The 13th International Conference on Environmental ... - Events

Abstracts
12) 40067 – An Analytical Model on the Sealing Performance of Space for the Design of Buffer Material and
Backfill Material
Haruo Sato, JAEA (Japan)
<strong>The</strong> self-sealing function of spaces between buffer material and overpack, tunnel wall and disposal pit by swelling
occurred with water penetration is expected for bentonite which will be used as buffer material and part of the backfill
material in the geological of high-level radioactive waste in Japan. <strong>The</strong> clearance filling properties of Na-bentonite for
buffer material and backfill material specifications have been studied for distilled water and saline water conditions, for
example, it is reported that Na-bentonite seals clearance even under saline water conditions in a range of effective
bentonite densities which are higher than 1.3 kg/dm3, for a bentonite dry density of 1.8 kg/dm3 and a clearance ratio
(volumetric ratio of clearance volume to total volume including pore and the clearance) of 10 % (1.11 in volumetric
swelling ratio: Rvs) in experiments for Kunigel-V1 (Na-montmorillonite content ca. 50 wt.%). Although such
information is useful for judging whether clearance is filled, the filling properties of bentonite depend on groundwater
condition, silica sand content, montmorillonite content in the bentonite and the bentonite dry density, even though at the
same effective bentonite density. In the present study, the author constructed an analytical model on the clearance filling
performance for the design of buffer material and backfill material, based on the swelling properties of
Na-montmorillonite which is the clay mineral constituent of bentonite. In the modelling, experimental data on the Rvs of
bentonite (Kunigel-V1) reported so far were analyzed. Consequently, it was found that dry density of the bentonite when
the free swelling reached equilibrium state was approximately in the range of 0.204-0.241 kg/dm3 for distilled water
condition. <strong>The</strong>se dry densities are equivalent to the range of 0.106-0.126 kg/dm3 in montmorillonite partial density. On
the other hand, the Rvs of bentonite decreased for saline water condition. Based on these experimental data for Rvs, the
author derived an analytical expression to be able to calculate Rvs values against various dry densities and bentonites
(different montmorillonite and silica sand contents), and showed the manner for judging whether clearance is sealed for
an arbitrary clearance ratio. In the paper, the author shows the calculated results of Rvs versus dry density under various
conditions.
13) 40069 – Current Status of Horonobe URL Project in Construction Phase
Hironobu Abe, Koichiro Hatanaka, JAEA (Japan)
Horonobe URL project has been pursued by JAEA (Japan Atomic Energy Agency) to establish and demonstrate site
characterization methodologies, engineering technologies, and safety assessment methodologies for HLW geological
disposal in relevant geological environment with sedimentary rock and saline groundwater distributing in Horonobe area,
Hokkaido, Japan. In the Horonobe URL project, surface-based investigation phase (Phase I) has already completed in the
year 2005, and then construction phase (Phase II) has initiated in the same year. Currently, construction of the
underground facilities such as shafts/drifts which were designed in Phase I, investigations of the geological environment
in the excavated shafts/drifts and confirmation of applicability of engineering technologies has been alternately carried
out as Phase II activities of the project. At the end of January, 2010, ventilation shaft has reached at the depth of
GL-250m and east access shaft has reached at the depth of GL210m. Concerning horizontal drifts, construction of
GL-140m gallery with total length of 184m has completed and GL-250m gallery has partially constructed with the length
of 42m. During the construction so far, monitoring for the construction safety such as convergence measurements, tunnel
wall observation, sampling of groundwater and rock, investigations for evaluating excavation damaged zone along
shaft/drift were carried out. In addition, shotcrete construction test and grout injection test by using low alkaline cement
material were carried in the horizontal drifts. In this paper, status of the URL construction and research activities
mentioned above are outlined as the current achievement of the Horonobe URL project.
14) 40074 – Development of New Ultrafiltration Techniques Maintaining In-Situ Hydrochemical Conditions for
Colloidal Study
Daisuke Aosai, Yuhei Yamamoto, Takashi Mizuno, JAEA (Japan)
Chemical state of elements in groundwater is one of the most important information for understanding behavior of
elements in underground environment. Chemical state of elements controlled mainly by groundwater physico-chemical
parameters. Because the change of physico-chemical parameters of groundwater, due to pressure release and oxidation
during sampling, causes changes in chemical state of elements, systematic methodologies for understanding in situ
chemical state is required. In this study, in order to understand chemical state of elements in groundwater, an
ultrafiltration instrument for maintaining in-situ pressure and anaerobic conditions was developed. <strong>The</strong> instrument
developed in this study for ultrafiltration made of passivated Stainless Used Steel (SUS) materials, was designed to keep
groundwater samples maintaining in-situ pressure/anaerobic conditions. Ultrafiltration of groundwater was conducted at
a borehole drilled from the 200 mbGL (meters below ground level) Sub-stage at a depth of 200 m at the Mizunami
Underground Research Laboratory. Chemical analyses of groundwater were also conducted using samples filtered under
both pressurized/anaerobic and atmospheric conditions and passivated SUS materials with different elapsed times after
passivation. <strong>The</strong> results indicate that our ultrafiltration method is suitable for collection of filtered groundwater and
passivation is an essential treatment before ultrafiltration. Keywords: groundwater, ultrafiltration.
106