27 research outputs found
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Calcite deposits in drill cores USW G-2 and USW GU-3/G-3 at Yucca Mountain, Nevada: Preliminary report
Yucca Mountain is being studied as a potential site for deep geologic disposal of high-level radioactive waste. Should a repository be developed at Yucca Mountain, the preferred location is within the upper unsaturated tuffaceous volcanic rocks. In this location, one factor of concern is the amount and rate of aqueous transport through the unsaturated rocks toward the underlying saturated intervals. Calcite, one of the most recently-formed minerals at Yucca Mountain, is of minor abundance in the unsaturated rocks but is widely distributed. Studies of calcite ages, isotopic systematics, chemistry and petrography could lead to a better understanding of transport processes at Yucca Mountain
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The importance of zeolites in the potential high-level radioactive waste repository at Yucca Mountain, Nevada
Zeolitic rocks play an important role in retarding the migration of radionuclides that occur in solution as simple cations (Cs, Sr, Ba). However, the interaction of zeolites with complex transuranic species in solution provides little if any advantage over other common silicate minerals. The most important consequences of zeolite occurrences near a high-level radioactive waste repository environment are likely to be their response to thermal loading and their impact on site hydrology. Partial zeolite dehydration during the early thermal pulse from the repository and rehydration as the repository slowly cools can have an important impact on the water budget of a repository in unsaturated rocks, provided that the long-term heating does not result in zeolite destabilization
The moon as a recorder of organic evolution in the early solar system: a lunar regolith analog study
The organic record of Earth older than ∼3.8 Ga has been effectively erased. Some insight is provided to us by meteorites as well as remote and direct observations of asteroids and comets left over from the formation of the Solar System. These primitive objects provide a record of early chemical evolution and a sample of material that has been delivered to Earth's surface throughout the past 4.5 billion years. Yet an effective chronicle of organic evolution on all Solar System objects, including that on planetary surfaces, is more difficult to find. Fortunately, early Earth would not have been the only recipient of organic matter–containing objects in the early Solar System. For example, a recently proposed model suggests the possibility that volatiles, including organic material, remain archived in buried paleoregolith deposits intercalated with lava flows on the Moon. Where asteroids and comets allow the study of processes before planet formation, the lunar record could extend that chronicle to early biological evolution on the planets. In this study, we use selected free and polymeric organic materials to assess the hypothesis that organic matter can survive the effects of heating in the lunar regolith by overlying lava flows. Results indicate that the presence of lunar regolith simulant appears to promote polymerization and, therefore, preservation of organic matter. Once polymerized, the mineral-hosted newly formed organic network is relatively protected from further thermal degradation. Our findings reveal the thermal conditions under which preservation of organic matter on the Moon is viable
Characterization and Calibration of the CheMin Mineralogical Instrument on Mars Science Laboratory
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Mineralogic summary of Yucca Mountain, Nevada
Quantitative x-ray powder diffraction analysis of tuffs and silicic lavas, using matrix-flushing techniques, has been used to obtain a model of three-dimensional mineral distributions at Yucca Mountain, Nevada. This method of analysis is especially useful in tuff, where the most abundant phases are commonly too fine grained for optical determination. The three-dimensional distributions of primary glass and of tridymite are particularly well constrained. Vitric nonwelded glasses occur above and below the welded devitrified Topopah Spring Member, but the glass in the lower nonwelded vitric zone is progressively altered to zeolites to the east where the zone is closer to the static water level. The zeolites clinoptilolite, mordenite, heulandite, and erionite have all been found at Yucca Mountain, but only mordenite and clinoptilolite are abundant and can be mapped between many drill holes and at many depths. Heulandite distribution is also mappable, but only below the densely welded devitrified part of the Topopah Storing Member. Erionite has been confirmed only once, as a fracture coating. There is a fairly continuous smectite-rich interval immediately above the basal vitrophyre of the Topopah Spring Member, but no evidence suggests that the smectites can provide information on the paleogroundwater table. There are at least four mappable zeolitized zones in Yucca Mountain, and the thicker zones tend to coincide with intervals that retained glass following early tuff devitrification. Problems in extrapolation occur where zones of welding pinch out. No phillipsite has been found, and some samples previously reported to contain phillipsite or erionite were reexamined with negative results. The deeper alteration to albite and analcime was not sampled in every drill hole, and the distribution of these phases is difficult to map
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Iron and manganese in oxide minerals and in glasses: preliminary consideration of Eh buffering potential at Yucca Mountain, Nevada
The tuffs of Yucca Mountain at the Nevada Test Site are currently under investigation as a possible deep burial site for high-level radioactive waste disposal. One of the main concerns is the effect of oxidizing groundwater on the transport of radionuclides. Rock components that may affect the oxygen content of groundwater include Fe-Ti oxides, Mn oxides, and glasses that contain ferrous iron. Some phenocryst Fe-Ti oxides at Yucca Mountain are in reduced states, whereas groundmass Fe-Ti oxides have been oxidized to hematite, rutile, and pseudobrookite (Fe{sup 3+}-bearing phases) exclusively. Estimates of Fe{sup 2+}-bearing oxides indicate that less than 0.33 vol% phenocrysts is available to act as solid buffering agents of Eh. Of this percentage, significant amounts of Fe-Ti oxides are isolated from effective interaction with groundwater because they occur in densely welded, devitrified tuffs that have low interstitial permeability. Manganese oxides occur primarily along fractures in the ash-flow tuffs. Because the Mn oxides are concentrated along the same pathways (fractures) where transport has occurred in the past, these small volume percentages could act as buffers. However, the oxidation states of actual Mn-oxide phases are high (Mn{sup 4+}), and these minerals have virtually no potential for reducing groundwater Eh. Manganese oxides may even act as oxidizing agents. However, regardless of their poor capabilities as reducing agents, the Mn oxides could be important as sorbents of heavy metals at Yucca Mountain. The lack of accessible, pristine Fe-Ti oxides and the generally high oxidation states of Mn oxides seem to rule out these oxides as Eh buffers of the Yucca Mountain groundwater system. Reduction of ferrous iron within glassy tuffs may have some effect on Eh, but further study is needed. At present it is prudent to assume that minerals and glasses have little or no capacity for reducing oxygen-rich groundwater at Yucca Mountain. 25 refs., 3 figs., 12 tab
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Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations
Volcanism studies of the Nevada Test Site (NTS) region are concerned with hazards of future volcanism with respect to underground disposal of high-level radioactive waste. The hazards of silicic volcanism are judged to be negligible; hazards of basaltic volcanism are judged through research approaches combining hazard appraisal and risk assessment. The NTS region is cut obliquely by a N-NE trending belt of volcanism. This belt developed about 8 Myr ago following cessation of silicic volcanism and contemporaneous with migration of basaltic activity toward the southwest margin of the Great Basin. Two types of fields are present in the belt: (1) large-volume, long-lived basalt and local rhyolite fields with numerous eruptive centers and (2) small-volume fields formed by scattered basaltic scoria cones. Late Cenozoic basalts of the NTS region belong to the second field type. Monogenetic basalt centers of this region were formed mostly by Strombolian eruptions; Surtseyean activity has been recognized at three centers. Geochemically, the basalts of the NTS region are classified as straddle A-type basalts of the alkalic suite. Petrological studies indicate a volumetric dominance of evolved hawaiite magmas. Trace- and rare-earth-element abundances of younger basalt (<4 Myr) of the NTS region and southern Death Valley area, California, indicate an enrichment in incompatible elements, with the exception of rubidium. The conditional probability of recurring basaltic volcanism and disruption of a repository by that event is bounded by the range of 10{sup -8} to 10{sup -10} as calculated for a 1-yr period. Potential disruptive and dispersal effects of magmatic penetration of a repository are controlled primarily by the geometry of basalt feeder systems, the mechanism of waste incorporation in magma, and Strombolian eruption processes
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Closer look at lunar volcanism
Although the American Apollo and Soviet Luna missions concentrated on mare basalt samples, major questions remain about lunar volcanism. Lunar field work will be indispensable for resolving the scientific questions about ages, compositions, and eruption processes of lunar volcanism. From a utilitarian standpoint, a better knowledge of lunar volcanism will also yield profitable returns in lunar base construction (e.g., exploitation of rille or lava-tube structures) and in access to materials such as volatile elements, pure glass, or ilmenite for lunar industry
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A preliminary comparison of mineral deposits in faults near Yucca Mountain, Nevada, with possible analogs
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 performances 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. 35 refs., 25 figs
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Microwave processing of lunar materials: potential applications
The microwave processing of lunar materials holds promise for the production of either water, oxygen, primary metals, or ceramic materials. Extra high frequency microwave (EHF) at between 100 and 500 gigahertz have the potential for selective coupling to specific atomic species and a concomitant low energy requirement for the extraction of specific materials, such as oxygen, from lunar ores. The coupling of ultra high frequency (UHF) (e.g., 2.45 gigahertz) microwave frequencies to hydrogen-oxygen bonds might enable the preferential and low energy cost removal (as H/sub 2/O) of implanted protons from the sun or of adosrbed water which might be found in lunar dust in permanently shadowed polar areas. Microwave melting and selective phase melting of lunar materials could also be used either in the preparation of simplified ceramic geometries (e.g., bricks) with custom-tailored microstructures, or for the direct preparation of hermetic walls in underground structures. Speculatively, the preparation of photovoltaic devices based on lunar materials, especially ilmenite, may be a potential use of microwave processing on the moon. Preliminary experiments on UHF melting of terrestrial basalt, basalt/ilmenite and mixtures show that microwave processing is feasible