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

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GEOLOGIC CONSIDERATIONS
The Teknekron, Inc. report prepared for PNL, "A Cost Optimization Study for Geologic
Isolation of Radioactive Wastes," May 1979, does not indicate any significant advantages to
great depths of burial except the reduced probability of repository disruption. If the
large meteorite strike is truly improbable and if erosion and glaciation can be avoided (at
least during the first 10's of thousands of years) then there may not be any advantages to
great burial depths, only disadvantages.
The following questions should be addressed:
1. Are there regions of the U.S. otherwise suitable for a repository which can provide a
safe environment for the waste at relatively shallow depths without a meaningful threat
of interruption by natural events?
2. If so, what is the reduction of risk between such a repository and a deep repository
(and what is the increase in cost)? What is the potential for an increase in confi-
dence which could result in a more complete site characterization and simpler modeling
of a shallow versus deep repository?
3. If not, what is the quantitative reduction in risk as a function of depth for a deep
Response
repository? (208-NRC)
For the reconnaissance and generic treatment of the geologic considerations, contain-
ment of the waste and isolation from man's environment were the prime considerations. Depth
to the repository has been an unresolved issue (draft p. 3.1.25) and the early estimates of
depth were made for bedded salt (draft p. 3.1.48). In general the reduced probability of
disruption provided by deeper burial was assumed to be desirable. Because neither a rock
type or geographic area is specified in this Statement and because cost was not consid-
ered to be an environmental factor, cost-depth considerations were only treated
qualitatively.
The Winograd concept would store waste in mesas and buttes in the arid west. The waste
would be placed in unsaturated (above the water table) material and could require shallow
depth because of the high elevation of the unsaturated material above the surrounding land
surface and/or the relatively great depth to saturated material. However, mesas and buttes
are erosional remnants that are exposed to surficial processes and they are being reduced
in area even under today's arid climate. These features were considered more temporary than
a buried rock unit that is not exposed to surface processes. The concept is worth consider-
ation as a special case and could well be useful if a time of containment is firmly fixed
and if the present arid conditions remain unchanged.
Sections 5.1 and 5.2 of the final Statement discusses disposal of waste, in geologic
units within the earth, from a generic standpoint; depth of repository is one of the rele-
vant geologic factors mentioned and discussed, but in general terms rather than specific.
These factors all are concerned with the location and/or performance of a repository. The