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Physics - The Chernobyl Incident

The 1986 Chernobyl incident

On the 25 th of April 1986, the Chernobyl power plant in Ukraine, was preparing for a test to determine how long the turbines would spin and supply the essential power to the main circulating pumps. This test had been carried out in 1985, but the power from the turbine rapidly ran down, so new voltage regulator designs were to be tested.

A series of operator actions preceded the attempted test early on the 25 th of April. By the time that the operator moved to shut down the reactor, the reactor was in an extremely unstable condition. The interaction of very hot fuel with the cooling water led to fuel fragmentation along with rapid steam production and an increase in pressure.

Intense steam generation spread throughout the whole core causing a steam explosion and releasing fission products into the Earth’s atmosphere. About two to three seconds later, a second explosion threw out fragments from the fuel channels and hot graphite.

Immediately following the incident, 31 people died, 28 of these deaths were due to radiation poisoning. The winds carried the radioactive dust as far as Wales in the UK. The incident killed 30 operators that were working at the Chernobyl 4 reactor. Nineteen individuals died between 1986 and 2004.

The Impact

Some of the casualties included fire-fighters who attended the initial fires on the roof of the turbine building. All these were put out in a few hours, but radiation doses on the first day were estimated to range up to 20,000 millisieverts (mSv), causing another 28 deaths.

The next task was to clean up the radioactivity at the site so that the remaining three reactors could be restarted, and the damaged reactor shielded more permanently. Over 200,000 individuals helped clean up during 1986 and 1987.

Chernobyl was a small town, but is now a ghost town. The incident at Chernobyl was the worst-ever nuclear incident. It was due to mistakes made by the plant operator and a design fault. The town of Chernobyl was evacuated because the number of thyroid cancers and leukaemia rose.

When it rained, the radioactive material settled on land, which contaminated it. In the UK, 9000 farms were contaminated.

Environmental and health effects of the Chernobyl incident

In 1986, the World Health Organisation (WHO) first raised concerns that the local medical scientists had incorrectly attributed various biological and health effects due to radiation exposure. Following this, the Government of the USSR requested the International Atomic Energy Agency (IAEA) to coordinate an international experts’ assessment of the incidents, environmental and health consequences.

50 field missions were conducted by 200 experts from 25 nations, significant health disorders were evident in both control and exposed groups, but, at that stage, none were related to radiation.

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