The operator of the Mihama nuclear power plant on the Sea of Japan coast has started loading nuclear fuel into an aging reactor.
The No.3 unit would be the first reactor that is more than 40 years old to be put back online in Japan since the Fukushima Daiichi nuclear accident of 2011.
Kansai Electric Power Company started loading the reactor at the plant in Fukui Prefecture on Thursday afternoon.
The utility hopes to complete the loading of 157 fuel assemblies on Sunday. It plans to restart the reactor in late June after an inspection by the Nuclear Regulation Authority.
After the Fukushima Daiichi nuclear accident, the operation of reactors in Japan was limited by law to 40 years in principle.
But old reactors can still be allowed to operate for up to 60 years if they pass a screening by the regulator and gain consent from local governments.
Two other aging reactors, the No.1 and No.2 units of Kansai Electric's Takahama plant in the same prefecture, have gone through similar procedures to operate beyond the 40-year limit.
But the utility says no decision has been made on when to restart these reactors because facilities are still being constructed at the plant to ensure safety in the event of emergencies such as terrorist attacks.