Tšernobõl, Chernobyl (0)

The Chernobyl accident in 1986 was the result of a flawed reactor design that was operated with inadequately trained personnel. The resulting steam explosion and fires released at least 5% of the radioactive reactor core into the atmosphere and downwind. Two Chernobyl plant workers died on the night of the accident, and a further 28 people died within a few weeks as a result of acute radiation poisoning.
The April 1986 disaster at the Chernobyl nuclear power plant in the Ukraine was the product of a flawed Soviet reactor design coupled with serious mistakes made by the plant operators.  It was a direct consequence of Cold War isolation and the resulting lack of any safety culture.
The accident destroyed the Chernobyl 4 reactor, killing 30 operators and firemen within three months and several further deaths later . Acute radiation syndrome was originally diagnosed in 237 people on-site and involved with the clean -up. Of these , 28 people died as a result of it within a few weeks of the accident. Nobody off-site suffered from acute radiation effects although a large proportion of childhood thyroid cancers diagnosed since the accident is likely to be due to intake of radioactive iodine fallout. Furthermore , large areas of Belarus , Ukraine, Russia and beyond were affected .
The Chernobyl site and plant
The Chernobyl Power Complex in Ukraine consisted of four nuclear reactors. Two reactors were under construction at the time of the accident. An artificial lake was constructed to provide cooling water for the reactors.
The 1986 Chernobyl accident
On 25 April the reactor crew at Chernobyl 4 began preparing for a test to determine how long turbines would spin and supply power to the main circulating pumps following a loss of main electrical power supply. This test had been carried out at Chernobyl the previous year, but the power from the turbine ran down too rapidly, so new voltage regulator designs were to be tested.
A series of operator actions, including the disabling of automatic shutdown mechanisms, preceded the attempted test early on 26 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 rapid steam production and an increase in pressure. The overpressure caused the cover plate of the reactor to become partially detached, rupturing the fuel channels and jamming all the control rods, which by that time were only halfway down. Intense steam generation then spread throughout the whole core causing a steam explosion and releasing fallout to the atmosphere. The second explosion threw out fragments from the fuel channels and hot graphite.
The graphite and fuel started a number of fires, causing the main release of radioactivity into the environment. From the second to tenth day after the accident, some 5000 tonnes of boron, dolomite, sand , clay and lead were dropped on to the burning core by helicopter in an effort to extinguish the blaze and limit the release of radioactive particles .

Immediate impact

Most of the released gases and fallouts were deposited close by as dust and debris, but the lighter material was carried by wind over the Ukraine, Belarus, Russia and to some extent over Scandinavia and Europe .
The casualties included firefighters who attended the fires. All these were put out in a few hours , but radiation doses on the first day were extremely high causing 28 deaths. Also the people involved in the clean-up received high doses of radiation.
Environmental and health effects
Studies in the Ukraine, Russia and Belarus say that over one million people possibly affected by radiation. By 2000, about 4000 cases of thyroid cancer had been diagnosed in exposed children . Ten years after the explosion, more and more children that survived the incident are developing cancer. Also the children who are born from parents exposed to high radiation levels may be in threat of deformities
Thyroid cancer is usually not fatal if diagnosed and treated early. Apart from the cancer, there is said to be no evidence of a major public health impact 14 years after the accident. There is little evidence of any increase in leukaemia, even among clean-up workers where it might be most expected. However many of those who survived the explosion might turn up with cancer some 20 years from the accident.

Progressive closure of the Chernobyl plant

In the early 1990s, some 400 million dollars was spent on improvements to the remaining reactors at Chernobyl to enchance their safety. Energy shortages necessitated the continued operation of one of them until December 2000. Unit 2 was shut down after a turbine hall fire in 1991, and unit 1 at the end of 1997.
Workers and their families now live in a new town, 30 km from the plant. This was built following the evacuation.
Ukraine depends upon Russia for energy supplies, particularly oil and gas, but also nuclear fuel. Although this dependence is gradually being reduced, continued operation of nuclear power stations is now even more important than in 1986.
When it was announced in 1995 that the two operating reactors at Chernobyl would be closed by 2000, a memorandum of understanding was signed by Ukraine and G7 nations to progress this, but its implementation was delayed. Alternative generating capacity was needed, either gas- fired or nuclear. Construction of these was halted in 1989 but then resumed, and both reactors came on line late in 2004.

Chernobyl today

Chernobyl unit 4 is now enclosed in a large concrete shelter which was built quickly to allow continuing operation of the other reactors. However, the structure is neither strong nor durable. Some 200 tonnes of highly radioactive material still remains deep within it.A new concrete and steel coffin is to be constructed around the radioactive reactor.