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Machida, Masahiko; Yamada, Susumu; Kim, M.; Okumura, Masahiko; Miyamura, Hiroko; Shikaze, Yoshiaki; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; Yamaguchi, Takashi; et al.
RIST News, (69), p.2 - 18, 2023/09
The contamination of radioactive materials leaked from the reactor has resulted in numerous hot spots in the Fukushima Daiichi Nuclear Power Station (1F) building, posing obstacles to its decommissioning. In order to solve this problem, JAEA has conducted research and development of the digital technique for inverse estimation of radiation source distribution and countermeasures against the estimated source in virtual space for two years from 2021 based on the subsidy program "Project of Decommissioning and Contaminated Water Management" performed by the funds from the Ministry of Economy, Trade and Industry. In this article, we introduce the results of the project and the plan of the renewal project started in April 2023. For the former project, we report the derivative method for LASSO method considering the complex structure inside the building and the character of the source and show the result of the inverse estimation using the method in the real reactor building. Moreover, we explain the platform software "3D-ADRES-Indoor" which integrates these achievements. Finally, we introduce the plan of the latter project.
Shi, W.*; Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji*
Progress in Nuclear Energy, 162, p.104792_1 - 104792_19, 2023/08
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)Predicting radioactive source distributions inside reactor building rooms based on monitoring air dose rates is one of the most essential steps towards decommissioning of nuclear power plants. However, the attempt is rather a difficult task, because it can be generally mapped onto mathematically ill-posed problem. Then, in order to successfully perform the inverse estimations on radioactive source distributions even in such ill-posed conditions, we suggest that a machine learning method, least absolute shrinkage and selection operator (LASSO) minimizing the loss function, is a promising scheme. For the purpose of its feasibility demonstrations in real building rooms, we employ PHITS code to make LASSO input as the above matrix C connecting the radioactive source vector P defined on surface meshes of structural materials with the air dose rate vector Q measured at internal positions inside the rooms. We develop a mathematical criterion on the number of monitoring points to correctly predict source distributions based on the theory of Candes and Tao. Then, we confirm that LASSO actually shows extremely high possibility for source distribution reconstructions as far as the number of detection points satisfies our criterion. Moreover, we verify that radioactive hot spots can be truly reconstructed in an experiment setup. At last, we examine an influence factor like detector-source distance to enhance the predicting possibility in the inverse estimation. From the above demonstrations, we propose that LASSO scheme is a quite useful way to explore hot spots as seen in damaged nuclear power plants like Fukushima Daiichi nuclear power plants.
Shi, W.*; Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji*
Annals of Nuclear Energy, 184, p.109686_1 - 109686_12, 2023/05
Times Cited Count:1 Percentile:63.33(Nuclear Science & Technology)Shi, W.*; Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji*
Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 8 Pages, 2023/02
Machida, Masahiko; Shi, W.*; Yamada, Susumu; Miyamura, Hiroko; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji; Aoki, Yuto; Ito, Rintaro; Yamaguchi, Takashi; et al.
Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 11 Pages, 2023/02
Machida, Masahiko; Yamada, Susumu; Kim, M.; Okumura, Masahiko; Miyamura, Hiroko; Malins, A.; Shikaze, Yoshiaki; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; et al.
RIST News, (68), p.3 - 19, 2022/09
no abstracts in English
Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*
ACS Omega (Internet), 7(33), p.29326 - 29336, 2022/08
Times Cited Count:3 Percentile:38.23(Chemistry, Multidisciplinary)Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count:44 Percentile:96.99(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*
Journal of Nuclear Science and Technology, 57(9), p.1062 - 1073, 2020/09
Times Cited Count:8 Percentile:69.90(Nuclear Science & Technology)The interaction of cesium hydroxide and a calcium silicate insulation material was experimentally investigated at high temperature conditions. A thermogravimetry equipped with differential thermal analysis was used to analyze thermal events in the samples of mixed calcium silicate and cesium hydroxide under Ar-5%H and Ar-4%H-20%H0 with maximum temperature of 1100C. Prior being mixed with cesium hydroxide, a part of calcium silicate was pretreated at high temperature to evaluate the effect of possible structural changes of this material due to a preceding thermal history and also the sake of thermodynamic evaluation to those available ones. Based upon the initial condition (preliminary heat treatment) of calcium silicate, it was found that if the original material consisted of xonotlite (CaSi0(0H)), the endothermic reaction with cesium hydroxide occurred over the temperature range 575-730C meanwhile if the crystal phase of original material was changed to wollastonite (CaSi0), the interaction occurred over temperature range 700-1100C. Furthermore, the X-ray diffraction analyses have indicated on both type of pretreated calsils that regardless of Ar-5%H and Ar-4%H-20%H0 atmosphere, cesium aluminum silicate, CsAlSi0 was formed with aluminum in the samples as an impurity or adduct.
Rizaal, M.; Saito, Takumi*; Okamoto, Koji*; Erkan, N.*; Nakajima, Kunihisa; Osaka, Masahiko
Mechanical Engineering Journal (Internet), 7(3), p.19-00563_1 - 19-00563_10, 2020/06
The adsorption of cesium (Cs) on calcium silicate insulation of primary piping system is postulated to contribute in high dose rate of surrounding pedestal area in Fukushima Daiichi NPP unit 2. In this study, room-temperature experiment of Cs adsorption on calcium silicate has been studied as an initial approach of Cs adsorption behavior toward higher temperature condition. As the result of analyzing of Cs adsorption kinetics, it was expected that the underlying adsorption mechanism is chemisorption. Furthermore, analysis of adsorption isotherm suggested unrestricted monolayer formation followed by multilayer formation.
Numakura, Masahiko*; Sato, Nobuaki*; Bessada, C.*; Okamoto, Yoshihiro; Akatsuka, Hiroshi*; Nezu, Atsushi*; Shimohara, Yasuaki*; Tajima, Keisuke*; Kawano, Hirokazu*; Nakahagi, Takeshi*; et al.
Progress in Nuclear Energy, 53(7), p.994 - 998, 2011/11
Times Cited Count:13 Percentile:69.42(Nuclear Science & Technology)X-ray absorption fine structure (XAFS) measurements on thorium fluoride in molten lithium-calcium fluoride mixtures and molecular dynamics (MD) simulation of zirconium and yttrium fluoride in molten lithium-calcium fluoride mixtures have been carried out. In the molten state, coordination number of thorium and inter ionic distances between thorium and fluorine in the first neighbor are nearly constant in all mixtures. However the fluctuation factors (Debye-Waller factor and C cumulant) increase until CaF = 0.17 and decrease by addition of excess CaF. It means that the local structure around Th is disordered until CaF=0.17 and stabilized over CaF = 0.17. The variation of fluctuation factors is related to the number density of F in ThF mixtures and the stability of local structure around Th increases with decreasing the number density of F in ThF mixtures. This tendency is common to those in the ZrF and YF mixtures.
Numakura, Masahiko; Yaita, Tsuyoshi; Shiwaku, Hideaki; Suzuki, Shinichi; Kobayashi, Toru*; Akutsu, Kazuhiro; Madden, P. A.*; Okamoto, Yoshihiro
JAEA-Research 2009-003, 26 Pages, 2009/04
We investigated the mixing behavior of molten TbCl in LiCl-KCl eutectuic melt by MD simulation. Also, simulation of molten YCl and LaCl systems were performed to elucidate the difference of the structural change by the difference in cation size (YTbLa). The coordination number of the molten pure YCl, TbCl and LaCl are mainly 6, 7 and 8 respectively. We consider that, in the molten pure state, the coordination number is influenced by the cation size. However, independent of cation size, the molten MCl tend to be formed the stable 6-fold structure by the mixing with LiCl-KCl eutectic. And, MD simulations on MCl-LiCl and MCl-KCl systems revealed that the mixing effect was different between LiCl and KCl.
Shiwaku, Hideaki; Yaita, Tsuyoshi; Kobayashi, Toru; Numakura, Masahiko; Suzuki, Shinichi; Okamoto, Yoshihiro
Proceedings of 4th Workshop on Speciation, Techniques, and Facilities for Radioactive Materials at Synchrotron Light Sources (Actinide-XAS-2006), p.301 - 306, 2007/05
no abstracts in English
Akutsu, Kazuhiro; Shiwaku, Hideaki; Okamoto, Yoshihiro; Suzuki, Shinichi; Ikeda, Atsushi; Kobayashi, Toru*; Numakura, Masahiko; Mahara, Saori*; Nakano, Yoshiharu*; Fujii, Yuki*; et al.
no journal, ,
no abstracts in English
Rizaal, M.; Nakajima, Kunihisa; Osaka, Masahiko; Saito, Takumi*; Okamoto, Koji*
no journal, ,
Shi, W.*; Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji
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Suzuki, Masahiro; Machida, Masahiko; Ito, Rintaro; Kawabata, Kuniaki; Yamaguchi, Takashi; Okamoto, Koji
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no abstracts in English
Suzuki, Masahiro; Aoki, Yuto; Yamaguchi, Takashi; Machida, Masahiko; Miyamura, Hiroko; Okamoto, Koji
no journal, ,
In order to facilitate the full-scale implementation of fuel debris removal at the Tokyo Electric Power Fukushima Daiichi Nuclear Power Plant (hereinafter referred to as 1F), it is necessary to establish a safe access route within the highly radiation-intensive reactor building (hereinafter referred to as "R/B"). For the purpose of the establishment, it requires environmental improvements such as decontamination of highly-intensive radiation sources and shielding measures. Based on the radiation dose measurement data at the site, Japan Atomic Energy Agency (JAEA) has examined inverse estimation scheme of highly-intensive radiation sources and developed a system that incorporates not only virtual reality (VR) but also mixed reality (MR, AR) to evaluate the effectiveness of decontamination and shielding measures. This report presents an overview of the research and development achievements to date and introduces necessary efforts for enhancing functionality to ensure practical applications at 1F.
Suzuki, Masahiro; Aoki, Yuto; Aoki, Kazuhisa; Yamada, Susumu; Kim, M.; Yamaguchi, Takashi; Machida, Masahiko; Okamoto, Koji
no journal, ,
Machida, Masahiko; Shi, W.*; Yamada, Susumu; Miyamura, Hiroko; Numata, Yoshiaki*; Sato, Tomoki*; Tobita, Yasuhiro*; Yoshida, Toru*; Yanagi, Hideaki*; Furutachi, Naoya*; et al.
no journal, ,
no abstracts in English