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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

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

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:100(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

 Percentile:100(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

Finding free-energy landmarks of chemical reactions

Shiga, Motoyuki; Tuckerman, M. E.*

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

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

Journal Articles

Nuclear quantum effects in the direct ionization process of pure helium clusters; Path-integral and ring-polymer molecular dynamics simulations on the diatomics-in-molecule potential energy surfaces

Suzuki, Kento*; Miyazaki, Takaaki*; Takayanagi, Toshiyuki*; Shiga, Motoyuki

Physical Chemistry Chemical Physics, 20(41), p.26489 - 26499, 2018/11

The direct photoionization of pure helium clusters and its subsequent short-time process have been studied by path integral molecular dynamics (PIMD) and ring-polymer molecular dynamics (RPMD) simulations. The PIMD simulations reproduced the experimental ionization spectra with a broad and asymmetric nature, which can be ascribed to the inhomogeneity of the energy levels of He atoms. From the RPMD simulations, it is found that the ionized helium cluster in the highly excited state brings about fast electronic state relaxation via nonadiabatic charge transfer and subsequently slow structural relaxation.

Journal Articles

Communication Reduced Multi-time-step Algorithm for Real-time Wind Simulation on GPU-based Supercomputers

Onodera, Naoyuki; Idomura, Yasuhiro; Yussuf, A.*; Shimokawabe, Takashi*

Proceedings of 9th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems (ScalA 2018) (Internet), p.9 - 16, 2018/11

We develop a communication reduced multi-time- step (CRMT) algorithm for a Lattice Boltzmann method (LBM) based on a block-structured adaptive mesh refinement (AMR). This algorithm is based on the temporal blocking method, and can improve computational efficiency by replacing a communication bottleneck with additional computation. The proposed method is implemented on an extreme scale airflow simulation code CityLBM, and its impact on the scalability is tested on GPU based supercomputers, TSUBAME and Reedbush. Thanks to the CRMT algorithm, the communication cost is reduced by $$sim 64%$$, and weak and strong scalings are improved up to $$sim 200$$ GPUs. The obtained performance indicates that real time airflow simulations for about 2km square area with the wind speed of $$5m/s$$ is feasible using 1m resolution.

Journal Articles

Communication avoiding multigrid preconditioned conjugate gradient method for extreme scale multiphase CFD simulations

Idomura, Yasuhiro; Ina, Takuya*; Yamashita, Susumu; Onodera, Naoyuki; Yamada, Susumu; Imamura, Toshiyuki*

Proceedings of 9th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems (ScalA 2018) (Internet), p.17 - 24, 2018/11

A communication avoiding (CA) multigrid preconditioned conjugate gradient method (CAMGCG) is applied to the pressure Poisson equation in a multiphase CFD code JUPITER, and its computational performance and convergence property are compared against CA Krylov methods. In the JUPITER code, the CAMGCG solver has robust convergence properties regardless of the problem size, and shows both communication reduction and convergence improvement, leading to higher performance gain than CA Krylov solvers, which achieve only the former. The CAMGCG solver is applied to extreme scale multiphase CFD simulations with $$sim 90$$ billion DOFs, and it is shown that compared with a preconditioned CG solver, the number of iterations is reduced to $$sim 1/800$$, and $$sim 11.6times$$ speedup is achieved with keeping excellent strong scaling up to 8,000 nodes on the Oakforest-PACS.

JAEA Reports

Error estimation in observed acceleration data toward V&V of a seismic simulation

Suzuki, Yoshio; Iigaki, Kazuhiko

JAEA-Data/Code 2018-009, 41 Pages, 2018/09

JAEA-Data-Code-2018-009.pdf:3.14MB

Toward Verification & Validation (V&V) of a seismic simulation of entire nuclear plant, an approach to estimate errors included in observed acceleration data is proposed. On the comparison between simulation results and experimental/observational results in the process of V&V, errors which might be included in experimental/observational data should be estimated. It is considered that there exist following two causes for errors in observed acceleration data; measurement accuracy of an accelerometer measurement system and disturbance included in measured data. Techniques based on the specification of an accelerometer measurement system and the time series analysis are respectively adopted to estimate those errors. To clarify the actual procedure, those techniques are applied to acceleration data observed at High Temperature engineering Test Reactor (HTTR) at the Oarai Research and Development Institute of Japan Atomic Energy Agency.

Journal Articles

Radiocesium interaction with clay minerals; Theory and simulation advances Post-Fukushima

Okumura, Masahiko; Kerisit, S.*; Bourg, I. C.*; Lammers, L. N.*; Ikeda, Takashi*; Sassi, M.*; Rosso, K. M.*; Machida, Masahiko

Journal of Environmental Radioactivity, 189, p.135 - 145, 2018/09

 Times Cited Count:1 Percentile:41.09(Environmental Sciences)

no abstracts in English

Journal Articles

Characterizing regional-scale temporal evolution of air dose rates after the Fukushima Daiichi Nuclear Power Plant accident

Wainwright, H. M.*; Seki, Akiyuki; Mikami, Satoshi; Saito, Kimiaki

Journal of Environmental Radioactivity, 189, p.213 - 220, 2018/09

 Percentile:100(Environmental Sciences)

In this study, we quantify the temporal changes of air dose rates in the regional scale around the Fukushima Daiichi Nuclear Power Plant in Japan, and predict the spatial distribution of air dose rates in the future. We first apply the Bayesian geostatistical method developed by Wainwright et al. (2017) to integrate multiscale datasets including ground-based walk and car surveys, and airborne surveys, all of which have different scales, resolutions, spatial coverage, and accuracy. We apply this method to the datasets from three years: 2014 to 2016. The temporal changes among the three integrated maps enables us to characterize the spatiotemporal dynamics of radiation air dose rates.

Journal Articles

Atomistic simulation of phosphorus segregation to $$Sigma$$3(111) symmetrical tilt grain boundary in $$alpha$$-iron

Ebihara, Kenichi; Suzudo, Tomoaki

Modelling and Simulation in Materials Science and Engineering, 26(6), p.065005_1 - 065005_10, 2018/09

 Percentile:100(Materials Science, Multidisciplinary)

Irradiation-induced grain boundary phosphorus segregation is an important factor for estimating the embrittlement of nuclear reactor pressure vessel steels, but the physical process of phosphorus migration to grain boundaries is still unclear. We numerically studied phosphorus migration toward $$Sigma$$3(111) symmetrical tilt grain boundary in $$alpha$$-iron using molecular dynamics. We found that, in the vicinity of the grain boundary within $$sim$$1 nm distance, an iron-phosphorus mixed dumbbell and an octahedral interstitial phosphorus atom push a self-interstitial atom into the grain boundary, and the phosphorus atom becomes a substitutional atom. A phosphorus vacancy complex in the region also becomes dissociated, and the vacancy is absorbed in the grain boundary without dragging phosphorus. The results claim that a novel view of the segregation process is required.

Journal Articles

Effects of stacking fault energies on formation of irradiation-induced defects at various temperatures in face-centred cubic metals

Nakanishi, Daiki*; Kawabata, Tomoya*; Doihara, Kohei*; Okita, Taira*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Philosophical Magazine, 98(33), p.3034 - 3047, 2018/09

 Percentile:100(Materials Science, Multidisciplinary)

By using the six sets of interatomic potentials for face-centredcubic metals that differ in the stacking fault energy (SFE) while most of the other material parameters are kept almost identical, we conducted molecular dynamics simulations to evaluate the effects of SFE on the defect formation process through collision cascades. The ratio of glissile SIA clusters tends to decrease with increasing SFE. This is because perfect loops, the edges of which split into two partial dislocations with stacking fault structures between them in most cases, prefer to form at lower SFEs. The enhanced formation of glissile SIA clusters at lower SFEs can also be observed even at increased temperature.

2285 (Records 1-20 displayed on this page)