Fukushima Daiichi Nuclear Power Plant - Incidents and Accidents

Incidents and Accidents

• In 1978, fuel rods fell in reactor No. 3, causing a nuclear reaction. It took about seven and a half hours to place the rods back into proper positions.
• On February 25, 2009 a manual shutdown was initiated during the middle of a startup operation. The cause was a high pressure alarm that was caused by the shutting of a turbine bypass valve. The reactor was at 12% of full power when the alarm occurred at 4:03 am due to a pressure increase to 1,029.8 psi (7,100 kPa), exceeding the regulatory limit of 1,002.2 psi (6,910 kPa) The reactor was reduced to 0% power, which exceeded the 5% threshold that requires event reporting, and pressure dropped back under the regulatory limit at 4:25 am. Later, at 8:49 am the control blades were completely inserted, constituting a manual reactor shutdown. An inspection then confirmed that one of the 8 bypass valves had closed and that the valve had a bad driving fluid connection. The reactor had been starting up following its 25th regular inspection which began on October 18, 2008.
• On March 26, 2009 unit 3 had problems with over-insertion of control blades during outage. Repair work was being done on equipment that regulates the driving pressure for the control blades, and when a valve was opened at 2:23 pm a control blade drift alarm went off. On later inspection it was found that several of the rods had been unintentionally inserted.
• On November 2, 2010 unit 5 had an automatic SCRAM while an operator was conducting an adjustment to the control blade insertion pattern. The SCRAM was caused by a reactor low water level alarm. The turbine tripped along with the reactor and there was no radiation injury to workers.