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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.
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：54 Percentile：71.62(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.
Washiya, Tadahiro; Tayama, Toshimitsu; Nakamura, Kazuhito*; Yano, Kimihiko; Shibata, Atsuhiro; Nomura, Kazunori; Chikazawa, Takahiro*; Nagata, Masanobu*; Kikuchi, Toshiaki*
Journal of Power and Energy Systems (Internet), 4(1), p.191 - 201, 2010/02
Japan Atomic Energy Agency (JAEA) and Mitsubishi Materials Corporation (MMC) are developing the crystallization process for elemental technology of FBR fuel reprocessing. The uranium (U) crystallization process is a key technology for New Extraction System for TRU Recovery (NEXT) process that was evaluated as the most promising process for future FBR reprocessing. We had developed an innovative crystallizer and fabricated an engineering-scale crystallizer and have carried out continuous operation test to investigate the stability of the equipment at steady and non-steady state conditions by using depleted uranium. As for simulating typical failure events in the crystallizer, crystal accumulation and crystal blockage were occurred intentionally, and monitoring method and resume procedure were tried and selected in this work.
Furusawa, Yoshiya*; Wang, X.*; Funayama, Tomoo; Kobayashi, Katsumi*; Imaseki, Hitoshi*; Takagi, Keiichi*; Nakamura, Masanobu*; Kashino, Genro*
no journal, ,
no abstracts in English
Shiotani, Hiroki; Sawazaki, Hiromasa; Nakamura, Yoshihide; Sato, Takeshi; Uchida, Takenobu; Arai, Masanobu
no journal, ,
We are evaluating operating data of about 20 years (Evaluation of "Monju Research Plan") through the collaboration of both older and younger engineers. In this study, we will propose the use of information technologies and/or statistics tools in future evaluation to make the data treatment in an effective and efficient manner. In addition to that, we will also present a vision for supporting and cooperating technical tradition and knowledge discovery, etc. nuclear engineers by machine learning technologies toward the commercialization of fast reactor cycle systems.
Choe, H.*; Mukai, Tomohisa*; Shobu, Takahisa; Ariki, Katsuyoshi*; Kinugasa, Hideyuki*; Takano, Yoshiki*; Sakashita, Masanobu*; Nakamura, Akihiro*
no journal, ,
no abstracts in English
Nakamura, Takemi; Tokunaga, Sho; Kikuchi, Masanobu
no journal, ,
Research reactor JRR-3 on Japan Atomic Energy Agency plans to replace the cold neutron source moderator vessel. Conceptual design for high-performance moderator vessel was carried out for the purpose of increasing the cold neutron source. Since the optimum geometry of the moderator vessel was determined by the nuclear characteristic analysis, its characteristics are reported.
Nakamura, Takemi; Tokunaga, Sho; Kikuchi, Masanobu
no journal, ,
JRR-3 plans to replace the moderator cell of cold neutron source. The purpose of improve the strength of the cold neutron source, a conceptual design was carried out to improve the performance of the moderator cell. Since the optimum shape was determined by nuclear characteristic analysis, the characteristics of the new moderator cell are introduced.
Tokunaga, Sho; Nakamura, Takemi; Kikuchi, Masanobu
no journal, ,
Research reactor JRR-3 on Japan Atomic Energy Agency plans to replace the cold neutron source moderator vessel. Conceptual design for high-performance moderator vessel was carried out for the purpose of increasing the cold neutron source. The optimum geometry determined by the nuclear characteristic analysis was evaluated by flow analysis. Its characteristics are reported.
Tokunaga, Sho; Nakamura, Takemi; Kikuchi, Masanobu; Noguchi, Hironori*; Oda, Yasushi*
no journal, ,
In order to examine a hydrogen flow analysis method for the high-performance moderator vessel including the entire CNS system, a pipe network analysis of the entire system including the moderator vessel using RELAP5/MOD3.2 and a CFD analysis of the moderator vessel using ANSYS-FLUENT which added physical models that were not considered in a conceptual design were evaluated in combination. The validity of these calculations was compared using Sudo's equation, which is in good agreement with the results of the out-of-reactor operating test in the current canteen bottle moderator vessel.
Nakamura, Takemi; Tokunaga, Sho; Kikuchi, Masanobu
no journal, ,
To improve the performance of the JRR-3 cold neutron source, we are developing a high-performance moderator vessel made of A6061. When the helium refrigerator stops and the cooling capacity of the condenser is lost, the supply of liquid hydrogen to the moderator vessel stops, and the temperature of the moderator vessel heated by decay gamma rays increases. The maximum temperature of the vessel must not exceed 100 degrees, because A6061 in the temperature range of 100 degrees or higher has lower mechanical strength and is easy to cause creep. We calculated the heat generation of the high-performance moderator vessel and evaluated the soundness of the vessel by calculating the temporal change in temperature of the vessel after the helium refrigerator was stopped.
Kikuchi, Masanobu; Nakamura, Takemi; Tokunaga, Sho; Oda, Yasushi*
no journal, ,
The vessel shape was changed from the conceptual design to take manufacturability into consideration. The inner surface of the vessel is filleted, and the flat section is reinforced and tapered. To verify its validity, check for plastic deformation at maximum pressure.
