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

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Draft pp. 3.1.33 and 3.1.138<br />

Issue<br />

Response<br />

243<br />

GEOLOGIC CONSIDERATIONS<br />

One commenter questioned why 600 m is selected as the disposal depth. (40)<br />

The use <strong>of</strong> 600 m is an arbitrary depth selected from work done at the Carlsbad, New<br />

Mexico site. It is based on the depth (700 m) and the thickness (600 m) <strong>of</strong> the Salado for-<br />

mation. See Section B.1 <strong>of</strong> the final Statement.<br />

Draft p. 3.1.33<br />

Issue<br />

Ground-water flowing into operating mines (in Canadian Shield Granite) is probably<br />

evaporated by ventilation airflow. In the long run, seepage rates low enough to appear<br />

negligible by visual inspection are expected to be significant. (208-NRC)<br />

Response<br />

See draft p. 3.1.,49, where it is mentioned that flow rates and velocities that are<br />

insignificant over a 50-year period could be important over hundreds to thousands <strong>of</strong> years,<br />

and that it is reasonable to assume as one possibility that free water, over a period <strong>of</strong><br />

thousands <strong>of</strong> years, may enter the repository (with the possible exception <strong>of</strong> a salt repos-<br />

itory). It may be unrealistic to believe that any repository (excepting salt) would remain<br />

totally free <strong>of</strong> water for times up to a million years or longer. However, with careful site<br />

selection investigation, construction and a detailed knowledge <strong>of</strong> the site it may be pos-<br />

sible to show that the time <strong>of</strong> water ingress and/or the rate are such that the repository<br />

serves its purpose.<br />

Draft p. 3.1.33<br />

Issue<br />

This section states "Thus, cost considerations dictate that the depth <strong>of</strong> emplacement<br />

should be minimized, whereas isolation requires that the depth be maximized." The first<br />

part <strong>of</strong> that statement is sufficiently clear. However, it is not clear that the second part<br />

<strong>of</strong> the statement is correct or if correct, significant. The support for this part <strong>of</strong> the<br />

statement is qualitative and intuitive rather than quantitative and rigorous.<br />

Geological Survey Circular 779 states: "The suggestion <strong>of</strong> Winograd (1974) that waste<br />

be placed at relatively shallow depths (30 to several hundred meters) in the thick (as<br />

thick as 600 m) unsaturated zones <strong>of</strong> the arid Western United States deserves consideration."<br />

We concur.

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