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

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Response<br />

237<br />

GEOLOGIC CONSIDERATIONS<br />

The potential can be evaluated when a specific interior drainage area is selected for<br />

investigation. For a first consideration the fact that all surface run<strong>of</strong>f is contained<br />

within a basin is more favorable than a basin with a perennial stream or river flowing from<br />

it.<br />

Draft p. 3.1.24<br />

Issue<br />

The repository host rock will not neccessarilly be the primary geological barrier to<br />

waste migration. Man's intrusion or natural processes may put the primary dependence on<br />

other geologic formations. (113-EPA)<br />

Response<br />

Site selection and qualification will consider the rates <strong>of</strong> natural processes at a pro-<br />

spective site and will be considered in accepting or rejecting a site. Intrusion by man's<br />

activities is an accidental or "unplanned" condition that cannot be predicted. If the esti-<br />

mated rates <strong>of</strong> natural processes are acceptable and if there is no intrusion by man, the<br />

host rock will provide the primary barrier to waste migration over long time periods.<br />

Draft p. 3.1.24<br />

Issue<br />

Thermal uplift around the repository may increase the effective hydraulic conductivites<br />

<strong>of</strong> the host rock and may even result in flow paths between overlying aquifers and the<br />

repository. (208-NRC)<br />

Response<br />

Heat radiated by the waste and its induced thermal stresses in the host rock and repos-<br />

itory are described as posing the "most difficult engineering uncertainities and could have<br />

the most significant impact on the design and cost..." (draft p. 3.1.34). In general, the<br />

heat effects are expected to affect a small volume <strong>of</strong> rock compared to the volume <strong>of</strong> the<br />

host rock. Also, some consideration is given to adjusting the heat load per unit area by<br />

canister spacing or possibly reducing the waste density per canister (draft p. 3.1.35), if<br />

research and field tests show this to be necessary.

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