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

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334<br />

ALTERNATIVE DISPOSAL CONCEPTS<br />

DOE philosophy <strong>of</strong> providing for retrievability <strong>of</strong> waste in the event <strong>of</strong> some unanticipated<br />

event or repository shortcoming cannot be readily met for the rock melt concept. For this<br />

reason, among others, the rock melt concept is not considered worthy <strong>of</strong> further development<br />

at this time. The reader is referred to Section 6.2 .for a more complete discussion <strong>of</strong> the<br />

situation.<br />

Draft p. 3.4.6<br />

Issue<br />

It is stated that the consequences <strong>of</strong> seismic activity appear minimal with proper<br />

facility design. Discuss the effects <strong>of</strong> seismic activity on surface facilities supplying<br />

cooling water and cleaning up the steam, and on the reliable supply <strong>of</strong> cooling water to the<br />

waste. (208-NRC)<br />

Response<br />

A waste repository should be located against rigid siting criteria that are assumed to<br />

specify an aseismic area. Moreover, the surface facilities should be designed to survive<br />

significant (probably about 0.5 g) ground accelerations with complete containment <strong>of</strong> radio-<br />

activity. If water to the waste cavity is shut <strong>of</strong>f, the facility should be designed so that<br />

the emplacement shaft will close automatically, and the rock melting process will start.<br />

Thus, the cavity would not be available for additional waste (early melting started); how-<br />

ever, this is not serious economically and should have no significant effect on safety.<br />

Before rock melt could be seriously considered for a disposal operation the impact <strong>of</strong> seis-<br />

mic events would have to be considered. Empirical observations indicate, that unless an<br />

underground structure is transversed by a capable supporting surface equipment, such as<br />

cooling and steam clean up equipment, it would have to be designed to withstand a seismic<br />

event appropriate to the region in which the facility is located. This would be in conso-<br />

nance with the precept that waste disposal facilities would be required to meet appropriate<br />

standards which are applied to other nuclear fuel cycle facilities.<br />

Draft p. 3.4.9<br />

Issue<br />

A major point missed with rock melting is the consequent melt cooling. Differentiation<br />

will result, and the last formed liquids will concentrate elements such as uranium. This<br />

will form late hydrothermal liquids <strong>of</strong> extreme radioactivity. Whether or not this might<br />

result in criticality should be investigated. (43)

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