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314 results on '"Denecke, M. A."'

109. An EXAFS Study of Uranium (VI) Sorption onto Silica Gel and Ferrihydrite

Author

Reich, T., Moll, H., Arnold, T., Denecke, M. A., Hennig, C., Geipel, G., Bernhard, G., Nitsche, H., Allen, P. G., Bucher, J. J., Edelstein, N. M., Shuh, D. K., Reich, T., Moll, H., Arnold, T., Denecke, M. A., Hennig, C., Geipel, G., Bernhard, G., Nitsche, H., Allen, P. G., Bucher, J. J., Edelstein, N. M., and Shuh, D. K.

Published
1998

112. Nuclear waste repository research at the micro- to nanoscale.

Author

Schäfer, T. and Denecke, M. A.

Subjects
*RADIOACTIVE wastes, *SYNCHROTRON radiation, *RADIOACTIVE waste disposal, *ACTINIDE elements, *RHEOLOGY, *CONFOCAL microscopy
Abstract

Micro- and nano-focused synchrotron radiation techniques to investigate determinant processes in contaminant transport in geological media are becoming especially an increasingly used tool in nuclear waste disposal research. There are a number of reasons for this but primarily they are driven by the need to characterize actinide speciation localized in components of heterogeneous natural systems. We summarize some of the recent research conducted by researchers of the Institute of Nuclear Waste Disposal (INE) at the Karlsruhe Institute of Technology using micro- and nano-focused X-ray beams for characterization of colloids and their interaction with minerals and of elemental and phase distributions in potential repository host rocks and actinide speciation in a repository natural analogues sample. Such investigations are prerequisite to ensuring reliable assessment of the long term radiological safety for proposed nuclear waste disposal sites. [ABSTRACT FROM AUTHOR]

Published
2010
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115. ROBL - a CRG Beamline for Radiochemistry and Materials Research at the ESRF

Author

Matz, W., Schell, N., Bernhard, G., Schlenk, R., Pröhl, D., Funke, H., Betzl, M., Brendler, V., Claußner, J., Dienel, S., Eichhorn, F., Hüttig, G., Krug, H., Neumann, W., Nitsche, H., Oehme, W., Prokert, F., Reich, T., Reichel, P., Strauch, U., Denecke, M. A., Matz, W., Schell, N., Bernhard, G., Schlenk, R., Pröhl, D., Funke, H., Betzl, M., Brendler, V., Claußner, J., Dienel, S., Eichhorn, F., Hüttig, G., Krug, H., Neumann, W., Nitsche, H., Oehme, W., Prokert, F., Reich, T., Reichel, P., Strauch, U., and Denecke, M. A.

Published
1997

117. Chemical Speciation Studies of Radionuclides by XAFS

Author

Allen, P. G., Shuh, D. K., Bucher, J. J., Edelstein, N. M., Reich, T., Denecke, M. A., Nitsche, H., Allen, P. G., Shuh, D. K., Bucher, J. J., Edelstein, N. M., Reich, T., Denecke, M. A., and Nitsche, H.

Published
1997

122. Characterization of hydrous uranyl silicate by EXAFS

Author

Reich, T., Moll, H., Denecke, M. A., Geipel, G., Bernhard, G., Nitsche, H., Allen, P. G., Bucher, J. J., Kaltsoyannis, N., Edelstein, N. M., Shuh, D. K., Reich, T., Moll, H., Denecke, M. A., Geipel, G., Bernhard, G., Nitsche, H., Allen, P. G., Bucher, J. J., Kaltsoyannis, N., Edelstein, N. M., and Shuh, D. K.

Abstract

Extended X-ray absorption fine structure (EXAFS) analysis was performed on uranyl orthosilicate, (UO2)(2)SiO4 . 2H(2)O, and uranium(VI) sorbed onto silicic acid and silica gel. Uranyl orthosilicate was investigated as a reference for EXAFS studies of similar but non-crystalline uranium, oxygen, and silicon containing samples. Fitting the EXAFS spectrum yields the following distances for the first four coordination shells of uranium: U-O-ax = 1.79 Angstrom, U-O-eq = 2.38 Angstrom, U-Si = 3.16 Angstrom, and U-U = 3.88 Angstrom. These values agree well with results from single-crystal X-ray diffraction (XRD) measurements. Structural parameters of light elements such as oxygen and silicon at distances greater than 3.5 Angstrom could not he detected without a priori knowledge of their presence. The EXAFS spectra of uranyl species sorbed at pH 4 onto silicic acid and silica gel are identical indicating similar uranyl coordination. The main characteristic of the surface species are two well-separated oxygen coordination shells in the equatorial uranyl plane at 2.27 and 2.50 Angstrom. The results of the EXAFS analysis favor the interpretation of the uranyl surface species as an inner-sphere, mononuclear, bidentate complex.

Published
1996

127. Concentration driven phase transitions in multiphase porous media with application to methane oxidation in landfill cover layers.

Author

Ricken, T., Sindern, A., Bluhm, J., Widmann, R., Denecke, M., Gehrke, T., and Schmidt, T.C.

Subjects
MANURE gases, METHANE, LANDFILLS, ALKANES, PHASE transitions
Abstract

This study focuses on a formulation within the theory of porus media for continuum multicomponent modeling of bacterial driven methane oxidation in a porous landfill cover layer which consists of a porous solid matrix (soil and bacteria) saturated by a liquid (water) and gas phase. The solid, liquid, and gas phases are considered as immiscible constituents occupying spatially their individual volume fraction. However, the gas phase is composed of three components, namely methane (CH4), oxygen (O2), and carbon dioxide (CO2). A thermodynamically consistent constitutive framework is derived by evaluating the entropy inequality on the basis of Coleman and Noll [8], which results in constitutive relations for the constituent stress and pressure states, interaction forces, and mass exchanges. For the final set of process variables of the derived finite element calculation concept we consider the displacement of the solid matrix, the partial hydrostatic gas pressure and osmotic concentration pressures. For simplicity, we assume a constant water pressure and isothermal conditions. The theoretical formulations are implemented in the finite element code FEAP by Taylor [29]. A new set of experimental batch tests has been created that considers the model parameter dependencies on the process variables; these tests are used to evaluate the nonlinear model parameter set. After presenting the framework developed for the finite element calculation concept, including the representation of the governing weak formulations, we examine representative numerical examples. [ABSTRACT FROM AUTHOR]

Published
2014
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128. Electrolyte layering at the calcite(104)–water interface indicated by Rb+- and Se(vi) K-edge resonant interface diffraction.

Author

Heberling, F., Eng, P., Denecke, M. A., Lützenkirchen, J., and Geckeis, H.

Abstract

Calcite–water interface reactions are of major importance in various environmental settings as well as in industrial applications. Here we present resonant interface diffraction results on the calcite(104)–aqueous solution interface, measured in solutions containing either 10 mmol L−1 RbCl or 0.5 mmol L−1 Se(vi). Results indicate that Rb+ ions enter the surface adsorbed water layers and adsorb at the calcite(104)–water interface in an inner-sphere fashion. A detailed analysis based on specular and off-specular resonant interface diffraction data reveals three distinct Rb+ adsorption species: one 1.2 Å above the surface, the second associated with surface adsorbed water molecules 3.2 Å above the surface, and the third adsorbed in an outer-sphere fashion 5.6 Å above the surface. A peak in resonant amplitude between L = 1.5 and L = 3.0 is interpreted as signal from a layered electrolyte structure. The presence of a layered electrolyte structure seems to be confirmed by data measured in the presence of Se(vi). [ABSTRACT FROM AUTHOR]

Published
2014
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129. ROBL – a CRG beamline for radiochemistry and materials research at the ESRF

Author

Matz, W., primary, Schell, N., additional, Bernhard, G., additional, Prokert, F., additional, Reich, T., additional, Claußner, J., additional, Oehme, W., additional, Schlenk, R., additional, Dienel, S., additional, Funke, H., additional, Eichhorn, F., additional, Betzl, M., additional, Pröhl, D., additional, Strauch, U., additional, Hüttig, G., additional, Krug, H., additional, Neumann, W., additional, Brendler, V., additional, Reichel, P., additional, Denecke, M. A., additional, and Nitsche, H., additional

Published
1999
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139. Characterization of Hydrous Uranyl Silicate by EXAFS

Author

Reich, T., primary, Moll, H., additional, Denecke, M. A., additional, Geipel, G., additional, Bernhard, G., additional, Nitsche, H., additional, Allen, P. G., additional, Bucher, J. J., additional, Kaltsoyannis, N., additional, Edelstein, N. M., additional, and Shuh, D. K., additional

Published
1996
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150. Structure of yttria stabilized zirconia beads produced by gel supported precipitation.

Author

Walter, M., Somers, J., Fernandez, A., Specht, E., Hunn, J., Boulet, P., Denecke, M. A., and Göbel, C.

Subjects
ZIRCONIUM oxide, TRANSMUTATION (Chemistry), ACTINIDE elements, THERMAL expansion, HEATING
Abstract

Yttria stabilized zirconia (YSZ) is one of the inert matrix candidates selected for investigation as host matrix for minor actinide (MA) transmutation. The structural properties of (Zr0.84, Y0.16)O1.92 beads prepared by a sol–gel method for MA infiltration, are characterized as calcined (850 °C) and sintered (1,600 °C) beads. The calcined YSZ beads are fine-grained and homogenous over the entire sphere and are surrounded by a uniform outer layer of approximately 30 μm thickness. After sintering at 1,600 °C, the beads are compacted to 51% of their initial volume and exhibit a granular structure. The thermal expansion is nearly linear for the calcined material, but shows a parabolic behavior for the sintered (1,400 °C) beads. In addition, the thermal expansion of calcined material is 20–25% less than after sintering. During heating up to 1,400 °C, two processes can be distinguished. The first occurs between 900 and 1,000 °C and is related to an increase in unit cell order. The second process involves grain-growth of the less crystalline calcined material between 1,100 and 1,300 °C. These results have implications for preparation of YSZ and its use as an inert MA transmutation matix. [ABSTRACT FROM AUTHOR]

Published
2007
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