Radioactive Waste Management by Burial in Salt Domes

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Ledbetter, Joe O.
Kaiser, W. R.
Ripperger, E. A.

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Questions regarding the suitability of salt domes as sites for high-level radioactive waste repositories are considered. Since wastes will have to be retained for thousands of years, the principal questions pertain to the geologic stability of the dome and the possibility of dissolution.

No direct evidence is available to show that movement is positively not occurring in any salt dome. However, it is shown through geologic reasoning that the likelihood of movement of domes in the interior basins is extremely remote. If movement is occurring, it is taking place at such a slow rate as to present no problems. It is also believed that the likelihood of future movement as a result of geological activity within the storage time span is very remote.

The possibility of dissolution to the point that it might become a threat to containment is found to be slight, particularly if the repository is surrounded by shale and below the base of fresh water or actively circulating groundwater. Other mechanisms which protect against dissolution are discussed, as well as evidence of dissolution, or non-dissolution in the past. The consequences of dissolution are also examined. Possible flooding of repositories in domes was found not to be a serious threat.

Temperature rise data from Project Salt Vault are used to estimate temperature rises which might occur in domes, and some simplified calculations are made to determine the temperature rise that would occur under certain hypothetical conditions. These data indicate that heating, to the extent expected, poses no threat to dome stability.

The available data indicate quite definitely that creep or plastic flow around a cavity mined in salt causes the cavity to close, but the rate of closure is so slow as to present no serious problems in the operation of a repository.

Dome and bedded salt are compared as to their suitability for radioactive waste repository sites. Neither is superior to the other in an overall sense. In fact, depending upon the ultimate repository design, dome salt may be the preferred geologic formation. In a survey of all known domes, 29 were identified as potentially acceptable candidates for a waste repository. Objections to domes based on their future tectonic stability and hydrologic integrity can be met. Characteristics of the ideal dome for a radioactive waste repository are summarized. At least five domes meet most of the criteria of the ideal dome. Recommendations are made to enable the selection of the right dome.


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