Chernobyl incident detailed story
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The Chernobyl disaster was a nuclear accident that occurred on Saturday 26 April 1986, at the No. 4 nuclear reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR. It is considered the worst nuclear disaster in history and is one of only two nuclear energy disasters rated at seven—the maximum severity—on the International Nuclear Event Scale, the other being the 2011 Fukushima Daiichi nuclear disaster in Japan.
The accident started during a safety test on an RBMK-type nuclear reactor, which was commonly used throughout the Soviet Union. The test was a simulation of an electrical power outage to aid the development of a safety procedure for maintaining cooling water circulation until the back-up generators could provide power - there is a time gap between the moment of power outage and the moment at which the back-up generators reach full power. This operating gap was about one minute and had been identified as a potential safety problem that could cause the nuclear reactor core to overheat. Three such tests had been conducted since 1982, but they had failed to provide a solution. On this fourth attempt, the test was delayed by 10 hours, so an unprepared operating shift had to perform it.
Upon test completion, the operators triggered a reactor shutdown, but a combination of unstable conditions and reactor design flaws caused an uncontrolled nuclear chain reaction instead.
The reactor explosion killed two of the reactor operating staff. In the emergency response that followed, 134 firemen and station staff were hospitalized with acute radiation syndrome due to absorbing high doses of ionizing radiation. Of these 134 men, 28 died in the days to months afterward and approximately 14 suspected radiation-induced cancer deaths followed within the next 10 years. Among the wider population, an excess of 15 childhood thyroid cancer deaths were documented as of 2011. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has, at multiple times, reviewed all the published research on the incident and found that at present, fewer than 100 documented deaths are likely to be attributable to increased exposure to radiation. Determining the total eventual number of exposure related deaths is uncertain based on the linear no-threshold model, a contested statistical model, which has also been used in estimates of low level radon and air pollution exposure. Model predictions with the greatest confidence values of the eventual total death toll in the decades ahead from Chernobyl releases vary, from 4,000 fatalities when solely assessing the three most contaminated former Soviet states, to about 9,000 to 16,000 fatalities when assessing the total continent of Europe.
Cause: Reactor design flaws and breach of protocol during simulated power outage safety test