| 1. |
- Cassimjee, Karim Engelmark, et al.
(author)
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Silica-immobilized His(6)-tagged enzyme : Alanine racemase in hydrophobic solvent
- 2008
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In: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 99:3, s. 712-716
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Journal article (peer-reviewed)abstract
- A new immobilization method for enzymes is presented to facilitate synthetic applications in aqueous as well as organic media. The enzyme Alanine racemase (AlaR) from Geobacillus stearothermophilus was cloned, overexpressed and then immobilized on a silica-coated thin-layer chromatography plate to create an enzyme surface. The enzyme, fused to a His(6)-tag at its N-terminal, was tethered to the chemically modified silica-coated TLC plate through cobalt ions. The immobilized enzyme showed unaltered kinetic parameters in small-scale stirred reactions and retained its activity after rinsing, drying, freezing or immersion in n-hexane. This practical method is a first step towards a general immobilization method for synthesis applications with any enzyme suitable for His(6)-tagging.
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| 2. |
- Lousada, Cláudio M., et al.
(author)
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Reactivity of H2O2 towards different UO2-based materials : The relative impact of radiolysis products revisited
- 2013
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 434:1/3, s. 434-439
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Journal article (peer-reviewed)abstract
- The reactivity of doped UO2 such as SIMFUEL towards H2O2 has been shown to be fairly similar to that of pure UO2. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H2O2 is significantly lower for doped UO2. In this work we have studied the mechanistic difference between SIMFUEL and pure UO2. H2O2 can be catalytically decomposed on UO2 in competition with the redox process in which U(IV) is oxidized. The latter process leads to the dissolution of oxidized uranium. The first step in the catalytic decomposition is the formation of hydroxyl radicals. The presence of hydroxyl radicals was verified using Tris buffer as a radical scavenger. For both UO2 and SIMFUEL pellets, significant amounts of hydroxyl radicals were formed. The results also show that the difference in dissolution yield between the two materials can mainly be attributed to differences in the redox reactivity. Based on this, the rate constants for electron transfer were revised and the relative impact of the radiolytic oxidants in oxidative dissolution of UO2 and SIMFUEL pellets were calculated. The impact of H2O2 is shown to be slightly reduced.
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| 3. |
- Pehrman, Reijo, et al.
(author)
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On the redox reactivity of doped UO2 pellets : Influence of dopants on the H2O2 decomposition mechanism.
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Other publication (other academic/artistic)abstract
- The reactivity of doped UO2 such as SIMFUEL, Y2O3 doped UO2 and Y2O3/Pd doped UO2 towards H2O2 has been shown to be fairly similar to that of pure UO2. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H2O2 is significantly lower for doped UO2. The rationale for the observed differences in dissolution yield is a difference in the ratio between the rates of the two possible reactions between H2O2 and the doped UO2. In this work we have studied the effect of doping on the two possible reactions, electron transfer and catalytic decomposition. The catalytic decomposition was studied by monitoring the hydroxyl radical production (the primary product) as a function of time. The redox reactivity of the doped pellets was studied by using MnO4- and IrCl62- as model oxidants, only capable of electron transfer reaction with the pellets. In addition, the activation energies for oxidation of UO2 and SIMFUEL by MnO4- were determined experimentally. The experiments show that the rate of catalytic decomposition of H2O2 varies by 30 % between the fastest and the slowest material. This is a negligible difference. The redox reactivity study shows that doping of UO2 influences the redox reactivity of the pellet. This is further illustrated by the observed activation energy difference for oxidation of UO2 and SIMFUEL by MnO4-. The redox reactivity study also shows that the sensitivity to dopants increases with decreasing reduction potential of the oxidant. These findings imply that the relative impact of radiolytic oxidants in oxidative dissolution of spent nuclear fuel must be reassessed taking the actual fuel composition into account.
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| 4. |
- Pehrman, Reijo, et al.
(author)
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On the redox reactivity of doped UO2 pellets - Influence of dopants on the H2O2 decomposition mechanism
- 2012
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 430:1-3, s. 6-11
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Journal article (peer-reviewed)abstract
- The reactivity of doped UO2 such as SIMFUEL, Y2O3 doped UO2 and Y2O3/Pd doped UO2 towards H2O2 has been shown to be fairly similar to that of pure UO2. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H2O2 is significantly lower for doped UO2. The rationale for the observed differences in dissolution yield is a difference in the ratio between the rates of the two possible reactions between H2O2 and the doped UO2. In this work we have studied the effect of doping on the two possible reactions, electron-transfer and catalytic decomposition. The catalytic decomposition was studied by monitoring the hydroxyl radical production (the primary product) as a function of time. The redox reactivity of the doped pellets was studied by using MnO4- and IrCl62- as model oxidants, only capable of electron-transfer reactions with the pellets. In addition, the activation energies for oxidation of UO2 and SIMFUEL by MnO4- were determined experimentally. The experiments show that the rate of catalytic decomposition of H2O2 varies by 30% between the most and least reactive material. This is a negligible difference compared to the difference in oxidative dissolution yield. The redox reactivity study shows that doping UO2 influences the redox reactivity of the pellet. This is further illustrated by the observed activation energy difference for oxidation of UO2 and SIMFUEL by MnO4-. The redox reactivity study also shows that the sensitivity to dopants increases with decreasing reduction potential of the oxidant. These findings imply that the relative impact of radiolytic oxidants in oxidative dissolution of spent nuclear fuel must be reassessed taking the actual fuel composition into account.
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| 5. |
- Puranen, Anders, et al.
(author)
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Can redox sensitive radionuclides be immobilized on the surface of spent nuclear fuel? - A model study on the reduction of Se(IV)(aq) on Pd-doped UO2 under H-2 atmosphere
- 2009
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 392:3, s. 505-509
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Journal article (peer-reviewed)abstract
- Spent nuclear fuel contains noble metal particles composed of fission products (Pd, Mo, Ru, Tc, Rh and Te, often referred to as ε-particles). Studies have shown that these particles play a major role in catalyzing oxidative dissolution as well as H2 reduction of the oxidized UO2 fuel matrix, depending on the conditions. Thus it is possible that these particles also could have a major impact on the state of other redox sensitive radionuclides (such as the long lived fission product 79Se) present in spent nuclear fuel. In this study, Pd-doped UO2 pellets are used to simulate noble metal particles inclusions in spent nuclear fuel and the effect on dissolved selenium in the form of selenite (250 μM selenite) in simulated ground water solution (10 mM NaCl, 10 mM NaHCO3) at 1 and 10 bar hydrogen pressure. The selenite was found to be reduced to elemental Se, forming colloidal particles. At hydrogen pressures of 10 bar, the rate of selenite reduction was found to be linearly correlated to the fraction of Pd in the UO2 pellets. No selenium was detected on the surface of the pellets. For the lowest Pd loading (0.1% Pd) the selenite reduction does not appear to proceed to completion indicating that the surface becomes less active.
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| 6. |
- Razdan, Mayuri, et al.
(author)
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Electrochemical and Surface Characterization of Uranium Dioxide Containing Rare-Earth Oxide (Y2O3) and Metal (Pd) Particles
- 2014
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In: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 130, s. 29-39
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Journal article (peer-reviewed)abstract
- Four specimens of uranium dioxide doped with rare-earth oxide (Y2O3) and/or metal particles (Pd) i.e., UO2, UO2-Y2O3, UO2-Y2O3-Pd, UO2-Pd were surface and electrochemically characterized using scanning electron microscopy (SEM/EDX), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. Surface analyses showed that the dopants are present as a separate phase in the UO2 matrix and all oxides are non-stoichiometric and contain a large number of defect clusters. Voltammetry shows anodic oxidation begins at sub-thermodynamic potentials and the presence of multiple cathodic reduction peaks indicates the presence of a number of structural domains with different electrochemical reactivities. Corrosion potential (E-CORR) and polarization resistance measurements (Rp) in the presence of H2O2 suggests that the anodic reactivity of all the specimens is comparable and high compared to 1.5 at% SIMFUEL. The lower Rp values obtained on the doped specimens is consistent with the presence of readily oxidizable cuboctahedral clusters in the oxide matrix.
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| 7. |
- Roth, Olivia, et al.
(author)
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Factors influencing the rate of radiation-induced dissolution of spent nuclear fuel
- 2009
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In: Research on chemical intermediates (Print). - : Springer Science and Business Media LLC. - 0922-6168 .- 1568-5675. ; 35:4, s. 465-478
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Journal article (peer-reviewed)abstract
- Several countries plan to store spent nuclear fuel in deep geological repositories. Accurate prediction of the spent fuel dissolution rate is a key issue in the safety assessment of a future deep repository. A reliable quantitative model for radiation-induced spent fuel dissolution must be based on an accurate description of the dose distribution around the spent fuel and fundamental knowledge about the elementary processes involved. In this paper, we discuss factors influencing the rate of radiation-induced dissolution of spent nuclear fuel, focusing on solutes (H-2, HCO3 (-), Fe(II) and organic substances affecting the H2O2 concentration and factors influencing the reactivity of the fuel surface towards H2O2. Taking these factors into account, we have also simulated dissolution of spent nuclear fuel under realistic deep repository conditions.
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| 8. |
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| 9. |
- Trummer, Martin, et al.
(author)
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H2 inhibition of radiation induced dissolution of spent nuclear fuel
- 2009
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 383:3, s. 226-230
-
Journal article (peer-reviewed)abstract
- In order to elucidate the effect of noble metal clusters in spent nuclear fuel on the kinetics of radiation induced spent fuel dissolution we have used I'd particle doped UO2 pellets. The catalytic effect of Pd particles on the kinetics of radiation induced dissolution Of UO2 during gamma-irradiation in HCO3- containing solutions purged with N-2 and H-2 was studied in this work. Four pellets with Pd concentrations of 0%, 0.1%, 1% and 3% were produced to mimic spent nuclear fuel. The pellets were placed in 10 mM HCO3- aqueous solutions and gamma-irradiated, and the dissolution of UO22+ was measured spectrophotometrically as a function of time. Under N-2 atmosphere, 3% I'd prevent the dissolution of uranium by reduction with the radiolytically produced H-2, while the other pellets show a rate of dissolution of around 1.6 x 10(-9) mol m(-2) s(-1). Under H-2 atmosphere already 0.1% Pd effectively prevents the dissolution of uranium, while the rate of dissolution for the pellet without Pd is 1.4 x 10(-9) mol m(-2) s(-1). It is also shown in experiments without radiation in aqueous solutions containing H2O2 and O-2 that epsilon-particles catalyze the oxidation of the UO2 matrix by these molecular oxidants, and that the kinetics of the catalyzed reactions is close to diffusion controlled.
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| 10. |
- Trummer, Martin, et al.
(author)
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On the effects of fission product noble metal inclusions on the kinetics of radiation induced dissolution of spent nuclear fuel
- 2008
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 378:1, s. 55-59
-
Journal article (peer-reviewed)abstract
- Radiation induced oxidative dissolution of UO2 is a key process for the safety assessment of future geological repositories for spent nuclear fuel. This process is expected to govern the rate of radionuclide release to the biosphere. In this work, we have studied the catalytic effects of fission product noble metal inclusions on the kinetics of radiation induced dissolution of spent nuclear fuel. The experimental studies were performed using UO2 pellets containing 0%, 0.1%, 1% and 3% Pd as a model for spent nuclear fuel. H2O2 was used as a model for radiolytical oxidants (previous studies have shown that H2O2 is the most important oxidant in such systems). The pellets were immersed in aqueous solution containing H2O2 and HCO3- and the consumption of H2O2 and the dissolution of uranium were analyzed as a function of H2 pressure (0-40 bar). The noble metal inclusions were found to catalyze oxidation of UO2 as well as reduction of surface bound oxidized UO2 by H2. In both cases the rate of the process increases with increasing Pd content. The reduction process was found to be close to diffusion controlled. This process can fully account for the inhibiting effect of H2 observed in several studies on spent nuclear fuel dissolution.
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