In one of the remaining steps before Japan decides to release more than one million metric tons of treated radioactive water from the Fukushima nuclear plant into the Pacific Ocean, the International Atomic Energy Agency declared on Tuesday that the government’s plan had met the agency’s safety standards.
The nuclear authority’s final report concluded that the treated water would “have a negligible radiological impact to people and the environment” once it is released.
Japan’s plan has provoked controversy both at home and abroad, as government officials in China and many residents in South Korea have protested the release as unsafe.
Rafael Grossi, the International Atomic Energy Agency’s director general, said that, should Japan proceed with its planned discharge, the IAEA would also open a station in Fukushima to continue reviewing the water’s safety “for decades to come.”
Japan announced its proposal to release the water from the Fukushima plant in 2019 and approved the plan two years later. Since then, an IAEA task force has conducted several reviews of the nation’s progress in treating the water.
For years, Tepco, the power company that operated the plant and that is now overseeing its decommissioning, said that treatment of the water — which involves sending it through a powerful filtration system to remove most radioactive material — was making it safe to release.
Critics say that the Japanese government and Tepco have not been transparent enough about the treatment process or the planned release.
Wu Jianghao, China’s ambassador to Japan, said in a news conference on Tuesday that “Japan should stop the plan to release the water into the sea, but seriously consult with the international community and consider a scientific, safe, transparent and convincing response.” He added that Japan had made its decision without “sufficient consultations.”
Even within Japan, opinion is divided. In a poll released over the weekend by JNN, a Japanese television network, 45 percent of respondents supported the plan, while 40 percent said they were against it.
“So many good scientists feel that the data presented so far has been incomplete,” said Azby Brown, lead researcher with Safecast, an independent radiation-monitoring group.
Mr. Brown said that the health risk posed by the released water will “be very low and a magnitude of thousands of times lower than everyday exposure” to radiation. “But the entire process has not been transparent enough,” he said. “It has not been inclusive, and they have not been thorough.”
Tokyo has offered repeated assurances that the water is safe enough to be released into the ocean, saying that filtration has removed most isotopes, though it does contain traces of tritium, an isotope that is hard to separate from water, as well as small traces of carbon-14 and iodine-129, according to Mr. Brown.
At a meeting with Mr. Grossi, Prime Minister Fumio Kishida of Japan said the nation “would not approve a release that could have a negative impact on people in Japan and the world and the environment.” He added that the government would “continue to thoroughly explain in and outside of Japan” its rationale for releasing the treated water into the sea, “based on scientific grounds with high transparency.”
Hirokazu Matsuno, chief cabinet secretary to Mr. Kishida, said on Tuesday that the discharge was still on target for this summer after the government had reviewed safety measures and considered “damages resulting from rumors” in other countries.
How to respond to the discharge of Fukushima water has become a deeply polarizing issue in South Korea, threatening the fragile rapprochement between Seoul and Tokyo that began earlier this year.
Recent surveys showed that 80 to 85 percent of South Koreans opposed Japan’s plan to dump the Fukushima water into the Pacific and worried about the impact it would have on seafood and the marine environment.
Mr. Grossi will visit Seoul on Friday to discuss the rising anxiety in South Korea, where salt prices have surged in recent weeks after people started hoarding sea salt harvested from salt ponds on the country’s west coast ahead of the discharge.
Park Gwangon, a leader of South Korea’s opposition Democratic Party, cited fears among South Koreans that the IAEA’s safety review would be “political, rather than scientific” and “tailored for Japan.”
The South Korean government has tried to dispel fears among its residents by vowing to ramp up efforts to monitor seawater, fisheries and natural salt farms for any rise in radioactive substances.
Government officials reassured the public on Monday that South Korea’s ban on seafood from the waters near Fukushima — first imposed following the 2011 disaster — would remain in place even after Japan began discharging the treated water.
Mr. Grossi said that the water release method being deployed in Japan has a “proven track record” in many other countries, including China, South Korea and the United States. Under the current plan, the water would be released in a controlled, gradual manner over the course of several decades.
The water Japan plans to discharge into the Pacific was mainly used to cool damaged reactors at the Fukushima power plant, which was destroyed in 2011 by an earthquake and tsunami. Japan says it needs to release the water that’s currently stored before the plant runs out of storage space.
Hisako Ueno contributed to this report.