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Ishido, Akio*; Hasegawa, Ken*; Hanaki, Tatsumi*; Ochiai, Yoji*; Shigeta, Naotaka*; Nagasaki, Yasushi*
JNC TN7400 2005-022, 224 Pages, 1996/04
JNC-TN7400-2005-022.PDF:9.36MB
None
Tsubota, Koji*; Ochiai, Yoji*; Hasegawa, Ken*; Nagasaki, Yasushi*; Yamagishi, Akiko*; Nakano, Katsushi*; Muneto, Masaru*
JNC TN7400 2005-021, 166 Pages, 1995/04
JNC-TN7400-2005-021.PDF:7.06MB
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Tsubota, Koji*; Ochiai, Yoji*; Hanaki, Tatsumi*; Hasegawa, Ken*; Okita, Masatoshi*; Koide, Kaoru*; Nagasaki, Yasushi*
JNC TN7400 2005-019, 114 Pages, 1993/04
JNC-TN7400-2005-019.PDF:7.46MB
None
Nohara, Tsuyoshi; Seo, Toshihiro; Ochiai, Yoji
PNC TN7410 91-030, 28 Pages, 1991/09
The Tsukiyosi uranium deposit, which is called Tertiary sandstone-type, can be regarded as a potentially useful analogue for geological isolation of radioactive wastes in Japan. In order to understand the geochemical behaviour of U-series nuclides (U-238, U-234, Th-230, Ra-226) under reducing condition, a study on radioactive disequilibrium of rocks was carried out. A total of 185 rock specimens were collected from 6 boreholes and gallery in the uranium mineralized zone, which is situated in paleo-river system, in the direction of east-west. In the system of groundwater flow, the mineralized zone was divided into four: the upper, the middle, the lower, and the lowermost reaches from the west to the east. The initial mineralization were occurred at the period of 10 Ma, and mostly focused on the middle reaches. The following results are obtained by the chemical analysis and alpha and gamma spectorometry. Activity ratios of U-234/U-238 and Th-230/U-234 (for 185 specimens) are mostly within the range of 1.2 and 0.8. In the middle reaches to lower reaches of groudwater flow, activity ratios of Th-230/U-234 are occasionally less than unity. In the middle reaches, the ratios of Th-230/U-234 are less than unity at particularly highly mineralized parts, while the ratios are nearly equal to unity at poorly mineralized parts. Activity ratios of Ra-226/Th-230 (for 185 specimens) were a wide range between 0.6 and 5.1. Combination of the result above-mentioned with chemical properties and decay constants of the nuclides leads to the following conclusions. (1)Uranium and thorium have not migrated significantly during the last one million years. The magnitude of the uranium migration is probably within the range of several ten centimeter. (2)Uranium at the middle to lower reaches has been concentrated during the past several hundred thousand years. It is noteworthy that uranium of severely mineralized parts at the middle reaches have highly redistributed. (3)Radium has been probabl
Tanigawa, Hiroyasu; Someya, Yoji; Sakasegawa, Hideo; Hirose, Takanori; Ochiai, Kentaro
no journal, ,
The practical implementation of F82H pertaining to the element control and mechanical properties was reviewed, and the reduced activation level was discussed based on the data. It is found that Ni is the element that should be removed to reduce the activation levels, while preventing contamination during the melting process is essential for reducing Ni concentrations. Another element discussed is N. The amount of 
C transmuted from N must be reduced to achieve the shallow land burial limit. However, N plays an important role in the realization of high-temperature properties. Furthermore, at least 100 ppm of N will remain in the steel when large-scale melting by electric arc furnace is employed. Using Al for deoxidation of the RAFM steel has no significant impact on the activation levels, and the impact of the minor elements such as Ag is negligible compared to that of Ni and N. There is no way to reduce the decay heat by an order of magnitude because the main source elements of the decay heat are the key elements of RAFM, which cannot be reduced.