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Abstracts
This research addresses the potential of microbial implications in bentonite for use as a buffer and backfill material
in final disposal site for low-level radioactive waste (LLRW) in Taiwan, where has a special island-type climate. Microbe
activities naturally present in this site were analyzed, and buffer materials (BM) consisted of 100%, 70% or 50%
bentonite were prepared for laboratory studies. A total of 39 microbial strains were isolated, and the predominant strains
included four bacterial, one yeast and four fungal strains. Growth inhibition was not detected in any tested strain cultured
in a radiation field with a dose rate of 0.2 Gy/h. Most of the isolated strains grew under a dose rate of 1.4 Gy/h. The D10
values of the tested strains ranged from 0.16 to 2.05 kGy. The mycelia of tested fungal strains could spread over 5 cm
during six months of inoculation in BM. The spreading activity of the tested bacteria was less than that of the fungi.
Moreover, biofilms were observed on the surfaces of the BM. Since a large and diverse population of microbes is present
in Taiwan, microbes may contribute to the mobilization of radionuclides in the disposal site.
2) 40153 – Assessing the gas transport mechanisms in the Swiss L/ILW concept using numerical modeling
Irina Gaus, Paul Marschall, Joerg Rueedi, Nagra (Switzerland);
Rainer Senger, John Ewing, Intera Inc. Swiss Branch (Switzerland)
In low/intermediate-level waste (L/ILW) repositories, anaerobic corrosion of metals and degradation of organic
materials produce hydrogen, methane, and carbon dioxide. Gas accumulation and gas transport in a L/ILW repository is
an important component in the safety assessment of proposed deep repositories in low-permeability formations. The
dominant gas transport mechanisms are dependent on the gas overpressures as with increasing overpressure the gas
transport capacity of the system increases. The dominant gas transport mechanisms occurring with increasing gas
pressure within the anticipated pressure ranges are: diffusion of gas dissolved in pore water (1), two phase flow in the
hostrock and the excavation damaged zone (EDZ) whereby no deformation of the pore space occurs (2), gas migration
within parts of the repository (if repository materials are appropriately chosen) (3) and pathway dilation (4). Under no
circumstances the gas is expected to induce permanent fractures in the hostrock. This paper focuses on the gas migration
in parts of the repository whereby materials are chosen aimed at increasing the gas transport capacity of the backfilled
underground structures without compromising the radionuclide retention capacity of the engineered barrier system (EBS).
These materials with enhanced gas permeability and low water permeability can supplement the gas flow that is expected
to occur through the EDZ and the host rock. The impact of the use of adapted backfill and sealing materials on the gas
pressure build-up and the major gas paths were assessed using numerical two-phase flow models on the repository scale.
Furthermore, both the gas and water fluxes as a function of time and gas generation rate can be evaluated by varying the
physical properties of the materials and hence their transport capacity. Results showed that by introducing seals with
higher gas permeability, the modeled gas flow is largely limited to the access tunnels and the excavation disturbed zone
for the case of a very low permeability host rock. The bulk of the gas flows through the repository seal and the adjacent
EDZ into the tunnel system. In addition to the demonstration of the gas flow in the seal and access tunnel system by
numerical models, laboratory results confirm the high gas transport capacity of the sand/bentonite mixtures. In a next step
a multi year demonstration scale experiment (GAST) at the Grimsel Test Site is envisioned.
3) 40283 – The progress and results of Demonstration Test of Cavern-Type Disposal Facility
Yoshihiro Akiyama, Kenji Terada, Nobuaki Oda, Tsutomu Yada, Takahiro Nakajima, RWMC (Japan)
The cavern-type disposal facilities for low-level waste (LLW) with relatively high radioactivity levels mainly
generated from power reactor decommissioning and for part of transuranic (TRU) waste mainly from spent fuel
reprocessing are designed to be constructed in a cavern 50 to 100 meters below ground, and to employ an engineered
barrier system (EBS) of a combination of bentonite and cement materials in Japan. In order to advance the feasibility
study for these disposal, a government-commissioned research project named Demonstration Test of Cavern-Type
Disposal Facility started in fiscal 2005, and since fiscal 2007 a full-scale mock-up test facility has been constructed under
actual subsurface environment. The main objective of the test is to establish construction methodology and procedures
which ensure the required quality of the EBS on-site. By fiscal 2009 some parts of the facility have been constructed, and
the test has demonstrated both practicability of the construction and achievement of the quality. They are respectively
taken as low-permeability of less than 5x10-13 m/s and low-diffusivity of less than 1x10-12 m2/s at the time of
completion of construction. This paper covers the project outline and the test results obtained by the construction of some
parts of a bentonite and cement materials.
SESSION H9: Repository Engineering and Demonstration
1) 40304 Keynote – Repository engineering and demonstration: special challenges for TRU
Ian G. McKinley, McKinley Consulting (Switzerland)
The diverse range of long-lived radioactive wastes without significant heat output specified for deep geological
disposal (here termed TRU) pose challenges that are potentially more serious than those from vitrified high-level waste
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