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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.
*; *; *; *; *; *; *
PNC TN9410 89-084, 61 Pages, 1989/03
A cold trap examination for measurements of dose rate, which purpose is to grasp the distribution of Captured oxygen impurity from the surface dose rate and distribution of nuclide, was carried out in the 6th and the 7th periodic Annual Inspection. The results obtained from this examination were as follows. (1)The surface dose rate of a new modeling Cold Trap at the 7th periodic Annual Inspection was about twice rate as much as the 6th. (2)
Na, 
C0, 
Mn, and 
Sb were detected from C0ld Traps. (3)The distribution of Co at a old modeling Cold Trap was same as the distribution of captured oxygen of CT4-1B which is mocked up for a old modeling Cold Trap of JOYO. Therefore the distribution at a Cold Trap will be expected that the distribution of Co is same as the distribution of captured oxygen impurity. (4)The new modeling Cold Trap was designed to Capture the oxygen impurity homogeneity at mesh territory. The distribution of Co at the new modeling Cold Trap was uniformed at mesh territory. Therefore, if there are the Correlation between the distribution of Co and the captured oxygen impurity, New modeling Cold Trap was displaied design function and Captured oxygen impurity homogeneity.
Kotaka, Yoshinori; *; *; *; *; *; *
PNC TN9410 88-108, 121 Pages, 1988/03
This paper describes operational experiences of Joyo Secondary Sodium Purification System which were obtained from September 1979 in the middle of the first annual inspection and maintenance to March 1987 in the middle of the 6th annual inspection and maintenance. The test results were as follows. (1)The impurities in the secondary sodium cooling system were oxygen and Hydrogen. The impurity density corresponded to the plugging-temperature. (2)The cold trap control temperature was changed from 150C to 130C on 16 May, 1982 in order to decrease corrosion due to the impurities in the secondary sodium cooling system. (3)The purification efficiency test of secondary cold trap was conducted on 26 through 29, December 1979. It was found that purification efficiency coefficient was 80%. While the test conducted, secondary cooling system was held at 200C constant. (4)Sodium charge in the secondary sodium purification system was conducted on 25 October 1980 and the secondary cold trap was started to be in use. In the secondary cold trap it was happened to be abnormal tendency, that is, the cold trap control temperature could not be abated to the set temperature, the heat exchange of economizer was not enough, and the mesh temperature changed. As a result of examination, the cause of the abnormal tendency was presumed that argon (Ar) gas space happened to exsist in sodium of secondary cold trap. The argon (Ar) gas space was supposed to be provided during the sodium drain in the secondary sodium purification system. Some recovery plant operation was proceeded ln order to reduce the argon (Ar) gas space out of the secondary cold trap. Thereafter, the secondary cold trap was operated without any trouble. (5)The number of cases of the secondary purification system trouble was 28. Among them, electrical troubles happened twelve times, mechanically oriented troubles happened sixteen times. Those troubles, however, did not affect to the ...
*; *; *; Kotaka, Yoshinori; *; *; *
PNC TN9410 88-045, 96 Pages, 1988/03
The Plugging Meter is used in JOYO Secondary Auxiliary Cooling System to monitor the sodium purity. This Plugging Meter have been operated more than 12 years since the coolant sodium was charged into JOYO Secondary Auxiliary Cooling System in 1975. Since its operation, some trouble conditions were observed and countermeasures have been taken. For these presume, the state of occurrence trouble conditions were investigated from 100MW 1st cycle operation to 100MW 14th cycle operation. The cause of some trouble conditions are as follows. (1)Increase of Plugging temperature during Reactor operation is supposed to be caused by unknown impurity precipitations except oxygen or hydrogen one. The unknown impurity is transfered from piping and component material in Secondary Auxiliary Cooling System after Reactor Power-up. (2)Sodium flow changes in Plugging Meter, like electric nois, are caused by gas into system sodium flow. (3)Sodium flow changes in Plugging Meter, in case that is not concerned with impurity precipitation, are caused by output voltage changes of the electromagnetic flow meter. This output voltage is shifted by sodium temperature changes. The researches and investigations of Plugging Meter in this system are continued to clear above and other specified matters, and take basically countermeasures.
Noguchi, Koji; Yasuo, Kiyoshi; Seto, Nobuhiko; Iwasaki, Shogo; Inami, Shinichi
no journal, ,
At the Tokai reprocessing plant, release of the low radioactive fluid to the ocean is carried out using sea release facilities. It was confirmed that there was a leak point on the sea release facilities. Therefore, check and investigation were performed and the leak point was identified. The leak part was cut and the part was then collected to investigate the cause of the leak. As a result, it was estimated that the leak occurred after the pipe was mechanically damaged and a successive change occurred on the part. For this leak point, a series of works for the cause investigation was carried out in detail, the repair work was performed, and preventive measures were taken against recurrences. This paper describes the summary of the sea release facilities, the situation of the outbreak of the leak, and the process that confirmed the leak point.
