Japan can finally release Fukushima waters into ocean, two-year UN review concludes

The treated water, enough to fill 500 Olympic-sized swimming pools, will be diluted to well below internationally approved levels of tritium

Protesters attend a rally against the Japanese government’s decision to release treated radioactive wastewater from the Fukushima nuclear power plant, in Seoul (AP)

The UN's nuclear watchdog on Tuesday gave Japan the green signal to dump treated radioactive water from the tsunami-wrecked Fukushima power plant into the ocean.

Japan is set to release more than 1 million metric tons of water into the Pacific that was used to cool damaged reactors at the power plant hit by an earthquake and a tsunami in 2011.

The move has been criticised by neighbours China and South Korea despite Tokyo's assurance that the water is safe and has been filtered to remove most isotopes though it does contain traces of tritium.

The International Atomic Energy Agency (IAEA), after a two-year review, found Japan's plans were consistent with global safety standards and that they would have a "negligible radiological impact to people and the environment".

"This is a very special night," IAEA chief Rafael Grossi told prime minister Fumio Kishida before handing him a thick blue folder containing the final report. Mr Grossi later told reporters that he would seek to allay lingering concerns and would station IAEA staff at the Fukushima plant to monitor the release.

"We have to recognise that such a thing has not happened before," he said, adding that Japan would have the final say on the release, which is due to span 30 to 40 years.

Tokyo has not specified a date to begin the water release pending official approval from the national nuclear regulatory body for Tokyo Electric Power (Tepco), whose final word on the plan unveiled in 2021 could come as early as this week.

The treated water, enough to fill 500 Olympic-sized swimming pools, will be diluted to well below internationally approved levels of tritium (an isotope of hydrogen hard to separate from water) before being released into the Pacific.

South Koreans stock up on sea salt and other sea products ahead of Fukushima wastewater release (Reuters)

Japanese fishing unions have opposed the wastewater dumping plan, saying it would undo work to repair reputations after several countries banned some Japanese food products after the 2011 disaster.

A petition from the regions around the plant has garnered more than 250,000 signatures since the proposal was first made.

"Japan will continue to provide explanations to the Japanese people and to the international community in a sincere manner based on scientific evidence and with high level of transparency," Mr Kishida said after meeting the nuclear watchdog chief.

Mr Grossi is scheduled to visit the Fukushima power plant on Wednesday and later head to South Korea, where consumers have been stockpiling sea salt due to fear of contamination.

South Korea's fisheries authorities have vowed to ramp up efforts to monitor natural salt farms for any rise in radioactive substances and maintain a ban on seafood from the waters near the power plant.

Chung Hwang-keun, the South Korean agricultural minister, said the country will not lift a ban on Japanese food products from the area around the nuclear plant until public concern over contamination is eased.

Because that ban will keep any affected items out, "there is no need to worry about agricultural products," he told Reuters.

China, which previously accused Japan of a lack of transparency, expressed regret over the "hasty" release of the nuclear watchdog's report.

"If the Japanese side is bent on going its own way, it must bear all the consequences," China's foreign ministry said in a statement.