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

Abstracts
Repository, Environmental Remediation, Computer Codes, Compliance Period, Benchmark.
3) 40196 – Effect of the Residual Heat Release of the Nuclear Waste Stored in an Unsaturated Zone on
Radionuclide Release
Lubna K. Hamdan, John C. Walton, Arturo Woocay, University of Texas at El paso (USA)
Over time, nuclear waste packages disposed in an unsaturated zone geological repository, such as the proposed
repository at Yucca Mountain, are expected to fail gradually due to localized and general corrosion. As a result, water
will have access to the nuclear waste and radionuclides will be transported to the accessible environment by ground water.
In this paper we consider a serious failure case in which penetrations at the top and bottom of the waste package will
allow water to flow through it (flow-through model). We introduce a new conceptual model that examines the effect of
the residual heat release of the nuclear waste stored in an unsaturated environment on radionuclide release. This model
predicts that the evaporation of water at the hotter sheltered areas (from condensate and seepage) inside the failed waste
package will create a capillary pressure gradient that drives water to wick with its dissolved and suspended contents
toward these relict areas, effectively preventing radionuclides release. We drive a dimensionless group to estimate the
minimum length of the sheltered areas required to sequester radionuclides and prevent their release. <strong>The</strong> implications of
this model on the performance of the proposed repository at Yucca Mountain or unsaturated zone geological repositories
in general are explored.
4) 40072 – Evaluation of behavior of rare earth elements based on determination of chemical state in
groundwater in granite
Yuhei Yamamoto, Daisuke Aosai, Takashi Mizuno, JAEA (Japan)
Rare earth elements (REEs) in natural environment have been studied as a useful geochemical tracer and analogues for trivalent
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). <strong>The</strong>refore, 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. <strong>The</strong>
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. <strong>The</strong>se 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
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