Causal study of the explosion in the fire and explosion incident at the Bituminization Demonstration Facility

The explosion occurred about 10 hours after the fire at the Bituminization Demonstration Facility (BDF) in the Tokai Reprocessing Plant (TRP) of Power Reactor and Nuclear Fuel Development Corporation (PNC) on March 11, 1997. We have investigated the cause of the explosion through facility observations, evaluation of operation records, experiments and analysis. From on the results of the investigation, the cause of the explosion is considered to have been as follows. After insufficient Spraying of water during the fire fighting, the bitumen mixture in the drums released in flammable gases into a low oxygen atmosphere. The in flammable gases could not be vented due to clogging of the filter and so gradually mixed with the air that reversed out from the outlet of the vessel ventilation system. The premixed gases were ignited by self-ignition of another heated drum. (author)