Yucca Mountain Tuffs Research Articles

Seismic modeling and analysis of a prototype heated nuclear waste storage tunnel, Yucca Mountain, Nevada

We have developed seismic velocity models for the heated rock surrounding a tunnel in Yucca Mountain tuff and compared the results with field data obtained at the Yucca Mountain drift scale test (DST) facility from 1998 to 2002. During that time, the tunnel was heated to replicate the effects of long-term storage of decaying nuclear waste and to study the effects of extreme temperatures on the surrounding rock and groundwater flow. Our velocity models are based on borehole temperature data, thermal models, and laboratory measurements on granite. Comparisons between field and synthetic seismograms show that superheating the rock around the tunnel causes thermally induced variations in P- and S-wave arrival-time separation. Barring out-of-plane reflections, 2D spectral element waveform modeling in the source plane consistently replicates seismic receiver waveforms and classic behavior of pulses reflected from cylinders. Our models constrain the in situ [Formula: see text] velocity/temperature derivative of the tuff to be approximately [Formula: see text] per [Formula: see text]. This velocity change is consistent with thermally induced wavespeed changes in dry rock samples and is lower than expected for water-to-steam conversion in saturated rock. We infer that velocity changes are controlled by thermal expansion and fracturing. Additionally, we have developed an improved method for monitoring tunnel conditions that uses waves diffracted around the tunnel in the region of changing velocity.

General Validity of Conductivity Means in Unsaturated Flow Models

A simple three-point grid test shows that some common and mathematically convenient intergrid hydraulic conductivity means violate the min–max principle for elliptic boundary value problems (steady-state flow). In some cases in models of Richard's equation for three types of homogenous rock matrix and fracture in Yucca Mountain tuff, these violations lead to nonphysical oscillations, eliminating these means as generally valid approaches in such models. These models are used to show that Darcian means and the upstream means have similar RMS errors in water content and flow in convergence to the fine-grid solution. But in the presence of vertical space step discretization error, the Darcian means produce sharper wetting fronts.

Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff

Plutonium oxidation state distribution on Yucca Mountain tuff and synthetic pyrolusite (beta-MnO2) suspensions was measured using synchrotron X-ray micro-spectroscopy and microimaging techniques as well as ultrafiltration/solventextraction techniques. Plutonium sorbed to the tuff was preferentially associated with manganese oxides. For both Yucca Mountain tuff and synthetic pyrolusite, Pu(IV) or Pu(V) was initially oxidized to more mobile Pu(V/VI), but over time, the less mobile Pu(IV) became the predominant oxidation state of the sorbed Pu. The observed stability of Pu(IV) on oxidizing surfaces (e.g., pyrolusite), is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. These findings have important implications in estimating the risk associated with the geological burial of radiological waste in areas containing Mn-bearing minerals, such as at the Yucca Mountain or the Hanford Sites, because plutonium will be predominantly in a much less mobile oxidation state (i.e., Pu(IV)) than previously suggested (i.e., Pu(V/VI).

Experimental and numerical simulation of dissolution and precipitation: implications for fracture sealing at Yucca Mountain, Nevada

Plugging of flow paths caused by mineral precipitation in fractures above the potential repository at Yucca Mountain, Nevada could reduce the probability of water seeping into the repository. As part of an ongoing effort to evaluate thermal-hydrological-chemical (THC) effects on flow in fractured media, we performed a laboratory experiment and numerical simulations to investigate mineral dissolution and precipitation under anticipated temperature and pressure conditions in the repository. To replicate mineral dissolution by vapor condensate in fractured tuff, water was flowed through crushed Yucca Mountain tuff at 94 °C. The resulting steady-state fluid composition had a total dissolved solids content of about 140 mg/l; silica was the dominant dissolved constituent. A portion of the steady-state mineralized water was flowed into a vertically oriented planar fracture in a block of welded Topopah Spring Tuff that was maintained at 80 °C at the top and 130 °C at the bottom. The fracture began to seal with amorphous silica within 5 days. A 1-D plug-flow numerical model was used to simulate mineral dissolution, and a similar model was developed to simulate the flow of mineralized water through a planar fracture, where boiling conditions led to mineral precipitation. Predicted concentrations of the major dissolved constituents for the tuff dissolution were within a factor of 2 of the measured average steady-state compositions. The mineral precipitation simulations predicted the precipitation of amorphous silica at the base of the boiling front, leading to a greater than 50-fold decrease in fracture permeability in 5 days, consistent with the laboratory experiment. These results help validate the use of a numerical model to simulate THC processes at Yucca Mountain. The experiment and simulations indicated that boiling and concomitant precipitation of amorphous silica could cause significant reductions in fracture porosity and permeability on a local scale. However, differences in fluid flow rates and thermal gradients between the experimental setup and anticipated conditions at Yucca Mountain need to be factored into scaling the results of the dissolution/precipitation experiments and associated simulations to THC models for the potential Yucca Mountain repository.

Colloid transport and deposition in water-saturated Yucca Mountain tuff as determined by ionic strength.

Colloid mobility and deposition were determined in model systems consisting of quartz sand or crushed Yucca Mountain tuff, latex microspheres (colloidal particles), and simulated groundwater. Ionic strength (I) was manipulated as a first step in defining limiting conditions for colloid transport in a system modeled after geochemical conditions at the Yucca Mountain site. Solutions of deionized water (DI), 0.1x, 1x, and 10x (the ionic strength of simulated groundwater) (I = 0.0116 M) were used in saturated columns under steady-state flow conditions. Separate experiments with conservative tracers indicated stable hydrodynamic conditions that were independent of I. Colloids were completely mobile (no deposition) in the DI and 0.1x solutions; deposition increased to 11-13% for 1x and to 89-97% for 10x treatments with similar results for sand and tuff. Deposition was described as a pseudo-first-order process; however, a decreasing rate of deposition was apparent for colloid transport at the 10x condition through the tuff. A linear dependence of colloid removal (extent and deposition rate coefficient) on I is illustrated for the model Yucca Mountain system and for a glass-KCl system reported in the literature. This simple relationship for saturated systems may be useful for predicting deposition efficiencies under conditions of varying ionic strength.

Physical and chemical determinants of colloid transport and deposition in water-unsaturated sand and Yucca Mountain tuff material.

Colloid mobility was determined in a system consisting of quartz sand or crushed Yucca Mountain tuff, simulated groundwater (J-13), and hydrophilic latex particles. Water content (theta) and ionic strength (I; DI water, 0.1x, 1x, 10x groundwater dilution) were manipulated to define limiting conditions for colloid transport atthe Yucca Mountain site. Colloid transport, measured with a centrifuge method at relatively high theta (saturation >36% for sand, >62% for crushed tuff) in DI water, was equivalent to transport at 100% saturation measured with conventional columns. When variables were isolated, increasing I and decreasing theta resulted in a greater extent of colloid deposition; I was more important at higher theta; physical properties were more important at lower theta. I and theta had an interactive effect on colloid deposition whereby synergism was generally observed, especially for simulated groundwater (1x); antagonism was observed at 10x groundwater dilution. At 19% moisture saturation on the crushed tuff, a decreasing rate of colloid deposition was observed. This corresponded to a hydrodynamic condition of 79% immobile water where solute tracers were excluded from a fraction of the pore volume. This suggests that a portion of the favorable sites for deposition were associated with the excluded or immobile water domain and were not accessible to colloids.

Investigation of Bacterial Transport in the Large-Block test, A Thermally Perturbed Block of Topopah Spring Tuff

AbstractTransport of bacteria is investigated as part of the Large-Block Test (LBT), a thermally perturbed block of Topopah Spring tuff. Two bacterial species,Bacillus subtilisandArthrobacter oxydans, were isolated from the Yucca Mountain tuff. Natural mutants that can grow under the simultaneous presence of the two antibiotics, streptomycin and rifampicin, were selected from these species by laboratory procedures, cultured, and injected into the five heater boreholes of the large block hours before heating was initiated. The temperature, as measured 5 cm above one of the heater boreholes, rose slowly over a matter of months to a maximum of 142°C and to 60°C at the top and the bottom of the block. Samples were collected from boreholes located approximately 5 ft below the injection points. Double-drug-resistant bacteria were found in the collection boreholes nine months after injection. Biochemical tests support the identification ofB. subtilisin the collection boreholes. Double-drug-resistant microbes also appeared in the heater boreholes where the temperature had been sustainably high throughout the test. The number of double-drugresistant bacteria that were identified in the collection boreholes increased with time until the heater was deactivated. Negative indications in the collection holes after the heater was deactivated support the supposition that these bacteria were the species that were injected. An apparent homogeneous distribution among the collection boreholes suggests no pattern to the migration of bacteria through the block. The relationship between bacterial migration and the movement of water is not yet understood. These observations indicate the possibility of rapid bacterial transport in a thermally perturbed geologic setting. The implications for colloid transport need to be reviewed.

Low-Temperature Alteration in Tuffs from Yucca Mountain, Nevada

AbstractThe structure, chemistry and distribution of hydrothermal alteration and weathering products of feldspars and glass in 3 samples of Yucca Mountain tuffs (GSW G4 borehole at a depth of 1531 ft (464 m) and USW GU3 borehole at 1406 ft (426 m) from the Calico Hills Formation and USW G4 at a depth of 272 ft (82.4 m) from the Topobah Springs Member) were examined by high-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM). Alteration products are of interest because they may influence the form and distribution of contaminants released from the proposed high-level nuclear waste repository. Samples from the Calico Hills Formation contain alkali-bearing aluminosilicate glass and its alteration products. Zeolites appear to have formed from compositionally similar glass by recrystallization, probably under hydrothermal conditions. Crystals are fibrous and frequently no more than a few tens of nanometers in diameter. Porous aggregates of few-nanometer-diameter, poorly crystalline silica spheres (probably opal C-T) develop adjacent to corroded glass surfaces and zeolite crystals. Finely crystalline Fe-rich smectites coat etched glass surfaces, zeolites and feldspar crystals and occur within opal-like silica aggregates. Microstructures in the clay-dominated coatings and details of smectite-glass interfaces suggest that clays grow in orientations controlled by heterogeneously retreating surfaces and from constituents released at associated glass dissolution sites. The alteration assemblage also includes finely crystalline hematite, goethite, Mn-oxide films and illite formed by alteration of muscovite. The zeolitized sample contains abundant opal-like silica whereas glass in the unzeolitized sample is weathered to smectite-like clays. These differences may be attributed to hydrological and consequent geochemical factors resulting from the higher porosity of zeolitized samples. Exsolved alkali feldspar, which occurs as micron-sized crystals in the Calico Hills Formation and as phenocrysts and in the groundmass of the devitrified Topobah Springs Member, are almost unaltered. Feldspar alteration is confined to cracks and grain boundaries, where minor, poorly crystalline, Fe-bearing aluminosilicate alteration products are developed. In these tuffs, most of the porosity, permeability, high surface area and capacity to affect solution chemistry are associated with products of glass alteration.

Geohydrological models and earthquake effects at Yucca Mountain, Nevada

Yucca Mountain, the proposed site for the high-level nuclear waste repository, is located just south of where the present water table begins a sharp rise in elevation. This large hydraulic gradient is a regional feature that extends for over 100 km. Yucca Mountain and its vicinity are underlain by faulted and fractured tuffs with hydraulic conductivities controlled by flow through the fractures. Close to and parallel with the region of large hydraulic gradient, and surrounding the core of the Timber Mountain Caldera, there is a 10- to 20-km-wide zone containing few faults and thus, most likely, few open fractures. Consequently, this zone should have a relatively low hydraulic conductivity, and this inference is supported by the available conductivity measurements in wells near the large hydraulic gradient. Also, slug injection tests indicate significantly higher pressures for fracture opening in wells located near the large hydraulic gradient compared to the opening pressures in wells further to the south, hence implying that lower extensional stresses prevail to the north with consequently fewer open fractures there. Analytical and numerical modeling shows that such a boundary between media of high and low conductivity can produce the observed, large hydraulic gradient, with the high conductivity medium having a lower elevation than the water table. Further, as fractures can close due to tectonic activity, the conductivity of the Yucca Mountain tuffs can be reduced to a value near that for the hydraulic barrier due to strain release by a moderate earthquake. Under these conditions, simulations show that the elevation of the steady-state water table could rise between 150 and 250 m at the repository site. This elevation rise is due to the projected shift in the location of the large hydraulic gradient to the south in response to a moderate earthquake, near magnitude 6, along one of the major normal faults adjacent to Yucca Mountain. As the proposed repository would only be 200–400 m above the present water table, this predicted rise in the water table indicates a potential hazard involving water intrusion.

Thermal expansion, thermal conductivity, and heat capacity measurements at Yucca Mountain, Nevada

Abstract A very extensive database for thermal properties of Yucca Mountain tuffs has been collected to characterize the Yucca Mountain, NV site. Cores from boreholes UE25 NRG-4, UE25 NRG-5, USW NRG-6, and USW NRG-7/7A, all drilled near the North Ramp of the Exploratory Studies Facility, were tested to determine thermal conductivity, thermal expansion, and specific heat. Specimens were tested from four thermal-mechanical units (TCw, PTn, TSw1, and TSw2) that included welded devitrified (TCw, TSw1, TSw2) and nonwelded vitric (PTn) tuff. The effects of moisture content, temperature, and composition were assessed. Petrologic data were obtained from 97 samples, all from USW NRG-6, to assess relationships between measured thermal properties and composition.

Creep and static fatigue of welded tuff from Yucca Mountain, Nevada

A very extensive database for thermal properties of Yucca Mountain tuffs has been collected to characterize the Yucca Mountain, NV site. Cores from boreholes UE25 NRG-4, UE25 NRG-5, USW NRG-6, and USW NRG-7/7A, all drilled near the North Ramp of the Exploratory Studies Facility, were tested to determine thermal conductivity, thermal expansion, and specific heat. Specimens were tested from four thermal-mechanical units (TCw, PTn, TSw1, and TSw2) that included welded devitrified (TCw, TSw1, TSw2) and nonwelded vitric (PTn) tuff. The effects of moisture content, temperature, and composition were assessed. Petrologic data were obtained from 97 samples, all from USW NRG-6, to assess relationships between measured thermal properties and composition.

Thermal expansion, thermal conductivity, and heat capacity measurements at Yucca Mountain Nevada

A very extensive database for thermal properties of Yucca Mountain tuffs has been collected to characterize the Yucca Mountain, NV site. Cores from boreholes UE25 NRG-4, UE25 NRG-5, USW NRG-6, and USW NRG-7/7A, all drilled near the North Ramp of the Exploratory Studies Facility, were tested to determine thermal conductivity, thermal expansion, and specific heat. Specimens were tested from four thermal-mechanical units (TCw, PTn, TSw1, and TSw2) that included welded devitrified (TCw, TSw1, TSw2) and nonwelded vitric (PTn) tuff. The effects of moisture content, temperature, and composition were assessed. Petrologic data were obtained from 97 samples, all from USW NRG-6, to assess relationships between measured thermal properties and composition.

Reservoir depletion and its effect on wellbore stability evaluation

A very extensive database for thermal properties of Yucca Mountain tuffs has been collected to characterize the Yucca Mountain, NV site. Cores from boreholes UE25 NRG-4, UE25 NRG-5, USW NRG-6, and USW NRG-7/7A, all drilled near the North Ramp of the Exploratory Studies Facility, were tested to determine thermal conductivity, thermal expansion, and specific heat. Specimens were tested from four thermal-mechanical units (TCw, PTn, TSw1, and TSw2) that included welded devitrified (TCw, TSw1, TSw2) and nonwelded vitric (PTn) tuff. The effects of moisture content, temperature, and composition were assessed. Petrologic data were obtained from 97 samples, all from USW NRG-6, to assess relationships between measured thermal properties and composition.

Paleogeothermal and Paleohydrologic Conditions in Silicic Tuff from Yucca Mountain, Nevada

AbstractThe clay mineralogy of tuffs from Yucca Mountain, Nevada, the potential site of the nation's first high-level radioactive waste repository, has been studied in order to understand the alteration history of the rocks and to predict potential future alterations. Bulk-rock samples and clay-mineral separates from three drill holes at Yucca Mountain (USW G-1, USW G-2, and USW GU-3/G-3) were studied using X-ray powder diffraction, and supporting temperature information was obtained using fluid inclusion data from calcite. Twelve K/Ar dates were obtained on illite/smectite (I/S) separated from the tuffs from the two northernmost drill holes, USW G-1 and G-2. The predominant clay minerals in the Yucca Mountain tuffs are interstratified I/S, with minor amounts of chlorite and interstratified chlorite/smectite. The I/S reactions observed as a function of depth are similar to those observed for pelitic rocks; I/S transforms from R = 0 interstratifications through R = 1 and R ≥ 3 interstratifications to illite in USW G-2 and to R ≥ 3 I/S in USW G-1. The R = 0 I/S clays in USW GU-3/G-3 have not significantly transformed. K/Ar dates for the I/S samples average 10.4 my. These data suggest that the rocks at depth in the northern portion of Yucca Mountain were altered 10.0-11 my ago, soon after creation of the Timber Mountain caldera to the north. Both I/S geothermometry and fluid inclusion data suggest that the rocks at depth in USW G-2 were subjected to postdepositional temperatures of at least 275°C, those in USW G-1 reached 200°C, and rocks from USW GU-3/G-3 probably did not exceed 100°C. These data suggest that no significant hydrothermal alteration has occurred since Timber Mountain time, ~ 10.7 my ago.Estimates of the temperature of formation of illite/smectites yield probable stability limits for several minerals at Yucca Mountain. Clinoptilolite apparently became unstable at about 100°C, mordenite was not a major phase above 130°C, and analcime transformed to albite above 175°-200°C. It appears that cristobalite transformed to quartz at 90°-100°C in USW G-2 but must have reacted at considerably lower temperatures (and for longer times) in USW GU-3/G-3. The reactions with increasing depth appear coupled, and clinoptilolite and cristobalite disappear approximately simultaneously, supporting aqueous silica activity as a controlling variable in the clinoptilolite-to-analcime reaction. The reaction of clinoptilolite to analcime also coincides with the appearance of calcite, chlorite, and interstratified chlorite/smectite. Although the hydrothermal fluids may have been a source for some cations, breakdown of clinoptilolite (and mordenite) probably provided the source of some of the Ca for calcite, Mg for chlorite, K for the I/S found deeper in the section, and Na for analcime and albite.Using the rocks in USW G-1, G-2, and GU/G-3 as natural analogs to repository-induced thermal alteration suggests that the bulk of the clinoptilolite- and mordenite-bearing rocks in Yucca Mountain will not react to less sorptive phases such as analcime over the required lifetime of the potential repository. The zeolites in zeolite interval I, directly underlying the proposed repository horizon, may transform at the predicted repository temperatures. However, the reaction of clinoptilolite to analcime in interval I may require the transformation of all of the abundant opal-CT and glass to quartz, an unlikely scenario considering the unsaturated nature of these rocks and the predicted temperatures of <100°C.

Diffusive Transport of Carbon Dioxide through USW-G4 Topopah Spring Tuffs

ABSTRACTThe estimation of diffusive transport of gases through tuffs is important in order to assess whether Yucca Mountain is an environmentally safe and acceptable repository for high-level radioactive waste. The purpose of this study is to provide effective diffusivity data which may be used to calculate the amount of diffusion of carbon dioxide through Yucca Mountain tuff layers to the environment. The effective diffusivity of carbon dioxide was measured for tuff samples from five different layers of the USW-G4 drillhole, which is located in the central part of the proposed repository horizon. The tuff samples studied are from the following layers and depths: Vapor Phase (83.6 m), Upper Lithophysal (130.1 m), Middle Nonlithophysal (224.5 m), Lower Lithophysal (243.9 m, 266.9 m, 297.3 m and 335.2 m), and Lower Nonlithophysal (356.3 m and 371.0 m). A steady-state, counter-diffusion method, using gas chromatographic analysis, was used to determine the effective diffusivity of carbon dioxide through tuff samples. Effective diffusivity increased with temperature between 25°C and 125°C for all layers. The effect of temperature on diffusivity correlated well using second-order polynomials. The porosity, specific surface area and mean pore radius were also determined. In general, diffusivity increased with porosity, specific surface area and mean pore radius, but did not correlate well. From the measured data , it appears that the diffusion takes place primarily in the combined Knudsen and bulk diffusion regimes.

Temperature and saturation effects on diffusion of carbon dioxide through “G” tunnel and Yucca Mountain tuffs

The effective diffusivity of carbon dioxide through various tuff samples is reviewed. The effective diffusivities of carbon dioxide through “G” tunnel tuff, the lower non-lithophysal zone of the Topopah Spring tuff (outcrop sample of proposed nuclear repository site layer), USW H-6 test well tuff, the lower lithophysal zone of the Topopah Spring tuff (outcrop sample of the layer right above the proposed repository) and Tiva Canyon tuff samples (proposed repository layer) have been evaluated. Empirical correlations were reported for each tuff to estimate the effective diffusivity of carbon dioxide through them. The effective diffusivity of carbon dioxide through all the tuff samples increased with temperature and decreased as the moisture content increased.

Detection of Trace Amounts of Erionite Using X-Ray Powder Diffraction: Erionite in Tuffs of Yucca Mountain, Nevada, and Central Turkey

AbstractRecent data in the biological literature suggest that the natural zeolite erionite may be more tumorigenic than asbestos minerals. Because of its potential biological importance, a technique has been developed to facilitate detection of erionite in tuffaceous rocks to a lower limit of detection (LLD) between 100 and 500 ppm. The method involves the use of automated X-ray powder diffraction instrumentation with long count times, as much as 360 s/step. The presence of interfering phases, such as smectite or clinoptilolite, raises the LLD. Ethylene glycol solvation of smectite improves the LLD, and profile fitting with clinoptilolite-bearing mixtures improves quantification. Application of these methods to tuffs from central Turkey allowed improved detection and more accurate quantification compared with previous scanning electron microscope examinations. Use of these methods with tuffs from Yucca Mountain, Nevada, the potential site for the nation's first high-level radioactive waste repository, showed that erionite occurs sporadically. Erionite is found only in the altered zone directly above the lower vitrophyre of the Topopah Spring Member. This altered zone is anomalous in that is contains a variety of zeolites that are either rare or absent in other Yucca Mountain tuffs. It appears that erionite is restricted to fractures and must have formed under unusual and variable conditions in the altered zone.

On thermohydrologic conditions near high‐level nuclear wastes emplaced in partially saturated fractured tuff: 1. Simulation studies with explicit consideration of fracture effects

We have performed modeling studies on the simultaneous transport of heat, liquid water, vapor, and air in partially saturated, fractured porous rock. Formation parameters were chosen as representative of the potential nuclear waste repository site in the Topopah Spring unit of the Yucca Mountain tuffs. The presence of fractures makes the transport problem very complex, both in terms of flow geometry and physics. The numerical simulator used for our flow calculations takes into account most of the physical effects believed to be important in multiphase fluid and heat flow. It has provisions for handling the extreme nonlinearities that arise in phase transitions, component disappearances, and capillary discontinuities at fracture faces. We model a region around an infinite linear string of nuclear waste canisters, taking into account both the discrete fractures and the porous matrix. Thermohydrologic conditions in the vicinity of the waste packages are found to depend strongly on relative permeability and capillary pressure characteristics of the fractures, which are unknown at the present time. If liquid held on the rough walls of drained fractures is assumed to be mobile, strong heat pipe effects are predicted. Under these conditions the host rock will remain in two‐phase conditions right up to the emplacement hole, and formation temperatures will peak near 100°C. If it is assumed that liquid cannot move along drained fractures, the region surrounding the waste packages is predicted to dry up, and formation temperatures will rise beyond 200°C. A substantial fraction of waste heat can be removed if emplacement holes are left open and ventilated, as opposed to backfilled and sealed emplacement conditions. Comparing our model predictions with observations from in situ heater experiments reported by Zimmerman and coworkers, some intriguing similarities are noted. However, for a quantitative evaluation, additional carefully controlled laboratory and field experiments will be needed.

Acoustic emission signatures of Yucca Mountain tuffs, Nevada : Watters, R J; Chuck, D M Rock Mechanics as a Guide for Efficient Utilization of Natural Resources: Proc 30th U.S. Symposium, Morgantown, 19–22 June 1989P245–252. Publ Rotterdam: A A Balkema, 1989

Acoustic emission signatures of Yucca Mountain tuffs, Nevada : Watters, R J; Chuck, D M Rock Mechanics as a Guide for Efficient Utilization of Natural Resources: Proc 30th U.S. Symposium, Morgantown, 19–22 June 1989P245–252. Publ Rotterdam: A A Balkema, 1989

Analysis of the elastic and strength properties of Yucca Mountain tuff, Nevada : Price, R H; Bauer, S J In: Research and Engineering Applications in Rock Masses (paper to the 26th US Symposium on Rock Mechanics, Rapid City, 26–28 June 1985)V1, P89–96. Publ Rotterdam: A. A. Balkema, 1985

Yucca Mountain, located near the southwest margin of the Nevada Test Site, in southern Nevada, is being evaluated as a potential site for a nuclear waste repository. Yucca Mountain consists primarily of layered volcanic tuff. Samples from four stratigraphic units have been tested for physical, thermal and mechanical properties as part of the Nevada Nuclear Waste Storage Investigations (NNWSI) Project, administered by the Nevada Operations Office of the U.S. Department of Energy. The four units, in order of increasing depth, are as follows: (1) Topopah Spring Member of the Paintbrush Tuff, (2) Tuffaceous Beds of Calico Hills, (3) Bullfrog Member of the Crater Flat Tuff, and (4) Tram Member of the Crater Flat Tuff. A large data base from more than 100 experiments on drillhole core samples of Yucca Mountain silicic tuff has been assembled for use in NNWSI site evaluation and repository design calculations. These data have been analyzed and empirical expressions were found which relate elastic properties and strength with porosity plus clay content. These relationships will be presented here, in addition to an application of simple elastic composite theory to explain the observed variation of bulk modulus with functional porosity.