B) Chernobyl Accident

The accident, which was of global concern was the accident in Ukraine in the Chernobyl power plant located in Polesye on the River

Pripyat.

On 26 April, 1986, Unit 4 of the Chernobyl nuclear plant suffered a major accident. The Chernobyl 4 reactor was a graphite-moderated, light-water-cooled system. The installed electrical generating capacity was 1 GW. The accident followed some engineering tests of a generator.

During the tests, basic operating safety rules were being violated. Most control rods were withdrawn from the core and the safety systems were switched off. Two explosions and a fire that followed them dam­aged the reactor and the containment building. The graphite started to burn. Explosive energy was released, which resulted in the 1000 ton cover plate of the reactor being lifted up.

A prolonged release of large quantities of radioactive products transported by the cloud from Chernobyl was detected not only in northern and southern Europe but also in Canada, Japan, and the US.

The major part of the release took place over the period of about ten days. There were two peaks in release rate (26th April and 5th May). Later on, the release continued for many weeks at a lower rate before the destroyed reactor was finally sealed, which took place some five months later.

Initially the cloud of radioactive material was carried over the Baltic Sea into Scandinavia. After a few days the wind direction rotated clockwise and the cloud travelled eastwards across the USSR and southwards to Turkey.

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Monday 28 April 1966

Wednesday 30 April 1986

Saturday 3 May 1986

Saturday 26 April 1986

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The total mass of the radioactive particles released in the accident was about 6000-8000 Kg. More than half of it was deposited near the plant but the rest travelled thousands of kilometres (see Fig. 26).

There is no doubt that the nuclear plant accidents offer a number of lessons to be learnt.

At present, over 200 nuclear power reactors for commercial elec­tricity production operate in Europe.

The accident at the Chernobyl nuclear plant has shown that large-scale accidents in nuclear power plants can lead to contamination of the entire continent.

1. What was the cause of the Chernobyl accident?

2. What was the path of the radioactive material released in the accident?

3. What can accidents at the nuclear plants lead to?

4. Make a talk on the Chernobyl accidents (use Fig. 26).

Fig. 26. Areas covered by the main body of the cloud on various days during

the release.

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