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

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Draft p. 3.1.124<br />

Issue<br />

254<br />

GEOLOGIC CONSIDERATIONS<br />

What the GEIS is really discussing is the creation <strong>of</strong> flowpaths by creating fractures<br />

or opening fractures that already exist. The question, then, is how does the predictive<br />

model treat the flow <strong>of</strong> liquids and transport <strong>of</strong> dissolved radionuclides through fractures?<br />

Both flow and transport could be significantly different in fractures than in porous media.<br />

We know that retardation is less and, also, that retardation is the most important attenua-<br />

tion mechanism that has been modeled. The term "thermally-induced permeability" does not<br />

convey the difference between porous flow and fracture flow. (208-NRC)<br />

Response<br />

The predictive models used do not treat flow or transport through fractures. A pre-<br />

vailing assumption for siting any nuclear waste repository is that ground-water flow rates<br />

will be very slow. If the flow velocity is high, then the repository will be located<br />

elsewhere.<br />

Retardation is not the "most" important attenuation mechanism modeled. Several disper-<br />

sion mechanisms exist that have a greater effect on maximum peak values. Examples include<br />

leach rate and spacial distribution <strong>of</strong> the waste in a repository. In certain instances,<br />

decay rate may have a larger attenuation than retardation.<br />

Draft pp. 3.1.136 and 3.3.3<br />

Issue<br />

Areas <strong>of</strong> uncertainty common to different alternatives should be treated equally. Tech-<br />

nology for long-term sealing, which has not been demonstrated, also does not receive uniform<br />

evaluation. (208-NRC)<br />

Response<br />

This type <strong>of</strong> treatment is being attempted in the revised Statement. Some <strong>of</strong> the prob-<br />

lems are not the kind that past experience has dealt with and others that may appear similar<br />

among the alternatives really are not. For example, to date, no structures have required a<br />

design life <strong>of</strong> even say one-thousand years, let alone to 10 thousand years. It is impracti-<br />

cal to try to demonstrate a thousand-year pro<strong>of</strong> period in real time. An example <strong>of</strong> apparent<br />

similarity is the sealing <strong>of</strong> a very deep hole and a mined repository in a deep hole, the<br />

"repository" is part <strong>of</strong> the drilled hole but in a mined repository the hole or shaft is only<br />

the access; the repository is constructed away from the hole and can be sealed separately.<br />

However, sealing the drilled surface to repository level will present similar problems.

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