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

K.2 REMOVAL OF EMPLACED WASTE
K.23
Once wastes are emplaced at a geologic repository it is considered unlikely that they
will require removal. Confidence inthe suitability of the repository to isolate wastes
will be high at the time waste emplacement operations commence because of extensive
preemplacement testing and exploration, thorough DOE and peer review, and NRC licensing.
In spite of this, repository design takes into account the possible need to remove emplaced
wastes. Conditions that may be postulated to require waste removal include:
* detection of defective canisters that require removal, repackaging, and
reemplacement
* disqualification of a portion of the repository that neccessitates removal and
reemplacement of the affected canisters
* failure of in-situ tests and data acquired during monitoring of repository opera-
tions to provide sufficient confidence in long-term repository performance, which
requires removal of wastes and abandonment of the repository site.
As discussd in Section 5.3.1.5, wastes are emplaced in a readily retrievable manner
during initial operations and are emplaced recoverably during the remainder of repository
operations. Removal of emplaced wastes will require different levels of effort depending
upon the phase of repository operations during which removal takes. place.
K.2.1 Readily Retrievable Emplacement
During the initial phase of repository operation wastes are emplaced so that they can
be readily retrieved. During this period emplacement holes are lined with steel sleeves
and sealed with removable concrete plugs. The sleeves and plugs ensure that the canisters
.are accessible and minimize corrosion or other damage. Verification of repository func-
tions continues throughout the period of ready retrievability; extensive in-situ testing
rock core analysis, and other confirmatory programs are performed. In-situ testing and
monitoring include sensors for temperature, strain and pressure, and sampling systems for
air and ground water installed with a statistically significant number of canisters. From
these activities, additional data will become available for use in the various mechanis-
tic, computational models that form the basis for long-term projections of performance.
Should a decision be made to extend the period of readily retreivable emplacement
beyond the initial 5 years, the use of sleeve-lined holes and concrete plugs would
continue and rooms would be left open. For extension beyond a few years, the areal
thermal density of emplaced wastes may need to be decreased. By decreasing the amount of
thermal energy stored in the rooms, thermal stresses in the ceiling and supporting pillars
are reduced to the point where room opening stability can be reasonably assured for the
longer period.
Table K.2.1 lists calculated near-field local thermal densities for 25-yr readily
retrievable emplacement of 10-year-old spent fuel at the conceptual repositories located
in salt, granite, shale, and basalt formations. Consistent with the conservative approach