Salt Disposal of Heat-Generating Nuclear Waste

6. Damage Induced Permeability. Mechanically or hydraulically
induced permeability is based on the same microphysical process of
percolation flow along grain boundaries after exceeding a threshold. In
both cases the induced permeability is created by removal of intergranular
cohesion.
7. Consolidation of Hot Granular Salt. Crushed salt used as backfill
may be an important element in a potential HLW repository. Relatively
little elevated temperature mechanical testing has been conducted for
crushed salt. The accelerating effect of moisture on consolidation needs
further investigation. Modeling concerned with long-term, low-porosity,
two-phase flow is likely required.
8. Solubility and Transport. The salt repository community continues to
research radionuclide solubility as if there will be ample brine available
within the salt to dissolve and transport the waste. There are at least two
parts to this important issue: one concerns brine sources and volume, and
the other concerns existence of a pressure gradient capable of driving the
soluble radionuclides to the biosphere.
9. Degradation. This research area addresses the underlying hypothesis that
waste forms placed in salt will degrade sufficiently that the residue can be
removed readily by a human drilling intrusion.
10. Radiolysis. Radiation is known to liberate hydrogen but further data are
needed on the effect of combining radiation and temperature on the waste
materials, waste packages, and the salt.
11. Climate Changes. The radioactivity of nuclear waste will decay over a
period of time (100,000 years or longer) in which major environmental
changes are possible. Climate driven changes such as glaciation,
permafrost, and changes in sea level could affect the subsurface
environment of a salt formation and must therefore be considered in
performance and safety assessments.
4.7.2 Future Direction
The topics given above pertain to specific phenomena, several of which could be
incorporated into the next generation of repository performance assessment and
supporting models. Future directions for research collaborations could be twofold:
(1) exploring fundamental processes using laboratory investigations and
(2) exercising powerful new computational tools.
Stone et al. (2010) have completed fully coupled, three-dimensional (3-D),
thermal-mechanical simulations for a generic salt disposal scheme. These
calculations demonstrate the available tools for coupled, multiphysics modeling
and repository systems engineering. Several aspects of this nonlinear, thermalmechanical
analysis are especially important. Past analyses of salt creep and room
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