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Journal Articles

Finding RHEED conditions sensitive to hydrogen position on Pd(100)

Kawamura, Takaaki*; Fukaya, Yuki; Fukutani, Katsuyuki

Surface Science, 722, p.122098_1 - 122098_8, 2022/08

 Times Cited Count:0 Percentile:0.01(Chemistry, Physical)

no abstracts in English

Journal Articles

Background issues encountered by cold-neutron chopper spectrometer AMATERAS

Kikuchi, Tatsuya*; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Nakamura, Mitsutaka; Wakai, Daisuke*; Aoyama, Kazuhiro*; Iwahashi, Takaaki*; Kambara, Wataru*

Physica B; Condensed Matter, 564, p.45 - 53, 2019/07

 Times Cited Count:1 Percentile:0(Physics, Condensed Matter)

Details of the background, that is, unwanted signals accumulated by the data acquisition system of neutron instruments, observed by the cold-neutron chopper spectrometer AMATERAS installed at the Materials and Life Science Experimental Facility at J-PARC are reported. In the design phase of AMATERAS, we carefully considered the achievement of high signal-to-noise ratio, and possible countermeasures were implemented. Actually, recent scientific outputs from AMATERAS indicates that the spectrometer is one of excellent neutron instruments with low background. In spite of that, in nine years of AMATERAS operation, we have encountered unwanted signals due to various reasons, including gamma-rays emitted at materials on or near the beam line including the sample itself, scattered neutrons from the beam line devices, air scattering, electronic noise in data acquisition system, cosmic rays, T0 burst, and other unknown sources. In this report, we discuss the background observed by AMATERAS, especially in the conditions of without samples, comprehensively. The possible sources of these signals and the countermeasures considered against the above sources are discussed, which may be helpful to those who are engaged in other existing or planned neutron-scattering instruments.

Journal Articles

AMATERAS; A Cold-neutron disk chopper spectrometer

Nakajima, Kenji; Kawamura, Seiko; Kikuchi, Tatsuya; Nakamura, Mitsutaka; Kajimoto, Ryoichi; Inamura, Yasuhiro; Takahashi, Nobuaki; Aizawa, Kazuya; Suzuya, Kentaro; Shibata, Kaoru; et al.

Journal of the Physical Society of Japan, 80(Suppl.B), p.SB028_1 - SB028_6, 2011/05

 Times Cited Count:101 Percentile:94.89(Physics, Multidisciplinary)

AMATERAS is a cold-neutron disk-chopper spectrometer in MLF, J-PARC. The construction of main part of the spectrometer has been completed in spring of 2009. Soon after that, we have started the commissioning work on AMATERAS. The performance of AMATERAS has been examined by test experiments in the course of commissioning. In parallel to these works, we have started the user program on AMATERAS from December 2009 and we are getting scientific results from our spectrometer. In this presentation, we will report the current status of AMATERAS including the results of performance tests and some of examples of scientific outputs.

JAEA Reports

Conceptual design of the SlimCS fusion DEMO reactor

Tobita, Kenji; Nishio, Satoshi*; Enoeda, Mikio; Nakamura, Hirofumi; Hayashi, Takumi; Asakura, Nobuyuki; Uto, Hiroyasu; Tanigawa, Hiroyasu; Nishitani, Takeo; Isono, Takaaki; et al.

JAEA-Research 2010-019, 194 Pages, 2010/08

JAEA-Research-2010-019-01.pdf:48.47MB
JAEA-Research-2010-019-02.pdf:19.4MB

This report describes the results of the conceptual design study of the SlimCS fusion DEMO reactor aiming at demonstrating fusion power production in a plant scale and allowing to assess the economic prospects of a fusion power plant. The design study has focused on a compact and low aspect ratio tokamak reactor concept with a reduced-sized central solenoid, which is novel compared with previous tokamak reactor concept such as SSTR (Steady State Tokamak Reactor). The reactor has the main parameters of a major radius of 5.5 m, aspect ratio of 2.6, elongation of 2.0, normalized beta of 4.3, fusion out put of 2.95 GW and average neutron wall load of 3 MW/m$$^{2}$$. This report covers various aspects of design study including systemic design, physics design, torus configuration, blanket, superconducting magnet, maintenance and building, which were carried out increase the engineering feasibility of the concept.

Journal Articles

Compact DEMO, SlimCS; Design progress and issues

Tobita, Kenji; Nishio, Satoshi; Enoeda, Mikio; Kawashima, Hisato; Kurita, Genichi; Tanigawa, Hiroyasu; Nakamura, Hirofumi; Honda, Mitsuru; Saito, Ai*; Sato, Satoshi; et al.

Nuclear Fusion, 49(7), p.075029_1 - 075029_10, 2009/07

 Times Cited Count:132 Percentile:98.09(Physics, Fluids & Plasmas)

Recent design study on SlimCS focused mainly on the torus configuration including blanket, divertor, materials and maintenance scheme. For vertical stability of elongated plasma and high beta access, a sector-wide conducting shell is arranged in between replaceable and permanent blanket. The reactor adopts pressurized-water-cooled solid breeding blanket. Compared with the previous advanced concept with supercritical water, the design options satisfying tritium self-sufficiency are relatively scarce. Considered divertor technology and materials, an allowable heat load to the divertor plate should be 8 MW/m$$^{2}$$ or lower, which can be a critical constraint for determining a handling power of DEMO (a combination of alpha heating power and external input power for current drive).

Journal Articles

Numerical analysis of platinum group particle behavior in vitrification melter

Kawamura, Takumi*; Ito, Kei; Sakai, Takaaki; Nakajima, Masayoshi; Fujiwara, Koji; Ohshima, Hiroyuki

Nihon Genshiryoku Gakkai Wabun Rombunshi, 7(3), p.297 - 307, 2008/09

In a vitrification process of high level radio-active liquid wastes, platinum group particles are mixed into molted glass and convected with the glass flow in vitrification melters. Though behaviors of the particles in the melters should be investigated to establish efficient melter operation, difficulties on observations in the high-radioactive melters have prevented enough investigation. In this paper, we present a numerical analysis method to evaluate the particles behaviors. Since thermal convection of the molten glass, electrical potential and particle distribution are interacting each other, we coupled these physical behaviors to evaluate the melter status with high accuracy. The simulation results for ten batches of operation showed that an effective discharge of the particles can be achieved as well as the mock-up experiments did. These results imply that our numerical method can evaluate transient behaviors of the platinum group particles in vitrification melters.

Journal Articles

SlimCS; Compact low aspect ratio DEMO reactor with reduced-size central solenoid

Tobita, Kenji; Nishio, Satoshi; Sato, Masayasu; Sakurai, Shinji; Hayashi, Takao; Shibama, Yusuke; Isono, Takaaki; Enoeda, Mikio; Nakamura, Hirofumi; Sato, Satoshi; et al.

Nuclear Fusion, 47(8), p.892 - 899, 2007/08

 Times Cited Count:55 Percentile:87.43(Physics, Fluids & Plasmas)

The concept for a compact DEMO reactor named "SlimCS" is presented. Distinctive features of the concept is low aspect ratio ($$A$$ = 2.6) and use of a reduced-size center solenoid (CS) which has a function of plasma shaping rather than poloidal flux supply. The reduced-size CS enables us to introduce a thin toroidal field (TF) coil system which contributes to reducing the weight and construction cost of the reactor. SlimCS is as compact as advanced commercial reactor designs such as ARIES-RS and produces 1 GWe in spite of moderate requirements for plasma parameters. Merits of low-$$A$$, i.e. vertical stability for high elongation and high beta limit are responsible for such reasonable physics requirements.

Journal Articles

Concept of compact low aspect ratio Demo reactor, SlimCS

Tobita, Kenji; Nishio, Satoshi; Sato, Masayasu; Sakurai, Shinji; Hayashi, Takao; Shibama, Yusuke; Isono, Takaaki; Enoeda, Mikio; Nakamura, Hirofumi; Sato, Satoshi; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2006/10

no abstracts in English

Journal Articles

Design study of fusion DEMO plant at JAERI

Tobita, Kenji; Nishio, Satoshi; Enoeda, Mikio; Sato, Masayasu; Isono, Takaaki; Sakurai, Shinji; Nakamura, Hirofumi; Sato, Satoshi; Suzuki, Satoshi; Ando, Masami; et al.

Fusion Engineering and Design, 81(8-14), p.1151 - 1158, 2006/02

 Times Cited Count:116 Percentile:99.1(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Numerical Analysis on Diffusion Layer at the Electrode of MOX Co-deposition in the Oxide-electrowining Process

Sakai, Takaaki; Kawamura, Takumi*

Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 0 Pages, 2005/09

Numerical analysis was conducted on MOX co-deposition in an oxide-electrowining process to predict the diffusion layer thickness of the boundary layer at the cathode surface. The boundary layer was calculated by using the 10 micron width mesh to evaluate the natural circulation by the mass transfer at the cathode surface. As a result, it became clear that the diffusion layer thickness calculated by the numerical analysis can be predicted by using the non-dimensional number correlations for the mass transfer. In addition, a new mass transfer correlation was proposed for the mixed convection between the natural and forced convection conditions. The numerical analysis method was applied to the MOX co-deposition condition. The deposition process depending on the cathode potential was able to be simulated successfully for both of PuO2 and UO2.

JAEA Reports

Numerical Analysis of the Electrode Reaction Mechanism in the Glass Melter

Sakai, Takaaki; Kawamura, Takumi*; Sakai, Takaaki

JNC TN9400 2004-049, 116 Pages, 2004/09

JNC-TN9400-2004-049.pdf:2.15MB

Electric corrosion is considered as one of the reason for the main electrode damage in the glass melter. Alternate current for the Joule heating in molten glass has a possibility to promote the dissolution (ionization) of the electrode material by the electrode reaction. In this report, in order to clarify the electrode corrosion mechanism in alternating voltage conditions, we developed the numerical analysis tool by which diffusion and the electrode reaction can be evaluated. The simulation of an alternating electrode reaction was carried out and it presumed about the corrosion mechanism of electrode material. In the result, when slight direct current voltage is superposed to the alternating voltage, it is possible that the oxide layer is lost and the anode dissolution is promoted. However, since the corrosion form by the scar omission of an oxide layer is also presumed, the further check by experiment is necessary for the elucidation of a glass corrosion mechanism.

JAEA Reports

Numerical Analysis of Historical Change of the Electric Resistance in the TVF Glass Melter

Kawamura, Takumi*; Sakai, Takaaki

JNC TN9400 2004-048, 41 Pages, 2004/09

JNC-TN9400-2004-048.pdf:1.05MB

Concerning to the TVF glass melter in the Tokai reprocessing center, it is being planned to detect the deposition of the platinoid elements in a glass melter and remove them periodically to extend the melter lifetime. Numerical analysis has been performed for the electric resistance evaluation in order to estimate the sedimentation situation and current density distribution from the melter resistance. Electric field analysis was carried out by using MAGNA-FIM code and the influence factors to melter resistance was evaluated concerning to the sedimentation situation and glass temperature. In addition, transition of the sedimentation and melter resistance was estimated from the operation history of the TVF-1 melter. As a result, the followings were obtained. From the evaluation of the influence factors to melter resistance, it turns out that the volume and the platinoid elements concentration of a sediment influence notably to melter resistance when the sediment contacts to electrodes. The sediment temperature at the melter bottom has small sensitivity in case of the contact situation. the glass temperature in the melter upper part, however, has big sensitivity in melter resistance irrespective of the existence of contact. Based on the above sensitivity evaluation, numerical analysis was carried out supposing the sedimentation process which suits to a melter resistance fall during the operation history of the TVF-1 melter. As input conditions, the voltage between electrodes and the temperature in the melter were referred from the operation history data. It was assumed that the platinoid elements concentration in a sediment increased constantly for every operation batch. As a result, the characteristics of melter resistance history was reproduced successfully in general. Thereby, it became prospective to predict the sedimentation situation by using the new resistance analysis model for the glass melter.

JAEA Reports

Numerical Analysis for electrode temperature increase by current density concentration caused by noble metal accumulation in the glass melter

Sakai, Takaaki; Kawamura, Takumi*; Miura, Akihiko; Iwasaki, Takashi*

JNC TN9400 2004-053, 77 Pages, 2004/08

JNC-TN9400-2004-053.pdf:2.62MB

Numerical analysis was performed to investigate the electric current concentration to the contact area between the electrode and the noble metal sediments in the glass melter of Tokai reprocessing center. The maximum temperature was evaluated by the simplified model for the current path. In addition, three dimensional temperature profile inside the electrode was calculated numerically, in order to evaluated the possibility to detect the temperature increase by the thermo-couple which settled in the electrode. As a result, current density in the melter showed high concentration at the contact area between the electrode and the sediments. It was found that the maximum temperature at the current path had a possibility to increase more than melting temperature of 1360 Centi-grade. In addition, the thermo-couple inside the electrode scarcely showed sensitivity to the melting temperature at the edge of the electrode header where the failure might occur. In conclusion, the possibility of the electrode melting by the temperature increase can not be excluded as a cause of the failure.

Oral presentation

Developments of numerical analysis method by electric-thermal-hydraulic coupling in glass melt

Kawamura, Takumi*; Nakajima, Masayoshi; Sakai, Takaaki

no journal, , 

no abstracts in English

Oral presentation

AMATERAS; A Cold-neutron disk-chopper spectrometer

Nakajima, Kenji; Kawamura, Seiko; Kajimoto, Ryoichi; Inamura, Yasuhiro; Takahashi, Nobuaki; Osakabe, Toyotaka; Wakimoto, Shuichi; Nakamura, Mitsutaka; Ito, Shinichi*; Aizawa, Kazuya; et al.

no journal, , 

no abstracts in English

Oral presentation

Performance evaluation of cold-neutron disk-chopper spectrometer AMATERAS

Nakajima, Kenji; Kawamura, Seiko; Nakamura, Mitsutaka; Kajimoto, Ryoichi; Inamura, Yasuhiro; Takahashi, Nobuaki; Osakabe, Toyotaka; Wakimoto, Shuichi; Aizawa, Kazuya; Suzuya, Kentaro; et al.

no journal, , 

AMATERAS is a cold-neutron disk-chopper spectrometer newly installed at MLF, J-PARC. The spectrometer has pulse shaping chopper which can cat the source pulse shape as it is required by the experiments. By using newly developed high-speed disk-choppers, the spectrometer realizes both high energy resolution and high intensity with high flexibility in the cold and thermal neutron energy region. The construction of the spectrometer has been completed in spring of 2009. After the commissioning works, now the spectrometer is open to users. In this presentation, we will show the evaluated performances which were obtained in commissioning works.

Oral presentation

Commissioning of the cold-neutron disk-chopper spectrometer AMATERAS

Nakajima, Kenji; Kawamura, Seiko; Nakamura, Mitsutaka; Kajimoto, Ryoichi; Inamura, Yasuhiro; Takahashi, Nobuaki; Osakabe, Toyotaka; Wakimoto, Shuichi; Aizawa, Kazuya; Suzuya, Kentaro; et al.

no journal, , 

no abstracts in English

Oral presentation

Starting-up of the chopper spectrometer 4SEASONS in J-PARC

Kajimoto, Ryoichi; Nakamura, Mitsutaka; Yokoo, Tetsuya*; Inamura, Yasuhiro; Mizuno, Fumio; Nakajima, Kenji; Takahashi, Nobuaki; Kawamura, Seiko; Maruyama, Ryuji; Soyama, Kazuhiko; et al.

no journal, , 

no abstracts in English

Oral presentation

Commissioning of cold-neutron disk-chopper spectrometer AMATERAS

Nakajima, Kenji; Kawamura, Seiko; Nakamura, Mitsutaka; Kajimoto, Ryoichi; Inamura, Yasuhiro; Takahashi, Nobuaki; Aizawa, Kazuya; Suzuya, Kentaro; Shibata, Kaoru; Nakatani, Takeshi; et al.

no journal, , 

AMATERAS is a cold-neutron disk-chopper spectrometer newly constructed in Materials and Life science Facility in J-PARC. Construction of the spectrometer has been completed in this spring and on 27 May, 2009 AMATERAS opened its shutter for the first neutron beam. AMATERAS is now in commissioning phase and will be ready for user program from this December. In this presentation, detail of the spectrometer, results from commissioning and plan of user program will be shown.

Oral presentation

Current status of the chopper spectrometer 4SEASONS at J-PARC

Kajimoto, Ryoichi; Nakamura, Mitsutaka; Yokoo, Tetsuya*; Inamura, Yasuhiro; Mizuno, Fumio; Nakajima, Kenji; Takahashi, Nobuaki; Kawamura, Seiko; Maruyama, Ryuji; Soyama, Kazuhiko; et al.

no journal, , 

no abstracts in English

36 (Records 1-20 displayed on this page)