The Experts below are selected from a list of 1479 Experts worldwide ranked by ideXlab platform
Enzo Curti - One of the best experts on this subject based on the ideXlab platform.
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A micro-XAS/XRF and thermodynamic study of CeIII/IV speciation after long-term aqueous alteration of simulated Nuclear Waste Glass: Relevance for predicting Pu behavior?
Applied Geochemistry, 2012Co-Authors: Enzo Curti, Daniel Grolimund, Camelia N. BorcaAbstract:Abstract In the present study, the dissolution and mobilization of Ce introduced in a simulated Nuclear Waste Glass (MW) as a surrogate of Pu was investigated after leaching in pure water over 12 a at 90 °C and pH ∼ 9.6. The microscopic distribution and oxidation state of Ce in the altered Glass were studied using micro-X-ray fluorescence (micro-XRF) mapping techniques and micro-X-ray near-edge absorption spectroscopy (micro-XANES). Distribution maps of Ce III and Ce IV were obtained by recording the L α fluorescence emission at two different incident X-ray energies, coinciding with the maximum contrast between Ce III and Ce IV fluorescence intensities. The micro-XRF maps revealed that Ce was dominantly present as oxidized species (Ce IV ) in the original Glass. After dissolution from the Glass matrix, Ce IV was partly reduced and re-immobilized as Ce III at grain boundaries or in the interstitial spaces between the Glass particles. The concentration of Ce III was found to correlate with the spatial distribution of secondary Mg-clay formed during the aqueous corrosion as the main Glass alteration product. Micro-XANES spectra collected at locations representative of both altered and non-altered Glass domains confirmed the findings obtained by the redox mapping. Because redox-sensitive elements in the pristine MW Glass (Fe, Cr, Se) occur almost exclusively as oxidized species, reduction of Ce IV was probably mediated by an external source of reductants, such as Fe(0) from the steel reaction vessel. These results, in conjunction with an Eh–pH stability diagram of the Ce III/IV –O–H–C IV –P–S VI –Na–Cl system, indicate that the Glass was leached at relatively low oxidation potentials (Eh IV to Pu III would require considerably more reducing conditions (Eh
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a micro xas xrf and thermodynamic study of ceiii iv speciation after long term aqueous alteration of simulated Nuclear Waste Glass relevance for predicting pu behavior
Applied Geochemistry, 2012Co-Authors: Enzo Curti, Daniel Grolimund, Camelia N. BorcaAbstract:Abstract In the present study, the dissolution and mobilization of Ce introduced in a simulated Nuclear Waste Glass (MW) as a surrogate of Pu was investigated after leaching in pure water over 12 a at 90 °C and pH ∼ 9.6. The microscopic distribution and oxidation state of Ce in the altered Glass were studied using micro-X-ray fluorescence (micro-XRF) mapping techniques and micro-X-ray near-edge absorption spectroscopy (micro-XANES). Distribution maps of Ce III and Ce IV were obtained by recording the L α fluorescence emission at two different incident X-ray energies, coinciding with the maximum contrast between Ce III and Ce IV fluorescence intensities. The micro-XRF maps revealed that Ce was dominantly present as oxidized species (Ce IV ) in the original Glass. After dissolution from the Glass matrix, Ce IV was partly reduced and re-immobilized as Ce III at grain boundaries or in the interstitial spaces between the Glass particles. The concentration of Ce III was found to correlate with the spatial distribution of secondary Mg-clay formed during the aqueous corrosion as the main Glass alteration product. Micro-XANES spectra collected at locations representative of both altered and non-altered Glass domains confirmed the findings obtained by the redox mapping. Because redox-sensitive elements in the pristine MW Glass (Fe, Cr, Se) occur almost exclusively as oxidized species, reduction of Ce IV was probably mediated by an external source of reductants, such as Fe(0) from the steel reaction vessel. These results, in conjunction with an Eh–pH stability diagram of the Ce III/IV –O–H–C IV –P–S VI –Na–Cl system, indicate that the Glass was leached at relatively low oxidation potentials (Eh IV to Pu III would require considerably more reducing conditions (Eh
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na mg ni and cs distribution and speciation after long term alteration of a simulated Nuclear Waste Glass a micro xas xrf xrd and wet chemical study
Geochimica et Cosmochimica Acta, 2009Co-Authors: Enzo Curti, Rainer Dähn, François Farges, Marika VespaAbstract:Microscopic distribution and speciation of Na, Mg, Ni and Cs in a simulated (inactive) Nuclear Waste Glass were studied using micro X-ray fluorescence (l-XRF) and micro X-ray absorption spectroscopy (l-XAS), after aqueous leaching during 12 years at 90 C. Na and Mg are major constituents of the Glass that can be used to determine the progress of the Glass corrosion process and the nature of secondary alteration phases. Ni and Cs represent dose determining long-lived radionuclides ( 59 Ni, 135 Cs) in vitrified Nuclear Waste. The Na-Mg l-XRF maps revealed that the core regions of the Glass fragments are apparently unaltered and compositionally homogeneous, whereas rims and interstitial spaces are enriched with Mg-rich smectite formed during the leaching process. The micro X-ray absorption near edge structure (l-XANES) spectra collected at the Mg K-edge in the altered zones show three sharp resonances typical for crystalline Mg-silicates. These resonances are distinctive of Mg occupying undistorted octahedral positions. In contrast, the l-XANES spectra collected in the core zones of the Glass fragments lack this resonance pattern and are identical to the spectra measured on the pristine (unleached) MW Glass. Micro extended X-ray absorption fine structure (l-EXAFS) and l-XANES analyses at the Ni K-edge revealed three distinct Ni(II) species: (a) Ni uniformly distributed in the Glass matrix, (b) micro-inclusions with high Ni concentrations and (c) Ni associated to the Mg-clay. The comparison with reference spectra of unleached MW and other Ni-bearing silicate Glasses indicated that species (a) represents the original coordinative environment of Ni in the Glass. The l-EXAFS analyses revealed that species (b) is structural Ni in trevorite (NiFe2O4), which probably formed through unmixing processes during the cooling of the Glass melt. The l-EXAFS of species (c) could be successfully modeled assuming specific adsorption or incorporation of Ni into the lattice of trioctahedral Mg-clay minerals. Alternative models assuming other elements (Ni, Al, Fe) in addition to Mg in the second shell could not be fitted successfully. Aqueous concentration data were used to calculate the speciation of the leaching solutions. Saturation index (SI) calculations indicate undersaturation with respect to NiCO3 and NiSO4� 7H2O, but oversaturation with respect to b-Ni(OH)2. The latter result is probably due to the omission of Ni borate and Ni silicate complexes in the speciation calculations, for which formation constants are not available. With the help of estimation techniques, we could infer that such complexes would dominate the Ni speciation and consequently reduce the SI below the saturation of b-Ni(OH)2.
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Na, Mg, Ni and Cs distribution and speciation after long-term alteration of a simulated Nuclear Waste Glass: A micro-XAS/XRF/XRD and wet chemical study
Geochimica et Cosmochimica Acta, 2009Co-Authors: Enzo Curti, Rainer Dähn, François Farges, Marika VespaAbstract:Microscopic distribution and speciation of Na, Mg, Ni and Cs in a simulated (inactive) Nuclear Waste Glass were studied using micro X-ray fluorescence (l-XRF) and micro X-ray absorption spectroscopy (l-XAS), after aqueous leaching during 12 years at 90 C. Na and Mg are major constituents of the Glass that can be used to determine the progress of the Glass corrosion process and the nature of secondary alteration phases. Ni and Cs represent dose determining long-lived radionuclides ( 59 Ni, 135 Cs) in vitrified Nuclear Waste. The Na-Mg l-XRF maps revealed that the core regions of the Glass fragments are apparently unaltered and compositionally homogeneous, whereas rims and interstitial spaces are enriched with Mg-rich smectite formed during the leaching process. The micro X-ray absorption near edge structure (l-XANES) spectra collected at the Mg K-edge in the altered zones show three sharp resonances typical for crystalline Mg-silicates. These resonances are distinctive of Mg occupying undistorted octahedral positions. In contrast, the l-XANES spectra collected in the core zones of the Glass fragments lack this resonance pattern and are identical to the spectra measured on the pristine (unleached) MW Glass. Micro extended X-ray absorption fine structure (l-EXAFS) and l-XANES analyses at the Ni K-edge revealed three distinct Ni(II) species: (a) Ni uniformly distributed in the Glass matrix, (b) micro-inclusions with high Ni concentrations and (c) Ni associated to the Mg-clay. The comparison with reference spectra of unleached MW and other Ni-bearing silicate Glasses indicated that species (a) represents the original coordinative environment of Ni in the Glass. The l-EXAFS analyses revealed that species (b) is structural Ni in trevorite (NiFe2O4), which probably formed through unmixing processes during the cooling of the Glass melt. The l-EXAFS of species (c) could be successfully modeled assuming specific adsorption or incorporation of Ni into the lattice of trioctahedral Mg-clay minerals. Alternative models assuming other elements (Ni, Al, Fe) in addition to Mg in the second shell could not be fitted successfully. Aqueous concentration data were used to calculate the speciation of the leaching solutions. Saturation index (SI) calculations indicate undersaturation with respect to NiCO3 and NiSO4� 7H2O, but oversaturation with respect to b-Ni(OH)2. The latter result is probably due to the omission of Ni borate and Ni silicate complexes in the speciation calculations, for which formation constants are not available. With the help of estimation techniques, we could infer that such complexes would dominate the Ni speciation and consequently reduce the SI below the saturation of b-Ni(OH)2.
Bernd Grambow - One of the best experts on this subject based on the ideXlab platform.
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Alteration of 29Si-doped SON68 borosilicate Nuclear Waste Glass in the presence of near field materials
Applied Geochemistry, 2019Co-Authors: Rachid Bouakkaz, Abdesselam Abdelouas, Yassine El Mendili, Karine David, Bernd GrambowAbstract:The leaching of 29Si-doped SON68 French Nuclear Waste Glass was investigated in Callovo-Oxfordian (COx) water in the presence of P235GH stainless steel and COx argillite. Experiments were carried out to understand the effect of near-field materials on the rate of Glass dissolution and the migration of 29Si in the claystone core. Tests were performed by using percolation cells containing Glass and stainless steel sandwiched between two clay cores in two different combinations: Glass/clay at 50 and 90 °C, and Glass/steel/clay/at 90 °C. COx water was injected through the percolation cells at 120 bars (solution flow rate 0.05–0.38 mL d−1). Results showed that the presence of steel did not enhance the dissolution rate of the Glass despite the retention of 29Si released from the Glass on the corrosion products. The Glass dissolution rate up to 17 months tends towards 10−4 and 10−3 g m−2 d−1 at 50 and 90 °C, respectively. The Glass alteration in the presence of clay leads to the formation of calcite and Mg-silicates at 50 °C in addition to apatite and powellite at 90 °C. The main steel corrosion products were siderite, magnetite, ferrosilicates, pyrite, pyrrhotite, troilite and mackinawite. MgSO4 and CaSO4 were also identified in the presence of steel.
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Kinetic study and structural evolution of SON68 Nuclear Waste Glass altered from 35 to 125 °C under unsaturated H2O and D2O18 vapour conditions
Corrosion Science, 2018Co-Authors: Rachid Bouakkaz, Abdesselam Abdelouas, Bernd GrambowAbstract:Abstract The French reference SON68 Nuclear Waste Glass corrosion under H2O and D2O18 atmosphere was investigated at 35−125 °C and different relative humidities (92–99.9%). The hydration kinetic was followed by FTIR and solid characterization was achieved using SEM/EDX, Raman and TOF-SIMS. The water diffusion coefficients in the Glass ranged from 8.7 × 10−22 to 5.3 × 10−19 m2 s−1. The alteration products were calcite, apatite, powellite and tobermorite. Pre-hydrated Glass alteration in synthetic groundwater at 50 °C showed an instantaneous release of elements from the surface, making it important to evaluate well the vapour hydration period of the Glass.
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Effect of Callovo-Oxfordian clay rock on the dissolution rate of the SON68 simulated Nuclear Waste Glass
Journal of Nuclear Materials, 2015Co-Authors: J. J. Neeway, Abdesselam Abdelouas, S. Ribet, Y. El Mendili, S. Schumacher, Bernd GrambowAbstract:Long-term storage of high-level Nuclear Waste Glass in France is expected to occur in an engineered barrier system (EBS) located in a subsurface Callovo-Oxfordian (COx) clay rock formation in the Paris Basin in northeastern France. Understanding the behavior of Glass dissolution in the complex system is critical to be able to reliably model the performance of the Glass in this complex environment. To simulate this multi-barrier repository scenario in the laboratory, several tests have been performed to measure Glass dissolution rates of the simulated high-level Nuclear Waste Glass, SON68, in the presence of COx claystone at 90 °C. Experiments utilized a High-Performance Liquid Chromatography (HPLC) pump to pass simulated Bure site COx pore water through a reaction cell containing SON68 placed between two COx claystone cores for durations up to 200 days. Silicon concentrations at the outlet were similar in all experiments, even the blank experiment with only the COx claystone (∼4 mg/L at 25 °C and ∼15 mg/L at 90 °C). The steady-state pH of the effluent, measured at room temperature, was roughly 7.1 for the blank and 7.3–7.6 for the Glass-containing experiments demonstrating the pH buffering capacity of the COx claystone. Dissolution rates for SON68 in the presence of the claystone were elevated compared to those obtained from flow-through experiments conducted with SON68 without claystone in silica-saturated solutions at the same temperature and similar pH values. Additionally, through surface examination of the monoliths, the side of the monolith in direct contact with the claystone was seen to have a corrosion thickness 2.5× greater than the side in contact with the bulk Glass powder. Results from one experiment containing 32Si-doped SON68 also suggest that the movement of Si through the claystone is controlled by a chemically coupled transport with a Si retention factor, Kd, of 900 mL/g.
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Dissolution mechanism of the SON68 reference Nuclear Waste Glass: New data in dynamic system in silica saturation conditions
Journal of Nuclear Materials, 2011Co-Authors: James J. Neeway, Abdesselam Abdelouas, Bernd Grambow, Stéphan SchumacherAbstract:Abstract The alteration of SON68 Glass (inactive R7T7 type Nuclear Waste Glass) was studied to measure the long-term residual dissolution rate under different conditions. Experiments were conducted in flow-through conditions (solution flow rate 3–5 mL/day) at pH 8.0, 9.5, and 10.5 under various initial Si concentrations, a Glass surface-to-volume ratio near 14,000 m−1 and at a temperature of 90 °C. This set of long-term experiments (200 days) showed leaching rates dependent on the initial silica concentration and the initial pH. Interpretation of results at pH 8.0 was difficult due to the use of a synthetic water used to represent waters found at a potential French repository site. Because very small Glass powder sizes were used (O = 1 μm), a complete dissolution of the pristine Glass was achieved at low initial silica concentrations where higher leaching rates were produced. In all cases, initial high normalized leaching rates were observed followed by a decrease in leaching rate with rate levels ranging from 9 (±4) to 5 (±3) × 10−4 g m−2 d−1 at 200 days under silica saturated conditions at pH 9.5 and 10.5, respectively. We have compared these results to previous results obtained in similar leaching conditions. Modeling using the GM2004 model program and model output values were shown to be in agreement with experimental results.
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Surface layers on a borosilicate Nuclear Waste Glass corroded in MgCl2 solution
Journal of Nuclear Materials, 1997Co-Authors: Abdesselam Abdelouas, J.l. Crovisier, W. Lutze, Bernd Grambow, Jean-claude Dran, R. MüllerAbstract:Surface layers on the French borosilicate Nuclear Waste Glass, R7T7, corroded in MgCl2 solution were studied to determine the composition, structure and stability of crystalline phases. The characteristics of the phases constituting the surface layer varied with the parameter SV × t, the Glass surface area (S) to solution volume (V) ratio, times time (t). At low SV × t values ( 98% of the neodymium released from the Glass were precipitated in the surface layer. In the 463 day experiment, 86% of the neodymium in the surface layer was in solid solution with powellite, the rest with saponite. Uranium was contained exclusively in saponite. High SV ratios, typical of disposal conditions for vitrified high-level radioactive Waste, favor retention of actinides in fairly insoluble corrosion products. Observation of similar corrosion products on natural Glasses as on Nuclear Waste Glasses lend support to the hypothesis that the host phases for actinides observed in the laboratory are stable over geological periods of time.
Marika Vespa - One of the best experts on this subject based on the ideXlab platform.
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na mg ni and cs distribution and speciation after long term alteration of a simulated Nuclear Waste Glass a micro xas xrf xrd and wet chemical study
Geochimica et Cosmochimica Acta, 2009Co-Authors: Enzo Curti, Rainer Dähn, François Farges, Marika VespaAbstract:Microscopic distribution and speciation of Na, Mg, Ni and Cs in a simulated (inactive) Nuclear Waste Glass were studied using micro X-ray fluorescence (l-XRF) and micro X-ray absorption spectroscopy (l-XAS), after aqueous leaching during 12 years at 90 C. Na and Mg are major constituents of the Glass that can be used to determine the progress of the Glass corrosion process and the nature of secondary alteration phases. Ni and Cs represent dose determining long-lived radionuclides ( 59 Ni, 135 Cs) in vitrified Nuclear Waste. The Na-Mg l-XRF maps revealed that the core regions of the Glass fragments are apparently unaltered and compositionally homogeneous, whereas rims and interstitial spaces are enriched with Mg-rich smectite formed during the leaching process. The micro X-ray absorption near edge structure (l-XANES) spectra collected at the Mg K-edge in the altered zones show three sharp resonances typical for crystalline Mg-silicates. These resonances are distinctive of Mg occupying undistorted octahedral positions. In contrast, the l-XANES spectra collected in the core zones of the Glass fragments lack this resonance pattern and are identical to the spectra measured on the pristine (unleached) MW Glass. Micro extended X-ray absorption fine structure (l-EXAFS) and l-XANES analyses at the Ni K-edge revealed three distinct Ni(II) species: (a) Ni uniformly distributed in the Glass matrix, (b) micro-inclusions with high Ni concentrations and (c) Ni associated to the Mg-clay. The comparison with reference spectra of unleached MW and other Ni-bearing silicate Glasses indicated that species (a) represents the original coordinative environment of Ni in the Glass. The l-EXAFS analyses revealed that species (b) is structural Ni in trevorite (NiFe2O4), which probably formed through unmixing processes during the cooling of the Glass melt. The l-EXAFS of species (c) could be successfully modeled assuming specific adsorption or incorporation of Ni into the lattice of trioctahedral Mg-clay minerals. Alternative models assuming other elements (Ni, Al, Fe) in addition to Mg in the second shell could not be fitted successfully. Aqueous concentration data were used to calculate the speciation of the leaching solutions. Saturation index (SI) calculations indicate undersaturation with respect to NiCO3 and NiSO4� 7H2O, but oversaturation with respect to b-Ni(OH)2. The latter result is probably due to the omission of Ni borate and Ni silicate complexes in the speciation calculations, for which formation constants are not available. With the help of estimation techniques, we could infer that such complexes would dominate the Ni speciation and consequently reduce the SI below the saturation of b-Ni(OH)2.
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Na, Mg, Ni and Cs distribution and speciation after long-term alteration of a simulated Nuclear Waste Glass: A micro-XAS/XRF/XRD and wet chemical study
Geochimica et Cosmochimica Acta, 2009Co-Authors: Enzo Curti, Rainer Dähn, François Farges, Marika VespaAbstract:Microscopic distribution and speciation of Na, Mg, Ni and Cs in a simulated (inactive) Nuclear Waste Glass were studied using micro X-ray fluorescence (l-XRF) and micro X-ray absorption spectroscopy (l-XAS), after aqueous leaching during 12 years at 90 C. Na and Mg are major constituents of the Glass that can be used to determine the progress of the Glass corrosion process and the nature of secondary alteration phases. Ni and Cs represent dose determining long-lived radionuclides ( 59 Ni, 135 Cs) in vitrified Nuclear Waste. The Na-Mg l-XRF maps revealed that the core regions of the Glass fragments are apparently unaltered and compositionally homogeneous, whereas rims and interstitial spaces are enriched with Mg-rich smectite formed during the leaching process. The micro X-ray absorption near edge structure (l-XANES) spectra collected at the Mg K-edge in the altered zones show three sharp resonances typical for crystalline Mg-silicates. These resonances are distinctive of Mg occupying undistorted octahedral positions. In contrast, the l-XANES spectra collected in the core zones of the Glass fragments lack this resonance pattern and are identical to the spectra measured on the pristine (unleached) MW Glass. Micro extended X-ray absorption fine structure (l-EXAFS) and l-XANES analyses at the Ni K-edge revealed three distinct Ni(II) species: (a) Ni uniformly distributed in the Glass matrix, (b) micro-inclusions with high Ni concentrations and (c) Ni associated to the Mg-clay. The comparison with reference spectra of unleached MW and other Ni-bearing silicate Glasses indicated that species (a) represents the original coordinative environment of Ni in the Glass. The l-EXAFS analyses revealed that species (b) is structural Ni in trevorite (NiFe2O4), which probably formed through unmixing processes during the cooling of the Glass melt. The l-EXAFS of species (c) could be successfully modeled assuming specific adsorption or incorporation of Ni into the lattice of trioctahedral Mg-clay minerals. Alternative models assuming other elements (Ni, Al, Fe) in addition to Mg in the second shell could not be fitted successfully. Aqueous concentration data were used to calculate the speciation of the leaching solutions. Saturation index (SI) calculations indicate undersaturation with respect to NiCO3 and NiSO4� 7H2O, but oversaturation with respect to b-Ni(OH)2. The latter result is probably due to the omission of Ni borate and Ni silicate complexes in the speciation calculations, for which formation constants are not available. With the help of estimation techniques, we could infer that such complexes would dominate the Ni speciation and consequently reduce the SI below the saturation of b-Ni(OH)2.
Abdesselam Abdelouas - One of the best experts on this subject based on the ideXlab platform.
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Alteration of 29Si-doped SON68 borosilicate Nuclear Waste Glass in the presence of near field materials
Applied Geochemistry, 2019Co-Authors: Rachid Bouakkaz, Abdesselam Abdelouas, Yassine El Mendili, Karine David, Bernd GrambowAbstract:The leaching of 29Si-doped SON68 French Nuclear Waste Glass was investigated in Callovo-Oxfordian (COx) water in the presence of P235GH stainless steel and COx argillite. Experiments were carried out to understand the effect of near-field materials on the rate of Glass dissolution and the migration of 29Si in the claystone core. Tests were performed by using percolation cells containing Glass and stainless steel sandwiched between two clay cores in two different combinations: Glass/clay at 50 and 90 °C, and Glass/steel/clay/at 90 °C. COx water was injected through the percolation cells at 120 bars (solution flow rate 0.05–0.38 mL d−1). Results showed that the presence of steel did not enhance the dissolution rate of the Glass despite the retention of 29Si released from the Glass on the corrosion products. The Glass dissolution rate up to 17 months tends towards 10−4 and 10−3 g m−2 d−1 at 50 and 90 °C, respectively. The Glass alteration in the presence of clay leads to the formation of calcite and Mg-silicates at 50 °C in addition to apatite and powellite at 90 °C. The main steel corrosion products were siderite, magnetite, ferrosilicates, pyrite, pyrrhotite, troilite and mackinawite. MgSO4 and CaSO4 were also identified in the presence of steel.
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Kinetic study and structural evolution of SON68 Nuclear Waste Glass altered from 35 to 125 °C under unsaturated H2O and D2O18 vapour conditions
Corrosion Science, 2018Co-Authors: Rachid Bouakkaz, Abdesselam Abdelouas, Bernd GrambowAbstract:Abstract The French reference SON68 Nuclear Waste Glass corrosion under H2O and D2O18 atmosphere was investigated at 35−125 °C and different relative humidities (92–99.9%). The hydration kinetic was followed by FTIR and solid characterization was achieved using SEM/EDX, Raman and TOF-SIMS. The water diffusion coefficients in the Glass ranged from 8.7 × 10−22 to 5.3 × 10−19 m2 s−1. The alteration products were calcite, apatite, powellite and tobermorite. Pre-hydrated Glass alteration in synthetic groundwater at 50 °C showed an instantaneous release of elements from the surface, making it important to evaluate well the vapour hydration period of the Glass.
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Understanding of the mechanical and structural changes induced by alpha particles and heavy ions in the French simulated Nuclear Waste Glass
Journal of Nuclear Materials, 2016Co-Authors: Gökhan Karakurt, Abdesselam Abdelouas, Jean-pierre Guin, M. Nivard, T. Sauvage, M. Paris, Jean-françois BardeauAbstract:Borosilicate Glasses are considered for the long-term confinement of high-level Nuclear Wastes. External irradiations with 1 MeV He+ ions and 7 MeV Au5+ ions were performed to simulate effects produced by alpha particles and by recoil nuclei in the simulated SON68 Nuclear Waste Glass. To better understand the structural modifications, irradiations were also carried out on a 6-oxides borosilicate Glass, a simplified version of the SON68 Glass (ISG Glass). The mechanical and macroscopic properties of the Glasses were studied as function of the deposited electronic and Nuclear energies. Alpha particles and gold ions induced a volume change up to −0.7% and −2.7%, respectively, depending on the Glass composition. Nano-indentations tests were used to determine the mechanical properties of the irradiated Glasses. A decrease of about −22% to −38% of the hardness and a decrease of the reduced Young's modulus by −8% were measured after irradiations. The evolution of the Glass structure was studied by Raman spectroscopy, and also 11B and 27Al Nuclear Magnetic Resonance (MAS-NMR) on a 20 MeV Kr irradiated ISG Glass powder. A decrease of the silica network connectivity after irradiation with alpha particles and gold ions is deduced from the structural changes observations. NMR spectra revealed a partial conversion of BO4 to BO3 units but also a formation of AlO5 and AlO6 species after irradiation with Kr ions. The relationships between the mechanical and structural changes are also discussed
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Effect of Callovo-Oxfordian clay rock on the dissolution rate of the SON68 simulated Nuclear Waste Glass
Journal of Nuclear Materials, 2015Co-Authors: J. J. Neeway, Abdesselam Abdelouas, S. Ribet, Y. El Mendili, S. Schumacher, Bernd GrambowAbstract:Long-term storage of high-level Nuclear Waste Glass in France is expected to occur in an engineered barrier system (EBS) located in a subsurface Callovo-Oxfordian (COx) clay rock formation in the Paris Basin in northeastern France. Understanding the behavior of Glass dissolution in the complex system is critical to be able to reliably model the performance of the Glass in this complex environment. To simulate this multi-barrier repository scenario in the laboratory, several tests have been performed to measure Glass dissolution rates of the simulated high-level Nuclear Waste Glass, SON68, in the presence of COx claystone at 90 °C. Experiments utilized a High-Performance Liquid Chromatography (HPLC) pump to pass simulated Bure site COx pore water through a reaction cell containing SON68 placed between two COx claystone cores for durations up to 200 days. Silicon concentrations at the outlet were similar in all experiments, even the blank experiment with only the COx claystone (∼4 mg/L at 25 °C and ∼15 mg/L at 90 °C). The steady-state pH of the effluent, measured at room temperature, was roughly 7.1 for the blank and 7.3–7.6 for the Glass-containing experiments demonstrating the pH buffering capacity of the COx claystone. Dissolution rates for SON68 in the presence of the claystone were elevated compared to those obtained from flow-through experiments conducted with SON68 without claystone in silica-saturated solutions at the same temperature and similar pH values. Additionally, through surface examination of the monoliths, the side of the monolith in direct contact with the claystone was seen to have a corrosion thickness 2.5× greater than the side in contact with the bulk Glass powder. Results from one experiment containing 32Si-doped SON68 also suggest that the movement of Si through the claystone is controlled by a chemically coupled transport with a Si retention factor, Kd, of 900 mL/g.
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Dissolution mechanism of the SON68 reference Nuclear Waste Glass: New data in dynamic system in silica saturation conditions
Journal of Nuclear Materials, 2011Co-Authors: James J. Neeway, Abdesselam Abdelouas, Bernd Grambow, Stéphan SchumacherAbstract:Abstract The alteration of SON68 Glass (inactive R7T7 type Nuclear Waste Glass) was studied to measure the long-term residual dissolution rate under different conditions. Experiments were conducted in flow-through conditions (solution flow rate 3–5 mL/day) at pH 8.0, 9.5, and 10.5 under various initial Si concentrations, a Glass surface-to-volume ratio near 14,000 m−1 and at a temperature of 90 °C. This set of long-term experiments (200 days) showed leaching rates dependent on the initial silica concentration and the initial pH. Interpretation of results at pH 8.0 was difficult due to the use of a synthetic water used to represent waters found at a potential French repository site. Because very small Glass powder sizes were used (O = 1 μm), a complete dissolution of the pristine Glass was achieved at low initial silica concentrations where higher leaching rates were produced. In all cases, initial high normalized leaching rates were observed followed by a decrease in leaching rate with rate levels ranging from 9 (±4) to 5 (±3) × 10−4 g m−2 d−1 at 200 days under silica saturated conditions at pH 9.5 and 10.5, respectively. We have compared these results to previous results obtained in similar leaching conditions. Modeling using the GM2004 model program and model output values were shown to be in agreement with experimental results.
Camelia N. Borca - One of the best experts on this subject based on the ideXlab platform.
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A micro-XAS/XRF and thermodynamic study of CeIII/IV speciation after long-term aqueous alteration of simulated Nuclear Waste Glass: Relevance for predicting Pu behavior?
Applied Geochemistry, 2012Co-Authors: Enzo Curti, Daniel Grolimund, Camelia N. BorcaAbstract:Abstract In the present study, the dissolution and mobilization of Ce introduced in a simulated Nuclear Waste Glass (MW) as a surrogate of Pu was investigated after leaching in pure water over 12 a at 90 °C and pH ∼ 9.6. The microscopic distribution and oxidation state of Ce in the altered Glass were studied using micro-X-ray fluorescence (micro-XRF) mapping techniques and micro-X-ray near-edge absorption spectroscopy (micro-XANES). Distribution maps of Ce III and Ce IV were obtained by recording the L α fluorescence emission at two different incident X-ray energies, coinciding with the maximum contrast between Ce III and Ce IV fluorescence intensities. The micro-XRF maps revealed that Ce was dominantly present as oxidized species (Ce IV ) in the original Glass. After dissolution from the Glass matrix, Ce IV was partly reduced and re-immobilized as Ce III at grain boundaries or in the interstitial spaces between the Glass particles. The concentration of Ce III was found to correlate with the spatial distribution of secondary Mg-clay formed during the aqueous corrosion as the main Glass alteration product. Micro-XANES spectra collected at locations representative of both altered and non-altered Glass domains confirmed the findings obtained by the redox mapping. Because redox-sensitive elements in the pristine MW Glass (Fe, Cr, Se) occur almost exclusively as oxidized species, reduction of Ce IV was probably mediated by an external source of reductants, such as Fe(0) from the steel reaction vessel. These results, in conjunction with an Eh–pH stability diagram of the Ce III/IV –O–H–C IV –P–S VI –Na–Cl system, indicate that the Glass was leached at relatively low oxidation potentials (Eh IV to Pu III would require considerably more reducing conditions (Eh
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a micro xas xrf and thermodynamic study of ceiii iv speciation after long term aqueous alteration of simulated Nuclear Waste Glass relevance for predicting pu behavior
Applied Geochemistry, 2012Co-Authors: Enzo Curti, Daniel Grolimund, Camelia N. BorcaAbstract:Abstract In the present study, the dissolution and mobilization of Ce introduced in a simulated Nuclear Waste Glass (MW) as a surrogate of Pu was investigated after leaching in pure water over 12 a at 90 °C and pH ∼ 9.6. The microscopic distribution and oxidation state of Ce in the altered Glass were studied using micro-X-ray fluorescence (micro-XRF) mapping techniques and micro-X-ray near-edge absorption spectroscopy (micro-XANES). Distribution maps of Ce III and Ce IV were obtained by recording the L α fluorescence emission at two different incident X-ray energies, coinciding with the maximum contrast between Ce III and Ce IV fluorescence intensities. The micro-XRF maps revealed that Ce was dominantly present as oxidized species (Ce IV ) in the original Glass. After dissolution from the Glass matrix, Ce IV was partly reduced and re-immobilized as Ce III at grain boundaries or in the interstitial spaces between the Glass particles. The concentration of Ce III was found to correlate with the spatial distribution of secondary Mg-clay formed during the aqueous corrosion as the main Glass alteration product. Micro-XANES spectra collected at locations representative of both altered and non-altered Glass domains confirmed the findings obtained by the redox mapping. Because redox-sensitive elements in the pristine MW Glass (Fe, Cr, Se) occur almost exclusively as oxidized species, reduction of Ce IV was probably mediated by an external source of reductants, such as Fe(0) from the steel reaction vessel. These results, in conjunction with an Eh–pH stability diagram of the Ce III/IV –O–H–C IV –P–S VI –Na–Cl system, indicate that the Glass was leached at relatively low oxidation potentials (Eh IV to Pu III would require considerably more reducing conditions (Eh
