全球海洋モデルにより福島第一原発から放出されるトリチウムの濃度分布を予測~放出計画をもとにした最新シミュレーション結果~

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2025-07-02 東京大学

東京大学・福島大学・海洋研究開発機構などの研究チームは、全球海洋モデル「COCO4.9」によるシミュレーションで、福島第一原発のALPS処理水から放出されるトリチウムの濃度分布を解析。結果、放出地点から25km以遠では、自然背景濃度と比べて増加はごくわずか(最大でも0.1%以下)で、国際基準(WHOの10,000Bq/L)を大きく下回ると判明。温暖化や海洋渦の影響を加味しても濃度上昇は検出限界以下であり、長期的にも放出の安全性が科学的に裏付けられた。

全球海洋モデルにより福島第一原発から放出されるトリチウムの濃度分布を予測~放出計画をもとにした最新シミュレーション結果~
トリチウム(3H または T と表記)は、水素(1H)の希少な放射性元素です。化学的に水素に類似しているため、環境中での移動性が高く、その99%以上はトリチウム水(HTO)の形で存在しています。これは、ALPS処理水に含まれるトリチウムの形態です。

<関連情報>

福島第一原子力発電所サイトからの人為起源トリチウム放出の海洋大循環モデルシミュレーション Ocean general circulation model simulations of anthropogenic tritium releases from the Fukushima Daiichi nuclear power plant site

Alexandre Cauquoin, Maksym Gusyev, Yoshiki Komuro, Jun Ono, Kei Yoshimura
Marine Pollution Bulletin  Available online: 2 July 2025
DOI:https://doi.org/10.1016/j.marpolbul.2025.118294

Highlights

  • Anthropogenic tritium releases from the FDNPP site to the ocean were modeled.
  • TEPCO release scenario was used as input to ocean general circulation model COCO4.9.
  • Except at the release point, anthropogenic tritium levels are below detection levels.
  • Global warming and marginally eddy-resolving resolution fasten the tritium transport.
  • However, their effects on tritium concentration values are below the detection limits.

Abstract

This study uses the ocean general circulation model COCO4.9 to examine for the first time the influence of climate conditions and horizontal resolutions on the spatial and temporal distributions of anthropogenic tritium released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) site into the ocean. For the tritium activities, the accidental discharge of March 2011 and the treated water release from TEPCO Scenario A (i.e., “largest amount of tritium” scenario) were used as inputs in COCO4.9 to perform global ocean tritium simulations extending up to the year 2099. Simulated tritium concentrations in the Pacific Ocean reveal similar spatial distributions and are below the detection limit, except for a tritium peak near the FDNPP discharge site during the accident. Under the SSP5–8.5 climate scenario (the highest CO2 emission case scenario), the shifting of the Kuroshio extension northward and the associated enhanced eastward transport affect the temporal variability of the tritium signal and increase the tritium concentration at the south of Japan, but still below the detection limit. In the high-resolution experiment, the Kuroshio current and its extension are narrower and stronger in the marginally eddy-resolving simulation and the transport of tritium is strengthened, allowing it to reach the western US or the Asian coast from the release point in a shorter time. However, except near the FDNPP discharge site, tritium concentration values are only slightly affected by the horizontal resolution, showing that the long-term safety threshold in terms of tritium concentration is not exceeded with the currently planned treated water release.

1702地球物理及び地球化学
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