[MAG44-14] Discovery of radiocesium-bearing microparticles from ocean samples emitted from the Fukushima Daiichi Nuclear Power Plant accident
Keywords:radiocesium-bearing microparticle, Fukushima Daiichi Nuclear Power Plant accident, Radioactive cesium
Method: We collected suspended particles (2011, 2013, 2015), sinking particles (2014), sediment cores (2011) from coastal area of Fukushima. By a wet separation method (Miura et al., 2018), we separated CsMPs from these samples. After measurement of radioactivity with a high-purity germanium semiconductor detector, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses were performed for separated CsMPs. Using autoradiography, we calculated 137Cs activity of unseparated hot spots over 0.1 Bq, which may be CsMPs.
Results and discussion: We separated 5 CsMPs from marine samples. The results of SEM-EDS analyses showed that these CsMPs have almost similar characteristics to the reported CsMPs because they mainly consist of Si, Cs, Fe, and Zn. Their 134Cs/137Cs showed that the CsMPs were from Unit 2 or 3 of FDNPP. 137Cs radioactivity per volume is also similar to reported CsMPs from Unit 2 or 3. In this presentation, we will show the effect of CsMPs on Kd values. CsMPs in the ocean samples will make apparent Kd values be higher than intrinsic Kd values related to the adsorption-desorption reaction to the clay minerals, which may explain the large variation of Cs concentration in marine samples.