In satellite pictures, they look like the pale blue and gray eggs of a giant butterfly, laid in tight patterns on some dismal leaf. The eggs, made of steel, are tanks brimming with radioactive fluid—contaminated water from Japan’s Fukushima nuclear plant. The water will soon be diluted and pumped into the sea. Núria Casacuberta Arola, of ETH Zürich, is among those who will be watching. Closely.
“We have access to a ship that goes to the coast of Fukushima every year, sometimes once, sometimes twice,” she says. Casacuberta Arola and her colleagues regularly drop an assembly of jars into waters near the incapacitated power plant to collect samples at different depths. The lids of the jars close automatically, one by one, as the device is slowly pulled back up to the surface.
By doing this, and also taking sediment samples from the seabed, they hope to be able to tell in the coming months and years whether the disposal of water from Fukushima is causing a noticeable rise in radiation in this corner of the Pacific Ocean. The water release could start as early as next month. If there is a significant bump in radiation levels in the surrounding waters, it will mean things have gone very wrong.
In 2011, a massive tsunami struck Fukushima Daiichi Nuclear Power Station. The defensive sea wall intended to protect the plant from such an onslaught was many meters too low to stop the monster wave. Seawater flooded the facility, ultimately leading to partial meltdowns and huge explosions at some of the reactors. It is considered one of the worst nuclear accidents in history.
In the years since, workers have had to constantly pump water into Fukushima’s stricken reactors, which still contain hot nuclear fuel. This water has, thankfully, done its job of keeping the reactors cool, but it has become irradiated in the process, meaning it can’t just be flushed away. Workers have kept the used cooling water on-site, building tank after tank in which to store it. All the while, they have known that they will eventually have to dispose of it. Today, there are 1.3 million metric tons of contaminated water on-site. And no space for any more tanks. The time to do something about it is here.
It has taken years of research, modeling, and sampling, but earlier this month the International Atomic Energy Agency gave its approval for a discharge plan. Japan’s Nuclear Regulation Authority signed off on the proposals at the same time, meaning that the Tokyo Electric Power Co (Tepco), which is in charge of the plant and its cleanup, has full authority to begin slowly releasing the water into the ocean via a 1-km-long underwater pipe.
Some aren’t happy. Local fishers are strongly opposed to the plan, and there have been street protests in South Korea. Yet many scientists are highly confident that the discharge will be perfectly safe.
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The contaminated water, enough to fill more than 30,000 fuel-truck semi-trailers, contains a mix of unstable chemical elements, known as radionuclides, that emit radiation. To keep these radioactive components to a minimum, Tepco has installed special water purification technology that treats the water before storage. In essence, it involves passing the contaminated water through a series of chambers containing materials that can adsorb radionuclides. The isotopes stick to those materials and the water flows on, a little cleaner than before.
However, it is not 100 percent effective, and many of the radionuclides it’s designed to extract, such as the isotopes caesium-137 and strontium-90, for example, can still be found in the stored water. There are also some isotopes the system can’t remove at all, such as carbon-14 and tritium, a form of hydrogen with two neutrons and one proton in its nucleus (hydrogen usually contains just one proton).
Despite this, the water is extremely safe because the concentrations of radionuclides are so low, explains Jim Smith, a professor of environmental science at the University of Portsmouth. “I’m not concerned,” he says of the plan to discharge the water.
Many of the above radioactive isotopes were released into the ocean at the time of the disaster in 2011—and some traveled. One study found them floating around 3,000 km away in the Arctic Ocean six years after the accident. Once the discharge begins, radionuclides will undoubtedly spread out into the Pacific, but this is very unlikely to have a noticeable effect on the environment, Smith says.
For context, he points out that he has many years of experience studying the effects of radiation on living things near the destroyed nuclear power plant in Chernobyl. Even there, where exposure to radiation is much greater, the impact appears to be tiny. “We know radiation damages DNA, probably there are subtle effects of radiation at these levels, but we don’t generally see a significant effect on the ecosystem,” he says, referring to that work.
Plus, tritium—one of the isotopes that can’t be removed from the stored water—is already present all around us at low concentrations, though higher levels are associated with nuclear-related activities. The authors of one 2018 study speculated that unusually high levels of tritium in the Rhône river delta in France were down to historical pollution from the watchmaking industry—tritium has been used to make glow-in-the-dark paint for watch dials.
What many people don’t realize is that water containing tritium is actually routinely released into the sea—sometimes in vastly greater quantities than are to be discharged from Fukushima—by nuclear facilities all around the world, including in the US, Europe, and East Asia. The Cap de la Hague nuclear processing site in France releases 11,400 terabecquerels (Tbq) of tritium every year, which is more than 13 times the total radioactivity of the tritium across every storage tank at Fukushima.
Tepco is regularly testing the stored water ahead of the release, the company says. The water will be re-treated, multiple times if necessary, and diluted more than 100 times to bring its tritium radioactivity concentration down to no more than 0.0000000015 TBq per liter, a level equivalent to a 1/40 of Japan’s national safety standards. Roughly 70 percent of the stored water also contains radionuclides other than tritium that are at concentrations exceeding regulatory limits, says the Japanese government—levels of these will also be brought down to below Japan’s regulatory standards. The water will then be tested again before being discharged.
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For a final point of comparison, Smith calculates that cosmic rays interacting with the Earth’s atmosphere over the Pacific Ocean annually cause the natural deposition of 2,000 times more tritium than will be introduced by the gradual Fukushima release.
Tatsujiro Suzuki at Nagasaki University remembers watching in horror as the disaster unfolded back in 2011. “We all thought that this kind of thing would never happen in Japan,” he says. At the time, he was working for the government. He recalls the confusion over what was happening to the reactors in the days following the tsunami. Everyone was gripped by fear.
“Once you experience that kind of accident, you don’t want to see another one,” he says. The long shadow cast by the disaster means that, for the water release plan, the stakes—at least in terms of public trust—could not be higher.
Suzuki argues that it’s not quite fair to compare the Fukushima water to fluids discharged from other nuclear facilities elsewhere in the world because of the challenge of cleaning up the many different radionuclides here. “This is an unprecedented event, we have not done this before,” he says, adding that he thinks the procedure is “probably safe” but that there is still room for human error or an accident, such as another tsunami, that could cause an uncontrolled release of the water into the sea.
Tepco and the International Atomic Energy Agency have considered such possibilities and still judge the risk to human and marine life to be extremely low. Sameh Melhem, now at the World Nuclear Association, formerly worked for the Atomic Energy Agency and was involved in some of the research to evaluate the discharge plan. “I think it’s very safe for the operators themselves and also for the public,” he says, adding: “The radionuclide concentrations coming from this release, it’s negligible.”
Last November, Casacuberta Arola and her colleagues collected samples of seawater off the coast of Fukushima, and they have recently begun to analyze them. The scientists measure the levels of various radionuclides that might be present. For tritium, that means removing all helium from the sample and waiting to see how much new helium emerges from the water as a product of radioactivity. This makes it possible to extrapolate the amount of tritium that must be present, explains Casacuberta Arola. She and her team have records of radionuclide measurements like this from the sea off Fukushima going back years.
“We already know that the values that we see now close to Fukushima are close to the background values,” she says. If that changes, they should find out fairly quickly. As will the International Atomic Energy Agency and other observers, who, separately, intend to sample water and wildlife in the area in the coming years to keep an eye on things.
Smith says that despite overwhelming evidence that the water release will be entirely safe and heavily scrutinized at every turn, it is not surprising that some people are skeptical of the plan. They have a right to be, he adds, given the troubled history of the plant.
At the same time, the threat posed by the release—even in a worst-case scenario where everything goes wrong—is miniscule compared to some of the other environmental risks in the region, such as the effects of the climate crisis on the Pacific Ocean, Smith says.
Casacuberta Arola agrees. Negative coverage of the discharge plan has been used to “brainwash” people, she argues, and to instill fear against the nuclear energy industry. “To me,” she adds, “it’s been very much exaggerated.”