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

Abstracts
21) 40137 – Development of Methodology to Construct a Generic Conceptual Model of River-valley Evolution
for Performance Assessment of HLW Geological Disposal
Makoto Kawamura, Kenichi Yasue, Tadafumi Niizato, Shin-ichi Tanikawa, JAEA (Japan)
In order to assess the long-term safety of a geological disposal system for high-level radioactive waste (HLW), it is
important to consider the impact of uplift and erosion, which cannot be precluded on a timescale in the order of several
hundred thousand years for many locations in Japan. Geomorphic evolution, caused by uplift and erosion and coupled to
climatic and sea-level changes, will impact the geological disposal system due to resulting spatial and temporal changes
in the disposal environment. Degradation of HLW barrier performance will be particularly significant when the remnant
repository structures near, and are eventually exposed at, the ground surface. In previous studies, river erosion was
identified as the key concern in most settings in Japan. Here, therefore, we present a methodology for development of a
generic conceptual model for performance assessment based on best current understanding of river erosion in Japan.
Critical considerations that have to be taken into account when interpreting the geological record of past river-valley
evolutions, as preserved in ancient fluvial deposits, include: 1) the spatial variation in the relative significance of erosion
and sedimentation at any time between upper- and lower-reaches of rivers originating in mountainous terrain 2) the
temporal variation in the extent of erosion / sedimentation at any specific location during glacial / interglacial cycles 3)
the balance between uplift and vertical erosion as a result of the hardness of the riverbed rock 4) the balance between
vertical and lateral erosion – ranging from formation of narrow gorges to wide meandering flood plains 5) the varying
duration and intensity (as assessed by sea level change) of past glacial / interglacial cycles.
Interpretation of the impact of such phenomena at relevant locations in Japan has led to development of a generic
conceptual model which contains the features typical of mid-reach rivers. This paper presents the methodology to
develop the conceptual model, identifies the simplifications and uncertainties involved and assesses their consequences in
the context of repository performance. Details of resultant analyses using this conceptual model will be discussed in
another paper presented in ICEM’10 by Miyahara et al.
22) 40162 – Long-term Stability of Bentonite Material Used as Engineered Barrier for Radioactive Waste
Disposal
Vera Jedinakova-Krizova, Katerina Videnska, Institute of Chemical Chechnology Prague (Czech Republic);
Eduard Hanslik, T.G.M. Water Research Institute (Czech Republic)
Geological concepts for the storage of radioactive waste are based on „multi-barrier“ systems, which are composed
of several elements: the waste packaging, an engineered barrier incorporating bentonite material and a geological barrier.
<strong>The</strong> stability of engineered barriers can be affected by long-term pressure and temperature gradients. <strong>The</strong> contribution is
focused on geotechnical, chemical, geochemical and mineralogical research of bentonite stability with the aim to
determine the effect of saturation medium composition and loading by heat on bentonite stability. <strong>The</strong> main part the
research is directed to the experimental results of bentonite and bentonite leachate samples obtained for the bentonite
interaction under laboratory or in situ experiments. <strong>The</strong> tested bentonite materials represent a series of compact loaded
bentonite samples taken from the dismantling process of the Mock-Up-Cz experiment, which constitute first vertical
model of a bench-scale buffer mass test of Czech smectitic clay in the Europe. Mineralogical composition, chemical and
physicochemical properties including uptake of long-term lived fission products in the form of 99TcO4- and 134Cs+
were utilised for the evaluation of the changes caused with the loading of this material. This work aims to characterise the
basic parameters (ion exchange capacity, mineralogical and chemical composition, specific surface area) of bentonite
materials, which are important for the retention of the anionic forms of redox-sensitive radionuclides (99Tc, 125I). In
particular, ion exchange capacity characterises bentonite’s ability to adsorb ions from an aqueous environment.
Geological concepts for the storage of radioactive waste are based on „multi-barrier“ systems: the waste packaging, an
engineered barrier incorporating bentonite material and a geological barrier. <strong>The</strong> stability of engineered barriers can be
affected by long-term pressure and temperature gradients. <strong>The</strong> contribution is focused on geotechnical, chemical,
geochemical and mineralogical research of bentonite stability with the aim to determine the effect of saturation medium
composition and loading by heat on bentonite stability. <strong>The</strong> main part the research is directed to the experimental results
of bentonite and bentonite leachate samples obtained for the bentonite interaction under laboratory or in situ experiments.
<strong>The</strong> tested bentonite materials represent a series of compact loaded bentonite samples taken from the dismantling process
of the Mock-Up-Cz experiment, which constitute first vertical model of a bench-scale buffer mass test of Czech smectitic
clay in the Europe. Mineralogical composition, chemical and physicochemical properties including uptake of long-term
lived fission products in the form of 99TcO4- and 134Cs+ were utilised for the evaluation of the changes caused with the
loading of this material. It was found that bentonite material was stable from the point of the long term loading under the
model conditions applied in the Mock-Up-Cz experiment and only small part of original bentonite material was
transformed under the occurrence of the newly formed mineral domains (about few weight percent) as result of the long
term loading bentonite material by pressure and temperature gradients. It can be concluded that listed above newly
formed mineral phases originated by transformation of bentonite material have no significant influence on the ion
exchange properties. Migration studies of 99TcO4-and 134Cs+ simultaneously confirmed these results, as well. Similar
behaviour of bentonite clay barrier can be expected in the long time therefore this material is suitable for the applications
as engineered barrier in the deep repository of the high level radioactive waste and spent fuel.
Acknowledgement: This research was supported by the Ministry of Education, Youth and Sports of Czech Republic
under the project MSM 60461373007 and by Ministry of Industry and Trade under the project FR-TI1/362.
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