Salt Disposal of Heat-Generating Nuclear Waste

several potential coordinated research areas. An abbreviated list of research topics
derived from the workshop is given here, and a more comprehensive summary
has been published (Karlsruher Institut für Technologie 2010). Some
collaboration topics are less research oriented, than they are recognized needs to
review and summarize existing information to address technical issues, before
embarking on research collaborations. In several instances, research topics for
collaboration were clearly identified.
The primary attributes of salt disposal are known and have been demonstrated at
an operational scale over many years. However, there remain issues that have
either not been substantially investigated or have not been reviewed to the point
of objective reconciliation. This section examines some of these issues identified
at the workshop. It is noted that some statements of technical sufficiency, or a
lack thereof, are technical judgments in the absence of supporting scientific
evidence. However, in most cases, the questions arise from established research
inquiries. For comprehensive pursuit of salt repository science, the investigators
should evaluate the full range of these issues.
The following list from the U.S./German Workshop-Mississippi salt workshop
gives the status of phenomena or processes, which may need to be incorporated
into PA or supporting models, and may require research collaboration:
1. Brine Migration. Brine exists in bedded salt in three forms: fluid
inclusions, hydrous minerals, and grain boundary water. Owing to the
characteristics and environments of the brine in salt, its transport or
migration occurs via three primary mechanisms: motion of the brine
inclusions in a temperature gradient, vapor-phase transport along
connected porosity, and liquid transport driven by the stress gradient.
2. Vapor Transport. One of the most important issues in a HLW
repository is the presence and fate of any brine that may be present.
3. Gas Generation and Pressure Buildup. Hydrogen gas generation
from anaerobic corrosion of steel container materials might inhibit rock
convergence and consolidation of crushed rock backfill. The associated
hydrogen volumes and rates require further quantification.
4. Buoyancy. Movement of canisters containing heat-generating wastes,
buried in salt-derived materials, has been postulated in the past. The
existence of buoyant forces due to density differences, and thermally
activated deformation, suggests the possibility of thermally driven
convection or flow resulting in canister movement.
5. Heat Effects. It is widely held that the heat load from HLW is
detrimental to operations and long-term isolation in salt. This perception
may be balanced by accounting for heat effects that are favorable to
operations and long-term safety.
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