IAEA to Conduct Third Extensive Sampling of Marine Environment Near Fukushima Daiichi Since Start of ALPS Treated Water Discharge

The International Atomic Energy Agency (IAEA) is in Japan this week to conduct marine sampling near the Fukushima Daiichi Nuclear Power Station (FDNPS). This visit forms part of the Agency's broader monitoring and assessment efforts, which contribute to its ongoing safety review of the ALPS (Advanced Liquid Processing System) treated water discharges.

During the mission, from 2 to 12 September, the IAEA team of scientists will observe the collection of seawater, marine sediment, fish and seaweed samples from coastal waters in the vicinity of the FDNPS. The mission will also include sampling at a local fish market and monitoring the preparation of samples prior to delivery to participating laboratories.

The IAEA Comprehensive Report on the Safety Review of the ALPS-Treated Water at the Fukushima Daiichi Nuclear Power Station - released on 4 July 2023 prior to the water discharge - found Japan's plan for handling the treated water to be consistent with international safety standards and that the discharge as planned would have a negligible radiological impact to people and the environment. Tokyo Electric Power Company Holdings (TEPCO) - operator of the FDNPS - started to discharge the water on 24 August 2023.

The IAEA team is joined by international experts from the French Authority for Nuclear Safety and Radiation Protection (L'Autorité de sûreté nucléaire et de radioprotection, ASNR), the Korea Institute of Nuclear Safety, and the Spiez Laboratory, Switzerland - all members of the IAEA's Analytical Laboratories for the Measurement of Environmental Radioactivity (ALMERA) network. These external scientists provide independent corroboration of Japan's environmental monitoring capabilities.

The IAEA conducts interlaboratory comparisons (ILCs) based on marine samples to verify Japan's radiological data for the ALPS treated water discharges. Identical samples are analysed by multiple independent laboratories, including the IAEA's own laboratories, to assess the comparability of radiological measurements.

Once the collection of samples is complete in Japan, they are homogenized, divided and sent for radionuclide analysis to all participating laboratories - the IAEA laboratories in Monaco and Vienna, ALMERA member laboratories in France, Republic of Korea and Switzerland, and Japanese institutions. The results will be submitted to the IAEA for evaluation, with focus on any statistically significant differences.

The findings will be publicly released in the second half of 2026. The extended timeline is required for sample distribution to laboratories worldwide and for the complex analytical methods required.

This mission is part of the IAEA's extensive monitoring and assessment activities for the safety review of ALPS treated water. In the series of ILCs, the Agency has already published several reports evaluating TEPCO's capabilities for accurately measuring the radionuclides in the treated water stored on site, and the capabilities of Japan's laboratories for accurate measuring of the radionuclides in seawater, sediment, fish and seaweed samples. An ILC to corroborate source monitoring based on samples of ALPS treated water collected in July 2025 is also ongoing.

Additionally, IAEA experts stationed at the Agency's office at FDNPS conduct regular independent on-site analyses of the batches of treated water. The IAEA has earlier confirmed that the tritium concentrations in the 14 batches of water already discharged were far below operational limits.

This week's mission will also provide samples for a separate IAEA ILC project initiated in 2014 to support the quality assurance of broader marine environmental monitoring by Japanese laboratories.