The Mihama Nuclear Power Station Unit 3 (pressurized water reactor with a rated electric power output of 826 MW and a rated thermal power output of 2,440 MW) was operating at the rated thermal power output, when an alarm indicating a nonconformance between 3A-SG feedwater and steam flow actuated at 15:28 on August 9. The alarm meant that the feedwater to one of steam generators of the unit was insufficient. This resulted in an automatic reactor trip, followed by an automatic turbine trip.

Immediately after the event, the turbine building was filled with steam and eleven people were injured. They were taken to the hospital by ambulances.

After the automatic reactor trip, the turbine-driven auxiliary feedwater pump and the motoroperated auxiliary feedwater pump automatically started operation, continuously supplying feedwater to the steam generators. There are no irregular conditions at the plant. The causes of the event are now under investigation.

There has been no release of radioactivity to the environment during and after this event.

[Reported at around 16:50 on August 9]

Of the eleven injured, eight were taken to Tsuruga City Hospital by ambulances (four were pronounced dead, one was transferred to Fukui Prefectural Hospital by helicopter, one was transferred to University of Fukui Hospital by an ambulance, and two are under medical treatment at Tsuruga City Hospital), and the remaining three were carried to NHO Fukui National Hospital (one of them was then transferred to Fukui Prefectural Hospital by helicopter).

The unit has been shut down in a safe condition.