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Scientists from the Institute of Industrial Science at The University of Tokyo and the Institute of Environmental Radioactivity at Fukushima University have used a global ocean circulation model to assess the spread of tritium from the Fukushima Daiichi Nuclear Power Plant (FDNPP). Their findings show that both short-term and long-term effects on oceanic tritium levels, even far from the discharge site, are minimal—even under future climate change scenarios.

Credit: Institute of Industrial Science, The University of Tokyo

Tokyo, Japan – Since the 2011 incident at the Fukushima Daiichi Nuclear Power Plant, cooling water has been circulated through the reactors and then purified using the Advanced Liquid Processing System (ALPS). This cutting-edge system removes most radioactive substances, except for tritium. Because tritium is part of the water molecule and has a relatively long half-life of 12.32 years, it is extremely difficult and expensive to separate. Over time, large amounts of treated water collected on site, leaving limited room for storage. In 2021, the Japanese government announced a plan to gradually release the ALPS-treated water through an undersea tunnel about one kilometer long. These diluted water discharges began in August 2023 and are scheduled to continue until 2050.

In their recent computational study, researchers from The University of Tokyo and Fukushima University evaluated how much additional tritium the Pacific Ocean would absorb due to these discharges. The simulations showed that the resulting increase in tritium concentration is extremely low—about 0.1% or less compared to typical background levels, which range from 0.03 to 0.2 Bq/L within 25 kilometers of the release point. Such levels fall below the limits of detection and are significantly lower than the World Health Organization’s safety threshold of 10,000 Bq/L. These findings are consistent with ongoing water quality monitoring efforts being conducted alongside the releases.

"Since the announcement in 2021, several studies have analyzed how the release of ALPS-treated water could affect radiation levels in seawater and marine organisms," said Alexandre Cauquoin, lead author of the study. "However, there had been no global simulations based on realistic long-term discharge scenarios that also consider climate change. Our models allowed us to explore how ocean circulation patterns—impacted by warming temperatures—and small-scale ocean currents influence the distribution of tritium over time and space."

The research revealed that although global warming and water currents accelerate the spread of tritium, the resulting concentrations remain uniformly low. "Our modeling clearly demonstrates that discharges from the ALPS system will result in negligible impacts on tritium levels in the world’s oceans, both now and into the future," added Maksym Gusyev from Fukushima University’s Institute of Environmental Radioactivity.

These findings may prove valuable for further development of models tracking how tritiated water moves through both the atmosphere and oceans. Since tritium can act as a natural tracer, such simulations can enhance our understanding of global hydrological processes—such as rainfall patterns, ocean and atmospheric circulation, moisture transport, river systems, and groundwater movement.

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The research paper, titled “Ocean general circulation model simulations of anthropogenic tritium releases from the Fukushima Daiichi nuclear power plant site,” was published in the journal Marine Pollution Bulletin with the DOI: 10.1016/j.marpolbul.2025.118294.

About Institute of Industrial Science, The University of Tokyo

The Institute of Industrial Science (UTokyo-IIS) at The University of Tokyo is among Japan’s largest academic research institutions affiliated with a university. It encompasses over 120 specialized laboratories led by faculty members and supports more than 1,200 researchers, including approximately 800 students. The institute engages in diverse areas of engineering and has been dedicated, since its founding in 1949, to connecting academic studies with practical innovation across disciplines.

Journal

Marine Pollution Bulletin

DOI

10.1016/j.marpolbul.2025.118294

Article Title

Ocean general circulation model simulations of anthropogenic tritium releases from the Fukushima Daiichi Nuclear Power Plant site

Article Publication Date

2-Jul-2025