The worst nuclear accident ever to take place began with a safety test. At 1:23 AM on Saturday, April 26, 1986, the operator of Reactor No. 4 at the Chernobyl nuclear power station started an experiment to see how long a spinning turbine could provide electricity in the event of a loss of power to the plant. If the power supply failed, it would take more than thirty seconds for the backup generators to come into play. The purpose of the test was to see whether the turbine could provide enough power to pump cooling water over the uranium fuel until the emergency generators took over.
The test was to be conducted just before the reactor was shut down for routine maintenance. At midday on April 25 reactor power was reduced to about 50 percent. The next step was to reduce power to about 30 percent, but this was delayed until 11:10 that night because of unexpectedly high demand for electricity in the Kiev region. As a result, the test was conducted by the night shift which, unlike the day shift, had not been instructed in advance about it and was, besides, less experienced.
The test called for operating the reactor at 30 percent of power, so that if the test failed the first time it could be repeated. When permission was given to reduce power at 11:10 PM, the operator made a mistake in setting the controls, and power fell to 1 percent, too low for the experiment. This caused a buildup of xenon in the uranium fuel and threatened to shut down the reactor completely.
In order to prevent this, the operator pulled out almost all the control rods, bringing the reactor up to about 7 percent of power. This was very dangerous, because some of the control rods are used for emergency shutdown. The reactor was now unstable: the xenon buildup was acting as a brake, pushing the reactor toward shutdown, while the operator was trying to drive up the power by removing the control rods. An automatic system should have shut down the reactor at this point, but the operator wanted to ensure that the test could be carried out, and he therefore blocked a number of the emergency shutdown signals.
At 1:23:04 AM the test began. The turbine was disconnected and its energy was fed to four of the eight main pumps. As the turbine slowed down, so too did the pumps and the flow of cooling water over the fuel elements. Power began to rise, and at 1:23:40 the operator pressed the button for an immediate shutdown of the reactor. The shutdown rods moved down too slowly to prevent a runaway increase in power (and they may even have contributed to it, because of faulty design).1 In any event, power rose to about one hundred times its normal full level within four seconds. The fuel disintegrated and caused a rapid boiling of the cooling water.
At 1:24, twenty seconds after the emergency shutdown button had been pressed, a steam explosion destroyed the roof of the reactor building; two or three seconds later another explosion threw out lumps of uranium and graphite, starting fires on the roof of the turbine hall. The firemen who soon arrived extinguished these by 5 AM, but many of the firefighters died shortly afterward from exposure to radiation.
The explosions released millions of curies of radioactive particles into the atmosphere, and the reactor continued to spew out radioactive materials over the next ten days. A graphite fire in the reactor core drew in air, which reacted with the uranium fuel and caused it to release radioactive particles. The local population was evacuated on Sunday, April 27; and everyone except emergency workers was later excluded from a zone within a radius of thirty kilometers.
It was now necessary to put out the fire and stop the release of radioactive material from the reactor. Five thousand tons of sand, lead, clay, and limestone were dropped by helicopter onto the reactor between April 28 and May 2. The aim was to create a cap that would smother the core, but radioactive particles continued to filter through. Moreover, the cap trapped the heat inside the reactor, creating the danger of another meltdown of the core. Holes were now drilled into the earth underneath the reactor, and liquid nitrogen was poured into them in order to freeze the ground.
The emission of radioactive materials from the reactor core dropped sharply, from about eight million curies on May 4 to 150,000 on May 5. The “battle of Chernobyl,” as the Soviet press called it, was now over, but the consequences of the accident will be with us for many years to come. The radioactive materials emitted only on May 5 were still more than the total release of radioactive particles in either the Windscale accident in Britain in 1957, or in the Three Mile Island accident in 1979. Only in October, when the reactor was finally entombed in a special “sarcophagus” of reinforced concrete, did it stop contaminating the environment.
The consequences of the accident for public health remain a matter of controversy. The official figure for the number of deaths is thirty-one, but the figure of three hundred has recently been mentioned in the Soviet press. Large areas of the countryside in the Ukraine and Byelorussia received heavy doses of radioactive fallout, with the result that many people have eaten contaminated food. About 600,000 people received significant exposure to radiation. The radioactive cloud spread across the whole of Europe. Estimates of the number of cancer deaths that may result from the Chernobyl accident range from 10,000 to 100,000.
Most accounts of the Chernobyl accident have explained it as a consequence of human error and faulty reactor design. The director of the power station and other senior managers have been tried for criminal negligence and sentenced to prison. The Soviet government has tightened safety regulations and improved the training of plant operators. It has also acknowledged that the design of the Chernobyl-type reactor, which is one of two main types in use in the USSR, is flawed. It immediately improved the emergency shutdown mechanism in existing reactors, and in 1988 decided not to build any more plants of this type.
The importance of human error in causing the accident cannot be denied; nor can the contribution of design faults in the reactor. But this explanation, while correct as far as it goes, is not ultimately satisfying: we still need to ask why the operators behaved as they did, and why the reactors were poorly designed. In The Legacy of Chernobyl the Soviet biochemist Zhores Medvedev seeks the causes of the accident not in the failings of individual men, but rather in the social structures in which they worked.
In the 1960s Medvedev wrote a study of the destruction of Soviet genetics that brought him into conflict with the Soviet authorities. 2 He was later forced into emigration when he was deprived of his Soviet citizenship during a visit to Britain. During the late 1970s he drew the attention of Western public opinion to the large nuclear accident in the Urals. When officials in the British nuclear industry questioned whether there had been any such accident, Medvedev wrote a book, Nuclear Disaster in the Urals, which proved that a major accident had indeed taken place in the late 1950s at Kyshtym, the site of a secret installation for the production of plutonium.3 Medvedev’s new book is a worthy successor to his earlier works, and provides a clear and well-informed analysis not only of the causes of the Chernobyl
accident, but also of its consequences for public health and the environment in the Soviet Union and the world. Medvedev uses evidence not only from official Soviet reports but from the many accounts of the disaster that have appeared in the Soviet press as well as in the West.
Medvedev argues that the Chernobyl accident can be understood only as an example of the modus operandi of Soviet bureaucracy. It was revealed at the trial of senior managers in 1987 that the power station director had signed a document in December 1983 certifying that the reactor, presumably including its safety systems, was in proper order, even though the safety systems had not been properly tested. Medvedev suggests that the safety test planned for April 1986 was one that should have been carried out before the reactor was certified. That might help to explain why the operators felt under pressure to perform the test, especially since the next reactor shutdown was not scheduled to take place for another year.
This is certainly a plausible argument. In the Soviet system targets are set at the top and pressure is exerted on those below to meet them. Those who meet the targets are rewarded, those who fail are punished. Although it has often been effective in a crude and brutal fashion, this system—the “command-administrative system,” as it has become known—encourages people to take shortcuts and to report false information to their superiors.
In one of the best Soviet accounts of Chernobyl, Grigorii Medvedev (no relation to Zhores) describes an exchange between Boris Shcherbina, the deputy premier with responsibility for energy, and R.G. Khenokh, director of the Zaporozhe nuclear power station, which took place at a meeting in the Kremlin two months before the Chernobyl accident. When Khenokh said that one of the units at his power station would not be ready in time because of delays in the delivery of equipment, Shcherbina exploded: “You see, what a hero! He sets his own deadlines.” And then he shouted, “Who gave you the right, comrade Khenokh, to establish your own deadlines in place of the government’s?” After the meeting, Khenokh remarked sadly to Medvedev, “We ourselves tell lies and teach our subordinates to lie. A lie even with a noble purpose is still a lie. And no good will come of it.”4
This attitude at the top naturally affected attitudes lower down in the hierarchy. Zhores Medvedev quotes one of the day-shift operators at Chernobyl who explained that, under the same circumstances, he too might have violated regulations, as the night-shift operator had done:
Why? Let me try to explain…. Firstly, we often don’t see the need to observe our laws to the letter because these laws are broken all around us before our eyes—and quite often!…Can it really be that the Government Commission that accepted block 4 as ready for operation did not know that it was accepting it incomplete? Of course they knew…. If you look more deeply, then the accident started not at 1.23 on 26 April 1986, but in December 1983, when the director of the AES, Bryukhanov, put his signature on the document of the Government Commission…without seeing the necessity of insisting that the run-down unit of the turbogenerator was tested…. And our Moscow comrades needed that rundown unit even less. They said, “The fourth block has been put into operation and will go into the report for this year. That’s good.”
Victor G. Snell, "The Cause of the Chernobyl Accident," in David R Marples, ed., The Social Impact of the Chernobyl Disaster (St. Martin's, 1988), p. 16. Snell provides a particularly clear summary of the sequence of events that led to the accident, and I have drawn on it here.↩
See David Joravsky's review of Medvedev's The Rise and Fall of T.D. Lysenko, in The New York Review (January 29, 1970).↩
Zhores A. Medvedev, Nuclear Disaster in the Urals (Norton, 1979).↩
Grigorii Medvedev, Chernobyl'skaia Khronika (Moscow: Sovremennik, 1989), p. 23.↩
Victor G. Snell, “The Cause of the Chernobyl Accident,” in David R Marples, ed., The Social Impact of the Chernobyl Disaster (St. Martin’s, 1988), p. 16. Snell provides a particularly clear summary of the sequence of events that led to the accident, and I have drawn on it here.↩
See David Joravsky’s review of Medvedev’s The Rise and Fall of T.D. Lysenko, in The New York Review (January 29, 1970).↩
Zhores A. Medvedev, Nuclear Disaster in the Urals (Norton, 1979).↩
Grigorii Medvedev, Chernobyl’skaia Khronika (Moscow: Sovremennik, 1989), p. 23.↩