6 April 1993 - A pressure buildup led to an explosive mechanical failure in a 34 m3 (1,200 cu ft) stainless steel reaction vessel buried in a concrete bunker under building 201 of the radiochemical works at the Tomsk-7 Siberian Chemical Enterprise plutonium reprocessing facility. The vessel contained a mixture of concentrated nitric acid, 8,757 kg (19,306 lb) uranium, 449 g (15.8 oz) plutonium along with a mixture of radioactive and organic waste from a prior extraction cycle. The explosion dislodged the concrete lid of the bunker and blew a large hole in the roof of the building, releasing approximately 6 GBq (160 mCi) of Pu 239 and 30 TBq (810 Ci) of other radionuclides into the environment. The contamination plume extended 28 km (17 mi) NE of building 201, 20 km (12 mi) beyond the facility property. The small village of Georgievka (pop. 200) was at the end of the fallout plume, but no fatalities, illnesses or injuries were reported. The accident exposed 160 on-site workers and almost two thousand cleanup workers to total doses of up to 50 mSv (the threshold limit for radiation workers is 20 mSv/yr).