Japan's Nuclear Regulation Authority (NRA) has approved a plan to release treated water stored at the Fukushima Daiichi NPP into the ocean, the government has said. The water, used to cool the melted reactor cores in the aftermath of the 2011 nuclear disaster, is stored in around 1,000 huge tanks at the plant containing more than 1.3 million tonnes. Total storage capacity has been reached and NRA has deemed it safe to release the water following treatment although it will still contain traces of tritium, the foreign ministry said in a statement.

NRA made the decision during an extraordinary meeting during which it discussed and gave final approval to the plan drawn up by plant operator, Tokyo Electric Power Company (Tepco), in line with a government decision. Tepco) will face additional inspections by regulators, the Ministry added.

The contaminated cooling water and groundwater is treated by the Advanced Liquid Processing System (ALPS), which removes most of the radioactive contamination, with the exception of tritium. The government therefore plans to dilute the treated water it so that tritium levels falls below national regulations and will then start releasing it next spring. NRA initially approved Tepco’s plan in May and then invited opinions from the public. Of the 1,233 responses, 670 were about technical matters such as the measurement of the concentration of tritium in the treated water and the plant's ability to withstand earthquakes. NRA officials discussed the opinions and concluded that Tepco’s plan is reasonable.

Japan initially announced plans to discharge treated water into the sea over a period of about 30 years in April 2021, asking the International Atomic Energy Agency (IAEA) to review these plans against IAEA safety standards. Tepco submitted the basic design of plans for a treated water dilution/discharge facility and related facilities to the NRA in December 2021. According to the plans, treated water would be diluted with seawater to reduce the amount of tritium to less than one-fortieth of government standards before it is released to the sea through a 1km undersea tunnel.

Tepco had already begun construction in December on the undersea tunnel and also plans to build another facility to dilute treated water following approval from Fukushima Prefecture and local municipalities of Okuma and Futaba. It aims to complete construction work by mid-April 2023.

Tepco said that regarding the design and security of the water dilution/discharge facility and related facilities and reports on radiological impact assessments regarding discharge tp the sea, it had “taken seriously the items pointed out by the NRA during review meetings and by the IAEA”. The suggestions were reflected in the revised applications for approval.

Japan's Ministry of Foreign Affairs said in its statement that its approval means safety of the installation of the ALPS-treated water discharge facility has been confirmed. "Nevertheless, this does not mean that Tepco can immediately start the discharge of the ALPS-treated water into the sea. Before doing so, remaining processes, such as NRA's Pre-Service Inspections to check and confirm the installation status of the discharge facilities, will continue.”

The Ministry added: “The discharge of the ALPS-treated water into the sea will not start until after these steps are duly taken. The IAEA will continue to conduct its independent review throughout, including while these steps are taken, and the Government of Japan will carefully consider the findings and observations from the IAEA's review."

Despite official approval, the plan continues to encountered opposition from fishing unions in the region which fear its impact on their livelihoods. China, South Korea, and Taiwan have also objected.