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Machida, Masahiko; Shi, W.*; Yamada, Susumu; Miyamura, Hiroko; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji; Aoki, Yuto; Ito, Rintaro; Yamaguchi, Takashi; et al.
Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 11 Pages, 2023/02
Kato, Masato; Machida, Masahiko; Hirooka, Shun; Nakamichi, Shinya; Ikusawa, Yoshihisa; Nakamura, Hiroki; Kobayashi, Keita; Ozawa, Takayuki; Maeda, Koji; Sasaki, Shinji; et al.
Materials Science and Fuel Technologies of Uranium and Plutonium mixed Oxide, 171 Pages, 2022/10
Innovative and advanced nuclear reactors using plutonium fuel has been developed in each country. In order to develop a new nuclear fuel, irradiation tests are indispensable, and it is necessary to demonstrate the performance and safety of nuclear fuels. If we can develop a technology that accurately simulates irradiation behavior as a technology that complements the irradiation test, the cost, time, and labor involved in nuclear fuel research and development will be greatly reduced. And safety and reliability can be significantly improved through simulation of nuclear fuel irradiation behavior. In order to evaluate the performance of nuclear fuel, it is necessary to know the physical and chemical properties of the fuel at high temperatures. And it is indispensable to develop a behavior model that describes various phenomena that occur during irradiation. In previous research and development, empirical methods with fitting parameters have been used in many parts of model development. However, empirical techniques can give very different results in areas where there is no data. Therefore, the purpose of this study is to construct a scientific descriptive model that can extrapolate the basic characteristics of fuel to the composition and temperature, and to develop an irradiation behavior analysis code to which the model is applied.
based on experimental data and density functional theory calculation resultWatanabe, Masashi; Nakamura, Hiroki; Suzuki, Kiichi; Machida, Masahiko; Kato, Masato
Journal of the American Ceramic Society, 105(3), p.2248 - 2257, 2022/03
Times Cited Count：1 Percentile：6.98(Materials Science, Ceramics)Properties of CeO
were evaluated by DFT simulation to determine band gap, Frenkel defect formation energy and defect migration energy. Band gap and Frenkel defect formation energy were used to analyze defect equilibria. Oxygen partial pressure dependence of defect equilibria was evaluated based on oxygen potential experimental data and DFT calculation, and a Brouwer diagram was derived. The defect formation energies, including Frenkel defect, electron-hole pair and so on, were determined and used to evaluate the properties, including oxygen diffusion coefficients, electrical conduction, heat capacity and thermal conductivity. Mechanisms of various properties were discussed for a deeper understanding based on defect chemistry, and the relationship among properties were systematically described.
Kim, M.; Malins, A.; Machida, Masahiko; Yoshimura, Kazuya; Saito, Kimiaki; Yoshida, Hiroko*; Yanagi, Hideaki*; Yoshida, Toru*; Hasegawa, Yukihiro*
RIST News, (67), p.3 - 15, 2021/09
no abstracts in English
Kim, M.; Malins, A.; Yoshimura, Kazuya; Sakuma, Kazuyuki; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*
Journal of Environmental Radioactivity, 210, p.105803_1 - 105803_10, 2019/12
Times Cited Count：4 Percentile：16.8(Environmental Sciences)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 
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 
Cs and 
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.
Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*
Isotope News, (765), p.30 - 33, 2019/10
Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The Cs and Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, individual conifer and broadleaf trees, and the topography of the land surface. 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.
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 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 Cs and 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.
Kushida, Noriyuki
PLOS ONE (Internet), 10(3), p.e0122331_1 - e0122331_16, 2015/03
Times Cited Count：7 Percentile：45.28(Multidisciplinary Sciences)The present paper introduces a condition number estimation method for preconditioned matrices. The newly developed method provides reasonable results, while the conventional method which is based on the Lanczos connection gives meaningless results. The Lanczos connection based method provides the condition numbers of coefficient matrices of systems of linear equations with information obtained through the preconditioned conjugate gradient method. Estimating the condition number of preconditioned matrices is sometimes important when describing the effectiveness of new preconditionerers or selecting adequate preconditioners. Operating a preconditioner on a coefficient matrix is the simplest method of estimation. However, this is not possible for large-scale computing, especially if computation is performed on distributed memory parallel computers. This is because, the preconditioned matrices become dense, even if the original matrices are sparse. Although the Lanczos connection method can be used to calculate the condition number of preconditioned matrices, it is not considered to be applicable to large-scale problems because of its weakness with respect to numerical errors. Therefore, we have developed a robust and parallelizable method based on Hager's method. The feasibility studies are curried out for the diagonal scaling preconditioner and the SSOR preconditioner with a diagonal matrix, a tri-daigonal matrix and Pei's matrix. As a result, the Lanczos connection method contains around 10% error in the results even with a simple problem. On the other hand, the new method contains negligible errors. In addition, the newly developed method returns reasonable solutions when the Lanczos connection method fails with Pei's matrix, and matrices generated with the finite element method.
Fujishima, Hironobu*; Okumura, Masahiko; Mine, Makoto*; Yajima, Tetsu*
Journal of the Physical Society of Japan, 81(10), p.104003_1 - 104003_7, 2012/10
Times Cited Count：1 Percentile：10.8(Physics, Multidisciplinary)We propose an indirect method for observing radiation from an incomplete soliton with a sufficiently large amplitude. We show that the radiation causes a notched structure on the envelope of the wave packet in the momentum space. The origin of this structure is the interference between the main body of oscillating solitons and the small radiation in the momentum space. We numerically integrate the nonlinear Schr
dinger equation and perform Fourier transformation to confirm that the predicted structure really appears. We also show a simple model which reproduces the qualitative result. The experimental detection of the notched structure with the Bose-Einstein condensation of neutral atoms is discussed and suitable parameters for this detection experiment are shown.
Uzawa, Ken; Watanabe, Tadashi
Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 8 Pages, 2011/10
When a spent fuel pool suffered from a huge seismic acceleration, a sloshing may occur and causes overflow of water and damage of structure. To prevent these phenomena from occurring, effects of turbulence on a sloshing height and fluid pressure on the structure should be taken into account, however they are not fully quantitatively evaluated. Therefore, we have performed numerical simulations of a dam break problem as an elementary process of the sloshing based on the Launder-Gibson (LG) model, which is one of Reynolds-averaged Navier-Stokes equations. Until now, we found that a fluid pressure based on the LG model is in good agreement with experimental fluid pressure. In this research, we have confirmed same results by performing Large Eddy Simulation (LES). We found that the overflow of water is an order of magnitude more accurate than previous work.
Miyamura, Hiroko; Kureta, Masatoshi; Segawa, Mariko; Kubo, Jun*; Saito, Takafumi*; Suzuki, Yoshio; Takemiya, Hiroshi
Visualization of Mechanical Processes (Internet), 1(3), 8 Pages, 2011/10
The use of high frame rate neutron radiography has been proposed as a method for recording images of oil in a running car engine. However, it is difficult to capture the behavior of oil from such images, because the images are dark and blurry. Therefore, we attempt to overcome this problem using a multi-scale image processing technique, in which the oil regions are classified based on scale. This method can be used to focus attention on objects with a particular scale. In addition, we propose a technique by which to capture the time-dependent behavior of oil using spatio-temporal image analysis. Using these techniques, the region of interest can be determined and observed carefully.
Uzawa, Ken
no journal, ,
When a spent fuel pool suffered from the earthquake, a sloshing may occur and causes overflow of water and damage of structure. To prevent these phenomena from occurring, effects of turbulence on a sloshing height and fluid pressure on the structure should be taken into account, however they are not fully quantitatively evaluated. In this work, numerical simulations of a dam break problem as an elementary process of the sloshing have been performed based on the Launder-Gibson (LG) model. As a result, a fluid pressure based on the LG model is in good agreement with experimental fluid pressure. It is also found that the effect of turbulent viscous dissipation on the fluid pressure near two-phase surface is comparable to that of the bulk fluid.
Yamamoto, Atsushi; Yamada, Susumu; Machida, Masahiko
no journal, ,
no abstracts in English
Yamamoto, Atsushi; Yamada, Susumu; Machida, Masahiko
no journal, ,
It is well known that atomic Fermi gas loaded on optical lattice can be described by a single-band Hubbard model in the simplest case. A remarkable feature is that the on-site interaction U is experimentally tunable parameter ranging from strongly attractive to repulsive. Moreover, the parameter U is spatially tunable, i.e., U is spatially dependent on the site. Thus, an interest aroused by the spatial tuning ability is quantum phases and transition between phases in Hubbard models whose parameter U spatially varies. In this study, we numerically examine a model with site alternative variation, i.e., U=U and U' in even and odd site, respectively. By using DMRG method, we reveal in the model that Mott-insulator transition occurs in half-filling phase diagram expanded by U and U' and compressibility diverges in the vicinity of the transition.
Uzawa, Ken
no journal, ,
CCSE/JAEA promotes the research and development of the three-dimensional vibration simulator for seismic evaluation of a nuclear power plant (NPP) to further improve reliability of seismic safety of NPPs. We started R&D of fluid analysis capability as one of element technologies of the three-dimensional vibration simulator since last year. Especially, we have investigated a two-phase flow simulation code to analyze sloshing under earthquake. In this research, we achieved high parallel efficiency up to approximately 950.2 in parallel calculation using 1024 cores by improving an environment for massive parallel calculation. The technical feasibility for massive sloshing simulation including effect of turbulence is more or less established.
Seki, Akiyuki; Takemiya, Hiroshi; Takahashi, Fumiaki; Saito, Kimiaki; Tanaka, Kei*; Takahashi, Yutaka*; Takemura, Kazuhiro*; Tsuzawa, Masaharu*
no journal, ,
Radioactive database and contamination map for the accident of Fukushima Dai-ichi Nuclear Power Plant are described. It is necessary to obtain precise data on the contamination conditions. Both systems have been developed to provide information to identify the current distribution of released materials and to support decontamination planning. The former is designed to provide quantitative data for detailed analysis, while another to provide intuitive images for the qualitative estimation. They contain air dose rates at around 2,200 locations within approximately 100 km from the plant, and radionuclide concentration data at each location. The vehicle-borne survey results are also included for the purpose of ascertaining the distribution of radioactive substances around roads in detail. All the data have been measured during the first investigation conducted in June, and the second in December 2011. The systems will become open to the public at the site of JAEA soon.
Seki, Akiyuki; Takemiya, Hiroshi; Takahashi, Fumiaki; Saito, Kimiaki; Tanaka, Kei*; Takahashi, Yutaka*; Takemura, Kazuhiro*; Tsuzawa, Masaharu*
no journal, ,
The construction of the database and map systems, which provide basic information for evaluations and countermeasures of the Fukushima nuclear accident, are explained. Fukushima Daiichi Nuclear Power Plant had been damaged and spread out radioactive materials around there on March 2011. There are still a lot of requests to know the distribution of radioactive material from government, local government, residents, and/or researchers. In order to meet those requests, we developed two systems to provide those data to the public. One of the systems is a database system which is designed to provide quantitative data for detailed analysis. Another is a map system which provides intuitive images for the qualitative estimation.
Guo, Z.; Nishida, Akemi; Nakajima, Norihiro
no journal, ,
Seismic estimation for huge plants including nuclear power facilities after the 2011 Tohoku Earthquake becomes more important. As usual, the joints connected different parts of structure have been often treated as boundary conditions based on a simple assumption in modeling of huge structures such as plants. However, the actual connections are complicated, so the stresses exceeding the designed value may occur sometimes. Therefore it is extremely important to investigate local stress distributions in detail for confirming the validity of design, and then if the situations unexpected in the design are found, it is necessary to modify the design. Our objective in the present study is to clarify modelling issues through comparisons of results from different modeling approaches and to propose a solution for the modelling issue. In this work, we apply different modelling approaches to a real plant structure, and analyze differences in their mechanical behaviors.
Kim, M.; Malins, A.; Yoshimura, Kazuya; Sakuma, Kazuyuki; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko
no journal, ,
There is a need for simulations of air dose rates in the environment to consider the differences in radiocesium levels between different land types, building surfaces and forest compartments. Moreover simulations should capture the complex shielding effects of buildings, terrain, trees and soil on air dose rates. In this research a tool was developed for making 3D models of the land surface, the land type, and buildings and trees within a target area for subsequent simulation of air dose rates in PHITS. The tool utilizes ortho-photographs of the target area, as well as digital elevation models (DEM) and digital surface models (DSM) of the land, for the creation of PHITS geometry input files. The tool incorporates models for nine common building types, as well as coniferous and broadleaf trees, such that models can be customized specific for the target area. Once the geometry of the model has been created, Cs and Cs radioactive sources can be set flexibly across the different elements of the model. In this presentation we report a model of a 200 m by 200 m area within Okuma Town, about 5 km away from the Fukushima Daiichi Nuclear Power Plant. The Cs and Cs activity distribution within the model was defined based on in-situ gamma spectroscopy measurements of radioactivities within the target area. Simulated air dose rates from PHITS were then compared to the results of a person-borne air dose rate survey across the study area. The effects of the different components of the model were tested by performing more simplistic air dose rate simulations considering flat topography without buildings and trees, as well as average uniform Cs and Cs activity distributions across the study area.
(Ce) airborne detector and shielded HPGe detector inside a vehicleMalins, A.; Ochi, Kotaro; Sanada, Yukihisa; Yamaguchi, Ichiro*; Sato, Tatsuhiko
no journal, ,
