In September 1957, the cooling
system in one of the tanks containing about 70-80 tons of liquid radioactive waste
failed and was not repaired. The temperature in it started to rise, resulting in evaporation
and a chemical
explosion of the dried waste, consisting mainly of ammonium nitrate and acetates (see ammonium nitrate bomb). The explosion, estimated to have a force
of about 70-100 tons of TNT threw the concrete lid, weighing 160 tons,
into the air.[3] There were no immediate casualties as a result of the
explosion, which released an estimated 2 to 50 MCi (74 to 1850 PBq) of radioactivity.[2][4][5]In the
next 10 to 11 hours, the radioactive cloud moved towards the northeast, reaching 300-350 kilometers from the accident. The fallout of the cloud resulted in
a long-term
contamination of an area of more than 800 square kilometers, primarily with caesium-137 and strontium-90.[2] This area is usually
referred to as the
East-Ural Radioactive Trace (EURT).[6]
Explosion