Test triggers nuclear disaster at Chernobyl | April 26, 1986

Seems like only yesterday.

S E E D E D   C O N T E N T

On April 26, 1986, the world's worst nuclear power plant accident occurs at the Chernobyl nuclear power station in the Soviet Union. Thirty-two people died and dozens more suffered radiation burns in the opening days of the crisis, but only after Swedish authorities reported the fallout did Soviet authorities reluctantly admit that an accident had occurred.

The Chernobyl station was situated at the settlement of Pripyat, about 65 miles north of Kiev in the Ukraine. Built in the late 1970s on the banks of the Pripyat River, Chernobyl had four reactors, each capable of producing 1,000 megawatts of electric power. On the evening of April 25, 1986, a group of engineers began an electrical-engineering experiment on the Number 4 reactor. The engineers, who had little knowledge of reactor physics, wanted to see if the reactor's turbine could run emergency water pumps on inertial power.

Children Testing Gas Masks for the US Government

As the Cold War wore on, the American government became increasingly concerned about a potential Soviet strike on the U.S. mainland. In this footage from the early 1960's, children are used to test the effectiveness of gas masks.

2:18m watch

As part of their poorly designed experiment, the engineers disconnected the reactor's emergency safety systems and its power-regulating system. Next, they compounded this recklessness with a series of mistakes: They ran the reactor at a power level so low that the reaction became unstable, and then removed too many of the reactor's control rods in an attempt to power it up again. The reactor's output rose to more than 200 megawatts but was proving increasingly difficult to control. Nevertheless, at 1:23 a.m. on April 26, the engineers continued with their experiment and shut down the turbine generator to see if its inertial spinning would power the reactor's water pumps. In fact, it did not adequately power the water pumps, and without cooling water the power level in the reactor surged.

To prevent meltdown, the operators reinserted all the 200-some control rods into the reactor at once. The control rods were meant to reduce the reaction but had a design flaw: graphite tips. So, before the control rod's five meters of absorbent material could penetrate the core, 200 graphite tips simultaneously entered, thus facilitating the reaction and causing an explosion that blew off the heavy steel and concrete lid of the reactor. It was not a nuclear explosion, as nuclear power plants are incapable of producing such a reaction, but was chemical, driven by the ignition of gases and steam that were generated by the runaway reaction. In the explosion and ensuing fire, more than 50 tons of radioactive material were released into the atmosphere, where it was carried by air currents.

A view of the Chernobyl Nuclear power plant three days after the explosion. Considered history's worst nuclear accident, the Chernobyl disaster on April 26, 1986 killed 31 people directly, many due to radiation poisoning during the cleanup. The area around the plant remains so contaminated that it's officially closed off to human habitation.    (Hone/Gamma-Rapho/Getty Images)

The Elephants Foot of the Chernobyl disaster is shown in the immediate aftermath of the meltdown. The Elephants Foot, named for its appearance, is a solid mass made of melted nuclear fuel mixed with lots of concrete, sand and core sealing material that the fuel had melted through. It lies in a basement area under the original location of the core.  (Universal History Archive/UIG/Getty Images)

A technician in one of the reactors of the Chernobyl nuclear power plant tests for high levels of radiation in May 1986 after the accident.  (Govfoto/UIG/Getty Images)

Under the sarcophagus, some 130 feet below ground, at the epicenter of the explosion, liquidator Georgi Reichtmann, a Chernobyl engineer, measures radiation levels in 1990.  (Igor Kostin/Sygma/Getty Images)

Over a hurried construction period of 206 days, crews erected a steel and cement sarcophagus to entomb the damaged reactor. Here, an employee stands in front of a radiation sign at the sarcophagus a few years after its construction. A 35,000-ton New Safe Confinement was built on tracks and then slid over the damaged reactor and existing sarcophagus in November 2016.  (Igor Kostin/Sygma/Getty Images)

The evacuation of 47,000 inhabitants of Pripyat in over a thousand buses, only took a few hours as local people were told to take few personal belongings and identity papers, as it was thought they would be returning several days later. Most would never return to their homes.  (Igor Kostin/Sygma/Getty Images)

A man scans his produce for radioactivity after the Chernobyl accident in May 1986 in Strasbourg, France.  (Dominique Gutekunst/Gamma-Rapho/Getty Images)

In this 2016 aerial view, a Soviet-era hammer and sickle stands on top of an abandoned apartment building in the ghost town of Pripyat not far from the Chernobyl nuclear power plant.  (Sean Gallup/Getty Images)

Pupils' chairs stand on rotting floorboards in an auditorium of abandoned School Number 3 on September 30, 2015 in Pripyat, Ukraine. Pripyat lies only a couple miles from the former Chernobyl nuclear power plant and was built in the 1970s to house the plant's workers and their families.  (Getty Images / Sean Gallup)

Bumper cars at a fair rust away in the ghost town of Pripyat, which was evacuated following the disaster. Today Pripyat remains a ghost-town, its apartment buildings, shops, restaurants, hospital, schools, cultural center and sports facilities derelict and its streets overgrown with trees. The city lies in the inner exclusion zone around Chernobyl where persistently high levels of radiation make the area uninhabitable for thousands of years to come.  (Igor Kostin/Sygma/Getty Images)

On April 27, Soviet authorities began an evacuation of the 30,000 inhabitants of Pripyat. A cover-up was attempted, but on April 28 Swedish radiation monitoring stations, more than 800 miles to the northwest of Chernobyl, reported radiation levels 40 percent higher than normal. Later that day, the Soviet news agency acknowledged that a major nuclear accident had occurred at Chernobyl.

In the opening days of the crisis, 32 people died at Chernobyl and dozens more suffered radiation burns. The radiation that escaped into the atmosphere, which was several times that produced by the atomic bombs dropped on Hiroshima and Nagasaki, was spread by the wind over Northern and Eastern Europe, contaminating millions of acres of forest and farmland. An estimated 5,000 Soviet citizens eventually died from cancer and other radiation-induced illnesses caused by their exposure to the Chernobyl radiation, and millions more had their health adversely affected. In 2000, the last working reactors at Chernobyl were shut down and the plant was officially closed.

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