‘Prompt critical’ suspected at Shika N-plant

   In a criticality accident at the No. 1 reactor in Hokuriku Electric Power Co.’s Shika Plant in 1999, a prompt critical condition, a spike in a fission chain reaction, might have occurred, the Japan Nuclear Technology Institute (JANTI) announced on April 11.

   Prompt critical conditions must be avoided because they could make a nuclear reactor uncontrollable and damage nuclear fuel.

   The accident occurred when three control rods of the reactor came off during a regular inspection. The JANTI concluded that after those rods fell off, the reactor’s peak output rose to 14 percent of the normal operation and the temperature of nuclear fuel rose by about 150 degrees.

   According to the JANTI, nuclear fuel temperature between 2,800 and 3,300 degrees will damage the fuel.                     - Akahata, April 12, 2007