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Journal Articles

Present status of the tandem accelerator at the JAEA-AMS-TONO; 2015

Fujita, Natsuko; Matsubara, Akihiro*; Watanabe, Takahiro; Kokubu, Yoko; Umeda, Koji*; Ishimaru, Tsuneari; Nishizawa, Akimitsu*; Miyake, Masayasu; Owaki, Yoshio*; Nishio, Tomohiro*; et al.

Dai-29-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, p.39 - 42, 2017/03

no abstracts in English

Journal Articles

Fission track dating of faulting events accommodating plastic deformation of biotites

Sueoka, Shigeru; Shimada, Koji; Ishimaru, Tsuneari; Niwa, Masakazu; Yasue, Kenichi; Umeda, Koji*; Danhara, Toru*; Iwano, Hideki*

Journal of Geophysical Research; Solid Earth, 122(3), p.1848 - 1859, 2017/03

no abstracts in English

Journal Articles

Event deposits recorded in coastal lowland areas of Ajigasawa Town, Aomori Prefecture

Kumagaya, Shuhei*; Umeda, Koji*; Kamataki, Takanobu*; Koiwa, Naoto*; Fujita, Natsuko

Tohoku Chiiki Saigai Kagaku Kenkyu, 53, p.7 - 13, 2017/03

no abstracts in English

JAEA Reports

Annual report for research on geosphere stability for long-term isolation of radioactive waste in fiscal year 2015

Ishimaru, Tsuneari; Umeda, Koji*; Yasue, Kenichi; Kokubu, Yoko; Niwa, Masakazu; Asamori, Koichi; Watanabe, Takahiro; Yokoyama, Tatsunori; Fujita, Natsuko; Shimizu, Mayuko; et al.

JAEA-Research 2016-023, 91 Pages, 2017/02

JAEA-Research-2016-023.pdf:13.33MB

This annual report documents the progress of research and development (R&D) in the 1st fiscal year during the JAEA 3rd Mid- and Long-term Plan (fiscal years 2015-2021) to provide the scientific base for assessing geosphere stability for long-term isolation of the high-level radioactive waste. The planned 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. In this paper, the current status of R&D activities with previous scientific and technological progress is summarized.

Journal Articles

Present status of the JAEA-AMS-TONO; 2015

Fujita, Natsuko; Matsubara, Akihiro; Watanabe, Takahiro; Kokubu, Yoko; Umeda, Koji; Nishizawa, Akimitsu*; Miyake, Masayasu*; Owaki, Yoshio*; Nishio, Tomohiro*; Kato, Motohisa*

Dai-18-Kai AMS Shimpojiumu Hokokushu, p.85 - 90, 2016/12

no abstracts in English

Journal Articles

Dating of crush zones associated with plastic deformation of biotite; Constraints by fission-track thermochronometry

Sueoka, Shigeru; Shimada, Koji; Ishimaru, Tsuneari; Niwa, Masakazu; Yasue, Kenichi; Umeda, Koji*; Danhara, Toru*; Iwano, Hideki*

Fisshion, Torakku Nyusureta, (29), p.5 - 7, 2016/12

no abstracts in English

Journal Articles

The Installation and the radiation protection of the optically stimulated luminescence reader with sealed beta source in the Toki Research Institute of Isotope Geology and Geochronology, Japan Atomic Energy Agency

Tokuyasu, Kayoko; Furuta, Sadaaki*; Kokubu, Yoko; Umeda, Koji

Nippon Hoshasen Anzen Kanri Gakkai-Shi, 15(1), p.80 - 87, 2016/07

An optically stimulated luminescence reader (Riso TL/OSL DA-20) was installed in Toki Research Institute of Isotope Geology and Geochronology (Toki-shi, Gifu Prefecture), Japan Atomic Energy Agency (JAEA) for dating the geological sample. An accumulated dose of the sample is obtained using the reader. Sealed beta source of strontium-90 is required to be mounted on the reader because repeated artificial irradiation is necessary for the accumulated dose estimation. However, there are not many introduction examples for the reader domestically, and the information as to radiation control of the reader is limited. We therefore report here the process of source loading on the reader and radiation control associated with the use of the source.

Journal Articles

Cooling and denudation history of the Tsuruga body of Kojaku granite, southwest Japan, constrained from multi-system thermochronology

Sueoka, Shigeru; Umeda, Koji; Yasue, Kenichi; Niwa, Masakazu; Shimada, Koji; Ishimaru, Tsuneari; Danhara, Toru*; Iwano, Hideki*; Yagi, Koshi*

Chigaku Zasshi, 125(2), p.201 - 219, 2016/04

We applied multi-system thermochronology to the Tsuruga body of the Kojaku granite to constrain the cooling/denudation history of the Tsuruga area. Based on the thermochronometric results and other data, we reconstructed the cooling and denudation histories of the Tsuruga body as below: (1) the Tsuruga body intruded at c.a. 68 Ma at the depth of 4-5 km, (2) rapidly cooled down to c.a. 200$$^{circ}$$C by heat conduction within a few million years or less, and (3) slowly cooled due to peneplanation during the Cenozoic. This cooling/denudation history is consistent with the observations that cataclasite and fault gouge are dominant in the crush zones of the Tsuruga body, that similar slow cooling histories over the Cenozoic are estimated in the surrounding areas based on thermochronometric ages, and that the amount of denudation in the last few million years in the Tsuruga area is inferred at less than several hundred meters from the elevations of the uplifted peneplains.

Journal Articles

Thermal constraints on clay growth in fault gouge and their relationship with fault-zone evolution and hydrothermal alteration; Case study of gouges in the Kojaku Granite, Central Japan

Niwa, Masakazu; Shimada, Koji; Tamura, Hajimu*; Shibata, Kenji*; Sueoka, Shigeru; Yasue, Kenichi; Ishimaru, Tsuneari; Umeda, Koji*

Clays and Clay Minerals, 64(2), p.86 - 107, 2016/04

 Times Cited Count:3 Percentile:65.67(Chemistry, Physical)

no abstracts in English

Journal Articles

Evaluation of dark current profile for prediction of voltage holding capability on multi-aperture multi-grid accelerator for ITER

Nishikiori, Ryo; Kojima, Atsushi; Hanada, Masaya; Kashiwagi, Mieko; Watanabe, Kazuhiro; Umeda, Naotaka; Tobari, Hiroyuki; Yoshida, Masafumi; Ichikawa, Masahiro; Hiratsuka, Junichi; et al.

Plasma and Fusion Research (Internet), 11, p.2401014_1 - 2401014_4, 2016/03

One of critical issues for high-energy high-current beam acceleration in ITER and JT-60SA is the high voltage holding which is dominated by vacuum discharges. The past results suggest that vacuum discharge occurs beyond the threshold of the dark current. The dark current can be derived from F-N theory where electric field enhancement factor beta is included. Though, beta could only be evaluated from the experiment previously. Therefore, the method to decide beta without experiment is required. This time dark currents were measured at three different areas to compare beta in different electric field. As a result, the effective electric field $$beta$$E, where E is average electric field, were found to be almost constant for different areas although the beta is largely different. By applying $$beta$$E, beta can be evaluated analytically, leading to the analytical prediction of the dark current and voltage holding capability without the measurements.

Journal Articles

Contributions of geosciences to nuclear safety, 1; Detecting geofluids and its implications for geological disposal

Umeda, Koji; Asamori, Koichi

Nippon Genshiryoku Gakkai-Shi, 58(2), p.110 - 114, 2016/02

Geofluid is regarded as a powerful tool to evaluate geosphere stability for geological disposal.

Journal Articles

Measurement of heat load density profile on acceleration grid in MeV-class negative ion accelerator

Hiratsuka, Junichi; Hanada, Masaya; Kojima, Atsushi; Umeda, Naotaka; Kashiwagi, Mieko; Miyamoto, Kenji*; Yoshida, Masafumi; Nishikiori, Ryo; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.

Review of Scientific Instruments, 87(2), p.02B137_1 - 02B137_3, 2016/02

 Times Cited Count:1 Percentile:85.87(Instruments & Instrumentation)

To understand the physics of the negative ion extraction/acceleration, the heat load density profile on the acceleration grid has been firstly measured in the ITER prototype accelerator where the negative ions are accelerated to 1 MeV with five acceleration stages. In order to clarify the profile, the peripheries around the apertures on the acceleration grid were separated into thermally insulated 34 blocks with thermocouples. The spatial resolution is as low as 3 mm and small enough to measure the tail of the beam profile with a beam diameter of 16 mm. It was found that there were two peaks of heat load density around the aperture. These two peaks were also clarified to be caused by the intercepted negative ions and secondary electrons from detailed investigation by changing the beam optics and gas density profile. This is the first experimental result, which is useful to understand the trajectories of these particles.

Journal Articles

Time evolution of negative ion profile in a large cesiated negative ion source applicable to fusion reactors

Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Umeda, Naotaka; Hiratsuka, Junichi; Ichikawa, Masahiro; Watanabe, Kazuhiro; Grisham, L. R.*; Tsumori, Katsuyoshi*; et al.

Review of Scientific Instruments, 87(2), p.02B144_1 - 02B144_4, 2016/02

 Times Cited Count:3 Percentile:73.23(Instruments & Instrumentation)

Time evolution of spatial profile of negative ion production during an initial conditioning phase has been experimentally investigated in the JT-60 negative ion source. Up to 0.4 g Cs injection, there is no enhancement of the negative ion production and no observation of the Cs emission signal in the source, suggesting the injected Cs is mainly deposited on the water-cooled wall near the nozzle. After 0.4 g Cs injection, enhancement of the negative ion production appeared only at the central segment of the PG. The calculation of the Cs neutral/ion trajectories implied that a part of Cs was ionized near the nozzle and was transported to this area. The expansion of the area of the surface production was saturated after ~2 g Cs injection corresponding to 6000 s discharge time. From the results, it is found that Cs ionization and its transport plays an important role for the negative ion production.

Journal Articles

Development of design technique for vacuum insulation in large size multi-aperture multi-grid accelerator for nuclear fusion

Kojima, Atsushi; Hanada, Masaya; Tobari, Hiroyuki; Nishikiori, Ryo; Hiratsuka, Junichi; Kashiwagi, Mieko; Umeda, Naotaka; Yoshida, Masafumi; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.

Review of Scientific Instruments, 87(2), p.02B304_1 - 02B304_5, 2016/02

 Times Cited Count:3 Percentile:61.24(Instruments & Instrumentation)

Optimization techniques of the vacuum insulation design have been developed in order to realize a reliable voltage holding capability of Multi-Aperture Multi-Grid accelerators for giant negative ion sources for nuclear fusion. In this method, the nested multilayer configuration of each acceleration stage in the MAMuG accelerator can be uniquely designed to satisfy the target voltage within given boundary conditions. The evaluation of the voltage holding capabilities of each acceleration stages were based on the past experimental results of the area effect and the multi-aperture effect on the voltage holding capability. Moreover, total voltage holding capability of multi-stage was estimated by taking the multi-stage effect into account, which was experimentally obtained in this time. In this experiment, the multi-stage effect appeared as the superposition of breakdown probabilities in each acceleration stage, which suggested that multi-stage effect can be considered as the voltage holding capability of the single acceleration gap having the total area and aperture. The analysis on the MAMuG accelerator for JT-60SA agreed with the past gap-scan experiments with an accuracy of less than 10% variation.

Journal Articles

Development of the negative ion beams relevant to ITER and JT-60SA at Japan Atomic Energy Agency

Hanada, Masaya; Kojima, Atsushi; Tobari, Hiroyuki; Nishikiori, Ryo; Hiratsuka, Junichi; Kashiwagi, Mieko; Umeda, Naotaka; Yoshida, Masafumi; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.

Review of Scientific Instruments, 87(2), p.02B322_1 - 02B322_4, 2016/02

 Times Cited Count:5 Percentile:43.38(Instruments & Instrumentation)

In International Thermo-nuclear Experimental Reactor (ITER) and JT-60 Super Advanced (JT-60 SA), the D$$^{-}$$ ion beams of 1 MeV, 40 A and 0.5 MeV, 22 A are required to produce 3600 s and 100 s for the neutral beam injection, respectively. In order to realize such as powerful D$$^{-}$$ ion beams for long duration time, Japan Atomic Energy Agency (JAEA) has energetically developed cesium (Cs)-seeded negative ion sources (CsNIS) and electro-static multi-aperture and multi-stage accelerators (MAMuG accelerator) which are chosen as the reference design of ITER and JT-60 SA. In the development of the CsNIS, a 100s production of the H$$^{-}$$ ion beam has been demonstrated with a beam current of 15 A by modifying the JT-60 negative ion source. At the higher current, the long pulse production of the negative ions has been tried by the mitigation of the arcing in the plasma inside the ion source. As for the long pulse acceleration of the negative ions in the MAMuG accelerator, the beam steering angle has been controlled to reduce the power loading of the acceleration grids A pulse duration time has been significantly extended from 0.4 s to 60 s at reasonable beam power for ITER requirement. The achieved pulse duration time is limited by the capacity of the power supplies in the test stand. In the range of $$<$$ 60 s, there are no degradations of beam optics and voltage holding capability in the accelerator. It leads to the further extension of the pulse duration time at higher power density. This paper reports the latest results of development on the negative ion source and accelerator at JAEA.

Journal Articles

Localized extensional tectonics in an overall reverse-faulting regime, Northeast Japan

Umeda, Koji

Geoscience Letters (Internet), 2, p.12_1 - 12_8, 2015/11

A particularly notable event was the shallow, normal-faulting earthquake swarms with a T-axis oriented in the E-W or NW-SE directions that occurred immediately after the 2011 Tohoku-Oki earthquake near the Pacific coast in the southeast Tohoku district. The stress tensor inversion represents the pre-Tohoku-Oki earthquake stress field in this area as a normal-faulting stress regime with the minimum principal horizontal stress oriented in a roughly NW-SE direction. Additionally, the stress regime varies with depth from normal faulting at shallow depths ($$<$$ 15 km) to thrust faulting at greater depths. A plausible explanation for these drastic changes in the stress regime is upward flexure of the upper crust due to partly anelastic deformation in the weakened lower crust. Spatial variation of the late Pleistocene uplift rates near the Pacific coast in the southeast Tohoku district can be interpreted as the interaction between regional upwraping and localized extensional tectonics.

JAEA Reports

Research plan on geosphere stability for long-term isolation of radioactive waste; Scientific programme for fiscal year 2015

Umeda, Koji; Yasue, Kenichi; Kokubu, Yoko; Niwa, Masakazu; Asamori, Koichi; Fujita, Natsuko; Shimizu, Mayuko; Matsubara, Akihiro; Tamura, Hajimu; Yokoyama, Tatsunori; et al.

JAEA-Review 2015-019, 42 Pages, 2015/09

JAEA-Review-2015-019.pdf:4.64MB

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 JAEA, in fiscal year 2015. The objectives and contents in fiscal year 2015 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.

JAEA Reports

Research on geosphere stability for long-term isolation of radioactive waste; Scientific programme for fiscal years 2015-2021

Umeda, Koji; Yasue, Kenichi; Kokubu, Yoko; Niwa, Masakazu; Asamori, Koichi; Fujita, Natsuko; Shimizu, Mayuko; Shimada, Akiomi; Matsubara, Akihiro; Tamura, Hajimu; et al.

JAEA-Review 2015-012, 43 Pages, 2015/08

JAEA-Review-2015-012.pdf:1.24MB

The concept of geological disposal of high-level radioactive waste (HLW) in Japan is based on a multibarrier system which combines a stable geological environment with an engineered barrier system. Potential geological host formations and their surroundings are chosen, in particular, for their long-term stability, taking into account the fact that Japan is located in tectonically active zone. This report is to outline 7 years plan (fiscal years 2015-2021) of research and development (R&D) for geosphere stability for long-term isolation of the HLW in JAEA. Background of this research is clarified with the necessity and the significance, and the past progress in this report. The objectives, outline, contents and schedule during the next 7 years are described in detail. 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.

JAEA Reports

Synthesized research report in the second mid-term research phase; Mizunami Underground Research Laboratory Project, Horonobe Underground Research Laboratory Project and Geo-stability Project

Hama, Katsuhiro; Mizuno, Takashi; Sasao, Eiji; Iwatsuki, Teruki; Saegusa, Hiromitsu; Sato, Toshinori; Fujita, Tomoo; Sasamoto, Hiroshi; Matsuoka, Toshiyuki; Yokota, Hideharu; et al.

JAEA-Research 2015-007, 269 Pages, 2015/08

JAEA-Research-2015-007.pdf:68.65MB
JAEA-Research-2015-007(errata).pdf:0.07MB

We have synthesised the research results from Mizunami/Horonobe URLs and geo-stability projects in the second mid-term research phase. It could be used as technical bases for NUMO/Regulator in each decision point from sitting to beginning of disposal (Principal Investigation to Detailed Investigation Phase). High quality construction techniques and field investigation methods have been developed and implemented and these will be directly applicable to the National Disposal Program (along with general assessments of hazardous natural events and processes). It will be crucial to acquire technical knowledge on decisions of partial backfilling and final closure by actual field experiments in Mizunami/Horonobe URLs as main themes for the next phases.

Journal Articles

Progress in long-pulse production of powerful negative ion beams for JT-60SA and ITER

Kojima, Atsushi; Umeda, Naotaka; Hanada, Masaya; Yoshida, Masafumi; Kashiwagi, Mieko; Tobari, Hiroyuki; Watanabe, Kazuhiro; Akino, Noboru; Komata, Masao; Mogaki, Kazuhiko; et al.

Nuclear Fusion, 55(6), p.063006_1 - 063006_9, 2015/06

 Times Cited Count:20 Percentile:9.28(Physics, Fluids & Plasmas)

Significant progresses in the extension of pulse durations of powerful negative ion beams have been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long pulse production/acceleration of negative ion beams in JT-60SA and ITER, the new technologies have been developed in the JT-60SA ion source and the MeV accelerator in Japan Atomic Energy Agency. As for the long pulse production of high-current negative ions for JT-60SA ion source, the pulse durations have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA ion source, which satisfies the required pulse duration of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform negative ion productions with the modified tent-shaped filter field configuration. Moreover, the each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER ion source because the sustainment of the cesium coverage in large extraction area is one of the common issues between JT-60SA and ITER. As for the long pulse acceleration of high power density beams in the MeV accelerator for ITER, the pulse duration of MeV-class negative ion beams has been extended by more than 2 orders of magnitude by modifying the extraction grid with a high cooling capability and a high-transmission of negative ions. A long pulse acceleration of 60 s has been achieved at 70 MW/m$$^{2}$$ (683 keV, 100 A/m$$^{2}$$) which has reached to the power density of JT-60SA level of 65 MW/m$$^{2}$$.

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