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

264
GEOLOGIC CONSIDERATIONS
Since equations have been developed which describe the behavior of salt a posteriori,
the GEIS should discuss whether they can predict the behavior of salt under thermomechanical
loading conditions. (208-NRC)
Response
Some amounts of creep can be tolerated with no adverse effects in a repository. Exces-
sive creep is not desirable and does present special engineering challenges. Stabilization
of openings against creep is generally possible.
The NWTS program includes study of existing data and ongoing laboratory and field tests
to. obtain the creep and other thermomechanical properties of salt. With this data and the
analytical studies also underway, it is anticipated that relationships will be developed to
adequately describe the creep behavior of salt. It has already been demonstrated, for exam-
ple, that the result of the Project Salt Vault field tests can be predicted to a reasonable
accuracy with the materials properties and analytical solutions now available. Predictions
of the behavior of salt under anticipated thermnnomechanical conditions will be included in
repository design studies.
Issue
It was noted that in view of recent news articles from Mississippi reporting accidental
releases of radioactive material from weapons testing sites, how does DOE view the integrity
of salt as waste repository media? (43)
Other commenters pointed out that disposal in salt repository will not work because
1) salt is often found near mineral deposits, 2) of drilling concerns, 3) presence of brines
will cause dissolution of waste form, 4) salt has low sorptive capacity, and 5) elevated
temperatures and pressures and the presence of water will compromise waste form. (62; 197)
Response
Some contamination by tritium has been observed at the Tatum Dome in Mississippi where
two test explosions of nuclear weapons took place in the mid-1960's. This contamination has
however been shown to be related.to disposal of tritiated water into surrounding aquifers
as part of the clean-up operations. Geologic repositories, as described in this Statement,
would only receive radioactive wastes in solid form. Contamination levels reported at the
Tatum Dome were caused by specific operations and practices completely different than those
to be undertaken in geologic repositories.
Salt is considered as a disposal medium because it has potentially useful properties
(plasticity, isolation from flowing water, etc.) and because of its stability. In the Stat-
ement it is treated as one of the four geologic materials that are being considered as can-
didate repository media. Salt has had relatively more investigation than. the other three
media types at this time, but as with the others, it requires continued study and
consideration.