Publications

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While deep borehole disposal of nuclear waste should rely primarily on off-the-shelf technologies pioneered by the oil and gas and geothermal industries, the development of new science and technology will remain important. Key knowledge gaps have been outlined in the research roadmap for deep boreholes (B. Arnold et al, 2012, Research, Development, and Demonstration Roadmap for Deep Borehole Disposal, Sandia National Laboratories, SAND2012-8527P) and in a recent Deep Borehole Science Needs Workshop. Characterizing deep crystalline basement, understanding the nature and role of deep fractures, more precisely age-dating deep groundwaters, and demonstrating long-term performance of seals are all important topics of interest. Overlapping deep borehole and enhanced geothermal technology needs include: quantification of seal material performance/failure, stress measurement beyond the borehole, advanced drilling and completion tools, and better subsurface sensors. A deep borehole demonstration has the potential to trigger more focused study of deep hydrology, high temperature brine-rock interaction, and thermomechanical behavior.

This paper describes technical, logistical, and sociopolitical factors to be considered in the development of guidelines for siting a facility for deep borehole disposal of radioactive waste. Technical factors include geological, hydro-geochemical, and geophysical characteristics that are related to the suitability of the site for drilling and borehole construction, waste emplacement activities, waste isolation, and long-term safety of the deep borehole disposal system. Logistical factors to be considered during site selection include: The local or regional availability of drilling contractors (equipment, services, and materials) capable of drilling a large-diameter borehole to approximately 5 km depth; the legal and regulatory requirements associated with drilling, construction of surface facilities, waste handling and emplacement, and postclosure safety; and access to transportation systems. Social and political factors related to site selection include the distance from population centers and the support or opposition of local and state entities and other stakeholders to the facility and its operations. These considerations are examined in the context of the siting process and guidelines for a deep borehole field test, designed to evaluate the feasibility of siting and operating a deep borehole disposal facility.

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Following the radionuclide release event of February 14, 2014 at the Waste Isolation Pilot Plant (WIPP), actinide contamination has been found on the walls and floor in Panel 7 as a result of a release in Room 7 of Panel 7. It has been proposed to decontaminate Panel 7 at the WIPP by washing contaminated surfaces in the underground with fresh water. A cost-effective cleanup of this contamination would allow for a timely return to waste disposal operations at WIPP. It is expected that the fresh water used to decontaminate Panel 7 will flow as contaminated brine down into the porosity of the materials under the floor – the run-of-mine (ROM) salt above Marker Bed 139 (MB139) and MB139 itself – where its fate will be controlled by the hydraulic and transport properties of MB139. Due to the structural dip of MB139, it is unlikely that this brine would migrate northward towards the Waste-Handling Shaft sump. A few strategically placed shallow small-diameter observation boreholes straddling MB139 would allow for monitoring the flow and fate of this brine after decontamination. Additionally, given that flow through the compacted ROM salt floor and in MB139 would occur under unsaturated (or two-phase) conditions, there is a need to measure the unsaturated flow properties of crushed WIPP salt and salt from the disturbed rock zone (DRZ).

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Significant laboratory and in situ testing has been conducted by both the United States and Germany on salt disposal of heat-generating radioactive waste. Coupled simulation capabilities recently developed in other fields are now being applied to repository design and performance confirmation. New efforts are underway to benchmark this latest generation of numerical models, requiring quality validation datasets. Datasets associated with historic high-level waste (HL W) field experiments at the Waste Isolation Pilot Plant in New Mexico, Avery Island in Louisiana, Asse II in Germany, and Project Salt Vault in Kansas should be considered before constructing new experiments. We constructed an online bibliographic database using the web reference database (Refbase) distribution to contain references to reports, and conference papers, along with associated electronic copies of reports and associated data. The database was populated using publically available Department of Energy sources and project-specific archives scanned for this project. The browser-based database facilitated an extensive collaborative review of experiments in geologic salt-primarily concerning heated salt that may be applicable to modern code validation efforts. We summarize historic in situ tests conducted in geologic salt, focusing on heated salt creep, heated brine migration, and crushed salt reconsolidation. We propose several candidate thermal, mechanical, and hydrological validation datasets for salt behavior under repository conditions.

The article briefly summarizes the siting history of salt nuclear waste repositories as it relates to the research that has been conducted in support of this overall mission. Project Salt Vault was a solid-waste disposal demonstration in bedded salt performed by Oak Ridge National Laboratory (ORNL) in Lyons, Kan. The US Atomic Energy Commission (AEC) intended to convert the project into a pilot plant for the storage of high-level waste. Despite these intentions, nearby solution mining and questionably plugged oil and gas boreholes resulted in the abandonment of the Lyons site. With help from the USGS, in 1972 ORNL began looking in the Permian Basin for a different disposal site in Texas or New Mexico. The WIPP project was discontinued in 1974 in favor of concentrating efforts on a Retrievable Surface Storage Facility. After the demise of that project in 1975, work resumed on WIPP and its scope was temporarily expanded to include defense HLW. A location a few miles northeast of the current WIPP site was chosen for further study.

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