bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Degradation of Cellulose in the Near Field of a Radioactive Waste Repository
Authors: Greenfield B.F. , Hurdus M.H. , Pilkington N.J. , Spindler M.W. , Williams S.J. 
Published: March 2011

ABSTRACTUK Nirex Ltd is seeking to develop a deep underground repository for the disposal of solid low- and intermediate-level radioactive wastes in the UK. The Nirex Safety Assessment Research Programme (NSARP) comprises scientific research to support the post-closure performance assessment of the repository. One of the investigations carried out by AEA Technology under the NSARP is the investigation of the formation of water-soluble complexants from the degradation of the solid organic polymers and cellulosic materials present in such wastes. The influence of these complexants on the solubility and sorption of a number of radionuclides is also being investigated by a combination of experimental measurements and thermodynamic modelling. Under the alkaline, anaerobic conditions representative of the near field of the repository, cellulose has previously been shown to degrade to yield soluble products which enhance the solubilities and reduce the sorption of several radionuclides. As part of this investigation, cellulose was chemically degraded under conditions similar to those expected in the near field and the leachate analysed. Separation of the products by HPLC gave direct identification of 2-C-(hydroxymethyl)-3-deoxy-D-erythro-pentonic (isosaccharinic) acid as one of the degradation products. More tentative assignments were made for glycolic, formic, lactic and acetic acids. A comparison was made with the degradation products suggested in the literature. The possible mechanisms and extent of cellulose degradation are discussed, as well as the factors affecting its degradation in the near field. The sorption of plutonium on to cement from a leachate produced under alkaline, anaerobic conditions is reported.
Effects of Recrystallization on Time Variant Sorption of Radionuclides onto Steel Corrosion Products
Authors: Smith Robert W. , Walton John C. , Rahman Masudur 
Published: March 2011

ABSTRACTCorrosion products resulting from the oxidation of steel containers and iron-containing waste can alter the local geochemical environment in radioactive waste disposal vaults and trenches. In addition, corrosion products can enhance the retention of radionuclides by providing a highly sorptive media. Initial hydrous corrosion products are poorly crystalline with large surface area, high sorption capacity, and large Kds. Over time, corrosion products recrystallize by step-wise dehydration to phases with significantly smaller surface areas. The decreased surface area results in decreased sorption and the potential for remobilization of previously sorbed radionuclides. The impact of time-dependent variation in sorption on radionuclide transport is a complex function of the rate of recrystallization and the radionuclide half-life.A mathematical model has been developed, which coupling mass transport with corrosion product recrystallization and equilibrium sorption of radionuclides. The model is applied release of radionuclides with a range of half-lives (year to 100,000s of years) from radioactive waste disposal facilities to illustrate the significance of corrosion product recrystallization on release.
Thermodynamics of Ion-Exchange Between Na+/Sr2+ Solutions and the Zeolite Mineral Cinoptilolite
Authors: Pabalan Roberto T. , Paul Bertetti F. 
Published: March 2011

ABSTRACTIon-exchange experiments were conducted at 25 °C between the zeolite mineral clinoptilolite and aqueous solutions of varying equivalent ratios of Na+ and Sr2+ and total concentrations of 0.005, 0.05, and 0.5 N. The experiments were designed to investigate the effects of changes in total solution concentration and in the relative concentrations of exchangeable cations on the following ion-exchange equilibrium:Sr2+ + 2NaZ ⇄ SrZ2 + 2Na+Using the isotherm data at 0.05 N solution concentration, a thermodynamic model for the ion-exchange reaction was derived using a Margules formulation for the activity coefficients of zeolite components and the Pitzer ion-interaction approach for activity coefficients of aqueous ions. The results of the forward experiments showed that the ion-exchange isotherm strongly depends on the total solution concentration. Additional experiments demonstrated that the above ion-exchange reaction is reversible. The derived equilibrium constant, K, and Gibbs energy of ion-exchange, ΔG°, are equal to 0.321±0.021 and 2,820±170 J/mol, respectively.Using thermodynamic parameters derived from the 0.05 N isotherm experiment, the model was used to predict isotherm values at 0.005 and 0.5 N, which showed excellent agreement with measured data. Because the thermodynamic model used in this study can be easily extended to ternary and more complicated mixtures, it may be useful for modeling ion-exchange equilibria in multicomponent geochemical systems.
Technical Workshop on Near-Field Performance Assessment of High-Level Waste Disposal
Authors: Apted Michael , Andersson Kjell 
Published: March 2011

ABSTRACTAn international Workshop was conducted to discuss the present state of modelling of near-field performance of high-level waste repositories, with emphasis on the conceptual and mathematical models for source-term calculations. The Workshop was based on an international survey and review of this topic by the authors. Technical position papers developed by the participants are summarized here. A Proceedings of the Workshop, including the full position papers and the survey and review document, are to be published by Nuclear Energy Agency by the end of 1993.
Testing Long-Term Predictions from Hydro-Geochemical Models
Authors: Glassley William E. , Bruton Carol J. , Bourcier William L. 
Published: March 2011

ABSTRACTThermally induced flow of liquid water and water vapor at the potential repository site at Yucca Mountain, Nevada, will extend hundreds of meters away from the repository edge. The resultant transfer of heat and mass will sufficiently perturb the ambient conditions such that a variety of mineralogical and chemical reactions will occur that may modify hydrological properties. The consequences of this “coupling” of geochemical and hydrological processes will vary through time, and will occur to different degrees in four regimes (T < Tboiling; T = Tboiling; T > T boiling; cooling) that will develop within the repository block. The dominant processes in the regimes differ, and reflect the local balance between: 1) kinetics and equilibrium; 2) dissolution and precipitation; 3) evaporation and boiling; and 4) fluid flow in matrix and fractures. Simulations were conducted of the evolution of these regimes, using laboratory derived kinetics and thermodynamic data, and site specific mineralogical and hydrological properties. These simulations identify regions where chemical and mineralogical equilibrium is likely to be achieved, and where net changes in hydrological properties will be concentrated. Tests of the results of these simulations have been initiated using field data from the Taupo Volcanic Zone, New Zealand. A preliminary series of calculations suggest that relative changes in porosity of as much as ± 20% to 30% may be possible for rocks with an initial porosity of 10%.
The Modification and Application of the Geochemical Modelling Code CHEQMATE to Simulate Transport and Chemical Processes within Fractured Media
Authors: Chambers A. V. , Smith A.C. 
Published: March 2011

ABSTRACTThe UK current plans for a repository for the disposal of intermediate-level radioactive waste involve the use of a cementitious backfill within the repository vaults. Radionuclide transport could be concentrated within cracks that may form in the cement, or in fractures within the rock surrounding the repository. A version of CHEQMATE (CHemical EQuilibrium with Migration And Transport Equations) that includes a representation of transport through fractured media has been developed. This paper describes modifications of the code, to allow simulation of transport through either a single fracture, or, by adopting a continuum approach to represent fracture distribution, through multiple fractures. Successful verification of the modified program against analytical solutions for transport through fractured rock and cracked cementitious media is presented. An application of the modified program to study the evolution of the aqueous chemistry within a repository vault containing a single fracture through the cementitious backfill is also discussed.
Performance Assessment Modeling of a Multi-Purpose Container
Authors: Bullen Daniel B. 
Published: March 2011

ABSTRACTA mathematical model to predict the cumulative failure distribution for the engineered barrier system employed in a deep geologic disposal facility as a function of container design and near-field environmental conditions has been developed. The model employs Weibull and exponential distributions to describe cumulative container failures as a function of time. Parameter values employed in the model are based upon simple, time-dependent, mechanistic models and relevant corrosion data, which describe failure of individual components of the container as a function of environmental conditions.Recent developments in container design for the Yucca Mountain site center on the possible deployment of Multi-Purpose Containers (MPC). These containers will be designed and constructed to serve as transport casks, interim storage containers, and disposal containers. The current container performance assessment model is applied to evaluate the long-term performance of various MPC designs under the areal power density and heat transfer regimes expected in the Yucca Mountain environment. This model has previously been employed to describe the performance of the container as one part of a risk-based performance assessment of the Yucca Mountain site.The relative importance of container design, areal power density, and dominant heat transfer mode on predicted MPC performance is demonstrated through comparison of the cumulative container failure distributions for each MPC design when exposed to expected Yucca Mountain environmental conditions.
Development of Modelling Criteria for Predicting Lifetimes of Titanium Nuclear Vaste Containers
Authors: Shoesmith D. W. , Ikeda B. M. 
Published: March 2011

ABSTRACTThe parameters that must be known if the extent of damage due to the crevice corrosion of Grade-2 titanium waste containers is to be predicted are discussed. These parameters include the kinetics of crevice propagation as a function of temperature and oxygen concentration, the critical values of temperature and oxygen concentration for which repassivation occurs, the rate of hydrogen absorption by the metal under crevice corrosion conditions, and the threshold value of absorbed hydrogen concentration above which the material may be susceptible to hydrogen-induced cracking. The results of experiments to measure these parameters are briefly summarized, and their significance as modelling parameters or criteria are discussed.
Modelling the Effects of Evolving Redox Conditions on the Corrosion of Copper Containers
Authors: King F. , LeNeveu D. M. , Jobe D. J. 
Published: March 2011

ABSTRACTThe corrosive environment around the containers in a Canadian nuclear fuel waste disposal vault will change over time from “warm and oxidizing” to “cool and anoxic”. As the conditions change, so too will the corrosion behaviour of the containers. For copper containers, uniform corrosion and, possibly, pitting will occur during the initial aggressive phase, to be replaced by slow uniform corrosion during the long-term anoxic period.The corrosion behaviour of copper has been studied over a range of conditions representing all phases in the evolution of the vault environment. The results of these studies are summarized and used to illustrate how a model can be developed to predict the corrosion behaviour and container lifetimes over long periods of time. Lifetimes in excess of 106 a are predicted for 25-mm-thick. copper containers under Canadian disposal conditions.
Perspectives on Performance Assessment and High-Level Waste Glass in a Geologic Repository
Authors: Mcgrail B.P. , Engel D.W. 
Published: March 2011

ABSTRACTThe design and analysis of waste package and engineered systems for geologic disposal of radioactive wastes are being conducted in most countries with so-called performance assessment models and associated computer codes that solve the governing equations. The models range in complexity from simple 1-D analytical solutions to multidimensional, multicomponent reactive transport models implemented in large computer codes. Borosilicate waste glass is certainly the most studied and probably best understood waste form that has been developed for encapsulating high-level waste. Reasonably good models are available that describe the reaction kinetics and transformation of the glass into a paragenetic sequence of more stable secondary phases. Given the broad range of computational tools and extensive database on glass/water reactions that is available, it is surprising that little progress has been made to link these models and data in a comprehensive performance assessment of waste glass in a repository setting. In this paper, we will explore reasons why this linkage has not been developed, give several examples illustrating the importance of doing so, and illustrate an approach to accomplish such a linkage.
Flexural Strength and Fracture Properties of a Fly Ash Blended Cement
Authors: Chanda S. , Bailey J. E. 
Published: March 2011

AbstractThe flexural strength, fracture toughness and Young's Modulus of an ordinary Portland cement plus 25 wt% fly ash paste (FACP) were compared with those of a control paste (HCP) at times ranging from one day to one year. At comparatively early times these properties develop more slowly in FACP. However, at comparatively late ages, e.g. ten months, FACP showed improvements over HCP for all of these properties. A complicating factor is that for both FACP and HCP, the flexural strength and toughness show maxima and the “crossover” times for the various properties differ. This paper analyses these results in terms of the observed fracture mechanism for HCP by taking into account the changes brought about in the microstructure of FACP, due to the incorporation of fly ash.
Properties and Potential Uses of the Products Resulting from Bed Combustion of Coal Washery Wastes the Fluidised
Authors: Montgomery Denis G. 
Published: March 2011

AbstractA fluidised bed combustion (FBC) process has been developed to a stage that both coarse rejects and tailings from coal washery plants may be successfully combusted. During the combustion process excess heat is produced, and the products from the process, spent rejects and primary and secondary cyclone fines, are reduced in volume compared to the input material. Results of preliminary investigations into the properties of the spent rejects and cyclone fines are reported. A program has been initiated to investigate and evaluate the potential uses of the FBC process, including the use of the products in stabilised and unstabilised forms in road construction, as a material suitable for the construction of embankments, and in lean concrete mixes either as an aggregate or as a pozzolan.The characteristics of the FBC products are compared, where appropriate, with those of the unburnt coal washery wastes.
Utilization of Fly Ash in Roadbed Stabilization: Some Examples of Western U.S. Experience
Authors: Manz Oscar E. , Manz Bradley A. 
Published: March 2011

AbstractIn contrast with pozzolanic bituminous fly ashes, the western American lignite and subbituminous fly ashes are both pozzolanic and cementitious. During the last three years, there has been much research and actual use of western ash alone and with lime or cement for roadbed stabilization. In contrast with lime stabilization which only applies to clay, the western ashes can be used to stabilize clay as well as silty and granular soils. Fly ash is moving from the experimental to standard alternative for pavement in many states. Some examples of western U.S. experience will be presented.
Utilization of Fly Ash in Oil and Gas Well Cementing Applications
Authors: Sarkar Asok K. 
Published: March 2011

AbstractDuring cementing operations, the hydrostatic pressure of the cement slurry column is utilized to control the reservoir pressure. However, when the well extends through weak formations, it is often necessary to lighten the hydrostatic pressure of the slurry by lowering the density to avoid hydraulically fracturing the reservoir rock. Densities of cement slurries can be lowered by adding pozzolanic lightweight additives such as fly ash. Fly ashes have found utility in numerous oil and gas well cementing applications, namely: 1) fly ash can be dry-blended with regular Portland cements or hydrated lime for use in primary cementing; 2) lightweight cement compositions can be formulated by adding lime and finely ground quartz to fly ash/cement mixtures; and 3) an ultralight-weight pozzolanic microsphere cement, with densities as low as 0.96–1.64 g/cm3, can be formulated by blending Portland cements with hollow microspheres isolated from fly ash. This paper discusses the physical and chemical properties of each of these cement slurries, along with their relative advantages and disadvantages. Areas of future research are also discussed.
Comparative Bconomics of Several Alternatives for Bulk Utilization of Fly Ash and Coal Gsification Ash
Authors: Severson D. E. , Manz O. E. , Mitchell N. J. 
Published: March 2011

AbstrctFly ash and gasification ash have been evaluated economically for the following uses: partial replacement of Portland cement; mineral wool; blended cement; Sulfurcrete®, high flexural strength ceramic products; ash to upgrade roads; glazed ceramic wall tile; and unglazed floor tile. The ash evaluated is a high-calcium, high-sodium material derived from the Beulah-Zap lignite mined in the Beulah region of North Dakota. Of the uses examined, concrete replacement provided an 8.0% cost saving, blended cement 37.3%, high flexural strength ceramics 52.8%, ash in road construction 44.4%, and wall tile 5.2%. Mineral wool had no replacement savings calculated because blast furnace slag is not available locally to provide a consistent basis. Sulfurcrete® did not provide a cost saving over concrete but its use life and properties are sufficiently different from those of concrete to justify use in some applications, provided that the raw materials are readily available.
Transmitted and Reflected Visible Light Microscopy of Two Bituminous Fly Ashes
Authors: Biggs Donald L. , Bruns Joseph J. 
Published: March 2011

AbstractFly ashes of high magnetic content taken from two midwestern power plants were examined to determine the mineralogy of the magnetic and nonmagnetic fractions. Fly ash spheres from the magnetic fraction are predominantly composed of ferrite spinel, hematite and silicate glass. The hematite appears to be a replacement product of the original ferrite spinel. Nonmagnetic phases include mullite, lime, small amounts of hematite and silicate glass. Quartz morphology indicates that it did not fuse in the furnace. Mullite and lime have morphologies indicative of crystallization in the furnace. Hematite is bonded to the nonmagnetic particles or as a complete replacement of ferrite spinel spheres.
Mobility of Organic and Inorganic Constituents from Energy and Combustion-Related Wastes Under Codisposal Conditions
Authors: Maskarinec M. P. , Francis C. W. , Goyert J. C. 
Published: March 2011

AbstractThe criteria for determining toxicity of a solid waste under the Resource Conservation and Recovery Act (RCRA) are the levels of NIPOW contaminants as determined using the extraction procedure (EPA-EP). This procedure is predicated on a scenario of disposal of the solid waste in a municipal landfill, resulting in contact with an acidic leaching medium. The scenario includes a 95/5 municipal waste/industrial waste ratio. The experimental definition of the leaching rates of various contaminants under the conditions of this scenario is the object of this work.The experimental design included the use of large scale lysimeters (1.8 M in diameter × 3.6 M height) packed with 1.5 metric tons of municipal waste. A flow rate of -6.5 1/day of distilled water was added to the lysimeters for the generation of municipal waste leachate (MWL). The MWL was used to leach a variety of industrial wastes, including resource recovery ashes, an API separator sludge/incinerator ash mixture, and a coking plant wastewater treatment sludge. The resulting leachates were analyzed for both inorganic and organic constituents.Inorganic constituents showed two distinct types of leaching behavior. Freely soluble elements (B, Na, Ca, etc.) gave leaching curves which showed exponential declines. Acid-soluble elements (Ni, Zn) eluted as “peaks” as the pH of the leachate decreased. Organic constituents gave leaching curves which were dependent on solubility: either an exponential decline (freely soluble compounds) or a relatively flat curve at or near the solubility limit. The availability of this data base has allowed the development of a laboratory extraction procedure for the prediction of contaminant migration in municipal landfills.
Technical Review of the Energy Authority Coal Waste Artificial Reef Program (C-WARP)
Authors: Hornibrook C. A. , Parker J. H. 
Published: March 2011

AbstractThe objective of the Coal Waste Artificial Reef Program (C-WARP) is to explore the technical feasibility and environmental effects of ocean disposal of stabilized fly ash and flue gas desulfurization scrubber sludge from power plants. This demonstration program has involved the construction of an artificial reef in the Atlantic Ocean off Long Island, New York using 15,000 blocks of these stabilized coal waste materials.In determinine the environmental acceptability of using stabilized copl waste blocks to build artificial reefs in the ocean, the two key considerations are whether the blocks will maintain their structural integrity, and whether the blocks will be a source of potentially toxic elements to affect the biological community. Analysis of the chemical composition of the blocks and an understanding of the processes occurring in them is necessary to address these questions. Therefore, this paper will focus on changes in chemical composition of blocks (e.g., Ca flux, Mg enrichment, and surface layer elemental concentrations) and compatibility of the blocks in terms of the physical and biological data collected during three years of monitoring.
Electrokinetic Phenomena and Surface Characteristics of Fly Ash Particles
Authors: Malek R. I. A. , Roy D. M. 
Published: March 2011

AbstractThe zeta-potentials of two fly ashes were studied (high-calcium and low-calcium). It was found that they possess a point of charge reversal at pH = 10.5 to 12. The point of zero charge (low-calcium fly ash) was found to be at pH = 5. Furthermore, it shifted to more acidic values after the fly ash is aged in several calcium-containing solutions. The surficial changes that could happen when mixing fly ashes with cement and concrete were further evaluated by aging fly ashes in different solutions: Ca(OH)2, CaSO4·2H2O, NaOH and water solutions. Information from analyses for different ionic species in the solutions and characterization of the solid residues (XRD and SEM) was used in tentative explanations for the different behavior of the two types of fly ash in cementitious mixtures and concrete.