X-ray radiography of fracture flow and matrix imbibition

X-ray radiography of fracture flow and matrix imbibition

Date: October 27, 1995
Creator: Roberts, J.J. & Lin, Wunan
Description: Knowledge of how water flows through unsaturated, fractured rock is critical for understanding and predicting the performance of a high- level nuclear waste repository. For instance, during gravity driven fracture flow, the distance that water can travel through a fracture network might be controlled by (1) the amount of water available, (2) the fracture aperture, (3) the capillary properties of the matrix, and (4) the saturation of the matrix. We have experimentally investigated fracture flow and fracture-matrix interactions using x- ray radiography to image some of the above factors and processes.
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Report on laboratory tests of drying and re-wetting of intact rocks

Report on laboratory tests of drying and re-wetting of intact rocks

Date: March 1, 1996
Creator: Roberts, J.J. & Lin, Wunan
Description: This report is an update on progress made during FY1995 on hydrological property measurements performed in the laboratory. The report contains descriptions of experimental designs and procedures, data, observations, preliminary analyses, and future work. The primary focus of this report is the measurement of moisture retention curves of tuff as a function of temperature for both drying and re-wetting conditions. This work is a continuation of work described in MOL80 (UCRL-ID-119033), Hydrological Property Measurements of Topopah Spring Tuff (Roberts and Lin, 1995). Knowledge of unsaturated transport properties is critical for understanding the movement of water through the unsaturated zone. Evaluation of the performance of a potential nuclear waste repository also depends on these properties. Moisture retention data are important input for models of moisture movement in unsaturated porous media. Also important is the effect of sample history on the moisture retention curves, whether or not a complete saturation cycle at elevated temperature affects the moisture retention curve at subsequent lower temperature cycles. This report addresses initial observations regarding this aspect of the research.
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Electrical properties of Topopah Spring tuff as a function of saturation

Electrical properties of Topopah Spring tuff as a function of saturation

Date: January 1, 1994
Creator: Roberts, J.J. & Lin, Wunan
Description: Much attention has been focused on the hydrologic properties of tuff from the potential nuclear waste repository at Yucca Mountain, Nevada. The successful characterization of the near-field environment of the potential repository depends on the ability to understand and predict the movement of water within the matrix and fractures when the rock mass is heated by nuclear waste. This understanding will come only after many combined laboratory experiments, field tests, and model calculations have been performed. Electrical properties, including electrical resistivity and dielectric permittivity, have been utilized in past studies to infer water content in partially saturated rocks. In this study we determine the electrical properties of Topopah Spring tuff from Yucca Mountain (Area 25), and Area 3, Nevada Test Site (NTS), NV, as a function of water content. These results will be used to (1) study the electrical properties of ted rocks as functions of saturation and water chemistry; (2) relate the observed electrical properties to the distribution of water and to the rnicrogeometry of the rock; and (3) to create a database of electrical resistivity ({rho}) and relative dielectric permittivity ({kappa}{prime}) versus water content (Sw) and temperature for rocks within the potential repository horizon. The database will be ...
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Permeability of fractured tuff as functions of temperature and confining pressure

Permeability of fractured tuff as functions of temperature and confining pressure

Date: October 1, 1994
Creator: Roberts, J.J. & Lin, Wunan
Description: Understanding the transport properties of water through fractured rock is critical to predicting and modeling the hydrothermal performance of a geologic nuclear waste repository. Previous studies indicate that intact Topopah Spring tuff from Yucca Mountain, Nevada has a low permeability, {approximately} 1 {times} 10 {sup {minus}18} m{sup 2} ({approximately}1 microDarcy). A single fracture in the tuff increases the permeability to {approximately}100 {times}10{sup {minus}15} m{sup 2} (hundreds of milliDarcies). However, fracture healing may occur when high temperature water flows through the fracture lowering the permeability by one or more orders of magnitude. We report progress on laboratory experiments on permeability of fractured Topopah Spring tuff as functions of confining pressure, temperature, and water/rock ratio.
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Relative humidity in the near-field environment

Relative humidity in the near-field environment

Date: October 27, 1995
Creator: Lin, W.; Roberts, J. & Ruddle, D
Description: The Yucca Mountain Site Characterization Project is investigating Yucca Mountain, Nevada, for its suitability as a potential repository for high-level nuclear wastes. United States federal regulation 10CFR60 requires that radioactive nuclides be substantially contained in waste packages for 300 to 1000 years after the emplacement. To meet the regulation, a waste package container should remain intact for several hundreds of years. It has been shown that high humidity increases the corrosion potential of metallic container materials. Relative humidity as a function of water saturation in intact rock is measured. The results of this test can be used to calibrate the relative humidity in the near-field environment predicted by model calculations using thermal-hydrological codes such as VTOUGH. This is a report on the progress of that experiment.
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Electrical resistivity measurements of brine saturated porous media near reservoir conditions: Awibengkok preliminary results

Electrical resistivity measurements of brine saturated porous media near reservoir conditions: Awibengkok preliminary results

Date: June 28, 1999
Creator: Bonner, B; Duba, A & Roberts, J
Description: Laboratory measurements of the electrical resistivity of rocks and synthetic rocks with confining pressures up to 100 bars and temperatures between 20 and 211 C were performed to further investigate how the pore-size distribution and capillarity affects boiling in porous media. Similar to previous measurements on samples from The Geysers, CA, we observed a gradual increase in resistivity when pore pressure was decreased below the phase-boundary pressure of free water, an indication that boiling is controlled not only by temperature and pressure, but also by pore size distribution. Other important phenomena observed were strong resistance fluctuations during boiling that may be chaotic, and salt deposition that caused sample cracking. If confirmed in further experiments, these results may lead to a new geophysical diagnostic for locating boiling in high permeability areas of geothermal reservoirs and for methods of permeability alteration.
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Assessment of cold neutron radiography capability

Assessment of cold neutron radiography capability

Date: December 31, 1998
Creator: McDonald, T.E. Jr. & Roberts, J.A.
Description: This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The authors goals were to demonstrate and assess cold neutron radiography techniques at the Los Alamos Neutron Science Center (LANSCE), Manual Lujan Neutron Scattering Center (Lujan Center), and to investigate potential applications of the capability. The authors have obtained images using film and an amorphous silicon detector. In addition, a new technique they have developed allows neutron radiographs to be made using only a narrow range of neutron energies. Employing this approach and the Bragg cut-off phenomena in certain materials, they have demonstrated material discrimination in radiography. They also demonstrated the imaging of cracks in a sample of a fire-set case that was supplied by Sandia National Laboratory, and they investigated whether the capability could be used to determine the extent of coking in jet engine nozzles. The LANSCE neutron radiography capability appears to have applications in the DOE stockpile maintenance and science-based stockpile stewardship (SBSS) programs, and in industry.
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Macrostrain measurement using radial collimators at LANSCE

Macrostrain measurement using radial collimators at LANSCE

Date: June 1, 1996
Creator: Bourke, M.A.M.; Roberts, J.A. & Davis, D.
Description: A series of `short` radial collimators have been implemented in the 90{degrees} scattering geometries on the neutron powder diffractometer at Los Alamos. The capability to perform macrostrain measurements has been improved by the commensurate ability to rapidly select a sampling volume appropriate to the specimen. The compact design of the collimators was dictated by the need to fit them in a cylindrical vacuum chamber as well as providing space in which to manipulate a specimen in three dimensions. Collimators of different vane lengths were fabricated to give 4 different resolutions for which 2/3 of the diffracted intensity comes form distances of 0.75, 1. 25, 2.5, and 4.0 mm along the incident beam. Qualifying scans and a demonstration of a cracked ring, containing a steep stress gradient, are included.
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Influence of microstructural properties on geophysical measurements in sand-clay mixtures

Influence of microstructural properties on geophysical measurements in sand-clay mixtures

Date: November 30, 1998
Creator: Carlberg, E D; Roberts, J J & Wildenschild, D
Description: We have performed a series of laboratory experiments on saturated sand-clay mixtures. Measurements include frequency-dependent electrical properties using the four-electrode technique (10 niHz to 1 MHz), permeability, porosity, and acoustic velocities. We mixed clean Ottawa (quartz) sand with Na-montmorillonite (Wyoming bentonite) in a number of different configurations containing 0 to 10% clay: as a dispersed mixture, as discrete clay clusters, and arranged in distinct layers. Solutions of CaCl{sub 2} ranging from 0.0005 N to 0.75 N (0.05 to 64 mS/cm) and deionized water were used as saturating fluids. We found the electrical properties to be dependent on clay content, fluid conductivity, and microstructure in a complex fashion. Increasing fluid conductivity and increasing clay content generally resulted in higher electrical conductivity. For an individual sample, two main regions of conduction exist: a region dominated by surface conduction and a region where the ionic strength of the saturating fluid controlled conduction. The sample geometry (dispersed, nondispersed, or layered clay configuration) was found to greatly affect the magnitude of the surface conductance in the range of low fluid conductivity.
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The effect of rock-water interaction on permeability

The effect of rock-water interaction on permeability

Date: June 1, 1995
Creator: Lin, Wunan; Roberts, J.J.; Glassley, W. & Ruddle, D.
Description: Current investigations for managing high-level nuclear wastes focus on studying deep geologic repositories. The Yucca Mountain Site Characterization Project of the US Department of Energy conducts studies on Yucca Mountain, Nevada, to determine its suitability as a potential high-level nuclear waste repository. The potential host rock in Yucca Mountain is a layer of devitrified Topopah Spring tuff that is densely welded, fractured, and lithophysae-poor. The suitability of a potential nuclear waste repository site depends on, among other factors, how the near-field environment affects the integrity of waste package materials and the transport of radioactive nuclides away from waste packages. Model calculations are needed to predict the near-field environment for the entire life-span of a repository. Radioactive decay heat from nuclear waste packages is likely to create coupled thermal-mechanical-hydrological-chemical (TMHC) processes in the near field of a repository. The coupled TMHC processes must be understood so they can be incorporated in the model calculations. One of the coupled TMHC processes is the effect of the rock-water interaction (a chemical-mineralogical process) on the fluid flow in the rock mass (a hydrological process).
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