In the middle of the night of Friday to Saturday, April 25 to 26, 1986, the reactor in Unit 4 of the Chernobyl Nuclear Power Station was being prepared for shutdown. This was a routine procedure, enabling technicians to carry out maintenance and repairs. It had been decided to use the opportunity to conduct a series of tests on the unit’s turbines. Anatoli Dyatlov, deputy chief engineer of Unit 4, was on hand, and Gennady Matlenko had come from the equipment manufacturers. Several Chernobyl engineers had also gathered in the control room, hoping to learn.
At the main control board stood Alexander Akimov, the shift foreman, and 26-year-old engineer Leonid Toptunov. As they scanned the complicated dials and gauges, they were nervous. Normally, emergency systems would come into operation automatically if anything went wrong in the reactor. But because the tests might make it appear that something was wrong those automatic emergency systems had been turned off. Akimov and Toptunov had the great responsibility of watching to see that the reactor stayed within control. The Soviet Union was chronically short of electricity, That is why the power station at Chernobyl had been built at such top speed, and the new town of Pripyat
had sprung up to house its workers. Unit 4 had begun operating in March 1984, without time for certain tests.
Unit 4 had begun operating in March 1984, without time for certain tests to be carried out. It was crucial to the electric power grid at Kiev, the country’s third largest city. That very Friday an order to postpone shutdown had arrived after the procedure had started-because Unit 4’s output was urgently needed. Late at night, permission to resume the procedure had finally been given. Shutdown involves lowering control rods into the core of a reactor (see page 30) to reduce its power to a minimum. Around midnight, Akimov and Toptunov realized that the power of the reactor had sunk too low for the tests to go ahead. All their training told them it would now be best to shut down the reactor and abandon the tests.
But Dyatlov, their superior, became impatient. The tests on the turbines had already been postponed once. He blamed the men’s incompetence and ordered the control rods to be withdrawn immediately to increase power. Reluctantly Akimov and Toptunov obeyed. By 1:00 A.M. power had risen just high enough for the tests on the turbines to start Seconds later, it was clear to the operators that things were going badly wrong. There was an enormous surge of power. Water flow through the reactor core increased, putting pressure on the pumps and causing vibrations in the pipes. The workers tried to adjust matters, but it was hard to know what was happening. At 1:23 A.M. the dials indicated a dangerous surge in power and radiation. Akimov shouted to Dyatlov that he was going to push the emergency AZ button to lower all the control rods into the core. There were several loud thuds. The descending control rods had jammed. Simultaneously there was a terrible tremor, described afterward as being like an earthquake. Reactor 4 had exploded. The force of the explosion was so great that it blew the 2,200-ton steel lid off the top of the core and dislodged the concrete outer shield. A huge fire followed.
As yet, none of those on duty believed the core had been demolished. In the confusion, men were sent off through dark wrecked passageways. Two were told to try to lower the rods manually-an impossibility. Others were sent to try to turn the huge valves of the emergency cooling system, knee-deep in radioactive water. Four men climbed from the 12th to the 35th level, and looked down. It was like looking into the crater of a burning volcano.
Firefighters arrived and battled heroically to prevent the fire from spreading to Unit 3. With no special protective clothing, they climbed the outer stairways and directed their hoses at the burning roof of the turbine hall. The bitumen was melting under their feet, ignited by chunks of black burning graphite from the reactor core. After a short while, many began to feel sick and were carried away.
By 4:00 A.M. fire crews were arriving from Kiev, 62 miles (100 km) away, and by 5:00 A.M. the fire on the roof had been brought under control. A security cordon had been placed around the Chernobyl complex, and guards checked everyone going in or out. The Soviet Union was a society where people were used to obeying orders from officialdom. No one felt authorized to shut down the other reactors. No one decided on an evacuation. No one warned the people of Pripyat. At the other three reactors, shifts of workers arrived and left as normal. At Unit 5, still under construction, building work did not stop. With daylight came a message: a government commission had been appointed and would arrive later that day. Meanwhile, everyone was to avoid panic.
At 10:00 A.M. on Saturday a team of experts arrived from Moscow. It was estimated that the temperature in the reactor core was at least 4,500° F (2482° C). The core might go on burning for weeks or months. It was decided to try to smother the fire with sacks of sand dropped from helicopters. The sand would be mixed with lead, boron, and dolomite to try to block the radiation that was rising in vapor from the inferno. Men rushed to commandeer supplies, including sand from the riverbanks. In the next few days hundreds of helicopter sorties were made, at great risk to the pilots. They had to fly low enough to hit their target, while avoiding the many pylons and tall chimneys. They suffered in the intense heat that rose from the core and were given iodine pills to counteract the effects of radiation.
It was not until Sunday morning that an official announcement was made that the town’s inhabitants were to be evacuated. Hundreds of buses were ready and waiting. From early afternoon 50,000 people, including 17,000 children, carrying a few hastily packed belongings, began to board. Most thought they would be away from Pripyat for two to three days. In fact, they were never to return.
On Monday, April 28, 1,000 miles (1,600 km) to the north, monitors in Sweden detected high levels of radiation. At first, it was assumed there had been a Soviet nuclear weapons test. But analysis showed that the radionuclides (radioactive atoms) were from a nuclear reactor. When Swedish diplomats urgently contacted Moscow, they received only denials. Finally, the Soviet authorities realized that they could no longer hide the truth. At 9:00 P.M.–the end of the third day – a statement was issued to the world by the official Soviet news agency TASS. The same statement was broadcast on Moscow television’s news program “Vremya.”
On May 1 the annual May Day parades went ahead in Moscow and Kiev. Crowds of people were on the streets enjoying the sunshine. But the danger was far from over. For one thing, the emission of radionuclides from the burning reactor started to increase again. What was happening? Had smothering the fire caused it to become hotter? Could it be burning downward, through the concrete base? Below, it might react with water to produce an explosion even greater than the first one.
Three men went on a dangerous mission to check conditions below the reactor. Then another three men dived into highly radioactive water to open valves to drain the bubbler pool, a large water reserve beneath the reactor. On May 6 radionuclide emissions suddenly decreased. On May 7 the pumping out of contaminated water from the flooded basement was completed. On May 9 the fire was still visible but, after a further 80 tons of lead had been dropped the next day, the glow ceased. At great human cost the fire had been prevented from spreading to other reactors in the
Chernobyl complex, and the danger of a second explosion had been averted. However, no one could foresee the long-term human, political, and environmental repercussions of the disaster at Chernobyl.
Once the immediate danger of a second explosion tackle the enormous problem of cleaning up after the accident and trying to prevent radioactive contamination from spreading farther. To protect them from radiation, men involved in the cleanup put on aprons of soft lead underneath overalls of rubberized lead. At Unit 4, the graphite had burned out, and the temperature of the reactor core had declined to about 520° F (271° C). but the condition of the nuclear fuel inside was not known. Moreover, lumps of graphite and uranium had been spewed out by the explosion across a wide area, including the roof of Unit 3.
Aerial photographs showed glowing spots where fragments of nuclear fuel had been cast on the ground. These were covered with concrete by remote- controlled bulldozers flown in by transport aircraft. The highly radioactive graphite on the roof posed a more difficult problem. Mobile robots bought from Germany proved unable to function on the melted bitumen of the roof. The only answer was to use humans. It was calculated that, in protective clothing, a person could spend between one and two minutes on the roof before accumulating the maximum dose of radiation considered allowable for a whole lifetime. Young soldiers and men press-ganged for the purpose were sent up the staircase leading to the roof.
One after the other they ran with a shovel, scooped up the radioactive fragments, rushed to the edge and threw them into the abyss of the burned-out shell of Unit 4, then hurried to take cover behind a concrete wall. Even though they were given protective clothing, the men feared for themselves and for any children they might have in the future, because of the genetic damage likely to be caused by the radiation. The danger came not only from the graphite and uranium, but from dust that now covered the whole area, including the abandoned town of Pripyat.
A large swathe of forest was singed brown: wildlife and domestic animals lay dead or foraged weakly for food. There was no simple solution to such widespread contamination. Trees were felled but could not be burned because the smoke and ash would be radio- active. In the months that followed, vast pits were dug and lined with concrete. Into them were pitched contaminated trees, vehicles, and topsoil.
The worst fear was that contamination would be washed into streams feeding the Pripyat and Dnieper rivers. The Kiev Sea and the waters of the Dnieper, on its way to the Black Sea, supply drinking water to 50 million people. Rain was forecast, so time was short. In just over a week-a seemingly impossible timescale a subterranean wall was built between the reactor and the Pripyat River to contain radioactive groundwater.
Reactor 4 itself was to be encased in a huge steel and concrete shell, or sarcophagus, designed to contain radiation. Because it was feared that the core of the reactor would burn down into the earth’s crust, miners and underground railroad workers, without protective clothing, tunneled beneath the foundations. Liquid nitrogen was pumped into the soil to freeze it solid. By the end of June 1986, a huge concrete cushion was also in place beneath the reactor. Above ground, steel tanks 60 feet by 20 feet by 20 feet (18m x 6m x 6m) were hauled into position and filled with concrete to make the giant bricks of a massive wall behind which construction workers could shelter from radiation. Then work on the sarcophagus itself began. Its walls were 26 feet (8 m) thick; the concrete struts were 180 feet (55 m) high. Huge girders were stretched across the top and covered in concrete to seal the roof. By the end of September, the giant tomb was complete.
The accident at Chernobyl had exposed people to radiation between 100 and 200 times greater than that from the explosion of the Hiroshima atomic bomb. At first, a 6-mile (10 km) exclusion zone had been established around the Chernobyl complex. This was extended on May 2, 1986, to 18 miles (30 km), and further evacuations took place. Thousands of children were sent away to summer camps. Many old people resisted leaving their homes, unable to understand the calamity that had overtaken them.
High fences and warning signs were set in place around the exclusion zone, but in fact, a part of the Soviet Union nearly as large as the whole of Western Europe had been affected. Ukraine and Belorussia (now Belarus) were two of the worst-hit regions.
The accident at Chernobyl and its aftermath tested the Soviet system to breaking point. Aside from the human suffering, the cleanup cost billions of rubles, to which must be added the cost of long-term medical treatment and resettlement, and the loss of production caused by reduced power generation. So great the need for electricity that the other three units at the Chernobyl power plant were forced to continue production. There was no question of the Soviet Union’s being able to compensate other countries that had been affected by the accident.
Other nations sent doctors, experts, and equipment. For the first time in Soviet history. records of technology and details of an accident were put before the international scientific community in reports to the International Atomic Energy Agency (IAEA) in 1986 and 1987. Even so, secret protocols signed by the Politburo restricted the information released.