Research Progress of Red Oil Explosion Accidents in Nuclear Fuel Reprocessing Plant

Since Westinghouse Savannah River Company (WSRC) of America first applied PUREX process in 1954, PUREX process is always the top priority in nuclear fuel reprocessing plant. And this process is based on liquid to liquid extraction with TBP as the extractant. TBP is irreplaceable in the development of PUREX process in nuclear fuel reprocessing, its advantages are well recognized. However TBP does have some disadvantages such as formation of red oil, which will appear in the system of high nitric acid concentration and heavy metal nitrate, once the red oil forms, it can lead a exothermic runaway decomposition in reasonable conditions, such as exceeding a certain temperature (typically 130°C) or high acid concentration. If gas products and energy released from the decomposition reaction could not be exported in time, it will lead to vessel overpressure and caused violent explosion accidents. By now, it has happened 6 times so-called red oil explosion accidents worldwide, resulting in different degrees of equipment and construction damage and environmental contamination. From 1953 to now, research related to red oil has never stopped. WSRC, Hanford Company, Oak Ridge National Laboratory and Los Alamos National Laboratory of America have conducted many studies, as well as some research institutions from Russia, UK, France and India. Defense Nuclear Facilities Safety Board of America issued a technical report in 2003, preventive measures for red oil explosion were established in this report, and these measures provided good practice experience and reference for other countries, and the temperature condition (⩽130°C)and nitric acid concentration (⩽10M)for preventing red oil explosion are employed in some countries which has built the reprocessing plant. Nevertheless, research conclusions and knowledge of red oil vary from country to country. Especially, Kumar and Smitha etc. conducted several experiments in adiabatic condition in recent years, and investigation on stability of TBP - nitric system was made, the results indicated that the red oil runway reaction will happen even in lower temperature and lower nitric acid concentration in contrast with the reported value, and they thought it would need a further study to assess the validity of present preventive measures, and to rebuild the safety limits for preventing red oil explosion in the operation of nuclear fuel reprocessing plants. In this paper, related research results of red oil explosion accidents were combed, and the characters of study work of different periods were summarized, and definition, formation conditions of red oil, pathway of runaway reaction, control and preventive measures for preventing red oil explosion of different countries were analyzed and compared, as well as the new viewpoints of recent literatures. And some research ideas for future investigation based on present work were also proposed.