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Journal Articles

Application of polynomial chaos expansion technique to dynamic probabilistic risk assessment of nuclear power plants

Kubo, Kotaro; Tanaka, Yoichi

Proceedings of Asian Symposium on Risk Assessment and Management 2021 (ASRAM 2021) (Internet), 13 Pages, 2021/10

Probabilistic risk assessment (PRA) is extensively used, e.g., in periodical safety review and the reactor oversight process, in nuclear regulation systems to improve the safety of nuclear power plants; however, one limitation of classical PRA is the handling of temporal information such as system failure and core damage timings. To resolve this limitation, the dynamic PRA method has been developed and applied for multiple safety issues; however, its improvement is accompanied by considerable computational costs. In this study, we applied the polynomial chaos expansion (PCE) technique to dynamic PRA with the expectation of reduction in computational cost. In particular, to estimate core damage timing, a PCE-based surrogate model was developed. Then, the surrogate model was applied to dynamic PRA to calculate the conditional core damage probability and core damage timing. Consequently, applying the PCE might efficiently perform these analyses without considerable reduction in accuracy.

Journal Articles

Evaluation of risk dilution effects in dynamic probabilistic risk assessment of nuclear power plants

Kubo, Kotaro; Tanaka, Yoichi

Proceedings of 31st European Safety and Reliability Conference (ESREL 2021) (Internet), p.810 - 817, 2021/09

Probabilistic risk assessment (PRA) is a method of effectively evaluating risks in nuclear power plants and is used in various agencies. Dynamic PRA is attracting considerable attention, as it enables realistic assessment by reducing the assumptions and engineering judgments related to time-dependent failure probability and/or human action reliability. However, it is difficult to remove all assumptions and engineering judgments. Therefore, their effects on assessment results should be understood. This study focuses on the "risk dilution effect," which arises from assumptions about uncertainty. Results showed that this effect causes a difference of about 10% to 20% in the relative change of the conditional core damage probability in the station blackout scenario. This effect should be fully considered when using dynamic PRA in critical decision-making, such as that on regulations.

Journal Articles

Identification of hydrogen species on Pt/Al$$_{2}$$O$$_{3}$$ by ${it in situ}$ inelastic neutron scattering and their reactivity with ethylene

Yamazoe, Seiji*; Yamamoto, Akira*; Hosokawa, Saburo*; Fukuda, Ryoichi*; Hara, Kenji*; Nakamura, Mitsutaka; Kamazawa, Kazuya*; Tsukuda, Tatsuya*; Yoshida, Hisao*; Tanaka, Tsunehiro*

Catalysis Science & Technology, 11(1), p.116 - 123, 2021/01

 Times Cited Count:3 Percentile:81.22(Chemistry, Physical)

Journal Articles

Dynamic PRA of flooding-initiated accident scenarios using THALES2-RAPID

Kubo, Kotaro; Zheng, X.; Tanaka, Yoichi; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Jang, S.*; Takata, Takashi*; Yamaguchi, Akira*

Proceedings of 30th European Safety and Reliability Conference and 15th Probabilistic Safety Assessment and Management Conference (ESREL 2020 and PSAM-15) (Internet), p.2279 - 2286, 2020/11

Probabilistic risk assessment (PRA) is one of the methods used to assess the risks associated with large and complex systems. When the risk of an external event is evaluated using conventional PRA, a particular limitation is the difficulty in considering the timing at which nuclear power plant structures, systems, and components fail. To overcome this limitation, we coupled thermal-hydraulic and external-event simulations using Risk Assessment with Plant Interactive Dynamics (RAPID). Internal flooding was chosen as the representative external event, and a pressurized water reactor plant model was used. Equations based on Bernoulli's theorem were applied to flooding propagation in the turbine building. In the analysis, uncertainties were taken into account, including the flow rate of the flood water source and the failure criteria for the mitigation systems. In terms of recovery action, isolation of the flood water source by the operator and drainage using a pump were modeled based on several assumptions. The results indicate that the isolation action became more effective when combined with drainage.

Journal Articles

Enhancement of the treatment of system interactions in a dynamic PRA tool

Tanaka, Yoichi; Tamaki, Hitoshi; Zheng, X.; Sugiyama, Tomoyuki

Proceedings of 30th European Safety and Reliability Conference and 15th Probabilistic Safety Assessment and Management Conference (ESREL 2020 and PSAM-15) (Internet), p.2195 - 2201, 2020/11

Journal Articles

A Comparative study of sampling techniques for dynamic probabilistic risk assessment of nuclear power plants

Kubo, Kotaro; Zheng, X.; Tanaka, Yoichi; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Jang, S.*; Takata, Takashi*; Yamaguchi, Akira*

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.308 - 315, 2020/10

Dynamic probabilistic risk assessment (PRA) is a method for improving the realism and completeness of conventional PRA. However, enormous calculation costs are incurred by these improvements. One solution is to select an appropriate sampling method. In this paper, we applied the Monte Carlo, Latin hypercube, grid-point, and quasi-Monte Carlo sampling methods to the dynamic PRA of a simplified accident sequence and compared the results for each method. Quasi-Monte Carlo sampling was found to be the most effective method in this case.

Journal Articles

Experimental investigation of the suppressed superconducting gap and double-resonance mode in Ba$$_{1-x}$$K$$_{x}$$Fe$$_{2}$$As$$_{2}$$

Ideta, Shinichiro*; Murai, Naoki; Nakajima, Masamichi*; Kajimoto, Ryoichi; Tanaka, Kiyohisa*

Physical Review B, 100(23), p.235135_1 - 235135_7, 2019/12

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

JAEA Reports

CHEMKEq; Evaluation code for chemical composition based on partial mixed model with Chemical Equilibrium and Reaction Kinetics (Contract research)

Ito, Hiroto*; Shiotsu, Hiroyuki; Tanaka, Yoichi*; Nishihara, Satomichi*; Sugiyama, Tomoyuki; Maruyama, Yu

JAEA-Data/Code 2018-012, 42 Pages, 2018/10

JAEA-Data-Code-2018-012.pdf:4.93MB

Chemical composition of fission products transported in nuclear facilities in severe accidents is controlled by slower chemical reaction rates, therefore, it could be different from that evaluated on the chemical equilibrium assumption. Hence, it is necessary to evaluate the chemical composition with reaction kinetics. On the other hand, databases applicable to the analysis of nuclear facilities have not been constructed because knowledge of reaction rates of complex chemical reactions in severe accidents is currently limited. Accordingly, we have developed the CHEMKEq code based on a partial mixed model with chemical equilibrium and reaction kinetics to decrease uncertainties of the chemical composition caused by the reaction rate. The CHEMKEq code, under mass conservation law, firstly evaluates chemical species obeying the chemical equilibrium model, and then, relatively slow reactions are solved by the reaction kinetics model. Moreover, the CHEMKEq code has a multiplicity of use in evaluations of chemical composition because general chemical equilibrium and reaction kinetics models are also available and databases required to calculation are external file formats. This report is the user's guide of the CHEMKEq code, showing models, solution methods, structure of the code and calculation examples. And information to run the CHEMKEq code is summarized in appendixes.

Journal Articles

Effect of electron correlations on spin excitation bandwidth in Ba$$_{0.75}$$K$$_{0.25}$$Fe$$_{2}$$As$$_{2}$$ as seen via time-of-flight inelastic neutron scattering

Murai, Naoki; Suzuki, Katsuhiro*; Ideta, Shinichiro*; Nakajima, Masamichi*; Tanaka, Kiyohisa*; Ikeda, Hiroaki*; Kajimoto, Ryoichi

Physical Review B, 97(24), p.241112_1 - 241112_6, 2018/06

 Times Cited Count:5 Percentile:39.54(Materials Science, Multidisciplinary)

We use inelastic neutron scattering (INS) to investigate the effect of electron correlations on spin dynamics in iron-based superconductor Ba$$_{0.75}$$K$$_{0.25}$$Fe$$_{2}$$As$$_{2}$$. Our INS data show a spin-wave-like dispersive feature, with a zone boundary energy of 200 meV. A first principles analysis of dynamical spin susceptibility, incorporating the mass renormalization factor of 3, as determined by angle-resolved photoemission spectroscopy, provides a reasonable description of the observed spin excitations. This analysis shows that electron correlations in the Fe-3d bands yield enhanced effective electron masses, and consequently, induce substantial narrowing of the spin excitation bandwidth. Our results highlight the importance of electron correlations in an itinerant description of the spin excitations in iron-based superconductors.

Journal Articles

Progress in the geological disposal program in Japan

Deguchi, Akira*; Umeki, Hiroyuki*; Ueda, Hiroyoshi*; Miyamoto, Yoichi; Shibata, Masahiro; Naito, Morimasa; Tanaka, Toshihiko*

LBNL-1006984 (Internet), p.12_1 - 12_22, 2016/12

The H12 report demonstrated the feasibility of safe and technically reliable geological disposal in 1999. The Government of Japan re-evaluated the geological disposal program in terms of technical feasibility based on state-of-the-art geosciences and implementation process, because more than 10 years have passed from H12 and the Great Earthquake and nuclear accident have increased public concern regarding nuclear issues and natural hazards to cause accidents at nuclear facilities. Following the re-evaluation, the Government concluded further to promote geological disposal program, and thus the Basic Policy for Final Disposal was revised in 2015 including a new approach to siting process with identification of "Scientifically Preferable Areas". NUMO and relevant research organizations such as JAEA have been carrying out R and D activities to increase technical reliability for geological disposal. NUMO has started to develop a generic safety case.

Journal Articles

Beam commissioning of the linac for iBNCT

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.

Journal Articles

Recent progress in the chopper spectrometer 4SEASONS at J-PARC

Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Kamazawa, Kazuya*; Ikeuchi, Kazuhiko*; Iida, Kazuki*; Ishikado, Motoyuki*; Nakajima, Kenji; Kawamura, Seiko; Nakatani, Takeshi; et al.

JAEA-Conf 2015-002, p.319 - 329, 2016/02

Journal Articles

Density and X-ray emission profile relationships in highly ionized high-Z laser-produced plasmas

Yoshida, Kensuke*; Fujioka, Shinsuke*; Higashiguchi, Takeshi*; Ugomori, Teruyuki*; Tanaka, Nozomi*; Kawasaki, Masato*; Suzuki, Yuhei*; Suzuki, Chihiro*; Tomita, Kentaro*; Hirose, Ryoichi*; et al.

Applied Physics Letters, 106(12), p.121109_1 - 121109_5, 2015/03

 Times Cited Count:6 Percentile:32.7(Physics, Applied)

Journal Articles

Drift simulation of tsunami debris in the North Pacific

Kawamura, Hideyuki; Kobayashi, Takuya; Nishikawa, Shiro*; Ishikawa, Yoichi*; Usui, Norihisa*; Kamachi, Masafumi*; Aso, Noriko*; Tanaka, Yusuke*; Awaji, Toshiyuki*

Global Environmental Research (Internet), 18(1), p.81 - 96, 2014/09

A drift simulation of tsunami debris flushed out from the Tohoku district, Japan, into the North Pacific due to the tsunami on March 11, 2011, has been conducted to monitor and forecast the drift path over the North Pacific. Results showed that tsunami debris was first transported eastward by the intense Kuroshio Extension and westerly, spreading in the north and south directions by both an energetic ocean eddy and a storm track over the ocean. Tsunami debris with larger windage was transported over the North Pacific by ocean surface wind rather than ocean current and arrived at the west coast of the North American Continent in the fall of 2011. Tsunami debris located near the North American Continent migrated, associated with the basin-scale seasonal change in the atmospheric pressure pattern. Our forecast run suggested that the tsunami debris belt will be formed from the North American Continent in the east to the Philippines in the west.

Journal Articles

Efficient extreme ultraviolet emission from one-dimensional spherical plasmas produced by multiple lasers

Yoshida, Kensuke*; Fujioka, Shinsuke*; Higashiguchi, Takeshi*; Ugomori, Teruyuki*; Tanaka, Nozomi*; Ohashi, Hayato*; Kawasaki, Masato*; Suzuki, Yuhei*; Suzuki, Chihiro*; Tomita, Kentaro*; et al.

Applied Physics Express, 7(8), p.086202_1 - 086202_4, 2014/08

 Times Cited Count:24 Percentile:75.15(Physics, Applied)

We demonstrate high conversion efficiency for extreme ultraviolet (EUV) emission at 6.5-6.7 nm from multiple laser beam-produced one-dimensional spherical plasmas. Multiply charged-state ions produce strong resonance emission lines, which combine to yield intense unresolved transition arrays in Gd, Tb, and Mo. The maximum in-band EUV conversion efficiency was observed to be 0.8%, which is one of the highest values ever reported due to the reduction of plasma expansion loss.

Journal Articles

Antiferromagnetic order of the Co$$^{2+}$$ high-spin state with a large orbital angular momentum in La$$_{1.5}$$Ca$$_{0.5}$$CoO$$_{4}$$

Okamoto, Jun*; Nakao, Hironori*; Yamasaki, Yuichi*; Wadachi, Hiroki*; Tanaka, Arata*; Kubota, Masato; Horigane, Kazumasa*; Murakami, Yoichi*; Yamada, Kazuyoshi*

Journal of the Physical Society of Japan, 83(4), p.044705_1 - 044705_6, 2014/04

 Times Cited Count:7 Percentile:53.57(Physics, Multidisciplinary)

Journal Articles

Feasibility demonstration of a new Fermi chopper with supermirror-coated slit package

Nakamura, Mitsutaka; Kambara, Wataru; Krist, T.*; Shinohara, Takenao; Ikeuchi, Kazuhiko*; Arai, Masatoshi; Kajimoto, Ryoichi; Nakajima, Kenji; Tanaka, Hiromichi; Suzuki, Junichi*; et al.

Nuclear Instruments and Methods in Physics Research A, 737, p.142 - 147, 2014/02

 Times Cited Count:3 Percentile:30.04(Instruments & Instrumentation)

The efficiency of inelastic neutron scattering measurements using a chopper spectrometer can be markedly improved by utilizing multiple incident energies (Multi-Ei method). However, in conventional chopper systems, optimization of the experimental condition for all incident energies is absolutely impossible. We developed a new Fermi chopper with a supermirror-coated slit package in order to overcome the problem and experimentally demonstrated that the full optimization of the experimental condition for multiple incident energies is nearly achieved.

Journal Articles

Simple method for high-density impregnation of Aliquat 336 onto porous sheet and binding performance of resulting sheet for palladium ions

Tanaka, Ryota*; Ishihara, Ryo*; Miyoshi, Kazuyoshi*; Umeno, Daisuke*; Saito, Kyoichi*; Asai, Shiho; Yamada, Shinsuke*; Hirota, Hideyuki*

Separation Science and Technology, 49(1), p.154 - 159, 2014/01

 Times Cited Count:4 Percentile:19.55(Chemistry, Multidisciplinary)

JAEA Reports

Horonobe Underground Research Laboratory Project; Investigation report for the 2011 fiscal year

Nakayama, Masashi; Amano, Kenji; Tokiwa, Tetsuya; Yamamoto, Yoichi; Oyama, Takuya; Amano, Yuki; Murakami, Hiroaki; Inagaki, Daisuke; Tsusaka, Kimikazu; Kondo, Keiji; et al.

JAEA-Review 2012-035, 63 Pages, 2012/09

JAEA-Review-2012-035.pdf:12.23MB

The Horonobe Underground Research Laboratory Project is planned to extend over a period 20 years. The investigations will be conducted in three phases, namely "Phase 1: Surface-based investigations", "Phase 2: Construction Phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase"(research in the underground facilities). This report summarizes the results of the investigations for the 2011 fiscal year (2011/2012). The investigations, which are composed of "Geoscientific research" and "R&D on geological disposal technology", were carried out according to "Horonobe Underground Research Laboratory Project Investigation Program for the 2011 Fiscal year". The results of these investigations, along with the results which were obtained in other departments of Japan Atomic Energy Agency (JAEA), are properly offered to the implementations and the safety regulations. For the sake of this, JAEA has proceeded with the project in collaboration with experts from domestic and overseas research organisations.

Journal Articles

Behavior of environmental tritium at NIFS Toki Site of Japan

Sugihara, Shinji*; Tanaka, Masahiro*; Tamari, Toshiya*; Shimada, Jun*; Takahashi, Tomoyuki*; Momoshima, Noriyuki*; Fukutani, Satoshi*; Atarashi-Andoh, Mariko; Sakuma, Yoichi*; Yokoyama, Sumi*; et al.

Fusion Science and Technology, 60(4), p.1300 - 1303, 2011/11

 Times Cited Count:1 Percentile:11.72(Nuclear Science & Technology)

The purpose of this study is to develop the technique to evaluate the environmental tritium behavior of the nuclear facility origin. Tritium concentrations of river water, precipitation and ground water around the NIFS site were determined by low background liquid scintillation measurement system combined with the electrolysis using solid polymer electrolyte. The electric conductivity and flow rate of the river and isotopic ratio of oxygen and hydrogen of water samples were also measured. The tritium concentrations in precipitation showed the seasonal variation and the range were 0.09-0.78 Bq/L. The tritium concentrations of river water and ground water were almost constant, 0.34 and 0.24 Bq/L respectively. The simple dynamic model for the site around the NIFS facilities was developed using measured data, and the behavior of tritium was simulated.

103 (Records 1-20 displayed on this page)