HCG34-01

Room:101A

Time:May 26 09:00-09:15

Formative process of fracture in granite on the basis of geological history at the Toki
Granite, central JapanSASAO, Eiji1∗ ; ISHIBASHI, Masayuki1 ; YUGUCHI, Takashi11Japan Atomic Energy Agency

Fractures in the crystalline rock (e.g. granite) can act as groundwater pathways. Therefore, understanding of the fracture
characteristics (e.g. frequency distribution and infilling minerals) is an important subject for the disposal of high-level nuclear
waste. Geological setting and formation process of the granite can influence the fracture characteristics. Thus, this study discuss
the relation between ’the formation of fracture and infilling mineral’ and geological history from the emplacement to present in
the Toki granite, Tono district, central Japan.
The thermochronology for the Toki granite (Suzuki and Adachi, 1998; Shibata and Ishihara, 1979; Yuguchi et al., 2011) andthe age determination for the basal layer of the Mizunami Group overlaying unconformably the Toki granite (Sasao et al., 2006)
gave the geological history (especially, cooling history) of the granitic pluton. The Toki granite cooled rapidly during about 20
million years after the emplacement to about 250 o C, and then the granite underwent exhumation with slowly cooling during
about 50-30 million years until the subaerial exposure.
Brittle fractures occurred below the temperature of about 300 to 400 o C in the cooling granite, and thus the fracture fillingminerals also occurred below such temperature. The fracture fillings collected from the Toki granite are hydrothermal mineralssuch as chlorite and mica clay mineral, hydrothermal and meteoric water-derived calcite. The hydrothermal calcite occurs inaccompany with plagioclase sericitization in the country rock, that is, such calcite was produced by supplement of anorthite(Ca) component form plagioclase through the hydrothermal fluid (Ishibashi et al., 2014). Chloritization temperature in theToki granite ranges from about 200 to 300 o C (Yuguchi et al., in press), which is indicator of formation temperature of thehydrothermal fracture fillings. The meteoric water-derived calcite was produced during the process in which the meteoric water
seeped underground through the fractures in the granite. This phenomenon occurred in a period between the sedimentation of
the Mizunami Group (20Ma) and present.
Reference
Ishibashi et al., 2014, Jour. Japan Soc. Engin. Geol., 55, 156-165.
Sasao et al., 2006, Jour. Geol. Soc. Japan, 112, 459-468.
Shibata and Ishihara, 1979, Geochem. Jour., 13, 113-119.
Suzuki and Adachi, 1998, Jour. Metamorphic Geol., 16, 23-37.
Yuguchi et al., 2011, Contrib. Mineral. Petrol., 162, 1063-1077.
Yuguchi et al., in press, Amer. Mineral. (DOI: http://dx.doi.org/10.2138/am-2015-5126).

Keywords: fracture, Toki Granite, geological history

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HCG34-02

Room:101A

Time:May 26 09:15-09:30

Significance of the Hydrogeological Compartment Structure in the Geological Disposal
Program
TAKEUCHI, Shinji1∗ ; KIJIMA, Mifumi1
1

Nihon University

As lots of major faults of low permeable fault core with higher permeable damaged zone on both side of the fault core havebeen reported in Japan, the fault compartment could generally exists. The existence of the fault core and damage zone could
result in permeability contrasts between perpendicular and parallel to the fault zone.
In hydrogeological characterization of a potential disposal site, one of the specific concerns is to understand what happens if
an underground facility is constructed in the fault compartment bounded by low permeable faults (hydrogeological compartment
structure (HGCS)) within a fractured rock. Groundwater cannot easily flow into such HGCS from its surroundings, causing ahuge drawdown in the HGCS. Hydraulic gradient and flow velocity would be lower value in the HGCS.
The existence of HGCS at a regional scale has also been suggested around the Mizunami area. Changes in static pressure
heads and pressures in response to earthquake and cross-hole pumping test have been observed within a larger block bounded by
the faults and/or lineaments.
If the HGCS could widely be distributed in Japan, site suitability of the HGCS for a high-level radioactive wastes (HLW)
repository should be evaluated by the site characterization
In this study we extracted fault compartment in Japan based on the Geomap Navi released by AIST. The extracted compartment
structures are about 1,400 from Hokkaido to Kyushu district. Based on the histogram of the size of the compartment structure,
the abundant size in Japan is 2.25-9 km2 except for the Shikoku district. This size is almost correspond to the HLW repository
area
Lower hydraulic gradient and flow velocity inside the HGCS could be suitable for the repository from hydrogeological view
point, while slow recovery of the groundwater in the structure causing the long duration of the oxidation condition could not besuitable from the hydrochemical view point. Characterization of the bounded fault of the HGCS should be studied in detail ineach case. Prediction of the groundwater flow and mass transport by the numerical simulations are also needed.

Keywords: hydrogeological copartment structure, geological disposal, site characterization, high-level radioactive waste, Geomap Navi

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HCG34-03

Room:101A

Time:May 26 09:30-09:45

A Bayesian approach to assess the probability of concealed active faults existing frommultiple datasets
MARTIN, Andrew1∗ ; ASAMORI, Koichi2 ; ISHIMARU, Tsuneari2 ; UMEDA, Koji2
1

NAGRA, 2 JAEA

Assessing the stability of the geological environment including the spatio-temporal distribution of active faulting is of particularconcern in the context of site selection of nuclear facilities such as radioactive waste repositories and nuclear power plants.
In order to assess the spatio-temporal distribution of active faults, one typically starts by looking at mapped active faults (e.g.
AIST’s active fault database) to estimate spatial frequencies and orientations. However, active faults listed in current databases
do not represent a complete picture of active faulting, as not all active faults have a surface rupture, and their existence might beunknown. In this case, additional datasets are needed that may imply the existence of active faulting.
Datasets such as high He-3/He-4 ratios which tend to be found in volcanic regions have been attributed to degassing fromthe mantle with faults potentially acting as conduits. Studies carried out in the western Tottori district have shown the potentialof using He-3/He-4 ratios as a means of providing indirect evidence of the existence of source fault(s) that caused the 2000
Western Tottori earthquake, but which had no apparent surface indication prior to the earthquake (e.g., Umeda and Ninomiya,2009). Other factors that may need to be taken into account when assessing the existence of active faults include horizontal stressorientation, change in stress regimes, regional stresses and so on.
The Bayesian approach can be used to construct probabilistic models from multiple datasets in order to assess the likelihood ofgiven natural phenomena occuring over defined time periods. This method has previously been applied to assessing future new
volcano formation (e.g. Martin et al., 2004, 2012) but not to new active fault segment formation. We have thus been developing
such a Bayesian model in the Western Tottori district as a case study. In the first step, known active faults are divided into equal
fault segments. We assume that unknown fault segments do not exist far from known fault segments. Also, the probabilityof unknown faults existing decreases with distance from the known faults. 2-D a priori probability distributions are calculatedusing kernel functions centered over the fault segments with varying values of standard deviation depending on the degree ofconservation required. A Cauchy probability density function (PDF) is assigned conservatively as the kernel function in the firststep so that probability is never zero.
In the second step, Kolmogorov-Smirnov statistical tests are used to remap additional datasets (e.g. He-3/He-4, horizontal
stress orientation) into a likelihood PDF. The a prior PDF from the first step above is then combined with the likelihood PDF
using Bayes’ rule to produce a a posteriori PDF. In the third and final step, the a posteriori PDF is evaluated by comparing
probability maps calculated from datasets before and after the 2000 Western Tottori Prefecture earthquake.
The whole procedure can be repeated as new information/data becomes available where the derived a posteriori PDF from thefirst cycle is then used as the starting point, i.e. the a prior PDF in the next cycle.
References
AIST, Active fault database of Japan, https://gbank.gsj.jp/active-fault/index gmap.html
Martin et al. (2004) J. Geophys. Res., 109, B10208, doi:10.1029/2004JB003201.
Umeda, K. and Ninomiya, A. (2009) Geochem. Geophys. Geosys., 10, Q08010, doi:10.1029/2009GC002501.
Martin, Umeda and Ishimaru (2012) InTech Pub., doi:10.5772/51859
Keywords: Active fault, Bayesian approach

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HCG34-04

Room:101A

Time:May 26 09:45-10:00

Cesium adsorption on redox zone pumice tuff at different geochemical condition
RAJIB, Mohammad1∗ ; OGUCHI, Chiaki T.2 ; SASAKI, Takayuki3 ; KOBAYASHI, Taishi3
1

Grad. Sch. Sc. Eng., Saitama University/Bangladesh Atomic Energy Commission, 2 Department of Civil and Environmental
Engineering, Saitama University, 3 Department of Nuclear Engineering, Kyoto University
Non-redox-sensitive element Cesium (Cs) was used to investigate the ionic strength effect on the adsorption behavior on apotential host rock for low and intermediate radioactive wastes. Now-a-days, formation of redox zones in subsurface host rockformation surrounding radioactive disposal facility is a major concern. As such, different geochemical reactions during waterrock interaction around the disposal facility have gained interest to nuclear researchers. The present study attempts to compare
the adsorption phenomena, an important geochemical reaction in waste disposal research field, between fresh rock and rock fromsuch redox zone of an underground research facility of Japan. The surrounding rock formation is rhyolitic pumice tuff belong
to tuffaceous sandstone which has been affected by redox environment and oxidation to the rock formation has been greatly
observed. Physical, mechanical and chemical analyses were carried out to distinguish between fresh and oxidized solid phase.
Batch adsorption study was carried out at different geochemical condition including several initial nuclide concentration of Cs,
ranging from 10−3 mol/dm3 to 10−7 mol/dm3 ; wide range of pH from 4-12, and very low to very high ionic strength ranging
from 0.001 to 3.0 mol/dm3 . The ionic strength was controlled by Na+ ion concentration of NaClO4 . Based on experimental
distribution coefficient values, K d , ionic strength was found to be the most influential for Cs adsorption on both oxidized andfresh pumice tuff. With increasing salt concentration, the K d of cesium apparently decreases, reflecting the competition of
the electrolyte Na+ with the sorption of Cs+ . However, such salt concentration effect became minimum at higher nuclide
concentration due to its saturation capacity and a threshold concentration has been observed. Oxidation of pumice tuff did notaffect the adsorption of Cs significantly even at variable salt concentration, due to being redox inactive element. Simple surface
complexation model without considering the electrostatic layer has also been adopted to explain the adsorption mechanism.
Keywords: Cesium, Redox zone, Pumice tuff, Salt concentration, Adsorption coefficient, Surface complexation model

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HCG34-05

Room:101A

Time:May 26 10:00-10:15

Preliminary study on the directional statistics of crush zones’ strikes in the Kojaku Granite
SHIMADA, Koji1∗
1

Japan Atomic Energy Agency

Introduction: Geological reports on crush zones in granitic basement rocks holding the FBR ”Monju” by JAEA were submitted to the NRA, and they are under examination. In relation to the ensuring safety of important installations, there is a newhorizon of open process of examination on practical geological problem between the NRA and electric power utilities. It is important to observe crush zones jointly and discuss objectively. In this preliminary study, more objective discrimination between
orientations of small crush zones was carried out by means of directional statistics based on an awareness of field data should be
discussed objectively. Then, a simple structural geologic interpretation was presented.
Problem: Intuitive discrimination that there were obvious two systems in crush zone (system alpha-3, strikes ca. 50 deg. ;system beta, strikes ca. 10 deg.) have been outlined from field observations. There should be an objective gauge.
Method: Prepare a sketch map of horizontal outcrop (1:200, ca. 15m squares) showing traces of high-angle crush zones andclay seams. Measure the strike and length of segments. The length is divided by unit length making a list of number of eachstrike. These strikes (0 - 180 deg.) are doubled for directional statistical approach. Mixture fitting method introduced by GarcíaPortugués (2013) by means of the R version 3.1.2 (R Core Team, 2014) with ”movMF” package (Hornik and Grun, 2014) is
carried out. Resultant mean directions of each von Mises distribution are divided by two to convert direction to strike.
Result: Fitted number of mixture components of von Mises distribution is eight. Each of them has mean strike in deg., concentration parameter (kappa) and fraction (total = 1) as follows 10/12.5/0.147 (≒ system beta), 14/3.79/0.117, 26/3.22/0.134,
44/15.3/0.145 (≒ system alpha-3), 47/3.55/0.116, 66/2.55/0.110, 132/4.14/0.066, 169/4.63/0.167. The two systems correspondto components with higher kappa. A probability distribution function curve of eight components mixture shows two peaks (fig.
1). Estimations of kappa via directional statistics give a basis of the description that there are principal two systems of crush
zone.
Discussion: Crush zones principally depict dextral sense of shear along the system beta, and sinistral one along the system
alpha-3. Plastically deformed biotite grains are observed in both crush zones. Deformation temperature of them seems to behigher. Statistically comparable development, nearly orthorhombic symmetry, and cross cutting relationship between the twosystems suggest the development of crush zones in conjugate manner. Bisect orientation of acute angle, 30 deg., indicate ashortening axis and elongation normal to it during deformation. This movement picture is inconsistent with continuing E-W
shortening during late Quaternary. These lines of evidence suggest that crush zones are old geologic structure which could not
be formed near the surface.
References
Eduardo Garcia-Portugues, 2013, Exact risk improvement of bandwidth selectors for kernel density estimation with directional
data. Electron Journal of Statistics, vol. 7, 1655-1685.
Hornik, K. and Grun, B., 2014, movMF: an R package for fitting mixtures of von Mises-Fisher
distributions. Journal of Statistical Software, 58(10):1?31
R Core Team, 2014, R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL http://www.R-project.org/.
Shimada et al., 2014, Shear sense inversion of small crush zones observed in the Kojyaku granite. Abstracts of the 121st annual
meeting of the geological society of Japan, 307.
Fig.1 A probability distribution function curve. x: strike in 0-360 deg., y: relative probability (mean=1).
Keywords: directional statistics, crush zone, Kojaku Granite, Monju

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HCG34-05

Room:101A

Time:May 26 10:00-10:15

2/2

HCG34-P01

Room:Convention Hall

Time:May 26 18:15-19:30

Identifying influence factors on permeability of granite core samples
MATSUDA, Norihiro1∗ ; KUBO, Taiki1 ; KASHIWAYA, Koki1 ; KOIKE, Katsuaki1
1

Kyoto University

A safe geological disposal of high-level radioactive waste for long term requires to evaluate the stability of facilities basedon the estimation of groundwater flow and mass transport. For the evaluation, it is indispensable to understand a regional
groundwater system and a slow diffusion phenomenon of radionuclide in the matrix of the rock body. However, the relation
between a permeability and macro/micro cracks in the rocks has not yet been clarified and the estimation accuracy of flow path islow. The main purpose of this study is to clarify the relationship by measuring spatial variation of permeability of granite rocks
and examining the dependence of permeability upon crack systems with different scales.
For the purpose, we used the core samples taken from a borehole in the Tono area (Gifu, central Japan) drilled by Japan
Atomic Energy Agency (JAEA). This area is mainly composed of Toki granite. Fault zones were drilled through the borehole.
First we measured the permeabilities of the 36 cores and compared them with the geological features. Next, in order to identify
the influence factors on the permeability of the rock matrix, thin-sections were produced from the cores after the infiltration offluorescent into the cores and cracks were extracted from the thin-section images. Furthermore, micro-scale features of the rocks
were compared with anisotropy of the permeability. We defined mesocrack as a visible crack with cm scale and microcrack as aninvisible cracks with mm scale, respectively. As the result, the permeabilities were enhanced in accordance with the degradationof rocks by the advanced weathering and alteration and the presence of faults. High permeabilities were also measured in the partsof thin-sections in which the mesocracks were developed. As for the microcracks, although the fluorescent infiltrated into themicrocracks, their attributes such as length, density, and angle did not have clear relationship with the magnitude of permeability.
These results suggest that mesocracks act as a path of fluids, while individual microcrack cannot have this function: formationof continuous network of microcracks is needed to enhance the permeability. Our next step is to add samples and undertake
image analyses more in detail to verify the interpretation.
Acknowledgement: We would like to express our sincere thanks to the co-researchers of Japan Atomic Energy Agency for
their supports and many constructive comments for this study.

Keywords: Permeability, Granite, Tono Area, Image analysis, Crack characteristics

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HCG34-P02

Room:Convention Hall

Time:May 26 18:15-19:30

Estimates of a sediment yield and a outflow of radioactive Cs with 3D laser scanner
WATANABE, Takayoshi1∗ ; OHYAMA, Takuya1 ; ISHII, Yasuo1 ; NIIZATO, Tadafumi1 ; ABE, Hironobu1 ;MITACHI, Katsuaki1 ; SASAKI, Yoshito1 ; KITAMURA, Akihiro1
1

Japan Atomic Energy Agency

For an estimate of movement from forest to living spheres, it is important to understand value of movement of soil andradioactive Cs from forest. We measured volumes of deposit with 3D laser scanner in an erosion control dam in Fukushima
prefecture on August 29, 2013 and December 3, 2014.
As a result of measurement, an amount of increase of sediment for 15 months is 0.5 m3 . A denudation rate is 0.02 mm/year.
This value is on the same level with denudation rates in meadows and forest, 10-2 - 10-1 mm/year (Fujiwara et al, 1999). And it
is estimated that a variation of radioactive Cs is Cs-137:200,000,000 Bq, Cs-134:80,000,000 Bq.

Keywords: F-TRACE project, accident at the Fukushima Daiichi Nuclear Power Station, 3D laser scanner, denudation rate

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