Date: 29 September 1957
Location: Mayak Scientific-Production Association, Kyshtym, Chelyabinsk, Russia, USSR
Type of event: chemical explosion in stored nuclear wastes
The accident occurred at a facility involved in processing and storage of nuclear wastes. Following removal of plutonium, liquid high-level nitrate-containing wastes were stored in underground stainless steel tanks in concrete trenches. The tanks were located about 2 km from the plant, each with a volume of about 300 cubic meters. The tanks included heat exchangers to remove heat buildup in the tanks. The heat exchanger on one tank was shut down in 1956 due to a fault, and it was concluded it was safe to leave the tank uncooled. Waste continued to be added to this tank until 10 April 1957. Due to lack of a working heat exchanger, water evaporation in the tank allowed a buildup of nitrates and acetates on the surface of the tank's contents, in contact with air. This was ignited by a spark from monitoring equipment on 29 Sept. 1957 at 16:20. This chemical explosion had an energy release of 5-10 tons of TNT, releasing about 70-80 tons of wastes with a total activity of about 20 megacuries. Of this, about 18 megacuries was deposited in the immediate area of the explosion site and about 2 megacuries was dispersed over a large area downwind. Of this an estimated 54,000 curies of strontium-90 was deposited. The area with deposition of at least 2 curies per square km (about 20 times the level of global fallout) extended 105 km downwind and was 4.5-6 km wide, for a total of about 560 sq. km; this corresponded to an initial exposure rate of about 0.7 rad per day. Area contaminated at 200 curies per square km or more was 50 sq. km. The contaminated region extended to the northeast towards Kamensk-Uralskiy.
About 600 residents were evacuated about 7 to 10 days after the accident, and by 18 months after the accident about 10,180 people had been evacuated. According to Russian reports maximum exposures reached 52 rem, with up to 150 rem to the gastrointestinal tract due to ingestion of radionuclides in food and water; some studies showed blood count changes, but no acute radiation injuries were observed. In 1958 590 sq. km in Chelyabinsk province and 470 sq. km in Sverdlovsk province were removed from agricultural use. Following ploughing under of surface soil, all but 220 sq. km was returned to agricultural use between 1961 and 1978. The Soviet government concealed evidence of the accident; it was first discussed in the West by Z. Medvedev in 1976, and first acknowledged by the Soviet government in 1989. The Soviet and Russian governments have denied reports that hundreds of casualties resulted from the accident.
Consequences: No confirmed casualties.
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Last modified 10 July 2022.
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