Tokyo Electric Power Company Holdings Inc. plans to construct an approximately 1 kilometer-long undersea tunnel to release treated radioactive water from the crippled Fukushima No. 1 nuclear power plant out to sea, sources close to the matter said Tuesday.

While the level of the radioactive substance tritium that remains in the treated water will be diluted to below regulatory standards, the decision to release it offshore into the Pacific is aimed at preventing reputational damage to local marine products amid an outcry from fishermen.

The undersea tunnel will be constructed by hollowing out bedrock on the seabed near the No. 5 reactor at the Fukushima plant.