The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986, at the Chernobyl Nuclear Power Plant in Ukraine (then in the Ukrainian Soviet Socialist Republic, part of the Soviet Union). It is considered the worst nuclear power plant accident in history and is the only level 7 event on the International Nuclear Event Scale.
The disaster occurred on 26 April 1986, at reactor number four at the Chernobyl plant, near the town of Pripyat (which had been built as home for the power plant workers) in the Ukrainian Soviet Socialist Republic, during a systems test. A sudden power output surge took place, and when an attempt was made for emergency shutdown, 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 components of the reactor to air and they ignited; the resulting fire sent a plume of radioactive fallout into the atmosphere and over an extensive geographical area, including Pripyat.
The Bridge of Death!
The nearby city of Pripyat was not immediately evacuated after the incident. Only after radiation levels set off alarms at the Forsmark Nuclear Power Plant in Sweden over one thousand miles from the Chernobyl Plant did the Soviet Union admit that an accident had occurred. Nevertheless, authorities attempted to conceal the scale of the disaster. For example, in evacuating the city of Pripyat, the following warning message was read on local radio: "An accident has occurred at the Chernobyl Nuclear Power Plant. One of the atomic reactors has been damaged. Aid will be given to those affected and a committee of government inquiry has been set up." This message gave the false impression that any damage or radiation was localized.
The evacuation began at 2 p.m. on 27 April. To speed up the evacuation, the residents were told to bring only what was necessary since the authorities said it would only be temporary and would last approximately three days. An exclusion zone of 30 km (19 mi) remains in place today. After the disaster, four square kilometers of pine forest in the immediate vicinity of the reactor turned reddish-brown and died, earning the name of the "Red Forest". Some animals in the worst-hit areas also died or stopped reproducing. Most domestic animals were evacuated from the exclusion zone, but horses left on an island in the Pripyat River 6 km (4 mi) from the power plant died when their thyroid glands were destroyed by radiation doses of 150–200 Sv. Some cattle on the same island died and those that survived were stunted because of thyroid damage. The next generation appeared to be normal. A robot sent into the reactor itself has returned with samples of black, melanin-rich radiotrophic fungi that are growing on the reactor's walls.
The plume drifted over large parts of the western Soviet Union, Eastern Europe, Western Europe, and Northern Europe. Large areas in Ukraine, Belarus, and Russia had to be evacuated, with over 336,000 people resettled. According to official post-Soviet data, about 60% of the fallout landed in Belarus.
Four hundred times more radioactive material was released during this disaster than had been by the atomic bombing of Hiroshima. Despite the accident, Ukraine continued to operate the remaining reactors at Chernobyl for many years. The last reactor at the site was closed down in 2000, 14 years after the accident.