The operator of the crippled Fukushima Daiichi nuclear power plant plans to build an undersea tunnel to send treated water into the sea.
Tokyo Electric Power Company made the announcement Wednesday, saying the tunnel is scheduled to be completed by early 2023.
Water is used to cool molten nuclear fuel at the plant. Most radioactive materials are taken out, but a substance called tritium is difficult to remove.
Under the new plan, treated water will be mixed with sea water until tritium is well below the national maximum allowed level. It will then be sent through the tunnel to a point about 1 kilometer off the coast.
The Japanese government decided in April that releasing treated water into the sea could begin in 2 years, as long as the water is diluted.
The plan has been met with strong opposition, especially from local fishermen.
TEPCO says it will boost monitoring of tritium's diffusion in the nearby waters.