Mihama-3 Restarted After Decade-long Hiatus: First Restart in Japan of a Reactor Operating Beyond 40 Years

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On June 29, the Mihama-3 Nuclear Power Plant (PWR, 826MW) of the Kansai Electric Power Co. (Kansai EP) began to again generate power after a hiatus of slightly more than 10 years.

Mihama-3 originally began commercial operation in December 1976. In May 2011, the unit entered a periodic inspection, when it underwent examinations by the Nuclear Regulation Authority (NRA) for compatibility with the new regulatory standards and for permission to extend its operating lifetime to up to 60 years.

The unit was restarted on June 23, 2021, becoming the first in Japan to be restarted after operating for more than 40 years. A period of adjustment operations is now underway before the final stage of the periodic inspection, i.e., connection to the grid. After a final inspection by the NRA, Mihama-3 is expected to resume commercial service on July 27.

In addition to work on safety measures based on the accident at the Fukushima Daiichi, Kansai EP carried out other kinds of work during the periodic inspection, including the replacement of the central control panel with the newest digital type,

However, given that required anti-terrorism facilities have not been completed, Kansai EP will halt the unit’s operation on October 23—before the deadline of October 25—after which Mihama-3 will enter yet another periodic inspection.

Upon the restart of Mihama-3, Kansai EP President Takashi Morimoto released a comment, saying, “At Mihama—the birthplace of our NPPs—we have taken another step forward, namely, operating a unit beyond 40 years. It is the first in Japan since the new regulatory standards became effective.”

Expressing again his gratitude to the siting municipalities, he said, “Each and every employee of our company, as well as of our partner companies, will carry out their work prudently, with firm determination to perpetually improve nuclear safety.”

At a meeting on June 30 of the Strategic Policy Committee, under the Advisory Committee for Natural Resources and Energy, Governor Tatsuji Sugimoto of Fukui Prefecture emphasized that utilization of all NPPs that can be restarted is essential.

The governor then expressed concern that, despite operation beyond 40 years, eventual shutdowns would affect regional development, so he asked the national government to “make its policy clear on the utilization of nuclear power in the next Strategic Energy Plan.”