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

https://doi.org/10.1038/s41550-020-01271-2

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.

Study on the behavior of radiolytically produced hydrogen in a high-level liquid waste tank of a reprocessing plant; Comparison between actual and simulated solutions

Kinuhata, Hiroshi*; Yamamoto, Masahiko; Taguchi, Shigeo; Surugaya, Naoki; Sato, Soichi; Kodama, Takashi*; Tamauchi, Yoshikazu*; Shibata, Yuki*; Anzai, Kiyoshi*; Matsuoka, Shingo*

Nuclear Technology, 192(2), p.155 - 159, 2015/11

https://doi.org/10.13182/NT15-15

Experiments using a small-scale apparatus with 30 ml actual high-level liquid waste from the Tokai Reprocessing Plant were carried out to show that the hydrogen concentration in the gas phase reaches a steady-state value of much less than 4% (lower explosive limit) in the absence of sweeping-air. The H concentration reached a steady-state value as was expected and it was compared with a value predicted from an equation with parameters which had been obtained using the simulated solution. Satisfactory agreement showed that the Pd-ion catalytic H consumption reaction previously found in the simulated solution proceeded equally well in the actual solution.

Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2010

Kunimaru, Takanori; Mikake, Shinichiro; Nishio, Kazuhisa; Tsuruta, Tadahiko; Matsuoka, Toshiyuki; Ishibashi, Masayuki; Ueno, Takashi; Tokuyasu, Shingo; Daimaru, Shuji; Takeuchi, Ryuji; et al.

JAEA-Review 2012-020, 178 Pages, 2012/06

JAEA-Review-2012-020.pdf:33.16MB

Japan Atomic Energy Agency (JAEA) at Tono Geoscience Center (TGC) is pursuing a geoscientific research and development project namely the Mizunami Underground Research Laboratory (MIU) Project in crystalline rock environment in order to construct scientific and technological basis for geological disposal of High-level Radioactive Waste (HLW). The MIU Project has three overlapping phases: Surface-based Investigation phase (Phase I), Construction phase (Phase II), and Operation phase (Phase III). The MIU Project has been ongoing the Phase II. And Phase III started in 2010 fiscal year. This report shows the results of the investigation, construction and collaboration studies in fiscal year 2010, as a part of the Phase II based on the MIU Master Plan updated in 2002.

Mizunami Underground Research Laboratory Project; Results of the borehole investigations to understand the geological environment in and around the Main-shaft fault

Tsuruta, Tadahiko; Takeda, Masaki; Ueno, Takashi; Daimaru, Shuji; Tokuyasu, Shingo; Onoe, Hironori; Shingu, Shinya; Ishibashi, Masayuki; Takeuchi, Ryuji; Matsuoka, Toshiyuki; et al.

JAEA-Technology 2012-001, 134 Pages, 2012/03

JAEA-Technology-2012-001.pdf:41.2MB
JAEA-Technology-2012-001(errata).pdf:0.44MB
JAEA-Technology-2012-001-appendix(CD-ROM).pdf:6.37MB

Tono Geoscientific Research Unit of Japan Atomic Energy Agency (JAEA) is performing the Mizunami Underground Research Laboratory (MIU) project in order to establish comprehensive techniques for the investigation, analysis and assessment of the deep geological environment in fractured crystalline rock. The borehole investigations (two boreholes; 10MI22 borehole and 10MI23 borehole) have been carried out to obtain information on geological, hydrological and hydrochemical characteristics in and around the Main-shaft fault. These investigations provided that features of fracture and alteration on rock mass in and around the Main-shaft fault. Hydrological and hydrochemical properties based on the geological features were also obtained.

Measurement and analysis of radiolytically generated hydrogen from HALW, 1; Measurement and evaluation of the hydrogen concentration in the vessel off-gas

Tomiyama, Masahiro; Yasuda, Takeshi; Tsutagi, Koichi; Yoshino, Yasuyuki; Shirato, Yoji; Nakamura, Yoshinobu; Kinuhata, Hiroshi*; Kodama, Takashi*; Nakano, Masanao*; Tamauchi, Yoshikazu*; et al.

no journal, , 

no abstracts in English

The Inhibitory effect of hydrogen release from high active liquid waste, 3; Estimation of the hydrogen concentration of upper space of tank

Kodama, Takashi*; Nakano, Masanao*; Hayashi, Yoshiaki*; Matsuoka, Shingo*; Ito, Yasuo*; Matsuura, Chihiro*; Shiraishi, Hirotsugu; Katsumura, Yosuke*

no journal, , 

We report here an evaluation for hydrogen concentration that may be attained in the upper space of the high-level liquid waste tank when the gas sweeping function happens to be lost. The parameters are the rate of radiolytic production of hydrogen, the rate of Pd-catalyzed hydrogen consuming reaction, and the solubility of hydrogen. For the first, a literature value on nitric acid solution was used, while for the second and third, experimental estimate was made in the present study with mock high-level liquid waste. All data have been taken at ambient temperature. For simplicity, it was assumed that both the gas and the liquid are homogeneous, and that the two phases are in equilibrium regarding hydrogen concentration. These led to an estimate of 0.6% for the hydrogen concentration in the gas phase, a value smaller than the lower limit of explosion.

Measurement of radiolytically generated hydrogen from HALW and analysis of the inhibitory effect on hydrogen release, 1; Measurement of hydrogen concentration and its evaluation

Yamamoto, Masahiko; Taguchi, Shigeo; Surugaya, Naoki; Sato, Soichi; Kinuhata, Hiroshi*; Tamauchi, Yoshikazu*; Shibata, Yuki*; Kodama, Takashi*; Matsuoka, Shingo*

no journal, , 

no abstracts in English

Spectral characteristics of asteroid (162173) Ryugu with Hayabusa2 NIRS3

Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.

no journal, , 

JAXA spacecraft and sample return mission Hayabusa2 has arrived at the near-Earth asteroid 162173 Ryugu, which is classified a primitive carbonaceous object. Here we report recent results of near-infrared spectrometer (NIRS3) on the Hayabusa2 spacecraft. The observations provide direct measurements of the surface composition of Ryugu and context for the returned samples. NIRS3 has detected a weak and narrow absorption feature centered at 2.72 micrometer across entire observed surface. This absorption feature is attributed to the presence of OH-bearing minerals. The NIRS3 observations also revealed that Ryugu is the darkest object to be observed up-close by a visiting spacecraft. The intensity of the OH feature and low albedo are consistent with thermally-and/or shock-metamorphosed, and/or carbon-rich space-weathered primitive and hydrated carbonaceous chondrites.

Study on hydrogeological structure around the Mizunami Underground Research Laboratory (MIU) site using self-potential method

Tokuyasu, Shingo; Matsuoka, Toshiyuki; Mizunaga, Hideki*; Sugimoto, Yoshihiro*

no journal, , 

no abstracts in English

Study on release and transport of aerial radioactive materials in reprocessing plant, 8; Cold large scale test

Abe, Hitoshi; Masaki, Tomoo; Watanabe, Koji; Suzuki, Shinya; Tashiro, Shinsuke; Amano, Yuki; Yamane, Yuichi; Yoshida, Kazuo; Uchiyama, Gunzo; Ueda, Yoshinori*; et al.

no journal, , 

The release and transport characteristics of radioactive materials under the boiling and desiccating accident of the high active liquid waste in a reprocessing plant have been studied. Ruthenium is one of the important nuclides for evaluating public dose from the volatile viewpoint. By using apparatus which can control the experimental condition of temperature and atmosphere composition in the gas phase, the transport characteristics data of RuO which is chemical form of Ru with volatility was acquired. As the results, it was found that RuO would transport in the gas phase without thermal decomposition and deposition onto the inner wall of glass under the experimental condition with nitric acid vapor.