knows, RBMK stands for , which is pronounced “Reaktor Bolshoi Moshchnosti Kanalnyy” and in English means “high-power channel-type reactor.” (Yes, the Chernobyl reactor’s name contains the word bolshoi, which might conjure images of leaping ballerinas. Forget that. The word in Russian means “great” or “grand” or “big,” and the label was appropriate for such a grandiose, high-power device.)

The RBMK had a number of inherent design flaws that were largely responsible for the 1986 disaster, although the precipitating cause was a very poorly conceived test by supervisors who lacked the knowledge to conduct such an operation and who then repeatedly mishandled the situation as things went awry. Nonetheless, several of the RBMK’s greatest deficiencies were fixed after Chernobyl, and eleven reactors of the same design continue to produce electricity in Russia to this day.

The RBMK was intended to be cheap and efficient in a number of different ways and to produce plutonium as a by-product, which would then be used for the Soviets’ nuclear-bomb production. It used ordinary filtered river water for cooling and standard inexpensive graphite rods for controlling the fission reactions. Natural unenriched uranium fueled the plant rather than the precious uranium isotope U-235 favored in Western designs, as U-235 was expensive to produce. All these features, as well as the absence of a concrete-and-steel containment building in case of a major accident, yielded the type of enormous reactor that could be built cheaply and in large numbers. In Lithuania, an RBMK reactor, which even today is one of the world’s largest, continues to produce 1.5 gigawatts of power.

(Argonne National Labs)

This design offers several undeniable benefits. For example, as we’ve seen, the first hour after a reactor shutdown is a perilous period when coolant must still be circulating in the core. However, the RBMK has an unusually low amount of fissions per cubic meter of its core, which lets it withstand a total loss of electrical power, including a complete circulating coolant failure, for up to an hour with no expected core damage. (If the later Fukushima reactor had had such a strength, it might not have been destroyed in the 2011 accident.) Unfortunately, more than balancing out that benefit is the fact that in an RBMK reactor using uranium as fuel, the circulating water doesn’t merely serve as a coolant; it also moderates the fission reactions and dampens them to safe levels. This is exactly the opposite of what water does in a Western B & W pressurized-water reactor, where the neutron production critically relies on nearby water molecules to proceed.

So when you lose the circulating cooling water in a Western power plant, bad things happen, but at least the fissioning power production automatically shuts down. Conversely, in an RBMK plant, the lack of water makes the fission process increase—and this runaway is exponential. It’s a double whammy and quickly makes the power and the heat rise radically. Known technically as having a positive void coefficient, this property of an RBMK is no small deficiency. It was central to the cataclysmic events of April 26, 1986.

But other design-safety aspects were wanting as well. The only thing blocking radiation from escaping the core was a massive, round, eight-foot-thick concrete cap on the top of the five-story-tall reactor. High above that, there was no outer containment building, merely a tin roof to keep out the rain.

And that still wasn’t the end of the problems. Each of Chernobyl’s four operating RBMK reactors’ power was controlled by 211 enormous, forty-foot-long graphite rods. When a rod was raised or lowered, its middle sixteen feet would make the fission reactions increase or decrease, thus enabling operators to regulate the heat and power. But when a rod was fully lowered in an emergency, the first few feet of it would radically increase the power, so if all of them were thrown down simultaneously, there’d be an initial catastrophic runaway power surge. In other words, operators would have to be calmly judicial when ordering the reactor to shut down, and they would have to extend rods a few at a time manually, as if it were all a video game. This was very different from Western reactors, where a single red Scram button punched by a frantic supervisor will drop all control rods within three seconds, abruptly stopping the power production, end of story.

With all these system quirks and design negatives, and with no fewer than four RBMK operating reactors and two more under construction just eleven miles outside the ancient historic Ukrainian town of Chernobyl, and with the new supporting village of Pripyat with fifty thousand people a mere 1.9 miles from the plant’s gates, you’d think extreme caution would be the daily buzzwords in the reactors’ operations. Yet in April of 1986, although all the supervisors and foremen were mechanical engineers and experts in areas such as turbines and wiring, there was not one person on the site who was deeply knowledgeable about graphite-moderated nuclear reactors or fully versed in nuclear theory.

And that’s when the men in charge decided to shut down all the plant’s safety systems to see what would happen.

Wait, scratch that; although it’s perfectly true, such a summary makes them seem unduly stupid. There was actually some logic behind that night’s protection-disabling idea. Essentially, their safety committee had long ago realized that in any kind of emergency shutdown, there would be some lag time between when their generators stopped and when they could get the diesel backup generators going. In that interval, the coolant pumps wouldn’t be running, and the buildup of heat in the reactor could cause damage, even though their system should theoretically not succumb to a full meltdown. But some engineer had theorized that at least one of the massive turbine rotors should keep spinning long enough from its own momentum to just barely be able to power the coolant pumps during those critical few minutes. A previous test had yielded pessimistic data, so they’d figured out a way to reduce the drag caused by the generators’ electrical fields and now wanted to run the test again. Thus there was some genuine purpose to this experiment.

In preparation for it, an engineer named Gennady Metlenko installed a special control-panel switch and had it labeled MPA, which stood for Russian words that meant “maximum design basis accident.” Essentially, anyone hitting that switch would instantly unleash the worst thing that could possibly happen. All at once, the turbine would be shut down, as would the emergency cooling system, including all of the pumps. The switch also blocked the diesel generators from starting. It would bypass all the automatic safety controls and disable everything that kept the reactor running properly.

In his analysis of the accident thirty years later, senior Georgia Tech research scientist James Mahaffey summarized that MPA switch in six words: “This was a monumentally bad idea.”¹

The team of supervisors and foremen began the experiment at 1:00 p.m. on April 25, 1986, when they reduced reactor number 4 from maximum power. An hour later, they disabled the emergency cooling system to prevent a hundred thousand gallons of cold water from crashing into the red-hot reactor and perhaps warping something.

Then an unexpected power demand from far-off Kiev made them postpone the test, and they temporarily powered it back up to maximum. They resumed their experiment at 11:10 p.m., but instead of the power reducing and holding at fifteen hundred megawatts, as planned, the reactor kept running down all the way to a mere thirty megawatts. They then correctly realized that the unintended spin-down was due to a fission-power sequence of radioactive isotope decays, which had disturbed the reactor’s normal equilibrium.

The engineer in charge of reactor number 4, Anatoly Stepanovich Dyatlov, well known for his temper and for his minimal understanding of operational nuclear fission, realized that the reactor was now stuck at a low power level and might require two full days to be restored. As the person leading the test, he told his employees to bring the power back up fast, then he paced, yelled, cursed, spat, waved his arms, and threatened the workers who were protesting that it was against protocol to bring the power back up too quickly. An operator, Leonid Toptunov, fearing for his job, began hitting switches that pulled out control rods until he’d managed to yank out 205 of the 211, which brought the power up to two hundred megawatts. But then, at 1:22:30 a.m., the operations computer sounded an alert warning that in the reactor’s current configuration, control might be lost; it announced that the reactor should be shut down right away.

Dyatlov wouldn’t listen. In another two or three minutes, everything would be fine, he shouted. Thirty-four seconds later, he and his team began their experiment. One turbine was shut down, and an operator hit the perilous, bizarre, newly installed MPA button.

The nearly red-hot reactor immediately responded by violently boiling away its coolant water. With the water disappearing, the fissioning increased explosively. The power level zoomed upward. As the cooling water disappeared, the reactor suddenly attained a state of supercriticality, where fissioning increases exponentially. In the control room, the power-level needle moved to its highest level on the gauge while an operator stared at it in disbelief for thirty-six seconds.

Then the stunned operator shouted a warning and, not even asking his boss for permission, hit the red button that dropped all the control rods, trying to kill the runaway reactions. The reactor went “prompt supercritical,” where neutrons all fly at once and don’t have to wait for any response from neighboring atoms. Now the reactor core started to melt. Vertical pipes that normally guided the graphite rods warped and twisted, rendering further control impossible. The reactor’s power level geysered upward to an unbelievable thirty billion watts as the structure began disintegrating. The jammed graphite rods in the middle of the core did more than merely prevent further human control or amelioration; they created a positive loop, which actually boosted the activity of the uranium fuel. This was later deemed the “final trigger” of the day’s catastrophic events.

The building shook, and the unprecedented high temperature boiled away every remaining ounce of coolant water, producing steam under enormous pressure. When the steam exploded a few seconds later, the five-hundred-ton concrete cap on the reactor roof blew into the air. Fragments from the reactor tore upward like shrapnel, destroying the tin roof.

All the plumbing lines into the reactor now came loose and broke, and water, instantly changed to steam by the intense heat, mixed with radioactive dust and debris and blew past the torn roof and out into the sky—the first moments of a giant fallout cloud that would soon envelop all of Europe.

A buildup of hydrogen gas, now refreshed with a sudden influx of oxygen from the missing roof, detonated in an enormous explosion of its own. The entire Chernobyl number 4 plant, already nearly totaled by the events of the past few minutes, was completely totaled this time. Vaporized metals, zirconium, graphite, and fifty tons of uranium fragments were hurled thirty-six thousand feet into the sky where they contaminated every commercial airliner within a hundred miles. The plant’s remaining graphite rods, eight hundred tons in all, started burning with intense flames.

The experiment was apparently over.

In the control room, the violent explosions had turned the concrete walls into rubble; sparking ceiling fluorescent fixtures now dangled from fallen electrical wires. All the gauges and instruments were dark and dead. Battery-powered emergency lights cast small spots of brightness here and there. Chernobyl number 4 had ceased to exist.

Radiation was intense, but the handheld monitoring instruments, designed to detect only reasonably high leaks or emissions, all had needles stuck uselessly flat against their upper limits. Even specialized monitoring equipment would have been unable to read the unbelievable levels; thirty thousand roentgens per hour was zapping out of the burst-open reactor. Pieces of previously flying fuel and graphite were littering the plant, and each of these chunks was emitting five thousand rem, five times a fatal dose to anyone who paused in their vicinity.

Meanwhile, Dyatlov, arrogant and ignorant as always, believed the inside of the reactor was unharmed and that all would be fine if cold water could be pumped in. He even said so in a call to Moscow, in which he assured his superiors there was nothing to worry about. Firemen arrived and rushed to the roof where the tar was burning furiously. No one warned them about the radiation hazard, and few of them lived to the end of that spring.

More than one hundred graphite rods remained furiously on fire. Blazing updrafts from this inferno continued unabated for the next nine days, and these lifted plumes of intensely radioactive debris from the torn-open reactor straight up into the atmosphere. The thin metal roof was now a grotesque scene of enormous gaping holes with more empty space than metal directly above the reactor.

In all, a hundred and twenty-seven control-room personnel and firemen came down with acute radiation sickness, and thirty-one died. Later, twenty-three more people in the immediate area perished from radiation effects. The radioactive cloud spread northward, first to Finland and Sweden and then to the rest of Europe, but the Soviet government warned no one, having considered Chernobyl a secret facility. The contamination from iodine-131, strontium-90, and cesium-137 was predicted to produce four thousand to ten thousand cancer deaths, and as of 2018, according to the Ukrainian government, around eight thousand have already perished.

Of the dozen people in the control room, five died agonizing deaths from radiation burns in the days immediately after the disaster. Anatoly Stepanovich Dyatlov received a dangerously high dose of radiation and was left a permanent invalid; six years later, he couldn’t walk more than a few steps without exhausting himself.

According to the official Soviet report, Dyatlov’s incompetence was directly responsible for the disaster, and soon after the catastrophe he was found guilty of criminal negligence and sentenced to ten years in prison, though he and the other convicted Chernobyl supervisors were pardoned after serving six years. The official version of events states that Dyatlov violated the most elementary safety precautions on the night of April 26, 1986, and bullied his subordinates into taking unnecessary risks that led directly to the destruction of the reactor and the spewing of radioactive particles across a wide area of Europe.

In terms of the amount of contamination it produced, the Chernobyl explosion was equivalent to more than ten of the atomic bombs dropped on Hiroshima, and hundreds of thousands of people were permanently forced from their homes. It was by far history’s greatest radiation accident.

In rankings of all industrial mishaps and in terms of sheer number of deaths, Chernobyl may well have been history’s very worst in this category as well. Factor in the fright-producing component of it happening in a nuclear power plant, and we’ve got the top candidate for an unnatural event that merits that big word on the cover of this book.