This report summarizes the 2021 fiscal year (FY21) status of ongoing borehole heater tests in salt funded by the disposal research and development (R&D) program of the Office of Spent Fuel & Waste Science and Technology (SFWST) of the US Department of Energy’s Office of Nuclear Energy’s (DOE-NE) Office of Spent Fuel and Waste Disposition (SFWD). This report satisfies SFWST milestone M2SF- 21SN010303052 by summarizing test activities and data collected during FY21. The Brine Availability Test in Salt (BATS) is fielded in a pair of similar arrays of horizontal boreholes in an experimental area at the Waste Isolation Pilot Plant (WIPP). One array is heated, the other unheated. Each array consists of 14 boreholes, including a central borehole with gas circulation to measure water production, a cement seal exposure test, thermocouples to measure temperature, electrodes to infer resistivity, a packer-isolated borehole to add tracers, fiber optics to measure temperature and strain, and piezoelectric transducers to measure acoustic emissions. The key new data collected during FY21 include a series of gas tracer tests (BATS phase 1b), a pair of liquid tracer tests (BATS phase 1c), and data collected under ambient conditions (including a period with limited access due to the ongoing pandemic) since BATS phase 1a in 2020. A comparison of heated and unheated gas tracer test results clearly shows a decrease in permeability of the salt upon heating (i.e., thermal expansion closes fractures, which reduces permeability).
Measuring the size and orientation of borehole breakouts is one of the primary methods for determining the orientation and magnitudes of the in situ stresses in the subsurface. To better understand the effects of anisotropy on borehole breakouts, experiments were conducted on Mancos Shale, a finely laminated mudrock. A novel testing configuration was developed to conduct borehole breakout experiments in a standard triaxial vessel and load frame. Samples were prepared at three different orientations and deformed under 6.9 to 20.7 MPa confining pressure. The results show a variation of peak strength and breakout geometry depending on the lamination orientation. Samples deformed parallel to laminations failed at a higher maximum compressive stress than samples deformed perpendicular to laminations, which were stronger than inclined samples. These relationships are quantified by a cosine-based failure envelope. Observed breakout shapes in perpendicular samples are V-shaped and symmetric around the borehole, which advance as a series of fractures of increasing size into the sidewalls. In inclined samples, fractures form along weaker laminations planes and grow in an en echelon pattern towards the axial stress direction. In parallel samples, long fractures grow from the wellbore towards the axial stress direction. The observed geometries highlight potential sources of error in calculating in situ stresses from borehole breakouts.
This project plan gives a high-level description of the US Department of Energy Office of Nuclear Energy (DOE-NE) Spent Fuel and Waste Disposition (SFWD) campaign in situ borehole heater test project being planned for the Waste Isolation Pilot Plant (WIPP) site This plan provides an overview of the schedule and responsibilities of the parties involved. This project is a collaborative effort by Sandia, Los Alamos, and Lawrence Berkeley National Laboratories to execute a series of small-diameter borehole heater tests in salt for the DOE-NE SFWD campaign. Design of a heater test in salt at WIPP has evolved over several years. The current design was completed in fiscal year 2017 (FY17), an equipment shakedown experiment is underway in April FY18, and the test implementation will begin in summer of FY18. The project comprises a suite of modular tests, which consist of a group of nearby boreholes in the wall of drifts at WIPP. Each test is centered around a packer-isolated heated borehole (5" diameter) containing equipment for water-vapor collection and brine sampling, surrounded by smaller-diameter (2" diameter) satellite observation boreholes. Observation boreholes will contain temperature sensors, tracer release points, electrical resistivity tomography (ERT) sensors, fiber optic sensing, and acoustic emission (AE) measurements, and sonic velocity sources and sensors. These satellite boreholes will also be used for plugging/sealing tests. The first two tests to be implemented will have the packer-isolated borehole heated to 120°C, with one observation borehole used to monitor changes. Follow-on tests will be designed using information gathered from the first two tests, will be conducted at other temperatures, will use multiple observation boreholes, and may include other measurement types and test designs.
The Waste Isolation Pilot Plant (WIPP), located in southeastern New Mexico of the United States (U.S.), has been developed by the U.S. Department of Energy (DOE) for the geologic disposal of transuranic (TRU) waste. The DOE demonstrates compliance with the WIPP containment requirements by means of performance assessment (PA) calculations. WIPP PA calculations estimate the probability and consequence of potential radionuclide releases from the repository to the accessible environment for a regulatory period of 10,000 years after facility closure. WIPP PA models are used (in part) to support the repository recertification process that occurs at five-year intervals following the receipt of the first waste shipment at the site in 1999. The PA executed in support of the 2014 Compliance Recertification Application (CRA-2014) for WIPP includes a number of parameter, implementation, and repository feature changes. Among these changes are the incorporation of a new panel closure system design, additional mined volume in the north end of the repository, a refinement to the PA representation of WIPP waste shear strength, and a gas generation rate refinement. These changes are briefly discussed, as is their cumulative impact on regulatory compliance for the facility. The federal recertification status of the WIPP is also discussed.
The first experiment of the Enhanced Geothermal Systems (EGS) Collab (a.k.a Stimulation Investigations for Geothermal Modeling Analysis and Validation (SIGMA-V)) project is designed to comprehensively monitor a series of hydraulic fracture stimulations and subsequent flow tests. This experiment is planned for the 4850 Level in the Sanford Underground Research Facility (SURF), located at the former Homestake Gold Mine, in Lead, South Dakota. The target host rock for these stimulations and flow tests is a phyllite schist known as the Poorman formation. This paper discusses at a high level the engineering design for the stimulation and fracture monitoring system, the considerations for the test bed construction, and the preliminary stimulation modeling. Furthermore, this paper will highlight the intricate ways that predictive modeling can be used for testbed and stimulation design. This project is funded by the United States Department of Energy, Geothermal Technologies Office (GTO).
Deep Borehole Disposal (DBD) of high-level radioactive wastes has been considered an option for geological isolation for many years (Hess et al. 1957). Recent advances in drilling technology have decreased costs and increased reliability for large-diameter (i.e., ≥50 cm [19.7”]) boreholes to depths of several kilometers (Beswick 2008; Beswick et al. 2014). These advances have therefore also increased the feasibility of the DBD concept (Brady et al. 2009; Cornwall 2015), and the current field test design will demonstrate the DBD concept and these advances. The US Department of Energy (DOE) Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste (DOE 2013) specifically recommended developing a research and development plan for DBD. DOE sought input or expression of interest from States, local communities, individuals, private groups, academia, or any other stakeholders willing to host a Deep Borehole Field Test (DBFT). The DBFT includes drilling two boreholes nominally 200m [656’] apart to approximately 5 km [16,400’] total depth, in a region where crystalline basement is expected to begin at less than 2 km depth [6,560’]. The characterization borehole (CB) is the smaller-diameter borehole (i.e., 21.6 cm [8.5”] diameter at total depth), and will be drilled first. The geologic, hydrogeologic, geochemical, geomechanical and thermal testing will take place in the CB. The field test borehole (FTB) is the larger-diameter borehole (i.e., 43.2 cm [17”] diameter at total depth). Surface handling and borehole emplacement of test package will be demonstrated using the FTB to evaluate engineering feasibility and safety of disposal operations (SNL 2016).
The numerical code DRSPALL (from direct release spallings) is written to calculate the volume of Waste Isolation Pilot Plant solid waste subject to material failure and transport to the surface (i.e., spallings) as a result of a hypothetical future inadvertent drilling intrusion into the repository. An error in the implementation of the DRSPALL finite difference equations was discovered and documented in a software problem report in accordance with the quality assurance procedure for software requirements. This paper describes the corrections to DRSPALL and documents the impact of the new spallings data from the modified DRSPALL on previous performance assessment calculations. Updated performance assessments result in more simulations with spallings, which generally translates to an increase in spallings releases to the accessible environment. Total normalized radionuclide releases using the modified DRSPALL data were determined by forming the summation of releases across each potential release pathway, namely borehole cuttings and cavings releases, spallings releases, direct brine releases, and transport releases. Because spallings releases are not a major contributor to the total releases, the updated performance assessment calculations of overall mean complementary cumulative distribution functions for total releases are virtually unchanged. Therefore, the corrections to the spallings volume calculation did not impact Waste Isolation Pilot Plant performance assessment calculation results.
The numerical code DRSPALL (from direct release spallings) is written to calculate the volume of Waste Isolation Pilot Plant (WIPP) solid waste subject to material failure and transport to the surface as a result of a hypothetical future inadvertent drilling intrusion. An error in the implementation of the DRSPALL finite difference equations was discovered as documented in Software Problem Report (SPR) 13-001. The modifications to DRSPALL to correct the finite difference equations are detailed, and verification and validation testing has been completed for the modified DRSPALL code. The complementary cumulative distribution function (CCDF) of spallings releases obtained using the modified DRSPALL is higher compared to that found in previous WIPP performance assessment (PA) calculations. Compared to previous PAs, there was an increase in the number of vectors that result in a nonzero spallings volume, which generally translates to an increase in spallings releases. The overall mean CCDFs for total releases using the modified DRSPALL are virtually unchanged, thus the modification to DRSPALL did not impact WIPP PA calculation results.
Oil leaks were found in two wellbores of the Big Hill Strategic Petroleum Reserve site. According to the field observations, two instances of casing damage occurred at the depth of the interbed between the caprock bottom and salt top. A three-dimensional finite element model, which contains wellbore blocks at the center of the caverns and allows each cavern to be configured individually, was constructed to investigate the wellbore damage mechanism. The causes of the damaged casing segments are a result of vertical and horizontal movements of salt dome top. To assess how much the wellbore impedes the movement of the salt top, a comparison of the analyses' results from meshes with and without the wellbore blocks was performed. This paper shows models that omit the wellbore blocks could be used for as an acceptable simplified simulation of Strategic Petroleum Reserve sites.
The present study results are focused on laboratory testing of surrogate materials representing Waste Isolation Pilot Plant (WIPP) waste. The surrogate wastes correspond to a conservative estimate of the containers and transuranic waste materials emplaced at the WIPP. Testing consists of hydrostatic, triaxial, and uniaxial tests performed on surrogate waste recipes based on those previously developed by Hansen et al. (1997). These recipes represent actual waste by weight percent of each constituent and total density. Testing was performed on full-scale and 1/4-scale containers. Axial, lateral, and volumetric strain and axial and lateral stress measurements were made. Unique testing techniques were developed during the course of the experimental program. The first involves the use of a spirometer or precision flow meter to measure sample volumetric strain under the various stress conditions. Since the manner in which the waste containers deformed when compressed was not even, the volumetric and axial strains were used to determine the lateral strains. The second technique involved the development of unique coating procedures that also acted as jackets during hydrostatic, triaxial, and full-scale uniaxial testing; 1/4-scale uniaxial tests were not coated but wrapped with clay to maintain an airtight seal for volumetric strain measurement. During all testing methods, the coatings allowed the use of either a spirometer or precision flow meter to estimate the amount of air driven from the container as it crushed down since the jacket adhered to the container and yet was flexible enough to remain airtight during deformation.
Deep Borehole Disposal (DBD) of high-level radioactive wastes has been considered an option for geological isolation for many years (Hess et al. 1957). Recent advances in drilling technology have decreased costs and increased reliability for large-diameter (i.e., ≥50 cm [19.7”]) boreholes to depths of several kilometers (Beswick 2008; Beswick et al. 2014). These advances have therefore also increased the feasibility of the DBD concept (Brady et al. 2009; Cornwall 2015), and the current field test, introduced herein, is a demonstration of the DBD concept and these advances.
Oil leaks were found in wellbores of Caverns 105 and 109 at the Big Hill Strategic Petroleum Reserve site. According to the field observations, two instances of casing damage occurred at the depth of the interbed between the caprock bottom and salt top. A three dimensional finite element model, which contains wellbore element blocks and allows each cavern to be configured individually, is constructed to investigate the wellbore damage mechanism. The model also contains element blocks to represent interface between each lithology and a shear zone to examine the interbed behavior in a realistic manner. The causes of the damaged casing segments are a result of vertical and horizontal movements of the interbed between the caprock and salt dome. The salt top subsides because the volume of caverns below the salt top decrease with time due to salt creep closure, while the caprock subsides at a slower rate because the caprock is thick and stiffer. This discrepancy produces a deformation of the well. The deformed wellbore may fail at some time. An oil leak occurs when the wellbore fails. A possible oil leak date of each well is determined using an equivalent plastic strain failure criterion. A well grading system for a remediation plan is developed based on the predicted leak dates of each wellbore.
The present study results are focused on laboratory testing of surrogate waste materials. The surrogate wastes correspond to a conservative estimate of degraded Waste Isolation Pilot Plant (WIPP) containers and TRU waste materials at the end of the 10,000 year regulatory period. Testing consists of hydrostatic, triaxial, and uniaxial strain tests performed on surrogate waste recipes that were previously developed by Hansen et al. (1997). These recipes can be divided into materials that simulate 50% and 100% degraded waste by weight. The percent degradation indicates the anticipated amount of iron corrosion, as well as the decomposition of cellulosics, plastics, and rubbers (CPR). Axial, lateral, and volumetric strain and axial, lateral, and pore stress measurements were made. Two unique testing techniques were developed during the course of the experimental program. The first involves the use of dilatometry to measure sample volumetric strain under a hydrostatic condition. Bulk moduli of the samples measured using this technique were consistent with those measured using more conventional methods. The second technique involved performing triaxial tests under lateral strain control. By limiting the lateral strain to zero by controlling the applied confining pressure while loading the specimen axially in compression, one can maintain a right-circular cylindrical geometry even under large deformations. This technique is preferred over standard triaxial testing methods which result in inhomogeneous deformation or (3z(Bbarreling(3y. (BManifestations of the inhomogeneous deformation included non-uniform stress states, as well as unrealistic Poisson<U+2019>s ratios (> 0.5) or those that vary significantly along the length of the specimen. Zero lateral strain controlled tests yield a more uniform stress state, and admissible and uniform values of Poisson<U+2019>s ratio.
A reference design and operational procedures for the disposal of high-level radioactive waste in deep boreholes have been developed and documented. The design and operations are feasible with currently available technology and meet existing safety and anticipated regulatory requirements. Objectives of the reference design include providing a baseline for more detailed technical analyses of system performance and serving as a basis for comparing design alternatives. Numerous factors suggest that deep borehole disposal of high-level radioactive waste 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 perhaps regional locations. The disposal borehole would be drilled to a depth of 5,000 m using a telescoping design and would be logged and tested prior to waste emplacement. Waste canisters would be constructed of carbon steel, sealed by welds, and connected into canister strings with high-strength connections. Waste canister strings of about 200 m length would be emplaced in the lower 2,000 m of the fully cased borehole and be separated by bridge and cement plugs. Sealing of the upper part of the borehole would be done with a series of compacted bentonite seals, cement plugs, cement seals, cement plus crushed rock backfill, and bridge plugs. Elements of the reference design meet technical requirements defined in the study. Testing and operational safety assurance requirements are also defined. Overall, the results of the reference design development and the cost analysis support the technical feasibility of the deep borehole disposal concept for high-level radioactive waste.
A sensitivity study was performed utilizing a three dimensional finite element model to assess allowable cavern field sizes in strategic petroleum reserve salt domes. A potential exists for tensile fracturing and dilatancy damage to salt that can compromise the integrity of a cavern field in situations where high extraction ratios exist. The effects of salt creep rate, depth of salt dome top, dome size, caprock thickness, elastic moduli of caprock and surrounding rock, lateral stress ratio of surrounding rock, cavern size, depth of cavern, and number of caverns are examined numerically. As a result, a correlation table between the parameters and the impact on the performance of a storage field was established. In general, slower salt creep rates, deeper depth of salt dome top, larger elastic moduli of caprock and surrounding rock, and a smaller radius of cavern are better for structural performance of the salt dome. Copyright 2010 ARMA, American Rock Mechanics Association.
A sensitivity study was performed utilizing a three dimensional finite element model to assess allowable cavern field sizes in strategic petroleum reserve salt domes. A potential exists for tensile fracturing and dilatancy damage to salt that can compromise the integrity of a cavern field in situations where high extraction ratios exist. The effects of salt creep rate, depth of salt dome top, dome size, caprock thickness, elastic moduli of caprock and surrounding rock, lateral stress ratio of surrounding rock, cavern size, depth of cavern, and number of caverns are examined numerically. As a result, a correlation table between the parameters and the impact on the performance of a storage field was established. In general, slower salt creep rates, deeper depth of salt dome top, larger elastic moduli of caprock and surrounding rock, and a smaller radius of cavern are better for structural performance of the salt dome.
The disturbed rock zone (DRZ) is an important feature which is evaluated in the Waste Isolation Pilot Plant (WIPP) performance assessment (PA) to predict post-closure repository performance. Mining of a WIPP disposal room disturbs the stress state sufficiently to cause fracturing of the surrounding rock, and this fracturing will alter the mechanical and hydrological properties of the salt. DRZ extent, and permeability, controls the majority of the brine that enters or exits the repository in PA modeling of the undisturbed scenario. Extensive laboratory data from experiments performed on rock salt demonstrate that damage can be modeled in terms of stress invariants. In this paper the DRZ extent is calculated based on a dilatant damage criterion. The calibrated damage factor C in the damage criterion is determined by comparing ultrasonic wave velocity field measurements obtained in the S-90 drift with a numerical analysis that predicts the salt's behavior. Ultrasonic velocities decrease in the presence of microcracks and loosened grain boundaries associated with salt damage. The most extensive DRZ exists during early times, within the first ten years of mining. The maximum predicted DRZ surrounding a WIPP disposal room is approximately 2.25 m below, 4.75 m above, and 2 m laterally. This paper also presents several lines of evidence, based on previous studies, that support the prediction of DRZ size by applying a WIPP specific damage criterion calibrated using ultrasonic velocity measurements. Copyright 2009 ARMA, American Rock Mechanics Association.