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

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Response<br />

335<br />

ALTERNATIVE DISPOSAL CONCEPTS<br />

This point is addressed in Section 3.4.2.8 <strong>of</strong> the draft Statement, Study <strong>of</strong> Criticality<br />

Potential in Rock Melting (p. 3.4.8). As pointed out in Section 6.1.2.2 <strong>of</strong> the final State-<br />

ment, only the use <strong>of</strong> liquid high level waste from reprocessing is assumed for the reference<br />

case, and this waste is relatively low in fissile isotopes. Thus, in the reference case,<br />

spent fuel is not.considered due to "uncertainties associated with emplacement, such as<br />

additional criticality concerns..." While it is not yet accepted unequovically that the<br />

last formed liquids will concentrate uranium, this is a distinct possibility. Other pos-<br />

sible mechanisms can be postulated also, so that the concern over criticality is quite<br />

pertinent.<br />

Draft p. 3.4.10<br />

Issue<br />

Figure 3.4.4 does not present the temperature pr<strong>of</strong>iles that are necessary to completely<br />

characterize the extent and duration <strong>of</strong> the thermal load on the host media. The maximum<br />

increase in temperature at the earth's surface can occur hundreds <strong>of</strong> thousands <strong>of</strong> years<br />

later than shown. (Numerical models can be very costly to run for long times and distances<br />

require, however any analytic model is available. See Reference 3 <strong>of</strong> Appendix C <strong>of</strong><br />

TID-28818 (Draft), "Subgroup Report on Alternative Technology Strategies for the Isolation<br />

<strong>of</strong> Nuclear <strong>Waste</strong>.") (208-NRC)<br />

Response<br />

Figure 3.4.4 was intended to be only illustrative <strong>of</strong> the relatively early temperature<br />

distribution around a rock melt repository. Future engineering studies would investigate<br />

this topic in the necessary detail. In addition, site-specific calculations should be made<br />

to determine the effects <strong>of</strong> different strata, aquifers, etc.<br />

Draft p. 3.4.13<br />

Issue<br />

If operations as unattractive as grinding solidified HLW to a powder are proposed, the<br />

full impact <strong>of</strong> those operations should be included. (58)<br />

Response<br />

This commenter raises an important point regarding the rock melt information in the<br />

draft Statement. The potential approach questioned has been eliminated from the reference<br />

concept in the final Statement since there is no obvious reason to first convert liquid<br />

high-level waste to glass and then to convert that to a powder. The high-level liquid<br />

itself has the desired properties for direct emplacement in this concept.

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