Nature and engineering Working Together for a Safe Repository Page: 1 of 4


S -. .MOL.20000912.0334
science and engineering
2002 Nature and engineering working
together for a safe repository

If a repository were built at Yucca Moun-
tain, it would rely on two distinct systems
to prevent radioactive materials from
escaping into the environment. These
systems act as barriers to the movement of
radionuclides. The first system involves
natural barriers - the rocks, water, and
climate at Yucca Mountain. The second
system is comprised of an array of engi-
neered, or man-made, barriers that give
the repository defense in depth and add
safety margins. These systems would
work together to protect the public and
the environment.
The mountain's natural features present a
formidable line of defense against possible
2000 movement by radionuclides. These
barriers include Yucca Mountain's unique
geology, the region's dry climate, and, in
general, a range of enclosed water systems
that should slow water that contains
radioactive particles from reaching rivers
or other groundwater systems. The
mountain's natural barriers and planned
man-made barriers should prevent most
moisture from ever reaching the waste
packages within a repository. Moreover,
the natural barriers would slow the
movement of radioactive particles that do
dissolve in water.
The engineering, or technological mea-
sures, that would be built into a reposi-
tory at Yucca Mountain would help ensure
that health and safety standards are
maintained even if some components of

the natural system do not perform as expected
for the first 10,000 years of repository opera-
tion.
Natural barriers act together to slow
movement of radioactive particles
The dry, desert climate at Yucca Mountain is an
important natural barrier to radionuclide
movement, as are the low levels of rainfall in
the area. Any radioactive particles that have the
potential to move out of a repository will most
likely do so in water. But the Yucca Mountain
area receives less than seven inches of rainfall or
snow each year. Most of this moisture flows off
the surface of the mountain or evaporates
before seeping into the rock. Only very small
amounts of moisture ever reach the repository
level at all.
Another important natural barrier can be
found in the rock and minerals at Yucca
Mountain. With few exceptions, water moves
very slowly through this rock. In most
instances, it would take thousands of years for
the small amounts of water reaching the
repository level to soak through to the water
table situated hundreds of feet below the
potential repository. Some minerals within the
rock actually strain radioactive particles from
contaminated water, holding them in place in
the rock. Those particles that do reach the
water table would disperse in a larger volume
of water. The radioactive particles must then
be transported more than 12 miles through
the rock in the underground water before the
particles would reach an area where the water

12L

U.S. Department of Energy, Office of Civilian Radioactive Waste Management

2001

1998

-j>- V~ 041

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United States. Department of Energy. Nature and engineering Working Together for a Safe Repository, report, September 12, 2000; Las Vegas, Nevada. (https://digital.library.unt.edu/ark:/67531/metadc782349/m1/1/ocr/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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