Exploratory Studies Facility Research Articles

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.

Commentary on Studies of 36Cl in the Exploratory Studies Facility at Yucca Mountain, Nevada

ABSTRACT36Cl data from the Exploratory Studies Facility (ESF) at Yucca Mountain, Nevada, reported by LANL researchers [1,2,3,4] provide important empirical constraints on the velocity and pathways for water flow under natural conditions in the unsaturated zone at Yucca Mountain. It has been concluded that some data exhibiting exceptionally high 36Cl/Cl ratios (i.e., greater than 1250×10−15 [3]) indicate unambiguous bomb pulse contamination and fast groundwater travel times to depths of the proposed waste emplacement horizon. Several lines of evidence indicate that some ESF samples with 36Cl/Cl ratios greater than 900×10−15 to 1000×10−15 are also affected by bomb pulse contamination. The distribution of 36Cl/Cl data can be well represented by a mixture of two normally distributed populations, which are hypothesized to represent uncontaminated and bomb pulse contaminated sets. The transition between these groups occurs at 36Cl/Cl between 600×10−15and 1000× 10−15, and the hypothesized contaminated samvles comprise 20 to 25 percent of the total. Shapiro-Wilk statistics confirm that when samples with 36Cl/Cl ratios greater than about 1000×10−15 are included, the distribution deviates from normality. Variation in the Earth's magnetic field, which is a primary mechanism for variation in natural 36Cl production, also appears to be normally distributed, supporting the hypothesis that natural, relatively undecayed 36Cl/Cl ratios are normally distributed. Further evidence that samples with 36Cl/Cl greater than 950×10−15 to 1000×10−15 are likely to have a bomb pulse component is provided by the spatial correlation of these samples with those containing unambiguous contamination at values greater than 1250×10−15. Zones in which elevated 36Cl/Cl ratios are localized constitute about 23 percent of the length of the ESF at the level of the proposed waste emplacement horizon.

Chlorine-36 Investigations of Groundwater Infiltration in the Exploratory Studies Facility at Yucca Mountain, Nevada

ABSTRACTChlorine-36, including the natural cosmogenic component and the component produced during atmospheric nuclear testing in the 1950's and 1960's (bomb pulse), is being used as an isotopie tracer for groundwater infiltration studies at Yucca Mountain, a potential nuclear waste repository. Rock samples have been collected systematically in the Exploratory Studies Facility (ESF), and samples were also collected from fractures, faults, and breccia zones. Isotopie ratios indicative of bomb-pulse components in the water (36Cl/Cl values > 1250 × 10-15), signifying less than 40-yr travel times from the surface, have been detected at a few locations within the Topopah Spring Tuff, the candidate host rock for the repository. The specific features associated with the high 36Cl/Cl values are predominantly cooling joints and syngenetic breccias, but most of the sites are in the general vicinity of faults. The non-bomb pulse samples have 36Cl/Cl values interpreted to indicate groundwater travel times of at least a few thousand to possibly several hundred thousand years. Preliminary numerical solute-travel experiments using the FEHM (Finite Element Heat and Mass transfer) code demonstrate consistency between these interpreted ages and the observed 36Cl/Cl values but do not validate the interpretations.

Alteration History Studies in the Exploratory Studies Facility, Yucca Mountain, Nevada, USA

AbstractBy mid-1995, the Exploratory Studies Facility (ESF) extended about 1.1 km from Exile Hill westward toward Yucca Mountain, mostly within densely welded, devitrified Tiva Canyon Tuff. Secondary mineral occurrences in this unit include breccia cements of mordenite, a fibrous zeolite, and vapor-phase deposits of silica, alkali feldspar, apatite, hollandite, amphibole, and zircon. Calcite is also a common secondary mineral in faults and fractures. Studies of water and gas contents in fluid inclusions in calcites from a fault in nonwelded tuff and a fracture in densely welded tuff suggest mineral deposition under transient locally saturated conditions. Calcite in the nonwelded tuff incorporated air from the unsaturated tuff adjacent to the fault.A highly altered interval within pre-Pah Canyon tuffs just above the top of the Topopah Spring Tuff may be a fossil fumarole or other hydrothermal feature associated with cooling pyroclastic deposits, overprinted by later zeolitic alteration. The observed quartz, cristobalite, opal-CT, and fluorite have been widely identified as products of syngenetic devitrification and vapor-phase alteration in and above the Topopah Spring Tuff. Smectite, also an abundant secondary mineral at the ESF site, has been observed elsewhere at this stratigraphic level.Zeolitic alteration of nonwelded tuffs above the Topopah Spring Tuff, as seen in the ESF, has also been noted in drill core and outcrop at northeastern Yucca Mountain. The hydrologic and geochemical conditions that favored zeolitization only in certain areas of this stratigraphic interval have yet to be determined.

Functional Analysis of a Nuclear Waste Repository System*

AbstractSystems engineering analysis results are presented and discussed for two related systems: (1) a geologic repository for the disposal of high‐level radioactive nuclear waste; and (2) an exploratory studies facility for use in site characterization.