On April 13, Japan announced plans to dump over 1 million tons of nuclear wastewater, contaminated by the 2011 Fukushima nuclear disaster, into the ocean. Prime Minister Yoshihide Suga said the proposal is a “realistic solution” to the issue of dwindling storage for water contaminated by radioactive debris left exposed by the disaster 10 years ago.

But the governments of neighboring South Korea and China have issued stern rebukes to the plan, with South Korean officials calling the proposal “absolutely unacceptable” and China describing it as “extremely irresponsible.”

But Tokyo is running out of options. The volume of contaminated water is growing by 170 tons a day, storing it in tanks indefinitely isn’t viable, and the silos need to be cleared before the remnants of the Fukushima power plant can be cleaned up for good. Flushing it out to sea might be the best option.

What’s the plan?

Tokyo Electric Power Co. (TEPCO), which operates the Fukushima power plant and is responsible for its cleanup, currently has over 1 million tons of wastewater siloed in storage tanks on the site of the Fukushima power plant ruins. The water is a combination of water pumped in to cool Fukushima’s exposed nuclear core reactor, and groundwater that passed through the plant’s contaminated remains.

But the volume of contaminated water in storage is growing, by a rate of around 170 tons a day, as the nuclear debris continues to contaminate groundwater and rain. TEPCO says it will run out of storage space for the wastewater by late 2022 and needs to begin discharging what it currently has.

Even so, TEPCO only plans to begin dumping the wastewater two years from now and estimates it will take 30 years to release it all.

Is it normal?

The U.S. and the International Atomic Energy Agency (IAEA) have approved the plan. The IAEA said TEPCO’s proposal was both “technically feasible and in line with international practice.”

Discharging wastewater into the sea is virtually the only way to deal with water contaminated by tritium—a radioactive hydrogen isotope that bonds with water. Luk Bing Lam, chairman of the Hong Kong Nuclear Society, says that “every nuclear power plant will do it every so often.”

Tritium is relatively harmless to human health, and the concentration of the tritium contained in TEPCO’s tanks is reportedly below the level of atmospheric tritium left over from global nuclear testing in the 1960s. But, Luk says, the water collected from Fukushima is different from the wastewater collected at functioning nuclear power stations.

“If it was purely tritium water then it probably wouldn’t be a problem,” Luk says. “But the core of the Fukushima power plant was damaged, so the water contaminated by the site contains hundreds of different chemicals, some of which are highly radioactive [and dangerous].”

Is it safe?

Radioactive contaminants can find their way from the sea into the food chain, posing an economic risk to the local fishery industry, which has already been decimated by the incident. Japan Fisheries Cooperatives chairman Hiroshi Kishi said TEPCO’s decision to discharge the water “is absolutely unacceptable.”

Japan has strict limits on acceptable levels of radioactivity in food, categorized by isotope, but public concern over sourcing food from contaminated areas is a threat to food exports. China, the U.S., and South Korea still prohibit imports of food sourced from certain areas exposed to the Fukushima disaster.

In 2018, TEPCO said that 70% of the water in storage would need to undergo “secondary treatment” to meet legal decontamination levels required for discharge. But some scientists say the long-term effects of even low-level radioactive isotopes on aquatic life are unknown.

TEPCO’s lack of transparency about its cleaning process is also cause for concern. Japan says the Fukushima water is treated with an advanced liquid processing system (ALPS) that filters out most of the radioactive elements. But Luk says colleagues in the nuclear industry can’t find any details on how the system actually works.

“They’re not sure how effective the ALPS is, and no filtration system is 100% effective,” Luk says.

Distrust over TEPCO’s claimed cleaning system has been an issue before. In 2011 a Japanese member of parliament drank a glass of treated water collected from the Fukushima power plant to prove it was safe.

Are there alternatives?

TEPCO says the bulging water tanks are preventing it from proceeding with work to fully decommission the Fukushima nuclear power plant—a process that involves dismantling and safely storing the contaminated ruins of the building. So long as the radioactive site remains exposed, it will continue to contaminate water.

Environmentalists argue TEPCO could store the water for longer if it was given permission to build new storage silos off-site—a request that would likely be met with objections from people living near the new sites. Prolonged storage would provide more time for some of the radioactive isotopes to decay to less-harmful levels.

But storage tanks also present a constant risk of leakage and require costly maintenance work.

“It’s a very difficult dilemma,” Luk says. “Contaminated liquid is the worst thing to handle, because it’s so hard to contain. Obviously Japan needs to sort out the problem as quickly as possible, but there are very few options for what to do.”