Chornobyl: 25th Anniversary

Chornobyl: 25th Anniversary
News and Events

Backgrounder – Chornobyl Disaster

The Chornobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chornobyl Nuclear Power Plant in Ukraine. It is considered the worst nuclear power plant accident in history, and it is the only one to be classified as a level 7 event on the International Nuclear Event Scale.

The disaster began during a systems test on 26 April 1986 at reactor number four of the Chornobyl plant, which is near the town of Pripyat, Ukraine. There was a sudden power output surge, and when an emergency shutdown was attempted, a more extreme spike in power output occurred, which led to a reactor vessel rupture and a series of explosions. This event exposed the graphite moderator of the reactor to air, causing it to ignite. The resulting fire sent a plume of highly radioactive smoke fallout into the atmosphere and over an extensive geographical area, including Pripyat. The plume drifted over large parts of Ukraine, Belarus andEurope. From 1986 to 2000, 350,400 people were evacuated and resettled from the most severely contaminated areas of Belarus, Russia, and Ukraine. According to official post-Soviet data, about 60% of thefallout landed in Belarus.

The accident raised concerns about the safety of the Soviet nuclear power industry, as well as nuclear power in general, slowing its expansion for a number of years and forcing the Soviet government to become less secretive about its procedures.

Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chornobyl accident. Thirty one deaths are directly attributed to the accident, all among the reactor staff and emergency workers, though estimates of the number of deaths potentially resulting from the accident vary enormously; the World Health Organization (WHO) suggest it could reach 4,000 while a Greenpeace report puts this figure at 200,000 or more.

On 26 April 1986, at 01:23, reactor four suffered a catastrophic power increase, leading to explosions in its core. This dispersed large quantities of radioactive fuel and core materials into the atmosphere and ignited the combustible graphite moderator. The burning graphite moderator increased the emission of radioactive particles, carried by the smoke, as the reactor had not been encased by any kind of hard containment vessel. The accident occurred during an experiment scheduled to test a potential safety emergency core cooling feature, which took place during the normal shutdown procedure.

Read more at http://www.ucc.ca/2011/04/06/backgrounder-chornobyl-disaster/