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

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6.12<br />

storage facility (Bechtel 1979a). The entire emplacement facility would be on rails for<br />

movement from hole to hole on the site.<br />

As described above, canisters would be transferred from the receiving facility to the<br />

temporary storage facility, which would provide shielding and an accumulation area for can-<br />

isters to accommodate differences between transfer and emplacement operations. Emplacement<br />

equipment with cable totaling at least 10,000 m in length would lift a waste canister from<br />

temporary storage into a shielded cask, position it over the very deep hole, and lower it<br />

through the bottom <strong>of</strong> the cask into the hole (Bechtel 1979a). The waste canisters would be<br />

lowered into the lower 1,500 m (5,000 ft) <strong>of</strong> the hole with metallic honeycomb spacers placed<br />

between each canister to absorb impact in case a canister is dropped (Bechtel 1979a). If<br />

required by canister structural design limits, a structural plug, anchored to the sides <strong>of</strong><br />

the hole, would be emplaced between groups <strong>of</strong> canisters to support the load.<br />

Sealing Systems. After all waste canisters are in place, the hole would be sealed to<br />

isolate the waste from the biosphere. Sealing could include plugging both the hole and the<br />

damaged rock zones around the hole.<br />

The components <strong>of</strong> the sealing system would have to have low permeability to limit nu-<br />

clide migration and sufficient strength to maintain mechanical integrity for a specified<br />

period. Possible plugging materials include inorganic cements, clays, and rock. The specific<br />

material or materials would be selected for compatibility with the geologic medium and<br />

down-hole conditions (Bechtel 1979a). Plugging could be done with standard equipment typi-<br />

cally used by a drilling rig crew. For final sealing and closure <strong>of</strong> the very deep hole,<br />

drill rigs, similar to those described for hole drilling, would be set up at the hole loca-<br />

tion.<br />

Retrievability/Recoverability. <strong>Waste</strong> canisters would be retrievable as long as they are<br />

attached to a cable during the emplacement process. Once the canister is disengaged, it<br />

would become essentialy irretrievable. Post-enclosure recovery is likewise considered nearly<br />

impossible.<br />

6.1.1.3 Status <strong>of</strong> Technical Development and R&D Needs<br />

Present State <strong>of</strong> Development<br />

The status <strong>of</strong> equipment facility, and process development for different operational<br />

phases <strong>of</strong> VDH emplacement are considered below.<br />

Drilling Techniques. Four methods to excavate a very deep hole have been considered.<br />

These are oil field rotary drilling, big hole drilling techniques, drill and blast shaft<br />

sinking, and blind hole shaft boring. The latter three methods are limited in the depths<br />

that can be attained at present and in the foreseeable future. They might have applications<br />

in specific geologic media but will not be considered further here since the possibility <strong>of</strong><br />

their use appears remote for waste emplacement in this concept. For details on these con-<br />

cepts, see LBL (1979).

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