A new approach to sample handling for powder X-ray diffraction analysis is presented that allows ... more A new approach to sample handling for powder X-ray diffraction analysis is presented that allows characterization of poorly prepared samples. The technique relies on vibrations generated in a sample holder to create movement of the powdered sample in the absence of macroscopic movement of the sample holder itself. The major benefits over conventional sample handling strategies are: 1) the ability to characterize materials with grain sizes up to two orders of magnitude larger than previously possible without degradation of the data; and 2) ease of loading and removal of the samples, with no requirement for complex mechanisms. The Vibrating Sample Holder technique was demonstrated in a laboratory XRD instrument as well as in a miniature XRD/XRF instrument intended for robotic planetary exploration by NASA. A dramatic improvement in data quality for coarse-grained materials was observed, yielding accurate and reproducible intensity data for such materials. The Vibrating Sample Holder w...
Several faults near Yucca Mountain, Nevada, contain abundant calcite and opal-CT, with lesser amo... more Several faults near Yucca Mountain, Nevada, contain abundant calcite and opal-CT, with lesser amounts of opal-A and sepiolite or smectite. These secondary minerals are being studied to determine the directions, amounts, and timing of transport involved in their formation. Such information is important for evaluating the future performance of a potential high-level nuclear waste repository beneath Yucca Mountain. This report is a preliminary assessment of how those minerals were formed. Possible analog deposits from known hydrothermal veins, warm springs, cold springs or seeps, soils, and aeolian sands were studied by petrographic and x-ray diffraction methods for comparison with the minerals deposited in the faults; there are major mineralogic differences in all of these environments except in the aeolian sands and in some cold seeps. Preliminary conclusions are that the deposits in the faults and in the sand ramps are closely related, and that the process of deposition did not require upward transport from depth. I.
Understanding the past and present habitability of the martian environment is the focus of the Cu... more Understanding the past and present habitability of the martian environment is the focus of the Curiosity Mars rover investigation. Since landing in Gale crater in August 2012, the instrument payload has provided evidence for an ancient lacustrine system with extensive deposits of finely layered mudstone (Murray formation) (Grotzinger et al., 2015). The Murray formation includes a localized occurrence of high-silica rocks with tridymite ("Buckskin" sample) previously interpreted as a detrital accumulation of silicic volcanic material (Morris et al., 2016). The sedimentary rocks of the Murray formation are overlain by a younger aeolian sandstone (Stimson formation) (Banham et al., 2018) that has been locally altered to form narrow, silica-rich alteration halos (Frydenvang et al., 2017; Yen et al., 2017).
Proceedings of the 3rd Unconventional Resources Technology Conference, 2015
Summary Microbial communities within unconventional hydrocarbon reservoirs in the oil to wet gas ... more Summary Microbial communities within unconventional hydrocarbon reservoirs in the oil to wet gas window are known to be present but sparse and believed also to be almost entirely dormant, due to heat, lack of space, and near-equilibrium redox conditions at the microscale – conditions that change when a rock is hydraulically fractured. In order to predict how microbial communities impact the geochemical response to such a perturbation, direct and indirect techniques are employed on select samples of the Point Pleasant Formation (OH and PA) to map organic filled pore space and migration pathways, and quantify the morphology, size, and surface mineralogy of fractures and pores. Samples containing these features have been selected for 3-D X-ray micro-computed tomographic (µXCT) imaging, performed at the Advanced Photon Source (APS). This effort has yielded microscale imaging, classification, and quantification of pores, organic matter, pyrite, and key pore-mineral associations. These data are complemented by Energy-dispersive X-ray spectroscopy (EDS) spot analysis and scanning electron microscope (SEM) backscattered electron (BSE) imaging to determine the spatial relationships of organic matter volumes with sufficient space for microbes. Mercury intrusion porosimetry (MIP) data permit quantification of pore throat size, vital to an understanding of nutrient, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) flux between otherwise isolated microbial communities. Results reported here include the quantification of the volumes able to accommodate microbes, the pore throat size distribution of the network connecting these volumes, a classification of organic matter and of its correlation with pyrite, and finally a discussion of certain implications for nutrient availability before and after the influx of drilling fluids. The findings of this study, although still preliminary, therefore contribute to our understanding and prediction of the biogeochemical evolution of a hydrocarbon-rich formation, and of its response to a perturbation such as hydraulic fracturing.
Preliminary measurements using the CheMin XRD/XRF instrument, which is flying on the 2009 MSL mis... more Preliminary measurements using the CheMin XRD/XRF instrument, which is flying on the 2009 MSL mission to Mars, show that the instrument can determine the mineralogy, including the total glass content, of lunar regolith and pyroclastic samples.
Los Alamos National Laboratory, an affirmative actionlequal opportunity employer, is operated by ... more Los Alamos National Laboratory, an affirmative actionlequal opportunity employer, is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the US. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, orto allow others to do so, for U.S. Government purposes. Los Alamos National Laboratory requests that the publisher identify this article as work performed under the auspices of the U.S. Department of Energy. Los Alamos National Laboratory strongly supports academic freedom and a researcher's right to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness. Form 836 (10/96) DISCLAIMER This rrpon was prepared as an atzount of work sponsored by an agency of the United States Government Neither the United States Goverament ow any agency thereof, nor my of their cmpioyas maku any wuraaty, exprrsr or implied, or assumes any legal liability or responsibility for the acamcy, campietcacss, or wfulntss of my information, apparatus, produa, or praccs ditciascd, ar represeau that its IUC would not infringe privately owaed rights. Reference he& to any s p afic cornmereid produn, proccs, or by tndc name, uodemnrk, iasaufacturn, or othenwirc does not necessarily colutjntte or impiy its eadonrmtnt, mommendktion. or favoring by the United States Goyeramcnt or my i%ncy thereof. The views and opinions of ruthon exprrucd hacin do nos o d y state or reflect those of the United State Governmeat or any agency t h d. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.
The high concentration of chlorine-36 ( 36 Cl) produced by above-ground nuclear tests (bomb-pulse... more The high concentration of chlorine-36 ( 36 Cl) produced by above-ground nuclear tests (bomb-pulse) provides a fortuitous tracer for infiltration during the last 50 years, and is used to detect fast flow in the unsaturated zone at Yucca Mountain, Nevada, a thick deposit of welded and nonwelded tuffs. Evidence of fast flow as much as 300 m into the mountain has been found in several zones in a 7.7-km tunnel. Many zones are associated with faults that provide continuous fracture flow paths from the surface. In the Sundance fault zone, water with the bomb-pulse signature has moved into subsidiary fractures and breccia zones. We found no highly distinctive mineralogic associations of fault and fracture samples containing bomb-pulse 36 Cl. Bomb-pulse sites are slightly more likely to have calcite deposits than are non-bomb-pulse sites. Most other mineralogic and textural associations of fast-flow paths reflect the structural processes leading to locally enhanced permeability rather than the effects of ground-water percolation. Water movement through the rock was investigated by isotopic analysis of paired samples representing breccia zones and fractured wall rock bounding the breccia zones. Where bomb-pulse 36 Cl is present, the waters in bounding fractures and intergranular pores of the fast pathways are not in equilibrium with respect to the isotopic signal. In structural domains that have experienced extensional deformation, fluid flow within a breccia is equivalent to matrix flow in a particulate rock, whereas true fracture flow occurs along the boundaries of a breccia zone. Where shearing predominated over extension, the boundary between wall rock and breccia is rough and irregular with a tight wall-rock/breccia contact. The absence of a gap between the breccia and the wall rock helps maintain fluid flow within the breccia instead of along the wall-rock/breccia boundary, leading to higher 36 Cl/Cl values in the breccia than in the wall rock.
Studies of mineralogy, petrology, and geochemistry at a candidate high-level waste repository sit... more Studies of mineralogy, petrology, and geochemistry at a candidate high-level waste repository site must address three primary concerns: (a) possible future geologic events that can compromise waste isolation, (b) possible conflicting site uses, and (c) the natural ability of the site to contain radionuclide waste. Data are being collected to address these concerns for a potential unsaturated repository location at
ABSTRACT Long-term integrity of wellbore cements is one of the major concerns for geologic seques... more ABSTRACT Long-term integrity of wellbore cements is one of the major concerns for geologic sequestration of CO2. This paper presents analyses of cement core recovered from a well used in a long-term CO2 enhanced oil recovery operation. A sidetrack system was used to obtain core from a 55 year-old well with 30 years of CO2 exposure as both an injector and a producer at the SACROC unit (Permian Basin, Texas). The mineralogy, chemistry, and hydrologic properties were evaluated for evidence of degradation by CO2. The recovered samples were located ~ 3 m above the contact with the reservoir. The recovered cement had permeabilities in the milliDarcy range and thus retained its capacity to prevent significant flow of CO2. There was evidence for CO2 migration along the casing-cement and cement-shale interfaces. The casing interface had a 1-2 mm thick rind of calcite-aragonite-halite. The CO2 producing this rind may have traveled up the casing wall or may have infiltrated through the casing threads. The cement in contact with the shale (within 1 cm) was heavily carbonated to an assemblage of calcite, aragonite, vaterite and amorphous alumino-silica residue and was transformed to a distinctive orange color. The heavily carbonated region is separated from less altered cement by a narrow, dense zone of silica and carbonate deposition. The CO2 for this carbonation process migrated from the cement-shale interface where the presence of shale fragments (wall cake) may have provided a fluid pathway. The carbonation reaction was associated with only small changes in the original cement chemistry including an increase in Na2O and decrease in CaO and MgO with a slight enrichment in SiO2. The carbonated zone also has a distinct carbon and oxygen stable isotope signature. Although the observed carbonation was intense, the measured hydrologic properties of the carbonated zone were not significantly different from those of relatively unaltered cement in adjacent parts of the core. Textural observations and numerical modeling indicate that the carbonation of the cement occurred by diffusion of CO2-saturated brine from the cement-shale interface. A 1-D diffusion simulation using FLOTRAN was able to reproduce the general features of the carbonation zone including carbonate deposition, alteration of the cement, width of the zone, and the presence of a dense interface with the less altered cement. The SACROC observations show, at least for the single well investigated, that Portland-based cement used in a CO2 reservoir environment can maintain hydrologic integrity for a period of 30 years despite significant carbonate mineralization. However, we were unable to quantify the amount of CO2 migration that occurred along cement interfaces with the casing and shale caprock. The quality of these interfaces appears to be the most critical issue in the performance of wellbore systems in a CO2 sequestration reservoir.
Uranium and neptunium were used as reactive tracers in long-term laboratory desorption studies us... more Uranium and neptunium were used as reactive tracers in long-term laboratory desorption studies using saturated alluvium collectedfrom south of Yucca Mountain, Nevada. The objective of these long-term experiments is to make detailed observations of the desorption behavior of uranium and neptunium to provide Yucca Mountain with technical bases for a more realistic and potentially less conservative approach to predicting the transport of adsorbing radionuclides in the saturated alluvium. This paper describes several long-term desorption experiments using a flow-through experimental method and groundwater and alluvium obtainedfrom boreholes along a potential groundwater flow path from the proposed repository site. In the long term desorption experiments, the percentages of uranium and neptunium sorbed as a firnction of time after different durations of sorption was determined. In addition, the desorbed activity as a function of time was Jit using a multi-site, multi-rate model to demonstrate that drfferent desorption rate constants ranging over several orders of magnitude exist for the desorption of uranium from Yucca Mountain saturated alluvium. This information will be used to support the development of a conceptual model that ultimately results,in effective Kd values much larger than those currently in use for predicting radionuclide transport at Yucca Mountain.
XTRA is a miniature XRD/XRF instrument intended for use on small rovers and landers destined for ... more XTRA is a miniature XRD/XRF instrument intended for use on small rovers and landers destined for solid solar system objects without substantive atmospheres (i.e., the Earth's Moon, asteroids, comets, Mercury, or the moons of Mars. The technology of XTRA derives from the CheMin XRD/XRF instrument on Mars Science Laboratory (MSL), augmented by improvements developed through Small Business Innovative Research (SBIR) grants and commercial product developments. XTRA utilizes a reflection geometry, a microfocus X-ray tube and a cooled CCD operated in direct detection mode. The reflection geometry allows for fine-grained regolith to be scooped and dumped into sample holders which are shaken during analysis to improve diffraction statistics during XRD pattern acquisition.
New 1:24,000 scale geologic mapping combined with previous and ongoing geoscientific studies are ... more New 1:24,000 scale geologic mapping combined with previous and ongoing geoscientific studies are revealing significant new findings on intracaldera stratigraphy and structure, initial development of intracaldera lakes, and the duration of resurgence within the ca. 1.25 Myr Valles caldera. The caldera is about 22 km in diameter and contains a resurgent dome that is a northeast-trending oval roughly11 x 9
Microautoradiography was used to evaluate the mineralogic basis of Pu(V) retention by tuffs from ... more Microautoradiography was used to evaluate the mineralogic basis of Pu(V) retention by tuffs from Yucca Mountain, Nevada. Altered orthopyroxenes and oxide minerals are associated with high Pu retention, but are limited to specific stratigraphic horizons. A weaker but more general association of Pu with smectite occurs in most samples. Thinsections that cross fractures allow comparative studies of Pu retention by fracturelining versus matrix minerals. Using Ag metal in emulsions as a measure of underlying Pu concentration, electron-microprobe (EMP) analysis can quantify Pu retention along fracture walls and provide mineral/mineral Pu retention factors. For smectite-lined microfractures in zeolitized tuff, the smectite/clinoptilolite Pu retention factor is <80.
A new approach to sample handling for powder X-ray diffraction analysis is presented that allows ... more A new approach to sample handling for powder X-ray diffraction analysis is presented that allows characterization of poorly prepared samples. The technique relies on vibrations generated in a sample holder to create movement of the powdered sample in the absence of macroscopic movement of the sample holder itself. The major benefits over conventional sample handling strategies are: 1) the ability to characterize materials with grain sizes up to two orders of magnitude larger than previously possible without degradation of the data; and 2) ease of loading and removal of the samples, with no requirement for complex mechanisms. The Vibrating Sample Holder technique was demonstrated in a laboratory XRD instrument as well as in a miniature XRD/XRF instrument intended for robotic planetary exploration by NASA. A dramatic improvement in data quality for coarse-grained materials was observed, yielding accurate and reproducible intensity data for such materials. The Vibrating Sample Holder w...
Several faults near Yucca Mountain, Nevada, contain abundant calcite and opal-CT, with lesser amo... more Several faults near Yucca Mountain, Nevada, contain abundant calcite and opal-CT, with lesser amounts of opal-A and sepiolite or smectite. These secondary minerals are being studied to determine the directions, amounts, and timing of transport involved in their formation. Such information is important for evaluating the future performance of a potential high-level nuclear waste repository beneath Yucca Mountain. This report is a preliminary assessment of how those minerals were formed. Possible analog deposits from known hydrothermal veins, warm springs, cold springs or seeps, soils, and aeolian sands were studied by petrographic and x-ray diffraction methods for comparison with the minerals deposited in the faults; there are major mineralogic differences in all of these environments except in the aeolian sands and in some cold seeps. Preliminary conclusions are that the deposits in the faults and in the sand ramps are closely related, and that the process of deposition did not require upward transport from depth. I.
Understanding the past and present habitability of the martian environment is the focus of the Cu... more Understanding the past and present habitability of the martian environment is the focus of the Curiosity Mars rover investigation. Since landing in Gale crater in August 2012, the instrument payload has provided evidence for an ancient lacustrine system with extensive deposits of finely layered mudstone (Murray formation) (Grotzinger et al., 2015). The Murray formation includes a localized occurrence of high-silica rocks with tridymite ("Buckskin" sample) previously interpreted as a detrital accumulation of silicic volcanic material (Morris et al., 2016). The sedimentary rocks of the Murray formation are overlain by a younger aeolian sandstone (Stimson formation) (Banham et al., 2018) that has been locally altered to form narrow, silica-rich alteration halos (Frydenvang et al., 2017; Yen et al., 2017).
Proceedings of the 3rd Unconventional Resources Technology Conference, 2015
Summary Microbial communities within unconventional hydrocarbon reservoirs in the oil to wet gas ... more Summary Microbial communities within unconventional hydrocarbon reservoirs in the oil to wet gas window are known to be present but sparse and believed also to be almost entirely dormant, due to heat, lack of space, and near-equilibrium redox conditions at the microscale – conditions that change when a rock is hydraulically fractured. In order to predict how microbial communities impact the geochemical response to such a perturbation, direct and indirect techniques are employed on select samples of the Point Pleasant Formation (OH and PA) to map organic filled pore space and migration pathways, and quantify the morphology, size, and surface mineralogy of fractures and pores. Samples containing these features have been selected for 3-D X-ray micro-computed tomographic (µXCT) imaging, performed at the Advanced Photon Source (APS). This effort has yielded microscale imaging, classification, and quantification of pores, organic matter, pyrite, and key pore-mineral associations. These data are complemented by Energy-dispersive X-ray spectroscopy (EDS) spot analysis and scanning electron microscope (SEM) backscattered electron (BSE) imaging to determine the spatial relationships of organic matter volumes with sufficient space for microbes. Mercury intrusion porosimetry (MIP) data permit quantification of pore throat size, vital to an understanding of nutrient, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) flux between otherwise isolated microbial communities. Results reported here include the quantification of the volumes able to accommodate microbes, the pore throat size distribution of the network connecting these volumes, a classification of organic matter and of its correlation with pyrite, and finally a discussion of certain implications for nutrient availability before and after the influx of drilling fluids. The findings of this study, although still preliminary, therefore contribute to our understanding and prediction of the biogeochemical evolution of a hydrocarbon-rich formation, and of its response to a perturbation such as hydraulic fracturing.
Preliminary measurements using the CheMin XRD/XRF instrument, which is flying on the 2009 MSL mis... more Preliminary measurements using the CheMin XRD/XRF instrument, which is flying on the 2009 MSL mission to Mars, show that the instrument can determine the mineralogy, including the total glass content, of lunar regolith and pyroclastic samples.
Los Alamos National Laboratory, an affirmative actionlequal opportunity employer, is operated by ... more Los Alamos National Laboratory, an affirmative actionlequal opportunity employer, is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the US. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, orto allow others to do so, for U.S. Government purposes. Los Alamos National Laboratory requests that the publisher identify this article as work performed under the auspices of the U.S. Department of Energy. Los Alamos National Laboratory strongly supports academic freedom and a researcher's right to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness. Form 836 (10/96) DISCLAIMER This rrpon was prepared as an atzount of work sponsored by an agency of the United States Government Neither the United States Goverament ow any agency thereof, nor my of their cmpioyas maku any wuraaty, exprrsr or implied, or assumes any legal liability or responsibility for the acamcy, campietcacss, or wfulntss of my information, apparatus, produa, or praccs ditciascd, ar represeau that its IUC would not infringe privately owaed rights. Reference he& to any s p afic cornmereid produn, proccs, or by tndc name, uodemnrk, iasaufacturn, or othenwirc does not necessarily colutjntte or impiy its eadonrmtnt, mommendktion. or favoring by the United States Goyeramcnt or my i%ncy thereof. The views and opinions of ruthon exprrucd hacin do nos o d y state or reflect those of the United State Governmeat or any agency t h d. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.
The high concentration of chlorine-36 ( 36 Cl) produced by above-ground nuclear tests (bomb-pulse... more The high concentration of chlorine-36 ( 36 Cl) produced by above-ground nuclear tests (bomb-pulse) provides a fortuitous tracer for infiltration during the last 50 years, and is used to detect fast flow in the unsaturated zone at Yucca Mountain, Nevada, a thick deposit of welded and nonwelded tuffs. Evidence of fast flow as much as 300 m into the mountain has been found in several zones in a 7.7-km tunnel. Many zones are associated with faults that provide continuous fracture flow paths from the surface. In the Sundance fault zone, water with the bomb-pulse signature has moved into subsidiary fractures and breccia zones. We found no highly distinctive mineralogic associations of fault and fracture samples containing bomb-pulse 36 Cl. Bomb-pulse sites are slightly more likely to have calcite deposits than are non-bomb-pulse sites. Most other mineralogic and textural associations of fast-flow paths reflect the structural processes leading to locally enhanced permeability rather than the effects of ground-water percolation. Water movement through the rock was investigated by isotopic analysis of paired samples representing breccia zones and fractured wall rock bounding the breccia zones. Where bomb-pulse 36 Cl is present, the waters in bounding fractures and intergranular pores of the fast pathways are not in equilibrium with respect to the isotopic signal. In structural domains that have experienced extensional deformation, fluid flow within a breccia is equivalent to matrix flow in a particulate rock, whereas true fracture flow occurs along the boundaries of a breccia zone. Where shearing predominated over extension, the boundary between wall rock and breccia is rough and irregular with a tight wall-rock/breccia contact. The absence of a gap between the breccia and the wall rock helps maintain fluid flow within the breccia instead of along the wall-rock/breccia boundary, leading to higher 36 Cl/Cl values in the breccia than in the wall rock.
Studies of mineralogy, petrology, and geochemistry at a candidate high-level waste repository sit... more Studies of mineralogy, petrology, and geochemistry at a candidate high-level waste repository site must address three primary concerns: (a) possible future geologic events that can compromise waste isolation, (b) possible conflicting site uses, and (c) the natural ability of the site to contain radionuclide waste. Data are being collected to address these concerns for a potential unsaturated repository location at
ABSTRACT Long-term integrity of wellbore cements is one of the major concerns for geologic seques... more ABSTRACT Long-term integrity of wellbore cements is one of the major concerns for geologic sequestration of CO2. This paper presents analyses of cement core recovered from a well used in a long-term CO2 enhanced oil recovery operation. A sidetrack system was used to obtain core from a 55 year-old well with 30 years of CO2 exposure as both an injector and a producer at the SACROC unit (Permian Basin, Texas). The mineralogy, chemistry, and hydrologic properties were evaluated for evidence of degradation by CO2. The recovered samples were located ~ 3 m above the contact with the reservoir. The recovered cement had permeabilities in the milliDarcy range and thus retained its capacity to prevent significant flow of CO2. There was evidence for CO2 migration along the casing-cement and cement-shale interfaces. The casing interface had a 1-2 mm thick rind of calcite-aragonite-halite. The CO2 producing this rind may have traveled up the casing wall or may have infiltrated through the casing threads. The cement in contact with the shale (within 1 cm) was heavily carbonated to an assemblage of calcite, aragonite, vaterite and amorphous alumino-silica residue and was transformed to a distinctive orange color. The heavily carbonated region is separated from less altered cement by a narrow, dense zone of silica and carbonate deposition. The CO2 for this carbonation process migrated from the cement-shale interface where the presence of shale fragments (wall cake) may have provided a fluid pathway. The carbonation reaction was associated with only small changes in the original cement chemistry including an increase in Na2O and decrease in CaO and MgO with a slight enrichment in SiO2. The carbonated zone also has a distinct carbon and oxygen stable isotope signature. Although the observed carbonation was intense, the measured hydrologic properties of the carbonated zone were not significantly different from those of relatively unaltered cement in adjacent parts of the core. Textural observations and numerical modeling indicate that the carbonation of the cement occurred by diffusion of CO2-saturated brine from the cement-shale interface. A 1-D diffusion simulation using FLOTRAN was able to reproduce the general features of the carbonation zone including carbonate deposition, alteration of the cement, width of the zone, and the presence of a dense interface with the less altered cement. The SACROC observations show, at least for the single well investigated, that Portland-based cement used in a CO2 reservoir environment can maintain hydrologic integrity for a period of 30 years despite significant carbonate mineralization. However, we were unable to quantify the amount of CO2 migration that occurred along cement interfaces with the casing and shale caprock. The quality of these interfaces appears to be the most critical issue in the performance of wellbore systems in a CO2 sequestration reservoir.
Uranium and neptunium were used as reactive tracers in long-term laboratory desorption studies us... more Uranium and neptunium were used as reactive tracers in long-term laboratory desorption studies using saturated alluvium collectedfrom south of Yucca Mountain, Nevada. The objective of these long-term experiments is to make detailed observations of the desorption behavior of uranium and neptunium to provide Yucca Mountain with technical bases for a more realistic and potentially less conservative approach to predicting the transport of adsorbing radionuclides in the saturated alluvium. This paper describes several long-term desorption experiments using a flow-through experimental method and groundwater and alluvium obtainedfrom boreholes along a potential groundwater flow path from the proposed repository site. In the long term desorption experiments, the percentages of uranium and neptunium sorbed as a firnction of time after different durations of sorption was determined. In addition, the desorbed activity as a function of time was Jit using a multi-site, multi-rate model to demonstrate that drfferent desorption rate constants ranging over several orders of magnitude exist for the desorption of uranium from Yucca Mountain saturated alluvium. This information will be used to support the development of a conceptual model that ultimately results,in effective Kd values much larger than those currently in use for predicting radionuclide transport at Yucca Mountain.
XTRA is a miniature XRD/XRF instrument intended for use on small rovers and landers destined for ... more XTRA is a miniature XRD/XRF instrument intended for use on small rovers and landers destined for solid solar system objects without substantive atmospheres (i.e., the Earth's Moon, asteroids, comets, Mercury, or the moons of Mars. The technology of XTRA derives from the CheMin XRD/XRF instrument on Mars Science Laboratory (MSL), augmented by improvements developed through Small Business Innovative Research (SBIR) grants and commercial product developments. XTRA utilizes a reflection geometry, a microfocus X-ray tube and a cooled CCD operated in direct detection mode. The reflection geometry allows for fine-grained regolith to be scooped and dumped into sample holders which are shaken during analysis to improve diffraction statistics during XRD pattern acquisition.
New 1:24,000 scale geologic mapping combined with previous and ongoing geoscientific studies are ... more New 1:24,000 scale geologic mapping combined with previous and ongoing geoscientific studies are revealing significant new findings on intracaldera stratigraphy and structure, initial development of intracaldera lakes, and the duration of resurgence within the ca. 1.25 Myr Valles caldera. The caldera is about 22 km in diameter and contains a resurgent dome that is a northeast-trending oval roughly11 x 9
Microautoradiography was used to evaluate the mineralogic basis of Pu(V) retention by tuffs from ... more Microautoradiography was used to evaluate the mineralogic basis of Pu(V) retention by tuffs from Yucca Mountain, Nevada. Altered orthopyroxenes and oxide minerals are associated with high Pu retention, but are limited to specific stratigraphic horizons. A weaker but more general association of Pu with smectite occurs in most samples. Thinsections that cross fractures allow comparative studies of Pu retention by fracturelining versus matrix minerals. Using Ag metal in emulsions as a measure of underlying Pu concentration, electron-microprobe (EMP) analysis can quantify Pu retention along fracture walls and provide mineral/mineral Pu retention factors. For smectite-lined microfractures in zeolitized tuff, the smectite/clinoptilolite Pu retention factor is <80.
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