Chernobyl

On April 26, 1986, an accident occurred at Unit 4 of the Chernobyl nuclear power plant in the former Ukrainian Republic of the Union of Soviet Socialist Republics, near the present borders of Belarus, the Russian Federation, and Ukraine. The accident destroyed the reactor, contaminated large areas surrounding the reactor, and led to an increase in radiation levels over practically the whole of the northern hemisphere.

The Chernobyl power station consisted of four Soviet-designed light water–cooled graphite-moderated (RBMK) reactors of 950 MW each. These units used graphite to moderate the nuclear reaction and used water flowing through channels holding the fuel elements to cool it. There was no containment structure. The immediate causes of the accident were a flawed reactor design coupled with serious mistakes made by the plant operators during a test procedure when many control systems had been deliberately overridden. There had been little communication between those responsible for the test and the plant operators, formal safety approvals were either bypassed or given perfunctory attention, and the experiment carried out on a less well-resourced night shift when it had been scheduled as a daytime activity.

The greatest doses of radiation were received by 200,000 workers, called liquidators, who participated in the cleanup. Thirty-one people died almost immediately; 237 occupationally exposed individuals were admitted to hospital with clinical symptoms attributable to radiation exposure, of whom 14 died over the next 10 years. This was the only time when radiationrelated fatalities occurred in a commercial nuclear power plant.

Those in the affected areas learned about the nature of the event and its hazards not from authoritative reports but from hearsay and international reports. This lack of transparency lowered public confidence. Some contemporary media reports emphasized the potential dangers, and thousands of mothers-to-be aborted unborn children. Evacuation of residents [Page 281]began the day after the accident and continued into August. The 116,000 people who were evacuated and those who remained living in the less affected regions will, over their lifetimes, receive doses of radiation comparable with doses they would receive from natural sources. Demographic indicators in the “contaminated” regions have worsened as people have been resettled or have migrated. Economic activity has also been limited.

A significant increase in the incidence of thyroid cancer among those in the affected areas, who were children in 1986, is directly linked to the accident, and continued incidence among exposed residents is expected. These cancers are not usually fatal if diagnosed and treated early. Other health effects have been reported but none have been confirmed as directly related to the accident.

Some radiosensitive local ecosystems received lethal doses in the first few weeks after the accident. Within 3 years the natural environment in these localities had begun to recover and no sustained severe impacts on animal populations or ecosystems have been observed. Long-term genetic effects remain a possibility, and some groups attribute many thousands of deaths to the accident. A concrete shell or sarcophagus was constructed around the destroyed reactor, which has provided protection since its construction. Its stability and the quality of its confinement are in doubt.

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