The simplest form of nuclear reactor requires no equipment at all. If the right quantity of uranium 235 is gathered in the presence of a neutron moderator—water, for example, or graphite, which slows down the movement of the uranium neutrons so that they can strike one another—a self-sustaining chain reaction will begin, releasing molecular energy as heat. The ideal combination of circumstances required for such an event—a criticality—has even aligned spontaneously in nature: in ancient subterranean deposits of uranium found in the African nation of Gabon, where groundwater acted as a moderator. There, self-sustaining chain reactions began underground two billion years ago, producing modest quantities of heat energy—an average of around 100 kilowatts, or enough to light a thousand lightbulbs—and continued intermittently for as long as a million years, until the available water was finally boiled away by the heat of fission.
But to generate power steadily inside a nuclear reactor, the behavior of the neutrons must be artificially controlled, to ensure that the chain reaction stays constant and the heat of fission can be harnessed to create electricity. Ideally, every single fission reaction should trigger just one more fission in a neighboring atom, so that each successive generation of neutrons contains exactly the same number as the one before, and the reactor remains in the same critical state.
Should each fission fail to create as many neutrons as the one before, the reactor becomes subcritical, the chain reaction slows and eventually ceases, and the reactor shuts down. But if each generation produces more than one fission, the chain reaction could begin to grow too quickly toward a potentially uncontrollable supercriticality and a sudden and massive release of energy similar to that in a nuclear weapon. To maintain a steady state between these two extremes is a delicate task. The first nuclear engineers had to develop tools to master forces perilously close to the limits of man’s ability to control.
Infinitesimal and invisible, the scale of subatomic activity inside a nuclear power reactor is hard to comprehend: generating a single watt of electricity requires more than 30 billion fissions every second. Around 99 percent of the neutrons generated in a single fission event are high-energy particles released at enormous speed—“prompt” neutrons that travel at twenty thousand kilometers a second. Prompt neutrons smash into their neighbors, where they cause more fission, continuing the chain reaction, within an average of just ten nanoseconds. This fraction of time—so small that the wits of the Manhattan Project measured it in “shakes,” for a “shake of a lamb’s tail”—is much too fast to be controlled by any mechanical means. Fortunately, among the remaining 1 percent of neutrons generated in every fission event are a tiny minority released on a timescale more readily perceptible by man, measured in seconds or even minutes. It is only the existence of these delayed neutrons, which emerge slowly enough to respond to human control, that make the operation of a nuclear reactor possible at all.
By inserting electromechanical rods containing neutron-absorbing elements—such as boron or cadmium, which act like atomic sponges, soaking up and trapping delayed neutrons, preventing them from triggering further fission—the growth of the chain reaction can be controlled incrementally. With the rods inserted all the way into the reactor, the core remains in a subcritical state; as they are withdrawn, fission increases slowly until the reactor becomes critical—and can then be maintained in that state and adjusted as necessary. Withdrawing the control rods farther, or in greater numbers, increases reactivity and thus the amount of heat and power generated, while inserting them farther has the opposite effect. But controlling the reactor using only this fraction of less than 1 percent of all neutrons in every fission makes the control process acutely sensitive: if the rods are withdrawn too quickly, too far, in too large a number—or any of the myriad safety systems fail—the reactor may be overwhelmed by the fission of prompt neutrons and become “prompt supercritical.” The result is a reactor runaway, a catastrophic scenario accidentally triggering a similar process to the one designed into the heart of an atomic bomb, creating an uncontrollable surge of power that increases until the reactor core either melts down—or explodes.
To generate electricity, the uranium fuel inside a reactor must become hot enough to turn water into steam but not so hot that the fuel itself starts to melt. To prevent this, in addition to control rods and a neutron moderator, the reactor requires a coolant to remove excess heat. The first reactors built in the United Kingdom used graphite as a moderator and air as a coolant; later commercial models in the United States employed boiling water as both a coolant and a moderator. Both designs had distinct hazards and benefits: water does not burn, although when turned to pressurized steam, it can cause an explosion. Graphite couldn’t explode, but at extreme temperatures, it could catch fire. The first Soviet reactors, copied from those built for the Manhattan Project, used both graphite and water. It was a risky combination: in graphite, a moderator that burns fiercely at high temperatures and, in water, a potentially explosive coolant.
Three competing teams of physicists produced the initial proposals for what became Atom Mirny-1. These included a graphite-water design, another that used a graphite moderator and helium as a coolant, and a third using beryllium as a moderator. But the Soviet engineers’ work on the plutonium production plants meant that they had far more practical experience with graphite-water reactors. These were also cheaper and easier to construct. The more experimental—and potentially safer—concepts never had a chance.
It wasn’t until late in the construction of Atom Mirny-1 that the physicists in Obninsk discovered the first major defect with their design: a risk of coolant water leaking onto the hot graphite, which could lead not only to an explosion and radioactive release but also to a reactor runaway. The team repeatedly delayed the launch of the reactor as they devised safety systems to address the problem. But when it finally went critical in June 1954, Atom Mirny-1 retained another profound drawback the scientists never fixed: a phenomenon known as the positive void coefficient.
When working normally, all nuclear reactors cooled by water contain some steam also circulating through the core, which forms bubbles, or “voids” in the liquid. Water is a more efficient neutron moderator than steam, so the volume of steam bubbles in the water affects the reactivity of the core. In reactors that use water as both coolant and moderator, as the volume of steam increases, fewer neutrons are slowed, so reactivity falls. If too much steam forms—or even if the coolant leaks out entirely—the chain reaction stops, and the reactor shuts itself down. This negative void coefficient acts like a dead man’s handle on the reactor, a safety feature of the water-water designs common in the West.
But in a water-graphite reactor like Atom Mirny-1, the effect is the opposite. As the reactor becomes hotter and more of the water turns to steam, the graphite moderator keeps doing its job just as before. The chain reaction continues to grow, the water heats further, and more of it turns to steam. That steam, in turn, absorbs fewer and fewer neutrons, and the chain reaction accelerates still further, in a feedback loop of growing power and heat. To stop or slow the effect, the operators must rely on inserting the reactor control rods. If they were to fail for any reason, the reactor could run away, melt down, or explode. This positive void coefficient remained a fatal defect at the heart of Atom Mirny-1 and overshadowed the operation of every Soviet water-graphite reactor that followed.
* * *
On February 20, 1956, Igor Kurchatov materialized before the Soviet public for the first time in more than ten years. The father of the bomb had been enveloped in the secrecy surrounding Problem Number One since 1943, isolated in the clandestine laboratories of Moscow and Obninsk or lost in the vastness of the weapons testing grounds of Kazakhstan. But he now stood before the delegates assembled for the 20th Congress of the Communist Party of the Soviet Union in Moscow, where he revealed a fantastical vision of a new USSR powered by nuclear energy. In a short but galvanizing speech, Kurchatov outlined plans for an ambitious program of experimental r
eactor technology and a futuristic Communist empire crisscrossed by atomic-propelled ships, trains, and aircraft. He predicted that cheap electricity would soon reach every corner of the Union through a network of giant nuclear power stations. He promised that Soviet nuclear capacity would reach 2 million kilowatts—four hundred times what the Obninsk plant could produce—within just four years.
To realize this audacious vision, Kurchatov—now named head of his own Institute of Atomic Energy—had convinced the chief of Sredmash to let him build four different reactor prototypes, from which he hoped to choose the designs that would prove the basis of the Soviet nuclear industry. But before construction could begin, Kurchatov also had to win over the economics mandarins of Gosplan, who controlled the distribution of all resources throughout the USSR. Gosplan’s own Department of Energy and Electrification set targets for everything from how much money could be allocated for building an individual power station to the quantity of electricity it would be expected to produce once complete. And the men and women of Gosplan cared little for ideology, Soviet prestige, or the triumph of Socialist over capitalist technology. They wanted rational economics and tangible results.
Like their counterparts in the West, the Soviet scientists’ arguments about how quickly and inexpensively nuclear power could become competitive with conventionally produced electricity were speculative and colored by wishful thinking about electricity “too cheap to meter.” But unlike the boosters of the nuclear future in the United States, the Soviets could not rely on golf course sales pitches and entrepreneurial investment from the free market. And economics were not on their side: the capital costs of building any nuclear reactor were colossal, and the USSR was rich in fossil fuels—especially beneath the remote wastes of Siberia, where new oil and gas deposits were being discovered all the time.
Yet the sheer size of the Union, and its poor infrastructure, favored nuclear power. The scientists pointed out that the Siberian deposits were thousands of miles from where they were most needed: in the western part of the Soviet Union, where the majority of its population and industry lay. Moving either raw materials or electricity over these distances was costly and inefficient. Meanwhile, the nuclear plants’ closest competition—hydroelectric stations—required flooding huge areas of valuable farmland. Nuclear stations, while expensive to build, had little environmental impact; they were largely independent of natural resources; they could be located close to the sources of demand in major cities; and, if constructed on a large enough scale, they could produce vast amounts of electricity.
Apparently convinced by Kurchatov’s promises, Gosplan released the money for two prototype plants: one with a pressurized water reactor of the kind already becoming standard in the United States, and another with a water-graphite channel type—a scaled-up version of Atom Mirny-1. But, just as in they would in the West, construction costs quickly skyrocketed, and Gosplan suspected the scientists had misled them. They scaled back the plans and called a halt to work on the PWR plant, and Kurchatov’s vision of the atom-powered future gradually collapsed. He pleaded for the flow of resources to be turned back on, writing to the head of Gosplan to insist that the plants were crucial for determining the future of the Soviet atom. But his pleas went unheeded, and in 1960 Kurchatov died without seeing his dream revived.
In the meantime, the Ministry of Medium Machine Building had completed a new project, hidden inside the clandestine nuclear site known as Combine 816, or Tomsk-7, in Western Siberia. The EI-2, or “Ivan the Second,” was a big military water-graphite reactor with a thrifty edge. Its predecessor, Ivan-1, had been a simple model built solely to manufacture plutonium for nuclear warheads. But EI-2 had been adapted to perform two tasks at once. It made weapons-grade plutonium and, as a by-product of the process, also generated 100 megawatts of electricity. And when work on the Soviet civil nuclear program finally restarted two years after Kurchatov’s death, by then lagging behind its competition in the United States, it did so with a new emphasis on reactors that were affordable to build and cheap to run. At that moment, it was not the sophisticated experimental reactors of Igor Kurchatov’s civilian nuclear program but the stalwart Ivan the Second that stood ready to carry the atomic banner for the Soviet Union.
* * *
Less than a year after Igor Kurchatov presented his imperial vision of an atom-powered USSR to the Party congress in Moscow, a toothy, young Queen Elizabeth II made her own ceremonial appearance, outside Calder Hall nuclear power station, on the northwest coast of England. Pulling a lever with elegantly gloved hands, she watched as the needle on an oversized meter began to spin, showing the first atomic electricity flowing into the British national grid from one of the station’s two gas-cooled reactors. It was pronounced the launch of the first commercial-scale nuclear power station in the world, the dawn of a new industrial revolution and a triumph for those who had kept the faith in the peaceful power of the atom when others had feared it would bring only destruction to the world. “For them,” a newsreel commentator reported, “this day is a milestone of victory!”
The event was a grand propaganda exercise; the truth was darker. Calder Hall had been constructed to manufacture plutonium for Britain’s own nascent atom bomb program. What electricity it did produce was a costly fig leaf. And the military roots of the civilian nuclear industry had entangled not only the technology it relied upon but also the minds of its custodians. Even in the West, nuclear scientists continued to dwell in a culture of secrecy and expedience: an environment in which sometimes reckless experimentation was married with an institutional reluctance to acknowledge when things went wrong.
A year after Calder Hall opened, in October 1957, technicians at the neighboring Windscale breeder reactor faced an almost impossible deadline to produce the tritium needed to detonate a British hydrogen bomb. Hopelessly understaffed, and working with an incompletely understood technology, they operated in emergency conditions and cut corners on safety. On October 9 the two thousand tons of graphite in Windscale Pile Number One caught fire. It burned for two days, releasing radiation across the United Kingdom and Europe and contaminating local dairy farms with high levels of iodine 131. As a last resort, the plant manager ordered water poured onto the pile, not knowing whether it would douse the blaze or cause an explosion that would render large parts of Great Britain uninhabitable. A board of inquiry completed a full report soon afterward, but, on the eve of publication, the British prime minister ordered all but two or three existing copies recalled and had the metal type prepared to print it broken up. He then released his own bowdlerized version to the public, edited to place the blame for the fire on the plant operators. The British government would not fully acknowledge the scale of the accident for another thirty years.
Meanwhile, in the USSR, endemic nuclear secrecy had reached fresh extremes. Under Khrushchev, Soviet scientists began to enjoy unprecedented autonomy, and the public—encouraged to trust unquestioningly in the new gods of science and technology—were kept in the dark. In this intoxicating atmosphere, the physicists’ early success in taming the power of the peaceful atom made them dangerously overconfident. They began using gamma rays to extend the shelf life of chicken and strawberries, they built mobile nuclear reactors mounted on tank treads or designed to float around the Arctic, and, like their US counterparts, they designed atomic-powered aircraft. But they also used nuclear weapons to put out fires and excavate underground caverns, restricting the size of their explosions only when the seismic shock began to destroy nearby buildings.
Following the death of Igor Kurchatov, the Institute of Atomic Energy had been renamed in his honor, and leadership of Soviet nuclear science had passed to his disciple, Anatoly Aleksandrov. An imposing man with a glisteningly bald head who’d helped build the first plutonium production reactors, Aleksandrov was appointed director of the Kurchatov Institute in 1960. A dedicated Communist who believed entirely in science as an instrument of the Soviet economic dream, he prized monumental projects over
cutting-edge research. As the Era of Stagnation began, the Soviet scientific establishment lavished resources on the immediate priorities of the state—space exploration, water diversion, nuclear power—while emergent technologies, including computer science, genetics, and fiber optics, fell behind. Aleksandrov oversaw the design of reactors for nuclear submarines and icebreakers, as well as the prototypes of the new channel-type graphite reactors designed to generate electricity. To reduce the cost of building these, he emphasized economies of scale and insisted on increasing their size to colossal proportions using standardized components and common factory materials. He saw no reason that manufacturing nuclear reactors should be any different from making tanks or combine harvesters. Aleksandrov regarded the serial production of these massive reactors as the key to Soviet economic development, and atomic power as the means to realize Ozymandian dreams of irrigating deserts, bringing tropical oases to the Arctic North, and leveling inconveniently situated mountains with atom bombs—or, as the Russian expression went, “correcting the mistakes of nature.”
Despite his breadth of vision and political influence, Aleksandrov did not have sovereignty over Soviet nuclear science. Behind him loomed the sinister, adamantine power of the Ministry of Medium Machine Building and its belligerent chief, the veteran revolutionary Efim Slavsky, variously known as “Big Efim” and “the Ayatollah.” Although as young men they had fought on opposite sides in the Russian Civil War—Slavsky on horseback as a political commissar with the Red Cavalry, Aleksandrov with the White Guard—the two atomic magnates were close, and enjoyed reminiscing together over vodka and cognac. But as the Cold War intensified, the military-industrial demands of Sredmash overwhelmed those of the pure scientists at the Kurchatov Institute. In the first few years of its existence, the national priority afforded the atom weapons program had allowed the ministry to consolidate control of a massive nuclear empire, with its own scientists, troops, experimental labs, factories, hospitals, colleges, and testing grounds. Sredmash could call upon almost unlimited resources, from gold mines to power stations, all maintained behind an impenetrable wall of silence.
Midnight in Chernobyl Page 5