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

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Response<br />

366<br />

ALTERNATIVE DISPOSAL CONCEPTS<br />

A list <strong>of</strong> major problems has been identified as needing resolution before technical<br />

and environmental feasibility can be demonstrated. Of those that remain to be addressed,<br />

one is the movement <strong>of</strong> the canister or the sediment due to heat after emplacement. It will<br />

be two more years before assessment <strong>of</strong> the risks associated with either the sinking <strong>of</strong> the<br />

waste can through the sediment or the rising <strong>of</strong> the sediment and canister can be made. In<br />

either case, however, the risks attendant upon such movement will be minimal unless the<br />

canister is breached, which should not happen until at least 500 years has passed.<br />

Draft p. 3.6.8<br />

Issue<br />

Under current EPA regulations the canister must act as a barrier until the material<br />

decays to innocuous levels. The conservative calculational assumption, that the canister<br />

will release its entire inventory <strong>of</strong> wastes, does not reflect this regulatory requirement.<br />

(113-EPA)<br />

Response<br />

Although the canister will be engineered to contain the waste during its initial per-<br />

iod <strong>of</strong> high activity, calculations based on instantaneous release <strong>of</strong> the entire canister<br />

inventory <strong>of</strong> radionuclides provide the upper limit for the rate <strong>of</strong> release.<br />

Draft 3.6.8<br />

Issue<br />

"Since repackaged spent fuel rods contain less (emphasis added) fissionable material<br />

and fewer fission fragments than does a similar volume <strong>of</strong> processed HLW." This is true for<br />

fission fragments, it is not true for fissionable material.<br />

"Sediments which are hot (over 200 0 C) and moist." Nowhere can we find any value for<br />

the thermal conductivity <strong>of</strong> these "moist" sediments. It would seem as though the value<br />

might be higher than for conventional geologic media being considered. If so, the surface<br />

temperature <strong>of</strong> the canisters should be lower than that otherwise expected in conventional<br />

disposal systems. (154)<br />

Response<br />

The discussion in the draft Statement addresses the thermal impact <strong>of</strong> the waste. The<br />

higher fissionable element but lesser high heat fission fragment content <strong>of</strong> spent fuel pro-<br />

duces much less heat in the first several hundred years than the fission fragments <strong>of</strong> HLW.<br />

The thermal conductivty <strong>of</strong> saturated sediments at temperatures <strong>of</strong> 200 0 C and pressures <strong>of</strong><br />

500 bars in the subject <strong>of</strong> current study. (See also Sandia 198Oa.)

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