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

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321<br />

ALTERNATIVE DISPOSAL CONCEPTS<br />

say for certain how deep fractures and joint patterns extend that do contain some water,<br />

not only in sedimentary rock but also crystalline rocks. Even very small amounts <strong>of</strong> water<br />

could be vaporized by radioactive decay. The steam would travel upward, lose temperature<br />

until it became a liquid and then could contaminate the surrounding groundwater. This<br />

water in turn could contaminate a major aquifer within a large area. (9, 36)<br />

Response<br />

Revised and updated information regarding the question <strong>of</strong> "How deep is deep enough?"<br />

is presented in the final Statement. The question <strong>of</strong> migration <strong>of</strong> nuclides to the bio-<br />

sphere, via steam particles or other means, would be the subject <strong>of</strong> possible future tech-<br />

nical studies for the very deep hole concept. It is important, however, to recognize that<br />

the pressure at depth is likely to prevent the formation <strong>of</strong> a phase fluid.<br />

Draft p. 1.24<br />

Issue<br />

The last paragraph implies that rock structures can be determined to be unfractured.<br />

Is this implication accurate, or should the statement be qualified or rewarded? (124)<br />

Response<br />

The draft Statement acknowledges that rock characteristics, including fracturing, are<br />

not well known at these depths. The sentence in question was intended to suggest that a<br />

good site selection for a deep hole would contain predominant unfractured rock. Whether<br />

such a deep rock section can be located remains to be determined. See Section 5.1.1 and<br />

Appendix B <strong>of</strong> the final Statement for a more complete discussion <strong>of</strong> the uncertainties <strong>of</strong><br />

geology and hydrology <strong>of</strong> depth.<br />

Draft p. 1.25<br />

Issue<br />

Experience <strong>of</strong> rock bursts in deep mines (approaching 4 km depth) is cited on p. 1.12<br />

in the geologic disposal section for mines 600 m deep but not here for deep holes 4 to 10 km<br />

deep. (181)<br />

Response<br />

The deep hole concept is somewhat different than the conventional geologic disposal<br />

concept in that the waste canisters will be placed directly into the drilled shafts. As a<br />

result, it is not anticipated that anyone will be physically inside these shafts at the<br />

depths considered for deep hole disposal. In addition these holes will have a drilling<br />

fluid in them to help keep the side wall material in place.

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