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Abstracts
actinides such as Am(III) which is contained in High-Level radioactive Waste (HLW). Since Am does not occur in natural
environment, behavior of REEs in deep groundwater gives us valuable information for research and development relating to the safety
assessment of geological disposal of HLW. In groundwater, REEs often form complexes with aqueous and colloidal ligands according
to their large ionic potential (ionic charge/ionic radius). Therefore, behavior of REEs strongly depends on physical and chemical
properties of these complexes. However, it is difficult to speciate complexes of REEs in groundwater mainly due to difficulties in
direct measurement of REEs complexes with their low concentrations and alteration of groundwater condition during collection. The
aim of this study is determination of chemical states of REEs in groundwater by combination of ultrafiltration techniques maintaining
in-situ pressure and anaerobic conditions, speciation calculation taking care about contribution of natural organic matters, and
finger-printing method using REE pattern of stability constants for probable complexes of REEs in groundwater. Groundwater samples
were collected from a borehole located in the 200 m substage of the Mizunami Underground Research Laboratory (MIU), Gifu, Japan.
Our results suggest that colloidal ligands play an important roll on the behavior of REEs in groundwater.
5) 40022 – Natural analogue studies of bentonite reaction under hyperalkaline conditions: overview of ongoing
work at the Zambales Ophiolite, Philippines
Naoki Fujii, M. Yamakawa, RWMC (Japan); K. Namiki, Obayashi Corporation (Japan);
T. Sato, Hokkaido University (Japan); N. Shikazono, Keio University (Japan);
C. A. Arcilla, C. Pascua, University of the Philippines (Philippines);
W Russell Alexander, Bedrock Geosciences (Switzerland)
Bentonite is one of the most safety-critical components of the engineered barrier system for the disposal concepts
developed for many types of radioactive waste. However, bentonite – especially the swelling clay component that
contributes to its essential barrier functions – is unstable at high pH. To date, results from laboratory tests on bentonite
degradation have been ambiguous as the reaction rates are so slow as to be difficult to observe in the laboratory. As such,
a key goal in this project is to examine the reaction of natural bentonites in contact with natural hyperalkaline
groundwaters to determine if any long-term alteration of the bentonite occurs.
Ophiolites have been identified as sources of hyperalkaline groundwaters that can be considered natural analogues
of the leachates produced by cementitious materials in repositories for radioactive waste. At the Zambales ophiolite in the
Philippines, widespread active serpentinisation results in hyperalkaline groundwaters with measured pH values of up to
11.1, falling into the range typical of low-alkali cement porewaters. These cements are presently being developed
worldwide to minimise the geochemical perturbations which are expected to result from the use of OPC-based concretes
(see Kamei et al., this conference, for details). In particular, it is hoped that the lower pH of the low-alkali cement
leachates will reduce, or even avoid entirely, the potential degradation of the bentonite buffer which is expected at the
higher pH levels (12.5 and above) common to OPC-based concretes. During recent field campaigns at two sites in the
Zambales ophiolite (Mangatarem and Bigbiga), samples of bentonite and the associated hyperalkaline groundwaters have
been collected by drilling and trenching. At Mangatarem, qualitative data from a ‘fossil’ (i.e. no groundwater is currently
present) reaction zone indicates some alteration of the bentonite to zeolite, serpentine and CSH phases. Preliminary
reaction path modelling suggests that the zeolites could have been produced as a product of smectite reaction in the
hyperalkaline groundwaters. Although not included in this calculation to date, the CSH phases identified are completely
consistent with reaction of clays with hyperalkaline groundwaters, as seen at other sites worldwide.
At the Bigbiga site, an active hyperalkaline groundwater/bentonite reaction zone (at the base of the bentonite
deposit) has recently been drilled and samples are currently undergoing analysis. A comparison of the data sets from both
sites will be included in the presentation. The paper will also outline the potential future programme of research at these
sites.
6) 40063 – Natural Analogues of Cement: Overview of the Unique Systems in Jordan
Gento Kamei, JAEA (Japan);
W Russell Alexander, Bedrock Geosciences (Switzerland); Ian D. Clark, University of Ottawa (Canada);
Paul Degnan, IAEA; Marcel Elie, Shell (UK); Hani Khoury, Elias Salameh, University of Jordan (Jordan);
Antoni E. Milodowski, British Geological Survey (UK); Alister F. Pitty, Pitty Consulting (UK);
John A.T. Smellie, Conterra (Sweden)
In L/ILW repository designs, cement-based materials are expected to dominate – for example, the proposed Swiss
repository will contain over 1.5 million tonnes of cementitious material. Models of cement evolution predict that leaching
of the cement in the repository by groundwater will produce an initial stage of hyperalkaline (pH~13.5) leachates,
dominated by alkali hydroxides, followed by a longer period of portlandite and CSH buffered (pH~12.5) leachates. It has
also been predicted that the hyperalkaline porewater leached out of the near-field will interact with the repository host
rock (and, where applicable, bentonite buffer and backfill). This could possibly lead to deterioration of those features for
which the host rock formation and bentonite were originally chosen.
Here, the safety assessment implications of the novel data from the Jordan Natural Analogue Study, which looked
into interaction of natural cementitious hyperalkaline leachates on repository host rocks and clays, are presented. Several
sites across Jordan have been studied, but the focus here will be on two particularly contrasting sites:
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