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Hayano, Akira; Sawada, Atsushi; Goto, Junichi*; Ishii, Eiichi*; Moriya, Toshifumi*; Inagaki, Manabu*; Kubota, Shigeru*; Ebashi, Takeshi*
no journal, ,
Detailed Investigation Areas have to be selected with focusing on suitability of the host rock in the siting process for high-level radioactive waste disposal in Japan. The suitability of the host rock is evaluated in terms of the preferable disposal condition such as thermal, hydraulic, mechanical and geochemical condition, and the feasibility of the geological disposal project relevant to volumetric capacity of host rock and economics, based on the site model. However, due to a limited number of surveys at relatively early stage of the investigation, the lack of understanding of geological environment at the site causes an uncertainty of the site model. It is essential to clarify an association the important factors relevant to safety assessment (SA) and a repository design (Design) with the information obtained by the site investigation through the site model. In this study, the methodology not only for defining evaluation factors relevant to SA in term of hydrogeology, but also for visualizing the methods to evaluate the factors through the site model is organized into a tree diagram. A method to evaluate groundwater travel time which is one of evaluation factors in granitic rock is organized into a first version of the tree diagram.
I/
I ratiosTogo, Yoko*; Takahashi, Yoshio*; Amano, Yuki; Matsuzaki, Hiroyuki*; Suzuki, Yohei*; Muramatsu, Yasuyuki*; Iwatsuki, Teruki
no journal, ,
Radioactive iodine (I) is one of the available indexes of long-term migration of groundwater solutes, because of its long half-life (15.7 million years) and low sorption characteristics. All rock and groundwater samples were collected at Horonobe underground research center. Species of iodine in groundwater was mainly I
. I/I isotope ratios in groundwater were lower than that in rocks and almost constant at various depths, demonstrating that iodine in groundwater was released from deeper than co-existing rocks.
Sueoka, Shigeru; Kohn, B.*; Ikeda, Yasutaka*; Kano, Kenichi*; Tsutsumi, Hiroyuki*; Tagami, Takahiro*; Hasebe, Noriko*; Tamura, Akihiro*; Arai, Shoji*
no journal, ,
Thermochronometric methods are used to identify the denudation history of the Akaishi Range, which has been uplifted since the late Pliocene. ZHe grain ages range 21.5-3.0 Ma and systematically younger to the east, implying a westerly tilting uplift of the Akaishi Range. We estimated denudation rates at 1.2-2.2 mm/yr or more in the Akaishi Range. These high denudation rates imply the topography of the Akaishi Range reflects post-uplift factors, e.g., spatial distribution of bedrock uplift rates and various denudation processes, rather than inherited geometry from the pre-uplift topography. Considering younger AFT ages previously reported in the southern part of the Akaishi Range, the Akaishi Range is considered to have had at least two uplifting stages, i.e., uplifting of the northern part since the late Pliocene and uplifting of the southern part since 1 Ma, probably attributable to reverse faulting of ISTL and collision of the Izu block to the south Fossa Magna area, respectively.
Umeda, Koji; Kusano, Tomohiro; Asamori, Koichi; Sueoka, Shigeru
no journal, ,
Following the 2011 Tohoku earthquake, aftershocks occurred not only near the source fault along the plate boundary, but also inland along several active faults in the overriding plate. This indicates that the static stress change caused by the fault slip of the earthquake considerably affected the seismicity pattern in inland areas. Helium isotope data had been observed from the hot spring and drinking wells near the Tokamachi fault and Itoigawa-Shizuoka tectonic line before the Tohoku earthquake occurred. In order to elucidate a significant emanation of mantle helium from the seismicity regions induced by the Tohoku earthquake, we measured helium isotopes from 20 wells around the Tokamachi fault and part of the Itoigawa-Shizuoka tectonic line. In the vicinity of the Tokamoachi fault, most gas samples showed changes in 
He/
He ratios within 10%. In contrast, the wells near the Itoigawa-Shizuoka tectonic line indicate no significant change in the He/He and He/
Ne ratios.
Mizuno, Takashi; Iwatsuki, Teruki; Matsuzaki, Tatsuji
no journal, ,
This study is aimed to develop the methodology for estimation salinity distribution based on the resistivity logging along sub-surfaced boreholes drilled around Horonobe Underground Research Laboratory in Hokkaido, northern Japan. In addition, the technical knowledge and know-how learnt through this study were picked up for the development of Knowledge Management System. As the result, the procedure to estimate the salinity of groundwater is summarized as follows; (1) Discussion about the advisability of using the data of resistivity logging, (2) Conversion the resistivity data to salinity based on the math formula shown in previous studies, (3) Comparison between chemical analysis result and calculated result. The technical knowledge and know-how are accumulated during this study as follows; Calculated salinity based on deep induction data agrees well with analysis result, it is important that the resistivity between rocks and groundwater should be different in several classes.
Trumbore, S.*; Schrumpf, M.*; Khomo, L.*; Koarashi, Jun
no journal, ,
Carbon content usually declines, and its age increases, with depth in soil profiles. These patterns reflect the operation of several different depth-dependent processes. We compare the depth trends of carbon and C-14 in density-fractionated soils sampled from locations that vary in parent material/mineralogy and vegetation/climate and use whole-profile averages to identify patterns across a range of edaphic factors. The depth-profile of the free light fraction is similar to that of roots, and its age remains modern regardless of soil depth. In contrast, the radiocarbon age of C associated with minerals, or occluded within aggregates, increases in most soils almost linearly with depth. The slope of C-14 in the mineral fraction versus depth is potentially a metric useful for distinguishing among mechanisms responsible for C stabilization.