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Journal Articles

Electronic structure of a (3$$times$$3)-ordered silicon layer on Al(111)

Sato, Yusuke*; Fukaya, Yuki; Cameau, M.*; Kundu, A. K.*; Shiga, Daisuke*; Yukawa, Ryu*; Horiba, Koji*; Chen, C.-H.*; Huang, A.*; Jeng, H.-T.*; et al.

Physical Review Materials (Internet), 4(6), p.064005_1 - 064005_6, 2020/06

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

no abstracts in English

JAEA Reports

Study on the applicability of the fiber-optic crack detection sensor as a safety technology (FY2015-FY2018) (Joint research)

Kono, Masaru*; Hayama, Kazunori*; Matsui, Hiroya; Ozaki, Yusuke

JAEA-Technology 2019-011, 35 Pages, 2019/07


To verify long-term safety performance of the sensor for decades, we decided the extension of the collaborative research and the evaluation test of long-term durability of fiber-optic crack detection sensor developed by Tokyo Measuring Instruments Laboratory Co., Ltd. at the Mizunami Underground Research Laboratory were continued from FY 2015 to FY 2018. As a result, the measurement system using of the fiber-optic crack detection sensor is applicable for long-term measurement in deep underground area and find the future subject.

JAEA Reports

DECOVALEX-2019 Task C; GREET Intermediate report

Iwatsuki, Teruki; Onoe, Hironori; Ishibashi, Masayuki; Ozaki, Yusuke; Wang, Y.*; Hadgu, T.*; Jove-Colon C. F.*; Kalinina, E.*; Hokr, M.*; Balv$'i$n, A.*; et al.

JAEA-Research 2018-018, 140 Pages, 2019/03


DECOVALEX-2019 Task C aims to develop modelling and prediction methods using numerical simulation based on the water-filling experiment to examine the post drift-closure environment recovery processes. In this intermediate report, the results of Step 1 (Modelling and prediction of environmental disturbance by CTD excavation) are summarized from each of the research teams (JAEA, Sandia National Laboratories, Technical University of Liberec). Groundwater inflow rates to the tunnel during the excavation, hydraulic drawdown, and variation of chlorine concentration at monitoring boreholes in the vicinity of the tunnel were chosen as comparison metrics for Step1 by mutual agreement amongst the research teams. It is likely to be possible to foresee the scales of inflow rate and hydraulic drawdown based on a data from the pilot borehole by current simulation techniques.

Journal Articles

Transient ionization of the mesosphere during auroral breakup; Arase satellite and ground-based conjugate observations at Syowa Station

Kataoka, Ryuho*; Nishiyama, Takanori*; Tanaka, Yoshimasa*; Kadokura, Akira*; Uchida, Herbert Akihito*; Ebihara, Yusuke*; Ejiri, Mitsumu*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Sato, Kaoru*; et al.

Earth, Planets and Space (Internet), 71, p.9_1 - 9_10, 2019/01

 Times Cited Count:3 Percentile:40.27(Geosciences, Multidisciplinary)

Transient ionization of the mesosphere was detected at around 65 km altitude during the isolated auroral expansion occurred at 2221-2226 UT on June 30, 2017. A general-purpose Monte Carlo particle transport code PHITS suggested that significant ionization is possible in the middle atmosphere due to auroral X-rays from the auroral electrons of $$<$$10 keV.

Journal Articles

Hydro-Mechanical-Chemical (HMC) simulation of Groundwater REcoverry Experiment in Tunnel (GREET)

Ozaki, Yusuke; Ishibashi, Masayuki; Onoe, Hironori; Iwatsuki, Teruki

Proceedings of 10th Asian Rock Mechanics Symposium & The ISRM International Symposium for 2018 (ARMS 2018) (USB Flash Drive), 11 Pages, 2018/11

Understanding of a post-closure geological environment around a large underground facility is important for the safety assessment of geological disposal of high-level radioactive waste. Japan Atomic Energy Agency (JAEA) has performed the GREET (Groundwater REcovery Experiment in Tunnel) at the Mizunami Underground Research Laboratory (MIU) to evaluate the environmental recovery process after closure. For understanding of coupled behavior of subsurface environment after closure of drift, we perform a Hydro-Mechanical-Chemical coupled simulation of GREET. This study presents the simulation results of excavation stage of test drift for closure test. Our simulation results show that the inflow rate into test drift after excavation is relatively predictable variavle comparing to the hydraulic pressure or chlorite concentration observed in borehole.

Journal Articles

Transition of near surface resistivity of tunnel wall during drift closure test

Ozaki, Yusuke; Ishibashi, Masayuki; Matsushita, Tomoaki*; Masumoto, Kazuhiko*; Imasato, Takehiko*

Proceedings of 13th SEGJ International Symposium (USB Flash Drive), 4 Pages, 2018/11

In the Mizunami Underground Research Laboratory, Groundwater REcoverty Experiment in Tunnel (GREET) is performed to understanding the recovery process of geological environment after the closure of drift. In this experiment, we performed 2D electrical resistivity surveys three times. First survey was performed before the closure of test drift. Second and third surveys were performed after the closure test. The first survey detected two layers conformation that consists of conductive and resistive zones at shallower and deeper part from the drift surface, respectively. These layers correspond to the shotcrete and host rock, respectively. Second and third measurements show that the conductive zone expanded to deeper resistive part while the shallower conductive part did not change. We concluded that we captured the saturation process of dried fractures near the drift wall by closure of drift as an electrical resistivity response.

JAEA Reports

Study on modeling and analysis of groundwater flow with inverse analysis, 2 (Joint research)

Onoe, Hironori; Yamamoto, Shinya*; Kohashi, Akio; Ozaki, Yusuke; Sakurai, Hideyuki*; Masumoto, Kiyoshi*

JAEA-Research 2018-003, 84 Pages, 2018/06


In this study, numerical experiments considered hydrogeological structures, which has high heterogeneity around the Mizunami Underground Research Laboratory and inverse analysis using in-situ data were carried out. The results showed that concentration of hydrogeological structure to be estimated and location of monitoring point is important for application of inverse analysis. Furthermore, it is concluded that inverse analysis using hydraulic response due to pumping test is effective for hydrogeological characterization.

Journal Articles

Investigations of fluid flow in fractured crystalline rocks at the Mizunami Underground Research Laboratory

Hadgu, T.*; Kalinina, E.*; Wang, Y.*; Ozaki, Yusuke; Iwatsuki, Teruki

Proceedings of 2nd International Discrete Fracture Network Engineering Conference (DFNE 2018) (Internet), 5 Pages, 2018/06

Experimental hydrology data from the Mizunami Underground Research Laboratory in Central Japan have been used to develop a site-scale fracture model and a flow model for the study area. The discrete fracture network model was upscaled to a continuum model to be used in flow simulations. A flow model was developed centered on the research tunnel, and using a highly refined regular mesh. In this study development and utilization of the model is presented. The modeling analysis used permeability and porosity fields from the discrete fracture network model as well as a homogenous model using fixed values of permeability and porosity. The simulations were designed to reproduce hydrology of the modeling area and to predict inflow of water into the research tunnel during excavation. Modeling results were compared with the project hydrology data. Successful matching of the experimental data was obtained for simulations based on the discrete fracture network model.

Journal Articles

Development and validation of a fracture model for the granite rocks at Mizunami Underground Research Laboratory, Japan

Kalinina, E. A.*; Hadgu, T.*; Wang, Y.*; Ozaki, Yusuke; Iwatsuki, Teruki

Proceedings of 2nd International Discrete Fracture Network Engineering Conference (DFNE 2018) (Internet), 7 Pages, 2018/06

The Mizunami Underground Research Laboratory is located in the Tono area (Central Japan). Its main purpose is providing a scientific basis for the research and development of technologies needed for deep geological disposal of radioactive waste in fractured crystalline rocks. The current work is focused on the experiments in the research tunnel (500 m depth). The collected tunnel and borehole data were shared with the participants of DEvelopment of COupled models and their VALidation against EXperiments (DECOVALEX) project. This study describes how these data were used to (1) develop the fracture model of the granite rocks around the research tunnel and (2) validate the model.

Journal Articles

NIRS3; The Near Infrared Spectrometer on Hayabusa2

Iwata, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Otake, Makiko*; Arai, Takehiko*; Arai, Tomoko*; Hirata, Naru*; Hiroi, Takahiro*; Honda, Chikatoshi*; Imae, Naoya*; et al.

Space Science Reviews, 208(1-4), p.317 - 337, 2017/07

 Times Cited Count:17 Percentile:33.19(Astronomy & Astrophysics)

NIRS3: The Near Infrared Spectrometer is installed on the Hayabusa2 spacecraft to observe the target C-type asteroid 162173 Ryugu at near infrared wavelengths of 1.8 to 3.2 micrometer. It aims to obtain reflectance spectra in order to detect absorption bands of hydrated and hydroxide minerals in the 3 micrometer-band. We adopted a linear-image sensor with indium arsenide (InAs) photo diodes and a cooling system with a passive radiator to achieve an optics temperature of 188 K, which enables to retaining sufficient sensitivity and noise level in the 3 micrometer wavelength region. We conducted ground performance tests for the NIRS3 flight model (FM) to confirm its baseline specifications. The results imply that the properties such as the signal-to-noise ratio (SNR) conform to scientific requirements to determine the degree of aqueous alteration, such as CM or CI chondrite, and the stage of thermal metamorphism on the asteroid surface.

JAEA Reports

Measurement of rock mass deformation around the closure test drift during groundwater recovery experiment at 500m depth of Mizunami Underground Research Laboratory

Kuwabara, Kazumichi*; Aoyagi, Yoshiaki; Ozaki, Yusuke; Matsui, Hiroya

JAEA-Research 2017-002, 39 Pages, 2017/03


Authors developed a displacement meter using optical fiber sensor. The displacement meter can be set at any locations in a borehole and guarantee the measurement accuracy up to 5MPa. Total twelve displacement meters were installed in three boreholes to measure the rock mass displacement during groundwater recovery test. The measurement of the rock mass displacement was stated on March, 27, FY 2014. During the first and second groundwater recovery experiments, compressive displacements were observed close to the closure test drift wall. Magnitude of the measured displacements, except vicinity of test drift wall, was smaller than that of calculated under the assumption of it is an isotropic elastic material.

JAEA Reports

Study on effects of coupled phenomenon on long-term behavior for crystalline rock; FY2015 (Contract research)

Ichikawa, Yasuaki*; Kimoto, Kazushi*; Matsui, Hiroya; Kuwabara, Kazumichi; Ozaki, Yusuke

JAEA-Research 2016-018, 23 Pages, 2016/12


It is important to evaluate the stability of a repository for high-level radioactive waste not only during the design, construction and operation phases, but also during the post-closure period, for time frames likely exceeding several millennia or longer. The rock mass around the tunnels could be deformed through time in response to time dependent behavior. On the other hand, it was revealed that the chemical reaction of groundwater in a rock had an influence on the long-term behavior. An evaluation of the microcracks to have an influence on this mechanical and chemical coupled phenomena should be worked on chiefly. In fiscal year 2015, using a laser Doppler vibrometer that extends a frequency band up to 20 MHz, and measuring the surface wave transmitted through the granite specimens were estimated group velocity. As a result, group velocity until 100 kHz $$sim$$ 500 kHz, revealed that tends to decrease while vibrating. The group speed estimate from a group delay was shown to be easier than the estimate by wave number - frequency spectrum. This is because in order to improve reliability, the estimated frequency band is by using a spatially averaged waveform. As a result obtained, in the case of the modeling by the viscoelastic theory of the granite and a microcrack nondestructiveness evaluation, it is thought that it is useful information in the future. In order to use the knowledge of this study, there is a need to clarify the correspondence between the microscopic properties of the medium such as a crack and crystal grain and the change of the group velocity.

JAEA Reports

Study on crystalline rock aiming at evaluation method of long-term behavior of rock mass; FY2015 (Contract research)

Fukui, Katsunori*; Hashiba, Kimihiro*; Matsui, Hiroya; Kuwabara, Kazumichi; Ozaki, Yusuke

JAEA-Research 2016-014, 52 Pages, 2016/09


With respect to high-level radioactive waste disposal, knowledge of the long-term mechanical stability of shafts and galleries excavated in rock is required, not only during construction and operation but also over a period of thousands of years after closure. On the other hand, it is known that rock and the rock mass surrounding the disposal gallery shows time dependent behavior such as creep or the stress-relaxation. It becomes the issue in the stability evaluation of the disposal gallery to grasp the behavior. In order to solve this issue, we pushed forward research development. we pushed forward research development. In the fiscal year of 2015, the creep testing machine for Tage tuff was moved to the new building. The creep test was continuously conducted and the total testing time exceeded 17 years. The testing equipment and procedure were examined to investigate the deformation, failure and time-dependency of rock under wet conditions and between room temperature and 100$$^{circ}$$C. The long-term strength of rock under triaxle stress state was researched with the aid of laboratory testing results and in situ stress measurement.

Journal Articles

Encapsulating mobile proton carriers into structural defects in coordination polymer crystals; High anhydrous proton conduction and fuel cell application

Inukai, Munehiro*; Horike, Satoshi*; Itakura, Tomoya*; Shinozaki, Ryota*; Ogiwara, Naoki*; Umeyama, Daiki*; Nagarker, S.*; Nishiyama, Yusuke*; Malon, M.*; Hayashi, Akari*; et al.

Journal of the American Chemical Society, 138(27), p.8505 - 8511, 2016/07

 Times Cited Count:68 Percentile:4.99(Chemistry, Multidisciplinary)

JAEA Reports

Three-dimensional stress analysis of reflooding tunnel during submerging process using crack tensor model at Mizunami Underground Research Laboratory

Ozaki, Yusuke; Matsui, Hiroya; Kuwabara, Kazumichi; Tada, Hiroyuki*; Sakurai, Hideyuki*; Kumasaka, Hiroo*; Goke, Mitsuo*; Kobayashi, Shinji*

JAEA-Research 2016-007, 125 Pages, 2016/06


In Mizunami Underground Research Laboratory (MIU), the stress analysis of fractured rock have been performed with crack tensor model. In MIU, a reflooding test is performed at 500m stage. In this study, stress analysis of rock during submerging process of the tunnel is performed by using crack tensor model. The deformation of the rock under different water levels in the tunnel is simulated. The stress condition by high pressure due to inflow of groundwater into tunnel is also estimated. These simulation are performed under assumption that groundwater does not permeate into rock for the estimation of maximum pressure acting on the rock. The stress analysis with consideration of permeation of groundwater into rock is also conducted for the estimation of stress condition after the diffusion of water pressure in tunnel. The results of these analyses lead the conclusion that the pressure of the rock reaches the groundwater pressure near the face of tunnel when the tunnel is submerged.

Journal Articles

Improvement of exchanging method of neutron startup source of high temperature engineering test reactor

Sawahata, Hiroaki; Shimazaki, Yosuke; Ishitsuka, Etsuo; Yamazaki, Kazunori; Yanagida, Yoshinori; Fujiwara, Yusuke; Takada, Shoji; Shinozaki, Masayuki; Hamamoto, Shimpei; Tochio, Daisuke

Proceedings of 24th International Conference on Nuclear Engineering (ICONE-24) (DVD-ROM), 8 Pages, 2016/06

In the HTTR, $$^{252}$$Cf is loaded in the reactor core as a neutron startup source and changed at frequency. In this exchange work, there were two technical issues; slightly higher radiation exposure of workers by neutron leakage and reliability of neutron source transportation container in handling. To reduce the radiation dose by neutron leakage, detail numerical evaluations using PHITS code were carried out, the effective shielding method for fuel handling machine was proposed. Easily removable polyethylene blocks and particles were used as the neutron shielding, and installed in the cooling paths of the fuel handling machine. As a result, the collective effective dose by neutron was reduced from about 700 man-microSv to about 300 man-microSv. As to the neutron source transportation container, the handling performance was improved and the handling work was safety accomplished by downsizing.

Journal Articles

Present status of J-PARC linac

Oguri, Hidetomo; Hasegawa, Kazuo; Ito, Takashi; Chishiro, Etsuji; Hirano, Koichiro; Morishita, Takatoshi; Shinozaki, Shinichi; Ao, Hiroyuki; Okoshi, Kiyonori; Kondo, Yasuhiro; et al.

Proceedings of 11th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.389 - 393, 2014/10

no abstracts in English

Journal Articles

Manufacturing and development of JT-60SA vacuum vessel and divertor

Sakasai, Akira; Masaki, Kei; Shibama, Yusuke; Sakurai, Shinji; Hayashi, Takao; Nakamura, Shigetoshi; Ozaki, Hidetsugu; Yokoyama, Kenji; Seki, Yohji; Shibanuma, Kiyoshi; et al.

Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2013/03

The JT-60SA vacuum vessel (VV) and divertor are key components for the performance requirements. Therefore the manufacturing and development of VV and divertor are in progress, inclusive of the superconducting magnets. The vacuum vessel has a double wall structure in high rigidity to withstand electromagnetic force at disruption and to keep high toroidal one-turn resistance. In addition, the double wall structure fulfills originally two functions. (1) The remarkable reduction of the nuclear heating in the superconducting magnets is made by boric-acid water circulated in the double wall. (2) The effective baking is enabled by nitrogen gas flow of 200$$^{circ}$$C in the double wall after draining of water. Three welding types were chosen for the manufacturing of the double wall structure VV to minimize deformation by welding. Divertor cassettes with fully water cooled plasma facing components were designed to realize the JT-60SA lower single null closed divertor. The divertor cassettes in the radio-active VV have been developed to ensure compatibility with remote handling (RH) maintenance in order to allow long pulse high performance discharges with high neutron yield. The manufacturing of divertor cassettes with typical accuracy of *1 mm has been successfully completed. Brazed CFC (carbon fiber composite) monoblock targets for a divertor target have been manufactured by precise control of tolerances inside CFC blocks. The infrared thermography test of monoblock targets has been developed as new acceptance inspection.

Journal Articles

Design of lower divertor for JT-60SA

Sakurai, Shinji; Higashijima, Satoru; Hayashi, Takao; Shibama, Yusuke; Masuo, Hiroshige*; Ozaki, Hidetsugu; Sakasai, Akira; Shibanuma, Kiyoshi

Fusion Engineering and Design, 85(10-12), p.2187 - 2191, 2010/08

 Times Cited Count:7 Percentile:48.59(Nuclear Science & Technology)

JT-60SA tokamak project has just started construction phase under both the Japanese domestic program and the Japan-EU international program "ITER Broader Approach". All of plasma facing components (PFC) shall be actively cooled due to high power long pulse plasma heating. Lower single null closed divertor with vertical target (VT) will be installed at the start of experiment phase. Each divertor module covers a 10-degree sector in toroidal direction. PFCs such as VTs, baffles and dome shall be assembled on a divertor cassette, which provides integrated coolant pipe connection to coolant headers in the VV. Static structural analysis for dead weight, coolant pressure and EM loads shows that displacement and stress of the divertor module are generally small but a part of support structure of PFC requires improvement.

Journal Articles

Characterization of homoionic Fe$$^{2+}$$-type montmorillonite; Potential chemical species of iron contaminant

Kozai, Naofumi; Inada, Koichi*; Adachi, Yoshifusa*; Kawamura, Sachi*; Kashimoto, Yusuke*; Kozaki, Tamotsu*; Sato, Seichi*; Onuki, Toshihiko; Sakai, Takuro; Sato, Takahiro; et al.

Journal of Solid State Chemistry, 180(8), p.2279 - 2289, 2007/08

 Times Cited Count:12 Percentile:52.95(Chemistry, Inorganic & Nuclear)

Fe$$^{2+}$$-montmorillonite with Fe$$^{2+}$$ ions occupying cation exchange sites is an ideal transformation product in bentonite buffer material. We previously prepared a Fe$$^{2+}$$-montmorillonite sample using a FeCl$$_{2}$$ solution under an inert gas condition. This study attempted to determine the potential contaminant iron chemical species in the sample. It was found that a small amount of Cl$$^{-}$$ ions remained dispersed throughout the sample. The Cl$$^{-}$$ ion retention may be due to the adsorption of FeCl$$^{+}$$ in the initial FeCl$$_{2}$$ solution and the subsequent containment of the Cl$$^{-}$$ ions that are dissociated from the FeCl$$^{+}$$ during excess salt removal treatment. The latter may be explained by the slow release of the remaining Cl$$^{-}$$ ions from the collapsed interlayer of the montmorillonite or the transformation of a minor fraction of the remaining FeCl$$^{+}$$ to iron (III) hydroxide chloride complexes having low solubility.

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