The IAEA Published a Report on its Fifth Review Mission of Safety Related Aspects of the Discharge of ALPS Treated Water into the Sea after the Start of the Discharge

1．Summary

From Monday, December 15 to Friday, December 19, 2025, IAEA officials and international experts (from Argentina, Canada, China, France, the Republic of Korea, Russia, the United Kingdom, the United States, and Vietnam) visited Japan to conduct IAEA's review mission of safety aspects of the discharge of ALPS treated water into the sea. This is the fifth review mission after the start of the discharge into the sea.

This fifth report after the start of the discharge into the sea presents conclusions of the review mission. The report highlights that, as in the previous four missions after the start of the discharge, the Task Force did not identify anything that is inconsistent with the requirements in the relevant international safety standards.

2．Key Points of the Report

(1) Viewpoints of Review

The report includes the key points of discussion between the IAEA Task Force and the Government of Japan and TEPCO, as well as a site visit to the FDNPS, and the Task Force's findings based on the following technical items:

1. Regulatory Control and Authorization
2. Safety Related Aspects of Systems and Processes for Controlling Discharges
3. Characterization of the Source
4. Radiological Environmental Impact Assessment
5. Source and Environmental Monitoring
6. Involvement of Interested Parties
7. Occupational Radiation Protection

(2) Main Review Results

The IAEA's overall conclusions are in line with those highlighted in the previous four missions after the start of the discharge:

• The Task Force did not identify anything that is inconsistent with the requirements in the relevant international safety standards. Therefore, the IAEA can reaffirm the fundamental conclusions of its safety review as outlined in the 4 July 2023 Comprehensive Report.
• The Task Force highlighted that the Nuclear Regulation Authority (NRA) has maintained effective regulatory oversight, including its onsite presence regarding the safety of the discharge of ALPS treated water.
• The Task Force confirmed that the equipment and facilities are installed and operated in a manner that is consistent with the Implementation Plan and the relevant international safety standards.
• The Task Force noted the importance of the IAEA's ongoing corroboration activities, based on interlaboratory comparisons assessing measurement quality and prompt onsite verification of tritium levels before and during discharge in providing a comprehensive, transparent and independent verification of the accuracy and reliability of the data reported by TEPCO and the Government of Japan.

(3) Future Plans

The Task Force will continue to review the activities of TEPCO, NRA and the Government of Japan to assess whether they are consistent with the relevant international safety standards.

The Task Force proposed that the next review mission taking place in the first half of 2026 focused on the Japan monitoring activities related to the discharge of ALPS treated water.

3. Response to the IAEA Report

Through the IAEA review, the Government of Japan will continue to take measures in accordance with international safety standards and take all possible measures to ensure the safety of the discharge. We will continue to maintain close coordination with the IAEA in sharing information with the international community in a highly transparent manner and fostering better understanding of the safety of the discharge of ALPS treated water within both the domestic and international communities.

Related Links

• The IAEA Press Release (April 30, 2026)
• The IAEA Report (Report 5: Fifth Review Mission to Japan after the Start of ALPS Treated Water Discharge (December 2025))
• The IAEA Conducted the Fifth Review Mission on the Safety of the Discharge of ALPS Treated Water into the Sea since the Start of the Discharge into the Sea (December 19, 2025)
• The IAEA Published a Report on its Fourth Review Mission of Safety Related Aspects of the Discharge of ALPS Treated Water into the Sea After the Start of the Discharge (September 16, 2025)
• The IAEA Published a Report on its Third Review Mission of Safety Related Aspects of the Discharge of ALPS Treated Water into the Sea after the Start of the Discharge (March 25, 2025)
• The IAEA Published a Report on Its Second Review Mission of Safety Aspects of Handling of ALPS Treated Water at Fukushima Daiichi Nuclear Power Station since the Start of the Discharge in April 2024 (July 18, 2024)
• The IAEA Published a Report on Its First Review Mission of Safety Aspects of Handling of ALPS Treated Water at Fukushima Daiichi Nuclear Power Station since the Start of the Discharge in October 2023 (January 30, 2024)
• Publication of the IAEA Comprehensive Report on the Safety Review of the ALPS Treated Water at TEPCO's Fukushima Daiichi nuclear Power Station (FDNPS) (July 4, 2023)
• Special Page explaining ALPS Treated Water [Ministry of Economy, Trade and Industry]
• Let's get to know and understand about ALPS treated water. [Ministry of Economy, Trade and Industry]
• IAEA Website about ALPS treated water

Division in Charge

Nuclear Accident Response Office, Agency for Natural Resources and Energy