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Sasaki, Takayuki*; Kokami, Takayuki*; Kobayashi, Taishi*; Kirishima, Akira*; Murakami, Hiroaki; Amano, Yuki; Mizuno, Takashi; Iwatsuki, Teruki; Sasamoto, Hiroshi; Miyakawa, Kazuya
Journal of Nuclear Science and Technology, 54(3), p.373 - 381, 2017/03
Trace amounts of natural thorium and uranium in deep groundwater were investigated at two underground research laboratories situated at Horonobe and Mizunami, Japan. The groundwater was sampled from underground boreholes, and the colloid contribution was checked by in situ two size-fractionated ultrafiltration systems. A decrease in the concentration after in situ filtration suggested the presence of natural colloids and suspended matter that were carriers of a portion of the elements. The result of the Th and U concentrations in groundwater after 10 kDa filtration was analyzed thermodynamically using existing hydrogeological and geochemical data such as the mineral components in the groundwater at a given pH, ionic strength, concentration of co-existing ions, redox potential, and solid phase assumed. A crystalline solid phase made the solubility very low compared with that of the amorphous phase, and the solubility agreed well with the concentrations measured.
Kokami, Takayuki*; Sasaki, Takayuki*; Amamiya, Hiroki; Murakami, Hiroaki; Amano, Yuki; Iwatsuki, Teruki; Mizuno, Takashi; Kubota, Takumi*; Kirishima, Akira*
no journal, ,
no abstracts in English
Murakami, Takuma; Mizuno, Takashi; Sasamoto, Hiroshi; Kokami, Takayuki*; Sasaki, Takayuki*
no journal, ,
no abstracts in English
Sasaki, Takayuki*; Kokami, Takayuki*; Amamiya, Hiroki; Murakami, Hiroaki; Amano, Yuki; Iwatsuki, Teruki; Mizuno, Takashi; Kobayashi, Taishi*; Kirishima, Akira*
no journal, ,
For thermodynamic analysis of the trace metals in groundwater, concentrations of Th, U, and rare earth elements (REEs) were investigated at Horonobe Underground Research Laboratory. Groundwater was sampled in anaerobic condition directly from a packed section in the boreholes drilled to 140 m and 250 m depth in drift. The colloidal distribution was checked by an on-site batch ultrafiltration unit using 0.2 
m or 10 kDa membranes. As the result, both Th and U concentrations could be estimated by thermodynamic calculations, assuming that the soluble solid phases are restricted to ThO
(cr) and UO(cr), respectively. Meanwhile, the concentrations of REEs were also very low, and significant colloidal distribution for lighter REEs was observed. In the thermodynamic analysis where the lanthanide phosphate was assumed to be a solid phase, the experimental plots matched better with the calculated one, even though the changing trend differs from each other.
