[en] On March 11, 1997, Bituminization Demonstration Facility (BDF) in Tokai Reprocessing Plant (TRP) of Power Reactor and Nuclear Fuel Development Corporation (PNC) made fire and explosion incident. Investigation of the cause of the fire and explosion incident at BDF was carefully conducted. The main cause of the fire is clarified to have been physical heating inside the extruder, which provided unusual high temperature of bituminized product at filling. Physical heating is considered to be derived from decrease of feed rate of liquid waste to the extruder. The causes of the explosion are accumulation of flammable gas generated from insufficiently extinguished bituminized product inside the filling room of which the ventilation system was shut down. The gas was ignited by self- ignition of another heated drum. (authors)