Japan's nuclear watchdog has approved extending the operation of two aging nuclear reactors in southwestern Japan for another 20 years.

The operational lifespan of Japanese reactors has been limited to 40 years in principle since the Fukushima Daiichi nuclear plant accident in 2011. But it can be extended by up to 20 years if the reactors pass screening by the Nuclear Regulation Authority.

At a meeting on Wednesday, the NRA granted extension approval to the No.1 and 2 reactors at the Sendai nuclear power plant in Kagoshima Prefecture, which is operated by the Kyushu Electric Power Company.

The No.1 reactor will turn 40 next July and the No.2 will reach that age in November 2025.

Discussed at the meeting were the results of special inspections of the reactors conducted by Kyushu Electric and an assessment that showed the reactors can be used for another 20 years.

The members of the meeting unanimously approved the extensions.

This decision brings the number of Japanese reactors whose operations have been extended beyond 40 years to six. The other four are the No.1 and No.2 reactors at the Takahama nuclear power plant and the No.3 reactor at the Mihama plant -- all in Fukui Prefecture -- as well as the Tokai No.2 plant's reactor in Ibaraki Prefecture.