Distribution, dynamics, and fate of radiocesium derived from FDNPP accident in the ocean

ABSTRACT

This paper gives an overview of the research results obtained in 10 years after the accident at Fukushima Daiichi Nuclear Power Plant (FDNPP), focusing on the distribution and dynamics of ¹³⁷Cs, which is one of major accident-derived radionuclides. Immediately after the FDNPP accident, 8–21 PBq of ¹³⁷Cs was transported to the ocean mainly due to direct discharge to the ocean, and deposition in the ocean via the atmosphere. ¹³⁷Cs in seawater traveled eastward on the surface of the North Pacific Ocean along the Kuroshio Extension over a period of several years. Some of ¹³⁷Cs is also recirculated to the western margin of the subtropical Pacific via the intermediate layer. The concentration of radiocesium in marine organisms also increased immediately after the accident, and then decreased over time. The concentration of radiocesium in brackish and demersal fishes decreased at a slower rate than the concentration of radiocesium in surface-dwelling fish. The amount of ¹³⁷Cs accumulated on the seafloor is only about 1% (0.2PBq) of the amount carried to the ocean, but it remains in the sediments in the coastal area for a long period of time and gradually migrates to the seawater and ecosystems near the seafloor.

KEYWORDS:

• Accident
• environment
• seawater
• seabed sediment
• marine biota
• numerical simulation
• cesium 137

Acknowledgments

The authors would like to thank Prof. Toshihiko Ohnuki for giving us the opportunity to write this review paper. We also thank the members of Research Group for Environmental Science (JAEA) and Marine Inorganic Chemistry Group (AORI, UTokyo) for their support in summarizing this review. In particular, we would appreciate Dr. Haruyasu Nagai and Dr. Takuya Kobayashi (JAEA) for their valuable comments. The observed data in this paper include those obtained from seven research cruises by R/V Shinsei-maru, Hakuho-maru, and Tansei-maru carried out from 2011 to 2018. This research was partially supported by Joint research program of the Institute for Cosmic Ray Research (ICRR), and Environmental Radioactivity Research Network Center [F19-48 and F20-50].

Disclosure statement

No potential conflict of interest was reported by the author(s).