Research, Development, and Demonstration Roadmap for Deep Borehole Disposal
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Research, Development, and Demonstration Roadmap for Deep Borehole Disposal Prepared for U.S. Department of Energy Used Fuel Disposition Campaign Bill W. Arnold, Palmer Vaughn, Robert MacKinnon, Jack Tillman, Dennis Nielson, Patrick Brady, William Halsey, and Susan Altman Sandia National Laboratories August 31, 2012 FCRD-USED-2012-000269 SAND2012-8527P DISCLAIMER This information was prepared as an account of work sponsored by an agency of the U.S. Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness, of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. References herein to any specific commercial product, process, or service by trade name, trade mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy‟s National Nuclear Security Administration under contract DE-AC04-94AL85000. Research, Development, and Demonstration Roadmap for Deep Borehole Disposal August 31, 2012 iii EXECUTIVE SUMMARY The research, development, and demonstration (RD&D) project presented in this roadmap is intended to advance deep borehole disposal (DBD) from its current conceptual status to potential future deployment as a disposal system for spent nuclear fuel (SNF) and high-level waste (HLW). The objectives of the DBD RD&D roadmap include providing the technical basis for fielding a DBD demonstration project, defining the scientific research activities associated with site characterization and postclosure safety, and defining the engineering demonstration activities associated with deep borehole drilling, completion, and surrogate waste canister emplacement. The activities, schedules, and cost estimates presented will provide the United States (U.S.) Department of Energy (DOE) and policymakers with information on the resource commitments and budget necessary to deploy the DBD demonstration project. DBD of SNF and HLW has been considered as an option for geological isolation for many years, including original evaluations by the U.S. National Academy of Sciences in 1957 (NAS, 1957). The generalized DBD concept is illustrated in Figure ES-1. The concept consists of drilling a borehole (or array of boreholes) into crystalline basement rock to a depth of about 5,000 m, emplacing waste canisters containing SNF or vitrified HLW from reprocessing in the lower 2,000 m of the borehole, and sealing the upper 3,000 m of the borehole. As shown in Figure ES- 1, waste in the DBD system is several times deeper than for typical mined repositories, resulting in greater natural isolation from the surface and near-surface environment. The disposal zone in a single borehole could contain about 400 waste canisters of approximately 5 m length. The borehole seal system would consist of alternating layers of compacted bentonite clay and concrete. Asphalt may also be used in the shallow portion of the borehole seal system. Figure ES-1. Generalized Concept for Deep Borehole Disposal of High-Level Radioactive Waste and Spent Nuclear Fuel. Research, Development, and Demonstration Roadmap for Deep Borehole Disposal iv August 31, 2012 Numerous factors suggest that DBD of SNF and HLW is inherently safe. Several lines of evidence indicate that groundwater at depths of several kilometers in continental crystalline basement rocks has long residence times and low velocity. High salinity fluids have limited potential for vertical flow because of density stratification and prevent colloidal transport of radionuclides. Geochemically reducing conditions in the deep subsurface limit the solubility and enhance the retardation of key radionuclides. A non-technical advantage that the deep borehole concept may offer over a repository concept is that of facilitating incremental construction and loading at multiple regional locations. This DBD RD&D Roadmap is a plan for RD&D activities that will help resolve key uncertainties about DBD and allow for a comprehensive evaluation of the potential for licensing and deploying DBD for SNF and HLW. The full-scale field DBD demonstration presented in this report will serve as a DBD laboratory and proof of concept and will not involve the disposal of actual waste. The demonstration will have four primary goals: demonstrate the feasibility of characterizing and engineering deep boreholes, demonstrate processes and operations for safe waste emplacement down hole, confirm geologic controls over waste stability, and demonstrate safety and practicality of licensing. There are four major RD&D tasks: Demonstration Site Selection – This task will locate the demonstration borehole at a site that is representative of the geology and other characteristics that would be encountered if DBD would be implemented in the future. In addition to establishing site selection guidelines, this task also ensures that regulatory permits for borehole construction and demonstration are in place for implementing the DBD demonstration project. Borehole Drilling and Construction – This task will develop a borehole design, establish borehole requirements, implement a contract for construction of the borehole, and ensure that the drilled and completed borehole meets requirements. Science Thrust – This task will identify and resolve data gaps in the deep borehole geological, hydrological, chemical, and geophysical environment that are important to postclosure safety of the system, materials performance at depth, and construction of the disposal system. This task uses a systematic approach to prioritize data gaps and methods for resolving them. This activity will also perform safety analyses demonstrating the safety of the DBD concept for disposal of SNF and HLW. Engineering Demonstration – This task will confirm the capacity and feasibility of the DBD concept and will include canister emplacement operations (in the borehole), canister transference, canister stringing, and operational retrieval. This task will also include design and fabrication of test canisters and other equipment unique to the demonstration. This task will also provide all documentation confirming the safety, capacity, and feasibility of the DBD concept. A 5-year high-level milestone schedule showing key milestones is provided in Figure ES-2. Research, Development, and Demonstration Roadmap for Deep Borehole Disposal August 31, 2012 v Figure ES-2. High-Level Milestone Schedule for Deep Borehole Disposal RD&D Demonstration Project. The science thrust of the DBD RD&D roadmap is aimed at data gaps in the deep borehole geological, hydrological, chemical, and geophysical environment that are important to postclosure safety of the system, materials performance at depth, and construction of the disposal system. The identification of data gaps and associated data collection and characterization methods relies on a process that includes identifying a comprehensive list of features, events, and processes (FEPs) for geologic disposal, screening each of the FEPs for potential relevance to deep borehole disposal, and identifying related information needs and data collection and characterization methods. Data gaps are addressed in the DBD RD&D roadmap by a proposed combination of surface-based, borehole, and laboratory testing and characterization activities. The engineering thrust of the DBD RD&D roadmap is focused on the conceptual design, analysis, and demonstration of key components of borehole drilling, borehole construction, waste canisters, handling, emplacement, and borehole sealing operations. Planning for drilling a deep demonstration borehole will concentrate on using existing technology, insuring technical success and achieving these aims within budget. Although the objectives of depth and completion diameter are not beyond existing drilling capabilities, experience in drilling a hole that incorporates all of the objectives is very limited. The DBD RD&D roadmap presents information relevant to a demonstration project on a reference deep borehole design and logging, reference waste canister design, testing, loading, handling, and emplacement. Information is also presented on borehole seal design and operational retrievability. The DBD RD&D roadmap also presents a systematic approach to identify and prioritize RD&D science and engineering activities during the demonstration phase of the DBD concept. This approach is similar to the systems engineering approach developed previously for the Used Fuel Disposition Campaign Research and Development (R&D) Roadmap (U.S. DOE, 2011) and involves the ranking of candidate activities against multiple metrics and combining these Research, Development, and Demonstration Roadmap for Deep Borehole Disposal vi August 31, 2012 multiple rankings into an overall priority score using objective functions and a set of weighting factors on the individual metric components. The prioritization of RD&D activities will also be informed by analysis and insights gained from existing and new safety analyses, including