bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion Process in LixW3O9F(1≤x≤3)
Authors: Menetrier Michel , Chang Soon-Ho , Suh Kyung-Soo , Senegas Jean , Chaminade Jean-Pierre , Delmas Claude
Published: March 2011

The structure of LiW3O9F is built up of a peculiar stacking of hexagonal tungsten bronze-type layers. Li can be reversibly intercalated in this material, electrochemically or chemically up to the Li3W3O9F composition.

Diffusion coefficients are determined by the Honders method using Li/LiClO4-PC/Lix W3O9F cells which are discharged galvanostatically for given periods of time. This method does not require the knowledge of the Darken factor nor of the material/electrolyte contact area, which are both rather delicate to determine precisely in pratice.

The evolution of D with the intercalation amount exhibits a drastic increase (by three orders of magnitude) from x = 1 to x = 1.15 and a constant and rather high value afterwards. Different sites for the preexisting lithim (x ≤ 1) and the intercalated ones are therefore expected.

7Li NMR spectra have been recorded for various intercalation amounts. For x = 1, two first order quadrupolar signals are observed, corresponding to the sites of the immobile lithium ion. When lithium is intercalated (x = 1.1), another signal is observed, as well as a modification of that of the first lithium, due to intra site mobility. A more important change is observed between x = 1.1 and x = 1.2, which suggests an exchange process. For larger values of x, a single signal is observed, corresponding to mobile Li+ ions.

The sites in which lithium may be intercalated and the diffusion pathways are discussed on the basis of these results.
Electrochemical Spectroscopy of Proton Intercalation in γ-Mno2
Authors: Chabre Yves , Ripert Michel
Published: March 2011

We have performed electrochemical studies of proton intercalation in several varieties of γ/ε-MnO2 using an original method which combines linear sweep voltammetry and potentiostatic intermittent titration technique. This technique gave for the first time a direct evidence of a two step intercalation process in the ramsdellite units of these compounds. Either 0.5 or 1 proton per manganese are accommodated in the 1×2 channels, as previously suggested by Maskell. The reversibility of these steps has been studied and is discussed in relation to the structural modifications induced by the proton intercalation.
Scanning Tunneling Microscopy and Spectroscopy of GuCl2 and CoCl2 Graphite Intercalation Compounds
Authors: Olk C.H. , Heremans J. , Dresselhaus M.S. , Speck J.S. , Nicholls J.T.
Published: March 2011

Scanning tunneling microscopy (STM) is used to visualize the structure of copper chloride and cobalt chloride graphite intercalation compounds (GICs). When the samples are biased negatively with respect to the tip, the images show details of the structure of the intercalant layers, and of its effects on the surface graphene layer. When the sample is under positive bias, symmetry properties of the uppermost graphite planes are revealed. Images of the CuCl2 stage 1 GIC display a hexagonal symmetry in which all the atoms of the graphite surface plane appear. This is in contrast to the three-fold symmetry usually seen in atomic resolution STM images of highly oriented pyrolytic graphite (HOPG), which we also observe on a reference sample of HOPG. The three-fold symmetry is attributed to the ABAB stacking of the atomic layers in HOPG. In GICs, this stacking sequence is interrupted by the layer of intercalate, so that for the stage 1 compound all carbon atoms in the plane become equivalent, and six-fold symmetry develops. For a stage 2 (CuC12 or CoCl2) GIC three-fold symmetry is expected to persist. Images of the CoCl2 stage 1 GIC, taken with the sample bias is positive with respect to the tip, display a mixed trigonal and hexagonal symmetry, and may be attributable to the fact that the surface of sample is of mixed stage.
Transport Properties and Lithium Insertion of Compounds Metal-Halogen-Chalcogenides
Authors: Julien C. , El-Farh L. , Samaras I. , Riess I. , Balkanski M. , Ziolkiewicz S. , Chevy A.
Published: March 2011

The transport properties and far-infrared reflectivity of BiSI, BiTel, SbTeI, Bi2 Se3 and Bi2S3 have been studied, and the results show a good agreement between the two techniques. Lithium insertion within metal-chalcogen-halogen compounds has been carried out using Li/LiC1O4-PC/MChI galvanic cells at room temperature. Electrochemical potential spectroscopy measurements show the different regimes involved in the insertion reaction.
A 207Pb NMR Study of Beta"-Alumina
Authors: Sass Bruce M. , Suits Bryan H. , White David
Published: March 2011

We report results of a nuclear magnetic resonance (NMR) study of lead(II) cations in β"-alumina. Measurements of line positions and spin-lattice relaxation times (T1) as a function of temperature are presented. The results show that Pb ions possess both static and dynamic disorder in low and intermediate temperature regimes, respectively. Also, a comparison is made between Lorentzian and logarithmic spectral density functions, from which we conclude that the latter provides a better fit to the dataat short correlation times (ωºτºα). The logarithmic form has been proposed to describe diffusive motion in 2-dimensional conductors.
The Structure of Salt Doped Superionic Oxide Glasses by Neutron Diffraction
Authors: BÖRjesson L.
Published: March 2011

Comparative neutron diffraction experiments have been performed on metal-halide MX (M = Ag, Li, Na; X = CI, Br, I) doped oxide glasses and their corresponding low conducting host glasses, e.g. M2O-2B2O3 and MPO3. The experiments reveal large changes in the intermediate range structure as the dopant salt is introduced, whereas the short range order of the host matrix is virtually unaffected by the dopant salts. An extra peak at anomalously low Q values (Q = 0.7-0.8 Å-I) appears in the structure factors of the silver-halide glasses which indicates the building up of a new type of intermediate range ordering with a characteristic length of 8-10 Å. The observation is tentatively ascribed to a-microscopic biphase system consisting of an expanded hosi glass network, unaffected on a microscopic scale, in which the silver-halide tends to form microclusters within the voids. In contrast, sodium- and lithiumhalides do not give rise to distinct new features in the structure factor. Instead a considerable smearing out of the first sharp diffraction peak of the host glaiss is observed. This indicates a partial breakdown of the intermediate range ordering of the host matrix. The results are discussed in relation to structure-conductivity models suggested for superionic glasses.
Studies on Ion Conducting Compounds with Cristobalite Related Structures.
Authors: Grins Jekabs , Frostäng S. , Nygren M.
Published: March 2011

This article summarises ionic conductivity and structural studies in the sodium—ion conducting systems NaxM'x/2M'' 2-x/2O4, 2 ≥ x ≥ 4/3 and (M',M'')(Zn,Si), (Be,Si) and (Zn,Ge). The best conductors are found at x ≈ 1.75–1.85, with conductivities in the range 10-2–10-3 (Ωcm)-1 at 600 K. They exhibit stuffed cristobalite type structures, isotypic with the structure of orthorhombic Na2BeSiO4. Based on single crystal data, the Na2BeSiO4 structure has been determined and refined, bothat 295 and 623 K. The structures of several other isotypic compounds have been refined by the Rietveld method, including Na1.8(Zn0.8.Ga0.2)MO4 with M = Si,Ge and Nal.8 Be0.8Si1.1O4. The ionic conductivity properties of the materials are discussed in relation to the obtained structural data.
Dielectric Loss in Vanadyl Pnictates
Authors: Lomax Joseph F. , Fontanella John J. , Wintersgill Mary C. , Kotarski Anthony
Published: March 2011

The results of audio frequency complex impedance studies for vanadyl phosphate and its hydrates (VOPO4*nH2O;n=0,1,2) are reported. Measurements were made at seventeen frequencies between 10 and 105 Hz over the temperature range 5.5-380K. Two lowtemperature features were observed and are correlated with particular water species between the VOPO4 layers. In light of chemical evidence and compleximpedance measurements on related compounds, it is speculated that VOPCO4*nH2O (Pc = P, As) can be thought of as a mixed nonstoichiometric compound [VO(HPcO4)]x[VOPcO4O4]1-x*nH2O and the solid Brϕnsted acid nature of the compound is related to proton movement between layer pnictates and intralayer waters.
Lithium Ionic Conductivity of Some Lithium Iodoles
Authors: Lewis Michael D.
Published: March 2011

The search for lithium ion conductors in crystalline or polycrystalline solid state ionic materials has resulted in finding a new class of compounds. Five new, stable, homogeneous compounds formed in the lithium alcohol systems, LiI—(ROH)x for R=CH3CH2OH, CH3CH2CH2OH, CH3CHOHCH3,, and CH3OH have been identified and characterized.
Oxidation State and Properties of Electrochromic Tungsten Oxide Films
Authors: Klein J. D. , Yen A.
Published: March 2011

Tungsten oxide films were deposited by reactively sputtering a metallic W target in O2Ar atmospheres. Plasma emission spectra were observed as a function of the oxygen content of the chamber inlet gas using an optical multichannel analyser. The gradual loss of W lines as the O2 content was increased to 10% was accompanied by a drastic reduction in deposition rate. Cyclic voltammetry of the films deposited on ITO-coated substrates reveals that films produced under high oxygen conditions have low charge capacities and retain substantial Li upon initial cycling. The photopic coloration efficiency increased with increasing oxygen in the inlet gas. The electrochemical and electrochromic data exhibit breaks in behavior at the 10% O2 break point defined by optical spectroscopy.
Fabrication of Carbon Fiber Reinforced Cement Composites
Authors: Park S. B. , Lee B. L
Published: March 2011

Portland cement was reinforced by carbon fibers (CF) with various additive materials -- silica powders, superplasticizer, polymer emulsion, fly ash, and foaming agent -- for different purposes. The variables affecting the composite properties were identified. The mechanical properties -- tensile, compressive, and flexural strengths -- were determined as a function of CF loading and length of the fibers. The bulk density of the composites decreased as the fiber loading increased. The tensile strength increased with the CF loading increase but the compressive strength decreased as the fiber content in the composite increased. Increasing difficulty in dispersing CF as the fiber loading increase and the fiber length was rectified by addition of silica aggregates. The mechanical properties were improved as the size of silica aggregate decreased which also exhibited greater effectiveness in CF dispersion. Addition of a polymer emulsion, ethyl vinyl acetate (EVA) to the composite decreased the bulk density but increased tensile and compressive strengths.
High-Strength Concrete with Increased Fracture-Toughness
Authors: Glavind Mette , Aarre Tine
Published: March 2011

The application of high-strength concrete in practice is strongly limited by its more brittle behaviour than normal strength concrete.

The present study deals with an investigation of the possibilities of increasing the fracture toughness of high-strength concrete by adding fibres. Tests are made with both normal strength concrete and high-strength concrete containing different amounts of steel and polypropylene fibres. Stress-strain curves in compression are obtained by a deformation controlled test system. The toughness is described with different toughness indexes.

By using a previously proposed expression for the stress-strain curves, it is possible to make a non-linear load carrying capacity calculation for reinforced concrete beams. The results of the load carrying capacity calculation are compared with results of similar calculations made with the Danish code extrapolated to be valid for high-strength concrete.

The investigation shows that the addition of especially steel fibres is effective in increasing toughness and the non-linear load carrying capacity for high-strength concrete. It is also shown that the compression strength of high-strength concrete is increased by addition of steel fibres. The results of the load carrying capacity calculation show that the Danish code cannot be extrapolated to be valid for high-strength concrete without any modifications.
A Description of the Kinetics and Mechanisms which Control the Release of Hlw Elements from Synroc
Authors: Smith K. L. , Hart K. P. , Lumpkin G. R. , McGlinn P. , Lam P. , Blackford M. G.
Published: March 2011

Leaching tests were carried out on well-characterised Synroc C specimens containing 10 wt% simulated HLW. The effect of temperature and leachant composition on the mechanisms and kinetics of leaching were investigated by leaching Synroc specimens in deionised water at 70°C and 150°C, and in silicate and bicarbonate solutions at 70°C. SEM and TEM were used before and after leaching to characterise the primary and secondary phases in and on the Synroc samples, and to describe the morphological and chemical changes which occurred. Leachants were analysed using ICP/optical emission spectroscopy and ICP/mass spectrometry.

Titaniferous surface layers were observed on the surface after exposure to leachants. Analysis of the leaching data has established that these surface layers can reduce the release of HLW elements from Synroc and that variations in temperature and leachant composition can hinder or promote the formation of secondary phases.
Spent Fuel Degradation
Authors: Forsyth Roy S.
Published: March 2011

The degradation and dissolution of spent nuclear fuel in groundwaters occurs by three partly concurrent processes: dissolution of mobile species which have migrated to the fuel rod void, grain boundary attack and matrix dissolution. Of the first two processes, both clearly dependent on the irradiation history of the fuel, the first is fairly well understood, but there is currently insufficient data on the migration of key nuclides to grain boundaries during reactor operation and their release kinetics during subsequent water corrosion to enable satisfactory modelling of this process to be performed.

This paper presents results from recent experiments included in the Swedish programme which are relevant to this issue.
Phase Relations of the Uranyl Oxide Hydrates and their Relevance to the Disposal of Spent Fuel
Authors: Finch R. J. , Ewing R. C.
Published: March 2011

Uranyl oxide hydrates, formed by the alteration of uraninite, are natural analogues for the long-term corrosion products of spent fuel in a geologic repository under oxidizing conditions. The uranyl oxide hydrates may be represented by the general formula:

Pb-bearing hydrates require the addition of a neutral uranyl group into the structural sheet (UO2(OH)2) for each interlayer Pb ion. Distortion of the structure associated with the additional uranyl groups is reduced by replacing two structural hydroxyls with a structural oxygen and a molecular water. The general formula for the Pb-uranyl oxide hydrates is:

This hypothesis explains the paragenetic sequences:

1) schoepite ➛ billietite ➛ protasite ➛ bauranoite

2) schoepite ➛ vandendriesscheite ➛ fourmarierite ➛ masuyite ➛ wölsendorfite

3) schoepite ➛ vandendriesscheite ➛ fourmarierite ➛ ± masuyite ➛ sayrite ➛ curite, and indicates that, under relatively high pH conditions, schoepite will not be the long-term solubility-controlling phase for uranium in uranium-rich groundwaters.
Container Materials for High-Level Nuclear Waste at the Proposed Yucca Mountain Site
Authors: McCright R. Daniel
Published: March 2011

Candidate container materials for high-level nuclear waste packages to be emplaced at the proposed Yucca Mountain repository site are being considered for their long-term resistance to corrosion, oxidation, embrittlement and other kinds of degradation. Selection criteria have been established, and a method has been developed for recommending a material for advanced container design activities. An extensive compilation of the degradation phenomena for six candidate materials is complete, and further studies have begun on the degradation modes affecting additional candidate materials. Phenomenological models for predicting container degradation rates are being advanced for environmental conditions applicable to Yucca Mountain. An experimental program is underway to evaluate the susceptibility of container materials to localized corrosion, stress corrosion cracking, and enhancement of corrosion and oxidation attack by gamma radiation. Initial evaluations of container fabrication and welding processes have identified some processes that appear to alleviate some long-term corrosion susceptibility concerns.
Effect of Oxygen Transport and Resistivity of the Environment on the Corrosion of Steel
Authors: Escalante E. , Oka T. , Bertocci U.
Published: March 2011

This study is directed at investigating the rate of corrosion and its spatial distribution that develop under conditions where transport of oxygen and conductivity of the environment are controlled over a wide range, including low conductivity as expected in the Yucca Mountain environment. The results indicate that the corrosion rate of steel is directly related to the rate of oxygen transport over several orders of magnitude, and increasing conductivity by one order of magnitude increases corrosion rate by a factor of two or three. Of greater significance is the result that indicates that as conductivity of the environment decreases, and corrosion rate decreases, the degree of localized attack increases.
Statistically Designed Lead Corrosion Experiments for Nuclear Waste Disposal
Authors: Mani Mathew P. , Krueger P.A.
Published: March 2011

This paper describes galvanic corrosion studies of lead, a candidate matrix metal, coupled vith ASTM Grade-2 titanium, a candidate container-shell material, to determine the barrier-lifetime for a lead matrix container - one container concept considered in the Canadian Nuclear Fuel Waste Management Program. In these studies the fractional factorial statistical design of Box-Behnken was used to develop mathematical relationships between the independent variables and the corrosion rate of lead.

Using the mathematical expressions derived in this study, the additional barrier-lifetime that a 25-mm-thick lead layer could provide to a titanium container, which eventually perforates by corrosion, was calculated to be at least 3500 years.
Uncertainties in Container Failure Time Predictions
Authors: Williford R. E.
Published: March 2011

Stochastic variations in the local chemical environment of a geologic waste repository can cause corresponding variations in container corrosion rates and failure times, and thus in radionuclide release rates. This paper addresses how well the future variations in repository chemistries must be known in order to predict container failure times that are bounded by a finite time period within the repository lifetime. Preliminary results indicate that a 5000 year scatter in predicted container failure times requires that repository chemistries be known to within ±10% over the repository lifetime. These are small uncertainties compared to current estimates.
The Long-Term Properties of Cement and Concretes
Authors: Atkins M. , Glasser F. P. , Moroni L. P.
Published: March 2011

The state of knowledge concerning the internal constitution of cement systems is reviewed. It is concluded that many properties relevant to radwaste immobilization are strongly influenced by the presence of thermodynamically metastable phases. In order to ascertain cement properties at long ages, models have been developed which include compositional and time-dependant factors. These require a validated data base. Progress in developing models and creating the data base are reviewed. In the course of accumulating data, specific radwaste species -cement interactions can also be quantified.
The Effect of Leaching on the Pore Structure of Cement-Based Grouts for Use in Nuclear Fuel Waste Disposal
Authors: Onofrei M. , Gray M. N. , Breton D. , Ballivy G.
Published: March 2011

Research on the longevity of cement-based grout materials for sealing a deep geological disposal vault is an important aspect of the Canadian and other nuclear waste management programs. These studies include assessments of the chemical durability of cement grouts, and the effects of leaching and phase transformation on the long-term hydraulic and diffusion characteristics of grouts.

This paper presents the results of laboratory studies carried out to assess the effects of leaching of cement phases on the pore structure of hardened grouts. Measurements of mercury intrusion and scanning electron microscopy with energy dispersive x-ray analysis, have been used to investigate the changes in pore structure of both a reference grout (90% Type 50 cement, 10% silica fume, water-to-cementitious materials ratio between 0.4 and 0.7) and ALOFIX-MC (a fine cement product of Japan), as a function of leaching time.

The work discussed here reveals that the porosity of hardened grout does change during leaching, but within limits that depend on grout composition and initial porosity. The results confirm that the materials have the potential to self-seal and maintain their performance for longer periods than those currently predicted by longevity models.

Our studies of the porosity and permeability of grouts suggest that pore size distribution rather than total porosity is the more important parameter in determining longevity.
Migration of Cesium, Strontium and Cobalt in Water-Saturated Concretes
Authors: Idemitsu K. , Furuya H. , Tsutsumi R. , Yonezawa S. , Inagaki Y. , Sato S.
Published: March 2011

Diffusivities of Cs, Sr and Co were measured in several kinds of water-saturated concretes. The measured penetration profile of every tracer was composed of two parts. Those were a steep slope near the surface and a gradual slope in the deeper part. This profile was successfully explained by considering two diffusion paths in concrete. One diffusion path was possibly fissure with a width of a few microns and another was network of submicron pores. The volume of submicron pores was approximately 90% of the total free space volume in every concrete. The orders of magnitude of apparent diffusivities for all tracers were 10−12–10−11 m2/s through the fissure and l0−16–10−15 m2/s through the network of pores. The difference between the diffusivities of the two paths is thought to be caused by small geometrical factor of the network of submicron pores.
The Effect of Silica Fume and Water/Cement Ratio on the Hydraulic Conductivity of Cement-Based Grout
Authors: Al-Manaseer A. A. , Onofrei M. , Gray M. N. , Shenton B.
Published: March 2011

In situ experiments at Atomic Energy of Canada Limited’s Underground Research Laboratory have demonstrated that a specially developed high-performance cement-based grout, called the reference grout, consisting of 90% sulphate-resistant cement (Canadian Type 50), 10% silica fume (SF) and superplasticizer can seal very fine fissures in granitic rock. Studies are now in progress to determine the longevity of these materials. This paper describes progress in studies of the hydraulic conductivity (i.e. coefficient of permeability), K, of the grout at water/cementitious materials ratios, w/c, between 0.4 and 0.8. The K was assessed with the grouts under compressive and tensile stress using specially designed radial flow permeameters. The results confirm that the K of the reference grout is two to three orders of magnitude lower than that typically observed for intact granite rock (10−12 m/s). Moreover, the data show that adding silica fume and reducing the w/c decreases K. The hydraulic conductivity data coupled with field work and other laboratory data strongly suggest that the reference grout can be successfully used to seal finely fractured rock in the vicinity of a nuclear fuel waste disposal vault.
Research Needs in Cement-Based Waste Forms
Authors: McDaniel E. W. , Spence R. D. , Tallent O. K.
Published: March 2011

Cement-based waste forms are one of the most widely used waste disposal options, yet definitive knowledge of the fate of the waste species inside the waste form is lacking. A fundamental understanding of the chemistry and microstructure of the waste forms would lead to a better understanding of the mass transfer of the waste species, more confidence in predicting and extrapolating waste-form performance, and improved design of waste forms. Better and cheaper leach tests would lead to quicker and more cost-effective screening of waste-form alternatives, cement-based and otherwise. In addition, assessment of durability may be important to predicting waste-form performance in the field over periods of decades and centuries.
Developments for in Situ Tests on Compacted Bentonite-Based Buffer Material
Authors: Kjartanson B. H. , Gray M. N. , Pulles B.C.M.
Published: March 2011

AECL Research is carrying out large-scale in situ experiments at its Underground Research Laboratory (URL). The Buffer/Container Experiment is designed principally to investigate the full scale, in situ performance of bentonite-based buffer material in a single emplacement borehole environment. In addition, the response of the rock to excavation and heating will be investigated. The experiment also allows for the development of the technologies needed to demonstrate some of the vault engineering activities proposed in the Canadian nuclear fuel waste disposal concept. These include excavation of large diameter boreholes for waste emplacement and in situ compaction of a bentonite/sand buffer mixture. Although these methodologies developed for the URL have not been optimized for the commercial, full-scale operations needed for a disposal vault, results show that the equipment and methodologies needed for vault operations are a reasonable extrapolation of existing technology.
Mechanistic Effects of Deuteration on the Aqueous Corrosion of Nuclear Waste Glasses
Authors: Feng X. , Fu L. , Choudhury T. K. , Pegg I. L. , Macedo P. B.
Published: March 2011

Isotopically labeled water has been utilized by several researchers to help elucidate the glass dissolution mechanism in aqueous media. However, most of the results have been obtained with simple silicate glasses and have utilized low surface-to-volume (S/V) ratios and relatively short time scales. In this paper we report the results of an extensive study of the leach behavior of the preliminary West Valley nuclear waste glass composition, WV205, in deuterium oxide using multiple S/V ratios at both short and long times. The WV205 glass was leached in parallel in both ordinary deionized water and in deuterated water at five S/V ratios (20, 100, 200, 2000 and 6000 m−1) at 90°C under PCT (the SRL-modified MCC3 procedure) conditions with sampling at 1, 3, 7, 28, 56, 120 days, and four times annually thereafter; the tests will continue for several years. Initial rates were determined by measurements at shorter times with polished monoliths. A significant isotope effect, as measured by the ratio of leach rates, RH20/RD20, was found at all S/V ratios and reached values as large as 360%. Our data yield different values for RH20/RD20 in the diffusion, matrix dissolution, and saturation dominated regimes with the largest effect in the middle stage. Large values of RH20/RD20 would be characteristic of a primary kinetic isotope effect suggestive of a bond breakage involving hydrogen in the rate determining step.
Effects of Mineralogy on the Sorption of Strontium and Cesium Onto Calico Hills Tuff
Authors: Meyer R. E. , Arnold W. D. , Case F. I. , O’Kelley G. D. , Land J. F.
Published: March 2011

Sorption and desorption measurements were made of strontium and cesium onto clinoptilolite and Calico Hills tuff. The object was to see whether there was a correlation between sorption of strontium and cesium onto Calico Hills Tuff and the clinoptilolite based on the content of clinoptilolite in the Calico Hills Tuff. If sorption onto Calico Hills Tuff is solely due to the presence of clinoptilolite, then the ratios of the sorption ratios on tuff to those on clinoptilolite at similar conditions should be the weight fraction of the clinoptilolite in the tuff. Since the tuff contained about 50% clinoptilolite, the ratios would be expected to be about 0.5 if sorption was due solely to clinoptilolite. The experimental evidence showed that the ratios were generally near 0.5 for both cesium and strontium sorption and that ion-exchange processes were operative for both the clinoptilolite and the tuff. However, the ratios differed to a small extent for different conditions, and there were indications that other sorption processes were also involved.
The Influence of Trace Elements in Consolidated Sedimentary Rocks on the Migration Behaviour of Radionuclides
Authors: Bode W. , Bode B.
Published: March 2011

The effects of trace contents of 15 elements in the sedimentary rocks on the Rs- and Rd-values (Maass, 1983) of the dissolved radionuclides of the elements C (as carbonates), Se, Sr, Tc, I, Cs, Pb, Ra, Ac, Pa, U, Np, Pu, Am. and Cm were investigated and discussed. For this purpose Sr, Ba, B, Corg., Pb, P, F, Cu, Zn, Cd, V, Mn, Fe, Co and N1 contents in the rocks were compared to the sorptlon/desorption coefficients of the above mentioned 15 radionuclides and plotted in x-y diagrammes (a total of 225). While the magnitude of most trace element contents has no or only a slight influence on the retention properties of most radionuclides, a distinct correlation between the trace element contents and the magnitude of the distribution coefficients was found for some radionuclides. Particularly copper, organic carbon, and barium are found to take a positive influence on the Rs-/Rd-values of certain radionuclides. The presence of other trace elements (eg. B and F) can have a negative effect on the retention behaviour of the rock matrix as regards certain dissolved radionuclides. Seen as a whole, the magnitude of the desorption coefficients (Rd-val-ues) appears to be more closely correlated to the trace element contents than to the sorption coefficients (Rs-values).
Diffusion Measurements of Radionuclides In site Specific Sediment/Groundwater-Systems
Authors: Meier Hans , Zimmerhackl E. , Zeitler G. , Menge P.
Published: March 2011

Results of systematic measurements on the diffusion of radionuclides through sandy, marlaceous and clayley sediment rocks from strata overlying the Gorleben salt dome are presented. The tracer nuclides used were U-233, Ra-226, Pb-210, and Ni-63. It is shown that, among other parameters, diffusion coefficients and distribution coefficients could be derived from breakthrough curves. Moreover, it is demonstrated that the diffusion behaviour of nuclides such as Pb and Ni can be enhanced enormously in sediment rocks by complex forming agents (EDTA).
Record of Past Contact Between Altered Rocks and Radioactive Solutions Through Radiation-Induced Defects in Kaolinite
Authors: Ildefonse Philippe , Muller Jean-Pierre , Clozel Blandine , Calas George
Published: March 2011

A U-deposit located in hydrothermally altered tuff in Mexico, and two tropical weathering systems from Brazil and Cameroon were studied as natural analogues of radionuclide release and migration in the geosphere. In these alteration systems, kaolinite is the main secondary phyllosilicate associated with variable amounts of iron oxides. Defect centers are detected in natural kaolinites by means of electron paramagnetic resonance. The origin of the paramagnetic defect centers (PDC) is from radionuclide irradiation. This interpretation is supported by laboratory experiments on kaolinite using four different types of radiation: x-rays, γ-rays, and He+ and Pb2+ ion beam implantations. Several types of PDC (designated A-, A‵- and B-centers) are clearly identified and can be distinguished with respect to their relative stability. The A-center is stable over geological periods (on the order of 109 years) at surface temperatures. Moreover, it is shown that PDC’s in kaolinites reflect the cumulative radiation dose.

PDC’s in kaolinite have been used to trace radionuclide migration in the three natural alteration systems studied. The kaolinites investigated show a significant concentration of PDC’s which corresponds to background natural irradiation. The different types of PDC detected may record successive irradiations of kaolinite directly linked to geochemical conditions prevailing during and after kaolinite growth. Because of their different thermal stability, these different PDC–s may be considered to have formed at different time periods. This makes a unique tool for tracing the dynamics of the transfer of radionuclides and allows the use of kaolinite as an in-situ dosimeter. Because some of the geological settings chosen for nuclear wastes are located in kaolinite-bearing strata, PDC dosimetry could be used in a safety assessment of these wastes.
Three-Dimensional Transient Advective Diffusion by Boundary Element Method using Direct Time Integral of the Fundamental Solution
Authors: Kawamura Ryuji , Isono Akira
Published: March 2011

The advective diffusion analyses have been applied to many fields of science and engineering, such as dispersion for chemically reacting(first-order reaction) substance, thermal transport in fluid, analysis of electromagnetic field caused by a moving magnet. electron transport in semiconductors, underground migration of radioactive waste, and so on. The boundary element method (BEM) has been developed extensively for the last decade to solve these transient advective diffusion equation. The time integrations of the fundamental solution in the boundary integral equation, however, make the BEM application to advective diffusion problems difficult. Therefore, the time integration has been approximated in the past relevant publications. This paper describes the BEM in which the time integration is done analytically, and technique is demonstrated with several examples. Good results have been obtained in the example calculations, where comparisons are made with the results from other numerical codes.
Modelling the Chemical Behaviour of Radionuclides in Waste Disposal Site in a Granitic Environment - a Chemical Thermodynamic Approach
Authors: Fabriol Robert , Ouzounian Gerald , Genter Albert
Published: March 2011

Limiting concentrations of radionuclides (RN) in a granitic environment are determined by computer modelling of a disposal site with quartz sand and clay engineered barriers. Six RN (Sr, U, Pu, Np, Th and Tc) are studied. Temperature is varied with distance from the host rock to waste from 25 to 200°C, The behaviour of these elements appears to be iindependent, of the barrier material and strongly dependent on temperature effect on mineral solubilities.
A Novel Conceptual Model for the Flow and Transport in Fractured Rock
Authors: Taivassalo V. , Hautojärvi A.
Published: March 2011

In crystalline rock groundwater flows predominantly in fractures and fissures. Strongly varying fracture aperture guides the flow preferentially in some parts of a fracture plane, in so called channels. In our hydraulic model the degree of channeling together with the aperture variation along a channel is included as a factor which is the ratio of the aperture from transmissivity measurements and the aperture from the tracer tests.

The developed transport model takes into account the coupling of molecular diffusion and advection in a velocity field varying linearly over a characteristic width. Various flow velocities in different parts of a channel cause a transient phase with non-Fickian behavior of dispersion. This might erroneously be attributed to other processes e.g. matrix diffusion when not taken into account in the migration modeling of tracers. Molecular diffusion across the flow field, however, tends to smooth out the transport time differences. With time the dispersion diminishes and becomes more symmetric in confined channels.

The concept and models have been applied to predict and interpret field experiments aimed to investigate transport over long distances in highly conductive fracture zones. The analyzed experiments have been performed at the Finnsjön research area in Sweden and they belong to the test case 5 of the INTRAVAL project.
Release and Transport of Gaseous C-14 from a Nuclear Waste Repository in an Unsaturated Medium
Authors: Light W.B. , Zwahlen E.D. , Pigford T.H. , ChambrÉ P.L. , Lee W.W.-L.
Published: March 2011

The potential nuclear waste repository at Yucca Mountain is to be in partially saturated rock. Released radioactive gases such as 14CO2 could have a direct pathway to the biosphere. We study the release of 14C released as 14CO2 from partly failed nuclear waste containers by analyzing the flow of gas into and out of a container. We analyze the transport of released 14CO2 in an unsaturated, fractured, porous medium with gas-phase advection and dispersion. We calculate the inhalation dose to a maximally exposed individual above ground, based on some conservative assumptions about release from containers. For the assumed parameter values, a simple atmospheric diffusion model gives very small doses when compared to background radiation doses.
Aqueous Diffusion Coefficients in Unsaturated Materials
Authors: Conca James L. , Wright Judith
Published: March 2011

Simple diffusion coefficients, D(θ), in most unsaturated media were found to be primarily a function of water content and not material characteristics except where the characteristics affect or determine water content. At high water contents, D(θ) gradually declines as water content decreases, from 10−5 cm2/sec at a volumetric water content of about 50% to 10−7 cm2/sec at a volumetric water content of about 5%, followed by a sharp decline as surface water films become thin and discontinuous and pendular water elements become very small, from 10−7 cm2/sec at a volumetric water content of about 5% to 10−9 cm2/sec at a volumetric water content of about 0.5% to 1%.
The Role of Laboratory Analog Experiments in Assessing the Performance of Waste Package Materials
Authors: Cunnane James C. , Bates John K.
Published: March 2011

There is an immediate need to begin to validate models that can be used for assessing the performance of waste package materials in an unsaturated repository environment. This paper examines available testing information and testing approaches that could support validation of models for engineering barrier system (EBS) radionuclide release. The content is presented in the context of the general methodology that has been proposed for validating performance assessment models [1], Available experimental observations are used to test some of the EBS release rate modeling premises. These observations include evidence of fluid film formation on waste glass surfaces in isothermal humid environments, accelerated waste glass reaction rates under repository service conditions of large glass surface area to water volume ratio, and mobilization of radionuclides as solutes and colloids. It is concluded that some important modeling premises may not be consistent with available experimental Information. However, it is also concluded that future laboratory testing, which simulates the Integrated waste package system (i.e., laboratory analog testing), is needed to evaluate the significance of these Inconsistencies and to test the system level models. A small-scale apparatus which was developed and tested to examine the feasibility of laboratory analog testing for the unsaturated Yucca Mountain repository environment is described.
Creep Deformation of Dispersion Strengthened NiAl and TiAl Intermetallics
Authors: Sadananda K. , Jones H. , Feng C.R. , Vasudevan A.K.
Published: March 2011

In this study, the creep properties of two intermetallics; NiAl and TiAl have been evaluated. The former was selected based on its relatively high melting point, and the latter was based on its specific strength and high melting point. Tensile creep deformation rates in range of 760 to 930°C were determined as a function of stress for both monolithic NiAl, NiAl reinforced with HfC dispersoids and TiAl reinforced with TiB2 dispersoid. Microstructure and dislocation structures were examined both beore and after creep in both alloys to identify the creep mechanisms. In both systems, deformation occurs by power-law creep with diffusion controlling creep rate. Power-law breakdown regimes have been identified for both systems. In addition, TiAl undergoes dynamic recrystallization during creep resulting in smaller grain sizes than the initial value.
Compression Studies on Particulate Composites of Ternary Al-Ti-Fe, and Quaternary Al-Ti-Fe-Nb and Al-Ti-Fe-Mn L12 Compounds
Authors: Kumar K.S. , Dipietro M.S. , Whittenberger J.D.
Published: March 2011

Compression studies were conducted on monolithic and TiB2 particulatereinforced composites of AI22 Fe3 Ti8, both with and without minor quaternary alloying additions (2 at.% Nb and 2 at.% Mn) as a function of temperature and as a function of strain rate at high temperature. The volume fraction of reinforcement was varied between 0 and 20 percent. The particulate reinforcements were found to be effective in increasing ambient- and warm-temperature strength; at high temperatures, the monolithic material is stronger than the composites, although the composites are superior at slow strain rates. The microstructures of the monolithic and composite specimens were examined before and after deformation to explain these observations.
An Investigation of Phase Equilibria in the Ternary Al-Ti-Ta System
Authors: Weaver M.L. , Guy S.L. , Stone R.K. , Kaufman M.J.
Published: March 2011

An investigation of the phase equilibria and phase transformation behavior in the Al-Ti-Ta system was conducted with an emphasis on developing alloys with stable microstructures and properties desirable for advanced aerospace applications. A series of ternary alloys containing 5 to 50 atomic percent Ta and varying amounts of Ti and Al were prepared by arc melting and characterized in the as-cast and heat treated (1450°C) conditions. Three stable two-phase regions (β-σ, β-α2. and Al2 Ta-η) were identified and characterized at 1450°C. A stable ternary B2 phase was identified near the composition 25Al-5OTi-25Ta1 and several binary phases were found to exhibit extensive solid solubilities. The results were used to construct a partial isothermal section at 1450°C for this system and to assess the complex phase transformations that occur upon cooling.
Comparison of TEM Observations with Dislocation Core Structure Calcuiations in B2 Ordered Compounds
Authors: Farkas D. , Pasianot R. , Savino E. J. , Miracle D.B.
Published: March 2011

Dislocation core structures have been calculated using atomistic computer simulations in NiAl and other B2 compounds. In the present work the calculated dislocation core structure are correlated with the known deforniatiorn behavior of B2 alloys. It is found that for the high ordering energy compounds <111> dislocations do not split in the simulations, in agreement with the experimental observations. It is also found that core structures for certain <111> and 1/2 <111> dislocations are spread in { 112} planes, which is consistent with the slip plane often reported for these dislocations. For the < 100> dislocations several orientations of the dislocation line produce sessile core configurations, whereas other orientations produce relatively more glissile cores. However, a structural transition of each of these dislocation cores may be required before < 100> dislocations become mobile, and this is consistent with the limited tensile ductility observed in NiAl “soft” single crystals below 200°C. Core structure simulations for < 110> dislocations are also reported and are discussed with respect to the importance of these dislocations in the deformation of NiAl.
Stress Induced Martensitic(SIM) Transformations In B2 NiAl Observed in Crack Propagation Computer Simulations
Authors: Kim Donghyun , Clapp P. C. , Rifkin J. A.
Published: March 2011

In molecular dynamics studies of 10,000 atom arrays of stoichiometric B2 NiAl containing a crack under external stress in Mode I loading, it has been observed that a martensitic transformation generally occurs (starting in the vicinity of the crack tip) prior to the generation of dislocations and/or the propagation of the crack. The martensitic phase appears to be 2H, in agreement with experimental observations of SIM at higher Ni compositions (62 at % Ni). The interatomic interactions used in the simulations were the Embedded Atom Method (EAM) potentials developed by Voter and Chen [1] for the Ni-Al alloy system.
The Crystallography of Cleavage Fracture in Al3 Sc
Authors: Schneibel J.H. , Hazzledine P.M.
Published: March 2011

The intermetallic compound Al3Sc is a trialuminide with the LI2 structure, which deforms easily in compression at room temperature, with yield stresses around 100 MPa. In tension Al3Sc fractures transgranularly in a brittle manner. The predominant cleavage plane is {011}. Regions, which are flat within experimental resolution are only occasionally observed. Numerous cleavage steps, which are aligned in 3 major crystallographic directions, are found. Some of these steps consist of {111} or {001} planes, but others are not distinctly crystallographic. Plastic deformation involving dislocation motion or twinning may have occurred at some of these steps. Reactions between different types of steps are also observed. One type of cleavage pattern found is strikingly similar to the typical appearance of fracture surfaces of fcc brass and Cu3Au after stress corrosion cracking. However, this particular pattern is only rarely observed in Al3Sc. Our observations indicate that an interpretation of cleavage fracture in Al3Sc in terms of surface energies alone is unlikely to be successful. A full understanding of the fracture morphology of Al3Sc will require detailed atomistic simulations taking dislocation motion and twinning into account.
Grain Boundary Structure as a Function of Aluminum Level in Ni3Al
Authors: Horton J.A. , Liu C.T. , Pennycook S.J.
Published: March 2011

Understanding the boron effect in Ni3Al currently centers on determining thestructure of the region near grain boundaries, especially the presence of a disordered γ phase. In this study, a series of alloys was examined by transmission electron microscopy (TEM) as a function of aluminum level, boron level, and cooling rate for thepresence of any grain boundary phases. The base alloy series all contained 0.5 at. % Hf. At 21.5 at. % Al,γ formed in the matrix as expected. However, in slowly cooled specimens with 22 and 22.5% Al, a second phase with thicknesses from 25 to 50 nm formed on some of the grain boundaries. At higher aluminum levels no evidence of any second phase was observed. The minimum width of grain boundary images formed by normal diffraction contrast imaging was generally 0.5 to 1 nm for grain boundaries that presumably had no second phase and were parallel to the electron beam. Therefore, a second phase with a thickness of 1 nm or less would not be discernable by TEM. High resolution Z-contrast imaging by scanning TEM of a very low angle boundary in directionally solidified (DS) material also showed no evidence of disordering, but did show a surprising amount of non-planarity of the boundary.

Whereas slower cooling rates might be expected to aid the formation of any grain boundary phase and thereby increase the ductility, the ductility was slightly lower for the more slowly cooled alloys than for the furnace cooled alloys. From 21.5 to 24% Al, the tensile elongations remain fairly constant with values ranging from 45 to 52%. Above 24%, the ductility drops off rapidly but is still much higher for the boron-doped material than for the undoped material. At 25.2% Al, the ductility is still 4% as compared to essentially zero for undoped material. Therefore the ductility improvements in boron-doped Ni3Al do not require the presence of any grain boundary disordered phases discernable by TEM.