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.
Photo:
The Bridge of Death!
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.
