Marine dispersion assessment of 137Cs released from the Fukushima nuclear accident

Highlights: • Radionuclides were released into the atmosphere and ocean by the Fukushima accident. • Simulations were carried out to evaluate the distribution of 137Cs in the ocean. • Calculated concentrations of 137Cs are compared with the measured data. • Results showed differences in seabed sediments with and without atmospheric fallout. -- Abstract: Radionuclides were released into the atmosphere and ocean due to an accident in the Fukushima Daiichi Nuclear Power Plant (NPP) in March 2011. Numerical simulations were carried out to evaluate the distribution of 137Cs in the ocean considering both direct releases to the sea and deposition from the atmosphere as source terms. A significant amount of atmospheric deposition occurred on the sea surface in the northeast direction from the Fukushima NPP, due to westerly winds and precipitations on March 15–31, 2011. In a previous study using local scale modeling, no significant differences in resulting 137Cs patterns in water and sediments with and without atmospheric deposition were found. However, this new research, on a regional scale, has pointed out meaningful differences in seabed sediment radionuclide concentrations in the Fukushima northeast area with and without atmospheric deposition