Rock Melt Borehole Sealing System

Deep geological disposal is a promising and widely accepted method for long- term disposal of nuclear waste and the option of deep borehole disposal is considered an inherently safe method. The feasibility of the deep borehole option relies upon the design and construction of an effective seal within the borehole that ensures the waste package does not communicate for thousands of years with the shallow subsurface and biosphere through the borehole itself. Recent work has suggested that encapsulating the waste in melted rock will create a seal that is more reliable and long-lasting than conventional sealing materials, such as cement and bentonite. In situ, field-scale demonstrations of the rock melt system are necessary to validate its effectiveness. The proposed project consists of designing a remote, electrical rock melt borehole sealing system and evaluating the feasibility of establishing an experimental area in an underground environment (the Sanford Underground Research Facility (SURF), located at the former Homestake Gold Mine in western South Dakota) where the performance of the system can be tested and validated. The major tasks envisaged for the Phase I work plan consist of the following: 1.Laboratory testing to obtain applicable thermal properties; 2. Preliminary modeling to determine the requirements of the heater system; 3. Preliminary design of a heater system; 4. Preliminary experiment design at SURF, including identification of underground candidate sites and preliminary experiment cost estimates. In situ melting experiments performed at the SURF provide a unique opportunity to both evaluate seal designs in a deep underground environment and perform a mine-back excavation and forensic analysis of the seal design system. Several of these types of experiments would evaluate and compare a number of different sealing technologies to assess which seal designs are the most effective. Commercial Applications and Other Benefits: The demonstration of a successful design rock melt borehole sealing system has the potential to significantly contribute to the U.S. Department of Energy Used Fuel Disposition Campaign and help address an issue of national (and international) importance. In addition to the obvious benefit to the Used Fuel Disposition Campaign, the validation of sealing technology will also benefit other entities which operate in deep borehole environments, such as the oil and gas industry and deep, hazardous waste disposal industries. The development of a retrievable heating system that could be used to melt either the host rock or backfill materials into an effective borehole seal could prove to be a more robust (and potentially cost-efficient) option than conventional sealing methods.