Radiation Exposures Due to the Chernobyl Accident

The 1986 accident at the Chernobyl nuclear power plant in the former Soviet Union was the most severe accident in the history of civilian nuclear power. In addition to causing large radiation exposures to the workers involved in emergency and clean-up tasks, the accident caused the largest uncontrolled radioactive release into the environment ever recorded for any civilian operation; large quantities of radioactive substances were released into the atmosphere for about 10 days. The radioactive cloud created by the accident dispersed over the entire northern hemisphere and deposited substantial amounts of radioactive materials over large areas of the former Soviet Union and other parts of Europe, contaminating land, water and biota and causing particularly serious social and economic disruption to large segments of the population in the countries known today as Belarus, the Russian Federation and Ukraine. Two radionuclides, the short-lived iodine-131 (with a half-life of 8 days) and the long-lived caesium-137 (with a half-life of 30 years), were particularly significant because of the radiation dose they delivered to the public. However, the doses delivered were quite different for the two radionuclides: the thyroid doses from iodine-131 ranged up to several grays within a few weeks after the accident, while the effective doses from caesium-137 ranged up to a few hundred millisieverts over the following few years. The contamination of fresh milk with iodine-131 and the lack of prompt countermeasures led to high thyroid doses, particularly among children, in the former Soviet Union and resulted in an elevated incidence of thyroid cancer among children and adolescents. In the longer term, mainly due to radiocaesium, the general population was also exposed to radiation, both externally from radioactive deposits and internally from consuming contaminated foodstuffs. However, the resulting long-term radiation doses were relatively low and should not lead to substantial health effects in the general population that could be attributed to radiation. The foregoing notwithstanding, the severe disruption caused by the accident resulted in a major social and economic impact and great distress for the affected populations.