Titanium hexacyanoferrate microspheres (diameter <70km) were obtained in the following steps: (1) extraction of chlorides from an aqueous solution of TiCl4 with long chain amine -Primene JMT- in paraffin diluent (the resulting sol has the concentration 320 g TiO2/dm3 and the mole ratio Cl-: Ti4+ = 1.83); (2) blending of titania sol with an aqueous solution of K4 Fe(CN)6. 3H2O (280 g/dm3) in order to obtain final sols with Fe(CN)64-: Ti4+ mole ratio of 0.05 - 0.1; (3) formation of multicomponent sol emulsion in 2-ethylhexanol-1 containing I vol. % of Ethomen S/15 (EH), (4) gelation of emulsion drops by extraction of water with partially dehydrated EH; (5) filtration and washing with acetone; (6) drying at 140°C using a special procedure elaborated on the basis of TG and DTA studies.

The final product is insoluble in water and exhibits high sorption efficiency of 137 Cs.

A new inorganic ion exchange material, called SNL-1, has been prepared at Sandia National Laboratories. Developmental samples of SNL-1 have been determined to have high selectivity for the adsorption of Sr from highly acidic solutions (1 M HNO3). This paper presents results obtained for the material in batch ion exchange tests conducted at various solution pH values and in the presence of a number of competing cations. Results from a continuous flow column ion exchange experiment are also presented.

This study was designed to investigate the effect of swelling pressure on local volume changes in unsaturated sand-bentonite based buffer material. A laboratory mixture of sodium bentonite and graded silica sand in equal proportion by dry weight was used in both ambient and elevated temperatures experiments. At high water content locations within the tested specimens, the density was reduced by 3.57% from its initial values due to swelling. The swelling pressure as a function of distance was calculated by 4 different models. The calculated results have indicated that the density distribution within the specimen is affected by swelling potential distribution. The calculated swelling pressure values vary as a function of water content, reaching 1 MPa at the source of water intake, i.e., at high water content zone, and 2 MPa at the heater side, i.e., at low water content zone.

The information available from the open literature and our studies on exclusion, sorption and diffusion mechanisms of ionic and neutral species in bentonite has been compiled and re-examined in relation to the microstructure of bentonite. The emphasis is placed on a more thorough understanding of the diffusion processes taking place in compacted bentonite. Despite the scarcity of experiments performed with neutral diffusants, these imply that virtually all the pores in compacted bentonite are accessible to neutral species. Anion exclusion, induced by the overlap of electrical double layers, may render the accessible porosity for anions considerably less than the porosity obtained from the water content of the clay. On the basis of the compiled data, it is highly probable that surface diffusion plays a significant role in the transport of cations in bentonite clays. Moreover, easily soluble compounds in bentonite can affect the ionic strength of porewater and, consequently, exclusion, equilibrium between cations, and surface diffusion.

In high-level waste repository, a carbon steel overpack will be corroded after closure. This will create a reducing environment in the vicinity of the repository. Reducing conditions are expected to retard the migration of redox-sensitive radionuclides such as uranium.

The apparent diffusion coefficients of uranium were measured in compacted bentonites (Kunigel VI® and Kunipia F®, JAPAN) in contact with carbon steel and its corrosion products under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusion coefficients measured were 10-12 to 10-14 m2/s under oxidizing conditions and 10-13 to 10-14 m2/s under reducing conditions. There were significant effects of redox conditions, dry density (0.8 to 2.0 g/cm3) and montmorillonite contents (60% for Kunigel VI or 100% for Kunipia F) on the apparent diffusion coefficients. The sorption of uranium on corrosion products of iron was smaller than that on montmorillonite. Montmorillonite density could be a good index to explain density dependence of the diffusion coefficients under the reducing conditions. Uranium would diffuse in free pore water with diffusion coefficients greater than 10-13 m2/s in low density bentonites under both redox conditions because the diffusion coefficients depended on sorption coefficients. Since diffusion coefficients were independent of sorption coefficients in high density bentonites where free pore water is scarce, surface diffusion might occur with coefficients were of about 10-13 m2/s.

The release of contaminants to the subsurface has lead to potential or actual contamination of groundwater resources. The remediation of these plumes requires improved capability for the prediction of contaminant fate and transport. Key to improving predictive capabilities is an increased understanding of natural chemical (or reactive) heterogeneity in subsurface media and how chemical and physical heterogeneity are related. Although the effects of physical heterogeneity on transport has received significant attention, similar investigations of chemical heterogeneity, and the correlation of chemical and physical heterogeneity are in their infancy.

Theoretical considerations for unconsolidated porous media composed of sand-sized grains of a single reactive phase suggest that chemical reactivity and permeability are inversely related. This correlation is consistent with measured permeability, porosity, and surface area data for unconsolidated sands. The correlation arises because both reactivity and permeability are functions of the surface area of the porous media. This relationship suggests that for a heterogeneous porous media, significant contaminant transport will occur in zones of minimal reactivity.

A two-dimensional capillary network model for gas migration through a water-saturated medium is presented. The model is an extension of previously developed capillary bundle models, and provides a discrete alternative to classical continuum Darcy models. The need for such an alternative has become apparent from recent experimental results that suggest gas migrates through low permeability water-saturated media via a small number of preferential pathways.

Characterization and performance assessment (PA) studies for the potential high-level nuclear waste repository at Yucca Mountain require an understanding of migration mechanisms and pathways of radioactive solutes. Measurements of 36C1 in samples extracted from boreholes at the site are being used in conjunction with recent infiltration estimates to calibrate a site-scale flow and solute transport model. This exercise using the flow and solute transport model, FEHM, involves testing different model formulations and two different hypotheses to explain the occurrence of elevated 36Cl in the Calico Hills unit (CHn) which indicates younger water than in the overlying Topopah Spring unit (TSw). One hypothesis suggests fast vertical transport from the surface via fractures in the TSw to the CHn. An alternative hypothesis is that the elevated 36C1 concentrations reflect rapid horizontal flow in the CHn or at the interface between the CHn and the TSw with the source being vertical percolation under spatially isolated regions of high infiltration or at outcrops of those units. Arguments in favor of and against the hypotheses are described in conjunction with the site-scale transport studies.

For a nuclear waste repository in the unsaturated zone at Yucca Mountain, there are two thermal loading approaches to using decay heat constructively-that is, to substantially reduce relative humidity and liquid flow near waste packages for a considerable time, and thereby limit waste package degradation and radionuclide dissolution and release. “Extended dryout” achieves these effects with a thermal load high enough to generate large-scale (coalesced) rock dryout. “Localized dryout”(which uses wide drift spacing and a thermal load too low for coalesced dryout) achieves them by maintaining a large temperature difference between the waste package and drift wail; this is done with close waste package spacing (generating a high line-heat load) and/or low-thermal-conductivity backfill in the drift. Backfill can greatly reduce relative humidity on the waste package in both the localized and extended dryout approaches. Besides using decay heat constructively, localized dryout reduces the possibility that far-field temperature rise and condensate buildup above the drifts might adversely affect waste isolation.

This paper presents theory intended for the design and interpretation of tracer tests in fractured rock. The objective is to provide an understanding of experiments in which particulate and solute tracers are injected simultaneously. In such experiments, it is expected that the solute tracer will diffuse into the rock matrix, while the particulates will be confined to the fractures. The theory allows information about matrix diffusion to be extracted from the breakthrough curve. Furthermore, it can accommodate tests in which a non-ideal source is used, and where some of the withdrawn fluid is re-injected. The solution is performed in Laplace space and transformed to the time domain using a commercial spreadsheet.

NRC is developing improved models for transport of chain decay radionuclides in porous and fractured/porous media using finite-difference for spatial discretization, and numerical inversion of Laplace transforms for time. This hybrid technique allows great flexibility for spatial variability, flow rate changes and boundary conditions that are difficult with analytical solutions, and are much faster than solutions fully in the time domain. This paper presents the status of NRC's development of a method for transport through fractured porous media at the proposed Yucca Mountain repository, building on the work of a number of authors.

In performance assessment of geological disposal systems the phenomenon of dispersion in geological media is one of the most important processes to be modeled and is dependent on the heterogeneity of the media. In order to understand the dispersion process in a well defined heterogeneous field, laboratory experimental apparatus, named MACRO, was constructed to study fluid flow and mass transport. A synthetic heterogeneous field was constructed in a flow-bed using six kinds of glass beads with diameters of 0.1, 0.15, 0.2, 0.4, 0.6 and 0.8 mm. Both dye (brilliant blue) and NaCI solution were used as tracers in the experiment. A particle tracking method, considering advection, was used in numerical simulations of the experiment, and the dispersion effect was assumed to be expressed by the variability of the local advective velocity in a high resolution numerical grid. The simulated results obtained by the particle tracking method agreed with the measurement, confirming the applicability of modelling approach used in this study.

An in situ heater test was performed at G-Tunnel, Nevada Nuclear Test Site, to investigate the thermal-hydrological response of unsaturated, fractured volcanic tuff under conditions similar to those at Yucca Mountain. The NUFT flow and transport code was used to model the test using discrete-fracture and equivalent-continuum approaches. Nonequilibrium fracture flow and thermal buoyant gas-phase convection were found to be the likely causes for observed lack of condensate imbibition into the matrix. The potential repository at Yucca Mountain was also modeled. Disequilibrium fracture flow is predicted to occur for less than a hundred years after emplacement followed by a period of fracture-matrix equilibrium, during which the equivalent-continuum and discrete-fracture models give almost identical results.

The purpose of this project was to determine the performance of a 5.5 year old active solid low-level radioactive waste disposal unit (Pit 37) located on a mesa top at Los Alamos National Laboratory (LANL), Los Alamos, NM, and to provide in-situ (vadose zone) site characterization information to Technical Area 54, Material Disposal Area (MDA) G's Performance Assessment. The vadose zone beneath Pit 37 was accessed by utilizing low-impact, air-rotary horizontal drilling technology. Core was sampled at approximately 5-foot intervals via wire-line core method in 3 horizontal holes fanning out below Pit 37. Samples were screened and prepared in-field following LANL Environmental Restoration Project guidelines. Samples were transferred from the field to the Mobile Radiation Analysis Laboratory for initial radiological screening. Following screening, samples were delivered to an analytical lab for analyses including moisture content, 23 inorganic compounds, 60 volatile organic compounds, 68 semivolatile organic compounds, tritium, lead 210, radium 226 's Pit 37 is performing well and no significant liquid phase migration of contaminants has occurred.

This paper describes a three-barrier system of engineered safety features for the cleaning of the Moscow SIA “Radon” surface water runoff.

The Tono uranium mine in Japan, consists of a granite basin infilled with layered marine sedimentary rocks, within which uranium is heterogeneously distributed. This site is being used as a natural analogue to study the migration of uranium. The irregular observed uranium distribution had not satisfactorily been explained by local geochemical properties. This paper examines the hypothesis that the distribution of uranium could be dominated by the accessibility of locations to the migrating uranium, i.e. by the heterogeneous hydrology of the site.

High resolution heterogenous transmissivity fields were generated, conditioned on data from four boreholes through the mine. Steady state Darcy flow calculations and particle tracking simulations of uranium migration have been carried out. The time dependent relative intensity of a set of sources on the boundary of the modelled region were used as parameters to fit the modelled uranium distribution to the observed.

The relative intensities so obtained could be interpreted in a physically reasonable way. Good qualitative agreement was achieved between the observed heterogenous irregular uranium distribution and that fitted. We conclude that this supports the hypothesis, and that detailed knowledge of channelling flows can provide a better understanding of possible radionuclide dispersal.

A combination of ultrasound, mechanical and petrographic results for long-term experimental compression of greenschist facies porphyritic andesite tuffs indicate a deformation mechanism that depends upon the mineral composition, textural-structural features of the rocks and the orientation of compression relative to the rock textures. Three dry samples of rock were investigated. Coaxial compression of a massive sample for 816 hours and a foliated sample for 1176 hours (pressure orthogonal to foliation) is characterized by solidification when the rocks are temporarily metastable. Compressive strength of the first sample is 850 kg/cm2 and of the second one, 800 kg/cm2. Experimentally, the rock behavior changes from a plastic to a brittle regime of deformation. In contrast, compression of the foliated sample parallel to foliation causes disintegration along the foliation within 480 hours without solidification. The rock is liable to brittle deformation and its compressive strength is 500 kg/cm2. These results may have implications for characterization of near-field processes in connection with numerous subhorizontal zones of schistosity within the strata that are targeted for underground disposal of high-level wastes (HLW) in the Mayak radiochemical complex area.

By 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.

Zeolite-rich Miocene tuffs are an important part of the principal hydrochemical barrier to water-borne radionuclide transport from a potential high-level nuclear waste repository at Yucca Mountain, Nevada. The timing of zeolitization is an issue that relates to paleohydrology, permeability, zeolite stability, and unsaturated-zone geochemical processes. Exploratory K/Ar dating of clinoptilolite, the most abundant and widespread zeolite, shows a striking and consistent pattern of increasing apparent ages (2–13 Ma) with depth. Only the isotopic ages from the saturated zone are compatible with geologic evidence suggesting an age >10 Ma for most of the zeolites.

Factors that may be responsible for the young apparent ages in the unsaturated zone were investigated. Cation exchange with recharge water and Ar diffusion under unsaturated conditions (processes that may be characteristic of the unsaturated zone) were evaluated experimentally for their effects on K/Ar systematics. Cation exchanging a natural clinoptilolite with Ca-, Cs-, K-, and Na-chloride solutions showed minimal effects on radiogenic Ar content. However, clinoptilolite heated at 2007deg;C for 16 hours in air lost a significant amount of its radiogenic Ar compared with minimal losses from clinoptilolite heated in water at 100°C for over 5 months. The preliminary results indicate that Ar loss from incompletely hydrated clinoptilolite may be a major factor contributing to the young apparent ages of clinoptilolite in the unsaturated zone at Yucca Mountain.

The gradual buildup of rare isotopes from interactions between cosmic rays and atoms in an exposed rock provides a new method of directly determining the exposure age of rock surfaces. The cosmogenic nuclide method can also provide constraints on erosion rates and the length of time surface exposure was interrupted by burial. Numerous successful applications of the technique have been imperative to the complete surface geologic characterization of Yucca Mountain, Nevada, a potential high level nuclear waste repository. The 10Be exposure age of Black Cone lava, within a ten mile radius of the proposed repository site, is 840 ± 210 kyr (in agreement with previous K/Ar dates of 1.0 ± 0.1 Ma). Rates of erosion of the tuff bedrock (< 0.4 cm/kyr from 7 10Be measurements) and of hillslope colluvium (∼ 0.5 cm/kyr from 10Be dates on boulder deposits) preclude denudation of the mountain as a concern. Neotectonic concerns (rate of slip and timing of last significant movement along faults) are also being addressed with in situ 14C and 10Be measurements on scarp surfaces and on fault-dissected landforms where no surficial expression of the fault is preserved.