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Journal Articles

Numerical simulation of MCCI based on MPS method with different types of concrete

Chai, P.; Kondo, Masahiro*; Erkan, N.*; Okamoto, Koji*

Annals of Nuclear Energy, 103, p.227 - 237, 2017/05

 Times Cited Count:8 Percentile:15.68(Nuclear Science & Technology)

A two-dimensional computational code was developed using multi-physics models to simulate MCCI phenomena based on the moving particle semi-implicit (MPS) method. In contrast to previous studies, gas generation was simulated by calculating the force balance of the bubbles in the liquid pool in order to investigate its influence on the ablation behavior. Moreover, chemical reaction was modeled by calculating the heat release from the redox reaction between the corium and melted concrete during the erosion process. CCI-2 and CCI-3 tests were simulated by applying this code to study the aspects that may affect the ablation profile with different concrete types. The simulation result generally matches the experimental results on both axial and radial ablation rates. Application of the gas release and chemical reaction model suggested that one possible reason for the anisotropic ablation profile observed in the siliceous concrete tests is the heat transfer enhancement near the sidewall from the gas release and chemical reaction. In contrast, the test using limestone-rich concrete generated an isotropic ablation profile because axial ablation was also enhanced by the large gas discharge from the bottom concrete. In addition to the ablation profile, the crust formation and concrete-corium interface profile at the bottom in the CCI-3 test were reproduced with the help of the proposed models.

Journal Articles

Effectiveness evaluation of filtered containment venting system using THALES-2

Kondo, Masahiro*; Yoshimoto, Tatsuya*; Ishikawa, Jun; Okamoto, Koji*

Hozengaku, 15(4), p.79 - 85, 2017/01

no abstracts in English

JAEA Reports

Annual report of Nuclear Emergency Assistance and Training Center (April 1, 2013 - March 31, 2014)

Sato, Takeshi; Muto, Shigeo; Akiyama, Kiyomitsu; Aoki, Kazufumi; Okamoto, Akiko; Kawakami, Takeshi; Kume, Nobuhide; Nakanishi, Chika; Koie, Masahiro; Kawamata, Hiroyuki; et al.

JAEA-Review 2014-048, 69 Pages, 2015/02

JAEA-Review-2014-048.pdf:13.91MB

JAEA was assigned as a designated public institution under the Disaster Countermeasures Basic Act and under the Armed Attack Situations Response Act. Based on these Acts, the JAEA has the responsibility of providing technical support to the national government and/or local governments in case of disaster responses or response in the event of a military attack, etc. In order to fulfill the tasks, the JAEA has established the Emergency Action Plan and the Civil Protection Action Plan. In case of a nuclear emergency, NEAT dispatches specialists of JAEA, supplies the national government and local governments with emergency equipment and materials, and gives technical advice and information. In normal time, NEAT provides various exercises and training courses concerning nuclear disaster prevention to those personnel taking an active part in emergency response institutions of the national and local governments, police, fire fighters, self-defense forces, etc. in addition to the JAEA itself. The NEAT also researches nuclear disaster preparedness and response, and cooperates with international organizations. In the FY2013, the NEAT accomplished the following tasks: (1) Technical support activities as a designated public institution in cooperation with the national and local governments, etc. (2) Human resource development, exercise and training of nuclear emergency response personnel for the national and local governments, etc. (3) Researches on nuclear disaster preparedness and response, and sending useful information (4) International contributions to Asian countries on nuclear disaster preparedness and response in collaboration with the international organizations

JAEA Reports

Annual report of Nuclear Emergency Assistance and Training Center (April 1, 2012 - March 31, 2013)

Sato, Takeshi; Muto, Shigeo; Okuno, Hiroshi; Katagiri, Hiromi; Akiyama, Kiyomitsu; Okamoto, Akiko; Koie, Masahiro; Ikeda, Takeshi; Nemotochi, Toshimasa; Saito, Toru; et al.

JAEA-Review 2013-046, 65 Pages, 2014/02

JAEA-Review-2013-046.pdf:11.18MB

When a nuclear emergency occurs in Japan, the Japan Atomic Energy Agency (JAEA) has the responsibility of providing technical support to the National government, local governments, police, fire stations and nuclear operators etc., because the JAEA has been designated as the Designated Public Institution under the Basic Act on Disaster Control Measures and the Act on Response to Armed Attack Situations, etc.. The Nuclear Emergency Assistance and Training Center (NEAT) of JAEA provides a comprehensive range of technical support activities to an Off-Site Center in case of a nuclear emergency. Specifically, NEAT gives technical advice and information, dispatches specialists as required, and supplies the National Government and local governments with emergency equipments and materials. NEAT provides various exercise and training courses concerning nuclear disaster prevention to those personnel taking an active part in emergency response organizations at normal times. The tasks of NEAT, with its past experiences as a designated public institution including the responses to TEPCO's Fukushima Accident, have been shifted to technical supports to the national government for strengthening its abilities to emergency responses; the NEAT therefore focused on maintenance and operation of its functions, and strengthening its response abilities in cooperation with the national government. This annual report summarized these activities of JAEA/NEAT in the fiscal year 2012.

Journal Articles

Measurements of electron-induced neutrons as a tool for determination of electron temperature of fast electrons in the task of optimization laser-produced plasma ions acceleration

Sakaki, Hironao; Nishiuchi, Mamiko; Maeda, Shota; Sagisaka, Akito; Pirozhkov, A. S.; Pikuz, T.; Faenov, A.*; Ogura, Koichi; Fukami, Tomoyo; Matsukawa, Kenya*; et al.

Review of Scientific Instruments, 85(2), p.02A705_1 - 02A705_4, 2014/02

 Times Cited Count:2 Percentile:85.32(Instruments & Instrumentation)

High intensity laser-plasma interaction has attracted considerable interest for a number of years. The laser-plasma interaction is accompanied by generation of various charged particle beams. Results of simultaneous novel measurements of electron-induced photonuclear neutrons (photoneutron), which are a diagnostic of the laser-plasma interaction, are proposed to use for optimization of the laser-plasma ion generation. The proposed method is demonstrated by the laser irradiation with the intensity os 1$$times$$10$$^{21}$$ W/cm$$^{2}$$ on the metal foil target. The photoneutrons are measured by using NE213 liquid scintillation detectors. Heavy-ion signal is registered with the CR39 track detector simultaneously. The measured signals of the electron-induced photoneutrons are well reproduced by using the Particle and Heavy Ion Transport code System (PHITS). The results obtained provide useful approach for analyzing the various laser based ion beams.

Journal Articles

Magnetization plateau of the quantum spin nanotube

Okamoto, Kiyomi*; Sato, Masahiro*; Okunishi, Koichi*; Sakai, Toru; Itoi, Chigaku*

Physica E, 43(3), p.769 - 772, 2011/01

 Times Cited Count:3 Percentile:81.21(Nanoscience & Nanotechnology)

The magnetization process of the 3-leg quantum spin nanotube is investigated by the numerical diagonalization of finite-size clusters and the density matrix renormalization group method. It is found that the magnetization plateau appears at 1/3 of the saturation magnetization for sufficiently large interchain coupling. In addition we find that in the presence of asymmetric lattice distortion, there are two different mechanisms of the magnetization plateau formation. We also successfully present a phase diagram of the magnetization plateau.

Journal Articles

Quantum spin nanotubes; Frustration, competing orders and criticalities

Sakai, Toru; Sato, Masahiro*; Okamoto, Kiyomi*; Okunishi, Koichi*; Itoi, Chigaku*

Journal of Physics; Condensed Matter, 22(40), p.403201_1 - 403201_13, 2010/10

 Times Cited Count:33 Percentile:56.74(Physics, Condensed Matter)

Recent developments of theoretical studies on spin nanotubes are reviewed, especially focusing on the S=1/2 three-leg spin tube. In contrast to the three-leg spin ladder, the tube has a spin gap in case of the regular-triangle unit cell when the rung interaction is sufficiently large. The effective theory based on the Hubbard Hamiltonian indicates a quantum phase transition to the gapless spin liquid due to the lattice distortion to an isosceles triangle. This is also supported by the numerical diagonalization and the density matrix renormalization group analyses. Furthermore, combining analytical and numerical approaches, we reveal several novel magnetic-field-induced phenomena: N$'e$el, dimer, chiral and/or inhomogeneous orders, new mechanism for the magnetization plateau formation, and others. The recently synthesized spin tube materials are also briefly introduced.

Journal Articles

Field induced exotic phenomena of the S=1/2 three-leg quantum spin nanotube

Sakai, Toru; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*; Sato, Masahiro*

Journal of Low Temperature Physics, 159(1-2), p.55 - 59, 2010/04

 Times Cited Count:8 Percentile:58.5(Physics, Applied)

The numerical study on the S=1/2 three-leg spin nanotube using the exact diagonalization and the density matrix renormalization group method indicated that the 1/3 magnetization plateau appears for sufficently large rung interaction caused by two different mechanisms, depending on the asymmetry.

Journal Articles

Modeling of ultra-cold and crystalline ion beams

Okamoto, Hiromi*; Sugimoto, Hiroshi*; Yuri, Yosuke; Ikegami, Masahiro*; Wei, J.*

Proceedings of 10th International Computational Accelerator Physics Conference (ICAP 2009) (Internet), p.151 - 156, 2009/08

Journal Articles

Quantum phase transitions of the asymmetric three-leg spin tube

Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Otsuka, Yuichi*; Okamoto, Kiyomi*; Itoi, Chigaku*

Physical Review B, 78(18), p.184415_1 - 184415_11, 2008/11

 Times Cited Count:45 Percentile:14.82(Materials Science, Multidisciplinary)

We investigate quantum phase transitions of the S = $$frac{1}{2}$$ three-leg antiferromagnetic spin tube with asymmetric inter-chain (rung) exchange interactions. On the basis of the electron tube system, we propose a useful effective theory to give the global phase diagram of the asymmetric spin tube. In addition, using other effective theories we raise the reliability of the phase diagram. The density-matrix renormalization-group and the numerical diagonalization analyses show that the finite spin gap appears in a narrow region around the rung-symmetric line.

Journal Articles

Basic analysis of weldability and machinability of structural materials for ITER toroidal field coils

Onozuka, Masanori*; Shimizu, Katsusuke*; Urata, Kazuhiro*; Kimura, Masahiro*; Kadowaki, Hirokazu*; Okamoto, Mamoru*; Nakajima, Hideo; Hamada, Kazuya; Okuno, Kiyoshi

Fusion Engineering and Design, 82(5-14), p.1431 - 1436, 2007/10

 Times Cited Count:2 Percentile:79.49(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Beam cooling experiment at ion storage ring, S-LSR

Shirai, Toshiyuki*; Tanabe, Mikio*; Soda, Hikaru*; Ikegami, Masahiro*; Fujimoto, Shinji*; Tongu, Hiromu*; Noda, Akira*; Noda, Koji*; Shibuya, Shinji*; Fujimoto, Tetsuya*; et al.

Proceedings of 9th Symposium on Accelerator and Related Technology for Application, p.19 - 22, 2007/06

Journal Articles

Crystalline beams in dispersion-free storage rings

Ikegami, Masahiro*; Okamoto, Hiromi*; Yuri, Yosuke

Physical Review Special Topics; Accelerators and Beams, 9(12), p.124201_1 - 124201_11, 2006/12

 Times Cited Count:5 Percentile:58.58(Physics, Nuclear)

Generating a multidimensional crystalline beam in a storage ring has been known to be difficult without a special cooling force, i.e., tapered cooling, because of the momentum dispersion induced by bending magnets. It is, however, possible to eliminate the dispersion all around the ring by adding an electric dipole field in each magnetic bending region. A storage ring with such unique deflectors should enable us to reach multidimensional crystalline states with an ordinary "untapered" cooling force. In order to verify this expectation, molecular dynamics simulations are performed to study beam crystallization in several dispersion-free storage rings including the S-LSR at Kyoto University. The present results show that various crystalline states can be established without relying on the tapered force.

Journal Articles

Angle-resolved photoemission study of the $$MX$$-chain compound [Ni(chxn)$$_2$$Br]Br$$_2$$; Spin-charge separation in hybridized $$d$$-$$p$$ chains

Fujimori, Shinichi; Ino, Akihiro; Okane, Tetsuo; Fujimori, Atsushi; Okada, Kozo*; Manabe, Toshio*; Yamashita, Masahiro*; Kishida, Hideo*; Okamoto, Hiroshi*

Physical Review Letters, 88(24), p.247601_1 - 247601_4, 2002/06

 Times Cited Count:12 Percentile:39.49(Physics, Multidisciplinary)

We report on the results of angle-resolved photoemission experiments on a quasi-one-dimensional $$MX$$-chain compound [Ni(chxn)$$_2$$Br]Br$$_2$$ (chxn = 1$$R$$,2$$R$$-cyclohexanediamine), a one-dimensional Heisenberg system with $$S=1/2$$ and $$Jsim3600$$K, which shows a gigantic non-linear optical effect. A "band" having about 500meV energy dispersion is found in the first half of the Brillouin zone $$(0le kb/pi <1/2)$$, but disappears at $$kb/pisim1/2$$. Two dispersive features, expected from the spin-charge separation, as have been observed in other quasi-one-dimensional systems like Sr$$_2$$CuO$$_3$$, are not detected. These characteristic features are well reproduced by the $$d$$-$$p$$ chain model calculations with a small charge-transfer energy $$Delta$$ compared with that of one-dimensional Cu-O based compounds. We propose that this smaller $$Delta$$ is the origin of the absence of clear spin- and charge-seperation in the photoemission spectra and strong non-linear optical effect in [Ni(chxn)$$_2$$Br]Br$$_2$$.

Journal Articles

Photoemission study of quasi-one-dimensional halogen-bridged compound [Ni(chxn)$$_{2}$$Br]Br$$_{2}$$

Fujimori, Shinichi; Ino, Akihiro; Okane, Tetsuo; Fujimori, Atsushi; Okada, Kozo*; Manabe, Toshio*; Yamashita, Masahiro*; Kishida, Hideo*; Okamoto, Hiroshi*

Surface Review and Letters, 9(2), p.1065 - 1069, 2002/04

 Times Cited Count:0 Percentile:100(Chemistry, Physical)

no abstracts in English

Journal Articles

Nuclear Material Research in Cross-Over Research Project

Okamoto, Makoto*; Kitajima, Masahiro*; Kobayashi, Yoshinori*; Kiuchi, Kiyoshi*; Kano, Shigeki

Nippon Genshiryoku Gakkai-Shi, 37(9), p.796 - 806, 1995/00

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

None

JAEA Reports

None

Ito, Masakazu*; Okamoto, Mayumi*; Shibata, Masahiro; Sasaki, Yasuo; Danhara, Toru*; Suzuki, Keizo*; Watanabe, Takashi*

PNC-TN8430 93-003, 119 Pages, 1993/08

PNC-TN8430-93-003.pdf:14.73MB

None

Journal Articles

Natural convection in a horizontal silicone oil layer in a circular cylinder heated below

Akino, Norio; Kunugi, Tomoaki; Shiina, Yasuaki; Seki, Masahiro; Okamoto, Yoshizo*

Nippon Kikai Gakkai Rombunshu, B, 55(509), p.152 - 158, 1989/01

no abstracts in English

Oral presentation

Cooling simulation of heavy ion beams

Ikegami, Masahiro*; Okamoto, Hiromi*; Yuri, Yosuke; Soda, Hikaru*; Tanabe, Mikio*; Noda, Akira*

no journal, , 

no abstracts in English

Oral presentation

Engineering tests for the manufacture of coil cases for the ITER superconducting coils

Onozuka, Masanori*; Shimizu, Katsusuke*; Urata, Kazuhiro*; Kimura, Masahiro*; Kadowaki, Hiroshi*; Okamoto, Mamoru*; Nakajima, Hideo; Hamada, Kazuya; Okuno, Kiyoshi

no journal, , 

no abstracts in English

42 (Records 1-20 displayed on this page)