The Nuclear Regulation Authority (NRA) has allowed Kansai Electric Power Co. to continue running the No. 3 reactor at its Mihama Nuclear Power Station in Fukui Prefecture beyond the 40-year limit.

This is the third nuclear reactor in the country that will have been allowed to continue to operate beyond the 40-year limit -- following the No. 1 and 2 reactors at the Takahama plant also in Fukui Prefecture.

The move contradicts rules stipulating that nuclear reactors should be decommissioned after being operated for 40 years, in principle.

It had been viewed as extremely difficult to extend the lifespan of Mihama's No. 3 reactor because of its old design and difficulties in improving the reactor's quake resistance as the plant operator is required to largely increase the estimate of the scale of the maximum earthquake that could hit the plant.

As such, the NRA once hinted that it would discontinue examinations of the reactor to see if it meets the new regulatory standards.

However, Kansai Electric Power spent 165 billion yen on measures to enhance the safety of the reactor. The NRA increased its personnel to accelerate the examination of the plant, and managed to approve the continuation of its operation by the deadline.

Six aging nuclear reactors across the country are set to be shut down and decommissioned. Their operators voluntarily decided to decommission these reactors, whose outputs are small, considering the units' cost-benefit performance.

However, if power companies apply for permission to extend the lifespan of nuclear reactors, the NRA will almost certainly grant permission.

The rules limiting the operation of a nuclear reactor to 40 years, in principle, was established with the aim of reducing Japan's reliance on atomic power stations following the outbreak of the Fukushima nuclear crisis in March 2011. Both the NRA and power companies should go back to the fundamentals of the rules.