Important Parameters in the Performance of a Potential Repository at Yucca Mountain (TSPA-1995) Page: 1 of 4
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IMPORTANT PARAMETERS IN THE PERFORMANCE OF A POTENTIAL REPOSITORY AT YUCCA MOUNTAIN
(TSPA-1995)Joel E. Atkins
CRWMS M&O/INTERA, Inc.
1261 Town Center Drive
Las Vegas, Nevada 89134
(702) 295-4755S. David Sevougian
CRWMS M&O/INTERA, I
1261 Town Center Drive
Las Vegas, Nevada 89134
(702) 295-4634Joon H. Lee
CRWMS M&O/INTERA, Inc.
1261 Town Center Drive
Las Vegas, Nevada 89134
(702) 295-4754Robert W. Andrews
CRWMS M&O/INTERA, Inc.
1261 Town Center Drive
Las Vegas, Nevada 89134
(702) 295-5549Jerry A. McNeish
CRWMS M&O/INTERA, Inc.
1261 Town Center Drive
Las Vegas, Nevada 89134
(702) 295-4630ABSTRACT
A total system performance assessment (TSPA) was
conducted to determine how a potential repository at Yucca
Mountain would behave. Using the results of this TSPA,
regression was done to determine which parameters had the
most important effect on the repository performance. These
results were consistent with the current conceptual
understanding of the repository.
I. INTRODUCTION
A total system performance assessment (TSPA) was
conducted to evaluate the effect of alternative repository
designs and alternative scenarios of natural-system behavior
at the potential Yucca Mountain high-level waste repository'.
The repository's predicted behavior is quantified using a
number of different performance measures, including the peak
engineered barrier system (EBS) release rate over the first
10,000 years, and the peak dose at the accessible environment
over the first 10,000 years and the first 1,000,000 years. Each
of these performance measures is affected by many repository
characteristics and parameters. It is important to devote the
available resources toward understanding those parameters
that have the most impact on the repository performance.
II. WORK DESCRIPTION
Latin Hypercube Sampling was used to sample the
approximately 260 stochastic parameters in the TSPA-1995
process models, for 100 realizations of the parameter
distributions. Based on simulations and expert judgement,
about 25 of these parameters were selected as potentially
being the most important. Stepwise regression was then used
to select the most important of these parameters, based on howDiSTRIBUTION OF THIS DOCUMENT
much of the variability in the performance measures could be
explained by subsets of these parameters.
Since the structure of the relationship between the model
parameters and the performance measures is unknown,
stepwise regression was performed on three transformations
of the data: rank regression, log-linear regression and log-log
regression. The log-log regression has the most intuitive
appeal, since many of the relationships are multiplicative, so
it is the only one presented here.
III. RESULTS
A. 10,000-Year Engineered-Barrier-System (EBS) Peak
Release Rate
For the cases analyzed, "Tc solubility, infiltration rate,
and spent-fuel dissolution rate are the three most important
parameters. Spent-fuel dissolution rate is important because
it determines the amount of radionuclides that are mobilized
allowing them to be transported out of the EBS. "Tc
solubility, in particular, is important because the "Tc
dominates the EBS releases rates. Also, since the EBS rate
is controlled by advection of the aqueous phase (water
dripping from fractures onto the waste packages), infiltration
rate is another important parameter.
B. 10,000-Year Peak Dose to the Accessible Environment
For the scenario analyzed, the top two variables are the
matrix velocity in the Calico Hills, nonwelded, vitric,
hydrogeologic unit (v,.,-CHnv) and the unsaturated-zone
Darcy flux or infiltration flux (. The latter is important
because the peak concentrations of the radionuclides do notUNUMT
MASTER
nc. 1
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Atkins, Joel E.; Sevougian, S. David; Lee, Joon H.; Andrews, Robert W. & McNeish, Jerry A. Important Parameters in the Performance of a Potential Repository at Yucca Mountain (TSPA-1995), article, June 1, 1996; United States. (https://digital.library.unt.edu/ark:/67531/metadc664666/m1/1/: accessed March 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.