Kansai Electric Power Co. on Friday rebooted a nuclear reactor at its Takahama power plant in central Japan's Fukui Prefecture for the first time in 12 years, making it the oldest operating reactor in Japan.

The operator plans to restart power generation and transmission at the No. 1 reactor on Wednesday before resuming commercial operation on Aug. 28, it said.

Photo taken from a Kyodo News helicopter on July 27, 2023, shows the No. 1 (R) and No. 2 reactors at Kansai Electric Power Co.'s Takahama nuclear power plant in Fukui Prefecture. (Kyodo)

The reactor, which started commercial operation 48 years ago, went offline in January 2011 for regular inspection and remained so following the Fukushima nuclear crisis, triggered by the earthquake and tsunami in March of that year.

The reboot comes after the Nuclear Regulation Authority gave the green light in 2016 for the reactor to operate beyond the 40-year service period, which was set in the wake of the crisis.

The reactor was originally scheduled to restart around early June, but the plan was postponed due to the need for additional work on fire protection infrastructure.

Three out of four reactors at the Takahama power station are now operating, with just the No. 2 reactor remaining suspended. The reactor is also scheduled to restart in September, according to the utility.

Of the more than 40 commercial reactors nationwide, 11 reactors are currently in operation.