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| Titel |
Colloid facilitated transport of lanthanides through discrete fractures in chalk |
| VerfasserIn |
Emily Tran, Ofra Klein Ben-David, Nadya Teutsch, Noam Weisbrod |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103516
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| Publikation (Nr.) |
 EGU/EGU2015-2931.pdf |
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| Zusammenfassung |
| Geological disposal of high-level radioactive waste is the internationally agreed-upon, long
term solution for the disposal of long lived radionuclides and spent fuel. Eventually, corrosion
of the waste canisters may lead to leakage of their hazardous contents, and the radionuclides
can ultimately make their way into groundwater and pose a threat to the biosphere.
Engineered bentonite barriers placed around nuclear waste repositories are generally
considered sufficient to impede the transport of radionuclides from their storage location
to the groundwater. However, colloidal-sized mobile bentonite particles eroding
from these barriers have come under investigation as a potential transport vector for
radionuclides sorbed to them. In addition, the presence of organic matter in groundwater
has been shown to additionally facilitate the uptake of radionuclides by the clay
colloids.
This study aims to evaluate the transport behaviors of radionuclides in colloid-facilitated
transport through a fractured chalk matrix and under geochemical conditions representative
of the Negev desert, Israel. Lanthanides are considered an acceptable substitute to actinides
for research on radionuclide transportation due to their similar chemical behavior. In this
study, the migration of Ce both with and without colloidal particles was explored and
compared to the migration of a conservative tracer (bromide). Tracer solutions containing
known concentrations of Ce, bentonite colloids, humic acid and bromide were prepared in a
matrix solution containing salt concentrations representative of that of the average rain water
found in the Negev. These solutions were then injected into a flow system constructed
around a naturally fractured chalk core. Samples were analyzed for Ce and Br using
ICP-MS, and colloid concentrations were determined using spectrophotographic
analysis. Breakthrough curves comparing the rates of transportation of each tracer were
obtained, allowing for comparison of transport rates and calculation of overall tracer
recovery.
Preliminary results suggest that mobility of Ce as a solute is negligible, and
in experiments conducted without bentonite colloids, the 2% of the Ce that was
recovered during the experiments travelled as "intrinsic" colloids in the form of
Ce2(CO3)3/
6H2O precipitate. However, the total recovery of the Ce increased to 9% when
it was injected into the core in the presence of bentonite colloids and 13% when
both bentonite and the carbonate precipitate colloids were injected. In addition, the
maximum relative concentration (C/C0) of the Ce in the samples from the experiments
conducted without bentonite colloids is about 0.002, whereas that of the experiments
conducted in the presence of bentonite colloids reaches almost 0.2. This indicates
that colloid presence does indeed markedly increase the mobility of radionuclides
through fractured chalk matrices and should therefore be considered in models
representing transport of radionuclide waste originating from nuclear repositories. |
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