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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.

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

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

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

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

Mechanical strategies for remediating radiocesium contaminated soils, e.g. at farms, schoolyards, gardens or parks, lower air dose rates in one of two characteristic ways. The first is to physically remove radiocesium from the environment, for example by stripping topsoil and sending it for disposal. The second is to redistribute the radiocesium deeper within the ground, e.g. by mixing the topsoil or switching the positions of different soil layers, in order that soil attenuates radiocesium gamma rays before they reach the surface. The amount that air dose rates reduce because of remediation can be calculated using radiation transport methods. This chapter summarizes modelling results for the effect of topsoil removal (with and without recovering with a clean soil layer), topsoil mixing, and soil layer interchange on dose rates. Using measurements of the depth profile of $$^{134}$$Cs and $$^{137}$$Cs activity in soil at un-remediated sites across North East Japan, the potential effectiveness of remediation work was estimated considering remediation to different soil depths and different time lags after the accident. The results show that remediation performance would have been essentially constant irrespective of the time at which it was undertaken in the initial five year period following the fallout.

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

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

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

アルミニウム合金中の水素が力学特性に与える影響を把握するには、水素の存在状態を理解することが必要である。そのため、アルミニウム中のポア内表面における水素解離吸着とそれによる表面エネルギー低下について、統計熱力学的取り扱いとともに、第一原理計算や実験データを参考にした具体的な数値データを示した。理想気体からのずれも取り入れた。実験的には不明な解離吸着エネルギーが0.0-0.1eV/atomHの範囲とすると、室温で圧力100MPaの高圧水素ガスに対して、表面吸着占有率は0.08-0.8程度、表面エネルギー低下は1-13%程度になるという見積り結果となった。

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.

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

東京電力福島第一原子力発電所事故により、環境中に放出された放射性セシウムは土壌中の粘土鉱物に強く吸着されていることがわかっているが、その吸着メカニズムは今も解明されていない。本論文は、これまで蓄積された粘土鉱物による放射性セシウム吸着現象に関する実験結果と、最新のシミュレーション研究の進展をまとめたものである。論文では、実験結果についてまとめられ、それらの結果を基にした最新のシミュレーション研究によって明らかにされた、次のような研究結果について説明されている:(1)粘土鉱物表面におけるセシウム吸着のエネルギースケール、(2)実験では観測が難しい粘土鉱物エッジの原子レベル構造についての理解の進展、(3)粘土鉱物の水和した層間におけるセシウム吸着現象の詳細、(4)ほつれたエッジにおけるイオン半径と層間距離の関係と吸着の選択性、(5)層間におけるセシウムの深部への移動、(6)放射性セシウムの核崩壊の影響。さらに、これらの知見に基づいた除染による廃棄土壌の減容技術開発の可能性についても述べられている。

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

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

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

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.

Journal Articles

New antiferromagnetic order with pressure-induced superconductivity in EuFe$$_2$$As$$_2$$

Ikeda, Shugo*; Tsuchiya, Yu*; Zhang, X.-W.*; Kishimoto, Shunji*; Kikegawa, Takumi*; Yoda, Yoshitaka*; Nakamura, Hiroki; Machida, Masahiko; Glasbrenner, J.*; Kobayashi, Hisao*

Physical Review B, 98(10), p.100502_1 - 100502_6, 2018/09

The interplay between magnetism and superconductivity is one of important subjects to investigate the pairing mechanism in novel superconductors. We have found new coexistence between an antiferromagnetic order in the Fe sublattice and superconductivity of the FeAs-based EuFe$$_2$$As$$_2$$ superconductor in the pressure range from 2.4 to 3.0 GPa by $$^{57}$$Fe nuclear forward scattering (NFS) using a single crystal sample. The magnetic state in the Fe sublattice changes to a new antiferromagnetic one with superconductivity from a stripe-type antiferromagnetic one observed in normal conducting state at 2.7 GPa. Below the superconducting transition temperature, the temperature dependence of $$^{57}$$Fe NFS spectra reveals that the new antiferromagnetic order develops with the superconductivity. This non-trivial coupling of two ordered states in EuFe$$_2$$As$$_2$$ under pressure demonstrates a new and intriguing relationship between magnetism and superconductivity in Fe-based superconductors.

Journal Articles

Development of an air dose rate evaluation system (3D-ADRES) for complex real environments in Fukushima Prefecture; Using remote sensing data and evaluating the influence of different features (topography, soil, buildings, trees, etc.)

Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

RIST News, (64), p.3 - 16, 2018/09

To improve the accuracy of simulations for air dose rates over fallout contaminated areas, the distribution of the radionuclides within the environment should be modelled realistically, e.g. considering differences in radioactivity levels between agricultural land, urban surfaces, and forest compartments. Moreover simulations should model the shielding of $$gamma$$ rays by buildings, trees and land topography. Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, based on nine common Japanese designs, individual conifer and broadleaf trees, and the topography of the land surface. Models are generated from Digital Elevation Model (DEM) and Digital Surface Model (DSM) datasets, and refined by users assisted with ortho-photographs of target sites. Completed models are exported from the system in a format suitable for the Particle and Heavy Ion Transport code System (PHITS) for the calculation of air dose rates and other radiological quantities. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Journal Articles

Quantum simulation verifies the stability of an 18-coordinated actinium-helium complex

Ozama, Eiki*; Adachi, Sadia*; Takayanagi, Toshiyuki*; Shiga, Motoyuki

Chemistry; A European Journal, 24(48), p.12716 - 12721, 2018/08

The structures of trivalent actinium cation in helium clusters (Ac$$^{3+}$$He$$_n^{}$$) have been studied by quantum path integral molecular dynamics simulations with different cluster sizes, $$n$$ = 18-200. The nuclear quantum effect of helium atoms plays an important role in the vibrational amplitude of the Ac$$^{3+}$$-He complex at low temperatures (1-3 K) where the complex is stable. We found that the coordination number of helium atoms comprising the first solvation shell can be as high as eighteen. In this case, the helium atoms are arranged in D$$_{4d}^{}$$ symmetry. The Ac$$^{3+}$$-He$$_{18}^{}$$ complex becomes more rigid as the cluster increases in sizes, implying that it becomes more stable. The simulation results are based on an accurate description of the Ac$$^{3+}$$-He interaction using relativistic ab initio calculations.

Journal Articles

First-principles study of solvent-solute mixed dumbbells in body-centered-cubic tungsten crystals

Suzudo, Tomoaki; Tsuru, Tomohito; Hasegawa, Akira*

Journal of Nuclear Materials, 505, p.15 - 21, 2018/07

 Times Cited Count:1

Tungsten (W) is considered as a promising candidate for plasma-facing materials for future nuclear fusion devices, and selecting optimal alloying constituents is a critical issue to improve radiation resistance of the W alloys as well as to improve their mechanical properties. We conducted in the current study a series of first-principles calculations for investigating solvent-solute mixed dumbbells in W crystals. The results suggested that titanium (Ti), vanadium (V), and chromium (Cr) are favorable as solutes for W alloys from irradiation-effect perspectives because these elements are expected to promote vacancy-interstitial recombination without causing radiation-induced precipitation that reduces ductility of irradiated materials.

Journal Articles

Current status and problems of modeling of thermal desorption analysis of hydrogen in steel materials

Ebihara, Kenichi

Materia, 57(7), p.338 - 344, 2018/07

鉄鋼材料における水素脆化の機構を理解するためには、材料中の水素の欠陥による捕獲状態やその変化を知る必要があり、その水素捕獲状態を推測するための有効な実験方法の1つとして昇温脱離解析がある。この解析では水素を含む試料の温度と脱離する水素量との関係である昇温脱離曲線が得られるが、その曲線から水素を捕獲する欠陥を同定するために数値シミュレーションが必要となる。本解説では、日本金属学会の依頼に基づき、数値シミュレーションモデルの種類や特徴、適用例を説明し、昇温脱離曲線のシミュレーションに関する最近の進展について記述した。

Journal Articles

Acceleration of plume dispersion simulation using locally mesh-refined lattice Boltzmann method

Onodera, Naoyuki; Idomura, Yasuhiro

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 7 Pages, 2018/07

A large-scale simulation of the environmental dynamics of radioactive substances is very important from the viewpoint of nuclear security. Recently, GPU has been emerging as one of high performance devices to realize a large-scale simulation with less power consumption. We design a plume dispersion simulation based on the AMR-based LBM. We measure the performance of the LBM code on the GPU-rich supercomputer TSUBAME 3.0 at Tokyo Tech. We achieved good weak scaling from 4 GPUs to 144 GPUs, and 30 times higher node performance with CPUs. The code is validated against a wind tunnel test which was released from the National Institute of Advanced Industrial Science and Technology (AIST). The computational grids are subdivided by the AMR method, and the total number of grid points is reduced to less than 10% compared to the finest meshes. In spite of the fewer grid points, the turbulent statistics and plume dispersion are in good agreement with the experiment data.

JAEA Reports

Materials for the information security education; FY 2013-2017

Ueno, Asuka; Yashiro, Shigeo; Uno, Kiichiro*; Aoki, Kazuhisa

JAEA-Review 2018-006, 115 Pages, 2018/06

JAEA-Review-2018-006.pdf:30.8MB

Cyberattacks causing serious damage are ongoing as seen in the incidents such as personal information leakage from the Japan Pension Service by unauthorized access in 2015, and a massive ransomware infection across the world in 2017. Recently, threats in the cyberspace has been growing, such as sending an order form, shipping notification, while pretending a real company to persuade recipient to open an attached file with embedded unforeseen malware, or to click on a link in the email to malicious website. In these circumstances, the information security countermeasures are important issues at the JAEA. CCSE therefore is striving to promote proactive information security countermeasures with the three aspects of (1) Maintenance of the information security regulations, (2) Countermeasures with information security products having a new protection technology, (3) Implementation of information security education and training for the employees to maintain and improve their ability to respond. This report is a summary of the contents of the information security education by e-learning.

Journal Articles

Interactions between clusters of self-interstitial atoms via a conservative climb in BCC-Fe

Hayakawa, Sho*; Okita, Taira*; Itakura, Mitsuhiro; Aichi, Masaatsu*; Suzuki, Katsuyuki*

Philosophical Magazine, 98(25), p.2311 - 2325, 2018/06

We conduct kinetic Monte Carlo simulations for the conservative climb motion of a cluster of self-interstitial atoms towards another SIA cluster in BCC Fe; the conservative climb velocity is inversely proportional to the fourth power of the distance between them, as per the prediction based on Einstein's equation. The size of the climbing cluster significantly affects its conservative climb velocity, while the size of the cluster that originates the stress field does not. The activation energy for the conservative climb is considerably greater than that derived in previous studies and strongly dependent on the climbing cluster size.

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