Compacted bentonite has been considered as a candidate buffer material in the underground repository for the disposal of highlevel
radioactive waste. An erosion of bentonite particles caused by a groundwater flow at the interface of a compacted bentonite and
a fractured granite was studied experimentally under various geochemical conditions. The experimental results showed that
bentonite particles could be eroded from a compacted bentonite buffer by a flowing groundwater depending upon the contact time,
the flow rate of the groundwater, and the geochemical parameters of the groundwater such as the pH and ionic strength.
A gel formation of the bentonite was observed to be a dominant process in the erosion of bentonite particles although an intrusion
of bentonite into a rock fracture also contributed to the erosion. The concentration of the eroded bentonite particles eroded by a
flowing groundwater was increased with an increasing flow rate of the groundwater. It was observed from the experiments that the
erosion of the bentonite particles was considerably affected by the ionic strength of a groundwater although the effect of the pH was
not great within the studied pH range from 7 to 10. An erosion of the bentonite particles in a natural groundwater was also observed
to be considerable and the eroded bentonite particles are expected to be stable at the given groundwater condition.
The erosion of the bentonite particles by a flowing groundwater did not significantly reduce the physical stability and thus the
performance of a compacted bentonite buffer. However, it is expected that an erosion of the bentonite particles due to a groundwater
flow will generate bentonite particles in a given groundwater condition, which can serve as a source of the colloids facilitating
radionuclide migration through rock fractures.
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