Fukushima Water Monitoring Earns IAEA Confidence as Global Labs Back TEPCO Results

The comparison examined samples collected in July 2025 from storage tanks containing water designated for Fukushima Daiichi’s 15th discharge batch.

The International Atomic Energy Agency (IAEA) has reported that Tokyo Electric Power Company Holdings (TEPCO) continues to show a high level of skill in measuring radioactive substances in treated water at Japan's Fukushima Daiichi Nuclear Power Station. Its fourth comparison of laboratory results found strong agreement between the plant operator's measurements and independent testing by international laboratories, giving the agency confidence in TEPCO's ability to produce reliable monitoring data for the ongoing discharge of Advanced Liquid Processing System (ALPS) treated water.

International laboratories put TEPCO's measurements to the test

The comparison examined samples collected in July 2025 from storage tanks containing water designated for Fukushima Daiichi's 15th discharge batch. TEPCO's results were assessed against measurements produced independently by IAEA laboratories in Austria and Monaco and expert laboratories in China, France, the Republic of Korea and Switzerland. Participating laboratories belong to the IAEA's Analytical Laboratories for the Measurement of Environmental Radioactivity, known as the ALMERA network, and submitted their findings to the agency for comparison.

Having several laboratories examine samples from the same water gives researchers a practical way to check whether measurements agree across different testing teams and facilities. The exercise forms part of the IAEA's continuing review of the safety-related aspects of Japan's discharge programme, with this latest assessment focusing on the quality of TEPCO's sampling and analysis. The 15th batch was subsequently released beginning in September 2025, when separate IAEA testing confirmed that its tritium concentration after dilution was far below Japan's operational limit.

Findings support confidence in sampling and detection methods

According to the supplied press release, the report found that TEPCO produced accurate results demonstrating a high degree of proficiency, collected representative samples using appropriate methodological standards, and chose analytical methods suited to the radionuclides being measured. Its reported detection limits were below one percent of the respective regulatory limits for every radionuclide included in its source term—the set of radionuclides covered by this monitoring assessment. That finding concerns how sensitively the methods can detect radioactive substances; it does not mean the measured concentrations themselves were all below one percent of regulatory limits.

These findings led the IAEA to conclude that TEPCO has a robust analytical system capable of supporting Fukushima Daiichi's technical needs during the discharge programme. Reliable source monitoring depends on the full process, from collecting water that properly represents a tank's contents to selecting suitable tests and reporting accurate measurements, so the assessment provides confidence in the operator's ability to carry out that work consistently.

Marine sampling extends the checks beyond the plant

The IAEA has maintained a continuous presence at Fukushima Daiichi since before releases began in August 2023, conducting on-site observations, independent sampling and analysis, laboratory comparisons and checks of Japan's monitoring data. A mission scheduled for 5–17 October 2026 will collect and pre-treat seawater, sediment and marine organisms around the plant for further laboratory comparisons supporting independent checks of Japan's marine environmental monitoring. Experts from China's Third Institute of Oceanography, the Korea Institute of Nuclear Safety and Switzerland's Spiez Laboratory will accompany the agency.

Samples from the mission will also support a separate IAEA comparison project launched in 2014 to strengthen quality assurance in broader Japanese marine monitoring. This work checks whether laboratories produce dependable, comparable environmental measurements, extending scrutiny from water held at the plant to the surrounding marine environment.