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

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Response<br />

219<br />

GEOLOGIC CONSIDERATIONS<br />

The assumption is made in the Statement that for a deeply buried (600--plus m) geologic<br />

repository groundwater is the most likely agent to transport waste from the repository to<br />

man's environment. Over the long-term, faulting is considered as a means <strong>of</strong> forming pos-<br />

sible conduits for ground-water flow (See "Faulting and Flooding" accidentscenario, draft<br />

p. 3.1.147). For a sealed geologic repository, faulting is not considered disruptive if it<br />

does not lead to ground-water movement into or through the repository.<br />

Draft p. 3.1.5<br />

Issue<br />

Several commenters indicated that the definition <strong>of</strong> convection is incorrect. Convec-<br />

tion signifies the transport <strong>of</strong> a contaminent by a moving fluid. Thermal differences may<br />

produce fluid motions and thermally-driven convection must be considered in the analysis <strong>of</strong><br />

a radioactive waste repository. The usual driving force for ground-water flow is the head<br />

gradient. (208-NRC, 218-DI0)<br />

Response<br />

Convection concerns the transfer <strong>of</strong> heat by a moving fluid and can operate whether a<br />

contaminant is present or not. Convection effects as described in this section are those<br />

occurring within a repository and impermeable host rock. The repository and host rock under<br />

expected operating conditions will not behave as if they were in a saturated porous medium<br />

with flowing water. The convection effects could transport nuclides if the repository were<br />

to eventually fill with water and the heat from the waste could cause some thermally driven<br />

convection, even in the absence <strong>of</strong> any flow through the repository.<br />

Draft p. 3.1.5<br />

Issue<br />

Advection <strong>of</strong> nuclides with the local ground-water flow should be added to the list <strong>of</strong><br />

major mechanisms related to nuclide transport through the disposal media. (208-NRC)<br />

Response<br />

Transport by migrating ground-water is not included in the general list <strong>of</strong> mechanisms<br />

related to movement <strong>of</strong> nuclides because under normal operating conditions in the essentially<br />

impermeable disposal media flowing groundwater should not occur. That is, barring any<br />

breaching <strong>of</strong> the repository that would establish flow paths, any water movement through the<br />

repository should be so slow that other processes would be more important.

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