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Araki, Shohei; Gunji, Satoshi; Arakaki, Yu; Yoshikawa, Tomoki; Murakami, Takahiko; Kobayashi, Fuyumi; Izawa, Kazuhiko; Suyama, Kenya
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 8 Pages, 2023/10
New experiments simulating fuel debris in the new criticality assembly, STACY, are designed to contribute to the validation of criticality calculations for criticality control of the fuel debris in the Fukushima Daiichi Nuclear Power Plant accident. In the new STACY experiment, a two-region core consisting of a driver region and a test region was investigated in order to configure a debris-simulated core with under-moderation condition (lattice pitch 1.27-cm) having the constraint of available fuel rod number. The test region with a 1.27-cm lattice pitch is surrounded by the driver region, in which fuel rods are arranged in a checkerboard pattern on a 1.27-cm lattice plate, with a 1.80-cm lattice pitch. Neutron spectra and sensitivity were calculated by using MCNP6 and ENDF/B-VII. The core which has a 17
17 test region with 373 fuel rods is the largest two-region core under the constraint. It was found that the core which has a 1717 test region can simulate the neutron spectra of under-moderation condition in a 1313 region inside the test region with the root-mean square percentage error of less than 5%. It was also confirmed that the sensitivity of 
Si and 
Ca (n,
) reactions when the concrete simulant, was loaded could be simulated.
molecular dynamics simulations reveal the hydration structure of the radium(II) ionYamaguchi, Akiko; Nagata, Kojiro*; Kobayashi, Keita; Tanaka, Kazuya; Kobayashi, Toru; Tanida, Hajime; Shimojo, Kojiro; Sekiguchi, Tetsuhiro; Kaneta, Yui; Matsuda, Shohei; et al.
iScience (Internet), 25(8), p.104763_1 - 104763_12, 2022/08
Times Cited Count：9 Percentile：68.46(Multidisciplinary Sciences)no abstracts in English
Matsuda, Shohei; Yokoyama, Keiichi; Yaita, Tsuyoshi; Kobayashi, Toru; Kaneta, Yui; Simonnet, M.; Sekiguchi, Tetsuhiro; Honda, Mitsunori; Shimojo, Kojiro; Doi, Reisuke; et al.
Science Advances (Internet), 8(20), p.eabn1991_1 - eabn1991_11, 2022/05
Times Cited Count：6 Percentile：58.16(Multidisciplinary Sciences)no abstracts in English
Yamaguchi, Akiko; Nagata, Kojiro*; Tanaka, Kazuya; Kobayashi, Keita; Kobayashi, Toru; Shimojo, Kojiro; Tanida, Hajime; Sekiguchi, Tetsuhiro; Kaneta, Yui; Matsuda, Shohei; et al.
Hosha Kagaku, (45), p.28 - 30, 2022/03
no abstracts in English
Araki, Shohei; Gunji, Satoshi; Tonoike, Kotaro; Kobayashi, Fuyumi; Izawa, Kazuhiko; Ogawa, Kazuhiko
Proceedings of European Research Reactor Conference 2020 (RRFM 2020) (Internet), 7 Pages, 2020/10
Critical experiments of thermal neutron system are still expected to be playing an important role for wide technical issues. The Japan Atomic Energy Agency (JAEA) is renovating the Static Experimental Critical Facility (STACY) to maintain the experimental capability. The new STACY is designed as a general-purpose criticality facility. Its core mainly consists of low enriched UO
fuel rods, grid plates, and light water moderator. The first experiment campaign in the new STACY aims to obtain criticality characteristics of fuel debris, which will be used in validation of criticality analysis methods. The designs of the experimental core configurations are in progress.
Segawa, Tomoomi; Kawaguchi, Koichi; Kato, Yoshiyuki; Ishii, Katsunori; Suzuki, Masahiro; Fujita, Shunya*; Kobayashi, Shohei*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*
Proceedings of 2019 International Congress on Advances in Nuclear Power Plants (ICAPP 2019) (Internet), 9 Pages, 2019/05
A solution of plutonium nitrate and uranyl nitrate is converted into a mixed oxide by microwave heating denitration method. In the present study, for improving the efficiency of microwave heating and achieving high-temperature uniformity to produce homogeneous UO
powder, the microwave heating test of potassium chloride and uranyl nitrate solution, and numerical simulation analysis were conducted. The potassium chloride agar was adjusted to the dielectric loss, which is close to that of the uranyl nitrate solution and the optimum support table height was estimated to be 50 mm for denitration of the uranyl nitrate solution by microwave heating. The adiabator improved the efficiency of microwave heating denitration. Moreover, the powder yield was improved by using the adiabator owing to ease of scraping of the denitration product from the bottom of the denitration vessel.
Naito, Fujio*; Anami, Shozo*; Ikegami, Kiyoshi*; Uota, Masahiko*; Ouchi, Toshikatsu*; Onishi, Takahiro*; Oba, Toshiyuki*; Obina, Takashi*; Kawamura, Masato*; Kumada, Hiroaki*; et al.
Proceedings of 13th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1244 - 1246, 2016/11
The proton linac installed in the Ibaraki Neutron Medical Research Center is used for production of the intense neutron flux for the Boron Neutron Capture Therapy (BNCT). The linac consists of the 3-MeV RFQ and the 8-MeV DTL. Design average beam current is 10mA. Target is made of Beryllium. First neutron production from the Beryllium target was observed at the end of 2015 with the low intensity beam as a demonstration. After the observation of neutron production, a lot of improvement s was carried out in order to increase the proton beam intensity for the real beam commissioning. The beam commissioning has been started on May 2016. The status of the commissioning is summarized in this report.
Nishimura, Kazuaki; Tanaka, Hideki; Kobayashi, Daisuke; Suzuki, Shohei; Numata, Shinji; Nakamichi, Hideo; Kurita, Tsutomu; Iida, Masayoshi*; Tajiri, Kazuma*; Sukegawa, Katsumi*
no journal, ,
no abstracts in English
Yamamori, Ryo*; Kobayashi, Hikaru*; Honta, Shohei*; Yoshino, Hiroshi*; Nozaki, Atsuo*; Ichijo, Yusuke*; Yoshida, Hiroko*; Furuta, Takuya
no journal, ,
Understanding radiation field is important to predict radiation dose rate in newly constructing buildings in an area widely contaminated by radioactive nuclei. Radiation dose rate at the site is not sufficient, and directional spectra of the radiations are important to consider the shielding effect of the building. Radiation directional spectra can be measured by scintillator partially shielded by lead collimators but the angle of view highly depends on the combination of the scintillator and the collimators. We adopts a method to measure the directional spectra by adopting 3 inch scintillator with placing a plate of lead collimator in front of the scintillator and subtract the values from the spectra measured without lead collimator. We simulates the optimal size of the lead collimator and found that the 15 cm diameter plate placing at 3 cm from the scintillator is the best for our purpose, 90 degree angle of view.
-ray directional radiation dose detector with good efficiency for field surveyYamamori, Ryo*; Kobayashi, Hikaru*; Honta, Shohei*; Yoshino, Hiroshi*; Nozaki, Atsuo*; Ichijo, Yusuke*; Hijikata, Yoshio*; Yoshida, Hiroko*; Furuta, Takuya
no journal, ,
Understanding radiation field is important to predict radiation dose rate in newly constructing buildings in an area widely contaminated by radioactive nuclei. Directional spectra of the radiations are important to consider the shielding effect of the building. We adopts a method to measure the directional spectra by adopting a plate of lead collimator in front of the scintillator and subtract the values from the spectra measured without lead collimator. We investigated a possible weight saving detection system having sufficient detection efficiency. The investigation was carried out for the condition of the collimator radius (
= 10, 15, 20 cm) and the distance between collimator and detector (
= 1, 3, 5 cm). We found that three combinations satisfied the 90
field view and the detection efficiency became better with larger collimator radius. On the other hand, larger collimator radius indicate heavier detection system. Therefore, we developed an optimum detection system for field survey with the 15 cm diameter plate (10kg), the scintillator (3.4kg), and the folder (1.0kg).
Kobayashi, Shohei*; Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*; Segawa, Tomoomi; Kato, Yoshiyuki; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
The microwave heating denitration method is used in the spent fuel reprocessing process. In order to develop the mass production of denitrification technology for the future, it is necessary to fully grasp the operating conditions to avoid flashing and overflow phenomena of solution. In this research, the conditions of the generation of flashing are evaluated using the potassium chloride aqueous solution as the simulated solution, and the concentration of potassium chloride and the microwave output as parameters. It is found that it is difficult to occur the flashing phenomenon as the concentration of potassium chloride increases.
Kobayashi, Shohei*; Abe, Yutaka*; Kaneko, Akiko*; Futsuta, Akihiro*; Fujiwara, Kota*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
To investigate the influence of the dielectric properties of a solution or a spacer on the heating process of the solution, a low dielectric Teflon or an airogel having a very low dielectric property almost equivalent to air was placed as a spacer directly below the vessel. And the influence of the geometry and the dielectric properties of the sample and the spacer on the heating properties of the sample were evaluated. The heating efficiency obtained by the experiment tended to decrease as the spacer height increased. It was confirmed that the heating efficiency obtained by the electromagnetic analysis almost agreed with the experimental results by a support height of 50 mm. When Teflon was used as a spacer, microwaves entered from the bottom of the solution, whereas when airogel was used as a spacer, microwaves tended to enter from the top of the solution, and it was clarified that the dielectric characteristics of the spacer were the heating characteristics of the sample.
Kobayashi, Shohei*; Abe, Yutaka*; Kaneko, Akiko*; Fujiwara, Kota*; Futsuta, Akihiro*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
The microwave heating denitration method is used in the nuclear fuel cycle. To clarify the mechanism of flashing phenomena during microwave heating, it was focused on the frequency of bubble nucleation in heterogeneous nucleation and considered the bubbles generated in the solution. From the visualization observation results, it was verified that a new bubble was generated below the single bubble. The bubbles generated at the gas-liquid interface are considered to be caused by heterogeneous nucleation. Moreover, the calculation results revealed that bubbles were generated at a large contact angle. It is suggested that many bubbles are generated at the gas-liquid interface, and many bubbles generated by heterogeneous nucleation in the superheated liquid phase influence the generation of flashing.
Kobayashi, Shohei*; Abe, Yutaka*; Kaneko, Akiko*; Fujiwara, Kota*; Futsuta, Akihiro*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
In the reprocessing process in the nuclear fuel cycle, a solution of plutonium nitrate and uranyl nitrate is converted into a mixed oxide by microwave heating denitration method. The objective of this study is to clarify the mechanism of the flashing phenomenon and to clarify the effect of the microwave heating characteristics of a high dielectric constant solution on the flashing phenomenon. Microwave heating experiments were conducted using KCl aqueous solution, which is the high dielectric constant solution simulating the reprocessing solution. It was clarified that the growth rate of bubbles in the KCl aqueous solution decreased with the time of microwave heating compared with distilled water. It is thought that in the KCl aqueous solution, the heating efficiency at the center of the solution is lower than that in the surroundings, and the growth rate of bubbles is reduced so that the flashing phenomenon does not easily occur in the high dielectric constant solution.
Matsuda, Shohei; Yokoyama, Keiichi; Yaita, Tsuyoshi; Kobayashi, Toru; Nakashima, Nobuaki*
no journal, ,
One of the spectroscopic properties for lanthanides and actinides is that they have f-f transitions in the visible region of their spectra. Those absorption appears at specific wavelength and has narrow line width even in the liquid phase owing to shielded f electrons. It has been reported that reduction reactions of Sm
, Eu, and Yb are induced by multiphoton excitation through each f-f transition depending on conditions. This photochemical process may be applicable to mutual separation of f elements. In this study, we tried to optically control the oxidation state of americium. As a result, we found that trivalent americium (Am) in nitric acid solution is oxidized to pentavalent one (AmO
) during nanosecond pulsed-laser irradiation at 503 nm corresponding to the 
L
F
transition of Am. Identification and quantification of the reactants and products were performed by absorption spectroscopy. Excitation wavelength dependence and fluence dependence of the oxidation suggest that it is initiated by a resonance-enhanced multiphoton process.
Matsuda, Shohei; Yokoyama, Keiichi; Yaita, Tsuyoshi; Kobayashi, Toru; Nakashima, Nobuaki*
no journal, ,
We have recently realized the oxidation of trivalent americium (Am
) in nitric acid by multiphoton excitation via an f-f transition. In this study, an effect of nitrate ion (NO
) on the Am photooxidation have been investigated. Our results of NO activity dependence of the Am photooxidation and density functional theory calculation indicate that the complex of Am with NO, in particular one-nitrate complex, contributes to it.
Yamaguchi, Akiko; Nagata, Kojiro*; Tanaka, Kazuya; Kobayashi, Keita; Okumura, Masahiko; Kobayashi, Toru; Shimojo, Kojiro; Tanida, Hajime; Sekiguchi, Tetsuhiro; Kaneta, Yui; et al.
no journal, ,
no abstracts in English
Araki, Shohei; Izawa, Kazuhiko; Gunji, Satoshi; Suyama, Kenya; Ishii, Junichi; Seki, Masakazu; Kobayashi, Fuyumi; Fukaya, Hiroyuki
no journal, ,
To measure critical characteristics of fuel debris, the Static Experiment Critical Facility (STACY) is being converted to the heterogeneous thermal system using fuel rods and light water moderator from the homogeneous system using solution fuel. This report presents an overview and progress of the modified STACY.
Yamaguchi, Akiko; Nagata, Kojiro*; Tanaka, Kazuya; Kobayashi, Keita; Okumura, Masahiko; Kobayashi, Toru; Shimojo, Kojiro; Tanida, Hajime; Sekiguchi, Tetsuhiro; Kaneta, Yui; et al.
no journal, ,
no abstracts in English
Maekawa, Tomoyuki; Seki, Masakazu; Sumiya, Masato; Araki, Shohei; Murakami, Takahiko; Hasegawa, Kenta; Yoshikawa, Tomoki; Mori, Takashi*; Ishii, Junichi; Kobayashi, Fuyumi; et al.
no journal, ,
As previously reported, to clarify critical characteristics of fuel debris, the Static Experiment Critical Facility (STACY) is being converted to the heterogenous thermal system using fuel rods and light water moderator from the homogenous system using solution fuel. Seismic reinforcement of the support structure of the core tank started in 2022. This report presents progress on manufacture and construction of the modified STACY in 2021 and 2022.
