Tohoku's Onawaga plant was closest among Japan's nuclear stations to the epicentre of the magnitude-9 quake in March 2011.
The company received a de facto regulatory approval to restart the No.2 reactor in 2020, by gaining a modification approval, but has seen a delay in the completion of safety constructions.
On Monday, the company said it was working to secure materials, equipment and workers for the safety construction works and was now aiming to restart the reactor around September. It was previously set for May.
Making a gradual comeback after the 2011 Fukushima disaster, nuclear power is key to Japan's efforts to decarbonise its economy and cut import costs of fossil fuels.
Nuclear energy has contributed to a reduction in Japan's imports of liquefied natural gas to its lowest in 14 years in 2023.
