bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Potassium on the Oxidation Rate of Carbon
Authors: Sjövall Peter , Hellsing Bo , Keck Karl-Erik , Kasemo Bengt 
Published: March 2011

AbstractThe influence of K, deposited on a carbon surface, on the oxidation of carbon in O2 was investigated. Reaction rate measurements, carried through in a UHV-system by use of AES, showed that potassium increases the reaction rate by up to ∼ 104 times. A theoretical model, based on the assumption that O2 dissociation is the rate limiting step, has been developed. The model shows that a charge transfer mechanism can explain the observed rate increase. Results from TPD/TPR-measurements indicate that the sticking probablility for O2 on a graphite surface with predeposited K is approximately independent on K coverage for coverages down to 0.5 × 1014 cm−2, corresponding to an effective radius of K of ∼ 7.3 Å.
A Single Turnover (STO) Characterization of Supported Palladium Catalysts
Authors: Augustine Robert L. , Baum David R. 
Published: March 2011

AbstractWhile the STO catalyst characterization procedure has been applied to a variety of supported Pt catalysts, application of this technique to the characterization of supported Pd catalysts showed that there were several significant differences between the Pt and the Pd catalysts. Under STO reaction conditions each surface site on a Pt catalyst reacts only once so there is a 1:1 relationship between the product composition and the densities of the various types of active sites present. With Pd catalysts under these same conditions, alkene isomerization takes place so readily that the amount of isomerized product formed depends on the contact time of the reactant pulse with the catalyst so there is no direct relationship between the amount of isomerization and the number of isomerization sites present. On Pt there are some direct saturation sites present on which H2 is rather weakly held. Such sites are not present on Pd catalysts. The reactive surface of supported Pt catalysts remains constant on long exposure to air. With Pd catalysts exposure to air results in a decrease in saturation site densities which can be reversed by re-reduction of the surface with H2 under ambient conditions but not completely under what can be termed “reaction conditions” where the extent of surface re-reduction decreases with catalyst age.
Secondary Cation Effects On Sodium And Potassium Zeolite Syntheses at Si/Al2 = 9: Part 1- Phase Development in the Sodium System
Authors: Vaughan David E. W. 
Published: March 2011

AbstractThe influence of Group 1A elements, and various alkyl ammonium cations, on a metastable faujasite synthesis at a silica/ alumina ratio of 9 are reported. Co-crystallization of faujasite, gmelinite and gismondine (P) occurs in reactions with Li+, K+ and Rb+, but the trapping of Cs+ in the FAU sodalite cage (CSZ-1/ CSZ-3) inhibits subsequent reactions to GIS, and blocks the formation of GME. Morphological effects of these cations include platelet formation and the promotion of small crystals. TMA addition promotes mazzite analogues; and DEDM stabilizes FAU, and at 140°C., induces the crystallization of ECR-1. The derivation of all these phases from a restricted number of secondary building units is
discussed.
Near-Field Mass Transfer in Geologic Disposal Systems: a Review
Authors: Pigford T. H. , Chambré P. L. 
Published: March 2011

AbstractA primary purpose of performance assessment of geologic repositories for radioactive waste is to predict the extent to which radioactive species are released from the waste solids and are transported through geologic media to the environment. Reliable quantitative predictions must be made of rates of release of radionuclides from the waste into the rock, transport through the geologic media, cumulative release to the accessible environment, and maximum concentrations in ground water and surface water. Here we review theoretical approaches to making the predictions of near-field release from buried waste solids, which provide the source terms for far-field release. The extent to which approaches and issues depend on the rock media and on regulatory criteria is discussed.
Laboratory Radionuclide Migration Experiments at a Scale of 1 m
Authors: Vandergraaf Tjalle T. , Grondin D. M. , Drew D. J. 
Published: March 2011

AbstractResults are presented from a migration experiment carried out in a natural fracture in a 1 m × 1 m × 0.6 m quarried granite block. Near-uniform flow in the fracture was achieved by controlling the groundwater flow from the fracture laterally across the exit face of the fracture. The longitudinal dispersion was determined from the elution profile of uranine, a non-sorbing tracer. The effect of matrix diffusion was determined by reducing the linear velocity of the transport solution from approximately 3 to 0.75 cm/h. The velocity of a sorbing tracer, Cs-137, was compared to that of non-sorbing I-131 and with that calculated from data obtained for Cs-137 in static sorption experiments on similar fracture surfaces. Information on channeling in the fracture was obtained by autoradiographing the fracture surface of the separated block after the termination of the experiment. Quantitative information on the sorbed Cs-137 inventory by two-dimensional gamma scanning of the fracture surfaces is underway.
Channeling and its Potential Consequences for Radionuclides Transport
Authors: Moreno Luis , Neretnieks Ivars 
Published: March 2011

SummaryRadionuclide transport through fractured media is usually calculated assuming that water flows in most of the fractures. Several observations in the field and the laboratory show that flow is very unevenly distributed in fractured crystalline rock. These observations indicate that most of the water flow takes place in a limited number of channels. The channels are seldom wider than a few meters and are often much narrower. This means that the surface of the fracture in contact with the flowing water (wetted surface) is less than one might expect.This low value of the wet surface of the fracture may considerably influence the transport of radionuclides through fractured media. If the channels do not intersect over a certain distance, then the channels may be modelled as a bundle of independent channels. Channels with a large flow and small sorption surface will carry the tracer rapidly and in large amounts.Calculations are performed for cases where channeling is assumed to take place. The most important entities to assess are the water flow distribution in the different channels, the wetted surface of the channels, the diffusivity into the rock matrix, and the sorption coefficient in the matrix. Experimental data for the water flow distribution are used and the transport of nuclides is calculated for the different channels. From these values the concentration of the effluent is determined. The results show that the retardation for the nonsorbing nuclides is negligible. Retardation is only important for the nuclides which are strongly sorbed on the granitic rock. Calculations are also done assuming other channel frequencies and other overall water flowrates.
State-of-the-Art Evaluation of Repository Sealing Materials and Techniques.
Authors: Gnirk Paul 
Published: March 2011

AbstractUnder the auspices of the OECD/NEA Stripa Project, a state-of-the-art evaluation of repository sealing materials and techniques has been undertaken with particular application to crystalline rock. The objectives of the evaluation were (1) to review progress to date in the development of repository sealing materials and emplacement techniques; (2) to identify priority materials for sealing narrow aperture fractures in crystalline rock, including issues of technical concern to the long-term effectiveness of such materials; and (3) to provide a framework for advancing an in situ fracture-sealing test program that can be designed and implemented at the Stripa Mine.The classes of sealing materials that were considered included cementitious materials, natural clay materials, chemical grouts, fracture-filling synthetic minerals, ceramics, and metals. Of these, cementitious materials and natural clay materials were recommended as high-priority materials for further study because they can be designed to meet desired repository performance characteristics, there is considerable history of successful use in similar engineering applications, and there is indirect evidence that they will continue to perform as expected for long periods of time. Techniques for the emplacement of these sealing materials in rock fractures include pressure injection, dynamic (or vibratory) injection, and electrophoresis.
Size and Density of A 242Pu Colloid
Authors: Rundberg Robert S. , Mitchell Alan J. , Triay Ines R. , Torstenfelt N. Börje 
Published: March 2011

AbstractThe size and density of a 242Pu colloid has been measured by autocorrelation photon spectrometry. The sedimentation rate of the colloid was determined by ultraspeed centrifugation. From the concentration profiles of 242Pu in the centrifuged test tubes, a standard sedimentation formula was used to calculate the density; the size of the colloid was known from the light scattering experiments. The determined density of the 242Pu colloid was only slightly lower than the estimated density of crystalline PuO2.
Analysis Of Congruent Matrix Release, Precipitation, And Time-Distributed Containment Failure On Spent Fuel Performance
Authors: Apted Michael J. , Engel David W. 
Published: March 2011

AbstractThe Analytical Repository Source-Term (AREST) code has been developed for source-term evaluation of spent fuel as a final waste form in geologic repositories. AREST contains a set of analytical equations for the timedependent diffusional mass transport of both solubility-limited and inventory-limited radionuclides from a spent fuel in a failed container surrounded by a shell of packing or other porous material imbedded in a porous host rock. Three factors that affect release performance are examined: 1) congruent dissolution of the UO2 matrix, 2) chemical instability of the UO2 matrix, with precipitation of a more stable uranium phase within the waste package, and 3) the attenuation of release rate by distribution of containment failures with time.For congruent matrix dissolution, the release rates of included nuclides are proportional to the product of solubility-limited release of uranium and the fractional abundance of the nuclide. For certain conditions, congruent release rates are calculated to be up to 10 orders of magnitude lower than release rates assuming individual solubility-limits. Precipitation of a more stable, lower solubility uranium phase within the waste package is shown to increase release rates from the UO2 matrix compared to the non-precipitation case, in agreement with previous calculations. During the first 300 to 1000 years after repository closure, the distribution of containment failures with time will act to attenuate the peak average release rates of soluble, longlived nuclides, such as iodine-129, to values smaller than release rates below regulatory limits. However, for soluble nuclides with short half-lives, such as cesium-137, a broader distribution of containment failure with constant mean time of failure can actually cause an increase In the peak average release rates.
A Vault Model for the Assessment of Used Fuel Disposal in Canada
Authors: Garisto N. C. , Leneveu D. M. 
Published: March 2011

AbstractThe environmental assessment of the geological disposal of used nuclear fuel involves the assimilation of experimental results to produce an estimate of the potential impact of a disposal vault on man and the environment. In this paper we briefly outline the assessment methodology and expand upon one aspect of the data assimilation process, namely, the incorporation of research results on the performance of engineered barriers into assessment models.The model to be discussed represents (i) failure modes for titaniumbased containers, including short-term failures due to undetected manufacturing defects and long-term failures due to uniform and local corrosion; (ii) release of radionuclides from used fuel, including relatively fast release of soluble fission products from gap and grain boundaries and slow, congruent release controlled by the dissolution of the fuel matrix itself; and (iii) mass transport of released radionuclides through the clay-based sealing materials surrounding the waste container, including diffusion, convection and radionuclide storage (sorption or retardation) effects.
Preliminary Geochemical/Geophysical Model of Yucca Mountain
Authors: Cederberg Gail A. , Greenwade L. Eric 
Published: March 2011

AbstractAs part of the Nevada Nuclear Waste Storage Investigations (NNWSI) Project, a comprehensive geochemical/geophysical model is being compiled. This model incorporates the current and relevant stratigraphic, petrologic, hydrogeologic, geochemical, and material data associated with a candidate repository at Yucca Mountain, Nevada. In this report the known repository data are compiled and unknown parameter values are estimated based on the available data. More data are needed before the geochemical/geophysical model of Yucca Mountain can be regarded as satisfactory and a suitable base for multidimensional predictive flow and transport simulations. Recommendations for future studies concerning site characterization and data aquisition are presented.
Numerical Simulation of Alteration of Sodium Bentonite by Diffusion of Ionic Groundwater Components
Authors: Jacobsen J. S. , Carnahan C. L. 
Published: March 2011

AbstractBecause of its ability to retard the movement of radionuclides, sodium bentonite is being considered as a packing and backfilling material in a number of nuclear waste isolation programs. Few studies, however, have considered how the chemical properties of the bentonite backfill will vary with distance from the canister and change in time as groundwater constituents diffuse through the bentonite. Of particular importance is the conversion of sodium bentonite to calcium bentonite by ion exchange, which will in turn affect the migration of cationic radionuclides, such as Cs+and Sr2+, leaking from a waste canister.Experiments measuring the movement of trace amounts of radionuclides through compacted bentonite have typically used unaltered bentonite. Models based on experiments such as these may not lead to accurate predictions of the migration through altered or partially altered bentonite of radionuclides that undergo ion exchange. To address this problem, we have modified an existing transport code to include ion exchange and aqueous complexation reactions. The code is thus able to simulate the diffusion of major ionic groundwater components through bentonite and reactions between the bentonite and groundwater. Numerical simulations have been made to investigate the conversion of sodium bentonite to calcium bentonite for a reference groundwater characteristic of deep granitic formations.
The Effects of Changes in pH within a Clay Surrounding a Cementitious Repository
Authors: Jefferies Nicholas L. , Tweed Cherry J. , Wisbey Simon J. 
Published: March 2011

AbstractThe effect of a concrete-based repository on local geological conditions and properties has been explored. As part of a complete description of repository behaviour, a static model of clay-alkali interactions has been set up. Parallel experiments have demonstrated the buffering capacity of clays, and are indicating the chemical and physical changes that may occur when an alkali plume interacts with a clay host rock.
Aqueous Corrosion of the French LWR Solution Reference Glass First Generation Model
Authors: Mouche E. , E. Vernaz 
Published: March 2011

AbstractExperiments have been performed on the aqueous dissolution of French LWR solution reference glass that have identified key dissolution mechanisms to be considered in modeling. The physical hypotheses on which the model relies are a dissolution rate governed by the silica concentration in solution according to a first order kinetic law, congruent release of the mobile elements at the gel-glass interface, and diffusion of silicic acid in the gel interstitial solution. A comparison of theoretical results obtained by a semi-analytical solution to the model and experimental results suggests some modifications to develop a more advanced model.
A Comparative Experimental Study of Glass Stability in Seawater and Distilled Water
Authors: Zhou Zhihong , Fyfe W. S. 
Published: March 2011

AbstractBoth PNL76−68 and ABS-118 glasses show greater stability in seawater (SW) than in distilled and deionized water (DDW), in the MCC-1 90°C corrosion test. After 180 days of corrosion, the boron release from PNL76- 68 and ABS-118 glasses is about five and two times lower respectively in SW than in DDW. Seawater leachates show less increase in pH than DDW leachates. Glass corroded in SW shows little or no total weight loss. Significant amounts of Mg from SW have been added to the surface layers of both types of glass. Mg-silicates were found in surface layers formed in SW, whereas Zn- and Fe-silicates in surface layers formed in DDW. Shortterm leaching tests in D2O, NaCl and MgCl2 solutions suggested that high salt content in leachant can impede glass hydration. Both silica saturation and Mg diffusion may be responsible for greater stability of the glasses in SW than in DDW.
Impact of Phase Stability on the Corrosion Behavior of the Austenitic Candidate Materials For NNSWI.
Authors: Bullen Daniel B. , Gdowski Gregory E. , McCright R. Daniel 
Published: March 2011

AbstractThe Nuclear Waste Management Program at Lawrence Livermore National Laboratory is responsible for the development of the waste package design to meet the Nuclear Regulatory Commission licensing requirements for the Nevada Nuclear Waste Storage Investigations (NNWSI) Project. The metallic container component of the waste package is required to assist in providing substantially complete containment of the waste for a period of up to 1000 years. Long term phase stability of the austenitic candidate materials (304L and 316L stainless steels and alloy 825) over this time period at moderate temperatures (100–250°C) can impact the mechanical and corrosion behavior of the metal barrier.A review of the technical literature with respect to phase stability of 304L, 316L and 825 is presented. The impact of martensitic transformations, carbide precipitation and intermediate (σ. χ, and η) phase formation on the mechanical properties and corrosion behavior of these alloys at repository relevant conditions is discussed. The effect of sensitization on intergranular stress corrosion cracking (IGSCC) of each alloy is also addressed. A summary of the impact of phase stability on the degradation of each alloy in the proposed repository environment is included.
A Study of the Hydrothermal Stability of Copper for Use as a Container Material for Nuclear Waste
Authors: Lazaar Paul I. , Ulmer G. C. , Grandstaff D. E. 
Published: March 2011

AbstractThe hydrothermal stability of copper has been studied to assess its suitability as a container material for disposal of nuclear waste in the proposed repository site at Hanford, Wa. The experiments (Cohassett basalt, synthetic Grande Ronde #4 groundwater, and copper powder with a water:rock:Cu-powder mass ratio of 20:1:1) were conducted at 300°C, 30 MPa, using Dickson rocking autoclaves for periods up to 3000 hours. Redox was calculated from dissolved H2 measured by gas chromatograph and He-ionization detector.After ca. 100 hours the solution Cu concentration stabilized at 2–3 ppm, near Cu saturation, and did not vary significantly during the remainder of the experiment. The in situ solution pH was slightly alkaline. The copper powder showed little evidence of etching. The Cu concentration did not reflect oxide-coating spallation effects such as those described by Johnston et al.[15]. Within 48 hours, the log fO2 values decreased rapidly toward the magnetite-hematite phase boundary (−31 at 300°C); this is well within the stability field of native copper. SEM and EDX analysis of the reaction products revealed a copper-iron sulfide. One experiment used copper powder containing ca. 5% cuprite. Oxygen released by the cuprite overwhelmed the buffering capacity of the basalt. The resulting log fO2 values stabilized near the copper-cuprite phase boundary (−23.1 at 300°C) with the solution remaining within the copper stability field. Copper purity is important as oxygen contamination or oxidation of the copper containers may strongly affect the repository redox and mobility of radionuclides.
A Method for Measuring the Self-Cementing Characteristics of Fly Ash Pastes
Authors: Malek R. I. A. , Roy D. M. 
Published: March 2011

SUMMARYThe development of an improved method of trimethylsilylation [1] made possible the assessment of different polysilicate fractions in hydrated cement pastes, as a means of structural characterization. Several laboratories have presented various gas-liquid chromatographic data on the polysilicate derivatives of C-S-H [2–5]. Identification of the different molecular weight fractions has been made, in most laboratories, by matching the gasliquid chromatographic peaks with the gel permeation chromatographic peaks. The success of this matching process is always dependent on type of instruments, length of columns and temperature range.In the present investigation, a mass spectrometer, in direct contact with the gas-liquid chromatograph, was used to identify the molecular weight of each of the fractions separated from the chromatograph. The technique was applied to determine the molecular weights and abundances of different polysilicate species in hydrated fly ash pastes.
Characterization of Products of Primary Flue Gas Desulphurization
Authors: Odler I. , Zysk K.-H. 
Published: March 2011

ABSTRACTIn primary flue gas desulphurization lime is introduced into the flame, in addition to modifications of the burners and/or equipment. An ash is thus obtained in which the sulphur present in the fuel becomes chemically bound, rather than leaving the heat-generating unit as gaseous SO2, a constituent of the flue gases. In the present paper the composition, particle shape and size distribution of a series of ashes formed in the primary flue gas desulphurization are reported. The options for their utilization need to be evaluated.
Influence of Physical and Chemical Properties on the Activity of Fly Ashes
Authors: Sybertz F. 
Published: March 2011

ABSTRACTIn an experimental program, the suitability of various methods for testing the pozzolanic activity of fly ash was investigated. The research was conducted on virtually all fly ashes approved as concrete additives in Germany. This paper discusses differences in the particle size distribution and the solubility on dissolution with hydrochloric acid and potassium hydroxide of the fly ashes. It also reports on interrelationships between the physical and chemical properties of the fly ashes and the workability and strength of mortars containing fly ash.
Fly Ash in Bricks and Tiles
Authors: Bacher V. , Ernstsen V. , Jeppesen K. G. , Kristiansen H. , Madsen P. 
Published: March 2011

ABSTRACTBased on the characterization of 12 clay and 5 fly ash samples, samples were selected for the following laboratory scale experiments: preparation of raw mixes, determination of the correlation between water content and plasticity, rate-controlled sintering in a laser-dilatometer, DTA-TGA-analyses, preparation, firing and testing of bars. Laboratory experiments have shown that it is necessary to bind the soluble sulphates as barium sulphate under acidic conditions and bind the free lime as phosphate when wet production methods are to be used. A full scale experiment has been carried out, resulting in the production of 16,000 red bricks containing 33% fly ash by volume in the raw mix. These fly ash bricks look satisfactory and have 10% higher strength and 2% less density than the corresponding bricks without fly ash. The water extractable matter in the two kinds of bricks were compared. The bricks were used for constructing a wall with the purpose of investigating their weather resistance.