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

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6.167<br />

fuel assemblies would be approximately 48 cm in diameter. After emplacement <strong>of</strong> approxi-<br />

mately 150 packages in the bottom 1,500 m <strong>of</strong> the hole, the hole would be sealed and filled.<br />

A reprocessing fuel cycle would require that prior to emplacement, high-level liquid<br />

waste be converted to an immobile solid and incorporated into a multibarrier package com-<br />

patible with the very-deep hole environment. TRU waste resulting from reprocessing would<br />

be disposed using other suitable disposal concepts (Table 6.2.1).<br />

6.2.1.3 Rock Melting<br />

In the rock melting concept, disposal <strong>of</strong> high-level and some TRU waste would be<br />

achieved by remote emplacement <strong>of</strong> liquid or slurried waste into a mined cavity. Decay heat<br />

would be allowed to melt the surrounding rock which eventually would solidify, and form a<br />

solid, relatively insoluble, rock-waste matrix. Engineered containment could be provided<br />

during the operational period by a temporary chamber lining; however, engineered barriers<br />

would not be present during the molten phase. Following solidification, the rock-waste<br />

matrix would provide quasi-engineered containment wherein the host rock and waste forms<br />

would provide suitable post-solidification properties. Isolation and natural barriers would<br />

be provided by the surrounding geologic and hydrologic environment which would be selected<br />

to provide stability, minimal hydrologic transport potential and low resource<br />

attractiveness.<br />

Spent fuel would be converted to a slurry or dissolved at a waste processing facility<br />

located at the repository site. Plutonium and uranium could be chemically separated and<br />

sent to a mixed oxide fuel fabrication facility if a reprocessing fuel cycle were utilized.<br />

High-level waste and contact-handled TRU waste in liquid or slurry form would be piped sep-<br />

arately to the repository. Here the waste would be injected into mined cavities approxi-<br />

mately 20 m in diameter and 2,000 m deep. Liquid or slurried contact-handled TRU waste,<br />

supplemented with water as required, could be injected into the cavity to provide cooling.<br />

After the cavity is filled, cooling would be terminated and the injection shaft sealed.<br />

Heat from radioactive decay would melt the surrounding rock, forming a molten rock-waste mix<br />

at a temperature 21000 0 C. The mix would eventually solidify, trapping the waste within a<br />

rock matrix. Solidification should be complete in about 1,000 years.<br />

Fuel hardware and TRU waste for which conversion to liquid or slurry is impractical<br />

would be packaged and emplaced using a suitable alternative disposal concept (Table 6.2.1).<br />

6.2.1.4 Island Mined Repository<br />

In the island mined repository concept, disposal <strong>of</strong> waste would be achieved by manned<br />

emplacement in mined chambers in stable geologic formations on continental islands. Engi-<br />

neered containment would be provided by the waste form and multibarrier package. Tailored<br />

sorptive backfill would provide an additional engineered barrier. Isolation and natural<br />

barriers would be provided by the host rock and the surrounding geologic and hydrologic<br />

environment which would be selected to provide stability, minimal hydrologic transport<br />

potential and low resource attractiveness.

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