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.

Enhancement of the methodology of repository design and post-closure performance assessment for preliminary investigation stage, 2; Progress report on NUMO-JAEA collaborative research in FY2012 (Joint research)

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.

Enhancement of the methodology of repository design and post-closure performance assessment for preliminary investigation stage; Progress report on NUMO-JAEA collaborative research in FY2011 (Joint research)

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.

Recovery of acceleration field gradients of superconducting booster resonators by high pressure water jet rinsing

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.

CARS study of deuterium clusters stabilized in solid helium

Gordon, E. B.*; Kumada, Takayuki; Ishiguro, Masazumi; Aratono, Yasuyuki

Journal of Experimental and Theoretical Physics, 99(4), p.776 - 783, 2004/10

The solid Deuterium clusters for the first time isolated in a matrix of solid Helium have been investigated at T = 1.3K and P = 3 MPa by CARS (Coherent anti-Stokes Raman spectroscopy) technique. The Q1(J=0) and Q1(J=1) lines intensity, shape and positions have been studied as the functions of ortho- para content in the solid, as well as of clusters size. The strong effect of Raman scattering cross section sensitivity to the molecular environment nuclear spin state has been found in CARS; the ratio of probabilities for the scattering by para (J=1) and ortho (J=0) deuterium being equal to 1 in a gas is as high as 10,000 in nearly pure o-D2, whereas it is about 50 in spontaneous Raman scattering. This effect has been shown to give rise starting from cluster size corresponding to the phonon band onset.

A Study and Modeling about Ground Water Flow Considering the Properties of Sedimentary Soft Rock

Inoue, Hiroyuki*; Ishiguro, Takeshi*; Kuji, Masayoshi*; Yoshino, Naoto

JNC TJ8400 2004-013, 137 Pages, 2004/02

JNC-TJ8400-2004-013.pdf:22.48MB

In this paper, authors examined the properties of sedimentary soft rock which might affect the groundwater flow rate and flow path in the sedimentary soft rock. As a general sample of sedimentary soft rock, we focused on the rock of HORONOBE area in HOKKAIDO prefecture. Then, following four issues were examined. 1) a study of numerical flow rate analysis considering the difference of water density in the sedimentary soft rock. 2) the hydro-geological modeling of HORONOBE area and a fundamental study of water pressure and saline density in HORONOBE area. 3) a fundamental study of numerical coupling analysis about groundwater flow rate ,the difference of underground temperature, rock pressure and deformation. 4) a study about best performance of numerical flow rate analysis program. As a result, hydro-geological modeling of HORONOBE area using the information before 2002 as input data was succeeded by using the basic geological model which was made by IMAI et al,. And the applicability of TOUGH2 program as analysis method considering the density difference of underground water in sedimentary soft rock was verified. Then, we will be able to simulate underground flow considering the difference of saline density and specific water pressure in HORONOBE area. In addition, the applicability of TOUGH-FLAC program in which TOUGH2 was coupled with FLAC3D and consider rock pressure and deformation was verified. The best numerical performance of TOUGH2 program was studied in order to deal with large scale simulations. Then, it was shown that efficient method of the best numerical performance about TOUGH2 was possible.

None

Shibutani, Tomoki; Yoshikawa, Hideki; Sato, Haruo; Yui, Mikazu; Umeki, Hiroyuki; Ishiguro, Katsuhiko

PNC TN8410 92-163, 51 Pages, 1992/09

PNC-TN8410-92-163.pdf:1.18MB

None

Production of fast reactor group constant set JFS3-J3T and analysis of ZPPR-9

Takano, Hideki*; Kaneko, Kunio*; Ishiguro, Yukio*

PNC TJ9500 89-001, 75 Pages, 1989/03

PNC-TJ9500-89-001.pdf:1.82MB

The fast reactor 70-group constant set JFS-3-J3T has been generated by using the JENDL-3T nuclear data. One-dimensional benchmark calculations and the analyses of the ZPPR-9 and FCA-VI-2 assemblies were performed with the JFS-3-J3T set. The results obtained are summarized as follows: (1)The k's are underestimated by 0.6% for Pu-fuel cores and overestimated by 2% for U-fuel cores. (2)The central reaction rate ratio (Pu-239)/(U-235)is in a good agreement with the experimental value and (U-238)/(Pu-239) is overestimated. (3)Doppler and Na-void reactivities are in a good agreement with the measured data. (4)The radial reaction rate distributions are improved in the comparison of the results obtained with the JENDL-2 data. Furthermore, the benchmark test of JENDL-3T/Rev.1 which was revised for several important nuclides on the basis of the results described above has been performed. It was shown that JENDL-3T/Rev.1 predicted nuclear characteristics more satisfactory than JENDL-2, excepting the overestimate for the reaction rate ratios of (U-238)/(Pu-239) and (U-238)/(U-235).

Experimental Approach to Performance of Engineered Barriers under Repository Conditions

Ishiguro, Katsuhiko; Kawamura, Kazuhiro; Sonobe, Hitoshi; Nodaka, Masayuki*; Arai, Takashi; Yusa, Yasuhisa; Tsunoda, Naomi

PNC TN8410 87-071, 37 Pages, 1987/08

PNC-TN8410-87-071.pdf:0.62MB

Experimental studies have been carried out in order to evaluate durability of engineered barriers in geological disposal system. These are as follows; (1) Leaching behavior of waste borosilicate glass. Leaching experiments of simulated waste glass were carried out for more than one year in both scale of laboratory and of engineering. The leachability was suppressed under the condition of high SA/V (the surface area of glass/leachant volume). Saturation of leachant with silicon reduces leaching rates of the other elements. (2) Corrosion behavior of candidate overpack materials. Corrosion behavior of carbon steel and titanium was studied in synthetic groundwater with or without bentonite. No localized corrosion was observed in both the materials. Corrosion rate of carbon steel depends on bentonite/water ratio. Crevice corrosion resistance of titanium and its alloy was also studied. (3) Permeability of compacted bentonite as buffer material. Hydraulic conductivity of saturated compacted bentonite decreases and the swelling pressure increases with the increase of density. Influence of cracks on permeability was also studied, and significant effect was not observed. Infiltration of water into dry compacted bentonite was also studied to evaluate permeability of buffer material at the initial stage of disposal.

Critical experiments and analysis of homogeneous heavy water system; 20% enriched U-DO reflector

Hirota, Jitsuya; Kuroi, Hideo; Goto, Yorio; Furuhashi, Akira; Yasuno, Takehiko; Yamamoto, Ken; Mitani, Hiroshi; Obu, Makoto; Ichimori, Toshihiro; Koyama, Kinji; et al.

JAERI 1034, 50 Pages, 1962/08

JAERI-1034.pdf:3.64MB

no abstracts in English