Sealing fractures in nuclear waste repositories concerns all programs investigating deep burial as a means of disposal. Because the most likely mechanism for contaminant migration is by dissolution and movement through groundwater, sealing programs are seeking low-viscosity sealants that are chemically, mineralogically, and physically compatible with their host. This paper presents the results of collaborative work directed by Sandia National Laboratories (SNL) and supported by Whitesell Laboratories (WL), operated by Atomic Energy of Canada, Ltd. The work was undertaken in support of the Waste Isolation Pilot Plant (WIPP). This effort addresses the technology associated with long-term isolation of nuclear waste in a natural salt medium. The work presented is part of the WIPP plugging and sealing program, specifically the development and optimization of an ultrafine cementitious grout that can be injected to lower excessive, strain-induced hydraulic conductivity in the fractured rock termed the Distributed Rock Zone (DRZ) surrounding underground excavations. Innovative equipment and procedures employed in the laboratory produced a usable cement-based grout; 90% of the particles are smaller than 10 microns and the average size is 4 microns (Ahrens et al., 1996). The process involved simultaneous wet pulverization and mixing. The grout was used for a successful in situ test underground at the WIPP. Injection of grout sealed microfractures as small as 8 microns and lowered the gas transmissivity of the DRZ by up to three orders of magnitude. Following the WIPP test, additional work produced an improved version of the grout containing particles 90% smaller than 6 microns and averaging 2 microns. This grout can be produced in a dry form ready to mix.
The Waste Isolation Pilot Plant (WIPP) is a research and development facility being evaluated for its suitability to dispose of approximately 185,000 cubic meters of transuranic, defense-generated wastes. The WIPP site is located in southeastern New Mexico within a vast geologic structure known as the Permian basin. The location of the WIPP relative to the surface is illustrated in Figure 1. The disposal horizon is situated in bedded salt (the Salado Formation) at a depth of 656 m. Fracturing from excavation-related stress redistribution creates a near-field zone of The Waste Isolation Pilot Plant (WIPP) is a mechanically altered rock within the first few meters research and development facility being evaluated for of the excavations. Within this disturbed rock zone its suitability to dispose of approximately 185,000 (DRZ), fractures increase the intrinsic rock permecubic meters of transuranic, defense-generated ability by a few orders of magnitude (Stormont, wastes. The WIPP site is located in southeastern New 1989). Fractures in the DRZ provide potential path- Mexico within a vast geologic structure known as the ways for contaminant transport, especially in higher Permian basin. The location of the WIPP relative to permeability interbeds (Ahrens et al., 1996). The surface is illustrated in Figure 1. The disposal WIPP sealing program is investigating the use of low horizon is situated in bedded salt at a depth of 656 m.