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

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6.102<br />

cases, the injection liquid would contain large amounts <strong>of</strong> actinides, which might affect the<br />

thermal properties and interaction mechanisms <strong>of</strong> the waste in the host media. Well injection<br />

might also be used to dispose <strong>of</strong> high-heat-level partitioned wastes, which could relieve high<br />

thermal loadings in a mined geologic repository for example. Note that retrieval would be<br />

difficult and incomplete using either concept, although deep well injection would have more<br />

potential for at least partial retrieval than'would the shale-grout method, which would fix<br />

the waste in a relatively insoluble solid.<br />

For deep well injection, the liquid waste would have to be substantially free from all<br />

solid matter to prevent clogging <strong>of</strong> the formation pores. Filtration down to 0.5 m particles<br />

is typical for process waste injection systems (Hartman 1968). The waste would have to<br />

remain acidic to ensure that all the waste products stay in solution.<br />

For shale grout injection, neutralized waste (sludge and supernate) would be mixed with<br />

cement, clay, and other additives.<br />

<strong>Waste</strong> System Description<br />

The fuel cycle and process flows associated with the two reference options are illus-<br />

trated on Figure 6.1.19. Significant features <strong>of</strong> these concepts are summarized in Table<br />

6.1.19.<br />

Both concepts are based on restricting the maximum temperature in the injection forma-<br />

tion to 100 C (212 F), assuming a geothermal gradient <strong>of</strong> 15 C/km (44 F/mile), to avoid unde-<br />

sirable mineralogical effects that would occur at higher temperatures. (For example, canpar-<br />

atively large amounts <strong>of</strong> waste would be released from the clay mineral montmorillonite if<br />

TABLE 6.1.19. Reference Concepts Summary (DOE 1979)<br />

Reference Concepts Depth <strong>of</strong> Injection Disposal Formation<br />

Deep well liquid 100-m-thick zone Sandstone with shale<br />

injection at average caprock at 950-m<br />

depth <strong>of</strong> 1,000 m depth; porosity<br />

10 percent<br />

Shale grout 100-m-thick zone Shale extending to<br />

injection at average depth within 50 m <strong>of</strong><br />

<strong>of</strong> 500 m ground surface

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