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

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Response<br />

240<br />

GEOLOGIC CONSIDERATIONS<br />

Collapse <strong>of</strong> tunnels, cavern walls and ro<strong>of</strong>s and the engineered methods <strong>of</strong> counteracting<br />

and preventing this is discussed in Section 3.1.2. Considerable experience from the mining<br />

and construction industries indicates that during the operational and retrievable storage<br />

phases this should not be a problem. Once a repository is backfilled and sealed, collapse<br />

or partial collapse into the remaining open space in the future is a possibility. This is<br />

not considered to be a threat to the repository integrity and could eventually be beneficial<br />

by adding additional rock material or increasing the density <strong>of</strong> the backfill in the<br />

repository.<br />

Draft p. 3.1.29<br />

Issue<br />

Salt and abyssal-sea clay are more favorable than other media with respect to "unfor-<br />

seen rock conditions," "number and spacing <strong>of</strong> fractures" and assurance that significant<br />

discontinuities are not over looked. (154)<br />

Response<br />

This is true. However, these properties are only part <strong>of</strong> the total conditions and<br />

properties for a site/disposal medium.<br />

Draft pp. 3.1.30 and 3.1.116<br />

Issue<br />

One commenter pointed out that ground support in a shale repository at a depth <strong>of</strong> 600 m<br />

is likely to be a major and costly problem; support costs on draft, p. 3.1.116 are clearly<br />

understated. (208-NRC)<br />

Response<br />

See draft, p. 3.1.31, first paragraph. It is pointed out that shales are the most dif-<br />

ficult to support in underground openings; that tunneling and support could add signif-<br />

icantly to the costs; that a study at the Nevada Test Site has concluded that costs in shale<br />

could increase at least 25%, and could be much greater.<br />

Draft pp. 3.1.30-31<br />

Issue<br />

The draft Statement missed stressing its main point because <strong>of</strong> attempts to discuss<br />

minor problems. For example, the positive statement "...strength has major impacts on

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