7/14/2023 0 Comments Nuke reactor meltdownLarge amounts of water contaminated with radioactive isotopes were released into the Pacific Ocean during and after the disaster. All told, some 110,000 residents were evacuated from the communities surrounding the plant due to the rising off-site levels of ambient ionizing radiation caused by airborne radioactive contamination from the damaged reactors. In the days after the accident, radiation released into the atmosphere forced the government to declare an ever-larger evacuation zone around the plant, culminating in an evacuation zone with a 20 kilometres (12 mi) radius. The spent fuel pool of the previously shut-down Reactor 4 increased in temperature on 15 March due to decay heat from newly added spent fuel rods, but did not boil down sufficiently to expose the fuel. The resulting loss of reactor core cooling led to three nuclear meltdowns, three hydrogen explosions, and the release of radioactive contamination in Units 1, 2 and 3 between 12 and 15 March. This flooding caused the failure of the emergency generators and loss of power to the circulating pumps. However, the earthquake had also generated a tsunami 14 metres (46 ft) high that arrived shortly afterwards, swept over the plant's seawall, and then flooded the lower parts of the reactor buildings at units 1–4. This continued circulation was vital to remove residual decay heat, which continues to be produced after fission has ceased. Critically, these were required to provide electrical power to the pumps that circulated coolant through the reactors' cores. Because of these shutdowns and other electrical grid supply problems, the reactors' electricity supply failed, and their emergency diesel generators automatically started. On detecting the earthquake, the active reactors automatically shut down their normal power-generating fission reactions. The accident was triggered by the Tōhoku earthquake and tsunami, which occurred in the Pacific Ocean about 72 kilometres (45 mi) east of the Japanese mainland at 14:46 JST on Friday, 11 March 2011. While the 1957 explosion at the Mayak facility was the second worst by radioactivity released, the INES ranks incidents by impact on population, so Chernobyl (335,000 people evacuated) and Fukushima (154,000 evacuated) rank higher than the 10,000 evacuated from the Mayak site in the rural southern Urals. The result was the most severe nuclear accident since the Chernobyl disaster in 1986, classified as level seven on the International Nuclear Event Scale (INES) after initially being classified as level five, and thus joining Chernobyl as the only other accident to receive such classification. The earthquake triggered a powerful tsunami, with 13- to 14-meter-high waves damaging the nuclear power plant's emergency diesel generators, leading to a loss of electric power. The proximate cause of the disaster was the Tōhoku earthquake and tsunami, which remains the most powerful earthquake ever recorded in Japan. On 11 March 2011, a nuclear accident occurred at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan. ġ6 with physical injuries due to hydrogen explosions, Ģ workers taken to hospital with possible radiation burns ģ7☂5′17″N 141☁′57″E / 37.42139°N 141.03250☎ / 37.42139 141.03250 Coordinates: 37☂5′17″N 141☁′57″E / 37.42139°N 141.03250☎ / 37.42139 141.03250ġ confirmed cancer death attributed to radiation exposure by the government for the purpose of compensation following opinions from a panel of radiologists and other experts, medical sources pending for long-term fatalities due to the radiation exposure. Water vapour/"steam" venting prevented a similar explosion in Unit 2. Hydrogen-air explosions in Units 1, 3, and 4 caused structural damage. The four damaged reactor buildings (from left: Units 4, 3, 2, and 1) on 16 March 2011.
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