Mihama Nuclear Power Plant Unit 3 shutdown caused by pipe corrosion

Kansai Electric Power Company has identified a construction error as the cause of a leak at Mihama Nuclear Power Plant Unit 3, which led to a manual reactor shutdown on September 17. Investigations revealed a hole measuring approximately 14mm by 4mm in a secondary system pipe located in an outdoor turbine building.

The leak was caused by corrosion resulting from rainwater entering through a gap in a stainless steel protective cover. Authorities determined that the cover had been installed upside down during work performed in 2010, leaving the pipe vulnerable to the elements for 16 years. The affected pipe is a carbon steel tube that has not been replaced or repaired since the plant began operations in 1976.

Kansai Electric Power stated that the leaking water did not contain radioactive substances and had no impact on the surrounding environment. However, the company confirmed that the scheduled resumption of commercial operations, originally set for October 9, will be delayed. The timing for restarting the reactor remains undecided. The company is currently conducting a detailed investigation and has been requested by Fukui Prefecture to inspect the installation status of covers on all other outdoor piping.