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佐藤 優樹; 寺阪 祐太
Journal of Nuclear Science and Technology, 60(8), p.1013 - 1026, 2023/08
被引用回数：5 パーセンタイル：98.48(Nuclear Science & Technology)The Fukushima Daiichi Nuclear Power Station (FDNPS) suffered a meltdown in the aftermath of the large tsunami caused by the Great East Japan Earthquake that occurred on 11 March 2011. A massive amount of radioactive substance was spread over a wide area both inside and outside the FDNPS site. In this study, we present an approach for visualizing a radioactive hotspot on a standby gas-treatment system filter train, a highly contaminated piece of equipment in the air-conditioning room of the Unit 2 reactor building of FDNPS, using radiation imaging based on a Compton camera. In addition to fixed-point measurements using only the Compton camera, data acquisition while moving using an integrated Radiation Imaging System (iRIS), which combines a Compton camera with a simultaneous localization and mapping device and a survey meter, enabled the three-dimensional visualization of the hotspot location on the filter train. In addition, we visualized the hotspot and quantitatively evaluated its radioactivity. Notably, the visualized hotspot location and estimated radioactivity value are consistent with the accident investigation report of the FDNPS. Finally, the extent to which the radioactivity increased the ambient dose equivalent rate in the surrounding environment was explored.
佐藤 優樹; 寺阪 祐太
Journal of Nuclear Science and Technology, 59(6), p.677 - 687, 2022/06
被引用回数：17 パーセンタイル：95.29(Nuclear Science & Technology)The Fukushima Daiichi Nuclear Power Station (FDNPS) went into meltdown after being hit by a large tsunami caused by the Great East Japan Earthquake on March 11, 2011. Measuring and understanding the distribution of radioactive contamination inside the FDNPS is essential for decommissioning work, reducing exposure to workers, and ensuring decontamination. This paper reports the visualization tests of radioactive contamination in the Unit 1/2 exhaust stack of the FDNPS using a compact Compton camera. Fixed-point measurements were conducted using only a Compton camera and moving measurements using an integrated radiation imaging system (iRIS) that combines a Compton camera with a simultaneous localization and mapping device. For the moving measurements, an operator carrying the iRIS acquires data continuously while walking in a passage near the stack. With both types of measurements, high-intensity contamination was detected at the base of the stack, and detailed three-dimensional (3D) visualization of the contamination was obtained from the moving measurement. The fixed-point measurements estimated the source intensity of the contamination from the reconstructed contamination image acquired by the Compton camera. Furthermore, workers can experience the work environment before actual work by importing a 3D structure model into a virtual reality system displaying the contamination image.
小嶋 拓治; 須永 博美; 瀧澤 春喜; 花屋 博秋; 橘 宏行*
JAERI-Review 2002-035, TIARA Annual Report 2001, p.123 - 124, 2002/11
Co
-線や2MeV電子線について特性が十分に明らかにされている、厚さ約10-200mmの薄いフィルム線量計をイオンビーム線量測定に応用した。線量範囲0.005-200kGyを
5%以内の精密度でカバーする線量測定技術の開発のため、高精密なフルエンス測定技術の開発とともに、薄いフィルム線量計の応答の線エネルギー付与(LET) 特性研究を行った。また、平面及び深度方向の空間分解能がそれぞれ約1
m及び10m未満の線量分布測定技術を開発した。最近の開発成果の概要をまとめて記す。
小嶋 拓治; 須永 博美; 瀧澤 春喜; 橘 宏行
JAERI-Review 99-025, TIARA Annual Report 1998, p.100 - 102, 1999/10
3
45MeV/amuのイオンビームのフルエンス測定について、これまでに総電荷量5nc/cm
以上では2%の高い精度が得られている。これに基づき、ファラデーカップのサプレッション電圧の最適化や非照射時の暗電流評価を行い、これ以下の電流域についても2%以内の精度が得られることを明らかにした。また、4種のフィルム線量計のLET特性を低LET放射線の場合に規格化して整理することにより、低LET放射線で得られる校正曲線への補正係数を4%以内で与えた。これにより、これまで着色量等の分布でしかなかった情報を線量分布として表すことが可能となった。このため、積層フィルム中の深度線量分布測定などの応用を進めている。
斎藤 公明
no journal, ,
The temporal change of environmental contamination conditions after the Fukushima accident have been clarified based on large-scale environmental monitoring data repeatedly obtained in the 80 km zone. The decreasing tendency of air dose rates was confirmed to obviously depend on land uses. In human-related diverse environments the air dose rates have decreased much faster than the physical decay of radiocesium. The horizontal movement of radiocesium in undisturbed fields were found to be generally quite small, though it has gradually penetrated into the deeper parts of the ground.
村上 冶子*; Sun, D.*; 関 暁之; 武宮 博; 斎藤 公明
no journal, ,
この研究では、複数のタイプの線量率の測定値を統合し、福島第一原子力発電所周辺の線量率の時空間分布を推定する階層ベイズ法を紹介する。この方法は、隣接するモニタリングポストデータに基づいて空間的に相関する対数線形の減衰傾向と空間線量率の変動を分離することにより、線量率の時間的変化を組み込んでいる。
佐藤 優樹
no journal, ,
This presentation introduces the technique for 3-D mapping of dose-rate distributions in radiation-work environments. By combining a survey meter and Structure from Motion (SfM) technology, the values of the dose rate acquired by the survey meter are mapped on the 3-D virtual model of the work environment reconstructed by SfM. In addition, this method makes it possible to map the dose rate in the work environment while freely moving the survey meter. If the distribution of the dose rate can be visualized three-dimensionally, it is possible to reduce the exposure dose of workers and contribute to the planning of an efficient work plan.
