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, 60(8), p.1013 - 1026, 2023/08

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.

Radiation imaging using an integrated radiation imaging system based on a compact Compton camera under Unit 1/2 exhaust stack of Fukushima Daiichi Nuclear Power Station

佐藤 優樹; 寺阪 祐太

Journal of Nuclear Science and Technology, 59(6), p.677 - 687, 2022/06

https://doi.org/10.1080/00223131.2021.2001391

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.

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; 京都大学*

JAEA-Review 2020-044, 79 Pages, 2021/01

JAEA-Review-2020-044.pdf:4.39MB

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「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。本研究では、ガンマ線イメージング装置であるETCCを高線量環境下で動作可能に改良するとともに、可搬型システムを構築して、福島第一原子力発電所(1F)の現場に導入できるようにする。また、ETCCを応用した定量的放射能分布解析法を開発し組み合わせることで、1Fの廃炉に係る解決すべき6つの重点課題に革新的な進歩をもたらす。これにより、3次元放射線分布、その由来の放射能分布を定量的に可視化できるシステムを実現させる。

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.

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); 平成30年度英知を結集した原子力科学技術・人材育成推進事業

廃炉国際共同研究センター; 京都大学*

JAEA-Review 2019-036, 65 Pages, 2020/03

JAEA-Review-2019-036.pdf:4.46MB

日本原子力研究開発機構(JAEA)廃炉国際共同研究センター(CLADS)では、平成30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「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」について取りまとめたものである。電子飛跡検出型コンプトンカメラ(ETCC)は、前段にガス増幅型位置検出器を用いて電子の3次元飛跡を測定することにより、従来型のコンプトンカメラの分解能を大幅に向上する技術として、これまで宇宙観測用として開発し医療への応用も進めて来た。本研究では、医療用に開発したETCCをもとに、現場での操作性を重視した軽ETCCを試作し、フィールド試験により実用性を評価する。

Electron-tracking Compton camera imaging of technetium-95m

初川 雄一*; 早川 岳人*; 塚田 和明; 橋本 和幸*; 佐藤 哲也; 浅井 雅人; 豊嶋 厚史; 谷森 達*; 園田 真也*; 株木 重人*; et al.

PLOS ONE (Internet), 13(12), p.e0208909_1 - e0208909_12, 2018/12

AA2018-0639.pdf:2.39MB

https://doi.org/10.1371/journal.pone.0208909

電子飛跡検出型コンプトンカメラ(ETCC)を用いて放射性同位元素Tcの画像撮像を実施した。Tcは、204, 582, 835keVの3本の線を放出し、濃縮同位体Moを用いてMo(p,n)Tc反応で合成される。濃縮Mo同位体三酸化物の再利用について実験を実施し、再生率7090%を達成した。画像は3本の線それぞれを用いて解析し取得した。その結果、線エネルギーが高いほど空間分解能が向上することが判り、Tcのような高エネルギー線放出核を利用することで、ETCCが人体の深部の組織や器官の医療画像撮像に有効であることを示唆する結果を得た。

Radiation imaging using a compact Compton camera inside the Fukushima Daiichi Nuclear Power Station building

佐藤 優樹; 谷藤 祐太; 寺阪 祐太; 宇佐美 博士; 冠城 雅晃; 川端 邦明; 宇津木 弥*; 菊地 弘幸*; 高平 史郎*; 鳥居 建男

Journal of Nuclear Science and Technology, 55(9), p.965 - 970, 2018/09

https://doi.org/10.1080/00223131.2018.1473171

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., went into meltdown after the occurrence of a large tsunami caused by the Great East Japan Earthquake of March 11, 2011. The radiation distribution measurements inside the FDNPS buildings are indispensable to execute decommissioning tasks in the reactor buildings. We conducted the radiation imaging experiment inside the turbine building of Unit 3 of the FDNPS using a compact Compton camera, and succeeded in visualizing the high-dose contamination (up to 3.5 mSv/h). We also drew a three-dimensional radiation distribution map inside the turbine building by integrating the radiation image resulting from the Compton camera into the point cloud data of the experimental environment acquired using the scanning laser range finder. The radiation distribution map shows the position of these contaminations on the real space image of the turbine building. The radiation distribution map helps workers to easily recognize the radioactive contamination and to decrease the radiation exposure; the contamination cannot be observed with the naked eye, naturally.

Development of compact Compton camera for 3D image reconstruction of radioactive contamination

佐藤 優樹; 寺阪 祐太; 小澤 慎吾*; 宮村 浩子; 冠城 雅晃; 谷藤 祐太; 川端 邦明; 鳥居 建男

Journal of Instrumentation (Internet), 12(11), p.C11007_1 - C11007_8, 2017/11

https://doi.org/10.1088/1748-0221/12/11/C11007

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., went into meltdown after the large tsunami caused by the Great East Japan Earthquake of March 11, 2011. Very large amounts of radionuclides were released from the damaged plant. Radiation distribution measurements inside the building of FDNPS are indispensable to execute the decommission tasks in the reactor buildings. We have developed a light-weight compact Compton camera to three-dimensionally measure the distribution of radioactive contamination inside FDNPS. The total weight of the Compton camera is lower than 1.0 kg. The -ray sensor of the Compton camera employs the Ce-doped GAGG scintillators coupled with a multi-pixel photon counter (MPPC: Hamamatsu Photonics K.K.,). We performed the 3D image reconstruction of the Cs-radioactive sources as shown in Fig. 1; the 3D radiation image is reconstructed using the multi-angle data measured with the Compton camera. Here, we introduce the development status of the 3D radiation imaging system consisting of the Compton camera. Moreover, we present the results of a performance evaluation test for 3D image reconstruction of radioactive contaminations in details.

Compact Compton camera for radiation distribution imaging under high dose rate environments

佐藤 優樹; 寺阪 祐太; 冠城 雅晃; 谷藤 祐太; 宇佐美 博士; 宮村 浩子; 小澤 慎吾*; 和泉 良*; 川端 邦明; 鈴木 敏和*; et al.

no journal, , 

The development of quick radiation imaging methods in the high dose rate environments is very important to accelerate decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS). We have developed a compact Compton camera for measurement of radioactive contamination inside FDNPS. We conducted a performance evaluation test inside the -ray irradiation facility, and the Compton camera can visualize the Cs-irradiation source under the dose rate of 1 mGy/h. We also developed the remote radiation imaging system consisting of the Compton camera and a multicopter-type drone. The drone system succeeded in observing the Cs-radioactive source, which was set on the floor surface, remotely. We plan to use the Compton camera and the drone system inside the buildings of FDNPS.

Visualization of radioactive substances on a 3D building model of the Fukushima Daiichi Nuclear Power Station

佐藤 優樹; 寺阪 祐太; 宇津木 弥*; 菊地 弘幸*; 高平 史郎*; 鳥居 建男

no journal, , 

The Fukushima-Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., went into meltdown after the occurrence of a large tsunami caused by the Great East Japan Earthquake on March 11, 2011. The radiation distribution measurements inside the site of the FDNPS are indispensable to execute decommissioning tasks. We have developed a three-dimensional (3D) radiation imaging technique for grasping the location of the high-dose rate region (hotspot) using a compact Compton camera and a photogrammetry technique to create 3D optical images. We succeeded in detecting the hotspot in a waste storage space inside the FDNPS using the Compton camera. We also created the 3D structural model of the waste storage space in the virtual space by using the photogrammetry and superimposed the image of the hotspot on the 3D structural model. Furthermore, we are developing a system that imports the 3D structural model including the image of the hotspot into the virtual reality and allows workers to experience the actual working environment. We believe that these visualization techniques help workers to easily recognize the hotspot at the actual working environment and to decrease their own exposure. These visualization techniques are also effective for planning decontamination and eventually accelerating the decommissioning of the FDNPS.