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Journal Articles

PANDORA Project for the study of photonuclear reactions below $$A=60$$

Tamii, Atsushi*; Pellegri, L.*; S$"o$derstr$"o$m, P.-A.*; Allard, D.*; Goriely, S.*; Inakura, Tsunenori*; Khan, E.*; Kido, Eiji*; Kimura, Masaaki*; Litvinova, E.*; et al.

European Physical Journal A, 59(9), p.208_1 - 208_21, 2023/09

no abstracts in English

Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:97.01(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Journal Articles

Study on plutonium burner high temperature gas-cooled reactor in Japan; Introduction scenario, reactor safety and fabrication tests of the 3S-TRISO fuel

Ueta, Shohei; Mizuta, Naoki; Fukaya, Yuji; Goto, Minoru; Tachibana, Yukio; Honda, Masaki*; Saiki, Yohei*; Takahashi, Masashi*; Ohira, Koichi*; Nakano, Masaaki*; et al.

Nuclear Engineering and Design, 357, p.110419_1 - 110419_10, 2020/02

 Times Cited Count:1 Percentile:12.83(Nuclear Science & Technology)

The concept of a plutonium (Pu) burner HTGR is proposed to incarnate highly-effective Pu utilization by its inherent safety features. The security and safety fuel (3S-TRISO fuel) employs the coated fuel particle with a fuel kernel made of plutonium dioxide (PuO$$_{2}$$) and yttria stabilized zirconia (YSZ) as an inert matrix. This paper presents feasibility study of Pu burner HTGR and R&D on the 3S-TRISO fuel.

Journal Articles

Ion species/energy dependence of irradiation-induced lattice structure transformation and surface hardness of Ni$$_{3}$$Nb and Ni$$_{3}$$Ta intermetallic compounds

Kojima, Hiroshi*; Kaneno, Yasuyuki*; Ochi, Masaaki*; Semboshi, Satoshi*; Hori, Fuminobu*; Saito, Yuichi*; Ishikawa, Norito; Okamoto, Yoshihiro; Iwase, Akihiro*

Materials Transactions, 58(5), p.739 - 748, 2017/05

 Times Cited Count:5 Percentile:26.72(Materials Science, Multidisciplinary)

Bulk samples of Ni$$_{3}$$Nb and Ni$$_{3}$$Ta intermetallic compounds were irradiated with 16 MeV Au, 4.5 MeV Ni, 4.5 MeV Al, 200 MeV Xe and 1.0 MeV He ions, and the change in near-surface lattice structure was investigated by means of the grazing incidence X-ray diffraction (GIXD)and EXAFS. The Ni$$_{3}$$Nb and Ni$$_{3}$$Ta lattice structures transform from the ordered structures (orthorhombic and monoclinic structures for Ni$$_{3}$$Nb and Ni$$_{3}$$Ta, respectively) to the amorphous state by the Au, Ni, Al and Xe ion irradiations. Irrespective of such heavy ion species or energies, the lattice structure transformation to the amorphous state almost correlate with the density of energy deposited through elastic collisions.

Journal Articles

Conceptual study of a plutonium burner high temperature gas-cooled reactor with high nuclear proliferation resistance

Goto, Minoru; Demachi, Kazuyuki*; Ueta, Shohei; Nakano, Masaaki*; Honda, Masaki*; Tachibana, Yukio; Inaba, Yoshitomo; Aihara, Jun; Fukaya, Yuji; Tsuji, Nobumasa*; et al.

Proceedings of 21st International Conference & Exhibition; Nuclear Fuel Cycle for a Low-Carbon Future (GLOBAL 2015) (USB Flash Drive), p.507 - 513, 2015/09

A concept of a plutonium burner HTGR named as Clean Burn, which has a high nuclear proliferation resistance, had been proposed by Japan Atomic Energy Agency. In addition to the high nuclear proliferation resistance, in order to enhance the safety, we propose to introduce PuO$$_{2}$$-YSZ TRISO fuel with ZrC coating to the Clean Burn. In this study, we conduct fabrication tests aiming to establish the basic technologies for fabrication of PuO$$_{2}$$-YSZ TRISO fuel with ZrC coating. Additionally, we conduct a quantitative evaluation of the security for the safety, a design of the fuel and the reactor core, and a safety evaluation for the Clean Burn to confirm the feasibility. This study is conducted by The University of Tokyo, Japan Atomic Energy Agency, Fuji Electric Co., Ltd., and Nuclear Fuel Industries, Ltd. It was started in FY2014 and will be completed in FY2017, and the first year of the implementation was on schedule.

Journal Articles

Effect of resistivity profile on current decay time of initial phase of current quench in neon-gas-puff inducing disruptions of JT-60U

Kawakami, Sho*; Shibata, Yoshihide; Watanabe, Kiyomasa*; Ono, Noriyasu*; Isayama, Akihiko; Takizuka, Tomonori*; Kawano, Yasunori; Okamoto, Masaaki*

Physics of Plasmas, 20(11), p.112507_1 - 112507_6, 2013/11

 Times Cited Count:2 Percentile:8.97(Physics, Fluids & Plasmas)

According to an early work on the behavior of the plasma current decay in the JT-60U disruptive discharges caused by the radiative collapse with a massive neon-gas-puff, the increase of the internal inductance mainly determined the current decay time of plasma current during the initial phase of current quench. To investigate what determines the increase of the internal inductance, we focus attention on the relationship between the electron temperature (or the resistivity) profile and the time evolution of the current density profile, and carry out numerical calculations. As a result, we find the reason of the increase of the internal inductance: The current density profile at the start of the current quench is broader than an expected current density profile in the steady state, which is determined by the temperature (or resistivity) profile. The current density profile evolves into peaked one and the internal inductance is increasing.

Journal Articles

Study of the applicability of CFD calculation for HTTR reactor

Tsuji, Nobumasa*; Nakano, Masaaki*; Takada, Eiji*; Tokuhara, Kazumi*; Ohashi, Kazutaka*; Okamoto, Futoshi*; Tazawa, Yujiro; Inaba, Yoshitomo; Tachibana, Yukio

Proceedings of 6th International Topical Meeting on High Temperature Reactor Technology (HTR 2012) (USB Flash Drive), 9 Pages, 2012/10

Passive heat removal performance of the reactor vessel cavity cooling system (RCCS) is of primary concern for enhanced inherent safety of HTGR. In a loss of forced cooling accident, decay heat must be removed by radiation and natural convection of RCCS. Thus thermal hydraulic analysis of reactor internals and RCCS is powerful means for evaluation of the heat removal performance of RCCS. The thermal hydraulic analyses using CFD computation tools are conducted for normal operation of the High Temperature Engineering Test Reactor (HTTR) and are compared to the temperature distribution of measured data. The calculated temperatures on outer faces of the permanent side reflector (PSR) blocks are in fair agreement with measured data. The transient analysis for decay heat removal mode in HTTR is also conducted.

Journal Articles

Core design and safety analyses of 600 MWt, 950$$^{circ}$$C high temperature gas-cooled reactor

Nakano, Masaaki*; Takada, Eiji*; Tsuji, Nobumasa*; Tokuhara, Kazumi*; Ohashi, Kazutaka*; Okamoto, Futoshi*; Tazawa, Yujiro; Tachibana, Yukio

Proceedings of 6th International Topical Meeting on High Temperature Reactor Technology (HTR 2012) (USB Flash Drive), 6 Pages, 2012/10

The conceptual core design study of High Temperature Gas-cooled Reactor (HTGR) is performed. The major specifications are 600 MW thermal output, 950$$^{circ}$$C outlet coolant temperature, prismatic core type, enriched uranium fuel. The decay heat in the core can be removed with only passive measures, for example, natural convection reactor cavity cooling system (RCCS), even if any electricity is not supplied (station blackout). The transient thermal analysis of the depressurization accident in the case the primary coolant decreases to the atmosphere pressure shows that the fuels and the reactor pressure vessel temperatures are kept under their safety limit criteria. The fission product release, $$^{rm 110m}$$Ag and $$^{137}$$Cs from the fuels under the normal operation is small as to make maintenance of devices in the primary cooling system, such as a gas turbine, without remote maintenance. The HTGRs can achieve the advanced safety features based on their inherent passive safety characteristics.

Journal Articles

New ORIGEN2 libraries based on JENDL-4.0 and their validation for long-lived fission products by post irradiation examination analyses of LWR spent fuels

Kojima, Kensuke; Okumura, Keisuke; Asai, Shiho; Hanzawa, Yukiko; Okamoto, Tsutomu; Toshimitsu, Masaaki; Inagawa, Jun; Kimura, Takaumi; Kaneko, Satoru*; Suzuki, Kensuke*

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 5 Pages, 2011/12

Accurate inventory estimation of long-lived fission products (LLFPs) in LWR spent fuels is important for the quality management and for long-term safety assessment of high-level radioactive vitrified wastes. In Japan, ORIGEN2 has been widely used to estimate the fuel compositions. However, equipped library data in the original ORIGEN2 are old and are not validated enough for LLFPs, such as $$^{79}$$Se, $$^{99}$$Tc, $$^{126}$$Sn and $$^{135}$$Cs, because available post irradiation examination (PIE) data are limited for these nuclides, which have difficulties in radiochemical analyses. For more accurate the estimation, new ORIGEN2 libraries are developed from the latest nuclear data library JENDL-4.0 for cross sections and fission yields, and from other libraries for half-lives, and so on. The new libraries are validated by PIE analyses of the sample fuels irradiated in Cooper, Calvert-Cliffs-1, H. B. Robinson-2, and Ohi-1. As a result, it was found that the new library gives good results for the estimation.

Journal Articles

Study of plasma current decay in the initial phase of high poloidal beta disruptions in JT-60U

Shibata, Yoshihide*; Watanabe, Kiyomasa*; Ono, Noriyasu*; Okamoto, Masaaki*; Isayama, Akihiko; Kurihara, Kenichi; Oyama, Naoyuki; Nakano, Tomohide; Kawano, Yasunori; Matsunaga, Go; et al.

Plasma and Fusion Research (Internet), 6, p.1302136_1 - 1302136_4, 2011/10

no abstracts in English

Journal Articles

Analyses of assay data of LWR spent nuclear fuels with a continuous-energy Monte Carlo code MVP and JENDL-4.0 for inventory estimation of $$^{79}$$Se, $$^{99}$$Tc, $$^{126}$$Sn and $$^{135}$$Cs

Okumura, Keisuke; Asai, Shiho; Hanzawa, Yukiko; Suzuki, Hideya; Toshimitsu, Masaaki; Inagawa, Jun; Okamoto, Tsutomu; Shinohara, Nobuo; Kaneko, Satoru*; Suzuki, Kensuke*

Progress in Nuclear Science and Technology (Internet), 2, p.369 - 374, 2011/10

For accurate inventory estimation of long-lived fission products in LWR spent fuels, a new burn-up chain model and decay data based on the latest nuclear data such as JENDL-4.0 was developed. MVP-BURN with the latest nuclear data was applied to several post irradiation examinations including inventory measurements of $$^{79}$$Se, $$^{99}$$Tc, $$^{126}$$Sn and $$^{135}$$Cs. One of them is a new measurement by JAEA. From the PIE analyses, it is found that the new PIE data obtained by JAEA is consistent with the other PIE data by different laboratory with different techniques. It is also confirmed that the present calculation results show good agreements with experimental ones within about 10% for productions of $$^{79}$$Se and $$^{135}$$Cs. In contrast, amounts of $$^{99}$$Tc and $$^{126}$$Sn are overestimated by about 50%. These discrepancies are likely due to the effect of insoluble residue produced during sample dissolution and/or errors of fission yields in the analyses.

Journal Articles

Computational study for inventory estimation of Se-79, Tc-99, Sn-126, and Cs-135 in high-level radioactive wastes from spent nuclear fuels of light water reactors

Okumura, Keisuke; Asai, Shiho; Hanzawa, Yukiko; Okamoto, Tsutomu; Suzuki, Hideya; Toshimitsu, Masaaki; Inagawa, Jun; Kimura, Takaumi; Suzuki, Kensuke*; Kaneko, Satoru*

Proceedings of 14th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2011) (CD-ROM), p.1443 - 1450, 2011/09

Inventory estimation of long-lived fission products (LLFPs) in high-level radioactive wastes (HLW) from spent nuclear fuels of light water reactors is important for a safety assessment of their disposal. In order to develop an inventory estimation method of difficult-to-measure LLFPs (Se-79, Tc-99, Sn-126, and Cs-135), a parametric study was carried out by using a sophisticated burnup calculation code and data. In the parametric study, fuel specifications and irradiation conditions are changed in the conceivable range. The considered parameters are fuel assembly types (PWR / BWR), U-235 enrichment, moderator temperature, void fraction, power density, and so on. From the calculated results, we clarify the burnup characteristics of the target LLFPs and their possible ranges of generations. Finally, candidates of the key nuclide are proposed for the scaling factor method of HLW.

Journal Articles

Study of current decay time during disruption in JT-60U tokamak

Shibata, Yoshihide*; Watanabe, Kiyomasa*; Okamoto, Masaaki*; Ono, Noriyasu*; Isayama, Akihiko; Kurihara, Kenichi; Nakano, Tomohide; Oyama, Naoyuki; Kawano, Yasunori; Matsunaga, Go; et al.

Nuclear Fusion, 50(2), p.025015_1 - 025015_7, 2010/01

 Times Cited Count:14 Percentile:52.73(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Nature of magnetic coupling between Mn ions in as-grown Ga$$_{1-x}$$Mn$$_{x}$$As studied by X-ray magnetic circular dichroism

Takeda, Yukiharu; Kobayashi, Masaki*; Okane, Tetsuo; Okochi, Takuo*; Okamoto, Jun*; Saito, Yuji; Kobayashi, Keisuke*; Yamagami, Hiroshi; Fujimori, Atsushi*; Tanaka, Arata*; et al.

Hoshako, 22(4), p.202 - 209, 2009/07

no abstracts in English

Journal Articles

Nature of magnetic coupling between Mn ions in as-grown Ga$$_{1-x}$$Mn$$_{x}$$As studied by X-ray magnetic circular dichroism

Takeda, Yukiharu; Kobayashi, Masaki*; Okane, Tetsuo; Okochi, Takuo; Okamoto, Jun*; Saito, Yuji; Kobayashi, Keisuke*; Yamagami, Hiroshi; Fujimori, Atsushi; Tanaka, Arata*; et al.

Physical Review Letters, 100(24), p.247202_1 - 247202_4, 2008/06

 Times Cited Count:39 Percentile:82.27(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Conceptual core design study of the Very High Temperature gas-cooled Reactor (VHTR); Upgrading the core performance by using multihole-type fuel

Ohashi, Kazutaka; Nishihara, Tetsuo; Kunitomi, Kazuhiko; Nakano, Masaaki*; Tazawa, Yujiro*; Okamoto, Futoshi*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 7(1), p.32 - 43, 2008/03

Interests on the development of the Very High-Temperature Gas-Cooled Reactor (VHTR), of which the reactor outlet temperature is 950$$^{circ}$$C or much higher, are recently increasing world-widely and it was selected as one of the candidate reactor types of the GIF. Japan Atomic Energy Agency has already initiated R&D efforts on the electricity and hydrogen co-generation plant with VHTR system, GTHTR300C. Although technical feasibility of its VHTR reactor using Pin-in-block fuel, which has experience to be already used in the HTTR, has been shown fundamentally, more improvements of the core performances, such as decrease of the occupational exposure doses during the plant maintenance, are desired. This report presents the results of the conceptual core design study using Multi-hole type fuel and the study on the occupational exposure doses. The latter results shows much better plant maintainability compared to the previous results of the GTHTR-300.

Journal Articles

Evaluation of dependence of current decay time on electron temperature measured by He I line intensity ratios in JT-60U tokamak

Okamoto, Masaaki*; Hiraishi, Takehiro*; Ono, Noriyasu*; Takamura, Shuichi*; Nakano, Tomohide; Kawano, Yasunori; Ozeki, Takahisa; Sugihara, Masayoshi

Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00

It is of importance to evaluate the decay time of the plasma current for estimation of the electromagnetic force acting on the vacuum vessel during plasma disruptions in tokamak devices. The L/R model predicts that the decay time is proportional to three-haves power of the electron temperature, indicating the importance of the electron temperature for the estimation. However, it is difficult to measure the electron temperature of the disruptive plasma with the Langmuir probe due to the heat flux and due to the significant electromagnetic force. We propose a measurement technique of the electron temperature by using temperature-sensitive He I lines with high time resolution. In this method, the incident light to a spectrometer is divided into three, each of which transmits a bandpass filter, and then is measured with an absolutely calibrated photo-multiplier. The measured intensity ratios are analyzed with a collisional-radiative model. It is confirmed that the electron temperature determined by this technique is in agreement with that measured by a Langmuir probe in some devices. In the present work, the temporal evolution of the electron temperature during the disruptive plasma of JT-60U is measured with this technique.

Journal Articles

Quantification of gas-entrainment using dynamic PIV

Takeyama, Kojiro*; Okamoto, Koji*; Ishikawa, Masaaki*; Kamide, Hideki

Proceedings of 6th International Symposium on Particle Image Velocimetry (CD-ROM), 7 Pages, 2005/09

The new visibility method of measurement was developed for gas-entrainment from liquid surface. The vortex is generated unsteadily and it exists less than 0.3. Dynamic PIV is carried out for this short time phenomenon using pulse laser and high-speed camera. In this study, the distribution of downward velocities and the value of circulation are obtained with high accuracy using galvano-mirror.

Journal Articles

High-resolution soft X-ray photoemission spectroscopy of spinel-type compound CuIr$$_{2}$$S$$_{4}$$

Okane, Tetsuo; Fujimori, Shinichi; Mamiya, Kazutoshi; Okamoto, Jun; Muramatsu, Yasuji; Fujimori, Atsushi; Suzuki, Hiroyuki*; Matsumoto, Takehiko*; Furubayashi, Takao*; Isobe, Masaaki*; et al.

Journal of Magnetism and Magnetic Materials, 272-276(Suppl.), p.e297 - e298, 2004/05

 Times Cited Count:5 Percentile:29.88(Materials Science, Multidisciplinary)

The electronic structure of spinel-type chalcogenide CuIr$$_{2}$$S$$_{4}$$, which exhibits a metal-insulator transition (MIT) as a function of temperature, has been studied by photoemission spectroscopy (PES). Below the transition temperature $$T_{mathrm{MI}}$$, the valence-band PES spectra indicate a gap formation, while the overall valence-band structure is shifted to the higher binding-energy side. The line shape of the Ir 4${it f}$ core-level PES spectra shows a dramatic change across $$T_{mathrm{MI}}$$, which may be associated with the variation of the Ir 5${it d}$ electron states.

Oral presentation

Comparison of He I line intensity ratio method and electrostatic probe for electron density and temperature measurements

Kajita, Shin*; Ono, Noriyasu*; Okamoto, Masaaki*; Nakano, Tomohide; Takamura, Shuichi*

no journal, , 

no abstracts in English

35 (Records 1-20 displayed on this page)