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General Information
Viability Assessment of a Repository at Yucca Mountain
Over the past 15 years, the U.S. Department of Energy (DOE) has
been studying a site at Yucca Mountain, Nevada, to determine whether
it is a suitable place to build a geologic repository for the
Nation’s spent nuclear fuel and high-level radioactive waste. In
1996, the DOE announced that it would prepare a Viability Assessment
of a Repository at Yucca Mountain to present the results of the
DOE’s study thus far and identify the critical issues that need to
be addressed.
What are the results of the Viability Assessment? No show
stoppers have been identified to date at Yucca Mountain.
- Work should proceed toward a decision in 2001 on whether to
recommend the site to the President for development as a geologic
repository.
- Uncertainties remain about key natural processes, the
preliminary design, and how the site and the design would work
together.
- To address these uncertainties, the DOE plans to improve the
preliminary design, complete critical tests and analyses, and
include a description in a final environmental impact
statement.
- When this work is completed in 2001, a decision will be made
by the Secretary of Energy on whether to recommend the site to the
President for development as a repository.
What is in the Viability Assessment?
The Overview of the Viability Assessment of a Repository at Yucca
Mountain describes the worldwide nuclear waste problem and explains
why the United States and other nations are considering deep
geologic disposal as the solution. The overview then discusses
highlights of the research described in Volumes 1 through 5
of the Viability Assessment.
Volume 1: "Introduction and Site Characteristics"
Yucca Mountain is located about 100 miles northwest of Las Vegas,
Nevada. Yucca Mountain is on the edge of the Nation’s nuclear
weapons test site, where more than 900 nuclear tests have been
conducted. This unpopulated land is owned by the federal
government.
Yucca Mountain is a flat-topped ridge running six miles from
north to south that has changed little over the last million years.
Based upon what is known about the site, disruption of a repository
at Yucca Mountain by volcanoes, earthquakes, erosion, or other
geologic processes and events appears to be highly unlikely.
Yucca Mountain has a desert climate. This is important because
water movement is the primary means by which radioactive waste could
be transported from a repository to the accessible environment. On
average, Yucca Mountain currently receives about seven inches of
rain and snow per year. Nearly all the precipitation, about 95
percent, either runs off or evaporates. Geological information
indicates that the regional climate has changed over the past
million years, and the long-term average precipitation has been
about 12 inches per year (comparable to that of present-day Santa
Fe, New Mexico). Even if this were to be the case in the future, it
is believed that most of the water would run off or evaporate rather
than soak into the ground and possibly reach the repository.
A repository would be built about 1,000 feet below the surface
and 1,000 feet above the water table. Any precipitation that does
not run off or evaporate at the surface would have to seep down
nearly 1,000 feet before reaching the repository and through another
1,000 feet of the unsaturated zone before reaching the water table.
The groundwater in the region is trapped within a closed desert
basin and does not flow into any river that reaches the ocean.
Volume 2: "Preliminary Design Concept for the Repository and
Waste Package"
The primary design objectives for the repository follow:
(1) protecting the health and safety of both the workers and
the public during the period of repository operations,
(2) minimizing the amount of radioactive material that may
eventually reach the accessible environment, and (3) keeping
costs down to an acceptable level. To achieve the design objectives,
engineers work with scientists to design the man-made components of
a repository to work with the natural barriers—the geology and
climate of Yucca Mountain—to contain and retard the movement of
waste for thousands of years.
According to the preliminary design, spent nuclear fuel and
high-level radioactive waste would be transported to Yucca Mountain
by truck or rail in specially designed shipping containers approved
by the Nuclear Regulatory Commission. It would then be (1) removed
from the shipping containers and placed in long-lived waste packages
for disposal, (2) carried into the underground repository by
rail cars, (3) placed on supports in the tunnels, and (4)
monitored until the repository is finally closed and sealed. The DOE
plans on improving the current design and is evaluating alternative
designs and design features that could reduce uncertainties and
improve performance.
Volume 3: "Total System Performance Assessment"
Using data about the site and the preliminary designs, scientists
build detailed mathematical models of the features, events, and
processes that could affect the performance of a repository’s design
if it were built and nuclear waste were emplaced. The performance
assessment shows that the most significant single factor affecting
the ability of the repository to protect public health and safety
would be the amount of water that eventually contacts the waste.
Volume 4: "License Application Plan and Costs"
To obtain a Nuclear Regulatory Commission license, the DOE must
demonstrate that a repository can be constructed, operated,
monitored, and eventually closed without unreasonable risk to the
health and safety of workers and the public. In the next four years,
the DOE will focus on improving the repository and waste package
design, strengthening the understanding of the natural processes,
preparing the environmental impact statement, and developing the
information needed to support a site recommendation decision.
Volume 5: "Costs to Construct and Operate the Repository"
The additional cost to license, construct, operate, monitor, and
close a repository is estimated to be $18.7 billion in constant 1998
dollars. This cost estimate includes monitoring a repository for 100
years and disposing of 70,000 metric tons of spent nuclear fuel and
high-level waste at Yucca Mountain, currently the legal limit that
can be disposed of.
A monitored geologic repository is only one component of the
total life cycle cost for the waste management system, however.
Other components include the following: (1) transporting waste
to, then storing it at the repository,
(2) payments-equal-to-taxes and other benefits to the State of
Nevada and affected units of local government, (3) expansion of
the repository beyond the 70,000 metric-ton statutory limit, if
authorized, and (4) overall system management. The total
estimated future cost is $36.6 billion in constant 1998 dollars.
This covers 1999 through repository closure in 2116.
What is the long-term plan?
The Nuclear Waste Policy Act sets forth a multi-step process for
deciding whether to proceed with development of a repository at
Yucca Mountain, and the DOE has a tentative schedule for completing
this process. A negative decision at any step would stop the process
and require the Secretary of Energy and the Congress to develop a
different approach to solving the Nation’s nuclear waste
problem.
- Before deciding whether to recommend the Yucca Mountain site
to the President, the Secretary of Energy will conduct a formal
evaluation of the site, hold public hearings in the vicinity of
Yucca Mountain to inform the residents of the possible
recommendation of the site, and receive the comments of interested
parties. The current schedule calls for the Secretary of Energy to
decide whether to recommend the site in 2001.
- If, after these considerations, the Secretary of Energy
decides to recommend the site, the President would then decide
whether to recommend the site to Congress.
- If the President recommends the site to Congress, the Governor
or legislature of Nevada may submit a notice of disapproval. If
either does so, Congress must decide whether to override the
notice of disapproval and approve the Yucca Mountain site.
- If Congress approves the Yucca Mountain site, then according
to the current schedule, in 2002, the DOE would submit an
application to construct a repository to the Nuclear Regulatory
Commission.
- If the Nuclear Regulatory Commission approves the application,
the DOE would construct a repository and apply for a license to
begin receiving waste for disposal in the repository.
- If construction proceeds as currently planned, and the DOE
receives a license to operate the repository, then waste
emplacement could begin in 2010.
Concluding observations: achieving reasonable assurance
Based on the results of the Viability Assessment, the Department
believes that scientific and technical work at Yucca Mountain should
proceed to support a decision by the Secretary of Energy in 2001 on
whether to recommend the site to the President for development as a
geologic repository.
The performance of a geologic repository over such long time
periods cannot be proven beyond all doubt. Forecasts about future
geologic and climatic conditions, and engineering estimates of how
long the waste packages will remain intact, cannot be directly
validated. The mathematical models used in the performance
assessment are subject to uncertainties that can be reduced but
never completely eliminated.
The challenge in licensing a geologic repository is demonstrating
compliance with long-term safety standards for many thousands of
years. The Nuclear Regulatory Commission’s general standard for
meeting geologic repository regulatory criteria and objectives is
reasonable assurance. While considerable uncertainties remain today,
DOE believes that reasonable assurance should be achievable in the
licensing process after the planned work is completed. The DOE
believes, therefore, that ongoing work at Yucca Mountain should
proceed as planned.
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Update June 1999 |
