Management of Commercially Generated Radioactive Waste - U.S. ...

B.1
APPENDIX B
GEOLOGIC DISPOSAL SUPPLEMENTARY INFORMATION
Factors relevant to selection of a geologic repository include the depth of the reposi-
tory; the size and properties of waste form and host rock; seismic, tectonic and magnetic
characteristics of the proposed repository; the hydrologic system and material resources
near the repository; and the use of multiple geologic barriers. These factors will be con-
sidered in a three-stage site selection process.
B.1 DEPTH OF REPOSITORY
The optimum depth of the waste emplacement zone is a function of the geologic media and
is thus site specific. A depth of 600 m is frequently cited because it is proposed depth
for a test facility in salt in New Mexico (Claiborne and Gera 1974). A 1000 m depth has
frequently been mentioned in the literature. The repository must be deep enough to rule out
any significant effects from disruption by surface phenomena and to provide as long a path-
way to man's environment as possible. Because of the variety of geologic media and settings
in the United States, it should be possible to find a number of sites having appropriate
host rock at suitable depths.
Because destructive natural surficial processes (for example, erosion, climate and
weathering) may reduce the depth to the repository, the host rock should be deep enough to
separate the repository from these processes and thus maintain geologic isolation. Base-
line data to evaluate these factors can be obtained from historic and geologic evidence.
Climatic conditions and associated erosional and weathering processes have an influence to
variable depths, depending upon local conditions.
Climate and rock properties provide the conditions for erosion and weathering. The
energy for transport of earth materials is provided by running water, moving ice, wind, and
gravity. Records of present and paleoclimatic conditions must be evaluated to predict
future climatic variations and to estimate possible depths of erosion. Typical climatic
and related factors to be evaluated at a repository site include:
* daily and seasonal atmospheric conditions
* latitude and longitude
* altitude
* position with respect to ocean and/or global wind circulation patterns.
These four parameters are basic data required to establish the types of weathering forces
and erosion that will act to reduce depth. For example, a high-latitude site and a pos-
sible past history of glaciation at these latitudes indicate a potential for glacial
erosion.
The repository site can be characterized by its topography (land-surface configura-
tion), unconsolidated surficial materials (soil), and underlying rock. Earth materials sur-
rounding the repository are the prime barriers to movement of radioactive waste to the