Japan’s Osaka District Court has rejected an injunction against continued operation of unit 3 at Kansai Electric Power Co’s Mihama NPP in Fukui Prefecture. The 46-year-old 826MWe Mihama 3 was restarted in June 2021 for the first time in some 10 years, after completing final inspections by the Nuclear Regulation Authority. It is the first and only unit to operate beyond the government-mandated 40-year service period introduced under post Fukushima rules.

The plaintiffs, comprising nine residents of Kyoto, Fukui and Shiga prefectures submitted the lawsuit seeking the temporary injunction on the grounds the risk of a major accident at the reactor had increased because of the more than four decades the plant has been in use.

"We have explained the safety of the Mihama 3 reactor since the lawsuit was filed and we believe that it was understood by the court," a Kansai Electric spokesperson said. "We will continue to strive to improve safety and credibility of the reactor," he said.

The plaintiffs also argued that a fault directly under and in the vicinity of the plant created the possibility of the foundation under the plant shifting. Noting the many nuclear plants in Fukui Prefecture, they also argued that Kansai Electric evacuation plan for the plant was inadequate and did not consider the possibility of simultaneous accidents at the other plants. Kansai Electric insisted that there were no safety issues of concern.

Mihama-3 is the only operating unit at the Mihama site. Two others units, the 320MWe Mihama 1 and the 470MWe Mihama 2, were permanently closed in 2015 after Kansai Electric decided the required upgrades would be uneconomic.

Kansai Electric said in November that it would apply for NRA approval to restart units 3&4 of its Takahama NPP, also in Fukui Prefecture. Takahama 1&2 were the first Japanese units to be granted a licence extension beyond 40 years under revised post-Fukushima regulations, but are currently offline pending completion of a backup control centre. Kansai Electric has said it plans to restart the 780MWe pressurised water reactors in mid-2023.

Image: Mihama nuclear power plant unit 3 (courtesy of Kyodo)