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.

A Consideration on the use of shear waves to improve the sensitivity of an optical ultrasonic sensor for under-sodium viewers

Saruta, Koichi; Shirahama, Takuma*; Yamaguchi, Toshihiko; Ueda, Masashi

E-Journal of Advanced Maintenance (Internet), 10(2), p.1 - 8, 2018/08

http://www.jsm.or.jp/ejam/Vol.10No.2/AA/AA148/AA148.html

R&D of multi-frequency ECT algorithms for FBR SG tubes

Mihalache, O.; Yamaguchi, Toshihiko; Shirahama, Takuma; Ueda, Masashi

E-Journal of Advanced Maintenance (Internet), 9(2), p.60 - 65, 2017/08

Effects of metallic diaphragms on sensitivity characteristics of an optical ultrasonic sensor and reduction of interrogation time based on wavelength division multiplexing for under-sodium visual inspection

Saruta, Koichi; Yamaguchi, Toshihiko; Ueda, Masashi

E-Journal of Advanced Maintenance (Internet), 7(4), p.NT75_1 - NT75_8, 2016/02

http://www.jsm.or.jp/ejam/Vol.7No.4/NT/NT75/75.html

Experimental measurements and simulations of ect signal for ferromagnetic SG tubes covered by a sodium layer

Yamaguchi, Toshihiko; Mihalache, O.; Ueda, Masashi

Electromagnetic Nondestructive Evaluation (XVII), p.144 - 154, 2014/00

https://doi.org/10.3233/978-1-61499-407-7-144

For a Fast Breeder Reactor (FBR) cooled by liquid sodium, the wall of steam generator tubes (SG) is the only barrier between sodium in the tubes vessel and water inside of tubes. By using eddy currents, the SG tube integrity is usually assured during the In-Service Inspection (ISI). During this procedure, the 500 degrees sodium is drained and then SG tubes cooled down slowly in 2 weeks to room temperature. After sodium draining, sodium adheres to SG tubes and other structures in the SG vessel in thin layers. Experimental data shows that sodium drops also appear in specific areas along tubes or tube support plates. The high electrical conductivity of sodium adhering to the outer SG tube surface influences the ECT signal according to sodium layer thickness or sodium deposits located on the outer SG tube surface. The sodium adhering properties depends on several factors among them being the surface roughness of tube material, sodium temperature and wetting time. The ECT effect of sodium adhering to the outer SG tube surface was measured using a small mock-up tank in which were introduced SG tubes similar with the ones in FBR (2.25Cr-1Mo alloy). Defects and support plates were added to tubes and ECT signal was measured before and after sodium draining. Variations in the sodium layer thickness and consequently its ECT effect were measured by filling and draining the tank three times in order to recreate each time new layers of sodium. The paper describes the experimental conditions for defects, SG support plates signal before and after draining of sodium. Additionally, sodium structures were visualized using a CCD camera, confirming the recorded ECT signals. The paper presents details about sodium layer measurements for several parts of the SG tubes by scratching and collecting the sodium on small areas 10x10 square mm. Numerical 3D simulations are performed using a 3D FEM code developed in our laboratory in order to validate the performance of the ECT sensors detection.

Functional test of the ISI system for pipes of MONJU primary heat transfer system

Maeda, Yukihiro; Yamaguchi, Toshihiko; Ueda, Masashi; Fujiki, Kazunari*

Nihon Hozen Gakkai Dai-10-Kai Gakujutsu Koenkai Yoshishu, p.599 - 601, 2013/07

An inspection system was developed for in-service inspection (ISI) of pipes in the primary heat transfer system of MONJU FBR. The system was updated and modified based on experience from the pre-service inspection and related tests. This paper describes the results of the functional tests of the new inspection system on a mockup and in MONJU, which confirmed it can satisfy the expected performance.

Development of inspection and repair technology for the micro cracks on heat exchanger tubes

Nishimura, Akihiko; Shobu, Takahisa; Oka, Kiyoshi; Yamaguchi, Toshihiko; Shimada, Yukihiro; Mihalache, O.; Tagawa, Akihiro; Yamashita, Takuya

Reza Kako Gakkai-Shi, 17(4), p.207 - 212, 2010/10

A prototype probe system with a hybrid optical fiber scope was designed for inspecting and re-pairing the micro cracks on heat exchanger tubes in fast breeder reactors (FBRs). It comprised a laser processing head combined with an eddy current testing unit. Ultrashort laser pulse ablation was used to remove work-hardened layers. And spot laser welding was used to repair the micro cracks. This system has both safe and economical options for the maintenance of FBRs because it extends the lifetime of the heat exchangers.

Development of inspection and repairing technology for FBR heat exchanger tubes, 2; Preparation of operation software and performance check

Nishimura, Akihiko; Oka, Kiyoshi; Yamaguchi, Toshihiko; Akatsu, Tomohiro*; Seki, Takeshi*; Mihalache, O.; Shimada, Yukihiro; Tagawa, Akihiro; Yamashita, Takuya

Nihon Hozen Gakkai Dai-6-Kai Gakujutsu Koenkai Yoshishu, p.250 - 253, 2009/08

In order to maintain FBR heat exchanger tubes, a new probe system was designed. A coupling unit and operational software are key components in the second year. The coupling unit to combine a high energy laser beam and optical fiberscope images was developed. The operational software successfully controlled an eddy current testing device and a laser processing head.

Development of the Kiso river delta during the last 10,000 years based on analyses of sedimentary cores and C datings

Ogami, Takashi*; Sugai, Toshihiko*; Fujiwara, Osamu*; Yamaguchi, Masaaki*; Sasao, Eiji

Chigaku Zasshi, 118(4), p.665 - 685, 2009/00

https://doi.org/10.5026/jgeography.118.665

The depositional process of the latest Pleistocene to Holocene shallow marine and fluvial sequences is investigated by using five drill cores from the Kiso river delta, central Japan. Based on facies analysis, the sediments were classified into 5 units; A: basal gravel, B: fluvial to intertidal sand and silt, C: transgressive lag deposit, prodelta mud or sandy silt, D: delta-front-slope sandy silt or sand, delta-front-platform sand, E: delta-plain to fluvial sand and silt. Detailed age-depth curves of each cores are reconstructed based on 107 AMS C ages. The curves are divided into four sections; I: mainly consists of unit B with rapid accumulation (7.3-21.4 mm/yr), II: mainly consists of unit C with moderate accumulation (2.4-2.8 mm/yr), III: mainly consists of unit D with rapid accumulation (6.7-17.8 mm/yr), IV: consists of unit D and E with moderate accumulation (1.3-3.9 mm/yr). The section boundaries of I/II and II/III reflect inundation into the bay and achievement of progradational delta-front slope, respectively. The expanding rate of the bay is 10 m/yr during 10,200-7,900 cal yrs BP. The progradation rates of the delta are 3-4 m/yr (6.500-4,100 cal yrs BP), 5 m/yr (4,100-1,300 cal yrs BP), 10 m/yr (1,300 cal yrs BP to the present). These indicate the transition from transgression to regression occurred between 7,800 to 7,300 cal yrs BP. The geological cross section along the Kiso river coupled with isochrones indicates following history. (1) 10,000-7,280 cal yrs BP (K-Ah horizon): During the expansion of the bay, onlap of unit C on unit B is visible, and unit C overlapped all the core sites. (2) 7,280 cal yrs BP to present: Isochrones younger than 6,500 cal yrs BP are similar each other and cross unit boundaries of C/D and D/E. This demonstrates units C, D and E are contemporaneous heterotopic facies formed by progradational delta.

High power test of 972 MHz waveguide systems for J-PARC Linac

Hori, Toshihiko; Yamazaki, Masayoshi; Yamaguchi, Seiya*; Hasegawa, Kazuo; Linac RF Group

NIFS-MEMO-55, p.289 - 292, 2008/03

no abstracts in English