The operator of the crippled Fukushima Daiichi nuclear power plant has shown to media work to dig an underwater tunnel for releasing treated water from the facility into the ocean.
Tokyo Electric Power Company began building the tunnel in early August to release the water about one kilometer offshore, after diluting it.
The operator gained approval for the work from the Nuclear Regulation Authority and local authorities. The project is in line with the Japanese government's policy.
On Tuesday, media were allowed to view the construction site, where workers used a huge excavator called a shield machine under the seabed.
The tunnel starts about 16 meters underground near a quay wall of the plant's No.5 and 6 reactor buildings.
TEPCO officials say the tunnel is being dug at a pace of five to six meters a day, and is so far 80 meters long.
The firm aims to complete the work next spring, but has suggested it may take until next summer, depending on weather.
Local fishery workers have expressed concern about possible reputational damage from the release. Fukushima Prefecture and other local authorities say the plan has yet to gain public understanding.
Reactors at the plant suffered meltdowns in the March 2011 earthquake and tsunami.
Water used to cool molten fuel at the facility mixes with rain and groundwater. Accumulated water is treated to remove most radioactive materials and stored in tanks on the plant's premises.
The filtered water still contains tritium. The government plans to dilute the water to bring the concentration of tritium well below the percentage permitted by national regulations.
The amount of tritium in the diluted water is also expected to be below World Health Organization guidance levels for drinking water quality.