A research team from Japan announced that even if contaminated water is discharged from the Fukushima nuclear power plant, the concentration of radioactive tritium in the Pacific Ocean does not change. This is the result of a simulation conducted up to 2099.
A joint research team from the University of Tokyo's Institute of Industrial Science and Fukushima University presented their findings on predicting changes in tritium concentration in the Pacific Ocean from 2023 to 2099 using an ocean general circulation model (OGCM) in the international journal "Marine Pollution Bulletin" on the 2nd.
The simulation results indicated that in the area within a 25 km radius of the Fukushima nuclear power plant, where contaminated water is discharged, the change in tritium concentration is less than 0.1%. The tritium concentration in this area is at a level of 0.03 to 0.2 Bq (becquerel, radiation unit) per liter, and predictions for the change in tritium concentration until 2099 indicate a change of less than 0.1%.
1 Bq means the amount of radiation produced when one atomic nucleus decays per second. This result suggests that tritium concentrations will remain at a level much lower than the World Health Organization (WHO) safe drinking water standard of 10,000 Bq per liter during the 21st century.
The Japanese government and Tokyo Electric Power Company (TEPCO) have been discharging contaminated water from the Fukushima nuclear accident site after treating it with a multi-nuclide removal facility (ALPS) since August 2023. ALPS removes radioactive substances such as cesium and strontium.
However, tritium, being a part of water molecules, is difficult to completely remove even with ALPS. The Japanese government dilutes it with a large volume of seawater to lower the tritium concentration below the standard before discharge.
Although the Japanese government has stated that the tritium concentration of the discharged contaminated water is below the standard, neighboring countries such as Korea and China have expressed concerns that the continuous discharge may increase tritium levels in the Pacific Ocean.
There have also been points raised within the scientific community regarding the need for sufficient verification. Although the Japanese government and the International Atomic Energy Agency (IAEA) are conducting real-time monitoring, there has been no verification of how long-term concentration changes or external factors such as climate change might affect the situation.
The scientific community believes that changes in ocean circulation due to global warming and the influence of small-scale currents tend to accelerate the dispersion of tritium. Thus, it was necessary to examine the long-term impacts of the Fukushima contaminated water discharge. This study is the first result of long-term research on how Fukushima's radioactive contaminated water affects tritium concentration in the Pacific Ocean.
Professor Alexandre Cauquoin from the University of Tokyo's Institute of Industrial Science, the corresponding author of the paper, explained, "This means that the difference in radiation resulting from the addition of ALPS-treated water to seawater is too small to measure."
Dr. Maksym Gusyev, a co-author from the Fukushima University Institute of Environmental Radioactivity, also noted, "Our simulations show that the discharge of ALPS-treated water will have little impact on tritium concentrations in the ocean in the short and long term." The research team stated that they will continue to study how tritium moves through vapor and ocean water.
References
Marine Pollution Bulletin (2025), DOI : https://doi.org/10.1016/j.marpolbul.2025.118294