The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
William M. Murphy - One of the best experts on this subject based on the ideXlab platform.
-
SwRI: Isotopic Studies, The Pena Blanca Natural Analog Project
2020Co-Authors: David A. Pickett, William M. MurphyAbstract:Chemical and U-Th isotopic data on unsaturated zone waters from the Nopal I Natural Analog reveal effects of water-rock interaction and help constrain models of radionuclide release and transport at the site and, by Analogy, at the proposed nuclear waste repository at Yucca Mountain. Geochemical reaction-path modeling indicates that, under oxidizing conditions, dissolution of uraninite (spent fuel Analog) by these waters will lead to eventual schoepite precipitation regardless of initial silica concentration provided that groundwater is not continuously replenished. Thus, less soluble uranyl silicates may not dominate the initial alteration assemblage and keep dissolved U concentration low. Uranium-series activity ratios are consistent with models of U transport at the site and display varying degrees of leaching versus recoil mobilization. Thorium concentrations may reflect the importance of colloidal transport of low-solubility radionuclides in the unsaturated zone.
-
Natural Analogs and Performance Assessment for Geologic Disposal of Nuclear Waste
MRS Proceedings, 1999Co-Authors: William M. MurphyAbstract:The use of Natural Analog studies in performance assessments has been widely discussed and debated, but its accomplishment has been limited. Given recognized uncertainties and challenges, scientific contributions to performance assessments and support for the validity of performance assessment models are valuable from all possible sources, including Natural Analog studies. The conceptual basis for geologic disposal of nuclear waste and for performance assessments relies on scientific expertise based largely on studies of Natural systems Analogous to possible repository systems, i.e., Natural Analogs. Natural Analog studies offer contributions to model validation based both on inductive and deductive reasoning. The utility of Analog studies as a deductive tool in performance assessment is enhanced by specificity of the Analog system to the repository system. As geologic sites are selected and repository designs detailed, the use of Analog data in supporting deductive performance assessments should increase. Consideration of Yucca Mountain for the proposed US high level nuclear waste repository affords site specificity conducive to applications of Natural Analog data in performance assessment. The primary use of Penia Blanca Natural Analog data in recent Yucca Mountain performance assessments stems from observations of mineral products formed by alteration of Natural uraninite, an Analog of spent fuel. Alternate performance assessment source term models based on the Penia Blanca oxidation rate model and the schoepite solubility model yield lower, yet comparable estimated doses than the base case model in the NRC performance assessment for Yucca Mountain.
-
alternate source term models for yucca mountain performance assessment based on Natural Analog data and secondary mineral solubility
MRS Proceedings, 1999Co-Authors: William M. Murphy, Richard B CodellAbstract:Performance assessment calculations for the proposed high level radioactive waste repository at Yucca Mountain, Nevada, were conducted using the Nuclear Regulatory Commission Total-System Performance Assessment (TPA 3.2) code to test conceptual models and parameter values for the source term based on data from the Pena Blanca, Mexico, Natural Analog site and based on a model for coprecipitation and solubility of secondary schoepite. In previous studies the value for the maximum constant oxidative alteration rate of uraninite at the Nopal I uranium body at Pena Blanca was estimated. Scaling this rate to the mass of uranium for the proposed Yucca Mountain repository yields an oxidative alteration rate of 22 kg/y, which was assumed to be an upper limit on the release rate from the proposed repository. A second model was developed assuming releases of radionuclides are based on the solubility of secondary schoepite as a function of temperature and solution chemistry. Releases of uranium are given by the product of uranium concentrations at equilibrium with schoepite and the flow of water through the waste packages. For both models, radionuclides other than uranium and those in the cladding and gap fraction were modeled to be released at a rate proportional to themore » uranium release rate, with additional elemental solubility limits applied. Performance assessment results using the Pena Blanca oxidation rate and schoepite solubility models for Yucca Mountain were compared to the TPA 3.2 base case model, in which release was based on laboratory studies of spent fuel dissolution, cladding and gap release, and solubility limits. Doses calculated using the release rate based on Natural Analog data and the schoepite solubility models were smaller than doses generated using the base case model. These results provide a degree of confidence in safety predictions using the base case model and an indication of how conservatism in the base case model may be reduced in future analyses.« less
-
unsaturated zone waters from the nopal i Natural Analog chihuahua mexico implications for radionuclide mobility at yucca mountain
MRS Proceedings, 1999Co-Authors: David A. Pickett, William M. MurphyAbstract:Chemical and U-Th isotopic data on unsaturated zone waters from the Nopal I Natural Analog reveal effects of water-rock interaction and help constrain models of radionuclide release and transport at the site and, by Analogy, at the proposed nuclear waste repository at Yucca Mountain. Geochemical reaction-path modeling indicates that, under oxidizing conditions, dissolution of uraninite (spent fuel Analog) by these waters will lead to eventual schoepite precipitation regardless of initial silica concentration provided that groundwater is not continuously replenished. Thus, less soluble uranyl silicates may not dominate the initial alteration assemblage and keep dissolved U concentrations low. Uranium-series activity ratios are consistent with models of U transport at the site and display varying degrees of leaching versus recoil mobilization. Thorium concentrations may reflect the importance of colloidal transport of low-solubility radionuclides in the unsaturated zone.
-
Natural Analog Support for Unsaturated Transport Modeling Using Data from the Akrotiri Archaeological Site
MRS Proceedings, 1995Co-Authors: William M. Murphy, C. PearcyAbstract:AbstractA review of the Natural Analog study at the Akrotiri archaeological site is provided with regard to its use in support of long-term predictive modeling of chemical transport. Evidence for a plume of contaminants was collected using samples taken from the area under the location where artifacts were buried in silicic tuff for 3600 years. A transport model was developed using site characterization data, but no data for the plume. Qualitative data from the field support the model result that flux of metals from the artifacts was small. However, transient transport characteristics and the role of notable system heterogeneities and complexities were not fully represented by the model. The Akrotiri Natural Analog study indicates that long term releases and transport may be limited in an unsaturated repository site, but releases may be strongly affected by unknown processes or processes that are neglected in simplified models.
Evgenevich Andrej Golubev - One of the best experts on this subject based on the ideXlab platform.
-
technical graphene reduced graphene oxide and its Natural Analog shungite
Technical Physics, 2016Co-Authors: Elena F. Sheka, Evgenevich Andrej GolubevAbstract:The wide structure and chemical-composition spectrum of the main technological material of molecular graphenics—reduced graphene oxide (RGO)—is explained from a quantum-chemical standpoint. The proposed concept is used to consider the results of experimental investigations of a Natural Analog of RGO, namely, shungite carbon, by high-resolution electron microscopy and nanopoint energy dispersive spectral analysis. The results obtained are used to propose an atomic-microscopic model for the structure of shungite carbon.
-
Technical graphene (reduced graphene oxide) and its Natural Analog (shungite)
Technical Physics, 2016Co-Authors: Elena F. Sheka, Evgenevich Andrej GolubevAbstract:© 2016, Pleiades Publishing, Ltd. The wide structure and chemical-composition spectrum of the main technological material of molecular graphenics—reduced graphene oxide (RGO)—is explained from a quantum-chemical standpoint. The proposed concept is used to consider the results of experimental investigations of a Natural Analog of RGO, namely, shungite carbon, by high-resolution electron microscopy and nanopoint energy dispersive spectral analysis. The results obtained are used to propose an atomic-microscopic model for the structure of shungite carbon.
Tom Meuzelaar - One of the best experts on this subject based on the ideXlab platform.
-
supercritical carbon dioxide and sulfur in the madison limestone a Natural Analog in southwest wyoming for geologic carbon sulfur co sequestration
Earth and Planetary Science Letters, 2011Co-Authors: John P Kaszuba, Alexis Navarresitchler, Geoffrey D Thyne, Curtis Chopping, Tom MeuzelaarAbstract:article i nfo The Madison Limestone on the Moxa Arch, southwest Wyoming, USA contains large volumes (65-95%) of supercritical CO2 that it has stored Naturally for 50 million years. This reservoir also contains supercritical H2S, aqueous sulfur complexes (SO4 2� and HS � ), and sulfur-bearing minerals (anhydrite and pyrite). Although SO2 is not present, these sulfur-bearing phases are known products of SO2 disproportionation in other water-rock systems. The Natural co-occurrence of SO4 2� ,S 2� , supercritical CO2 and brine affords the opportunity to evaluate the fate of a carbon-sulfur co-sequestration scenario. Mineralogic data was obtained from drill core and aqueous geochemical data from wells outside and within the current supercritical CO2-sulfur-brine-rock system. In addition to dolomite, calcite, and accessory sulfur- bearing minerals, the Madison Limestone contains accessory quartz and the aluminum-bearing minerals feldspar, illite, and analcime. Dawsonite (NaAlCO3(OH)2), predicted as an important carbon sink in sequestration modeling studies, is not present. After confirming equilibrium conditions for the Madison Limestone system, reaction path models were constructed with initial conditions based on data from outside the reservoir. Addition of supercritical CO2 to the Madison Limestone was simulated and the results compared to data from inside the reservoir. The model accurately predicts the observed mineralogy and captures the fundamental changes expected in a Madison Limestone-brine system into which CO2 is added. pH decreases from 5.7 to 4.5 at 90 °C and to 4.0 at 110 °C, as expected from dissolution of supercritical CO2, creation of carbonic acid, and buffering by the carbonate rock. The calculated redox potential increases by 0.1 V at 90 °C and 0.15 V at 110 °C due to equilibrium among CO2, anhydrite, and pyrite. Final calculated Eh and pH match conditions for the co-existing sulfur phases present in produced waters and core from within the reservoir. Total dissolved solids increase with reaction progress, mostly due to dissolution of calcite with an accompanying increase in dissolved bicarbonate. The Madison Limestone is a Natural example of the thermodynamic end point that similar fluid-rock systems will develop following emplacement of a supercritical CO2-sulfur mixture and is a Natural Analog for geologic carbon-sulfur co-sequestration.
Pauline N Mollema - One of the best experts on this subject based on the ideXlab platform.
-
a Natural Analog for a fractured and faulted reservoir in dolomite triassic sella group northern italy
AAPG Bulletin, 2000Co-Authors: Marco Antonellini, Pauline N MollemaAbstract:We have used outcrops of dolomite exposed in the Triassic Sella Group of the Italian Central Dolomites as an Analog for subsurface low-porosity faulted and fractured dolomite reservoirs. The Sella Group was mildly deformed at shallow burial depth (21,000 m) in a tectonic strike-slip regime during the Eocene-Miocene Alpine compression that caused the formation of joints and strike-slip faults. Because the matrix porosity in the dolomites is low (<5%) and poorly connected, joints and faults are essential to connect vugs and to provide permeability. Field observations of the Sella Group explain why many dolomite reservoirs and aquifers in strike-slip/compressive tectonic regimes are intensely jointed when they are mildly deformed. In this type of tectonic regime, in fact, pervasive jointing over a wide area accommodates small strains and is strictly associated with the formation of strike-slip faults. Our observations allow us to recognize different kinds of fault architectures that correspond to different stages of fault development. In addition, theoretical models and microscopic observations were used to estimate the petrophysical properties of the faulted and jointed dolomite. Small-offset faults (offsets up to 30 mm), characterized by en echelon arrays of joints and pockets or seams of breccia up to 10 mm wide, form areas of high permeability (100-3000 md) due to the presence of many joints and high-porosity breccia. Faults with 1-10 m offsets, characterized by a breccia zone (1-2 m in width) and associated with high joint density in the wall-rock, contain high-porosity (10%) breccia and represent areas of preferred fluid flow. Large-offset faults with offsets more than 10 m contain a wide zone of low-porosity (<1%) breccia and form potential permeability barriers. The areas adjacent to the intermediate- and large-offset faults have high permeability (100-3000 md) because of high joint densities. An important implication of the way faults develop in dolomite is the consistent relationship between the orientation of joints and faults: the fault's strikes differ 15-35° from the strikes of the pervasive joint systems. Joint density also increases four to five times in the proximity of the faults. Such relationships can be used to predict the distribution and orientation of joints and faults in subsurface dolomite reservoirs.
-
A Natural Analog for a Fractured and Faulted Reservoir in Dolomite: Triassic Sella Group, Northern Italy
AAPG Bulletin, 2000Co-Authors: Marco Antonellini, Pauline N MollemaAbstract:We have used outcrops of dolomite exposed in the Triassic Sella Group of the Italian Central Dolomites as an Analog for subsurface low-porosity faulted and fractured dolomite reservoirs. The Sella Group was mildly deformed at shallow burial depth (21,000 m) in a tectonic strike-slip regime during the Eocene-Miocene Alpine compression that caused the formation of joints and strike-slip faults. Because the matrix porosity in the dolomites is low (
Hari S Viswanathan - One of the best experts on this subject based on the ideXlab platform.
-
Carbon Sequestration and Its Role in the Global Carbon Cycle - Natural Analogs of geologic CO2 sequestration: Some general implications for engineered sequestration
Geophysical monograph, 2013Co-Authors: Julianna E. Fessenden, Philip H. Stauffer, Hari S ViswanathanAbstract:Carbon dioxide emissions from geologic systems occur primarily from geothermal release of carbon in rock or subsurface biologic reservoirs. These systems can be very useful Natural Analogs for evaluating the impact of carbon dioxide leaks from engineered geologic storage reservoirs used to sequester CO 2 . We describe three Natural Analog sites that illustrate very different leak scenarios that could occur at such engineered repositories. The Mammoth Mountain site, located in California, provides an example of diffuse C0 2 seepage. Crystal Geyser, Utah, is an example of a highly focused, episodic leakage geyser. Bravo Dome, NM, is an example of a CO 2 reservoir where no leakage has been observed. We discuss monitoring techniques, technology placement, and modeling approaches that can be used at these Natural Analog sites to gain further insight into the viability of geologic CO 2 sequestration.
-
co2 leakage impacts on shallow groundwater field scale reactive transport simulations informed by observations at a Natural Analog site
Applied Geochemistry, 2013Co-Authors: Elizabeth H Keating, Alexandra J Hakala, Hari S Viswanathan, William J Carey, Rajesh J Pawar, George D Guthrie, Julianna FessendenrahnAbstract:Abstract It is challenging to predict the degree to which shallow groundwater might be affected by leaks from a CO2 sequestration reservoir, particularly over long time scales and large spatial scales. In this study observations at a CO2 enriched shallow aquifer Natural Analog were used to develop a predictive model which is then used to simulate leakage scenarios. This Natural Analog provides the opportunity to make direct field observations of groundwater chemistry in the presence of elevated CO2, to collect aquifer samples and expose them to CO2 under controlled conditions in the laboratory, and to test the ability of multi-phase reactive transport models to reproduce measured geochemical trends at the field-scale. The field observations suggest that brackish water entrained with the upwelling CO2 are a more significant source of trace metals than in situ mobilization of metals due to exposure to CO2. The study focuses on a single trace metal of concern at this site: U. Experimental results indicate that cation exchange/adsorption and dissolution/precipitation of calcite containing trace amounts of U are important reactions controlling U in groundwater at this site, and that the amount of U associated with calcite is fairly well constrained. Simulations incorporating these results into a 3-D multi-phase reactive transport model are able to reproduce the measured ranges and trends between pH, pCO2, Ca, total C, U and Cl− at the field site. Although the true fluxes at the Natural Analog site are unknown, the cumulative CO2 flux inferred from these simulations are approximately equivalent to 37.8E−3 MT, approximately corresponding to a .001% leak rate for injection at a large (750 MW) power plant. The leakage scenario simulations suggest that if the leak only persists for a short time the volume of aquifer contaminated by CO2-induced mobilization of U will be relatively small, yet persistent over 100 a.
-
developing a robust geochemical and reactive transport model to evaluate possible sources of arsenic at the co2 sequestration Natural Analog site in chimayo new mexico
International Journal of Greenhouse Gas Control, 2012Co-Authors: Hari S Viswanathan, Elizabeth H Keating, Alexandra J Hakala, George D Guthrie, Christina L Lopano, Kirk G Scheckel, Liange Zheng, Rajesh J PawarAbstract:Abstract Migration of carbon dioxide (CO 2 ) from deep storage formations into shallow drinking water aquifers is a possible system failure related to geologic CO 2 sequestration. A CO 2 leak may cause mineral precipitation/dissolution reactions, changes in aqueous speciation, and alteration of pH and redox conditions leading to potential increases of trace metal concentrations above EPA National Primary Drinking Water Standards. In this study, the Chimayo site (NM) was examined for site-specific impacts of shallow groundwater interacting with CO 2 from deep storage formations. Major ion and trace element chemistry for the site have been previously studied. This work focuses on arsenic (As), which is regulated by the EPA under the Safe Drinking Water Act and for which some wells in the Chimayo area have concentrations higher than the maximum contaminant level (MCL). Statistical analysis of the existing Chimayo groundwater data indicates that As is strongly correlated with trace metals U and Pb indicating that their source may be from the same deep subsurface water. Batch experiments and materials characterization, such as: X-ray diffraction (XRD), scanning electron microscopy (SEM), and synchrotron micro X-ray fluorescence (μ-XRF), were used to identify As association with Fe-rich phases, such as clays or oxides, in the Chimayo sediments as the major factor controlling As fate in the subsurface. Batch laboratory experiments with Chimayo sediments and groundwater show that pH decreases as CO 2 is introduced into the system and buffered by calcite. The introduction of CO 2 causes an immediate increase in As solution concentration, which then decreases over time. A geochemical model was developed to simulate these batch experiments and successfully predicted the pH drop once CO 2 was introduced into the experiment. In the model, sorption of As to illite, kaolinite and smectite through surface complexation proved to be the key reactions in simulating the drop in As concentration as a function of time in the batch experiments. Based on modeling, kaolinite precipitation is anticipated to occur during the experiment, which allows for additional sorption sites to form with time resulting in the slow decrease in As concentration. This mechanism can be viewed as trace metal “scavenging” due to sorption caused secondary mineral precipitation. Since deep geologic transport of these trace metals to the shallow subsurface by brine or CO 2 intrusion is critical to assessing environmental impacts, the effective retardation of trace metal transport is an important parameter to estimate and it is dependent on multiple coupled reactions. At the field scale, As mobility is retarded due to the influence of sorption reactions, which can affect environmental performance assessment studies of a sequestration site.
-
the challenge of predicting groundwater quality impacts in a co2 leakage scenario results from field laboratory and modeling studies at a Natural Analog site in new mexico usa
Energy Procedia, 2011Co-Authors: Elizabeth H Keating, Alexandra J Hakala, Hari S Viswanathan, William J Carey, George D Guthrie, Rosemary C Capo, Brian W Stewart, James Gardiner, Julianna FessendenAbstract:Abstract A vital aspect to public and regulatory acceptance of carbon sequestration is assurance that groundwater resources will be protected. Theoretical and laboratory studies can, to some extent, be used to predict the consequences of leakage. However, direct observations of CO 2 flowing through shallow drinking water aquifers are invaluable for informing credible risk assessments. To this end, we have sampled shallow wells in a Natural Analog site in New Mexico, USA, where CO 2 from Natural sources is upwelling from depth. We collected major ion, trace element, and isotopic ( 3 H, 18 O, and Sr) data and, coupled with laboratory experiments and reactive transport modeling, have concluded that the major control on groundwater quality at this site is not chemical reaction of CO 2 with the aquifer but intrusion of saline waters upwelling with the CO 2 . Using reactive transport modeling based on field data, we show the difference in reactivity of the CO 2 and CO 2 /saline water source terms, particularly with respect to carbonate mineralogy. Sr isotopes were used to investigate whether aquifer waters were affected by carbonate mineral reaction with CO 2 or by saline water intrusion. Preliminary data suggest that Sr isotopes can successfully be used to discriminate between the two types of source terms at Chimayo; this technique shows promise for monitoring CCS sites. In developing predictive capabilities for future sites, it is critical to identify the solid phases and specific reactions controlling dissolved trace metal concentrations in both the presence and absence of CO 2 . We have conducted laboratory experiments to identify these phases and have found that some elements (e.g., U, Ca) are largely controlled by ion exchange and/or carbonate minerals. In the experiments, the concentration of some metals increases after exposure to CO 2 (although concentrations remain below the U.S. EPA primary drinking water standards); we are currently extending these experiments to determine if the reactions causing the increase are reversible and, if so, on what time scales. Metal scavenging by secondary mineral precipitation, as observed at other Natural Analog sites, may be important at certain temporal scales. We are using the information gained from this field and laboratory study to develop predictive models for application to risk assessment at future CCS sites. The models will be particularly useful in identifying the temporal and spatial scales of water quality changes and in developing possible mitigation strategies in the case of leaks at engineered CCS sites.