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AREST: TIE NEXT GENERATION
David W. Engel, B. Pete McGrail, Paul W. Eslinger
Pacific Northwest Laboratory"
P.O. Box 999
Richland, Washington 99352
Simple mass transport models using constant boundary con-
ditions at the waste form surface and at the host rock
boundary do not always result in realistic predictions of the
performance of an underground repository for the disposal
of high-level radioactive waste. What is needed is a model
that couples the important processes that can not be
modeled independently, including 1) thermal modeling,
2) geochemical modeling, 3) containment degradation,
4) waste form dissolution, and 5) radionuclide transport.
Such a model is being developed by modifying the AREST
The Department of Energy (DOE) has assigned the
task of leading the performance assessment (PA) studies at
the potential sit:: for the underground nuclear waste reposi-
tory, at Yucca Mountain, to the Civilian Radioactive Waste
Management System (CRWMS) Management and Operat-
ing Contractor (M&O). In turn, the M&O has selected the
AREST code as the waste package model for analyzing the
engineered barrier system (EBS) of the potential reposi-
tory.' The AREST code was developed for the DOE at
the Pacific Northwest Laboratory (PNL). 2
Within the next few years, the Yucca Mountain Site
Characterization Project (YMP) will be examining alterna-
tive EBS concepts that cannot, however, be analyzed with
the current version of the AREST code or any other exis-
ting DOE model. The limits of the capabilities of the
fundamental structure of the AREST code has been
reached. It relies on relatively simple analytical models to
describe release and transport of radionuclides in the waste
package of the EBS. Consequently, a fundamental restruc-
turing of the AREST code is needed to implement robust
but computationally efficient models for EBS and waste
package performance assessment.
'Operated for the U.S. Department of Energy by Battelle
Memorial Institute under Contract DE-AC06-76RLO
Marty K. Altenhofen
Waste Management Consultant
2000 Logston Blvd.
Richland, WA 99352
This report describes the modeling capabilities for the
development of the next generation of the AREST code.
Defining the requirements for the capabilities of the
AREST code is an iterative process, with this report
describing the latest iteration.
A. Current Version
The current version of the AREST code incorporates
a sophisticated graphical user interface to simplify and
organize problem setup and provide visualization of the
computational results. The AREST code was developed
to perform probabilistic analyses of the EBS; thus the
process models are simplified from the more rigorous
models that are needed in a detailed waste package model.
The current version of the AREST code contains several
analytical models and a simple one-dimensional finite differ-
ence numerical model for calculating nuclide transport to
the host rock.4
The models use constant boundary conditions for both
the waste form surface and the backfill/host rock interface.
The detailed processes of the near-field environment are
modeled external to the AREST code, in support code
analyses, with the results being input into the AREST code
as look-up tables and transfer functions. The processes
which are modeled externally to the AREST code include
the following: 1) radiolysis, 2) water mass transfer, 3) heat
transfer, 4) rock mechanics, 5) geochemistry, and 6) the
waste/barrier/rock interactions. These processes were
assumed to be independent of waste form dissolution, cor-
rosion, and transport processes and thus were modeled
To illustrate the need for the next generation of the
AREST code, which will utilize coupled chemical reactive
transport models, a simple analysis is presented. In this
analysis, the mass transport properties of a 0.5 meter thick
backfill surrounding a glass waste form are varied. A
detailed description of this analysis has been presented
elsewhere.5 For this analysis the diffusion coefficient has
been varied over two orders of magnitude from Dr = 10-
to 10-7 cm2/sec.
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Engel, D.W.; McGrail, B.P.; Eslinger, P.W. & Altenhofen, M.K. AREST: The next generation, article, April 1, 1993; Richland, Washington. (digital.library.unt.edu/ark:/67531/metadc620561/m1/2/: accessed November 19, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.