Thirty-six seconds. That’s how long the test that sealed Chernobyl’s fate lasted. The test itself was not unreasonable, and could only be performed as a reactor — one of four in operation at the power station in 1986 — was being shut down. It was designed to provide data to understand how the reactor and the systems surrounding it performed under certain unusual circumstances, data that were intended to make long-term operation safer and more reliable. Almost all of the decisions leading up to those thirty-six seconds were reasonable, and even the few that were questionable were well within the norms of Soviet industry, which rewarded getting things done regardless of circumstances, which often set unreasonable goals, and which generally operated among shortages and cutting corners. Each of those choices, some made as far back as when the reactors were designed, had the effect of narrowing the margin for error.
Some uranium atoms naturally shed neutrons. Most of the time, the result of this process is unremarkable. Bring enough uranium close enough, though, and the neutrons will cause other uranium atoms to split and shed additional neutrons. If more neutrons are produced by splitting uranium than are absorbed by nearby materials, the process continues as a chain reaction that releases vast amounts of energy and produces a variety of other materials, some of them highly radioactive. Starting a nuclear chain reaction requires nothing more than the material and proximity. Controlling a chain reaction requires quite a bit more: some kind of medium to make sure that the reaction continues at a steady rate, neither stopping nor accelerating out of control, plus cooling to ensure that the heat is dispersed, and the systems necessary to guide and monitor all of these processes. Making use of a chain reaction requires a further layer: a means to convert the heat that fission releases into electricity. The heat converts water near the reaction into steam, which is then piped to spin a turbine, which spins and generates electricity. The steam then condenses back into liquid water. After sufficient cooling, it is piped back through the system, and the cycle continues.
The kind of design used in Chernobyl is known by its Russian acronym: RBMK. Reactors of this type use graphite control rods as the medium to moderate the fission reaction. When the rods are placed deep enough between the reactor’s fuel rods, the graphite will absorb the neutrons that the uranium fuel is producing. That prevents the neutrons from dividing additional uranium atoms. Selective use of the control rods can slow and then stop the chain reaction. One crucial element of the design is that initially the control rods provide additional neutrons; that is, if just a small portion of the control rods is between the fuel rods, the chain reaction will increase. Only as more of the control rods go deeper into the reactor does the chain reaction slow down. That would prove fateful in April 1986. The RBMK design had originally come from the Soviet military, and knowledge of the design flaw was kept secret from the civilian operators of the Chernobyl power station. Following an 1982 incident at a power plant near Leningrad, RBMK operators throughout the Soviet Union received instructions on improving the design of their reactors’ control rods, but were not told why. (p. 68)
The power station’s Unit 4 was due to stop for repairs late that month. Plokhy describes the test that was to prove Chernobyl’s undoing, and the thinking behind the procedure:
As usual in such cases, the shutdown of the reactor would be used to test its numerous systems at a low level of radioactivity. One of the tests to be conducted on the unit before shutting it down concerned the steam turbine and was designed to find a way to make the reactor more secure during SCRAM—the Safety Control Rods Activation Mechanism, which automatically inserted all the control rods into the active zone of the reactor and halted the reaction in case of emergency. The idea behind the test was fairly simple. In case of an emergency leading to the shutdown of the reactor, it was expected that the electricity would go off when the unit still needed it to pump coolant into the overheated reactor and prevent its meltdown. Emergency diesel generators were supposed to take care of that problem and provide badly needed electricity to continue pumping the water, but at present they would kick in only forty-five seconds after the shutdown, creating a supply gap and thus a potential safety problem. It had to be fixed.
Engineers … had come up with a solution to the problem. They pointed out that just as the reactor did not cool down immediately after the shutdown, so the turbine driven by residual steam pressure would also keep rotating for some time. Energy produced by that continuing rotation could be used to produce enough electricity to cover the forty-five second gap. How long the rotation produced by the momentum of the turbine generator would continue and how much energy it would produce was the question that the Donetsk engineers wanted to answer with the help of their Chernobyl partners during the shutdown of reactor No. 4. That was the essence of the test. (pp. 63–64)
One issue was that because the test was meant to simulate a failure in the automatic shutdown mechanisms, those mechanisms would have to be disabled to conduct the test.
After three chapters setting the stage and describing the construction of the Chernobyl power plant, Plokhy gives a detailed description of the night of the accident. He relates the delays that caused the test to be moved from a shift that had been planning for it to people who were familiarizing themselves with the documents not long before the test was to begin. He notes how requests for regular levels of power from the city of Kyiv led to further changes in the schedule. No single choice was unreasonable — indeed, Chernobyl’s whole reason for existing was to supply Kyiv with electricity — but each choice along the way reduced the operators’ margin of error and took key people away from the operation. Significantly, there was no one willing to cancel the whole process when delays and changes accumulated. The operators had a can-do attitude and were accustomed to outperforming. (I’ve only seen the first episode of the HBO miniseries, but I am still haunted by the stunned faces of the control-room personnel who keep saying “But we did everything right.”)
Shortly after midnight on April 26, 1986, events began cascading. Operators had been reducing the power produced by the reactor to get to the level where the test was supposed to take place. “Everything went as planned until an emergency signal indicated that the supply of water to the reactor had reached an unacceptably low level.” (p. 80) The actions the operators took to solve that problem, along with a control rod regulator that was out of order, caused the output to fall by nearly 90 percent. They withdrew rods to recover and kept the reactor from a premature shutdown, but that left them at a level only one-third of what was prescribed for the test. The staff on hand decided to proceed with the testing. “It was all part of the test program, but, given the reactor’s low power level, the addition of two pumps to the six already in operation further destabilized the reactor.” (pp. 81–82) Keeping the reactor going at that level was a problem that they solved by removing still more control rods. “Soon, only 9 rods out of close to 167 available remained in the core of the reactor—all the rest had been withdrawn, making the reaction difficult to control and the reactor highly unstable.” (p. 82) As they began the test, water in the cooling system was turning to steam, another factor that would, seconds later, contribute to a spike in the intensity of the reaction.
Over the next four pages, Plokhy describes in bare but chilling detail how the reaction raced out of control, how the emergency measures failed, how the design flaw turned control efforts into disaster accelerants, and what it sounds like when an unstoppable nuclear reaction creates enough steam pressure to lift a 200-ton concrete plate up through the roof of the containment building and into the air. The second explosion followed two seconds later and “destroyed a good part of the containment building and threw graphite blocks into the air—the moderator core of the reactor, along with part of its fuel.” (p. 86) Chernobyl had just become the world’s worst nuclear disaster.
As a book, Chernobyl is gripping and horrifying. Plokhy introduces readers to numerous people who played crucial roles; his approach humanizes the catastrophe. The plant director, the chief engineer, the technicians, the firemen — all had their ambitions and foibles, in Plokhy’s account the choices they made are all understandable. It is easy to see making the same mistakes. Plokhy also sets the story of Chernobyl in the Soviet context, from the secrecy surrounding the RBMK design flaw to the pressure to produce, from tensions between ministries competing for resources within a closed system to the power of long-time apparatchiks and the desire of newly-installed Gorbachev to bring about reform. Plokhy further describes the changing role of Chernobyl in Ukrainian national views. Initially welcomed as an indicator of modernity and progress, it became after the accident a symbol of Moscow’s indifference to Ukrainian lives. In the remaining years of the Soviet Union, Chernobyl was a rallying issue for both environmentalism and Ukrainian nationalism. Once the USSR disintegrated, though, the government of independent Ukraine was left to pay for the after-effects and also to find a way to produce enough power for the country while fulfilling its promises to the world to close the stricken power plant.
I would have liked more about the years following the disaster, particularly because Plokhy says in his preface that his book “is the first comprehensive history of the Chernobyl disaster from the explosion of the nuclear reactor to the closing of the plant in December 2000 and the final stages in the completion of the new shelter over the damaged reactor in May 2018.” (p. x) The period from 1994 to 2018 is given short shrift in just over a dozen pages. On balance, he kept this focus on the accident, its causes and its immediate aftermath, and he kept the book to a very manageable length. I can’t fault those choices.
I suspect that the parts of the account that will stay with me longest are those of the firemen. They rushed to the scene, as they were trained to do, no different from first responders under any system of government. They did their best to make sense of what they found, to rescue and repair as best they could. They came home radioactive, and many of them died. Chernobyl was a human-made disaster, and Chernobyl never fails to keep that fact front and center.