bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of the Monte Carlo Method in the Performance Assessment of a Hypothetical HLW Repository in Salt
Authors: Nies Alexander 
Published: March 2011

ABSTRACTRecent advances in complementing the capabilities of our safety assessment code development allow for an explicit investigation of the consequences of parameter uncertainties by Monte Carlo simulation of the disposal system. The implemented methods aire described and applied to impact assessment of a brine intrusion scenario on a high level waste repository in a salt dome. Results display the strong effect of parameter uncertainties on the analysis results. With help of several sensitivity estimators input parameters are ranked according to their influence on output uncertainty.
Source-Term Comparison Using the Arest and Syvac-Vault Models: Effects of Decay-Chain In-Growth and Precipitation
Authors: Apted M. J. , Engel D. W. , Garisto N. C. , Leneveu D. M. 
Published: March 2011

ABSTRACTA series of calculations of radionuclide release was performed with the AREST and SYVAC-Vault models (SVM) in order to assess concurrance. Specifically, the effects of precipitation and decay chain in-growth on the predicted release of nuclides from waste packages containing spent nuclear fuel were compared between each code. The results for maximum release rates generally agreed within a factor of 10. The differences in results can be explained based on the differences in geometry and boundary conditions between the two codes. Both codes showed nearly identical enhancement factors in release rates of uranium-series nuclides (U-238, U-234, Th-230, Ra-226) arising from the effect of decay-chain in-growth. Calculated enhancement factors in release rates for precipitation of a new uranium-bearing solid within the waste package were also in good agreement between AREST and SVM.
In Situ Migration Experiments in the Boom Clay at Mol ; Experimental Method and Preliminary Results
Authors: Put M. , Monsecour M. , Fonteyne A. , Yoshida H. , De Regge P. 
Published: March 2011

ABSTRACTA first generation of underground migration experiments is described, consisting of labelled clay cores emplaced in boreholes drilled in the Boom clay formation. The boreholes are sealed by natural convergence of the clay and porewater percolates through the labelled clay cores which are consolidated in situ. After monitoring of the radioactive tracers in the percolating porewater, the experiment is retrieved from the borehole and the tracer profile is measured in the clay cores. With the exception of accelerated porewater flow, due to the existence of a high hydraulic head around the underground gallery, the experimental conditions are close to those expected in the far-field of a closed repository for radioactive waste. The main advantage of this approach is the availability of real porewater during relatively long-term experiments. Results are reported for the experiments performed with europium and strontium tracers.
Chemical Evolution of Water and Brines in Contact with Different Zechstein Salt Formations
Authors: Herbert H.-J. , Sander W. 
Published: March 2011

ABSTRACTThe paper gives a quantitative description of the chemical reactions, the dissolution and precipitation processes which take place when water or brines come into contact with the main mineral assemblages of the German Zechstein salt formation, rock salt with Ca-sulfates, and the potash beds hartsalz and carnallitite. The results of two large scale in situ dissolution tests are presented. These results have been successfully reproduced by computer modelling using the geochemical code EQ3/6.
Near-Field Geochemistry of Vitrified HLW in a Sedimentary Host Rock
Authors: Mckinley Ian G. , Bradbury Mike 
Published: March 2011

ABSTRACTThe Project Gewähr 1985 (PG'85) safety analysis considered the practicality of HLW disposal in the crystalline bedrock of Northern Switzerland. More recently, an alternative disposal option in the argillaceous sediments overlying the crystalline basement has been examined. This paper examines some aspects of the performance of the near-field engineered barriers in an argillaceous environment, with specific comparison to the PG'85 crystalline case. Two phenomena are considered in particular detail: oxidation of the host rock during the operational phase and the related failure mode of the steel tunnel liner.
Formation and Evolution of Alteration Layers on Borosilicate and Basalt Glasses: Initial Stage
Authors: Murakami T. , Banba T. , Jercinovic M. J. , Ewing R. C. 
Published: March 2011

ABSTRACTAn experimentally altered (1–14 days, deionized water, 90°C), synthetic borosilicate glass and naturally altered (104 years, fresh water, 0–100°C), basalt glass were characterized by analytical electron microscopy to evaluate the development of alteration layers. Layers formed on borosilicate glass are initially amorphous. With increasing age, nontronite, chlorite, septechlorite, and/or stilpnomelane appear to precipitate and grow within the amorphous matrix and on the surface of the layer. Crystals are enriched in Fe, Co, and Ni, and depleted in Si relative to the surrounding amorphous matrix. Alteration layers on basalt glass are texturally and mineralogically similar to layers formed on borosilicate glass, but the degree of crystallinity is less.
Water Uptake and Swelling Pressure in a Bentonite-Based Backfill
Authors: Kahr G. , Bucher F. , Mayor P. A. 
Published: March 2011

ABSTRACTThe partial specific enthalpy and the partial specific entropy for the water uptake of two bentonites was investigated by means of the water vapor adsorption-desorption isotherms and the heat of immersion with liquid water. From these experiments, and as confirmed by X-ray measurements, it is evident that the interlayer water shows a high degree of order. Calculations of the swelling pressure from the adsorption isotherms show good agreement with measured swelling pressures.The uptake of liquid water by the compacted bentonites under conditions of restrained swelling can be described as a non-steady state diffusion with constant surface concentration. The water uptake of two bentonites in their natural sodium and calcium forms has been investigated. The measurements were carried out in a swelling pressure apparatus with water supply from one or both sides, and in a device modelling the repository conditions with radial water supply. In this modelling experiment, the water uptake was measured and the enclosed air determined. In addition, the swelling pressure was observed and compared to earlier test results.
Modelling the Behaviour of Organic Degradation Products
Authors: Cross J. E. , Ewart F. T. , Greenfield B. F. 
Published: March 2011

ABSTRACTResults are presented from recent studies at Harwell which show that the degradation products which are formed when certain organic waste materials are exposed to the alkaline conditions typical of a cementitious environment, can enhance the solubility of plutonium, even at pH values as high as 12, by significant factors. Characterisation of the degradation products has been undertaken but the solubility enhancement does not appear to be related to the concentration of any of the major organic species that have been identified in the solutions. While it has not been possible to identify by analysis the organic ligand responsible for the increased solubility of plutonium, the behaviour of D-Saccharic acid does approach the behaviour of the degradation products. The PHREEQE code has been used to simulate the solubility of plutonium in the presence of D-Saccharic acid and other model degradation products, in order to explain the solubility enhancement. The extrapolation of the experimental conditions to the repository is the major objective, but in this work the ability of a model to predict the behaviour of plutonium over a range of experimental conditions has been tested.
Diffusion of Plutonium(IV) in Dense Bentonite-Based Materials
Authors: Sharma H. D. , Oscarson D. W. 
Published: March 2011

ABSTRACTDiffusion coefficients were measured (Dm) for Pu(IV) in dense mixtures of bentonite and sand (soil) saturated with a synthetic groundwater solution (SGW) at a pH of 8 and at 25°C. The Dm values were approximately 10-14 m2/s. The clay content of the soil, in the range of 10 to 50%, did not have a significant effect on Dm. The Dm values were also compared with diffusion coefficients calculated (Dc) from a model based on a distribution coefficient. Fair agreement between Dm and Dc for Pu(IV) was found for the soils and SGW examined here. It is unlikelv. however, that the model will accurately estimate Dm for Pu, which has a complex solution and sorption chemistry, over a wide range of conditions.
Uranium Transport in Topopah Spring Tuff: An Ion-Microscope Investigation
Authors: McKeegan K. D. , Phinney D. , Oversby V. M. , Buchholtzten Brink M. , Smith D. K. 
Published: March 2011

ABSTRACTWe investigated the effect of different methods of surface preparation on ion-microscope profiles of uranium concentration (added to the sample by diffusion from an aqueous solution) vs depth in a welded, devitrified, tuffaceous rock from Yucca Mountain. The concentration profiles were used to study transport of uranium in the tuff. Four wafers of rock were prepared from primary drill core material and finished by polishing with increasingly finer abrasive material. Final polishes were made with 400 grit SiC, 600 grit SiC, 0.3μm alumina, and 0.05μm alumina. The polished tuff wafers were exposed for eight hours to a solution of groundwater doped with 2 ppm 235-U. The wafers were then examined by SEM and the ion microscope was used to measure the lateral and depth distributions of 235-U and other isotopes in the wafer. No systematic correlation of the measured 235-U concentration- vs-depth profiles with the degree of surface finish was observed, indicating that the polishing does not affect the measurable transport of U in the tuff. A zone of enhanced 235-U concentration was observed in the upper few microns, which we attribute to sorption onto surfaces of exposed pores. Concentrations of 235-U were elevated above background to depths > 15μm, indicating that rapid transport paths exist. When the uranium distribution near the surface of the wafer was modelled by an error function, an upper limit for a slower transport path was defined by an apparent diffusion coefficient of approximately 10−3 cm3/s.
Validation of the SKBU1 Uranium Thermodynamic Data Base for its use in Geochemical Calculations with EQ3/6
Authors: Bruno Jordi , Puigdomenech Ignasi 
Published: March 2011

ABSTRACTA validation of the SKBUl uranium thermodynamic data base is performed. Experimental solubilities for schoepite, rutherfordite, UO2(am) and UO2(c) determined in a wide range of pH, PCO2, carbonate concentration and temperature are compared to calculated ones by using EQ3NR.
Complexation of Europium(III) with Carbonate Ions in Groundwater
Authors: Chatt A. , Rao R. R. 
Published: March 2011

ABSTRACTThe equilibrium extraction behavior of Eu(III) studied in chloroform solutions containing l-nitroso-2-naphthol (HA), either alone or combined with 2, 2'-dipyridyl, 1, 10-phenanthroline (phen), or trioctylphosphine oxide (TOPO) shows that the metal ion is extracted as either EuA, EuA3.2, 2'-dipyridyl, EuA3·phen, or EuA3·2TOPO, respectively. The synergic effect of phen or TOPO on the extraction of Eu(III) with l-nitroso-2-naphthol is more pronounced over that of 2, 2'-dipyridyl. The carbonate complexation of Eu(III) has been studied in 1.0 M ionic strength solutions at pH 8.0–9.0 and 25 °C using the synergic extraction system of 1-nitrşso-2-naphthol and pheo. The following complexes have been identified: EuCO34, Eu(CO3)2-, Eu(CO3)33-, and Eu(CO3)45- the results suggest that the first two species predominate at carbonate concentrations and pH similar to those found in most groundwaters. The formation constants of these species have been calculated at zero ionic strength using both SIT and ion pairing models.
The Importance of Variables and Parameters in Radiolytic Chemical Kinetics Modeling
Authors: Piepho M. G. , Turner P. J. , Reimus P. W. 
Published: March 2011

ABSTRACTRadiolysis may significantly affect the long-term performance of nuclear waste packages in a geologic repository. Radiolysis of available moisture and air in an unsaturated or saturated environment will create transient species that can significantly change the pH and/or Eh of the available moisture. These changes can influence rates of containment corrosion, waste form dissolution, and radionuclide solubilities and transport.Many of the pertinent radiochemical reactions are not completely understood, and most of the associated rate constants are poorly characterized. To help identify the important radiochemical reactions, rate constants, species, and environmental conditions, an importance theory code, SWATS (Sensitivity With Adjoint Theory-Sparse version)-LOOPCHEM, has been developed for the radiolytic chemical kinetics model in the radiolysis code LOOPCHEM. The LOOPCHEM code calculates the concentrations of various species in a radiolytic field over time. The SWATS-LOOPCHEM code efficiently calculates: 1) the importance (relative to a defined response of interest) of each species concentration over time, 2) the sensitivity of each parameter of interest, and 3) the importance of each equation in the radiolysis model. The calculated results will be used to guide future experimental and modeling work for determining the importance of radiolysis on waste package performance. A demonstration (the importance of selected concentrations and the sensitivities of selected parameters) of the SWATS-LOOPCHEM code is provided for illustrative purposes, and no attempt is made at this time to interpret the results for waste package performance assessment purposes.
A Uranium Geochemical Study at the Natural Analogue Site of Needle's Eye. SW Scotland
Authors: Roberts P. D. , Ball T. K. , Hooker P. J. , Milodowski A. E. 
Published: March 2011

ABSTRACTA detailed study is being carried out at the Needle's Eye locality, on the Solway Firth, into the movement and fixation of U and its daughter isotopes. The site contains pitchblende veins, some of which have acted as a source of soluble uranium flowing into and through estuarine silts laid down in the last 2000 years or so. A section through these has provided samples for detailed analysis by X-ray fluorescence and neutron activation techniques. High resolution gamma spectrometry has contributed information on the distributions and disequilibria between uranium and its daughters. These data have been combined with analyses from groundwaters to produce a geochemical model of the origins of the U radioisotope distributions and transport mechanisms. There are thought to be two main inputs of dissolved U(VI) into this system; the surface flow of groundwater from the exposures of the mineralisation in the cliff, and upward flow from the bedrock below. The fixation of U in the sediments is controlled by the presence of organic matter in the upper humic layers, and by an iron oxy-hydroxide sorption reaction in the deeper silts at about 110cm. This concentration of U in the silt is divorced from the sub U-234 daughters. In contrast. Th is coherently associated with its daughters within detrital resistate phases. This study is a prelude to a more rigorous modelling investigation in collaboration with the Ecole des Mines de Paris.
Modeling of the Mixing of Cement Pope Water and Groundwater Using the Phreeqe Code
Authors: Ijundén Irene , Andersson Karin 
Published: March 2011

ABSTRACTThe equilibria between cement solids and pore water as well as between groundwater and rock/fracture filling minerals have been modeled, using the PHREEQE geochemical code. Additions of mineral phases to the original PHREEQE data base have been necessary for both systems. Comparisons of the predicted saturation state of the different waters with fracture filling mineralogy determined in the same area was performed.When a satisfactory modeling of the separate cement and rock systems was achieved, a modeling of the mixing of the two waters was performed. The state of saturation with respect to the minerals considered in the initial calculations as well as to potential “new” minerals was evaluated.The main mineral phases that are predicted to be supersaturated when mixing the waters are in the initial stage calcite, hydroxyapatite, chlorite, and laumontite.
A Method for Determining the Oxidation State of Uranium at Concentration as Low AS 1010M
Authors: Hussonnois M. , Guillaumont R. , Brillard L. , Fattahi M. 
Published: March 2011

ABSTRACTThis paper describes the development and testing of a chemical procedure for determining the tetravalent and hexava-lent states of uranium in aqueous media at concentration as low as 10−10M. Results show the U(IV) stability towards fast modifications of the pH of the solution with oxygen free hydrochloric acid. Some results on the oxidation kinetic of the uranium tetravalent state versus the HCl and uranium concentrations as well as the Fe(III) content are presented.
Ion Beam Deposition of Diamond-Like Coatings
Authors: Greenwald Anton C. , Hirvonen James K. , Jaggi Narendra K. 
Published: March 2011

ABSTRACTMass analyzed and non-mass analyzed carbon ion beams were used to deposit coatings on polished silicon wafers. Extremely, hard dense coatings that are structurally similar to i-carbon as determined by Ramon spectroscopy were achieved with high current beams of methane and argon. Residual contaminants of oxygen and nitrogen were minimized.
Diffusion in Irradiated AgZn Alloys using Defect-Concentration Dependent Migration Energies
Authors: Andreadis T. D. , Rosen M. , Eridon J. M. 
Published: March 2011

ABSTRACTConcentration dependent migration and reaction migration energies, calculated with the molecular dynamics code DYNAMD using Embedded Atom Method Potentials, were inserted into the appropriate diffusion and rate coefficients. The time and space evolution of the concentration of interstitials, vacancies, Zn impurity, interstitial-inpurity, aid vacancy-impurity complexes was calculated for an irradiated AgZn alloy in the framework of the approach presented in Johnson and Lam. A significant effect on defect segregation and profiles was found.
Amorphous and Metastable Phase Formation in Systems with Positive Heats of Mixing using High-Rate Sputter Deposition
Authors: Rizzo H. F. , Echeverria A. , Massalski T. B. , Baxi H. 
Published: March 2011

ABSTRACTThe triode sputtering technique and a “split-target” arrangement were used to produce metastable crystalline and amorphous phases in the Cu-W, Mo-Cu, Ag-Fe, Ag-Cu, Pu-Ta and Pu-V systems. These systems all exhibit liquid and solid immiscibility and have positive heats of mixing and atomic radii that differ by at least 10%. The sputtered coatings, whose thickness varied between 25 and 200 microns, were formed at deposition rates between 35 and 200 Å/s. They were characterized using x-ray diffraction, TEM, microprobe, microhardness, and DSC techniques. The observed amorphous and metastable solid solution phases are discussed in terms of predicated heats of formation for these phases using Miedema's thermodynamic approximations [1] that include chemical, elastic, and structural contributions. Differences in compositional ranges observed by high rate sputter deposition compared to other vapor deposition techniques (e.g., coevaporation) appeared to arise as a result of processes that occur during deposition or immediately following deposition.
Composition- and Temperature-Dependence of Ion Mixing in Amorphous Si/Ge Artificial Multilayers
Authors: Park B. , Spaepen F. , Poate J. M. , Priolo F. , Jacobson D. C. 
Published: March 2011

ABSTRACTAmorphous Si/Ge artificial multilayers with a repeat length of around 60A have been partially mixed with 1.5 MeV Ar+ ions at temperatures in the range 77–673K. The change in the intensity of the first X-ray diffraction peak resulting from the composition modulation is used to determine the mixing lengths. The diffusive component of the square of the mixing length, at a given dose, is independent of the dose rate and has an Arrhenius-type temperature dependence, with activation enthalpies between 0.19 and 0.22 eV, depending on the average composition.
Ge Heteroepitaxy on (100) Si Substrates by Ion Assisted Deposition
Authors: Holesinger T. G. , Heim D. J. , Lakin K. M. , Shanks H. R. 
Published: March 2011

ABSTRACTGe films have been grown by ion-assisted deposition on Si(100) substrates. Initial studies were conducted to determine the growth and morphology of Ge using a modified crucible arrangement and ionization chamber. It was observed that a narrow substrate temperature range existed for the deposition of smooth Ge films without ion assistance. Ionization and acceleration appear to induce additional damage to the film without improving crystalline quality.
Phase Stability of Ni2Al3under Electron Irradiation
Authors: Kenik E. A. , Nastasi M. 
Published: March 2011

ABSTRACTIn-situ electron irradiations at 200, 300, and 1000 keV have been performed on Ni2Al3at 100 and 300 K. At low doses, the Ni2Al3partially disorders to a B2 structure with a lattice parameter of 0.284 nm, close to that extrapolated for β-NiAl at 60 at.% Al, the Ni2Al3composition. The electron dose required to disorder the Ni2Al3decreased with increasing accelerating voltage and possibly with decreasing temperature. At high doses, precipitation of aluminum from the B2 matrix occurs, along with radiation-induced sputtering and radiation-induced segregation. Lattice parameter changes for the B2 structure observed during irradiation are explained in terms of the compositional dependence of the lattice parameter of β-NiAl. The B2 structure remains stable to a dose of 6 × 1028electrons/m2, with no amorphization detected.
Amorphization of Zr3Al by Hydrogenation and Subsequent Electron Irradiation
Authors: Meng W. J. , Koike J. , Okamoto P. R. , Rehn L. E. 
Published: March 2011

ABSTRACT1-MeV electron irradiation of hydrogenated Zr3Al (Zr3AlH0.96) at 10K is studied. A more than 20 fold reduction in the critical dose required for complete amorphization is observed for the hydrogenated specimen as compared to the un-hydrogenated Zr3Al under identical irradiation conditions.
Microstructures in Sic and Si3N4Implanted with Ti and Heat Treated
Authors: Vardiman R. G. 
Published: March 2011

ABSTRACTBulk SiC and Si3N4have been implanted with Ti at room temperature, and subsequently vacuum heat treated between 800° and 1100°C. All specimens were backthinned by ion milling and examined in TEM. SiC becomes amorphous on implantion, and develops a fine dispersion of TiC precipitates up to 800°C. At 900°C recrystallization has begun, possibly nucleated by the TiC particles. Si3N4shows fine TiN particles in an amorphous matrix even as implanted. This structure is retained up to 900°C. At 1000°C, regrowth of the Si3N4apparently from the substrate begins, and the TiN particles also grow as large as 200nm.
Tribology of Amorphous Alloys Formed With Ion Beams
Authors: Follstaedt D. M. , Knapp J. A. , Pope L. E. 
Published: March 2011

ABSTRACTThe changes in friction and wear properties (i.e., tribology) of steels due to thin surface alloys formed by ion beams are surveyed, and considered in light of their microstructures. Amorphous alloys containing both Ti and C are found to give superior performance in comparison to alloys with N, B, C, P or Ti. All the amorphous layers reduce friction, but the duration of benefits and wear resistance at high loads vary with composition. By examining similar amorphous alloys with Ti alone or C alone, the critical roles played by each in resisting wear are demonstrated. Amorphous alloys with Ti and C appear to be quite hard.