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 designing and constructing an effective seal within the borehole that ensures the waste package does not communicate through the borehole itself with the shallow subsurface and biosphere for thousands of years. Recent work has suggested that encapsulating the waste in melted rock will create a seal that is more reliable and lasts longer than conventional sealing materials, such as cement and bentonite. The proposed project consists of designing a remote, electrical rock melt borehole sealing system and testing the performance of the system both in a laboratory and then with field tests in an underground environment (the Sanford Underground Research Facility [SURF]), which is located at the former Homestake Gold Mine in western South Dakota). Phase I of the project evaluated the overall feasibility of the rock melt sealing concept by incorporating laboratory testing and numerical modeling to develop a preliminary design of a downhole heater. Phase I also estimated costs for in situ field testing at the SURF and indicated that the necessary field evaluation could be completed within a reasonable budget. The major tasks envisaged for the Phase II Work Plan consist of the following: 1. Design and construct the initial prototype heater 2. Perform laboratory-scale prototype testing 3. Prepare the SURF field experiment site 4. Perform field-scale rock melt testing within the SURF 5. Conduct a mine-back investigation to access the borehole seal 6. Design a full-scale heater for use in the deep borehole environment. In situ melting experiments performed at the SURF provide a unique opportunity to evaluate the rock melt seal system in a deep underground environment and perform a mine- back excavation and forensic analysis, which is necessary to build confidence in the system. 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. Confidence in a more robust sealing method is expected to be advantageous for the consent-based approach to siting waste facilities.