Radiation imaging of a highly contaminated filter train inside Fukushima Daiichi Nuclear Power Station Unit 2 using an integrated Radiation Imaging System based on a Compton camera

佐藤 優樹; 寺阪 祐太

Journal of Nuclear Science and Technology, 14 Pages, 2023/00

https://doi.org/10.1080/00223131.2022.2159894

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.

ガンマ線画像スペクトル分光法による高放射線場環境の画像化による定量的放射能分布解析法(委託研究); 令和2年度英知を結集した原子力科学技術・人材育成推進事業

廃炉環境国際共同研究センター; 京都大学*

JAEA-Review 2022-027, 85 Pages, 2022/11

JAEA-Review-2022-027.pdf:5.72MB

日本原子力研究開発機構(JAEA)廃炉環境国際共同研究センター(CLADS)では、令和2年度英知を結集した原子力科学技術・人材育成推進事業(以下、「本事業」という)を実施している。本事業は、東京電力ホールディングス株式会社福島第一原子力発電所(1F)の廃炉等をはじめとした原子力分野の課題解決に貢献するため、国内外の英知を結集し、様々な分野の知見や経験を、従前の機関や分野の壁を越えて緊密に融合・連携させた基礎的・基盤的研究及び人材育成を推進することを目的としている。平成30年度の新規採択課題から実施主体を文部科学省からJAEAに移行することで、JAEAとアカデミアとの連携を強化し、廃炉に資する中長期的な研究開発・人材育成をより安定的かつ継続的に実施する体制を構築した。本研究は、研究課題のうち、平成30年度に採択された「ガンマ線画像スペクトル分光法による高放射線場環境の画像化による定量的放射能分布解析法」の平成30年度から令和3年度の研究成果について取りまとめたものである(令和3年度まで契約延長)。本課題は令和3年度が最終年度となるため4年度分の成果を取りまとめた。本研究では、ガンマ線イメージング装置であるETCCを1F廃炉事業での使用可能な可搬型装置でかつ高線量環境下で動作可能なように改良し、廃炉の現場に導入できるようにした。ETCCは世界初の光学カメラと同じ全単射撮像が可能なガンマ線カメラである。そのためETCCは一般的な定量的画像解析法を放射線にも適用可能とすることが可能で、1Fの廃炉に係る解決すべき6つの重点課題に革新的進展をもたらす。例えば廃炉工事で発生する汚染の飛散を3次元ガンマ線イメージングによりオンラインで検知、さらに拡散の動的な検知から精度の高い拡散予想を可能にする。それを実証するため令和元年に、1F敷地内1㎞四方を一度に画像モニタリングし、同時に100か所以上のスペクトル観測を実現し、今まで不明だったスカイシャインガンマ線スペクトル及び分布の計測に成功した。さらに京都大学複合原子力科学研究所原子炉建屋内の3次元線量計測を実施、微量なAr41の大気拡散を3次元の動画撮像に成功。廃炉を超え一般の原子炉での高精度な放射線3次元画像モニタリング及び放射能拡散予想システムが実現できることを示す画期的な成果が得られた。

Noninvasive imaging of hollow structures and gas movement revealed the gas partial-pressure-gradient-driven long-distance gas movement in the aerenchyma along the leaf blade to submerged organs in rice

尹 永根*; 森 欣順*; 鈴井 伸郎*; 栗田 圭輔; 山口 充孝*; 三好 悠太*; 長尾 悠人*; 芦苅 基行*; 永井 啓祐*; 河地 有木*

New Phytologist, 232(5), p.1974 - 1984, 2021/12

https://doi.org/10.1111/nph.17726

イネ植物()は中空の器官を持ち、これが水上の葉から水没した器官へ空気を供給する経路として機能すると推定される。しかし、イネにおけるガス移動はリアルタイムで可視化されていない。本研究では、部分的に水没したイネの葉に窒素13標識窒素([N]N)トレーサーガスを供給し、葉身、葉鞘、節間に沿って下方に移動するガスの動きを経時的に観察した。

Practical tests of neutron transmission imaging with a superconducting kinetic-inductance sensor

Vu, TheDang; 宍戸 寛明*; 相澤 一也; 小嶋 健児*; 小山 富男*; 及川 健一; 原田 正英; 奥 隆之; 曽山 和彦; 宮嶋 茂之*; et al.

Nuclear Instruments and Methods in Physics Research A, 1006, p.165411_1 - 165411_8, 2021/08

https://doi.org/10.1016/j.nima.2021.165411

We found that the sizes of the Gd islands determined from the transmission image correlated strongly with those determined from the SEM image. We demonstrated the CB-KID could be used to identify (1) tiny voids in a thermally sprayed continuous GdO film in and (2) various mosaic morphologies and different eutectic microstructures in Wood's metal samples. The fact that the CB-KID system could be used to identify features of samples with a wide distribution of sizes and thicknesses is promising for real application of the device for imaging samples of interest to material scientists. Operating the CB-KID at higher temperatures appreciably improved the efficiency for simultaneously identifying the X and Y positions of hotspots. We also compared the detection efficiency with the PHITS simulations. We now plan to improve the detection efficiency by increasing the thickness of the B neutron conversion layer

Analysis and mapping of detailed inner information of crystalline grain by wavelength-resolved neutron transmission imaging with individual Bragg-dip profile-fitting analysis

櫻井 洋亮*; 佐藤 博隆*; 足立 望*; 諸岡 聡; 戸高 義一*; 加美山 隆*

Applied Sciences (Internet), 11(11), p.5219_1 - 5219_17, 2021/06

https://doi.org/10.3390/app11115219

As a new method for evaluating single crystal and oligocrystal, pulsed neutron Bragg-dip transmission analysis/imaging method is being developed. In this study, a single Bragg-dip profile fitting analysis method was newly developed, and applied for analyzing detailed inner information in a crystalline grain position-dependently. In the method, the spectrum profile of a single Bragg-dip is analyzed at each position over a grain. As a result, it is expected that changes of crystal orientation, mosaic spread angle and thickness of a perfect crystal can be evaluated from the wavelength, the width and the integrated intensity of the Bragg-dip, respectively. For confirming this effectiveness, the method was applied to experimental data of position-dependent Bragg-dip transmission spectra of a Si-steel plate consisting of oligocrystals. As a result, inner information of multiple crystalline grains could be visualized and evaluated. The small change of crystal orientation in a grain, about 0.4, could be observed by imaging the Bragg-dip wavelengths. By imaging the Bragg-dip widths, both another grain and mosaic block in a grain were detected. Furthermore, imaging results of the integrated intensities of Bragg-dips were consistent with the results of Bragg-dip width imaging. These small crystallographic changes have not been observed and visualized by previous Bragg-dip analysis methods.

Neutron Bragg-edge transmission imaging for microstructure and residual strain in induction hardened gears

Su, Y. H.; 及川 健一; 篠原 武尚; 甲斐 哲也; 堀野 孝*; 井戸原 修*; 三阪 佳孝*; 友田 陽*

Scientific Reports (Internet), 11, p.4155_1 - 4155_14, 2021/02

https://doi.org/10.1038/s41598-021-83555-9

A time-of-flight Bragg-edge neutron transmission imaging was used to investigate the microstructure and strain distributions in a gear hardened by a newly developed two-step induction-heating method: precursor (Sample 1) and final product (Sample 2). The edge- position and edge-broadening were determined and mapped with high spatial resolution, which enabled us to confirm the two-dimensional distributions of the microstructure and residual strain. A deep hardened layer was made for Sample 1 in which martensite was formed on the entire teeth and the outer peripheral portion of the gear body. Sample 2 was subjected to double induction-hardening, where a tempered martensite was formed as the thermal refined microstructure between a fine-grained martensite at the tooth surface and a ferrite-pearlite microstructure at the core. The relationship between edge-broadening and the Vickers hardness described by a linear equation was employed to derive the elastic residual strain. The residual strain map for Sample 2 revealed that a steep compressive strain was introduced into the fine-grained martensite at the tooth surface by the super rapid induction- heating and quenching process. The reversal of tension was speculated to occur below 2 mm from the tooth tip, and the strain was almost zero in the core region.

アルファダストの検出を目指した超高位置分解能イメージング装置の開発(委託研究); 令和元年度英知を結集した原子力科学技術・人材育成推進事業

廃炉環境国際共同研究センター; 東北大学*

JAEA-Review 2020-039, 59 Pages, 2021/01

JAEA-Review-2020-039.pdf:4.18MB

日本原子力研究開発機構(JAEA)廃炉環境国際共同研究センター(CLADS)では、令和元年度英知を結集した原子力科学技術・人材育成推進事業(以下、「本事業」という)を実施している。本事業は、東京電力ホールディングス福島第一原子力発電所の廃炉等をはじめとした原子力分野の課題解決に貢献するため、国内外の英知を結集し、様々な分野の知見や経験を、従前の機関や分野の壁を越えて緊密に融合・連携させた基礎的・基盤的研究及び人材育成を推進することを目的としている。平成30年度の新規採択課題から実施主体を文部科学省からJAEAに移行することで、JAEAとアカデミアとの連携を強化し、廃炉に資する中長期的な研究開発・人材育成をより安定的かつ継続的に実施する体制を構築した。本研究は、研究課題のうち、平成30年度に採択された「アルファダストの検出を目指した超高位置分解能イメージング装置の開発」の令和元年度の研究成果について取りまとめたものである。本研究は、福島第一原発の廃炉を進めるうえで、ある段階からは作業員が実際に炉内、ないしは、炉のがれき・破片を解体・撤去する際に、ダストとして舞う放射線核種、特に体内被曝の影響が高いアルファ線を放出する核種などの把握を目指した撮像カメラの開発を行うものである。ダストの把握に必要な10m程度以下の優れた位置分解能を達成するために、シンチレータの高性能化、カメラの最適化などに取り組んできた。また、ここで得られた技術をもとに、光ファイバーを用いた超高線量場でのリアルタイム線量モニタの開発も取り組んだ。

Measurements of intensity of produced light in water during irradiations of electron beams with energies above and below the Cerenkov-light threshold

山本 誠一*; 長尾 悠人*; 栗田 圭輔; 山口 充孝*; 河地 有木*

Journal of Instrumentation (Internet), 16(1), p.P01007_1 - P01007_9, 2021/01

https://doi.org/10.1088/1748-0221/16/01/P01007

最近、チェレンコフ光の閾値以下のエネルギーを持つ粒子を照射した際の水の発光が、様々な種類の放射線で発見された。しかしながら、チェレンコフ光の強度とチェレンコフ閾値以下のエネルギーを持つ放射線を照射した際の水の発光強度との関係はよく分かっていない。この点を明らかにするために、チェレンコフ光の閾値以上と閾値以下の最大エネルギーを持つ電子線を水に照射し、発生する光を測定した。

Remote detection of radioactive hotspot using a Compton camera mounted on a moving multi-copter drone above a contaminated area in Fukushima

佐藤 優樹; 小澤 慎吾*; 寺阪 祐太; 峯本 浩二郎*; 田村 智志*; 新宮 一駿*; 根本 誠*; 鳥居 建男

Journal of Nuclear Science and Technology, 57(6), p.734 - 744, 2020/06

https://doi.org/10.1080/00223131.2020.1720845

The Fukushima Daiichi Nuclear Power Station, operated by Tokyo Electric Power Company Holdings, Inc., suffered a meltdown as a result of a large tsunami triggered by the Great East Japan Earthquake on March 11, 2011. To proceed with the environmental recovery by decontamination, drawing a radiation distribution map that can indicate the distribution of radioactive substances is extremely important to establish detailed decontamination plans. We developed a remote radiation imaging system consisting of a lightweight Compton camera and a multi-copter drone to remotely measure the distribution of the radioactive substances. This system can perform radiation imaging using a Compton camera while flying and moving. In addition, it is also possible to draw the distribution of radioactive substances three-dimensionally by projecting the radiation image measured with the Compton camera on a three-dimensional topography model separately acquired by a 3D-LiDAR. We conducted a survey of radioactive hotspots in difficult-to-return zone in the coastal area of Fukushima, Japan. The drone system succeeded in three-dimensional visualization of several hotspots deposited on the ground. Such remote technology would be useful not only for monitoring the difficult-to-return zone, but also for monitoring distribution of radioactive substances inside the site of the FDNPS where decommissioning work is ongoing.

Visualization of radioactive substances using freely moving gamma-ray imager based on Structure from Motion

佐藤 優樹; 鳥居 建男

Proceedings of International Youth Nuclear Congress 2020 (IYNC 2020) (Internet), 4 Pages, 2020/05

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., suffered a meltdown as a result of a large tsunami triggered by the Great East Japan Earthquake on March 11, 2011. We have been conducting demonstration tests for detection of radioactive hotspots inside the FDNPS buildings using a Compton camera, a kind of gamma-ray imager. In this work, we introduced the 3D visualization of radioactive substances by using combination of the Compton camera and optical camera based on Structure from Motion (SfM). By taking photographs of the experimental environment while freely moving, a 3D structural model of the environment can be reconstructed from the multiple photographs, and the movement trajectory of the optical camera can be estimated simultaneously using the SfM. Furthermore, the radioactive substances can be visualized by drawing an image of the radioactive substances on the 3D structural model using gamma-ray data acquired by the Compton camera. In the demonstration, we succeeded in visualizing a Cs-radiation source on the 3D structural model of the experimental environment while freely moving these devices. This technology is useful for making it easy to recognize radioactive substances in decommissioning work site such as the FDNPS.