Radiological consequences of the Chernobyl accident in the Soviet Union and measures taken to mitigate their impact

As a result of the accident that occurred at 1:23 a.m. on 26 April 1986 at Unit 4 of the Chernobyl nuclear power plant, a significant quantity of the radioactive materials accumulated in the reactor during its operation escaped from the plant. Because of the meteorological air mass transfer conditions prevailing, the cloud formed at the time of the accident left a radioactive trail over the area to the west and north of the plant. In the following 10 days, an intense release of radioactive gases and aerosols continued, resulting in the contamination of terrain in different directions and at considerable distances from the plant. The total release of radioactive substances (excluding radioactive noble gases) was calculated on 6 May 1986 to be about 1.9 EBq (exabecquerel, or 1018 Bq), or 3.5% of the total inventory of radionuclides in the reactor at the time of the accident. Releases of the biomedically most significant nuclides such as strontium-90, iodine-131, and caesium-137 amounted to 8.1, 270, and 37 PBq (peta-becquerel, or 1015 Bq), respectively