Abstract
The leaching and migration of active radionuclides, emanating from
radioactive waste disposal sites, poses immense risk to the natural
environment in general, and specifically to groundwater reservoirs.
Colloid facilitated transport (CFT), in which the contaminant is
attached to naturally-occurring mobile colloids, has been identified as
a major source for enhanced migration of radioactive species in
groundwater. Since many underground repositories of radioactive waste
are situated within fractured rock formations, it is crucial to assess
the mobility of colloid-borne radionuclides in discrete fractures. More
specifically, transport behavior in fractured carbonate rock, which
constitutes the local bedrock in the Negev desert in southern Israel, is
not well understood. While recent laboratory-scale experiments have
shown the significant impact of CFT on contaminant migration, including
some of the radionuclides, in natural fractured carbonate rock, the
micro-scale origin of this behavior remains largely unknown. In this
work, we study two specific questions: (a) what is the distribution of
colloids within the fracture, along the flow path; and (b) how this
distribution is related to the chemical and mineral heterogeneity of the
fracture surface. We use two types of rock samples: a naturally
fractured core drilled from the chalk rock, representing a mature and
highly heterogeneous fracture surface, and a fresh cut sample from a
non-fractured core, representing a more homogeneous and recently formed
fracture surface. We develop a novel experimental setup, consisting of a
small slab of natural fractured chalk surface, encased in a flow cell
under a glass cover, and mounted under a fluorescence microscope. Clay
particles labelled with a fluorescent dye are injected into the cell,
while the fluorescence intensity of the rock surface is captured using
the microscope. This setup allows us to monitor the distribution of
labelled clay particles over the fracture surface, with high temporal
and spatial resolution. Initial experiments show that fluorescence,
hence clay deposition, increases over time during the flow experiment,
over a small section of a homogeneous rock surface. Our preliminary
results suggest that surface topography and flow pattern impact colloid
deposition on the fracture surface.
| Original language | English |
|---|---|
| Title of host publication | Proceedings from the conference held 7-12 April, 2019 in Vienna, Austria |
| Volume | 21 |
| State | Published - 1 Apr 2019 |