Salt Disposal of Heat-Generating Nuclear Waste

To the extent that regulatory guidance has bearing on the technical basis for
disposal of HLW in salt, the following assumptions are made:
• This analysis focuses on the isolation provided by the disposal formation and
avoids speculation about site-specific aspects of geology closer to the ground
surface.
• EPA standards and NRC regulations pertaining to HLW disposal in salt would
place specific requirements on PA models that are intended to demonstrate
compliance with regulatory performance objectives.
• Screening criteria for potentially relevant features, events, and processes
(FEPs) would be defined through regulation and would be similar to those
summarized in Appendix A.
• New regulatory requirements would be developed for human intrusion
scenarios, which depend more on the overall setting of the repository than on
the geologic medium being considered.
• Requirements in both the EPA standards and the NRC regulations specific to
the retrievability of waste would be met by the existing technologies available
for HLW disposal in salt.
1.2 Salt Formations in the United States
Use of salt formations for nuclear waste disposal has been a widely embraced
concept for more than 50 years. Disposal of nuclear waste in salt remains a viable
concept in the U.S., as has been successfully demonstrated by virtue of more than
ten years of successful operations at the Waste Isolation Pilot Plant (WIPP) near
Carlsbad, New Mexico. As shown in Figure 1 and Table 1, the conterminous U.S.
has many salt formations, including bedded and domal salt.
For repository considerations and other uses, such as
petroleum storage, salt formations are often categorized as
“bedded” or “domal.” Bedded formations of salt (sodium
chloride) are found in layers interspersed with materials
such as anhydrite, shale, dolomite, and other salts such as
potassium chloride. These formations are tabular and can
range across enormous land areas (see Figure 1). Bedded
salt formations are often between 200 to 600 meters thick,
but in some cases they can have thicknesses of up to 1,000
meters in the U.S. Domal formations (i.e., salt domes)
form from salt beds when the density of the salt is less than
that of surrounding sediment. Under such conditions, the
salt has a tendency to move slowly upward toward the
Advantages of salt for HLW disposal
• Salt can be mined easily
• Salt has a relatively high thermal
conductivity
• Wide geographic distribution (many
potential sites)
• Salt is plastic
• Salt is essentially impermeable
• Fractures in salt are self-sealing
• Salt has been geologically stable for
millions of years
surface. As the buoyant salt moves upward, it deforms plastically into mushroomshaped
diapirs and many other cylindrical and anticlinal shapes. The top of some
domal salt can be near surface, while the root may extend to a great depth.
Typically the diameter of a salt dome is on the order of 5 kilometers.
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