About seven tonnes of water containing radioactive elements leaked at the third reactor of the Mihama nuclear power plant in Fukui Prefecture, central Japan, The Nikkei reported on Monday, citing the operator Kansai Electric Power Company.

The Mihama nuclear power plant in Fukui Prefecture, central Japan, May 30, 2019. /CFP

The over 40-year-old reactor is currently out of service. The company is investigating whether the leak will affect the reactor's scheduled restart in mid-August.