Japan’s Kansai Electric Power Company on 20 May began loading 157 fuel assemblies into unit 3 of its Mihama NPP in Fukui Prefecture. Mihama 3 will 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 plans to restart the reactor in late June after an inspection by the Nuclear Regulation Authority (NRA).

After the Fukushima Daiichi nuclear accident, the operation of reactors in Japan was limited by law to 40 years in principle. However, a further 20 years of operation is possible if they pass a screening by NRA and gain consent from local governments.

Two other aging reactors, units 1&2 at Kansai Electric's Takahama plant in the same prefecture, have gone through similar procedures to operate beyond the 40-year limit. All three are 826MWe presuriosed water reactors.

In 2016, NRA confirmed the compatibility of the three units with the new regulatory standards, and Kansai was granted approval to make changes to the reactor installations (basic design approval) and to extend their operating lifetimes to 60 years. On April 28, the governor of Fukui Prefecture agreed to restarting the reactors.

However, Mihama 3 will be suspended again as Kansai has not yet completed facilities for responding to specific severe accidents – specific safety facilities – which are required under the new regulatory standards as anti-terrorism measures. The deadline for completing those facilities is 25 October, and their design and (initial) work plans were only approved by NRA in April.

Fuel began to be loaded at Takahama 1 on 14 May while Takahama 2, meanwhile, is undergoing work on safety improvement measures.

However, the deadlines for completing specific safety facilities or both units is 9 June and they will only be restarted once the required work is completed.