Assessment of the amount of cesium-137 released into the Pacific Ocean after the Fukushima accident and analysis of its dispersion in Japanese coastal waters

Numerical modeling was used to provide a new estimate of the amount of 137Cs released directly into the ocean from the Fukushima Daiichi nuclear power plant (NPP) after the accident in March 2011 and to gain insights into the physical processes that led to its dispersion in the marine environment du...

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Bibliographic Details
Published in:Journal of Geophysical Research: Oceans 2012-11, Vol.117 (C11), p.n/a
Main Authors: Estournel, C., Bosc, E., Bocquet, M., Ulses, C., Marsaleix, P., Winiarek, V., Osvath, I., Nguyen, C., Duhaut, T., Lyard, F., Michaud, H., Auclair, F.
Format: Article
Language:English
Subjects:
Applied sciences
Biological oceanography
cesium
Chemical oceanography
Computer Science
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Fukushima
Geophysics
inverse method
Marine
Marine pollution
Modeling and Simulation
Natural water pollution
nuclear accident
numerical modelling
Oceanography
Physical oceanography
Pollution
Pollution, environment geology
Seawaters, estuaries
Water treatment and pollution
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Summary:Numerical modeling was used to provide a new estimate of the amount of 137Cs released directly into the ocean from the Fukushima Daiichi nuclear power plant (NPP) after the accident in March 2011 and to gain insights into the physical processes that led to its dispersion in the marine environment during the months following the accident. An inverse method was used to determine the time‐dependent137Cs input responsible for the concentrations observed at the NPP's two liquid discharge outlets. The method was then validated through comparisons of the simulated concentrations with concentrations measured in seawater at different points in the neighborhood of the plant. An underestimation was noticed for stations located 30 km offshore. The resulting bias in the release inventory was estimated. Finally, the maximum 137Cs activity released directly to the ocean was estimated to lie between 5.1 and 5.5 PBq (Peta Becquerel = 1015 Bq) but uncertainties remain on the amount of radionuclides released during the first few days after the accident. This estimate was compared to previous ones and differences were analyzed further. The temporal and spatial variations of the 137Cs concentration present in the coastal waters were shown to be strongly related to the wind intensity and direction. During the first month after the accident, winds blowing toward the south confined the radionuclides directly released into the ocean to a narrow coastal band. Afterwards, frequent northward wind events increased the dispersion over the whole continental shelf, leading to strongly reduced concentrations. Key Points Assessment of cesium‐137 released from Fukushima power plant Dispersion of radionuclides induced by winds
ISSN:0148-0227
2169-9275
2156-2202
2169-9291
DOI:10.1029/2012JC007933