资源环境科技发展态势分析平台

By Adam Vaughan

KIMIMASA MAYAMA/EPA-EFE/Shutterstock

Around 1.2 million tonnes of water contaminated by radioactive substances from the 2011 Fukushima nuclear disaster will be dumped in the Pacific Ocean, as part of a plan expected to be approved by the Japanese government within weeks.

The water is sitting in around 1000 tanks at the former nuclear power station, but the amount is growing daily as rainfall and groundwater entering the site continue to be contaminated. With an average of 160 tonnes a day being added last year, the International Atomic Energy Agency expects existing capacity will be full by mid-2022.

That is why the Japanese government is reportedly going to approve a strategy of discharging the water to the ocean, as recommended by scientific advisers. The release would start in around 2022 and continue for decades. The news sparked immediate complaints from Japanese fishing groups and veiled warnings that China would ban Japanese seafood imports. But are people right to be worried about the environmental and health effects of releasing such a large amount of contaminated water?

Much of the existing water has already been filtered by a process designed to remove more than 62 radioactive contaminants. The Japanese government and Tokyo Electric Power Company (TEPCO), the firm that runs the site, have emphasised that the main radionuclide remaining is tritium. Francis Livens at the University of Manchester, UK, says this is very hard to separate because it is a radioactive isotope of hydrogen, and so part of the water molecules themselves.

TEPCO has looked at technology to remove the tritium, but a presentation by the firm shows most methods wouldn’t work for the low concentrations in the tanks. Livens points out that most operating nuclear sites release this isotope.

Tritium is light, so could reach as far afield as the US west coast within two years, says Ken Buesseler at Woods Hole Oceanographic Institution in Falmouth, Massachusetts. Fortunately, tritium is relatively harmless for marine life as the low-energy particles it emits do little damage to living cells, he says.

A more serious matter is other, potentially more dangerous radionuclides in the water, including strontium-90 and iodine-129. TEPCO first published a list of contaminants in 2018. While filtering has reduced their concentrations, around 70 per cent of the water has yet to go through a secondary filtering process. “There are major questions as to whether it will work as planned,” says Shaun Burnie at Greenpeace.

Livens says filtering reduces the concentrations of non-tritium isotopes, but not to zero. Still, we shouldn’t be too worried about the levels that will be discharged, says Pascal Bailly du Bois at the Cherbourg-Octeville Radioecology Laboratory in France. “The radiological impact on fisheries and marine life will be very small, similar to when the Fukushima reactors were operating under normal conditions.” Buesseler thinks the impact on marine life – and humans who eat it – is unknown until we have a “better accounting” of the radionuclides in the tanks.

Simon Boxall at the University of Southampton, UK, says any potential risk would be from radionuclides building up in shellfish in coastal waters, but he thinks this risk is probably low. Further out in the Pacific Ocean, the risk is extremely low, but close monitoring and adherence to scientific advice will be key, he says.

There is no easy alternative. Another option, expanding capacity and storing the water on land or underground, would see 97 per cent of the tritium decay within 60 years due its short half-life, but that needs to be weighed against cost and the risk of tanks leaking in an earthquake-prone region, says Buesseler. “[Discharging to the sea] is probably the sensible option because anything else causes bigger problems,” says Livens.