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Journal Articles

Numerical investigations on the coolability and the re-criticality of a debris bed with the density-stratified configuration

Li, C.; Uchibori, Akihiro; Takata, Takashi; Pellegrini, M.*; Erkan, N.*; Okamoto, Koji*

Dai-25-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 4 Pages, 2021/07

The capability of stable cooling and avoiding re-criticality on the debris bed are the main issues for achieving IVR (In-Vessel Retention). In the actual situation, the debris bed is composed of mixed-density debris particles. Hence, when these mixed-density debris particles were launched to re-distribute, the debris bed would possibly form a density-stratified distribution. For the proper evaluation of this scenario, the multi-physics model of CFD-DEM-Monte-Carlo based neutronics is established to investigate the coolability and re-criticality on the heterogeneous density-stratified debris bed with considering the particle relocation. The CFD-DEM model has been verified by utilizing water injection experiments on the mixed-density particle bed in the first portion of this research. In the second portion, the coupled system of the CFD-DEM-Monte-Carlo based neutronics model is applied to reactor cases. Afterward, the debris particles' movement, debris particles' and coolant's temperature, and the k-eff eigenvalue are successfully tracked. Ultimately, the relocation and stratification effects on debris bed's coolability and re-criticality had been quantitatively confirmed.

Journal Articles

Effects of surface tension and viscosity on liquid jet breakup

Zhan, Y.*; Kuwata, Yusuke*; Maruyama, Kiyotaka*; Okawa, Tomio*; Enoki, Koji*; Aoyagi, Mitsuhiro; Takata, Takashi

Experimental Thermal and Fluid Science, 112, p.109953_1 - 109953_8, 2020/04

 Times Cited Count:5 Percentile:75.81(Thermodynamics)

Journal Articles

Controlled growth of boron-doped epitaxial graphene by thermal decomposition of a B$$_{4}$$C thin film

Norimatsu, Wataru*; Matsuda, Keita*; Terasawa, Tomoo; Takata, Nao*; Masumori, Atsushi*; Ito, Keita*; Oda, Koji*; Ito, Takahiro*; Endo, Akira*; Funahashi, Ryoji*; et al.

Nanotechnology, 31(14), p.145711_1 - 145711_7, 2020/04

 Times Cited Count:3 Percentile:58.93(Nanoscience & Nanotechnology)

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of B$$_{4}$$C on SiC and graphene on B$$_{4}$$C had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on B$$_{4}$$C acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on B$$_{4}$$C was highly boron doped, and the hole concentration could be controlled over a wide range of 2$$times$$10$$^{13}$$ to 2$$times$$10$$^{15}$$ cm$$^{-2}$$. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.

Journal Articles

Droplet generation during liquid jet impingement onto a horizontal plate

Zhan, Y.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi

Experimental Thermal and Fluid Science, 98, p.86 - 94, 2018/11

 Times Cited Count:7 Percentile:54.73(Thermodynamics)

Journal Articles

A Study on splashing during liquid jet impingement onto a horizontal plate

Kuwata, Yusuke*; Zhan, Y.*; Enoki, Koji*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 10 Pages, 2018/10

This study aims improvement of safety analysis for sodium fire accidents in sodium-cooled fast reactors. In the experiment, effect of viscosity on liquid jet impact on solid surface was studied.

Journal Articles

Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex, 2; Neutron scattering instruments

Nakajima, Kenji; Kawakita, Yukinobu; Ito, Shinichi*; Abe, Jun*; Aizawa, Kazuya; Aoki, Hiroyuki; Endo, Hitoshi*; Fujita, Masaki*; Funakoshi, Kenichi*; Gong, W.*; et al.

Quantum Beam Science (Internet), 1(3), p.9_1 - 9_59, 2017/12

The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.

Journal Articles

Sample environment at the J-PARC MLF

Kawamura, Seiko; Oku, Takayuki; Watanabe, Masao; Takahashi, Ryuta; Munakata, Koji*; Takata, Shinichi; Sakaguchi, Yoshifumi*; Ishikado, Motoyuki*; Ouchi, Keiichi*; Hattori, Takanori; et al.

Journal of Neutron Research, 19(1-2), p.15 - 22, 2017/11

Sample environment (SE) team at the Materials and Life Science Experimental Facility (MLF) in J-PARC has worked on development and operation of SE equipment and devices. All the members belong to one sub-team at least, such as Cryogenic and magnet, High temperature, High pressure, Soft matter and special environment including Pulse magnet, Hydrogen environment, Light irradiation and $$^3$$He spin filter. Cryostats, a magnet, furnaces, a VX-6-type Paris-Edinburgh press and a prototype of a Spin-Exchange Optical Pumping (SEOP) based $$^3$$He spin filter for polarized neutron beam experiments are in operation. Furthermore, a prototype of compact power supply for a pulsed magnet system is currently developed. In the J-PARC Research Building, several pieces of equipment for softmatter research such as a rheometer and a gas and vapor adsorption measurement instrument have been prepared.

Journal Articles

Splash during liquid jet impingement onto a horizontal plate

Zhan, Y.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Ohno, Shuji; Aoyagi, Mitsuhiro; Takata, Takashi

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 6 Pages, 2017/07

It is important to set the amount of sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. In the present work, fundamental experiments are performed to measure the splash ratio during the vertical water jet impact onto a horizontal wall. It is shown that the splash ratio can be correlated well as a function of the impact Weber number and dimensionless impact frequency.

Journal Articles

Production of droplets during liquid jet impingement onto a flat plate

Yi, Z.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Ohno, Shuji; Aoyagi, Mitsuhiro; Takata, Takashi

Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 7 Pages, 2016/11

It is important to set the amount of sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. In the present work, fundamental experiments were performed to measure the splash ratio during the vertical water jet impact onto a horizontal wall. It was shown that the splash ratio can be correlated well as a function of the impact Weber number, the Strouhal number and the Ohnesorge number of the droplets impinging the liquid film.

Journal Articles

Study on self-wastage phenomenon at heat transfer tube in steam generator of sodium-cooled fast reactor with consideration of thermal coupling of fluid and structure

Kojima, Saori*; Uchibori, Akihiro; Takata, Takashi; Ohno, Shuji; Fukuda, Takeshi*; Yamaguchi, Akira*

Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 8 Pages, 2016/11

Analytical evaluation on a self-wastage phenomenon at heat transfer tubes in the steam generator of sodium cooled fast reactors has been performed by using the sodium-water reaction analysis code SERAPHIM. In this study, a fluid-structure thermal coupling model was developed and incorporated in the SERAPHIM code to evaluate heat transfer between the sodium-side reacting flow and the outer surface of the heat transfer tube. The effect of the fluid-structure thermal coupling model on the temperature field was demonstrated through the numerical analyses.

Journal Articles

Stripline beam position monitors with improved frequency response and their coupling impedances

Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*; Toyama, Takeshi*; Nakamura, Keigo*

Proceedings of 57th ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams (HB 2016) (Internet), p.523 - 528, 2016/08

In J-PARC MR, there is a concern that electron cloud instabilities may appear and limit the beam current at future higher power operations. For the case, we have developed a wider-band beam position monitor by deforming the electrode shapes. The modification of the electrode can be done without significant enhancement of the beam coupling impedance. For typical electrode shapes, we show the coupling impedances as well as the frequency responses of the electrodes.

Journal Articles

Triangle and concave pentagon electrodes for an improved broadband frequency response of stripline beam position monitors

Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*; Toyama, Takeshi*; Nakamura, Keigo*

Physical Review Accelerators and Beams (Internet), 19(2), p.021003_1 - 021003_15, 2016/02

 Times Cited Count:1 Percentile:13.76(Physics, Nuclear)

The frequency domain performance of a stripline beam position monitor depends largely on the longitudinal shape of its electrode. To attain a good impedance matching along the electrode, it needs to be precisely bent down toward its downstream in proportion to its width. In this report, we first propose a triangle electrode for easy fabrication and set-up. Theoretical and simulation results show that the simple triangle electrode has a remarkably flatter frequency response than the rectangle one. The frequency response, in particular at high frequencies, can be further improved by attaching an "apron" plate, perpendicular to the upstream edge of the electrode. The overshooting of the frequency response at low frequency can be eliminated by replacing the straight sidelines of the triangle by three-point polylines. We found that the concave pentagon electrode achieves a wide and flat frequency response up to about $$4$$ GHz for the J-PARC Main Ring.

Journal Articles

Simulation of phase modulation for longitudinal emittance blow-up in J-PARC MR

Yamamoto, Masanobu; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Nomura, Masahiro; Omori, Chihiro*; Schnase, A.*; Shimada, Taihei; Takagi, Akira*; Takata, Koji*; et al.

JPS Conference Proceedings (Internet), 8, p.012015_1 - 012015_6, 2015/09

The J-PARC MR provides a coasting proton beam for nuclear physics experiments by slow extraction. The longitudinal emittance should be enlarged until the MR flat top to mitigate the microwave instability. We have investigated a Phase Modulation (PM) method by using a High Frequency Cavity (HFC) to increase the emittance. We have performed extensive simulation studies to find the appropriate parameters of the PM through the particle tracking simulation. We found that the effective HFC frequency has linear dependence with the PM frequency, where the emittance is smoothly enlarged. Furthermore, we found that the required HFC voltage is inverse proportional to the square root of the duration time of the PM. These PM properties will be used for the design of the HFC. We describe the particle tracking simulation results of controlled emittance blow-up by the PM.

Journal Articles

Resonance structures in the impedance of a ceramic break and the measured results

Shobuda, Yoshihiro; Toyama, Takeshi*; Chin, Y. H.*; Takata, Koji*

Proceedings of 54th ICFA Advanced Beam Dynamics Workshop on High-Intensity, High Brightness and High Power Hadron Beams (HB 2014) (Internet), p.74 - 78, 2015/03

Journal Articles

Impedance of a ceramic break and its resonance structures

Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*

Physical Review Special Topics; Accelerators and Beams, 17(9), p.091001_1 - 091001_41, 2014/09

 Times Cited Count:5 Percentile:42.25(Physics, Nuclear)

Journal Articles

Ribbon thickness dependence of the magnetic alloy core characteristics in the accelerating frequency region of the J-PARC synchrotrons

Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Takata, Koji*; Toda, Makoto*; Yoshii, Masahito*; et al.

Nuclear Instruments and Methods in Physics Research A, 749, p.84 - 89, 2014/06

 Times Cited Count:1 Percentile:11.75(Instruments & Instrumentation)

We have been developing high shunt impedance Magnetic Alloy (MA) cores. The MA core shunt impedance is a key parameter to achieve a higher field gradient for increasing a beam power. We increase the MA core shunt impedance by two different ways. One way is applying an external magnetic field during annealing to increase the MA core magnetic properties. The other way is using thinner ribbons to reduce the eddy current. In this paper, we discuss the latter way.

Journal Articles

Reaction path analysis to sodium-water chemical reaction field using laser diagnostics

Tamura, Kenta*; Deguchi, Yoshihiro*; Muranaka, Ryota*; Kusano, koji*; Takata, Takashi*; Kikuchi, Shin; Kurihara, Akikazu

Proceedings of 24th International Symposium on Transport Phenomena (ISTP-24) (USB Flash Drive), 5 Pages, 2013/11

The purpose of this study aims to clarify the gas phase sodium-water reaction path and reaction products. The counter-flow diffusion experiment device is in the form of introducing the argon-based water vapor from the top of depressurized reaction chamber to the liquid sodium pool. Na, Na$$_{2}$$, H$$_{2}$$O, and reaction products in the counter-flow sodium-water reaction field were measured using laser diagnostics. The temperature controlled device was also improved to reduce the condensation of Na in the reaction zone for the better measurement performance. The main product in the sodium-water reaction was determined to be NaOH from the experimental results and its reaction path was discussed using Na-H$$_{2}$$O elementary reaction analysis.

Journal Articles

Dielectric constant measurement using resonant frequencies for minimizing the reflection of pillbox RF windows

Ao, Hiroyuki; Asano, Hiroyuki; Tamura, Jun; Ouchi, Nobuo; Takata, Koji*; Naito, Fujio*

Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1124 - 1126, 2013/08

In the case of the RF window operated with the standing-wave cavity coupled to waveguides using coupling apertures, the reflection of the RF window affects the total coupling factor (voltage standing wave ratio, VSWR) consisted of the RF window and the cavity. Hence, the reflection (VSWR) of the RF window should be minimized not to change the cavity VSWR optimized separately, and to prevent standing waves between the RF window and the cavity. For minimizing the VSWR of the pillbox-type RF window, this report proposes that the dielectric constant of the ceramic is measured directly using the resonant frequency in the fabrication process of the RF window. In this work, three RF windows are fabricated additionally using the same type ceramic (NTK HA95), the small VSWR $$(< 1.05)$$ could be achieved using this procedure. This result also shows that the dielectric constant increases linearly with increasing the density.

Journal Articles

Simulation of controlled longitudinal emittance blow-up in J-PARC RCS

Yamamoto, Masanobu; Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Tamura, Fumihiko; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Takagi, Akira*; et al.

Proceedings of 3rd International Particle Accelerator Conference (IPAC '12) (Internet), p.2952 - 2954, 2012/05

In J-PARC RCS, the high intensity beam is delivered to the MR. The longitudinal beam emittance at the RCS extraction should be optimized to avoid the beam loss after the MR injection. In order to match the longitudinal emittance shape between the RCS and the MR, it is desirable to enlarge the longitudinal emittance during the RCS acceleration. We have performed the particle tracking simulation for the controlled longitudinal emittance blow up in the RCS.

Journal Articles

Condition of MA cut cores in the RF cavities of J-PARC main ring after several years of operation

Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Sato, Tomonori; Yamamoto, Masahiro; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; et al.

Proceedings of 2nd International Particle Accelerator Conference (IPAC 2011) (Internet), p.107 - 109, 2011/09

J-PARC 3 GeV Rapid Cycling Synchrotron (RCS) and 50 GeV Synchrotron (MR) employ the Magnetic Alloy (MA) loaded RF cavities. We observed the impedance reductions of MR RF cavities. Opening the RF cavities, we found that the impedance reductions were caused by the corrosion on the core cutting surfaces. The copper ions in the cooling water from hollow conductors of main magnets might accelerate the corrosion process.

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