On April 6, 1993, the Associated Press reported that an underground tank exploded and burned at the Tomsk-7 Nuclear Reprocessing Plant in Siberia, contaminating 46 square miles of uninhabited land. The chemical explosion occurred in a processing tank used for the separation of uranium and plutonium. Combustible chemicals added to the tank contributed to the explosion.
The Russian Nuclear Energy Ministry blamed a rise in pressure in the tank caused when nitric acid was added as a cleanser. Soviet officials report that the explosion tore off a concrete slab covering the stainless-steel tank and short-circuited the plant electrical systems, which set off a fire. Plant personnel contained the fire within 15 minutes. According to news sources, no deaths were reported and one fireman received a high dose of radiation.
The State Emergency Committee said radiation levels around Tomsk-7 were three to four millirem per hour nine miles from the plant. Monitoring stations in Scandinavia and western Europe reported no increase in levels of radiation. The Russian Air Defenses Unit detected a radioactive cloud moving through Siberia on April 7, 1993. Soviet soldiers worked to remove contaminated snow and dirt in an effort to prevent contamination of the nearby Tom River before the snow melted.
The accident was one of a series in the former Soviet Union. In 1986, a reactor at the Chernobyl nuclear power plant in Ukraine exploded, spreading contamination over portions of Ukraine and Belarus. NS reported in OE Weekly Summary 93-2, about several fires that have occurred at the Chernobyl complex. In 1990, an accident at the Tomsk-7 facility hospitalized 38 people and was blamed for the contamination of the Tom River. In 1967, approximately 9,000 people were evacuated when Lake Karachay (used to store radioactive waste) within the Chelyabinsk-65 plutonium production complex, dried up and winds spread radioactive particles. The Chelyabinsk-65 facility was also the scene of another event in 1957, when a nuclear waste explosion resulted in radiation contamination of 217 towns and villages. Nearly 11,000 people were evacuated as a result of that event.
The DOE Intra-Agency Coordinating Committee for the New Independent States has formed a working group to review the Tomsk-7 event. The objective of the working group is to identify lessons learned from the event that may be applicable to DOE facilities. NS is following the activities of the working group and will provide updates on lessons learned from the event in future OE Weekly Summaries as this information becomes available.
NS previously reported on smaller scale chemical explosions involving nitric acid in OE Weekly Summaries 92-21 and 92-23. In one event, a fire and explosion occurred on September 10, 1992, during conversion of highly enriched uranium with nitric acid at the Nuclear Fuel Services, Inc., facility in Erwin, Tennessee. The explosion damaged two protective glovebox Plexiglas shields. A similar event occurred on February 9, 1991, at the Idaho National Engineering Laboratory when a small explosion ruptured a 6-inch diameter borosilicate glass dissolver containing 1.9 kg of highly enriched uranium fuel and other scrap material and 4 liters of heated nitric acid solution. The explosion sprayed uranium-bearing nitric acid solution out of the confinement hood onto three operators. As a result of that event, NS issued Safety Notice 92-3, "Explosion Hazards of Uranium-Zirconium Alloys," that described explosions involving uranium-zirconium alloys in nitric acid. Additional information concerning nitric acid reactions can be found in Westinghouse Savannah River Company report WSRC-TR-91-22, "Adverse Experiences With Nitric Acid at the Savannah River Site," by William Durant, D. K. Craig, M. J. Vitacco, and J. A. McCormick. This report documents a number of adverse situations in handling nitric acid, including significant explosions. The report also discusses process upsets, fires, injuries, and toxic effects of nitric acid and its decomposition products.