The Japanese government on 13 April formally announced that the treated water stored at the Fukushima Daiichi NPP site will be discharged into the sea, “based on more than six years of comprehensive study by experts, reviews by the IAEA, and engagement with parties concerned”. Five disposal methods had earlier been considered by the government: controlled discharge into the sea, ground injection, discharge as steam, discharge as hydrogen, and solidification for underground burial.

Tokyo Electric Power Company (Tepco) is expected to begin the process in 2023 in line with international standards and regulations. The water used to cool the damaged reactors at Fukushima Daiichi has been treated using an advanced liquid processing system (ALPS) to remove all radioactive material apart from tritium. The treated water is currently stored on the Fukushima Daiichi site in more than 1000 large tanks with a storage capacity of about 1.37 million cubic metres. However, the complex is expected to run out of water storage capacity by the summer of 2022, with contaminated water increasing by about 170 tons a day.

Japan's Ministry for Economy, Trade and Industry (METI) has now released a basic policy for disposing of the stored treated water. The 15-page document by the Inter-Ministerial Council for Contaminated Water, Treated Water and Decommissioning issues said Tepco has been “making efforts to reduce the risks associated with the continuously generated contaminated water”. It said measures were taken to reduce the amount of contaminated water “using multi-layered approaches including the construction and operation of sub-drains and the land-side impermeable walls (frozen soil walls)”. The water is stored “after radioactive materials are removed from the contaminated water to the maximum extent using the Multi-nuclides Removal Equipment (ALPS3) and other facilities”.

The document notes: "Regarding the tanks installed on the site of Fukushima Daiichi nuclear power plant, it has been pointed out that the existence of the tanks themselves is a cause of the adverse impacts on reputation, and that the risk of leakage and other risks due to deterioration or disaster may increase along with long-term storage," the document says. "Moreover, building additional tanks in surrounding areas outside the Fukushima Daiichi plant for additional storage would require more land and result in an additional burden on the people who are working diligently toward reconstruction."

The basic policy calls for the ALPS-treated water to be discharged into the sea "on the condition that full compliance with the laws and regulations is observed, and measures to minimise adverse impacts on reputation are thoroughly implemented". Before any action can be taken, Tepco will have to obtain approval for its detailed plan from Nuclear Regulation Authority (NRA), as well as approval for construction of the necessary facilities. Discharge is expected to begin in about two years with a small amount of water being released initially to assess its impacts on the surrounding environment.

According to the policy document, the tritium will be diluted to 1500 becquerels per litre, which is one-40th of the concentration permitted under Japanese safety standards and one-seventh of the World Health Organisation's guideline for drinking water. The total annual amount of tritium to be discharged "will be at a level below the operational target value for tritium discharge of the Fukushima Daiichi plant before the accident (22 trillion becquerels per year)". The amount will be reviewed periodically. "This operational value for tritium discharge is within the range of the amount of discharge from each nuclear power station inside and outside the county."

Under the basic policy, the government will provide support to various industries such as the fisheries industry in Fukushima prefecture, its neighbouring prefectures and others. This support will include setting up and developing sales channels both in local areas and areas of major consumption, including overseas.

In a 13 April statement, Tepco said the government decision on the water “comes after more than six years of debate by the Tritiated Water Task Force and the Subcommittee on Handling of ALPS Treated Water, and is based on the opinions of the residents of the local communities and many other parties concerned, it is a decision that we take very seriously”.

Given public concern about the impacts that the discharge of treated water will have on the environment “and adverse impacts on reputation”, Tepco will “take a proactive and leading role in initiatives that focus on each stage of production, processing, distribution and consumption in order to minimise the adverse impacts on reputation, and shall provide suitable compensation for reputational damage that occurs despite the implementation of these countermeasures”.

Japan’s decision was welcomed by International Atomic Energy Agency (IAEA) Director General Rafael Mariano Grossi, who described it as “a milestone that will help pave the way for continued progress in the decommissioning of the Fukushima Daiichi nuclear power plant”. He noted:"Tanks with the water occupy large areas of the site, and water management, including the disposal of the treated water in a safe and transparent manner involving all stakeholders, is of key importance for the sustainability of these decommissioning activities." He added that the decision “is in line with practice globally, even though the large amount of water at the Fukushima plant makes it a unique and complex case”.

Japan has requested IAEA cooperation in the disposal of the water including international expert missions to review the plans and activities against IAEA safety standards, and participation in environmental monitoring operations. "We will work closely with Japan before, during and after the discharge of the water," said Grossi. "Our cooperation and our presence will help build confidence – in Japan and beyond – that the water disposal is carried out without an adverse impact on human health and the environment."

Approval also came from the USA, which sain on 14 April that Japan “appears to have adopted an approach in accordance with globally accepted nuclear safety standards”. The Department of State said in a statement on its website that the Japanese government has “been transparent about its decision”.

However the decision met with a negative response from the fishing industry, concerned that it would undermine consumer confidence in the region’s seafood. Hiroshi Kishi, president of JF Zengyoren, the federation of Japanese fisheries cooperatives, said: “Seeing this decision being made is completely outrageous and it is something we absolutely cannot accept. We will strongly protest.”

China and South Korea also protested about the decision. China said it was “extremely irresponsible”. Its foreign ministry said t discharging the water would, “seriously damage international public health and safety and the vital interests of the people of neighbouring countries”. South Korea said it could have a “direct and indirect impact on the safety of our people and surrounding environment”.