The International Atomic Energy Agency (IAEA) has published a new report confirming the consistency of independent analyses of marine samples collected near Japan’s Fukushima Daiichi NPP under the IAEA Additional Measures related to the discharge of Advanced Liquid Processing System (ALPS) treated water into the sea.
The ALPS system removes 62 types of radionuclides, except for tritium (3H), a radioactive isotope of hydrogen. In addition, carbon-14 (C-14), potassium-40 (K-40), strontium-90 (Sr-90), iodine-129 (I- 129), and some isotopes of caesium (Cs) and plutonium (Pu) remain in the water, albeit in smaller quantities.
The report presents the results of analyses of seawater and fish samples collected near the plant in September 2025 and independently analysed by laboratories in Japan, China, the Republic of Korea, New Zealand, the Russian Federation and Switzerland, as well as by the IAEA’s Marine Environment Laboratories in Monaco. The results were almost uniformly comparable and consistent with the Japanese monitoring data examined through the exercise.
The measured radionuclide concentrations support the conclusion of the IAEA’s 2023 Comprehensive Report that the discharges as planned would have a negligible radiological impact on people and the environment.
Tokyo Electric Power Company Holdings (Tepco), operator of the Fukushima plant, began discharging the ALPS treated water into the sea in August 2023. The discharge remains subject to the IAEA’s ongoing safety reviews to verify that it continues to be conducted in accordance with relevant international safety standards.
The IAEA began implementing the Additional Measures in October 2024 with the aim of broadening international participation and enhancing transparency in the Agency’s sampling and analysis activities, while enabling third parties to conduct hands-on, independent verification of radionuclide concentration levels. The Additional Measures covers key stages of the discharge process: ALPS treated water before dilution with seawater, ALPS treated water after dilution with seawater, and seawater and fish in the vicinity of the plant.
For the marine environmental monitoring exercise, surface seawater was collected from a monitoring location in the vicinity of the NPP A batch of fish caught in the vicinity were selected the following day. The participating laboratories analysed the seawater for tritium, strontium-90 and caesium-137, while the fish samples were analysed for caesium-137. The IAEA subsequently compiled and evaluated the results to assess their comparability and consistency.
IAEA has also confirmed that the tritium concentration in the 25th batch of ALPS-treated water, which Tepco has begun discharging is far below Japan’s operational limit and consistent with international safety standards.
As part of its ongoing safety review, the IAEA independently tested samples from the latest batch before its release into the sea. On-site analysis confirmed that tritium levels were far below Japan’s operational limit of 1,500 becquerels per litre and tritium levels met international safety standards.
Japan has so far discharged roughly 188,000 cubic metres of ALPS-treated water in batches since August 2023. The IAEA has confirmed that the tritium levels in the first 24 batches were far below the operational limits set by Japan.
