Journal Article

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

Osvath, I., Nguyen, C., Auclair, F., Winiarek, V., Marsaleix, P., Duhaut, T., Michaud, H., Lyard, F., Bosc, E., Bocquet, M., Estournel, C., Ulses, C.

2012

Overview

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

• Publisher: Blackwell Publishing Ltd,American Geophysical Union,Wiley-Blackwell
• Subject: Applied sciences / Biological oceanography / Cesium / Cesium radioisotopes / Chemical analysis / Chemical oceanography / Coastal waters / Computer Science / Continental shelves / Earth sciences / Earth, ocean, space / Engineering and environment geology. Geothermics / Exact sciences and technology / Fukushima / Geophysics / inverse method / Marine / Marine environment / Marine pollution / Modeling and Simulation / Natural water pollution / nuclear accident / Nuclear power plants / numerical modelling / Oceanography / Physical oceanography / Pollution / Pollution, environment geology / Seawater / Seawaters, estuaries / Water analysis / Water treatment and pollution / Wind