The Mainichi newspaper reported earlier that Tepco was likely to decommission the No.1 reactor at the Fukushima Daini power plant as it was the worst-hit of the facility's four reactors after the quake and tsunami, temporarily losing cooling functions.

Local governments have been calling for the decommission of all four reactors at Fukushima Daini. The government and the ruling Liberal Democratic Party have also pressed Tepco to make a decision on decommissioning the No.1 reactor.

Dozens of reactors elsewhere in Japan are still going through a relicensing process by a new regulator set up after the Fukushima disaster in 2011, the world's worst since Chernobyl 25 years previously, highlighted regulatory and operational failings by the country's nuclear utilities.

(This version of the story corrects typo in third paragraph)

(Reporting by Osamu Tsukimori)