Japan’s Kansai Electric Power Co closed unit 3 of its Mihama NPP in Fukui Prefecture after discovering steam leaking from near a high-pressure turbine. Kansai Electric said it cannot say when it will restart the 780 MWe pressurised water reactor.
The leak, which originated in the plant’s secondary system and was stopped shortly after the shutdown, involved no release of radioactive materials into the environment, and the company has begun investigating the cause while signalling it will disclose any subsequent effects on operations or earnings if they arise.
In 2021, Mihama 3, which began operations in 1976, became the first nuclear reactor in Japan to operate beyond 40 years under the new rules introduced after the 2011 Fukushima Daiichi nuclear disaster. The regulations limit a reactor’s service period to 40 years, but extensions of up to 20 years are permitted if approved by regulators.
In November 2025, Kansai Electric launched a survey for possible construction of a new reactor at Mihama. Units 1&2 at the Mihama NPP are set to be decommissioned, leaving only unit 3 in operation. However, in 2026, unit 3 will reach its 50th year in operation, 10 years beyond the standard design life of 40 years.
