Evaluation of off-site distribution of radionuclides near the Fukushima Dai-ichi Nuclear Power Station in order to estimate on-site distribution

福島第一原子力発電所サイト内における放射性核種分布推測のためのサイト外核種分布の評価

飯島 和毅  ; 土肥 輝美   ; 駒 義和  ; 高畠 容子  ; 藤原 健壮 ; 新里 忠史  

Iijima, Kazuki; Dohi, Terumi; Koma, Yoshikazu; Takahatake, Yoko; Fujiwara, Kenso; Niizato, Tadafumi

福島第一原子力発電所(FDNPS)サイト内の放射性核種の分布状況を推測するため、サイト外の詳細な核種分布状況を調査した。FDNPSから5km圏内の走行サーベイにより、6本の放射性プルームが確認できた。サイト外のサンプリングで得られたSrおよびPuの表土中輸送比の傾向は、南方向に比べて西方向で大きく、過去に得られているサイト内の試料と同様であった。したがって、本法のアプローチは適用可能と考えられた。

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.