Providing a Scientific and Technical Basis for Repository Decisions Page: 1 of 3
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Total System Performance Assessment:
2002 Providing a scientific and technical
basis for repository decisions
The Nuclear Waste Policy Act (NWPA) of
1982 directed the U. S. Department of
Energy (DOE) to research sites and design
a deep geologic repository for the disposal
of our nation's spent nuclear fuel and
high-level radioactive waste. In 1987,
Congress amended the NWPA and
directed the DOE to focus only on Yucca
Mountain, Nevada, to determine whether
it is a suitable site for a repository.
For more than 15 years, the DOE has
been studying Yucca Mountain and has
accumulated an enormous amount of
scientific and technical information about
the mountain and the area surrounding it.
The secretary of energy will decide
2000 whether to recommend Yucca Mountain
to the president as a suitable site for a
repository. This decision will be based on
the scientific and technical information
resulting from the Department of Energy's
studies of Yucca Mountain and on the
views and comments submitted by other
governmental groups and the public. One
required basis for the secretary's decision
will be a scientific analysis called a total
system performance assessment.
Total system performance
Total system performance means the
complete behavior of a geologic
repository system at Yucca Mountain in
response to the features, processes, and
events that may affect it. A geologic repository
would involve both natural and man-made
(engineered) systems. These systems would
interact with each other, acting as barriers to
water - the primary means by which
radioactive materials might escape from a
repository. Aspects of the natural system at
Yucca Mountain include the dry climate and the
nearly 2,000 feet of rock between the surface of
the mountain and the water table. The
engineered system includes such elements as
very durable waste packages, corrosion-
resistant drip shields over them, and the solid
form of the waste itself. These natural and
engineered systems would work together as
one overall repository system. How well they
would work together is a key question.
To answer this question, the DOE, the Nuclear
Regulatory Commission, and the Environmental
Protection Agency require what is called a total
system performance assessment, or TSPA.
Before such an overall assessment can be done,
however, scientists must understand the
features, events, and processes that could affect
the natural and engineered systems of a deep,
To do its job effectively, a TSPA must include
all relevant features, events, and processes that
could significantly affect the repository's
performance. Such a total assessment, however,
goes much further. A TSPA projects the total
combined behaviors of the various features,
events, and processes that would be involved.
These combined behaviors include such things
U.S. Department of Energy, Office of Civilian Radioactive Waste Management
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Providing a Scientific and Technical Basis for Repository Decisions, report, February 28, 2001; Las Vegas, Nevada. (https://digital.library.unt.edu/ark:/67531/metadc722861/m1/1/: accessed April 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.