State-of-the-Art Evaluation of Repository Sealing Materials and Techniques.

Abstract

Under the auspices of the OECD/NEA Stripa Project, a state-of-the-art evaluation of repository sealing materials and techniques has been undertaken with particular application to crystalline rock. The objectives of the evaluation were (1) to review progress to date in the development of repository sealing materials and emplacement techniques; (2) to identify priority materials for sealing narrow aperture fractures in crystalline rock, including issues of technical concern to the long-term effectiveness of such materials; and (3) to provide a framework for advancing an in situ fracture-sealing test program that can be designed and implemented at the Stripa Mine.The classes of sealing materials that were considered included cementitious materials, natural clay materials, chemical grouts, fracture-filling synthetic minerals, ceramics, and metals. Of these, cementitious materials and natural clay materials were recommended as high-priority materials for further study because they can be designed to meet desired repository performance characteristics, there is considerable history of successful use in similar engineering applications, and there is indirect evidence that they will continue to perform as expected for long periods of time. Techniques for the emplacement of these sealing materials in rock fractures include pressure injection, dynamic (or vibratory) injection, and electrophoresis.

Initial field testing definition of subsurface sealing and backfilling tests in unsaturated tuff; Yucca Mountain Site Characterization Project

“…Chemical grouts can strengthen the geologic media into which they have penetrated and they can reduce the permeability of the grouted mass. Gnirk (1987) found that chemical grouts tend to shrink and the grouted zones tend to increase in permeability with time.…”

Bentonite as a waste isolation pilot plant shaft sealing material

“…Bentonite has excellent sealing performance and has been selected as a principal sealing component for numerous nuclear waste repositories. Bentonite has an extremely low hydraulic conductivity, is self-healing, and has good chemical stability that would provide effective long-term sealing (Gnirk, 1988). Bentonite can penetrate rock fractures either by viscous flow or by expansion (Pusch, 1978).…”