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

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6.87<br />

It appears possible, as an alternative, that the same shipping cask might be used for<br />

handling a waste canister first at the reprocessing plant, then for marine transport to the<br />

ice sheet, and finally for over-ice transport to the disposal site.<br />

Debarkation ports on the ice sheets with handling systems for unloading casks directly<br />

onto the over-ice transport system would be possible in the Antarctic or in Greenland, but<br />

might be very expensive. The currently preferred alternative is to dock the transport ship<br />

at a land-based port in an ice-free area to unload the casks into the over-ice transport<br />

vehicles.<br />

Emplacement. The waste canisters would be disposed <strong>of</strong> using one <strong>of</strong> the three basic con-<br />

cepts described in detail below.<br />

The meltdown or free flow concept is shown in Figure 6.1.17 (ERDA 1976). <strong>Waste</strong> would be<br />

disposed <strong>of</strong> by selecting a suitable location in the ice sheets, predrilling a shallow hole,<br />

lowering the canister into the hole, and allowing it to melt down or free flow to the ice<br />

sheet base and bedrock beneath (EPA 1979).<br />

The surface holes would be predrilled to depths from 50 to 100m and would provide pro-<br />

tective shielding from radiation during canister emplacement. To avoid individual canisters<br />

interfering with each other during descent and possible concentration at the ice sheet base,<br />

the suggested spacing between holes is about 1000 m.<br />

The canister meltdown rate is based on calculations from the penetration rates <strong>of</strong> ther-<br />

mal ice probes. It is estimated that the rate <strong>of</strong> descent for each canister would be on the<br />

order <strong>of</strong> 1.0 to 1.5 m/day. Assuming only vertical movement and an ice sheet 3000 m (9900 ft)<br />

thick, meltdown to the bedrock would take 5 to 10 years.<br />

t D n Anchored Surface<br />

Melt Down<br />

Emplacement Facility<br />

Drilling Surface Anchors<br />

Rig and Site Markers<br />

Melt .<br />

Heat<br />

Extended Legs<br />

Up to<br />

4000 Meters<br />

ce<br />

6117Surfa IceFIGURE Ice Sheet Emplacement Concepts<br />

;<br />

FIGURE 6.1.17. Ice Sheet Emplacement Concepts

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