With an abundance of scientific information in hand, what are the remaining geomechanics issues for a salt repository for heat-generating nuclear waste disposal? The context of this question pertains to the development of a license application, rather than an exploration of the entire breadth of salt research. The technical foundation supporting a licensed salt repository has been developed in the United States and Germany since the 1960s. Although the level of effort has been inconsistent and discontinuous over the years, site characterization activities, laboratory testing, field-scale experiments, and advanced computational capability provide information and tools required for a license application, should any nation make that policy decision. Ample scientific bases exist to develop a safety case in the event a site is identified and governing regulations promulgated. Some of the key remaining geomechanics issues pertain to application of advanced computational tools to the repository class of problems, refinement of constitutive models and their validation, reduction of uncertainty in a few areas, operational elements, and less tractable requirements that may arise from regulators and stakeholders. This realm of issues as they pertain to salt repositories is being addressed in various research, development and demonstration activities in the United States and Germany, including extensive collaborations. Many research areas such as constitutive models and performance of geotechnical barriers have industry applications beyond repositories. And, while esoteric salt-specific phenomenology and micromechanical processes remain of interest, they will not be reviewed here. The importance of addressing geomechanics issues and their associated prioritization are a matter of discussion, though the discriminating criterion for considerations in this paper is a demonstrable tie to the salt repository safety case.
Geomechanical response of the geologic formation to perturbations caused by excavation, structural evolution over time, subsequent disposal of heat-generating waste, and emplacement of sealing systems are first-order concerns for heat-generating nuclear waste disposal in salt. Use of salt formations for toxic waste and transuranic waste disposal is supported by broad technical understanding and experience gained from operating facilities in the United States (U.S.) and Germany. The Waste Isolation Pilot Plant (WIPP) in New Mexico represents a successful process of site characterization and licensing of a salt repository in the U.S., while Germany has compiled the Preliminary Safety Analysis for Gorleben (Vorläufige Sicherheits-analyse Gorleben or VSG) . Sufficient scientific bases exist to develop a viable safety case for heat-generating waste if a national program should decide to move in that direction.