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Journal Articles

Long-term simulations of radiocesium discharge in watershed with improved radiocesium wash-off model; Applying the model to Abukuma River basin of Fukushima

Liu, X.; Machida, Masahiko; Kurikami, Hiroshi; Kitamura, Akihiro

Journal of Environmental Radioactivity, 203, p.135 - 146, 2019/07

In order to simulate the long-term migration and distribution of radiocesium after the Fukushima accident, a numerical model, Soil and Cesium Transport (SACT) based on universal soil loss equation (USLE), has been developed in previous studies. Although the SACT model's results on radiocesium discharge in 2011 are in reasonable agreement with field measurements, it fails to capture the sharp decrease of radiocesium flux in subsequent years, especially in the case of Abukuma River. We therefore have improved SACT by implementing the vertical migration and fixation of radiocesium in soil. For validation purpose, the annual average radiocesium concentration in sediments discharged from Abukuma River has been evaluated from measurement data. New model achieved much better agreement with the measurement results without parameter tuning.

JAEA Reports

Construction of thin-client system with hosted desktop infrastructure

Yashiro, Shigeo; Shoji, Makoto; Ueno, Tokio; Ueno, Asuka

JAEA-Testing 2019-001, 28 Pages, 2019/06

JAEA-Testing-2019-001.pdf:3.51MB

Center for Computational Science & e-Systems of Japan Atomic Energy Agency, provides an environment for using PCs with thin client systems to our organization's officers, operation management organization, common business organization, base management department, and offices for each research and development department. Supports the efficient and smooth implementation of our decision-making, core operations and related tasks. This report is the characteristics and construction policy (basic requirements) of the thin client system and hardware newly obtained in the subsequent operation, which were arranged and examined on the introduction of the existing thin client system updated in October 2017. It is a summary of the results, findings, etc. of the occupied thin client system.

Journal Articles

Smooth self-energy in the exact-diagonalization-based dynamical mean-field theory; Intermediate-representation filtering approach

Nagai, Yuki; Shinaoka, Hiroshi*

Journal of the Physical Society of Japan, 88(6), p.064004_1 - 064004_5, 2019/06

no abstracts in English

JAEA Reports

Technical report on the development of finance and contract information system Ver.4

Kimura, Hideo; Hikasa, Naoki*; Kugenuma, Yuji*; Doi, Toshiharu*; Kikuchi, Yoshitaka*

JAEA-Technology 2019-004, 25 Pages, 2019/05

JAEA-Technology-2019-004.pdf:3.02MB

JAEA has developed the "Financial and contract information system" for effective and efficient accomplishment of the mission-critical tasks. Because the development of the next system was necessary with the end in the support time limit of the current system, we carried out the development of the next system in 2018. While the addition of the electronic approval function or the adoption of the latest package software largely performed a functional enhancement until now by applying distributed systems construction technique based on the separation procurement that we devised progressively, in development, we extremely realized procurement with the low cost.

Journal Articles

Quasiparticle bound states around fractional vortices in $$s$$-wave superconductor

Nagai, Yuki; Kato, Yusuke*

Journal of the Physical Society of Japan, 88(5), p.054707_1 - 054707_8, 2019/05

no abstracts in English

Journal Articles

Synergy of turbulent and neoclassical transport through poloidal convective cells

Asahi, Yuichi*; Grandgirard, V.*; Sarazin, Y.*; Donnel, P.*; Garbet, X.*; Idomura, Yasuhiro; Dif-Pradalier, G.*; Latu, G.*

Plasma Physics and Controlled Fusion, 61(6), p.065015_1 - 065015_15, 2019/05

 Percentile:100

The role of poloidal convective cells on transport processes is studied with the full-F gyrokinetic code GYSELA. For this purpose, we apply a numerical filter to convective cells and compare the simulation results with and without the filter. The energy flux driven by the magnetic drifts turns out to be reduced by a factor of about 2 once the numerical filter is applied. A careful analysis reveals that the frequency spectrum of the convective cells is well-correlated with that of the turbulent Reynolds stress tensor, giving credit to their turbulence-driven origin. The impact of convective cells can be interpreted as a synergy between turbulence and neoclassical dynamics.

Journal Articles

Development of the ReaxFF methodology for electrolyte-water systems

Fedkin, M. V.*; Shin, Y. K.*; Dasgupta, N.*; Yeon, J.*; Zhang, W.*; van Duin, D.*; Van Duin, A. C. T.*; Mori, Kento*; Fujiwara, Atsushi*; Machida, Masahiko; et al.

Journal of Physical Chemistry A, 123(10), p.2125 - 2141, 2019/03

 Percentile:100(Chemistry, Physical)

no abstracts in English

JAEA Reports

Summaries of research and development activities by using supercomputer system of JAEA in FY2017; April 1, 2017 - March 31, 2018

Information Technology Systems' Management and Operating Office

JAEA-Review 2018-018, 167 Pages, 2019/02

JAEA-Review-2018-018.pdf:34.23MB

Japan Atomic Energy Agency (JAEA) conducts research and development (R&D) in various fields related to nuclear power and utilizes computational science and technology in many activities. As shown in the fact that about 20 percent of papers published by JAEA are concerned with R&D using computational science, the supercomputer system of JAEA has become an important infrastructure to support computational science and technology. In FY2017, the system was used for R&D aiming to restore Fukushima (environmental recovery and nuclear installation decommissioning) as a priority issue, and for JAEA's major projects such as R&D of fast reactor cycle technology, research for safety improvement in the field of nuclear energy, and basic nuclear science and engineering research. This report presents a great number of R&D results accomplished by using the system in FY2017, as well as user support, operational records and overviews of the system, and so on.

JAEA Reports

Review of research on advanced computational science in FY2017

Center for Computational Science & e-Systems

JAEA-Evaluation 2018-002, 32 Pages, 2019/02

JAEA-Evaluation-2018-002.pdf:1.09MB

Research on advanced computational science for nuclear applications, based on "Plan to Achieve Medium to Long-term Objectives of the Japan Atomic Energy Agency (Medium to Long-term Plan)", has been performed at Center for Computational Science & e-Systems (CCSE), Japan Atomic Energy Agency. CCSE established the committee consisting outside experts and authorities which does research evaluation and advices for the assistance of the research and development. This report summarizes the followings. (1) Results of the R&D performed at CCSE in FY 2017 (April 1st, 2017 - March 31st, 2018), (2) Results of the evaluation on the R&D by the committee in FY 2017

Journal Articles

Implementation of a gyrokinetic collision operator with an implicit time integration scheme and its computational performance

Maeyama, Shinya*; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki*; Nunami, Masanori*

Computer Physics Communications, 235, p.9 - 15, 2019/02

 Percentile:100(Computer Science, Interdisciplinary Applications)

We have implemented the Sugama collision operator in the gyrokinetic Vlasov simulation code, GKV, with an implicit time-integration scheme. The new method is versatile and independent of the details of the linearized collision operator, by means of an operator splitting, an implicit time integrator, and an iterative Krylov subspace solver. Numerical tests demonstrate stable computation over the time step size restricted by the collision term. An efficient implementation for parallel computation on distributed memory systems is realized by using the data transpose communication, which makes the iterative solver free from inter-node communications during iteration. Consequently, the present approach achieves enhancement of computational efficiency and reduction of computational time to solution simultaneously, and significantly accelerates the total performance of the application.

Journal Articles

Abnormally enhanced diamagnetism in Al-Zn-Mg alloys

Nishimura, Katsuhiko*; Matsuda, Kenji*; Lee, S.*; Nunomura, Norio*; Shimano, Tomoki*; Bendo, A.*; Watanabe, Katsumi*; Tsuchiya, Taiki*; Namiki, Takahiro*; Toda, Hiroyuki*; et al.

Journal of Alloys and Compounds, 774, p.405 - 409, 2019/02

 Percentile:100(Chemistry, Physical)

Journal Articles

Optimization of mechanical properties in aluminum alloys $$via$$ hydrogen partitioning control

Toda, Hiroyuki*; Yamaguchi, Masatake; Matsuda, Kenji*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*; Su, H.*; Fujiwara, Hiro*; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito; et al.

Tetsu To Hagane, 105(2), p.240 - 253, 2019/02

 Percentile:100(Metallurgy & Metallurgical Engineering)

no abstracts in English

Journal Articles

First-principles calculation of multiple hydrogen segregation along aluminum grain boundaries

Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito; Matsuda, Kenji*; Toda, Hiroyuki*

Computational Materials Science, 156, p.368 - 375, 2019/01

 Times Cited Count:1 Percentile:15.49(Materials Science, Multidisciplinary)

The segregation of multiple hydrogen atoms along aluminum (Al) grain boundaries (GBs) and fracture surfaces (FSs) was investigated through first-principles calculations considering the characteristics of GBs. The results indicate that hydrogen segregation is difficult along low-energy GBs. The segregation energy of multiple hydrogen atoms along GBs and FSs and the cohesive energy was obtained for three types of high-energy Al GBs. With increasing hydrogen segregation along the GBs, the cohesive energy of the GB decreases and approaches zero with no decrease in GB segregation energy. The GB cohesive energy decreases in parallel with the volume expansion of the region of low electron density along the GB.

Journal Articles

Modelling the effect of mechanical remediation on dose rates above radiocesium contaminated land

Malins, A.; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko

Remediation Measures for Radioactively Contaminated Areas, p.259 - 272, 2019/00

Journal Articles

Primary radiation damage; A Review of current understanding and models

Nordlund, K.*; Zinkle, S. J.*; Sand, A. E.*; Granberg, F.*; Averback, R. S.*; Stoller, R. E.*; Suzudo, Tomoaki; Malerba, L.*; Banhart, F.*; Weber, W. J.*; et al.

Journal of Nuclear Materials, 512, p.450 - 479, 2018/12

 Times Cited Count:5 Percentile:40.87(Materials Science, Multidisciplinary)

Scientific understanding of any kind of radiation effects starts from the primary damage. We consider the extensive experimental and computer simulation studies that have been performed over the past several decades on what the nature of the primary damage is. We review both the production of crystallographic or topological defects in materials as well as radiation mixing, i.e. the process where atoms in perfect crystallographic positions exchange positions with other ones in non-defective positions. We also consider the recent effort to provide alternatives to the current international standard for quantifying this energetic particle damage, the Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model for metals. We present in detail new complementary displacement production estimators ("athermal recombination corrected dpa": arc-dpa) and atomic mixing ("replacements per atom": rpa) functions that extend the NRT-dpa, and discuss their advantages and limitations.

Journal Articles

Visiting Professor's Research Division

Nakajima, Norihiro; Aoki, Keiko*

Tokyo Daigaku Jinkobutsu Kogaku Kenkyu Senta 2017-Nendo Kenkyu Nempo, p.51 - 53, 84, 2018/12

Visiting professors research division in the Research into Artifacts, Center for Engineering (RACE) has been conducting research collaboration in Socio-Artifactology and Human-Artifactology, in order to establish the methodology of the fusion research in sociology and science for artifacts engineering for the third era activity of RACE. The division decided to observe how the methodology works in applications with social experiments and numerical experiments for 2017.

Journal Articles

Finding free-energy landmarks of chemical reactions

Shiga, Motoyuki; Tuckerman, M. E.*

Journal of Physical Chemistry Letters, 9(21), p.6207 - 6214, 2018/11

 Percentile:100(Chemistry, Physical)

Predicting reaction pathways is one of the most important goals in theoretical and computational chemistry. In this paper, we propose a novel approach to search for free-energy landmarks, i.e., minima and the saddle points, of chemical reactions in an automated manner using a combination of steepest descent and gentlest ascent methods. As demonstrations, we present applications to the ring-opening reaction of benzocyclobutene and an SN2 reaction in aqueous solution.

Journal Articles

Surface energy reduction by dissociative hydrogen adsorption on inner surface of pore in aluminum

Yamaguchi, Masatake; Tsuru, Tomohito; Ebihara, Kenichi; Itakura, Mitsuhiro

Keikinzoku, 68(11), p.588 - 595, 2018/11

no abstracts in English

Journal Articles

Interpretation of thermal desorption spectra of hydrogen from aluminum using numerical simulation

Ebihara, Kenichi; Yamaguchi, Masatake; Tsuru, Tomohito; Itakura, Mitsuhiro

Keikinzoku, 68(11), p.596 - 602, 2018/11

Hydrogen embrittlement (HE) is considered as one cause of stress corrosion cracking. HE is a serious problem in the development of high strength aluminum alloy as with steels. For understanding HE, it is inevitable to know hydrogen trapping states in the alloys and it can be identified using thermal desorption spectrometry of H. In this study, we numerically simulated thermal desorption spectra of hydrogen in aluminum for a cylindrical and a plate specimens and interpreted the desorption peaks included in them on the basis of the trap site concentration and the trap energy. As a result, we found that the peak at the lowest-temperature side can result from grain boundaries and confirmed that the reported interpretation for other peaks is reasonable. We also obtained the result showing the possibility that the trap site concentration of defects changes during heating the specimens. This result may give a suggestion for the interpretation of temperature desorption spectra of steels.

Journal Articles

Microstructure evolution in a hydrogen charged and aged Al-Zn-Mg alloy

Bendo, A.*; Matsuda, Kenji*; Lee, S.*; Nishimura, Katsuhiko*; Toda, Hiroyuki*; Shimizu, Kazuyuki*; Tsuru, Tomohito; Yamaguchi, Masatake

Materialia, 3, p.50 - 56, 2018/11

2318 (Records 1-20 displayed on this page)