FUKUSHIMA DISASTER
S贸nia Leite
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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 TĹ?hoku earthquake and tsunami on 11 March 2011. The plant comprises six separate boiling water reactors originally designed by General Electric (GE), and maintained by the Tokyo Electric Power Company (TEPCO). The Fukushima disaster is the largest of the 2011 Japanese nuclear accidents and is the largest nuclear accident since the 1986 Chernobyl disaster.
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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, with emergency generators starting up to run the control electronics and water pumps needed to cool reactors. The entire plant was flooded by the 15 m (49 ft) tsunami wave, including low-lying generators and electrical switchgear in reactor basements and external pumps for supplying cooling seawater.
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The connection to the electrical grid was broken as the Tsunami destroyed the power lines. 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 hindered external assistance.
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In the hours and days that followed, reactors 1, 2 and 3 experienced full meltdown. It has been estimated that the upper 75% of the core of unit one melted and slumped into the lower quarter of the core at 15:10 on 12 March; the core mass would have cooled again as it entered the water in the bottom part of the reactor tank before reheating during the time before sea water was added at 20:20. Hydrogen explosions destroyed the upper cladding of the buildings housing Reactors 1, 3, and 4, with the explosions at Reactors 1 and 3 damaging the secondary containment of Reactor 2; multiple fires broke out at Reactor 4.
THE REAL HEROES OF FUKUSHIMA •
A group of 50 persons who worked in Fukushima have become known
as the “Fukushima 50.” This group of courageous technicians has remained at their posts throughout the reactor crisis in Japan, evacuating only briefly when radiation levels spiked during a procedure to cool the reactors with seawater.
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There has been a lot of hysterical media coverage of the Japanese nuclear crisis, but one thing is certain: the valiant efforts of the technicians have kept a lot of worst-case scenarios in check.
The
brightest moments in human history have occurred when too much was
asked of brave men and women… and they gave even more. When the history of the twenty-first century is written, the Fukushima 50 will stand among its greatest heroes.
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With the remnants of its reactor core fallen to the bottom of its damaged reactor vessel, Unit 1 continued to leak cooling water approaching three months after the initial events; similar conditions are hypothesized to exist at the other two melted-down reactors in the complex.
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Measurements taken by the Japanese science ministry and education ministry in areas of northern Japan 30–50 km from the plant showed radioactive caesium levels high enough to cause concern. Food grown in the area was banned from sale. Based on worldwide measurements of iodine-131 and caesium-137, it was suggested that the initial daily release of those isotopes from Fukushima are of the same order of magnitude as those from
Chernobyl in 1986, and that the total release of radioactivity is about one-tenth that from the Chernobyl disaster; Tokyo officials temporarily recommended that tap water should not be used to prepare food for infants.
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Plutonium contamination has been detected in the soil at two sites in the plant, although further analysis revealed that the detected densities are within limits from fallout generated from previous
atmospheric nuclear weapons tests. Two workers hospitalized with non-life threatening radiation burns on 25 March had been exposed to between 2 and 6 Sv of radiation at their ankles when standing in water in Unit 3. Follow up examination at 11 April from National Institute of Radiological Sciences was without confirmation.
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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. Foreign experts have said that a workforce in the hundreds or even thousands would take years or decades to clean up the area. On 20 March, the Chief Cabinet Secretary Yukio Edano announced that the plant would be decommissioned once the crisis was over. •
2 Years ago, Fukushima still worries all…