An International Atomic Energy Agency (IAEA) task force has carried out a second mission to Japan to review the country's updated technical plans for the discharge of treated water from the damaged Fukushima Daiichi nuclear power plant into the sea.

The IAEA task force inspects tanks of treated water at the Fukushima Daiichi site (Image: Tepco)

At the Fukushima Daiichi site, contaminated water - in part used to cool melted nuclear fuel - is treated by the ALPS system, which removes most of the radioactive contamination, with the exception of tritium. This treated water is currently stored in about 1000 tanks on site. The total tank storage capacity amounts to about 1.37 million cubic metres and all the tanks are expected to reach full capacity in mid to late-2023.

Japan announced in April 2021 it planned to discharge treated water stored at the Fukushima Daiichi plant into the sea over a period of about 30 years, and asked the IAEA to review its plans against IAEA safety standards.

This week the task force met with plant owner Tokyo Electric Power Company (Tepco) and Japan's Ministry of Economy, Trade and Industry (METI) in Tokyo as part of its second mission to assess safety-related elements of Tepco's implementation plan.

The updates by Japan to the technical plans for the discharge - made in part due to the feedback provided during the ongoing IAEA safety review process - include changes to the radiological environmental impact assessment prior to the discharge and the associated monitoring programmes.

In the report of the first meeting with Tepco/METI in February this year, the task force, among other points, called for further clarification of Tepco's characterisation of the treated water that will be discharged. In reviewing the updated plans this week, the task force noted that Japan had addressed this issue in its amendments. The IAEA said the task force will continue its consideration of these specific aspects.

"The task force's findings from its first mission in February 2022 were considered in depth and have been reflected in Japan's revisions to the plan," said IAEA Director General Rafael Mariano Grossi. "The IAEA will continue its impartial and science-based review of the proposed discharge plan."

During its latest mission, the task force also visited the Fukushima Daiichi plant to review the progress made in the design and construction of equipment and facilities for the discharge, including the tunnel that is being built to transport the treated water one kilometre out to sea.

“It was vital that the task force saw for themselves the advances made in the construction of the water dilution facility and the undersea tunnel," said Gustavo Caruso, director of the IAEA's Department of Nuclear Safety and Security and chair of the task force. "Our visit to see the equipment and facilities to be used for the discharge is essential to further reinforce our understanding of the process as part of our safety review."

The task force will release a report on its second mission within three months.

The IAEA said it will publish a comprehensive assessment on the safety of the discharge, including all components of the review - technical, regulatory and independent sampling and analysis - prior to the planned release in 2023.

The task force will conduct its next mission to meet with Japan's Nuclear Regulation Authority to continue its direct discussions on the regulatory aspects of the discharge from 16 to 20 January 2023.

Researched and written by World Nuclear News