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JAEA Reports

Design and safety assessment of cooling facilities for air system

Asano, Norikazu; Nishimura, Arashi; Takabe, Yugo; Araki, Daisuke; Yanai, Tomohiro; Ebisawa, Hiroyuki; Ogasawara, Yasushi; Oto, Tsutomu; Otsuka, Kaoru; Otsuka, Noriaki; et al.

JAEA-Technology 2021-045, 137 Pages, 2022/06

JAEA-Technology-2021-045.pdf:2.97MB

A collapse event of a cooling tower for secondary cooling system in the Japan Materials Testing Reactor (JMTR) was caused by the strong winds of Typhoon No.15 on September 9, 2019. As measures against the event, the working group for the renewal of the UCL (Utility Cooling Loop) cooling tower was established in the department of JMTR, and the integrity of the UCL cooling tower, which is the same type of wooden cooling tower as the secondary cooling tower in the JMTR, was investigated. As a result of this investigation, we have decided to replace the existing UCL cooling tower with a new cooling system. After investigations, in order to reduce the risk of collapse due to wood decay, the new cooling system was installed as a component of the air system to be managed as a performance maintenance facility after decommissioning. This report describes the design of and the evaluation results of the facility.

JAEA Reports

Microbial activity in the subsurface environment of the Tono area and its relation to geochemical conditions -Study of the abundance and diversity of groundwater microorganisms-

Naganuma, Takeshi*; Iwatsuki, Teruki; Murakami, Yuki; Hama, Katsuhiro; Okamoto, Takuji*; Tanimoto, Daisuke*; Fujita, Yuka*; Watanabe, Fumiko*; Adachi, Nahomi*; Sato, Makoto*

JNC TY7400 2003-001, 116 Pages, 2003/05

JNC-TY7400-2003-001.pdf:4.97MB

The abundance and diversity of groundwater microorganisms was studied in the Tono area, central Japan. Total cell counts were estimated by epifluorescence microscopy. Cell viability, based on cell membrane integrity, respiration-based metabolism, and esterase activity was estimated to be from 0.001% to approximately 100% of the total counts. The distribution of microbial abundance wad related to a variety of environmental factors, including fracture numbers, hydrological, and geochemical conditions in the groundwater. In the groundwater, profiles of redox sensitive solutes such as sulphate and sulphide ions, abundance and viability of microbes, and sulphur isotope rations of sulphate ions suggest that microbial sulphate redution involving organic matter and subsequent pyrite precipiration are dominant redox reactions at the depths of the uranium ore body. Concentrations of both the sulphate and chloride increase with increasing depth. The dissoloved sulphate is surmised to have originated from dissolution of sulphate and sulphide minerals in a geologic marine formation precipitated in marine environments, in the upper part of the sedimentary rocks. Such a redox process in the water-mineral-microbe system is inferred to have continued from the time when the marine formation underwent uplift above sea-level, because sulphate-reducing bacteria can use sulphate ions dissolved in fresh water that infiltrates from the marine formation and organic matter located in the deeper sedimentary rocks. Calculations by using the sulphate-S contents of the rocks and the sulphate dissolution rate suggest that microbial sulphate redution alone could maintain sufficiently reducing conditions of preserve the uranium ore for several hundred thousand years, in the case where a hydrogeological system continues to exist without much change. On the other hand, iron-oxidizing/reducing bacteria seem to play an important role in iron redox cycling in the granite groundwater.

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