A Comparative Analysis of Fractured and Porous Medium Radionuclide Transport
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A COMPARATIVE ANALYSIS OF FRACTURED AND POROUS MEDIUM RADIONUCLIDE TRANSPORT
TRAVIS* AND H. E.
B. J.
NUTTALL**
*Earth and Space Sciences Division, Los Alamos National Laboratory, Los Alamos, Univerity
New Mexico 87131
Albuquerque,
of New Mexico,
Engineering,
**Department of Chemical and Nuclear
New Mexico 87545,
INTRODUCTION
Modeling of
radionuclide
transport
in
formations
geological
has
been limited to the treatment of nonfractured porous media.
recently
researchers in
Sweden,
the
of
problems
fractures.
Since
available,
the
Canada,
France, and the USA have
become
until
Recently
interested
in
nuclide transport in geological formations which may contain many question
conventional arises
as
ion-transport
porous-medium to
when
fracture
widths
codes
are
and fracture
frequency dictate the use of these existing codes.
This paper provides a comparative nuclide
types of geomedia, porous study
study
of
transport by modeling the far field (I medium, the
a
homogeneous
multi-fracture medium. and
single
fracture
fractured
medium
problem for three different
a homogeneous porous medium,
i.e.,
and
and
porous km)
a single fracture in
the
Analytical models were used to geometries
while
an
advanced
numerical code was used to model the multi-fractured medium.'
Analytical Models
An
analytical
model
for
the
homogeneous
instantaneous point source, radioactive decay, Nuttall
and
RayI.
Several
porous
medium.
medium
an
and retardation was presented by
The
single paper
fracture by
with
diffusion
into
the
Nuttall and RayI presents a more
complex model permitting flow and nuclide migration in both the and the fracture.
with
case
papers2,3,4 have presented essentially identical
models for nuclide transport in a surrounding
porous
porous
medium
822 Multi-Fracture Model
For the study of multi-fractured medium, a numerical model and code recently developed
by
Travis
5
was
used.
The TRACR3D code is
code used to study tracer migration and breakthrough &hale retorts.
The
code
solves
a modified version of a
in
large
the three-dimensional,
rubblized
conservation equations and modified momenta equations for single- or flow
with
transport
of a tracer in either phase.
oil
time-dependent mass two-phase
The code can handle single
phase (air or water) flow or two-phase (air and water) flow in steady state transient
conditions with (or without) tracer transport.
include advection, diffusion and velocity dependent dispersionS. simply
a
dual
or
Transport mechanisms This
is
not
porosity model but a detailed treatment of both the porous and
fracture regions.
In addition the code models radioactive decay, and has linear, Langmuir Freundlich Discrete,
sorption models. finite width,
orthogonal.
fractures can be modeled as well but fractures must
Each fluid phase (air, water) has its
either be specified as an input (in calculated
by
the
code.
conservation
equation,
(Forchheimer
flow
in
If
equ
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