Migration in a Single Fracture
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ON IN A SINGLE FRACTURE Harald Abelin, Jard Gidlund, Ivars Neretnieks Department of Chemical Engineering Royal Institute of Technology S-100 44 STOCKHOLM, Sweden SUMMARY It has
been
decided
to
investigate
flow and sorbtion in a readily
identifiable fracture which can be excavated for a detailed examination of flow path and sorbtion sites. The investigation is performed in the Stripa mine, 360 m below ground, where there is a natural water flow towards
the
drift. The bedrock is granite. A method
of
tracer
injection into a fracture, either as a step or a
pulse, and of collection of water samples under anoxic atmosphere has been suggested and tested in a preparatory investigation. The introduction of tracers can be done either under natural pressure
or
by
injection
with
over pressure. An injection
of
Na-iodide and Na-Fluorescein with over
Rhodamine-WT,
pressure has been performed.
It
has
been
found
that
Rhodamine-WT
is
influenced in some way along the the flow path. BACKGROUND In the KBS (Swedish nuclear fuel supply co/division KBS) report (1),
it
is proposed that the final repository for radioactive waste should
at
500
be
m depth in crystalline rock. The safety analysis for this repository
is based on the assumption that if and when any radionuclides are
leached
from the waste , the majority of the important radionuclides will interact chemically or retarded.
This
physically
with
retardation
the
bedrock
and
will
be
considerably
and interaction depends upon the velocity of
water, the sorbtion rates and equilibria of the reactions as well surface area of the rock in contact with the flowing water.
as
the
530
Most
are
studies
described as porous distances
based media
upon flow.
the This
assumption might
be
that
the flow can be
true
for
very
large
where the flow would encounter a multitude of channels and some
averaging may be conceivable on the scale considered. scale
tracer
However, no large tests have been performed in fissured crystalline rock with
known flow paths. Transport over short distances, a
canister,
most
probably
occurs
in
i.e in the near field of
individual
fissures.
intermediate scale where more than a few fissures conduct the
On
flow,
an well
type
tracer tests alone cannot give the detailed information needed to understand dispersion and sorbtion phenomena in fissured rock. It has therefore been decided to investigate flow and sorption in readily identifiable fissures which can be excavated for a detailed examination of flow paths and sorption sites. Several
investigations
on migration in single fractures are under way
both in the laboratory and in the field. The laboratory runs are done with migration distances of up to 0.3 m (see Neretnieks field
et
al
(2))
and
the
experiments with a migration distance of up to 30 m (see Gustavsson
and Klockars (3)).
In the present investigation a
about 5 m is used.
The fracture will be excavated afterwards.
migration
distance
of
PURPOSE The study to be performed has
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