Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
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：44 Percentile：97.1(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 
C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 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.
Goto, Takahiro*; Mitsui, Seiichiro; Takase, Hiroyasu*; Kurosawa, Susumu*; Inagaki, Manabu*; Shibata, Masahiro; Ishiguro, Katsuhiko*
MRS Advances (Internet), 1(63-64), p.4239 - 4245, 2016/00
NUMO and JAEA have conducted a joint research since FY2011, which is designed to enhance the methodology of repository design and performance assessment in preliminary investigation stage for deep geological disposal of radioactive waste. As a part of this joint research, we have been developing glass dissolution models which consider various processes in EBS, such as precipitation of Fe-silicates associated with iron overpack corrosion, and Si transport through corrosion products in the cracked overpack. The objectives of the modeling work are to evaluate relative importance of relevant processes and to identify further R&D issues towards development of a convincing safety case. Sensitivity analyses suggested that predicted glass dissolution time ranges from 1
10
to 110
years or more due to uncertainties in the current understanding of the key processes, namely precipitation of Fe-silicates and transport characteristics of the altered glass layer.
Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Hayano, Akira; Makino, Hitoshi; Wakasugi, Keiichiro; Mitsui, Seiichiro; Oda, Chie; Kitamura, Akira; Osawa, Hideaki; et al.
JAEA-Research 2013-037, 455 Pages, 2013/12
JAEA-Research-2013-037.pdf:42.0MB
Following FY2011, JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and performance assessment in preliminary investigation stage. With regard to (1) study on rock suitability in terms of hydrology, the tree diagram of methodology of groundwater travel time has been extended for crystalline rock, in addition, tree diagram for sedimentary rock newly has been organized. With regard to (2) study on scenario development, the existing approach has been improved in terms of a practical task, and applied and tested for near field focusing on the buffer. In addition, the uncertainty of some important processes and its impact on safety functions are discussed though analysis. With regard to (3) study on setting radionuclide migration parameters, the approaches for parameter setting have been developed for sorption for rocks and solubility, and applied and tested through parameter setting exercises for key radionuclides.
Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Makino, Hitoshi; Hayano, Akira; Mitsui, Seiichiro; Taniguchi, Naoki; Oda, Chie; Kitamura, Akira; Osawa, Hideaki; et al.
JAEA-Research 2012-032, 298 Pages, 2012/09
JAEA-Research-2012-032.pdf:33.68MB
JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and performance assessment in preliminary investigation phase. The topics and the conducted research are follows; (1) Study on selection of host rock: in terms of hydraulic properties, items for assessing rock property, and assessment methodology of groundwater travel time has been organized with interaction from site investigation. (2) Study on development of scenario: the existing approach has been embodied, in addition, the phenomenological understanding regarding dissolution of and nuclide release from vitrified waste, corrosion of the overpack, long-term performance of the buffer are summarized. (3) Study on setting nuclide migration parameters: the approach for parameter setting has been improved for sorption and diffusion coefficient of buffer/rock, and applied and tested for parameter setting of key radionuclides. (4) Study on ensuring quality of knowledge: framework for ensuring quality of knowledge has been studied and examined aimed at the likely disposal facility condition.
Kabumoto, Hiroshi; Takeuchi, Suehiro; Ishizaki, Nobuhiro; Yoshida, Takahiro*; Ishiguro, Takayuki*; Yamaguchi, Kazushi*
Proceedings of 6th Annual Meeting of Particle Accelerator Society of Japan (CD-ROM), p.1120 - 1122, 2010/03
The JAEA-Tokai tandem accelerator was built for basic science researches with heavy ions. Its superconducting booster was completed in 1994 for increasing the acceleration energy of ions. The booster consists of 40 superconducting acceleration resonators and 10 cryostats. Every resonator is a coaxial quarter wave resonator (QWR) of which frequency is 129.8MHz, and optimum beam velocity is 10% of the light velocity. When it was built, the acceleration field gradients of superconducting resonators were 5.0MV/m at RF power input of 4W on their average. The performance decrease little by little, and it become 4.0MV/m now. Some of the resonators generate X-rays from a low electric field. A field emission will be occurred from small contaminations accumulated on the surfaces of niobium. We examined the high pressure water jet rinsing (HPWR) to re-recondition the superconducting booster. The HPWR is the technology of removing small contaminations on resonator surfaces, and very effective for the improvement of acceleration field gradients. The acceleration field gradients of 20 on-line resonators were improved from 4.4MV to 5.7MV on their average.
Kabumoto, Hiroshi; Takeuchi, Suehiro; Ishizaki, Nobuhiro; Yoshida, Takahiro*; Ishiguro, Takayuki*; Yamaguchi, Kazushi*
Dai-22-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, p.129 - 132, 2010/01
The JAEA-Tokai tandem accelerator was built for basic science researches with heavy ions. Its superconducting booster was completed in 1994 for increasing the acceleration energy of ions. The booster consists of 40 superconducting acceleration resonators and 10 cryostats. Every resonator is a coaxial quarter wave resonator (QWR) of which frequency is 129.8 MHz, and optimum beam velocity is 10% of the light velocity. When it was built, the acceleration field gradients of superconducting resonators were 5.0 MV/m at RF power input of 4 W on their average. The performance decrease little by little, and it become 4.0 MV/m now. Some of the resonators generate X-rays from a low electric field. A field emission will be occurred from small contaminations accumulated on the surfaces of niobium. We examined the high pressure water jet rinsing (HPWR) to re-recondition the superconducting booster. The HPWR is the technology of removing small contaminations on resonator surfaces, and very effective for the improvement of acceleration field gradients. The acceleration field gradients of 20 on-line resonators were improved from 4.4 MV to 5.7 MV on their average.
Mitsui, Seiichiro; Oe, Toshiaki*; Inagaki, Yaohiro*; Okubo, Takahiro*; Kurosawa, Susumu*; Goto, Takahiro*; Inagaki, Manabu*; Ishiguro, Katsuhiko*; Takase, Hiroyasu*; Takahashi, Hirokazu*
no journal, ,
In order to develop robust performance assessment models, we have been preparing an information basis regarding glass properties and glass dissolution/alteration processes under disposal conditions as a part of NUMO-JAEA joint project. Our iterative working process for the preparation of the information basis comprises five steps: (1) integration of current knowledge; (2) development of glass dissolution scenarios based on current knowledge; (3) development of conceptual model; (4) sensitivity analyses to evaluate relative importance of relevant processes and associated uncertainties; and (5) identification of future R&D issues towards further improvement of the information basis. The current status will be presented in this talk.
Ishiguro, Takahiro; Hattori, Shushi*; Hattori, Tsukasa*; Shirahama, Takuma*; Ueda, Masashi
no journal, ,
In sodium cooled fast-reactors, opaque and highly chemical reactive sodium is used as coolant. Therefore, in the event of a loose part (dropped part) occurring, it is difficult to search and recover them under liquid sodium, potentially stopping the plant operation for a long time. The paper presents a prototype of the recovery mechanism, which is an important component of recover device for loose parts, and reports measurements and testing of it in liquid sodium.
Ueda, Masashi; Ishiguro, Takahiro*; Hattori, Shushi*; Hattori, Tsukasa*; Shirahama, Takuma*
no journal, ,
Sodium-cooled fast reactors need special maintenance technologies such as remote maintenance, under sodium viewer etc., because sodium is opaque, chemically active and the maintenance works must be performed in high temperature. To acquire basic knowledge for remote maintenance technology in liquid sodium, a trial product of recover device for loose parts was fabricated and tested in sodium. The positions of loose parts were approximately estimated by using ultrasound, and the parts were recovered by the device successfully.
Matsubara, Ryuta*; Fujisaki, Kiyoshi*; Ishida, Keisuke*; Ishiguro, Katsuhiko*; Inagaki, Yaohiro*; Okubo, Takahiro*; Mitsui, Seiichiro; Iwata, Hajime; Sekine, Nobuyuki*
no journal, ,
Restriction of radionuclide release by low dissolution rate is expected for the vitrified waste as a one of safety functions of the geological disposal system. In order to assess the performance of vitrified waste, it is important to understand how its safety function works under the environmental condition of a deep geological repository. This presentation provides the recent progress on the R&D to improve the current understanding of the key processes affecting glass dissolution rate and the predictive modeling of long-term behavior of the vitrified waste.
Matsubara, Ryuta*; Fujisaki, Kiyoshi*; Ishida, Keisuke*; Ishiguro, Katsuhiko*; Inagaki, Yaohiro*; Okubo, Takahiro*; Mitsui, Seiichiro; Iwata, Hajime; Sekine, Nobuyuki*
no journal, ,
Since the performance of vitrified High-level Radioactive Waste depends on thermal, hydraulic, mechanical, and chemical (THMC) conditions, NUMO, as the implementer of geological disposal, has been promoting R&D of operational model the long-term performance of vitrified High-level Radioactive Waste in consideration of THMC conditions. NUMO has identified R&D issues regarding the glass dissolution and planed the R&D program through FEP (Features, Events, and Processes) analysis and parametric study with numerical model to evaluate relative importance of relevant processes. At present, three R&D programs are ongoing as joint researches with JAEA and two universities: long term glass dissolution experiment to understand evolution of glass dissolution kinetics, glass dissolution experiment at various environmental conditions to assess the performance under several potential repository conditions with the time evolution, and molecular dynamics simulation to understand elemental migration at the interface between glass surface and groundwater. The current status of R&D programs will be introduced in this presentation.
Matsubara, Ryuta*; Ishida, Keisuke*; Fujisaki, Kiyoshi*; Ishiguro, Katsuhiko*; Inagaki, Yaohiro*; Okubo, Takahiro*; Iwata, Hajime
no journal, ,
In order to improve reliability of performance assessment of vitrified waste for geological disposal, we have been developing a model to predict the long-term glass dissolution under disposal conditions. This presentation provides our R&D plan and the recent progress.
