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The Fukushima nuclear disaster is a series ofequipment failures, nuclear meltdowns, andreleases of radioactive materials at the Fukushima Nuclear Power Plant, following the 9.0

magnitude earthquake and tsunami on 11 March 2011. The plant comprises six separateboilingwater reactors maintained by the Tokyo Electric Power Company (TEPCO). This accident is the

largest of the 2011 Japanese nuclear accidents arising from the earthquake and tsunami, and

experts consider it to be the second largest nuclear accident after the Chernobyl disaster, butmore complex as multiple reactors are involved.

At the time of the quake, Reactor 4 had been de-fueled while 5 and 6 were in cold shutdown forplanned maintenance. The remaining reactors shut down automatically after the earthquake, with

emergency generators starting up to run the control electronics and water pumps needed to coolreactors. The plant was protected by a seawall designed to withstand a 5.7 m (19 ft) tsunami but

not the 14 m (46 ft) maximum wave which arrived 4160 minutes after the earthquake.The entireplant was flooded, including low-lying generators and electrical switchgear in reactor basements

and external pumps for supplying cooling seawater. The connection to the electrical grid wasbroken. All power for cooling was lost and reactors started to overheat, owing to natural decay of

the fission products created before shutdown. The flooding and earthquake damage hinderedexternal assistance.

Reactors 1, 2 and 3 experienced a full meltdown. Hydrogen explosions destroyed the upper

cladding of the buildings housing Reactors 1, 3, and 4; an explosion damaged the containment ofreactor 2; multiple fires broke out at Reactor 4. With the remnants of its reactor core fallen to the

bottom of its damaged reactor vessel, Unit 1 continues to leak cooling water approaching threemonths after the initial events; similar conditions are hypothesized to exist at the other two

melted-down reactors in the complex.

Despite being initially shut down, Reactors 5 and 6 began to overheat. Fuel rods stored in pools

in each reactor building began to overheat as water levels in the pools dropped. Fears ofradioactivity releases led to a 20 km (12 mi) radius evacuation around the plant while workers

suffered radiation exposure and were temporarily evacuated at various times. One generator atUnit 6 was restarted on 17 March allowing some cooling at Units 5 and 6 which were least

damaged. Grid power was restored to parts of the plant on 20 March, but machinery for Reactors

1 through 4, damaged by floods, fires and explosions, remained inoperable

The Chernobyl disaster (locally, Chornobyl Catastrophe) was a nuclear accident that occurredon 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine (officially Ukrainian SSR),

which was under the direct jurisdiction of the central Moscow's authorities. An explosion andfire released large quantities of radioactive contamination into the atmosphere, which spread

over much of Western USSR and Europe. It is considered the worst nuclear powerplant accidentin history, and is one of only two classified as a level 7 event on the International Nuclear Event

Scale (the other being the Fukushima I nuclear accidents).The battle to contain the contaminationand avert a greater catastrophe ultimately involved over 500,000 workers and cost an estimated

18 billion rubles, crippling the Soviet economy

The disaster began during a systems test on Saturday, 26 April 1986 at reactor number four ofthe Chernobyl plant, which is near the city ofPrypiat and within a close proximity to the

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administrative border with Belarus and Dnieperriver. 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 ofexplosions. These events exposedthe graphitemoderatorof 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 the western Soviet Union and Europe.From 1986 to 2000, 350,400 people were evacuated and resettled from the most severelycontaminated areas ofBelarus, Russia, and Ukraine. According to official post-Soviet data,about

60% of the fallout landed in Belarus.

The accident raised concerns about the safety of the Soviet nuclear power industry, as well asnuclear 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 substantialdecontamination and health care costs of the Chernobyl accident. A report of the International

Atomic Energy Agency, examines the environmental consequences of the accident. Estimates ofthe number of deaths potentially resulting from the accident vary enormously: Thirty one deaths

are directly attributed to the accident, all among the reactor staff and emergency workers. AUNSCEARreport places the total confirmed deaths from radiation at 64 as of 2008. The World

Health Organization (WHO) suggests it could reach 4,000.A 2006 report predicted 30,000 to60,000 cancer deaths as a result of Chernobyl fallout.A Greenpeace report puts this figure at

200,000 or more.A Russian publication, Chernobyl, concludes that 985,000 excess deathsoccurred between 1986 and 2004 as a result of radioactive contamination.