Fukushima Nuclear Disaster

The Fukushima Daiichi nuclear disaster is a series of equipment failures, nuclear meltdowns, and releases of radioactive materials at the Fukushima I Nuclear Power Plant, following the Tōhoku earthquake and tsunami on 11 March 2011. It is the largest nuclear disaster since the Chernobyl disaster of 1986.

The plant comprises six separate boiling water reactors originally designed by General Electric (GE), and maintained by the Tokyo Electric Power Company (TEPCO). At the time of the quake, Reactor 4 had been de-fuelled while 5 and 6 were in cold shutdown for planned maintenance. The remaining reactors shut down automatically after the earthquake, and emergency generators came online to control electronics and coolant systems. The tsunami broke the reactors' connection to the power grid and also resulted in flooding of the rooms containing the emergency generators. Consequently those generators ceased working and the pumps that circulate coolant water in the reactor ceased to work, causing the reactors to begin to overheat. The flooding and earthquake damage hindered external assistance.

In the hours and days that followed, reactors 1, 2 and 3 experienced full meltdown. As workers struggled to cool and shut down the reactors, several hydrogen explosions occurred. The government ordered that seawater be used to attempt to cool the reactors—this had the effect of ruining the reactors entirely. As the water levels in the fuel rods pools dropped, they began to overheat. Fears of radioactivity releases led to a 20 km (12 mi)-radius evacuation around the plant. During the early days of the accident workers were temporarily evacuated at various times for radiation safety reasons. Electrical power was slowly restored for some of the reactors, allowing for automated cooling.

Japanese officials initially assessed the accident as Level 4 on the International Nuclear Event Scale (INES) despite the views of other international agencies that it should be higher. The level was successively raised to 5 and eventually to 7, the maximum scale value. The Japanese government and TEPCO have been criticized in the foreign press for poor communication with the public and improvised cleanup efforts. On 20 March, the Chief Cabinet Secretary Yukio Edano announced that the plant would be decommissioned once the crisis was over.

The Japanese government estimates the total amount of radioactivity released into the atmosphere was approximately one-tenth as much as was released during the Chernobyl disaster. Significant amounts of radioactive material have also been released into ground and ocean waters. Measurements taken by the Japanese government 30–50 km from the plant showed caesium-137 levels high enough to cause concern, leading the government to ban the sale of food grown in the area. Tokyo officials temporarily recommended that tap water should not be used to prepare food for infants.

On 24 May 2012, more than a year after the disaster, TEPCO released their estimate of radioactive material emitted due to the Fukushima Daiichi Nuclear Disaster. An estimated 538.1 PBq of non noble gas radionuclides iodine-131, caesium-134 and caesium-137 was released. This 520 PBq of radioactive material was released into the atmosphere between 12 March to 31 March 2011 and 18.1 PBq into the ocean from 26 March to 30 September 2011. This represents 10% of the 5300 PBq of non noble gas radionuclides released in the 1986 Chernobyl disaster. A total of 511 PBq of iodine-131 was released into both the atmosphere and the ocean, 13.5 PBq of caesium-134 and 13.6 PBq of caesium-137.

In May 2012, TEPCO reported that at least 900 PBq had been released "into the atmosphere in March last year [2011] alone".

A few of the plant's workers were severely injured or killed by the disaster conditions resulting from the earthquake. There were no immediate deaths due to direct radiation exposures, but at least six workers have exceeded lifetime legal limits for radiation and more than 300 have received significant radiation doses. Predicted future cancer deaths due to accumulated radiation exposures in the population living near Fukushima have ranged from none to 100 to a non-peer-reviewed "guesstimate" of 1,000. Fear of ionizing radiation could have long-term psychological effects on a large portion of the population in the contaminated areas. On 16 December 2011 Japanese authorities declared the plant to be stable, although it would take decades to decontaminate the surrounding areas and to decommission the plant altogether.