Development of 0.5 mm gauge size radial collimators for high-pressure neutron diffraction experiments at PLANET in J-PARC

Hattori, Takanori; Suzuki, Koji*; Miyo, Tatsuya*; Ito, Takayoshi*; Machida, Shinichi*

Nuclear Instruments and Methods in Physics Research A, 1059, p.168956_1 - 168956_9, 2024/02

https://doi.org/10.1016/j.nima.2023.168956

Radial collimators (RC) with a 0.5 mm gauge size (GS) were specially designed for high-pressure neutron diffraction experiments and their performance and efficacy were investigated. The RCs with nominal GS of 0.75 mm, 1.5 mm, and 3.0 mm effectively exhibited GS of 0.50 mm, 1.07 mm, and 2.78 mm, respectively. The transmissions of all three RCs were almost equivalent. The assessment using a P-E press and a DAC revealed that the anvil scattering was considerably minimized and the sample-to-anvil signal ratio reached values of 0.5 and 2.0 for the PE press and DAC, respectively, when using the 0.5 mm-GS RCs. These results indicate that the 0.5mm-GS RCs have been fabricated as intended and exhibit efficacy for the high-pressure-neutron diffraction experiments, specifically those exceeding 30 GPa. Among those ever manufactured for neutron scattering experiments, the RCs display the smallest GS.

Estimation of temporal variation of discharged inventory of radioactive strontium Sr (Sr) from port of Fukushima Daiichi Nuclear Power Plant; Analysis of the temporal variation from the accident to March 2022 and evaluation of its impact on Fukushima coast and offshore areas

Machida, Masahiko; Iwata, Ayako; Yamada, Susumu; Otosaka, Shigeyoshi*; Kobayashi, Takuya; Funasaka, Hideyuki*; Morita, Takami*

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(4), p.119 - 139, 2023/11

https://doi.org/10.3327/taesj.J22.016

We estimate monthly discharged inventory of Sr from port of Fukushima Daiichi Nuclear Power Plant (1F) from Jun. 2013 to Mar. 2022 by using the Voronoi tessellation method inside the port, following the monitoring of Sr sea water radioactivity concentration inside the port. The results suggest that the closure of sea side impermeable wall is the most effective for the reduction of discharged one. In addition, the results roughly reveal the monthly discharged inventory required to observe visible enhancement of the sea radioactivity concentration from the background level in each area. Such outcome is significant for considering environmental impacts on the planned future releasing of the treated water accumulated in 1F site.

An X-ray and neutron scattering study of aqueous MgCl solution in the gigapascal pressure range

Yamaguchi, Toshio*; Fukuyama, Nami*; Yoshida, Koji*; Katayama, Yoshinori*; Machida, Shinichi*; Hattori, Takanori

Liquids, 3(3), p.288 - 302, 2023/09

https://doi.org/10.3390/liquids3030019

We report the structure of an aqueous 2 mol/kg MgCl solution at pressures from 0.1 MPa to 4 GPa and temperatures from 300 to 500 K revealed by X-ray and neutron scattering measurements. The scattering data are analyzed by empirical potential structure refinement (EPSR) modeling to derive the pair distribution functions, coordination number distributions, angle distributions, and spatial density functions as a function of pressure and temperature. Mg forms rigid solvation shells extended to the third shell; the first solvation shell of six-fold octahedral coordination with about six water molecules at 0 GPa transforms into about five water molecules and one Cl due to the formation of the contact ion pairs in the GPa pressure range. The Cl solvation shows a substantial pressure dependence; the coordination number of a water oxygen atom around Cl increases from 8 at 0.1 MPa/300 K to 10 at 4 GPa/500 K. The solvent water transforms the tetrahedral network structure at 0.1 MPa/300 K to a densely packed structure in the GPa pressure range; the number of water oxygen atoms around a central water molecule gradually increases from 4.6 at 0.1 MPa/298 K to 8.4 at 4 GPa/500 K.

Inverse estimation scheme of radioactive source distributions inside building rooms based on monitoring air dose rates using LASSO; Theory and demonstration

Shi, W.*; Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji*

Progress in Nuclear Energy, 162, p.104792_1 - 104792_19, 2023/08

https://doi.org/10.1016/j.pnucene.2023.104792

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.

Fundamental research of X-ray absorption imaging for elemental identification using a secondary target

Nakae, Masanori*; Matsuyama, Tsugufumi*; Murakami, Masashi; Yoshida, Yukihiko; Machida, Masahiko; Tsuji, Koichi*

Advances in X-Ray Chemical Analysis, Japan, 54, p.89 - 99, 2023/03

Fundamental research on X-ray absorption imaging for elemental identification was studied. A secondary target was applied to obtain X-ray absorption images above and below the X-ray absorption edge of the target element. X-rays from an X-ray tube were irradiated to the secondary target, where the characteristic X-rays were emitted that were irradiated to the sample. X-ray absorption images were acquired with an exposure time of a few seconds with an X-ray camera. In this technique, it is difficult to change the energy of X-rays as we want, however we can apply this technique for imaging the specific element. Metal foil sample composed of Al, Cu, and Ni was analyzed. To obtain an X-ray elemental image of Ni, two X-ray absorption images were taken using the X-rays above and below the Ni K-edge. X-rays of Cu K and Zn K were prepared by using Cu and Zn plates as the secondary target. Finally, the Ni elemental image was obtained by subtracting two images. Furthermore, the X-ray camera had a function of setting critical energies for imaging, thus it was demonstrated that an X-ray elemental image of Ni was obtained using a single secondary target without changing the secondary target.

LASSO reconstruction scheme to predict radioactive source distributions inside reactor building rooms; Theory & demonstration

Shi, W.*; Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji*

Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 8 Pages, 2023/02

Tritium inventory and its temporal variation in Fukushima Front Sea Area; Comparison between coastal and offshore tritium inventories and 1f treated water and operational target values for discharge per year

Machida, Masahiko; Iwata, Ayako; Yamada, Susumu; Otosaka, Shigeyoshi*; Kobayashi, Takuya; Funasaka, Hideyuki*; Morita, Takami*

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(1), p.12 - 24, 2023/01

https://doi.org/10.3327/taesj.J22.001

We estimate inventory of tritium in two sea areas corresponding to coastal and offshore ones around Fukushima Daiichi Nuclear Power Plant (1F) based on the measurement results of sea-water tritium concentration monitored constantly from 2013 to Jan. 2021 by using Voronoi tessellation scheme. The obtained results show that the offshore area inventory and its temporal variation amount correspond to approximately 1/5 and 1/40 of that of the treated-water accumulated inside 1F, respectively. These results just suggest that the presence of tritium already included in sea-water as the background is non negligible in evaluating the environmental impact by releasing the accumulated treated-water into the sea region. We also estimate the offshore area inventory before 1F accident and find that it had exceeded over 1F stored inventory over about 30 years from 1960s to 1980s with approximately 4 times larger in the peak decade, 1960s. This fact means that we had already experienced more contaminated situation over 30 years in the past compared to the conservative case appeared by just releasing whole the present 1F inventory. Here, it should be also emphasized that the past contaminated situation was shared by the entire world. We further extend the estimation region into a wider region including an offshore area from Miyagi to Chiba prefectures and find that the area average inventory is now comparable to a half of the present 1F one. Finally, we estimate internal dose per year via ingesting fishes caught inside the area when 1F inventory is just added inside the area and kept for a year. The result indicates that it approximately corresponds to 1.0 of the dose from natural radiation sources. From these estimation results, it is found that all the tritium inventory stored inside 1F never contribute to significant dose increment even when it is instantly released into the area.

Neutron scattering on an aqueous sodium chloride solution in the gigapascal pressure range

Yamaguchi, Toshio*; Yoshida, Koji*; Machida, Shinichi*; Hattori, Takanori

Journal of Molecular Liquids, 365, p.120181_1 - 120181_10, 2022/11

https://doi.org/10.1016/j.molliq.2022.120181

Neutron scattering measurements were performed on an aqueous 3 mol/kg NaCl solution in DO at temperature and pressure conditions of 0.1 MPa/298K, 1 GPa/298K, 1 GPa/523K, and 4 GPa/523K. The empirical potential structure refinement method was applied to the obtained data to extract the pair correlation function, coordination number distribution, angular distribution (orientation correlation), and spatial density function (3-D structure). From those results, pressure and temperature dependence of solvation and association of ions and solvent-water structure were discussed.

Accumulation mechanisms of radiocaesium within lichen thallus tissues determined by means of microscale localisation observation

Dohi, Terumi; Iijima, Kazuki; Machida, Masahiko; Suno, Hiroya*; Omura, Yoshihito*; Fujiwara, Kenso; Kimura, Shigeru*; Kanno, Futoshi*

PLOS ONE (Internet), 17(7), p.e0271035_1 - e0271035_21, 2022/07

https://doi.org/10.1371/journal.pone.0271035

Development and evaluation of XRF imaging instrument for moving objects

Fuchita, Tomoki*; Urata, Taisei*; Matsuyama, Tsugufumi*; Murakami, Masashi; Yoshida, Yukihiko; Ueda, Akihiko; Machida, Masahiko; Sasaki, Toshiki; Tsuji, Koichi*

Advances in X-Ray Chemical Analysis, Japan, 53, p.77 - 87, 2022/03

X-ray fluorescence (XRF) analysis is an analytical method to obtain elemental information by detecting fluorescence X-rays emitted from a sample irradiated with X-rays. It is possible to obtain two-dimensional elemental distribution images by scanning a sample with micro X-ray beam. In this study, we developed an XRF analytical instrument to rapidly obtain the elemental distributions for moving samples on a belt conveyor by applying the micro XRF technique. X-rays were widely irradiated to the belt conveyor. The elemental distributions were measured by scanning an X-ray detector, crossing above the belt conveyor. A collimator was attached to the top of the detector to limit the analyzing area. Both detection limit and spatial resolutions for moving directions of the detector and the belt conveyor were evaluated. Finally, it was demonstrated that the multi-elemental imaging was possible with the developed XRF instrument.