Summary: | The program for disposal of high-level and transuranic radioactive
waste in the United States calls for establishment of a mined repository
in geologic formations that will provide for retreivability of the vaste
for 50 years. The goal of radioactive waste isolation in mined
repositories is to prevent unacceptable concentrations of radionuclides
from migrating to the accessible environment. Early concepts of highlevel
radioactive vaste disposal assumed that containment of the waste
by the enclosing rock would be virtually complete. With the application
of broader scientific and engineering disciplines, specifically geology
and hydrology to the study of prospective environments for vaste
disposal, the realization came that total isolation of the vaste in the
immediate vicinity of the repository cannot be ensured. Furthermore, it
vas realized that the geological and hydrological methods available today
are not appropriate for predicting conditions or events that may prevail
during the extremely long time required for waste isolation. Earth
processes that are of major concern during the waste-isolation storage
time include: (1) rates of radionuclide transport in the ground-water
flow system which, in turn, reflect chemical reactions of radionuclides
with ground water and earth materials; (2) climatic changes; and (3)
tectonic and associated erosional events. To compensate for the
limitations in our knowledge, the current rationale for waste isolation
emphasizes the need for a series of independent barriers to vaste
migrations. Multiplicity of these barriers, both engineered and natural,
will compensate for uncertainties in predicting natural and man-induced
conditions and events that may occur during the time required for waste
isolation.
The site selected for intense study for suitability of high level
and transuranic radioactive waste isolation is Yucca Mountain in the
desert of the southern part of the State of Nevada. The target buiial
zone is in welded tuff at a depth below the surface of about 300 meters.
The burial zone is in the unsaturated ?^np about inn me fers above the
water table. The climate is arid; the average precipitation is about
150 mm/yr. Studies are currently ongoing to determine if the site vill
provide long term isolation of radioactive waste.
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