66 research outputs found
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Recapitalizing EMSL: Meeting Future Science and Technology Challenges
EMSL, located in Richland, Washington, is a national scientific user facility operated for the U.S. Department of Energy (DOE) by the Pacific Northwest National Laboratory. The vision that directed the development of EMSL as a problem-solving environment for environmental molecular science has led to significant scientific progress in many areas ranging from subsurface science to atmospheric sciences, and from biochemistry to catalysis. Our scientific staff and users are recognized nationally and internationally for their significant contributions to solving challenging scientific problems. We have explored new scientific frontiers and organized a vibrant and diverse user community in support of our mission as a national scientific user facility that provides integrated experimental and computational resources in the environmental molecular sciences. Users from around the world - from academia to industry and national laboratories to international research organizations - use the resources of EMSL because of the quality of science that we enable
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Thermodynamic Modeling of Hanford Waste Tank 241-AN-107
The high level waste storage double-shell tanks at the Hanford site are highly basic. The high basicity is a key factor in controlling the chemical behavior of different components of the waste and in influencing the corrosion rate of the carbon steel primary tanks. However, the introduction of atmospheric CO2 can act to reduce the pH of the tank wastes over time and possibly alter the corrosion rate of the carbon steel tanks. In order to at least partially address this issue for waste tank 241-AN-107, thermodynamic modeling calculations were performed to predict the changes in pH and carbonate concentration that could occur as CO2 is absorbed from the atmosphere. The calculations extended to complete equilibrium with the partial pressure of CO2 in the atmosphere (i.e. pCO2 = 10-3.5 atm). Simulations were performed for both the “upper” segments of tank 241-AN-107, which have been influenced by the introduction of high concentrations of NaOH to the supernatant, and for the “lower” segments where the salt cake/interstitial liquid have not been substantially altered by the introduction of base concentration
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Chemical Speciation of Americium, Curium and Selected Tetravalent Actinides in High Level Waste
Large volumes of high-level waste (HLW) currently stored in tanks at DOE sites contain both sludges and supernatants. The sludges are composed of insoluble precipitates of actinides, radioactive fission products, and nonradioactive components. The supernatants are alkaline carbonate solutions, which can contain soluble actinides, fission products, metal ions, and high concentrations of major electrolytes including sodium hydroxide, nitrate, nitrite, phosphate, carbonate, aluminate, sulfate, and organic complexants. The organic complexants include several compounds that can form strong aqueous complexes with actinide species and fission products including ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), citrate, glycolate, gluconate, and degradation products, formate and oxalate
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Thermodynamics and Complexation Reactions of Anionic Silicate Species
Highly basic tank wastes contain several important radionuclides, including {sup 90}Sr, {sup 99}Tc, and {sup 60}Co as well as actinide elements (isotopes of U, Pu and Am). A fraction of these wastes are known to have leaked into the vadose zone at the Hanford Site. Upon entering the sediments in the vadose zone, such highly basic solutions dissolve concentrations of silica from the silica and aluminosilicate minerals present in subsurface. These dissolution reactions alter the chemical composition of the leaking solutions, transforming them from highly basic (as high as 2 M NaOH) solution into a pore solution with dissolved silica and significantly reduced pH. This moderately basic (pH 9 to 10), high-silica solution has the potential to complex radionuclides and promote migration through the subsurface. This path of radionuclide migration currently is not a recognized transport mode in the factors that are modeled for radionuclide transport through the vadose zone beneath leaking tanks. The goal of this project is to ascertain the free monosilicic acid concentration, and the degree of polymerization as a function of pH and total concentration of silicate ions, and to use this data to measure the interaction of radionuclides of Co(II), Sr(II), Nd(III), Eu(III), Am(III), U(VI) and Th(IV) with the ionic silicate
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Application of Pitzer's Equations for Modeling the Aqueous Thermodynamics of Actinide Species in Natural Waters : A Review
A review of the applicability of Pitzer's equations to the aqueous thermodynamics of actinide species in natural waters is presented. This review includes a brief historical perspective on the application of Pitzer's equations to actinides, information on the difficulties and complexities of studying and modeling the different actinide oxidation states, and a discussion of the use of chemical analogs for different actinide oxidation states. included are tables of Pitzer ion-interaction parameters and associated standard state equilibrium constants for each actinide oxidation state. These data allow the modeling of the aqueous thermodynamics of different actinide oxidation states to high ionic strength
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The Aqueous Thermodynamics and Complexation Reactions of Anionic Silica and Uranium Species to High Concentration.
Highly basic tank wastes contain several important radionuclides, including 90Sr, 99Tc, and 60Co, as well as actinide elements (i.e., isotopes of U, Pu, and Am). These highly basic tank wastes are known to have leaked into the vadose zone at the Hanford Site. In particular, wastes from the bismuth phosphate process contained very high concentrations of U as well as carbonate, phosphate, nitrate, and other components (AEC 1951) and these solutions have leaked into the subsurface at the Hanford site. The tanks containing the bismuth phosphate wastes were frequently saturated with respect to the solid phases of these components [e.g., NaUO2PO4(c) and Na4UO2(CO3)3(c)]. These solids were referred to as ''hard sludge'' (Na4UO2(CO3)3(c)) and ?soft sludge? [NaUO2PO4(c)] because of their different crystal forms. The preliminary studies of the solubility of these solids in tank wastes (AEC 1951) indicate that aqueous U carbonate complexes dominate the solution chemistry of uranium even when the equilibrium solid was NaUO2PO4. Thus there was a need to develop an accurate thermodynamic model for the solubility of potentially important U(VI) phosphate and carbonate phases as well as to develop a model for the uranium carbonate complexes valid to high ionic strength. In this project we are examining the solubility of these important solid phases as well as the aqueous thermodynamics of U(VI) species under strongly basic conditions. Also included is a description of our efforts to include these thermodynamic models in the reactive transport and residual leaching models being used at the Hanford site and elsewhere
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Chemical Speciation of Strontium, Americium, and Curium in High Level Waste: Predictive Modeling of Phase Partitioning During Tank Processing
In this research program, Pacific Northwest National Laboratory (PNNL) and Florida State University (FSU) are investigating the speciation of strontium and americium/curium in the presence of selected organic chelating agents (ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl) aethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), and iminodiacetic acid (IDA)) over ranges of hydroxide, carbonate, ionic strength, and competing metal ion concentrations present in high-level waste tanks. The project is composed of integrated research tasks that approach the problem of chemical speciation using macroscopic thermodynamic measurements of metal-ligand competition reactions, molecular modeling studies to identify structures or complexes of unusual stability, and mass spectrometry measurements of complex charge/mass ratio that can be applied to mixed metal-chelate systems. This fundamental information is then used to develop thermodynamic models, which allow the prediction of changes in chemical speciation and solubility that can occur in response to changes in tank processing conditions. In this way, we can develop new approaches that address fundamental problems in aqueous speciation and at the same time provide useful and practical information needed for tank processing
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Technetium Chemistry in HLW
Tc contamination is found within the DOE complex at those sites whose mission involved extraction of plutonium from irradiated uranium fuel or isotopic enrichment of uranium. At the Hanford Site, chemical separations and extraction processes generated large amounts of high level and transuranic wastes that are currently stored in underground tanks. The waste from these extraction processes is currently stored in underground High Level Waste (HLW) tanks. However, the chemistry of the HLW in any given tank is greatly complicated by repeated efforts to reduce volume and recover isotopes. These processes ultimately resulted in mixing of waste streams from different processes. As a result, the chemistry and the fate of Tc in HLW tanks are not well understood. This lack of understanding has been made evident in the failed efforts to leach Tc from sludge and to remove Tc from supernatants prior to immobilization. Although recent interest in Tc chemistry has shifted from pretreatment chemistry to waste residuals, both needs are served by a fundamental understanding of Tc chemistry
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The Development of New User Research Capabilities in Environmental Molecular Science: Workshop Report
On August 1, and 2, 2006, 104 scientists representing 40 institutions including 24 Universities and 5 National Laboratories gathered at the W.R. Wiley Environmental Molecular Sciences Laboratory, a National scientific user facility, to outline important science challenges for the next decade and identify major capabilities needed to pursue advanced research in the environmental molecular sciences. EMSL’s four science themes served as the framework for the workshop. The four science themes are 1) Biological Interactions and Interfaces, 2) Geochemistry/Biogeochemistry and Surface Science, 3) Atmospheric Aerosol Chemistry, and 4) Science of Interfacial Phenomena
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