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

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Response<br />

263<br />

GEOLOGIC CONSIDERATIONS<br />

Brine migration <strong>of</strong> liquid already present in the salt (0.1 to 1% by weight) and its<br />

migration up the thermal gradient toward the waste package is under extensive study. If the<br />

environment produced by elevated temperatures and the presence <strong>of</strong> brine have an adverse<br />

effect on the performance <strong>of</strong> the waste package, then materials must be selected which can<br />

withstand this environment. Data from package material design and performance testing would<br />

be used for package design and material selection to insure optimum waste package<br />

performance.<br />

Issue<br />

There are many problems specific to salt as a repository medium that should be<br />

addressed. (42, 68)<br />

Response<br />

Problems specific to salt as a repository material (e.g., thermal effects, lack <strong>of</strong><br />

sorption, closure rates, corrosive brines) are addressed in generally qualitative terms in<br />

Section 5.2. There are additional data in other reports (ERDA 1976b and Brandshaw et. al.<br />

1971). These have been incorporated into Section 5.2. The DOE Position Paper to the NRC<br />

rulemaking proceedings on nuclear waste storage and disposal (DOE 1980a) also contains an<br />

extensive discussion <strong>of</strong> the environmental conditions in a salt repository.<br />

Issue<br />

One commenter noted that linear thermomechanical analysis is applied to a repository<br />

in salt. Such an analysis can result in significant error in predicting thermomechanical<br />

effects. Even with this analysis a surface uplift up to 1.5 m is predicted. The important<br />

question not addressed in the GEIS is what effect will this have on shaft and borehole<br />

seals, thermally driven convection and breccia pipe formation? (208-NRC)<br />

Response<br />

The NWTS program has developed analytical and numerical solutions, and material proper-<br />

ties to apply non-linear thermomechanical analysis to the behavior <strong>of</strong> a repository in salt.<br />

These solutions and properties have been used to model the behavior <strong>of</strong> field experiments<br />

such as Project Salt Vault and Avery Island. These studies are continuing and the accuracy<br />

<strong>of</strong> modeling or predicting the behavior is expected to be improved. These improved models<br />

will be used to analyze the total behavior <strong>of</strong> a potential repository in salt.<br />

Issue<br />

"(Creep) is difficult to stabilize in tunnel openings."<br />

"From experiments...equations can be developed to describe the creep behavior <strong>of</strong> salt."

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