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Journal Articles

Modelling heterogeneous hydration behaviour of bentonite by a FracMan-Thames coupling method for the Bentonite Rock Interaction Experiment (BRIE) at $"{A}$sp$"{o}$ HRL

Sawada, Atsushi; Sakamoto, Kazuhiko*; Watahiki, Takanori*; Imai, Hisashi*

SKB P-17-06, 154 Pages, 2023/08

Journal Articles

Design and actual performance of J-PARC 3 GeV rapid cycling synchrotron for high-intensity operation

Yamamoto, Kazami; Kinsho, Michikazu; Hayashi, Naoki; Saha, P. K.; Tamura, Fumihiko; Yamamoto, Masanobu; Tani, Norio; Takayanagi, Tomohiro; Kamiya, Junichiro; Shobuda, Yoshihiro; et al.

Journal of Nuclear Science and Technology, 59(9), p.1174 - 1205, 2022/09

 Times Cited Count:3 Percentile:80.29(Nuclear Science & Technology)

In the Japan Proton Accelerator Research Complex, the purpose of the 3 GeV rapid cycling synchrotron (RCS) is to accelerate a 1 MW, high-intensity proton beam. To achieve beam operation at a repetition rate of 25 Hz at high intensities, the RCS was elaborately designed. After starting the RCS operation, we carefully verified the validity of its design and made certain improvements to establish a reliable operation at higher power as possible. Consequently, we demonstrated beam operation at a high power, namely, 1 MW. We then summarized the design, actual performance, and improvements of the RCS to achieve a 1 MW beam.

JAEA Reports

Study of natural fracture topography in 50cm scale granodiorite rock block including natural fracture intersection measured by precision grinder

Tetsu, Keiichi*; Takayama, Yusuke; Sawada, Atsushi

JAEA-Research 2022-005, 84 Pages, 2022/08

JAEA-Research-2022-005.pdf:10.32MB
JAEA-Research-2022-005-appendix(CD-ROM).zip:35.68MB

Nuclide migration analyses are conducted for the safety assessment in geological disposal system of HLW. Nuclide migration evaluation of fractured host rock mainly uses a model that approximates the fracture with parallel flat plates. However, the actual fractures in the host rock are different from the parallel flat plates, the fractures have complex characteristics such as roughness of fracture surface and the fillings in the fracture. In approximating a fracture model, the methodology development how to set parameter values such as the transmissivity coefficient and the fracture aperture is an issue. One of the issues is to investigate the geometrical features of actual fractures in the host rock. In this study, for the purpose of understanding the geometrical features of fractures including fracture intersection, the internal fracture shape was measured in detail using the method of surface grinding on 50cm scale granodiorite with natural fracture intersection. Thus, the fracture width, fracture aperture, and the shape of the fracture surfaces were obtained. From the obtain data, characteristics such as the average value of the fracture width, the roughness of the fracture surfaces, and the distribution of the fracture aperture were evaluated. As a result, it was confirmed that one of the fractures near the fracture intersection has a particularly large fracture width and fracture aperture as compared with the other part of fractures. Thus, in the granodiorite rock block used in this study, it was inferred that the most permeable path is not the fracture intersection itself, but the particularly large fracture aperture in the vicinity of the fracture intersection.

Journal Articles

Long-term density-dependent groundwater flow analysis and its effect on nuclide migration for safety assessment of high-level radioactive waste disposal with consideration of interaction between fractures and matrix of rock formation in coastal crystalline groundwater systems

Park, Y.-J.*; Sawada, Atsushi; Ozutsumi, Takenori*; Tanaka, Tatsuya*; Hashimoto, Shuji*; Morita, Yutaka*

Proceedings of 3rd International Conference on Discrete Fracture Network Engineering (DFNE 2022) (Internet), 8 Pages, 2022/00

Safety analysis for underground disposal facilities for high-level radioactive waste requires thorough understanding of long-term groundwater flow and nuclide migration processes in geologic media. In the coastal subsurface systems, groundwater flow is defined by the complex interactions between freshwater of meteoric origin and denser saline water from the sea. In addition, sea levels are expected to fluctuate significantly due to a transgression and regression of the sea over the millions of years for safety analysis. This study presents long-term evolution of groundwater environment such as salinity concentration and flow velocity with focus of the interaction between fractures and matrix blocks in regional and near-field scale analysis framework for groundwater flow and nuclide migration for underground disposal facilities in hypothetical fractured crystalline coastal systems.

Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

JAEA Reports

Development of technique for acquiring fracture void structure data for a single fracture and acquisition of hydraulic/mass transport properties in a fracture

Sato, Hisashi*; Sawada, Atsushi; Takayama, Yusuke

JAEA-Research 2020-012, 37 Pages, 2020/11

JAEA-Research-2020-012.pdf:2.66MB
JAEA-Research-2020-012-appendix(DVD-ROM).zip:468.23MB

In the safety assessment of the geological disposal of high-level radioactive waste, it is important to fully understand the permeability and mass transport properties of actual fractures when setting parameters for permeability and mass transport properties of fractures. Permeability and mass transport properties of a fracture are affected by the void structure of the fracture. Therefore, it is necessary not only to conduct a hydraulic test but also to evaluate hydraulic properties based on the void structure of the fracture. Therefore, the purpose of this study is to develop a technique to acquire a three-dimensional void structure of a fracture from fracture surface shape data, and to obtain a dataset of three- dimensional void structure data and hydraulic data of the fracture. Specifically, we made a transparent replica sample of fracture and measure the fracture surface shape data in the exact coordinates. The three-dimensional void structure data was constituted from fracture surface shape data in the same coordinates. In addition, we conducted a permeability test and tracer test for the same sample to obtain a permeability and mass transport properties of the fracture. To assess the validity of the acquired data, we compared it with the apertures evaluated based on different methods. As a result, the average aperture from the fracture void structure was almost same as the average aperture acquired by different methods, from the above that the test result was validated.

Journal Articles

An Experimental setup for creating and imaging $$^{4}$$He$$_{2}$$$$^{ast}$$ excimer cluster tracers in superfluid helium-4 via neutron-$$^{3}$$He absorption reaction

Sonnenschein, V.*; Tsuji, Yoshiyuki*; Kokuryu, Shoma*; Kubo, Wataru*; Suzuki, So*; Tomita, Hideki*; Kiyanagi, Yoshiaki*; Iguchi, Tetsuo*; Matsushita, Taku*; Wada, Nobuo*; et al.

Review of Scientific Instruments, 91(3), p.033318_1 - 033318_12, 2020/03

 Times Cited Count:0 Percentile:0(Instruments & Instrumentation)

Journal Articles

Generation of $$^{4}$$He$$_2^{*}$$ clusters via neutron-$$^{3}$$He absorption reaction toward visualization of full velocity field in quantum turbulence

Matsushita, Taku*; Sonnenschein, V.*; Guo, W.*; Hayashida, Hirotoshi*; Hiroi, Kosuke; Hirota, Katsuya*; Iguchi, Tetsuo*; Ito, Daisuke*; Kitaguchi, Masaaki*; Kiyanagi, Yoshiaki*; et al.

Journal of Low Temperature Physics, 196(1-2), p.275 - 282, 2019/07

Journal Articles

Conceptual uncertainties in modelling the interaction between engineered and natural barriers of nuclear waste repositories in crystalline rocks

Finsterle, S.*; Lanyon, B.*; ${AA}$kesson, M.*; Baxter, S.*; Bergstr$"o$m, M.*; Bockg${aa}$rd, N.*; Dershowitz, W.*; Dessirier, B.*; Frampton, A.*; Fransson, ${AA}$.*; et al.

Geological Society, London, Special Publications, No.482, p.261 - 283, 2019/00

 Times Cited Count:8 Percentile:67.25

Nuclear waste disposal in geological formations relies on a multi-barrier concept that includes engineered components which in many cases includes a bentonite buffer surrounding waste packages and the host rock. An SKB's (Swedish Nuclear Fuel and Waste Management Co.) Modelling Task Force project facilitated to improve the overall understanding of rock - bentonite interactions, as 11 teams used different conceptualisations and modelling tools to analyse the in-situ experiment at the $"A$ps$"o$ Hard Rock Laboratory. The exercise helped identify conceptual uncertainties that led to different assessments of the relative importance of the engineered and natural barrier subsystems and of aspects that need to be better understood to arrive at reliable predictions of bentonite wetting.

Journal Articles

Revising the 4${it f}$ symmetry in CeCu$$_{2}$$Ge$$_{2}$$; Soft X-ray absorption and hard X-ray photoemission spectroscopy

Aratani, Hidekazu*; Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Kawada, Moeki*; Kanai, Yuina*; Yamagami, Kohei*; Fujioka, Shuhei*; Hamamoto, Satoru*; Kuga, Kentaro*; Kiss, Takayuki*; et al.

Physical Review B, 98(12), p.121113_1 - 121113_6, 2018/09

AA2018-0352.pdf:1.16MB

 Times Cited Count:4 Percentile:26.15(Materials Science, Multidisciplinary)

Journal Articles

Termination of electron acceleration in thundercloud by intracloud/intercloud discharge

Wada, Yuki*; Bowers, G. S.*; Enoto, Teruaki*; Kamogawa, Masashi*; Nakamura, Yoshitaka*; Morimoto, Takeshi*; Smith, D.*; Furuta, Yoshihiro*; Nakazawa, Kazuhiro*; Yuasa, Takayuki*; et al.

Geophysical Research Letters, 45(11), p.5700 - 5707, 2018/06

 Times Cited Count:28 Percentile:83.17(Geosciences, Multidisciplinary)

JAEA Reports

An Influence of the conceptualization between host rock and buffer on nuclide migration in host rock

Sawada, Atsushi; Sakamoto, Kazuhiko

JAEA-Research 2015-020, 21 Pages, 2016/02

JAEA-Research-2015-020.pdf:4.97MB

An influence of the conceptual model for interface between host rock and buffer upon performance measures defined as the indices for evaluating repository safety was examined, as a part of the safety assessment methodology development programs for high level radioactive waste disposal. Three dimensional discrete fracture network model was made based on the parameters used in H12 report, and a line object mimicking disposal tunnel was realized at the center of the model. The groundwater travel time distribution along the migration paths from the line object to the downstream boundary was calculated by the particle tracking analysis. The variation of the groundwater travel time affected by the length of the line object was analyzed, changing from 100m used in H12 report to 50m, 10m, 5m, 3m and 1m, respectively. The influence on the retardation of nuclide migration was also studied. The case study for migration of Cs-135 shows that the shorter line object leads lower nuclide migration rate. Moreover, the nuclide migration rate could be decreased by taking additional measure, that waste package would not be allocated at relatively high permeable location detected by high spatial resolution (1m $$sim$$ 10m) hydraulic tests at the pilot boreholes.

Journal Articles

Task 7 groundwater flow and transport modelling of fracture system at regional, block, and single-fracture scale flow and transport, Olkiluoto

Sawada, Atsushi; Saegusa, Hiromitsu; Takeuchi, Shinji*; Sakamoto, Kazuhiko*; Dershowitz, W. S.*

SKB P-13-46, 82 Pages, 2015/12

Journal Articles

Segmentation of granite and single fracture through microfocus X-ray CT and its application

Ishikawa, Tomohiro*; Yasuhara, Hideaki*; Sawada, Atsushi; Kishida, Kiyoshi*

Dai-50-Kai Jiban Kogaku Kenkyu Happyokai Rombunshu, p.515 - 516, 2015/06

no abstracts in English

Journal Articles

Measurements of fracture aperture in granite core using microfocus X-ray CT and fluid flow simulation

Kishida, Kiyoshi*; Ishikawa, Tomohiro*; Higo, Yosuke*; Sawada, Atsushi; Yasuhara, Hideaki*

Proceedings of 49th US Rock Mechanics/Geomechanics Symposium (CD-ROM), 6 Pages, 2015/06

In order to estimate the changes in fracture aperture under various long-term confining and thermal conditions, measurements of the fracture aperture are conducted using microfocus X-ray CT. Through the imaging data, the altitude of the fracture surface and the contact points are evaluated, and contact ratios for the fracture, the JRC and the aperture distribution are estimated. On the other hand, measurements are also conducted using a laser scan profile sensor, and some parameters are estimated. In comparing these parameters, the validity of the X-ray CT data and an analysis of the data will be discussed. In addition, a fracture flow simulation will be conducted using the altitude and aperture data obtained by the microfocus X-ray CT.

Journal Articles

Stabilization of a high-order harmonic generation seeded extreme ultraviolet free electron laser by time-synchronization control with electro-optic sampling

Tomizawa, Hiromitsu*; Sato, Takahiro*; Ogawa, Kanade*; Togawa, Kazuaki*; Tanaka, Takatsugu*; Hara, Toru*; Yabashi, Makina*; Tanaka, Hitoshi*; Ishikawa, Tetsuya*; Togashi, Tadashi*; et al.

High Power Laser Science and Engineering, 3, p.e14_1 - e14_10, 2015/04

 Times Cited Count:6 Percentile:34.58(Optics)

no abstracts in English

JAEA Reports

Enhancement of the methodology of repository design and post-closure performance assessment for preliminary investigation stage, 3; Progress report on NUMO-JAEA collaborative research in FY2013 (Joint research)

Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Makino, Hitoshi; Wakasugi, Keiichiro; Mitsui, Seiichiro; Kitamura, Akira; Yoshikawa, Hideki; Oda, Chie; Ishidera, Takamitsu; et al.

JAEA-Research 2014-030, 457 Pages, 2015/03

JAEA-Research-2014-030.pdf:199.23MB

JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and post-closure performance assessment in preliminary investigation stage. With regard to (1) study on rock suitability in terms of hydrology, based on some examples of developing method of hydro-geological structure model, acquired knowledge are arranged using the tree diagram, and model uncertainty and its influence on the evaluation items were discussed. With regard to (2) study on scenario development, the developed approach for "defining conditions" has been reevaluated and improved from practical viewpoints. In addition, the uncertainty evaluation for the effect of use of cementitious material, as well as glass dissolution model, was conducted with analytical evaluation. With regard to (3) study on setting radionuclide migration parameters, based on survey of precedent procedures, multiple-approach for distribution coefficient of rocks was established, and the adequacy of the approach was confirmed though its application to sedimentary rock and granitic rock. Besides, an approach for solubility setting was developed including the procedure of selection of solubility limiting solid phase. The adequacy of the approach was confirmed though its application to key radionuclides.

Journal Articles

Heterophase fluctuations near $$T_{rm c}$$ in the relaxor ferroelectrics (1-x)Pb(Zn$$_{1/3}$$Nb$$_{2/3}$$)O$$_{3}$$-xPbTiO$$_{3}$$ ($$x$$ = 0.09) studied by X-ray diffuse scattering and coherent X-ray scattering

Owada, Kenji; Mizuki, Junichiro*; Matsushita, Mitsuyoshi*; Namikawa, Kazumichi*

Physical Review B, 90(10), p.104109_1 - 104109_12, 2014/09

 Times Cited Count:6 Percentile:28.29(Materials Science, Multidisciplinary)

The paraelectric (PE) to ferroelectric (FE) first-order phase transition of 0.91Pb(Zn$$_{1/3}$$Nb$$_{2/3}$$)O$$_{3}$$-0.09PbTiO$$_{3}$$ ($$T_{c}^{c}$$ = 455 K on cooling) has been studied by the complementary use of X-ray diffuse scattering (XDS) and coherent X-ray scattering (CXS). XDS was mainly used to investigate the FE regions, while CXS was mainly used to investigate the PE regions above $$T_{c}^{c}$$ on cooling. The diffuse scattering intensity due to the appearance of FE regions shows a maximum at $$T_{rm max}= 460$$ K. The diffuse scattering is dynamic in nature and the softening trend changes to a hardening trend at $$T_{rm max}$$. This means that the FE instability is maximum at $$T_{rm max}$$ and therefore the FE regions are well stabilized below $$T_{rm max} $$. The spatial autocorrelation function obtained by CXS, corresponding to the texture of PE regions, starts to rapidly change at about $$T_{rm max}$$ and is most unstable at $$T_{c}^{c}$$. We conclude that a heterophase fluctuation occurs between $$T_{c}^{c}$$ and $$T_{rm max}$$ near the phase transition. The heterophase fluctuation can be expected to correlate to the low-frequency dielectric dispersion and contribute to the phase transition as a precursor phenomenon of the first-order phase transition.

Journal Articles

Discrete fracture network modeling based on in-situ data at underground gallery, 1

Ishibashi, Masayuki; Onoe, Hironori; Sawada, Atsushi; Atsumi, Hiroyuki*; Masumoto, Kazuhiko*; Hosoya, Shinichi*

Dai-42-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.101 - 106, 2014/01

Japan Atomic Energy Agency is proceeding with the Mizunami Underground Research Laboratory Project in order to establish comprehensive techniques for the investigation, analysis and assessment of the deep geological environment in fractured crystalline rock for geological disposal of high level radioactive wastes. We have carried out discrete fracture network modeling, groundwater flow and particle tracking simulation in order to understand the important factors for the solute transport characterizations. In this paper, a method of discrete fracture network modeling based on in-situ data at underground gallery and the influences of different data interpretation are described.

Journal Articles

Discrete fracture network modeling based on in-situ data at underground gallery, 2

Nakajima, Makoto*; Seno, Shoji*; Onoe, Hironori; Ishibashi, Masayuki; Saegusa, Hiromitsu; Sawada, Atsushi

Dai-42-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.107 - 112, 2014/01

Japan Atomic Energy Agency is proceeding with the Mizunami Underground Research Laboratory Project in order to establish comprehensive techniques for the investigation, analysis and assessment of the deep geological environment in fractured crystalline rock for geological disposal of high level radioactive wastes. We have carried out discrete fracture network modeling, groundwater flow and particle tracking simulation in order to understand the important factors for the solute transport characterizations. In this paper, a method for estimating hydraulic parameter of discrete fracture network model based on in-situ data at underground gallery are described.

217 (Records 1-20 displayed on this page)