The Office of Nuclear Safety reported in Operating Experience Weekly Summary 93- 14 about the April 6, 1993, explosion of an underground tank at the Tomsk-7 Plutonium Reprocessing Plant in Siberia that released radioactive contamination to the environment. On April 14, 1993, the Russian Ministry for Nuclear Energy reported that the explosion resulted in plutonium contamination, but the levels measured did not require special safety measures. The Ministry reported the plutonium levels were 0.008 curies per square kilometer. A spokesman for the International Atomic Energy Agency in Vienna said plutonium levels after the blast did not appear to be dangerous, but there could be hot-spots in the contaminated area where radiation levels were higher. They were sending a team of experts to the Tomsk-7 facility to review damage caused by an explosion.
Updated information supplied by the Ministry indicated that contamination of 6 mrem per hour was observed on 14 square miles of land. Officials said earlier that the total contaminated area was 46 square miles. Russian officials also said there was no risk to health as a result of the explosion and that there were no plans to evacuate either the plant or the nearby city of Tomsk.
The exact circumstances of the explosion at the Tomsk-7 plant are still unclear. A preliminary report from the State Nuclear Safety Oversight Committee said the explosion resulted when nitric acid was poured into the processing tank as a cleanser while the equipment was being readied for repairs. The acid apparently reacted with an unknown organic substance in the tank, causing the chemical explosion. The Russian Parliament newspaper Rossiskaya Gazeta reported that a preliminary investigation blamed a senior operator for "severe negligence" for carrying out improper operations that led to a sudden increase in temperature and pressure in the processing tank. Officials said that most of the plutonium had already been extracted from the tank, but that traces inevitably remained in the estimated 700 cubic feet of liquid that was dispersed. As previously reported, the explosion blew a reinforced concrete lid off the tank and punched holes in the building roof. The blast also short- circuited the plant electrical systems and started a fire.
As a result of the accident, Russian President Boris Yeltsin ordered tighter safety measures at all Russian nuclear installations after the incident. The Office of Nuclear Safety will provide future updates on the Tomsk-7 event as additional information is available.