The Tokaimura Accident

Michael E. Ryan
Department of Chemical Engineering
University at Buffalo, State University of New York

Part VII: Historical Perspective

Several criticality accidents have occurred in the past. Similar incidents to the Tokaimura accident involving the mixing of uranium solutions have taken place in Oak Ridge, Tennessee, in 1958, in Mayak in the Urals in 1958, and in Wood River Junction, Rhode Island, in 1964. On October 7, 1957, at Windscale Pile No. 1, north of Liverpool, England, a fire in a graphite-cooled reactor released a large amount of radioactive pollution over the countryside contaminating a 520-km2 (200-mi2) area. On March 28, 1979, a nuclear accident occurred at the Three Mile Island nuclear power plant near Harrisburg, Pennsylvania. One of two reactors lost its coolant, which caused overheating and partial meltdown of its uranium core. Some radioactive water and gases were released. On April 26, 1986, an explosion and fire in the graphite core of one of four reactors occurred at the Chernobyl nuclear power plant near Kiev in the Ukraine. A vast amount of radioactive material was released and spread over the Soviet Union, Eastern Europe, Scandinavia, and later Western Europe. Thirty-one people were claimed dead in the immediate aftermath of the accident. The total number of casualties is unknown.


  1. Research the accident that occurred at Three Mile Island. What were the factors that led to this accident?

  2. Research the accident that occurred at Chernobyl. What were the factors that led to this accident?

  3. Research fast-breeder reactor technology. What are the benefits that could be derived from this technology?