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

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6.10<br />

The canister would have to provide for safe handling, shipping, and emplacement <strong>of</strong> the<br />

waste. Both the HLW and the spent fuel canisters would have to be packed solidly to avoid<br />

crushing due to hydrostatic pressure <strong>of</strong> drilling "mud" (lubricant) left in the hole to coun-<br />

ter lithostatic pressure. The canisters and spacers would have to be dense enough to sink<br />

through the mud slurry to the bottom <strong>of</strong> the hole. Carbon steel is considered as one candi-<br />

date canister material that will fulfill these requirements (Bechtel 1979a). However, more<br />

complex designs using multiple barriers may be required.<br />

The canisters for both HLW and spent fuel would have to be small enough for emplacement<br />

in a hole lined with a steel casing. HLW canister dimensions identified for the reference<br />

case accommodate the fuel. Dimensions identified for the reference case are 36 cm (14 in.)<br />

diameter and 4.6 m (16 ft) long (Bechtel 1979a and TID 1978).<br />

Site. The critical geologic parameters that will determine the feasibility and impact <strong>of</strong><br />

nuclear waste disposal in a deep hole system and that must be considered in site selection<br />

are:<br />

* Lithology<br />

* Tectonics and structural setting<br />

e Hydrologic conditions<br />

* States <strong>of</strong> stress<br />

* Mechanical properties <strong>of</strong> the rocks at depth<br />

* Natural thermal regime<br />

* Geochemical reactions.<br />

The interactions <strong>of</strong> these parameters and the effect <strong>of</strong> heating by the waste (thermomechani-<br />

cal factors) may also be significant. Geologic assumptions underlying the VDH concept are<br />

that the hole will be drilled, or a shaft excavated, in a regime <strong>of</strong> moderate to low geother-<br />

mal gradient in rock with high strength and low permeability. Furthermore, the wastes are to<br />

be deposited irretrievably - not stored (LBL 1979). The specific geotechnical considerations<br />

are addressed in detail in LBL (1979) and Brace (1979).<br />

Since more holes would be needed, emplacement <strong>of</strong> spent fuel during a 40-year period would<br />

require a total land area <strong>of</strong> approximately 140 km 2 . Canisters would be shipped by rail<br />

from a processing and encapsulation facility to the repository site, which would consist <strong>of</strong> a<br />

number <strong>of</strong> drilled holes around a centrally located receiving facility (Bechtel 1979a).<br />

<strong>Waste</strong> Receiving Facility. The central waste receiving facility at the deep hole site<br />

would be used to unload the waste canisters, store them temporarily, and perform any work re-<br />

quired to assure prompt emplacement in the hole. The receiving building would contain a cask<br />

handling area, a canister storage area, a hot cell, and auxiliary facilities (see Bechtel<br />

1979a).<br />

The cask handling area would contain facilities for receiving, cleaning, and decontami-<br />

nating shipping casks and for reloading empty casks on rail cars. Upon arrival, an overhead

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