JAPAN - Japan became nuclear power-free for the first time in 14 months Sunday night, when the No. 4 reactor of the Oi nuclear power plant in Oi, Fukui Prefecture, went offline for regular maintenance.
Among 50 reactors in the country, the Oi reactor had been the only one in operation in the country.
The Nuclear Regulation Authority is currently conducting safety checkups of 12 reactors at six nuclear power plants operated by four utility firms, including the Nos. 3 and 4 reactors at the Oi plant.
The administration led by Prime Minister Shinzo Abe plans to allow restart of nuclear reactors once their safety is confirmed. But there is a growing view that they will not be restarted until next year at the earliest.
Kansai Electric Power Co. began lowering the No. 4 reactor's power output at 4:40 p.m. Sunday and stopped its power transmission at 11 p.m. before the reactor came to a full stop in the early hours of Monday.
"We hope safety inspections will end soon and we'll be able to resume the reactor's operation after gaining understanding from local residents," said KEPCO Vice President Hideki Toyomatsu to reporters in Oi on Sunday afternoon.
According to government projections, the Oi reactor's operation suspension reduces KEPCO's combined output capacity to 24.9 million kilowatts, which is below the record demand of 25.77 million kilowatts in fiscal 2011, when the country experienced extremely cold winter.
To make up for the shortfall, KEPCO will take measures to increase its output capacity, adding new thermal power plants and buying surplus power from other utility firms.
The country previously became nuclear power-free for about two months from May 2012. This time, the nuclear power-free period is likely to be longer, prompting the government to consider ways to cope with expected power demand after closely examining output capacity of individual utility firms.
Of the 12 reactors subject to the NRA's safety inspections, the agency has started full-scale examinations of six reactors at four nuclear power plants to see whether measures taken at individual reactors are appropriate. The six reactors are No. 3 reactor of the Ikata nuclear power plant of Shikoku Electric Power Co., Nos. 1 and 2 reactors at the Sendai plant and Nos. 3 and 4 reactors of the Genkai plant of Kyushu Electric Power Co., and No. 3 reactor of the Tomari plant of Hokkaido Electric Power Co.
NRA's safety inspections at No. 3 reactor of the Ikata nuclear power plant are more advanced than those at other reactors. The plant already has started preparations to apply to restart its operation.
On Friday, NRA members conducted on-site inspections at the Ikata plant prior to inspections at other plants, making it highly likely that the reactor will be the first one to be restarted.
As for Nos. 3 and 4 reactors at the Oi nuclear power plant, the NRA team of experts earlier this month determined that a fault under the reactor compound is not active.
In response, the agency plans to resume safety checkup meetings on Tuesday. The agency has already concluded that the reactors do not represent any major problems following its preliminary verification that was conducted earlier this year before actual safety checkups to see whether they meet the agency's new safety standards.
Many observers believe that NRA safety checkups of Oi reactors are likely to proceed faster than those at other power plants.
Yet, the probability of damage to the containment vessel and likelihood of core meltdown have yet to be calculated at any of the reactors in Japan.
"The safety inspection, which is expected to take at least six months, has not reached the most important stage," an NRA member said.
It remains uncertain when any of the idled reactors will be reactivated, observers said.