The verdict ends years of debate over how to dispose of roughly 1 million cubic meters of the water, enough to fill 400 Olympic-sized swimming pools, that leaked into the power stations that suffered core meltdowns after an quake and tsunami in 2011.
Environmental and fishing groups oppose the idea but many scientists say the risk it would pose is low.
"It's not true that the government has decided on a direction, or the timing for a decision", Chief Cabinet Secretary Katsunobu Kato told reporters in Tokyo on Friday.
The water would be diluted inside the plant before release so it is 40 times less concentrated, the Yomiuri Shimbun said, with the whole process taking 30 years.
That's according reports from the Kyodo news agency and other media on Friday (October 16).
Photo by William Daniels/The New York TimesIn this January 25, 2018, file photo, an installation of a dome-shaped rooftop cover housing key equipment is near completion at Unit 3 reactor of the Fukushima Dai-ich nuclear power plant ahead of a fuel removal from its storage pool in Okuma, Fukushima Prefecture, northeast Japan.
The water has been treated using an advanced liquid processing system, or ALPS, to remove most contaminants other than relatively less toxic tritium and is stored in tanks on the facility's premises.
Plant operator TEPCO is building more tanks, but all will be full by mid-2022.
The release of the water "could deal a fatal blow to the future of Japanese fishery", said Hiroshi Kishi, the chairman of the Federation of Japan Fisheries Cooperatives. To avoid delays in decommissioning, we need to make a decision quickly, "he said at a press conference".
The International Atomic Energy Agency's Director General Rafael Grossi said during his visit to the plant in February, the release of the contaminated water into the sea meets global standards of practice in the industry.
The court said regulators could have prepared for the 9.1-magnitude natural disaster and tsunami which swamped the power plant.
"The closure of the plant in Fukushima Daiichi is an important prerequisite for restoring the nuclear disaster in Fukushima".
In 2018, Tokyo Electric apologised after admitting its filtration systems had not removed all unsafe material from the water, collected from the cooling pipes used to keep fuel cores from melting when the plant was crippled.
According to Japanes media, the Japanese government will make formal announcement this month.