Kansai Electric's Oi Unit 3 Auto-Stops on Field Loss, Enters Cold Shutdown

Kansai Electric Power reported to Fukui Prefecture, the local government hosting the nuclear station, on March 10 regarding the automatic shutdown of Oi Unit 3 on the night of March 8, detailing the fault and the company's subsequent response measures. After completing inspections of the generator and surrounding cables, the company plans to formally launch its cause investigation from March 12. The specific timeline for resuming operations has not yet been determined.

At around 11:56 pm on March 8, Oi Unit 3 issued a de-excitation alarm indicating loss of magnetic field in the generator. The generator subsequently halted, triggering an automatic reactor shutdown. By 9:21 am on March 10, the reactor had entered cold shutdown state, with its temperature below 93 degrees Celsius.

The malfunction occurred in equipment belonging to the secondary system, where the generator is located, rather than in primary-system equipment that directly handles radioactive materials. As a result, no radioactive impact was caused to the surrounding environment. According to Kansai Electric Power, reactor shutdowns due to de-excitation have occurred previously. In April 2000, Unit 2 of the Mihama nuclear power station in Mihama-cho, Fukui Prefecture, a unit since slated for decommissioning, experienced the same problem, caused by poor contact in cables supplying power to the generator's excitation device.