Visualization of radiocesium distribution in surface layer of seafloor around Fukushima Daiichi Nuclear Power Plant

Large quantities of volatile radionuclides were released into the atmosphere and the hydrosphere following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March, 2011. Monitoring of radiocesium in sediment is important for evaluating the behavior of radiocesium in the environment and its effect on aquatic organisms. In this study, the radiocesium distribution in the surface sediment around the FDNPP was visualized as a radiocesium concentration map using periodical survey data from a towed gamma-ray detection system. The uncertainty of the radiocesium map was evaluated via comparison with a large amount of sediment core sample data. The characteristics of the radiocesium distribution were examined considering the seafloor topography and a geological map, which were obtained via acoustic wave survey. The characteristics of the formation of Cs-137 anomaly at the estuaries were analyzed using a contour map of Cs-137 concentration combined with water depth. Validation of the created map showed that it was comparable with actual sediment core samples. The map generated using the towed radiation survey depicted the Cs-137 concentration distribution as the position resolution of a 1 km mesh. Finally, the Cs-137 concentration decreased with time in consideration of such uncertainty.

Automated summary

This study visualized the distribution of radiocesium in sediment around the Fukushima Daiichi Nuclear Power Plant using data from a towed gamma-ray detection system, with the uncertainty of the map evaluated through comparison with sediment core sample data. The characteristics of radiocesium distribution were analyzed considering seafloor topography and geological maps, while the formation of Cs-137 anomaly at estuaries was studied using contour maps. Validation of the map showed good agreement with actual sediment core samples, with the Cs-137 concentration decreasing over time due to uncertainties.