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Yamamoto, Yojiro*; Hayakawa, Sho*; Okita, Taira*; Itakura, Mitsuhiro
Computational Materials Science, 229, p.112389_1 - 112389_9, 2023/10
Times Cited Count:1 Percentile:52.07(Materials Science, Multidisciplinary)He bubbles are characteristic microstructures under fusion reactor conditions. They approach and coalesce through their own migration, which significantly impacts the microstructure and material properties. However, these processes, which involve multiple migrations of metal atoms, cannot be treated by molecular dynamics (MD) due to its timescale limitation. In this study, self-evolving atomistic kinetic Monte Carlo (SEAKMC) was used to expand the timescale and reproduce bubble coalescences in Fe. To enhance selections of events that led to the process by avoiding trivial events with an extremely low activation energy such as tiny vibrations of a He atom or short-range displacements of the Fe atom, we introduced two algorithms into SEAKMC, a two-step saddle point search for the former measure and setting a threshold for a displacement distance of the Fe atom for the latter. Furthermore, by adding another algorithm to set an upper bound for the activation energy to prevent selections of events with an impractically high activation energy, we succeeded to reproduce the change in the configuration from dumbbell to elliptical up to a simulated time of s, 8 orders longer than MD timescales. The developed method is effective for analyzing microstructures of metallic materials containing light elements and is the only method that can reach timescales comparable to those of experiments.
Ueki, Taro
Progress in Nuclear Energy, 159, p.104630_1 - 104630_9, 2023/05
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)In this work, the methodology of Generalized Extreme Value (GEV) is applied to criticality tallies in Monte Carlo fission source cycles in order to evaluate the utility value of the distribution tail ends. Numerical results obtained under a sufficiently large number of particles per cycle show that the extreme value index (EVI) in GEV falls within the range of Weibull distribution including the EVI of Gumbel distribution as the role of a boundary value layer. GEV is also applied to a historically-challenging loosely-coupled system for demonstrating population diagnosis under an insufficient number of particles per cycle. It turns out that the transition from one equilibrium to other equilibrium makes the EVIs of upper and lower distribution tail ends depart from each other so that one of them falls in the range of Weibull distribution and the other in that of Frechet distribution.
Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Yokoya, Akinari*
RSC Advances (Internet), 13(11), p.7076 - 7086, 2023/03
Times Cited Count:3 Percentile:81.33(Chemistry, Multidisciplinary)Scientific insights of water radiolysis are widely used in the life sciences and so on, however, the formation mechanism of radicals, a product of water radiolysis, is still not well understood. We are challenging to develop a simulation code to solve this formation mechanism from the viewpoint of radiation physics. Our first-principles calculations have revealed that the behavior of secondary electrons in water is governed not only by collisional effects but also by polarization effects. Furthermore, from the predicted ratio of ionization to electronic excitation, based on the spatial distribution of secondary electrons, we successfully reproduce the initial yield of hydrated electrons predicted in terms of radiation chemistry. The code provides us a reasonable spatiotemporal connection from radiation physics to radiation chemistry. Our findings are expected to provide newly scientific insights for understanding the earliest stages of water radiolysis.
Kobayashi, Keita; Nagai, Yuki; Itakura, Mitsuhiro; Shiga, Motoyuki
Journal of Chemical Physics, 155(3), p.034106_1 - 034106_9, 2021/07
Times Cited Count:5 Percentile:44.89(Chemistry, Physical)no abstracts in English
Zhao, C.*; Suzudo, Tomoaki; Toyama, Takeshi*; Nishitani, Shigeto*; Inoue, Koji*; Nagai, Yasuyoshi*
Materials Transactions, 62(7), p.929 - 934, 2021/07
Times Cited Count:3 Percentile:25.78(Materials Science, Multidisciplinary)We succeeded in measuring the diffusion coefficient of Cu in Fe in a low temperature range that had not been measured so far. Since the diffusion couple, which is a general method for measuring the diffusion coefficient, can be applied only at high temperature, atom probe tomography and Cu precipitation rate theory were used in this study. The estimated diffusion coefficient was found to be more reliable than that obtained in previous studies. Therefore, it is considered that the estimation by the atom probe provided higher accuracy. Furthermore, the kinetic Monte Carlo simulation revealed that the diffusion coefficient estimated by this method tends to be slightly overestimated as the temperature decreases.
Yoshitomi, Hiroshi; Nishino, Sho; Tanimura, Yoshihiko; Takahashi, Masa
Radiation Measurements, 133, p.106279_1 - 106279_6, 2020/04
Times Cited Count:5 Percentile:53.85(Nuclear Science & Technology)Uncertainty of the body size on the counting efficiency of a newly developed thyroid monitor was estimated by Monte Carlo simulations using several voxel phantoms. Overlying tissue thickness was a major impact factor on the counting efficiency. As a result, uncertainty related to the body size of the monitored subject was found to be 25%.
Kai, Takeshi; Yokoya, Akinari*; Fujii, Kentaro*; Watanabe, Ritsuko*
Yodenshi Kagaku, (8), p.11 - 17, 2017/03
It is thought to that the biological effects such as cell death or mutation are induced by complex DNA damage which are formed by several damage sites within a few nm. We calculated dynamic behavior of secondary electrons produced by primary electron and positon of high energy in water whose composition ratio is similar to biological context. The secondary electrons induce the ionization or electronic excitation near the parent cations. The decelerated electrons about 10% are distributed to their parent cations by the attractive Coulombic force. From the results, we predicted the following formation mechanism for the complex DNA damage. The electrons ejected from DNA could induce the ionization or the electronic excitation within the DNA. The electrons attracted by the Coulombic force are pre-hydrated in water layer of the DNA. The pre-hydrated electrons could induce to the DNA damage by dissociative electron transfer. As the results, the complex DNA damage with 1 nm could be formed by the interaction of not only the primary electron or positon but also the secondary electrons.
Fukaya, Yuji; Nishihara, Tetsuo
JAEA-Research 2016-001, 23 Pages, 2016/05
A study on Correlation effect between elements of statistical hot spot factor for High Temperature Gas-cooled Reactor (HTGR) Design had been performed. Both of safety and reactor specification can be remained if the uncertainty is correctly propagated by revising hot spot factor. In this context, it is reported for light water reactor design that the propagated uncertainty can be reduced by statistical hot spot factors with numerical statistical approach, that is Monte Carlo method, because correlation effects for each factor can be considered. For HTGR with sleeve covered fuel, it is expected that the fuel temperature also reduces by employing the same approach because the gap between sleeve and fuel compact, which shows significant temperature increase, have direct correlation. In addition, Monte Carlo method treats correlation effect at the price of evaluating contribution of individual factor. Therefore, improved method based on conventional method has been developed in this study. Then, statistical hot spot factor for fuel temperature of HTGR was evaluated by Monte Carlo method and the improved method. As a result, it is not found significant difference between the result of the conventional method and the improved method. Moreover, usage of hot spot factor is investigated and we proposed new one reflecting the investigation.
Yamauchi, Michinori*; Ochiai, Kentaro; Morimoto, Yuichi*; Wada, Masayuki*; Sato, Satoshi; Nishitani, Takeo
Radiation Protection Dosimetry, 116(1-4), p.542 - 546, 2005/12
Times Cited Count:3 Percentile:24.22(Environmental Sciences)no abstracts in English
Sato, Tatsuhiko
Hoshasen, 31(4), p.313 - 318, 2005/10
Evaluation of high-energy neutron dose is one of the key issues in the shielding design of accelerator facilities and in the planning of long-term space missions. High-energy neutron transport simulation codes play an important role in the evaluation, since there is a large difficulty in the precise measurement of high-energy neutron doses. This paper reviews the Monte-Carlo simulation codes applicable to the purpose, and summarizes the requirements for the future development of the codes.
Kohara, Shinji*; Suzuya, Kentaro
Journal of Physics; Condensed Matter, 17(5), p.S77 - S86, 2005/02
Times Cited Count:82 Percentile:90.9(Physics, Condensed Matter)The total structure factors, S(Q), obtained from high-energy X-ray and neutron diffraction measurements on vitreous SiO (v-SiO) and vitreous GeO (v-GeO) have been analysed by the reverse Monte Carlo (RMC) modelling technique to generate a three-dimensional structural model. The bond angle distributions and the ring size distributions from the model indicated that the sixfold ring and six- and sevenfold rings are dominant in v-SiO and v-GeO, respectively. However, the fraction of threefold rings of Ge in v-GeO is larger than that of Si in v-SiO glass. These features are consistent with the published neutron diffraction and Raman scattering studies.
Nagaya, Yasunobu; Mori, Takamasa; Brown, F. B.*
Monte Karuro Keisanho Kodoka No Genjo; Dai-3-Kai Monte Karuro Shimyureshon Kenkyukai Hobunshu, p.105 - 115, 2004/12
The Monte Carlo perturbation method based on the differential operator sampling method has been widely used to obtain a small change in neutronic parameters or sensitivity. The method is very effective for fixed-source problems but a difficulty arises for eigenvalue problems because the fission source distribution is perturbed. Most Monte Carlo codes assume that the source distribution is unchanged after a perturbation is introduced. However, this assumption can lead to a significant error in the perturbation estimate. Recently, a method to estimate the perturbed fission source effect has been proposed. In this method, the additional weights for the differential coefficient of the fission source at fission sites are normalized in each cycle, and the effect is estimated by propagating the normalized additional weight between cycles. The method and benchmark results have been reviewed. It has been found that this method is very effective in perturbation calculations for the effective multiplication factor.
Kinase, Sakae
RIST News, (37), p.10 - 19, 2004/03
no abstracts in English
Nuclear Code Evaluation Special Committee of Nuclear Code Research Committee
JAERI-Tech 2003-078, 107 Pages, 2003/11
no abstracts in English
Sakurai, Kiyoshi; Nojiri, Ichiro*
JAERI-Conf 2003-019, p.855 - 857, 2003/10
This paper provides overview of sub-criticality safety analysis seminar (July 2000-July 2003, JAERI, total 40 engineers from universities, research institutes and enterprises) for nuclear fuel cycle facility with the Monte Carlo method in Japan. MCNP-4C2 system (MS-DOS version) was installed in each note-type personal computer. Fundamental theory of reactor physics and Monte Carlo simulation including MCNP-4C manual was lectured. Effective neutron multiplication factor and neutron spectrum were calculated for JCO deposit tank, JNC uranium solution storage tank, JNC plutonium solution storage tank and JAERI TCA core. In the seminar, methodology of safety management for nuclear fuel cycle facility was discussed in order to prevent criticality accident.
Sakurai, Kiyoshi
Nihon Genshiryoku Gakkai Wabun Rombunshi, 2(3), p.368 - 374, 2003/09
no abstracts in English
Sato, Satoshi; Maki, Koichi*
Fusion Engineering and Design, 65(4), p.501 - 524, 2003/07
Times Cited Count:8 Percentile:49.89(Nuclear Science & Technology)no abstracts in English
Sato, Satoshi; Nakamura, Takashi*; Nishitani, Takeo
Fusion Science and Technology, 43(4), p.559 - 568, 2003/06
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)no abstracts in English
Nomura, Yasushi; Takada, Tomoyuki; Kadotani, Hiroyuki*; Kuroishi, Takeshi
JAERI-Tech 2003-020, 88 Pages, 2003/03
no abstracts in English
Sato, Satoshi; Nishitani, Takeo
Journal of Nuclear Materials, 313-316, p.690 - 695, 2003/03
Times Cited Count:11 Percentile:56.43(Materials Science, Multidisciplinary)no abstracts in English