Japan will begin releasing treated radioactive wastewater from the ruined Fukushima Daiichi nuclear plant into the ocean this week, its government said on Tuesday, setting aside regional and domestic objections as it moves to eventually discharge over a million tons of the water into the sea.
Prime Minister Fumio Kishida made the announcement after a meeting of his cabinet, saying the release would begin on Thursday if weather and ocean conditions allowed.
The International Atomic Energy Agency said in July that the government’s plan met the agency’s safety standards, and it has said that releasing the treated water is not likely to pose a serious health threat to humans.
But some scientists have raised questions about whether the Japanese government and the company that operated the plant, Tokyo Electric Power, have been sufficiently forthcoming about what radioactive material may remain in the holding tanks.
The Chinese government has opposed the plan, as has a large segment of the South Korean public. Fishing groups and others in Japan have also expressed opposition.
Mr. Kishida visited the wrecked nuclear plant on Sunday and met with leaders of the Japanese fishery industry in Tokyo on Monday, vowing to ensure that fishermen can continue to make a living after the release.
Masanobu Sakamoto, head of the National Federation of Fisheries Cooperative Associations, said that while many of his group’s members had come to accept the government’s assurances on the safety of the discharge, it remained opposed because of the potential effects on fishermen’s livelihoods.
Since an earthquake and tsunami triggered a triple meltdown in Fukushima in 2011, the question of what to do with the accumulating tons of water used to cool nuclear fuel rods has been one of the biggest challenges facing both the government and Tokyo Electric.
For Japan, it is as much a political problem as it is an engineering or environmental one. Despite the determination by the international agency that it was safe to release the water, opponents at home and in neighboring countries have questioned both the government and the agency’s motives. When Japan’s cabinet approved the treated-water plan in 2021, it described the controlled ocean release as the best available disposal option.
People’s Daily, a state media organization owned by the Communist Party in China, has referred to the treated water as Japan’s “nuclear sewage.” And in South Korea, where seafood imports from waters near Fukushima are still banned, an opposition lawmaker warned that “no one can tell or predict for sure what the discharging of radioactive materials into the sea over an extended period of time will bring about.”
In Japan, both Fukushima and national fisheries associations have said they fear that once Tokyo Electric starts releasing the water, both domestic and international customers may be reluctant to eat fish from the region.
Although it has been a dozen years since the worst nuclear crisis since Chernobyl forced tens of thousands of people to flee the area around the ruined Fukushima plant, the cleanup is still in an early phase. The government says the water release is likely to take place over a period of 30 years.
The water is stored in more than 1,000 sky-blue tanks lined up on the site of the plant. Tokyo Electric — or Tepco, as it is known — pumps the water through the destroyed reactors to cool melted fuel that is still too hot and radioactive to remove.
As the water passes through the reactors, it accumulates radioactive nuclides. Tepco is putting the water through a powerful filtration system, in some cases repeatedly, that is designed to remove all the radioactive material except for tritium, a hydrogen isotope. Experts say tritium does not harm human health in small doses, and it is prohibitively expensive to remove in any case.
Other nuclear plants around the world, including in China, South Korea and the United States, use similar processes to treat cooling water, and also release water containing tritium into the oceans after such filtration.
Still, some scientists have questions. According to Tepco’s website, just 30 percent of the approximately 473,000 tons of water in the tanks have been fully treated to the point that only tritium remains.
“The idea is, ‘just trust us,’” said Ken Buesseler, a marine radiochemist at the Woods Hole Oceanographic Institution, who said he wanted to see more detailed analyses of what remains in the tanks, particularly those that have already undergone some treatment.
Dr. Buesseler said that while tritium is “one of the least dangerous” radioactive materials, others, like cesium or cobalt, could be more hazardous if they are released into the ocean.
He said the government had not investigated alternative options such as building more tanks or using the treated water to make cement. “I think they just want the cheapest, fastest solution, which is a pipe in the ocean,” Dr. Buesseler said.
Japan’s Ministry of Economy, Trade and Industry describes water treated in its filtration system as “purified” and has said any water that is released into the ocean will be “treated until it satisfies safety standards for all radioactive materials other than tritium.”
Kazuya Idemitsu, a professor of nuclear engineering at Tohoku University, said he was confident that the international agency would monitor the water release to ensure that only water containing tritium and no other radioactive material will be piped into the sea.
Dr. Idemitsu said that much of the public’s anxiety stemmed from the highly technical nature of the treatment process and the government’s difficulties in communicating the science.
“When it comes to this kind of scientific information, there are a lot of people who don’t understand or don’t know about it,” Dr. Idemitsu said. “And it may take more time to get to that understanding.”
Among fishermen who rely on the ocean waters off Fukushima for their daily catches, what matters is what would-be customers think.
“It’s a life-or-death issue for fishermen,” said Masatsugu Shibata, 67, who took his 40-foot fishing trawler out from a port at Iwaki in Fukushima before dawn on a recent morning and caught about a dozen large flounder. “I will be in trouble if they discharge” the water.
Mr. Shibata, who hopes to pass his fishing operation on to his son and grandson some day, said the fishing business had recovered only about 20 percent of its pre-disaster levels. When the water is released, he said, “there will definitely be reactions, for sure,” adding, “Many people would stop eating fish.”
“Now the government says it’s safe,” he said. “But safety and peace of mind are different.”
The government has already paid a total of 10 trillion yen ($68.4 billion) in compensation to fishermen, farmers and evacuated residents from Fukushima and other affected prefectures since 2011 to help make up for losses that resulted from the disaster.
Some countries have signaled their support for the government’s plan. Last week, before President Biden hosted Mr. Kishida and President Yoon Suk Yeol of South Korea at Camp David, Secretary of State Antony J. Blinken said that the United States was satisfied with Japan’s plan. In July, the European Union lifted all restrictions on fish and agricultural imports from Fukushima. The region had blocked shipments of products since the disaster.
While South Korea still bans seafood imports from waters off Fukushima, Mr. Yoon has endorsed the Japanese government plan amid recent warming relations between the two countries.
At a recent rally in downtown Seoul, protesters suggested that Japan use the treated water in farming or industry instead.
Opposition lawmakers have attacked Mr. Yoon for supporting the plan, with one accusing him of defending Japan “like a parrot.”
“We cannot let a government policy crucial for the people’s life and safety be decided by the president’s personal friendly feeling and intimacy toward Japan,” said Lee Byunghoon, an opposition lawmaker.
The Chinese government has been especially critical of Japan’s plan to release treated water at Fukushima, and has rejected the international agency’s report as insufficient proof that the release poses no undue risks.
“The report should not be the ‘shield’ or ‘greenlight’ for Japan’s discharge of nuclear-contaminated water into the ocean,” Wang Wenbin, a spokesman for China’s foreign ministry, said on July 5 at the ministry’s daily briefing.
China itself operates nuclear reactors along its seacoast, using seawater instead of scarce freshwater to cool the steam from reactors.
Keith Bradsher contributed reporting from Beijing, and Choe Sang-Hun from Seoul.
