TOKYO – A global watchdog on nuclear safety on Tuesday vouched for the safety of Japan’s controversial plan to discharge treated wastewater from its crippled Fukushima Daiichi nuclear plant into the Pacific Ocean.

The 129-page final report by the International Atomic Energy Agency (IAEA) paves the way for Japan to green-light and begin the release within weeks.

The process, once begun, will be irreversible, although safeguards are in place to halt the release in case of emergency. Because water is continuously being generated and accumulated, the discharge will last for decades until Fukushima Daiichi’s full decommissioning, which is expected around 2051.

Despite Japan’s safety avowals, its plan has been lambasted by its neighbours including China, South Korea and some Pacific Island nations. Local fishermen, fearing damage to their livelihoods, have likewise opposed the discharge.

While the IAEA stressed that its report was “neither a recommendation nor an endorsement” of Japan’s water discharge decision, Tokyo regards it as a neutral approval to proceed.

Contaminated water is first treated to remove radioactive nuclides except tritium, a naturally occurring isotope of hydrogen that is a routine by-product of nuclear plants worldwide. It is then further diluted with seawater before ejection 1km from shore.

IAEA director-general Rafael Mariano Grossi told a news conference in Tokyo that his agency’s “comprehensive, neutral, objective and scientifically sound” evaluation showed that the planned discharge was consistent with global industry and safety standards.

He stressed that the discharge will have “negligible radiological impact to people and the environment”, including marine animals and plants.

“This process of dilution, and chemical and other filtering, is nothing new. It’s something that exists in the industry,” he said, adding that the method is also used by nuclear plants in countries such as China, South Korea, the United States and France.

Japanese Prime Minister Fumio Kishida said: “I will not allow a release that would harm people or the environment in Japan or around the world.”

He vowed “a high degree of transparency” in the process, saying that he will continuously give explanations “based on scientific rationale”.

The IAEA panel comprised nuclear safety experts from 11 countries including China, Marshall Islands, Russia and South Korea. Inter-laboratory tests were also held, involving the Korea Institute of Nuclear Safety in South Korea.

But the prospect of dumping tonnes of water from Fukushima – a word scarred by the magnitude 9.0 earthquake and tsunami on March 11, 2011, that triggered one of the world’s worst nuclear disasters – into the Pacific Ocean has dredged up raw fears.

Any hopes Japan might have held that the IAEA’s report would smoothen the way forward for the water release – and Tokyo says there is no other way – were quickly dashed.

China, which has previously accused Japan of treating the Pacific Ocean as its “sewage dump”, said the report does not give Tokyo any legitimacy to proceed.

A Foreign Ministry spokesman said the report “failed to fully reflect views from experts that participated in the review” and that its conclusion “was not shared by all experts”.

“The Chinese side regrets the hasty release of the report,” the spokesman said. “We believe that the IAEA report should not be the ‘shield’ or ‘green light’ for Japan’s discharge of nuclear-contaminated water into the ocean.”

Earlier on Tuesday, China’s Ambassador to Japan Wu Jianghao urged Japan to change course, noting that there was no precedent for the release of wastewater into the ocean after a nuclear accident.

“Japan says that nuclear power plants around the world are all discharging wastewater. But this water has not been exposed to a reactor core that has melted,” he said.

Reaction was mixed in South Korea, where President Yoon Suk-yeol has sought to mend bilateral ties that soured under his predecessor Moon Jae-in.

Mr Yoon’s administration, which has had to fight assertions that it was siding with Japan, said that any release of treated water must be “in compliance with international law and standards in a way that is scientifically and objectively safe”.

Still, ruling party floor leader Yun Jae-ok said on Tuesday: “It could be 10 years, it could be 100 years – until the public is assured, seafood imports from Fukushima will be banned.”

South Korea, which dispatched an inspection team to Fukushima in May, is planning to publish its own review report on the matter.

Meanwhile, South Koreans are panic-buying sea salt amid fears that future supplies will be tainted. Allegations are also swirling in Seoul that the IAEA had been bribed by a Japanese bureaucrat and that the conclusions were long fixed.

A South Korean reporter ambushed Dr Grossi after the news conference with a question about the alleged corruption. She was subdued by his bodyguards as the IAEA chief asserted: “I didn’t receive money, okay. This is absurd. Is that clear?”

Dr Grossi will go to South Korea, New Zealand and the Cook Islands after his Japan visit to discuss the report.

Japan’s stance is that it cannot put off the water discharge any longer as it hinders the decommissioning process, with no more space available to build new storage tanks at the Fukushima Daiichi nuclear plant.

More than 1.3 million tonnes of water – enough to fill 500 Olympic-sized swimming pools – has accumulated in over 1,000 storage tanks. The water is treated using the Advanced Liquid Processing System, a pumping-and-filtration system that removes 62 types of radionuclides, except tritium.

Tritium is deemed to be relatively harmless because it is naturally occurring in tap water and rainfall and cannot penetrate human skin. The IAEA said that tritium, which has a half-life of about 12 years, is dangerous only if inhaled or ingested in very large doses.

Japan will further dilute the water before discharge, with plant operator Tokyo Electric Power Company estimating that up to 22 trillion becquerels of tritium will be released annually. A Japan fact sheet shows that this is far below tritium levels in water pumped out from China’s and South Korea’s nuclear power plants.

This also equates to less than 1,500 becquerels per litre, well below the regulatory standard of 60,000 becquerels per litre and under the 10,000 becquerel level set by the World Health Organisation.

The necessary equipment for the discharge, including dilution pumps, shutoff valves and gauges to measure the rate of water flow, has been installed and Japan’s Nuclear Regulatory Authority has begun verification inspections.

The water will be discharged 1km from shore via an underground tunnel, beyond an area where fishermen routinely operate. This is also to avoid mixing the discharged ALPS-treated water with seawater to be used for dilution.

The IAEA will set up a permanent office in Fukushima, Dr Grossi said, emphasising the need to establish a constant, impartial presence to monitor the discharge, and to build trust with stakeholders including local fishermen and leaders.

He also acknowledged concerns raised by other countries, which he suggested was because there is no precedent.

“We have to recognise that such a thing has not happened before, even if the release of treated water is nothing new... I suppose every country has different motivations to have concerns”, he said. 

The IAEA will “give good answers” to any questions, he said, but added that it was not his job to persuade them of Japan’s decision.