An aging nuclear reactor in central Japan's Fukui Prefecture was restarted Wednesday, becoming the country's first nuclear unit to operate beyond the government-mandated 40-year service period introduced under new rules set after the 2011 Fukushima disaster.

Kansai Electric Power Co. said it began operating the No. 3 unit at the Mihama plant for the first time in about 10 years, after completing final inspections. The reactor had stopped operations after the crisis at the Fukushima Daiichi plant triggered by a massive earthquake and tsunami.

The No. 3 unit of Kansai Electric Power Co.'s Mihama plant in Fukui Prefecture is pictured on June 23, 2021. (Kyodo)

However, the Mihama No. 3 unit, which began commercial operation in 1976, is expected to be halted in about four months before the Oct. 25 deadline for the implementation of counterterrorism measures which Kansai Electric is unlikely to meet, according to the company.

The restart of the reactor comes as the Japanese government looks to achieve a new goal of a 46 percent cut in greenhouse gas emissions by fiscal 2030 compared with fiscal 2013, while showing a stance to be less dependent on the use of nuclear power.

The Nuclear Regulation Authority granted approval in 2016 for the reactor to operate beyond the 40-year limit for an additional period of up to 20 years, after screening the company's safety measures for the unit.

In February, Mihama Mayor Hideki Toshima also gave his consent for the resumption, followed by approval from Fukui. Gov. Tatsuji Sugimoto on April 28, despite increasing worries about aging nuclear reactors among local residents.

Sugimoto told reporters that he was relieved to hear that Wednesday's operation went smoothly, adding, "I hope Kansai Electric will make every effort to ensure safe and stable operation."

Kanai Electric said in a statement, "We will proceed with operations cautiously, giving top priority to safety."

Meanwhile, civic groups protested against the operation in Mihama, with people holding up antinuclear banners in Japanese, one of them saying, "Don't allow the restart of the reactor!"

On Monday, a group of nine people in Fukui as well as neighboring Kyoto and Shiga prefectures filed a lawsuit with the Osaka District Court, seeking suspension of the Mihama No. 3 reactor.

They argued aging reactors are prone to accidents when a massive earthquake occurs and that the 40-year operation period should be strictly applied in the country, which could be hit by a natural disaster anytime.

The Nos. 1 and 2 units of the Mihama plant were terminated in April 2015 in line with the 40-year limit.

Two other Kansai Electric reactors in Fukui Prefecture have also secured nuclear watchdog approval and local consent to operate beyond the 40-year limit.

But the Nos. 1 and 2 reactors at the Takahama plant will not resume operation as the utility failed to meet a June 9 deadline to complete the implementation of counterterrorism measures.

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