Photo/IllutrationThe No. 1 reactor, right, and the No. 2 reactor at Kansai Electric Power Co.’s Oi nuclear power plant in Oi, Fukui Prefecture (Ryo Kato)

Kansai Electric Power Co. is set to decommission the first large-scale reactors outside of Fukushima Prefecture since the 2011 nuclear disaster, a move that could affect the government’s Basic Energy Plan.

The utility apparently decided that it would not be worth the effort and money to upgrade and continue operating the aging No. 1 and No. 2 reactors at the Oi nuclear plant in Oi, Fukui Prefecture.

Kansai Electric, based in Osaka, is expected to make the decision official at an extraordinary board meeting on Dec. 22.

Each reactor has the capacity to generate 1.175 gigawatts.

The smaller No. 1 to No. 3 reactors suffered meltdowns after the Great East Japan Earthquake and tsunami struck the Fukushima No. 1 nuclear plant in March 2011. Operator Tokyo Electric Power Co. has said the entire plant will be decommissioned, including the still-operational No. 6 reactor with a capacity of 1.1 gigawatts.

The Ministry of Economy, Trade and Industry has set a target of supplying 20 percent of Japan’s electricity needs through nuclear power generation in 2030. The decommissioning of the two high-output reactors in Oi could force a review of that target, according to experts.

The No. 1 reactor, which has been offline since December 2010, and the No. 2 reactor, idle since December 2011, both turn 40 years old in 2019.

Kansai Electric had considered applying to the Nuclear Regulation Authority for a 20-year extended operation of the reactors.

But after the Fukushima disaster, the NRA introduced more stringent regulations for reactors.

The utility would not only have to pay costs to upgrade the safety features of the two reactors, but it would have also faced a technological challenge.

The two reactors feature a unique design called “the ice condenser system,” which uses ice to cool steam and reduce pressure in the containment vessel in the event of an accident.

About 1,250 tons of ice blocks are installed around the containment vessel of each reactor.

Some experts say it would take the NRA a considerable amount of time to determine whether the reactors--and their ice condenser systems--meet the new safety regulations.

Kansai Electric in April 2015 decided to decommission the No. 1 and No. 2 reactors at its Mihama nuclear plant in Mihama, also in Fukui Prefecture.

These reactors were also aged but had only up to half of the output of the two reactors at the Oi plant.

Kansai Electric had 11 reactors at its plants in Fukui Prefecture before the Fukushima disaster, and the utility relied on nuclear energy for about 40 percent of its energy output, the highest percentage among all electricity suppliers in Japan.

The company plans to spend a combined 830 billion yen ($7.38 billion) on enhanced safety measures to bring seven reactors back online, including the No. 3 and No. 4 reactors at the Oi plant.