3D-SEM height maps series to monitor materials corrosion and dissolution

Podor, Renaud; Goff, X. Le; Cordara, Théo; Odorico, Michaël; Favrichon, Julien; Claparède, Laurent; Szenknect, Stéphanie; Dacheux, Nicolas

doi:10.1016/j.matchar.2019.02.017

Cited by 16 publications

(18 citation statements)

References 29 publications

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“…Grain and phase boundaries in ceramics and rocks are another source of defects and become important in dissolutions as the grain size decreases below the submicrometer scale. The excess free energy from the interfacial energy is expected to enhance the grain boundary dissolution as a number of experiments have suggested [67,68,69,70]. Dissolution at the boundaries may penetrate to a great depth assisted by the enhanced dissolution kinetics if the transport of reactive species within gain boundaries is not the rate-determining step.…”

Section: Effect Of the Structure Of Oxides On Chemical Durabilitymentioning

confidence: 99%

Thermodynamic equilibrium and kinetic fundamentals of oxide dissolution in aqueous solution

Wang

2020

J. Mater. Res.

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Section: Effect Of the Structure Of Oxides On Chemical Durabilitymentioning

confidence: 99%

Thermodynamic equilibrium and kinetic fundamentals of oxide dissolution in aqueous solution

Wang

2020

J. Mater. Res.

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“…During the leaching experiment, the surface of the pellet was also regularly observed under environmental conditions. According to Podor et al 42 , the pellet was directly introduced in the ESEM chamber equipped with a Peltier stage without any further preparation. The Peltier stage was cooled down to 2 °C prior the introduction of the sample.…”

Section: Characterizations Of Uo 2 Pelletmentioning

confidence: 99%

Coffinite formation from UO2+x

Szenknect

Alby

García

et al. 2020

Sci Rep

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Most of the highly radioactive spent nuclear fuel (SNF) around the world is destined for final disposal in deep-mined geological repositories. At the end of the fuel's useful life in a reactor, about 96% of the SNF is still UO 2. Thus, the behaviour of UO 2 in SNF must be understood and evaluated under the weathering conditions of geologic disposal, which extend to periods of hundreds of thousands of years. There is ample evidence from nature that many uranium deposits have experienced conditions for which the formation of coffinite, USiO 4 , has been favoured over uraninite, UO 2+x , during subsequent alteration events. Thus, coffinite is an important alteration product of the UO 2 in SNF. Here, we present the first evidence of the formation of coffinite on the surface of UO 2 at the time scale of laboratory experiments in a solution saturated with respect to amorphous silica at pH = 9, room temperature and under anoxic conditions. Uraninite, UO 2+x is the most common U 4+ mineral in nature followed by coffinite, USiO 4 , which is found as a primary phase or an alteration product in many uranium deposits. Coffinite, tetragonal, is isostructural with zircon (ZrSiO 4) and thorite (ThSiO 4); however, coffinite can contain some water either as H 2 O or OH groups 1. Altered uraninite and coffinite have been documented from Oklo, Gabon 2-5 , deposits in the Athabasca Basin 4,6,7 and Elliot Lake, Canada 8. Other examples include Jachymov, Czech Republic 9 or La Crouzille district, France 10. For many years, coffinite had gone unrecognized in most uranium deposits, particularly uranium roll-front deposits, as a distinct phase because of its fine grain size and intimate association with uraninite 5,6,11,12. The alteration of uraninite to coffinite is a key event for UO 2 in nature and UO 2 in spent fuel in a geologic repository. Coffinite, being a U 4+-silicate, is associated with reducing environments, with sulphides and organic matter 1 , where it likely precipitated from neutral to weakly alkaline fluids. Coffinite formation in sedimentary uranium deposits is associated with relatively low temperatures, 80-130 °C. A detailed investigation of meteoric roll-front deposits in the Athabasca basin, suggest an estimated temperature of coffinite precipitation in the uranium front of no greater than 50 °C 13. Even though laboratory experiments report coffinite formation at 150-250 °C 14,15 , it appears that these elevated temperatures are not required to form coffinite in nature. Although coffinite is abundant in uranium ore deposits, its synthesis has been a major challenge since its initial description as a mineral in 1955 16. A number of investigators have sought to obtain pure synthetic coffinite, but only a few have succeeded 14,15,17-21. Synthetic coffinite was always obtained under hydrothermal conditions. Systematically, the samples obtained were a mixture of phases, mainly composed of fine grains of USiO 4 , nanoparticles of UO 2 and amorphous SiO 2. All of these attempts to synthesize coffinite indicate that there i...

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“…The surface area of each of these two investigated zones was S image = 552 µm². ESEM-optimized images were recorded using the conditions optimized by Podor et al 38…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…In addition, the heterogeneous evolution of the microstructure of the pellet under these conditions allowed to obtain better 3D reconstruction accuracy. Indeed, Podor et al 38 showed that the greater the height differences at the surface of the pellet, the smaller the errors on the height maps. A selection of ESEM images recorded in the zone of interest at the surface of UO 2 + 3 mol.% PGMs pellet dissolved in 0.1 mol.L -1 HNO 3 at 60°C, with a tilt angle of 0° and at the highest magnification, is provided in Figure S2.…”

Section: Quantitative Monitoring Of Pellet Microstructure Changes Durmentioning

confidence: 99%

Microstructural evolution of UO2 pellets containing metallic particles of Ru, Rh and Pd during dissolution in nitric acid solution: 3D-ESEM monitoring

et al. 2019

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Uranium dioxide containing 3 mol.% platinum group metals (PGMs) (Ru, Rh, Pd) was synthesized by hydroxide precipitation. The powders were converted to oxides, pelletized and sintered to prepare dense pellets of UO 2 incorporating PGMs particles. The characterization techniques performed revealed a microstructure similar to that of spent nuclear fuel (SNF). Dissolution tests in nitric acid demonstrated that in the presence of PGMs, the uranium dissolution rate was increased and the induction period was shortened. We used a new method based on the acquisition of Environmental Scanning Electron Microscopy (ESEM) micrographs recorded at three tilt angles and at different dissolution times. This method allowed the reconstruction of the topography of the solid/liquid interface. By monitoring the evolution of the solid/liquid interface during dissolution by means of 3D reconstructions, we were able to observe preferential dissolution zones in the vicinity of the PGMs particles and to determine microscopic dissolution rates for several regions of interest. PGMs particles were found mainly at the grain boundaries. In 0.1 M HNO 3 solution at 60˚C, the normalized dissolution rate for uranium at the grain boundaries reached R L (U) = (7 ± 1)×10-2 g.m-2 .d-1 , a value similar to the normalized dissolution rate determined for the whole image over the first 30 days of the experiment. This result showed that the dissolution occurred mainly at the UO 2 grain boundaries in the vicinity of PGMs particles. Furthermore, the 3D reconstructions of the solid/liquid interface were used to determine the evolution of the surface area of the pellet. By combining the weight losses determined at the macroscopic scale using the uranium concentrations in solution with the reactive surface area values, it was possible to estimate an effective normalized dissolution rate for the whole pellet.

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3D-SEM height maps series to monitor materials corrosion and dissolution

Cited by 16 publications

References 29 publications

Thermodynamic equilibrium and kinetic fundamentals of oxide dissolution in aqueous solution

Thermodynamic equilibrium and kinetic fundamentals of oxide dissolution in aqueous solution

Coffinite formation from UO2+x

Microstructural evolution of UO2 pellets containing metallic particles of Ru, Rh and Pd during dissolution in nitric acid solution: 3D-ESEM monitoring

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