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Tanaka, Kazuya; Yamasaki, Shinya*
no journal, ,
We collected riverbed sediments at two sites (Yamakiya and Kuroiwa) in the Abukuma River system in Fukushima, and analyzed their size-fractioned samples. The size distributions of stable Cs and radiocesium were similar in the sediments. Silt size fractions contained high stable Cs and radiocesium concentrations possibly due to clay minerals. Their concentrations decreased with increasing particle size at the Yamakiya site. However, the coarse sand fractions at the Kuroiwa site showed higher concentrations than the fine sand fractions. The coarse sand fractions contained many weathered biotite grains, whereas hornblende was the major component in the fine sand fractions. It is well known that clay minerals and weathered biotite (micaceous minerals) adsorb Cs strongly at their edge sites. Therefore, the size distribution of stable Cs and radiocesium reflects their mineralogical compositions.
Iijima, Kazuki; Dohi, Terumi; Koma, Yoshikazu; Takahatake, Yoko; Fujiwara, Kenso; Niizato, Tadafumi
no journal, ,
To develop a model to estimate on-site distribution, detailed evaluation of the off-site distribution of radionuclides deposited on the soil and trees in the environment was carried out. Six traces of the radioactive plume, which we defined as NNW, W (divided into W-N and W-S), SW and S (divided into S-W and S-E) from a north to south direction, were clearly identified based on the off-site distribution of air dose rate measured by a car-borne survey within 5 km from the FDNPS. The tendency that the Transport Ratios for Sr and Pu to topsoils obtained in the west direction were higher than those of south direction was consistent with that observed in the previous on-site sampling. Therefore, the data suggest that the estimation of on-site distribution of radionuclides inventory based on the off-site distribution was applicable.
Dohi, Terumi; Iijima, Kazuki; Omura, Yoshihito*; Fujiwara, Kenso; Kikuchi, Naoyuki*
no journal, ,
The local radioactive contaminations (i.e. radioactive plume's trace) around the FDNPS were caused by the releasing radionuclides from each reactor, weather conditions, etc. Japan Atomic Energy Agency is carrying out the project to evaluate off-site distribution of radionuclides and to determine the origin of plume's traces at each point, since we develop the model to estimate on-site distribution. As lichens are known to be effective tools to monitor environmental radionuclides in both time and space because of their ability to retain radionuclides for a long period, lichen samples are expected to be used to examine initial fallout distribution. The purpose of this study is to measure radionuclides concentrations in lichens and analyse elemental composition in particles captured on lichen thalli, in order to evaluate initial distribution of radionuclides and clarify the contamination characteristics of the plume's traces nearby the FDNPS.