Takahashi, Hiroaki*; Tachi, Yukio
Applied Clay Science, 168, p.211 - 222, 2019/02
Microstructural and mass transport properties of compacted Na- and Cs-montmorillonites with different swelling properties were investigated by combining 3D microstructure analysis using nanofocus X-ray CT and diffusion measurement of HDO. The X-ray CT observations indicated that macropores in the dry state of compacted Na-montmorillonite are filled with gel phases, and the grain sizes of clay particles shifted toward smaller values through the saturation and swelling processes. By contrast, no gel phase and no decrease in the grain and pore volumes were observed for saturated Cs-montmorillonite. The geometrical factors of the macropores including tortuosity and geometric constrictivity of saturated Cs-montmorillonite determined by the X-ray CT was consistent with the corresponding values derived in the HDO diffusion test. In the case of Na-montmorillonite, the larger differences between the geometric factors evaluated by the X-ray CT and the diffusion tests can be explained by the electrostatic constrictivity factor and the additional geometrical factors in gel phase and interlayer that are smaller than the detection limit of the X-ray CT.
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.
Arakawa, Ryoki; Nosaki, Nobuhisa; Hirata, Yuji*
JAEA-Technology 2018-009, 28 Pages, 2019/01
The Naraha Center for Remote Control Technology Development consists of a mock-up test building and a research management building, and various test facilities are installed in them for the decommissioning work after the accident of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings. In the test facilities, the robot test pool for the underwater robot can be tested under temperature conditions raised from room temperature to 60C. Then, for the purpose of grasping the temperature distribution inside of the pool and the temperature rising behavior in temperature raising condition, a temperature heating test with room temperature to 60C. (maximum setting temperature) was performed, and as well as an analytical study was performed. This report summarizes the obtained both experimental and analytical studies.
Ishimaru, Tsuneari; Ogata, Nobuhisa; Shimada, Akiomi; Asamori, Koichi; Kokubu, Yoko; Niwa, Masakazu; Watanabe, Takahiro; Saiga, Atsushi; Sueoka, Shigeru; Komatsu, Tetsuya; et al.
JAEA-Review 2018-020, 46 Pages, 2019/01
This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency, in fiscal year 2018. The objectives and contents in fiscal year 2018 are described in detail based on the outline of 7 years plan (fiscal years 2015-2021). Background of this research is clarified with the necessity and the significance for site investigation and safety assessment, and the past progress in this report. In addition, the plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques.
Sanada, Yukihisa; Nishizawa, Yukiyasu*; Ochi, Kotaro; Yuki, Yoichi*; Ishizaki, Azusa; Osada, Naoyuki*
JAEA-Research 2018-009, 48 Pages, 2019/01
At the accident of nuclear facilities, a prediction of the behavior of released radioactive plume is indispensable to make a decision on a refuge plan of inhabitants. Currently, prediction system which is based on atmospheric dispersion simulation has been implemented as a tool of the atomic energy disaster prevention. However, the direct measurement method of the radioactive plume has not existed. In this study, some component technologies were developed for the establishment of direct measurement methods of radioactive plume using unmanned aerial vehicle whose technological innovation is remarkable. In addition, the spray test using mock aerosol was conducted to obtaining the deposition rate to the airplane body. The algorism of making a flight plan was developed based on a prediction model of the radioactive plume. This report summarized the outcome of the second year of the three-year plan.
Kitamura, Yasunori*; Fukushima, Masahiro; Kitamura, Yasunori*
Annals of Nuclear Energy, 125, p.328 - 341, 2019/01
It has been taken for granted that the neutron correlation methods that employ two sets of neutron counting systems, e.g., the covariance-to-mean and the cross-correlation methods, are free from the count-loss effect for determination of the neutron decay constant. It was however found in the present study that these methods overestimate the neutron decay constant under high counting rate conditions. New formulae of these methods were hence obtained on the basis of a rigorous theoretical approach for treating the count-loss process. It is expected that the present formulae work better than conventional ones for determination of the neutron decay constant.
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.
Otsuka, Satoshi; Kaito, Takeji
Enerugi Rebyu, 39(1), p.44 - 46, 2019/01
For performance improvement of next-generation nuclear system such as fast reactor, it has been expected to develop advanced material resistant to severe in-reactor environment (i.e. high-dose neutron irradiation at high-temperature). Japan Atomic Energy Agency (JAEA) has been developing Oxide Dispersion Strengthened (ODS) ferritic steel for long life fuel cladding tube of fast reactor. Application of ODS ferritic steel to fast reactor fuel can extend the fuel life time twice or more as long as the fuel with conventional cladding tube (i.e. modified SUS316), thus reducing fuel exchange frequency and fuel cost. It can be adaptable to high-temperature plant operation, which is favorable for improvement of power generation efficiency. This paper interprets the development of ODS ferritic steel cladding tube for sodium-cooled fast reactor, which has been led by JAEA for dozens of years.
Yuguchi, Takashi*; Sueoka, Shigeru; Iwano, Hideki*; Izumino, Yuya*; Ishibashi, Masayuki; Danhara, Toru*; Sasao, Eiji; Hirata, Takafumi*; Nishiyama, Tadao*
Journal of Asian Earth Sciences, 169, p.47 - 66, 2019/01
This study presents position-by-position t-T paths within a granitic pluton based on thermochronological data, and describes their constraints and their relationship with fracture frequency, as an example from the Toki granite, central Japan. The cooling paths have position-specific characteristics; a single t-T path does not represent the cooling behavior of the entire pluton. Such position-specific t-T paths enable us to evaluate three-dimensional thermal evolution within the granitic pluton, and thus can clarify the detailed formation history of the entire pluton after the incipient intrusion of the granitic magma into the shallow crust. This study reveals the relationship between position-specific t-T paths and fracture frequency, and thus provides a criterion for evaluating the fracture population in terms of thermal stress.
Manabe, Kentaro; Matsumoto, Masaki*
Journal of Nuclear Science and Technology, 56(1), p.78 - 86, 2019/01
If an insoluble cesium-bearing particle is incorporated into the human body, the radioactivity will move as a single particle. In this case, it is impossible to estimate the number of disintegrations by considering the average behavior of countless nuclei. Then, a method was developed to simulate the behavior of the particle stochastically; and a biokinetic model was constructed to consider the characteristics of insoluble particles. Combination of the method and the model enables to estimate the number of disintegrations, and consequently the internal doses considering the stochastic behavior of the single cesium particle. We evaluated a probability density function of committed equivalent and effective doses and its 99th percentile value and arithmetic mean by repeating the above described procedure, and compared them to the reference values based on the existing models. As a result, the 99th percentile value of committed effective doses was 70 times the reference value when the number of incorporated particles was one, and consequently the dose level was quite low. When the exposure level is 1 mSv in committed effective dose, the uncertainty originating in the insolubility of cesium particles was negligibly small.
Kaneko, Koji; Frontzek, M. D.*; Matsuda, Masaaki*; Nakao, Akiko*; Munakata, Koji*; Ohara, Takashi; Kakihana, Masashi*; Haga, Yoshinori; Hedo, Masato*; Nakama, Takao*; et al.
Journal of the Physical Society of Japan, 88, p.013702_1 - 013702_5, 2019/01
Magnetic transitions in chiral antiferromagnet EuPtSi were investigated by means of single crystal neutron diffraction. In the ground state, magnetic peaks emerge at positions represented by =. Upon heating, an additional magnetic peak splitting around 2.5 K was uncovered, indicating a presence of a first-order transition with =. An half-polarized neutron scattering for polarization parallel to Q reveled that polarization antiparallel to Q has stronger intensity in both magnetic phases. This feature clarifies single chiral character of helical structure with moments normal to the ordering vector in both ordered states. Under vertical magnetic field along [1,1,1] in the phase, magnetic peaks form hexagonal patterns in the equatorial scattering plane around nuclear. An ordering vector of the -phase has the similar size in the periodicity to , and could be a hallmark of a formation of skyrmion lattice in EuPtSi.
Uchibori, Akihiro; Watanabe, Akira*; Takata, Takashi; Ohshima, Hiroyuki
Nuclear Technology, 205(1-2), p.119 - 127, 2019/01
To evaluate a sodium-water reaction phenomenon in a steam generator of sodium-cooled fast reactors, a computational fluid dynamics code SERAPHIM, in which a compressible multicomponent multiphase flow with sodium-water chemical reaction is computed, has been developed. The original SERAPHIM code is based on the difference method. In this study, unstructured mesh-based numerical method was developed to advance a numerical accuracy for the complex-shaped domain including multiple heat transfer tubes. Numerical analysis of an underexpanded jet experiment was performed as part of validation of the unstructured mesh-based numerical method. The calculated pressure profile and location of the Mach disk showed good agreement with the experimental data. Applicability of the numerical method for the actual situation was confirmed through the analysis of water vapor discharging into liquid sodium.
Murray, I.*; MacCormick, M.*; Bazin, D.*; Doornenbal, P.*; Aoi, Nori*; Baba, Hidetada*; Crawford, H. L.*; Fallon, P.*; Li, K.*; Lee, J.*; et al.
Physical Review C, 99(1), p.011302_1 - 011302_7, 2019/01
理化学研究所のRI Beam Factory(RIBF)にて中性子過剰核Neの低励起状態を1陽子あるいは2陽子ノックアウト反応によって生成し、そこからの脱励起ガンマ線の測定によって、エネルギー準位を構築した。1410(15)keVのガンマ線を初めて測定し、反応断面積の系統性などからからへの遷移に対応すると提案した。既に知られている準位を用いて、との励起エネルギー比2.99(6)が得られた。この値は、回転スペクトルの値に近く、Neは強く変形していることがわかった。この実験結果は、大規模殻模型計算の結果とよく一致した。
Laskar, Md. S. R.*; Saha, S.*; Palit, R.*; Mishra, S. N.*; Shimizu, Noritaka*; Utsuno, Yutaka; Ideguchi, Eiji*; Naik, Z.*; Babra, F. S.*; Biswas, S.*; et al.
Physical Review C, 99(1), p.014308_1 - 014308_6, 2019/01
Takahara, Shogo; Iijima, Masashi*; Yoneda, Minoru*; Shimada, Yoko*
Risk Analysis, 39(1), p.212 - 224, 2019/01
A dose assessment model was developed based on measurements and surveys of individual doses and relevant contributors in Fukushima City for four population groups: Fukushima City Office staff, Senior Citizens' Club, Contractors' Association, and AgriculturalCooperative. In addition, probabilistic assessments were performed for these population groups by considering the spatial variability of contamination and interpopulation differencesresulting from behavior patterns. As a result of comparison with the actual measurements, the assessment results for participants from the Fukushima City Office, Senior Citizens' Club and the Agricultural Cooperative agreed with the measured values. By contrast, the measurements obtained for the participants from the Contractors' Association were not reproduced well in the present study. To assess the doses to this group, further investigations of association members' work activities and the related dose reduction effects are needed.
JAEA-Review 2018-021, 79 Pages, 2018/12
Japan has vast marine environment. Therefore, the marine environmental assessment to grasp oceanic structure of shelf and coastal area in the vicinity is important from various viewpoints, such as marine and seafloor resources, national defense, and disaster prevention for Japan. For instance, preserving the coral coasts around the Ryukyu Islands, and assessing marine pollution due the raidionuclides released form the Fukushima Daiichi Nuclear Power Plant are urgent matters for Japan. In the present study, submesoscale-eddy-resolving numerical experiments using Regional Oceanic Modeling System (ROMS) were conducted for areas around the Ryukyu Islands and the northeast Pacific coast of Japan to investigate the applicability of the high-resolution model to the marine assessment system. In addition, we considered improving the Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) to reproduce more realistic oceanic dispersal of radionuclide by introducing multiple-nested downscaling ocean modeling system using the ROMS. Extensive model-data comparison demonstrated that the submsoscale eddy-resolving models, with a lateral grid resolution of 1km, could successfully reproduce the synoptic and mesoscale oceanic structures. According to the eddy heat flux analysis and energy conversion analysis relevant to the eddy-generation mechanisms revealed that both of shear instability and baroclinic instability enhanced the three-dimensional mixing of tracers induced by submesoscale eddy. These results suggested that the multiple-nested, high resolution, downscaling ocean modeling has important role to develop the accurate marine environmental assessment system.
Takeuchi, Ryuji; Iwatsuki, Teruki; Matsui, Hiroya; Ikeda, Koki; Mikake, Shinichiro; Hama, Katsuhiro; Iyatomi, Yosuke; Sasao, Eiji
JAEA-Review 2018-019, 29 Pages, 2018/12
The Mizunami Underground Research Laboratory (MIU) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of geological disposal technologies through investigations of the deep geological environment in the crystalline host rock (granite) at Mizunami, Gifu Prefecture, central Japan. On the occasion of the reform of the entire JAEA organization in 2014, JAEA identified three important issues on the geoscientific research program: "Development of countermeasure technologies for reducing groundwater inflow", "Development of modelling technologies for mass transport" and "Development of drift backfilling technology", based on the latest results of the synthesizing research and development (R&D). The R&D on three remaining important issues have been carrying out on the MIU Project. This report summarizes the R&D activities planned for fiscal year 2018 on the basis of the MIU Master Plan updated in 2015 and Investigation Plan for the Third Medium to Long-term Research Phase.
Saegusa, Jun; Koma, Yoshikazu; Ashida, Takashi
JAEA-Review 2018-017, 259 Pages, 2018/12
Collaborative Laboratories for Advanced Decommissioning Science (CLADS) is responsible to promote international cooperation in the R&D activities on the decommissioning of Fukushima Daiichi Nuclear Power Station and to develop the necessary human resources. CLADS held the Fukushima Research Conference on Development of Analytical Techniques in Waste Management (FRCWM 2018) on 19th and 20th June, 2018. This report compiles the abstracts and the presentation materials in the above conference.
Iketani, Shotaro; Yokobori, Tomohiko; Ishikawa, Joji; Yasuhara, Toshiyuki*; Kozawa, Toshiyuki*; Takaizumi, Hirohide*; Monma, Takeshi*; Kurosawa, Shingo*; Iseda, Hirokatsu; Kishimoto, Katsumi; et al.
JAEA-Review 2018-016, 46 Pages, 2018/12
Japan Atomic Energy Agency (JAEA) adopts melting process for the waste processing and packaging method of radioactive miscellaneous solid waste in NSRI because melting process is effective in radioactivity evaluation, volume reduction, and stabilization treatment. Metal melting processing facilities, Incinerator, and Nonmetal melting processing facilities (hereinafter referred to as melting process facilities) have taken lots of safety measures, including measures for preventing the recurrence of the fire accidents. To exchange opinions and discuss the validity of these measures and so on with internal personnel and external experts, "Discussions on Melting Process Facilities" was held. As a document collection, this paper summarizes presentation materials of discussion meetings. Presentation materials describe "Outline of AVRF", "Safety measures in the melting facilities in WVRF", "Operation management of the melting facilities in WVRF", "Comparison of the past accident cases between facilities in and outside Japan and WVRF", and "Introduction of past accident cases and safety measures in other facilities from each committee".
Naraha Center for Remote Control Technology Development, Fukushima Research Insitute
JAEA-Review 2018-014, 52 Pages, 2018/12
The Naraha Remote Technology Development Center (Naraha Center) consists of a mock-up test building and a research management building, and various test facilities necessary for the decommissioning work after the accident of TEPCO Fukushima Daiichi Nuclear Power Station are installed. Using these test facilities, a wide range of users, such as companies engaged in decommissioning work, research and development institutions, educational institutions, etc., can efficiently develop robots through characterization and performance evaluation of remote-controlled robots. Furthermore, it is possible to make various uses such as exhibitions that many companies have met together, experts' meetings on decommissioning. This report summarizes the activities of the Naraha Center such as development of remote control technologies, maintenance and training of remote control equipment for emergency response, use of component test areas, and so on in FY2016.