Research for the Safe Management of Nuclear Waste at Forschungszentrum Jülich: Materials Chemistry and Solid Solution Aspects

Bosbach, Dirk; Brandt, Felix; Bukaemskiy, Andrey; Deissmann, Guido; Kegler, Philip; Klinkenberg, Martina; Kowalski, Piotr M.; Modolo, Giuseppe; Niemeyer, Irmgard; Neumeier, Stefan; Vinograd, Victor L.

doi:10.1002/adem.201901417

Cited by 14 publications

(7 citation statements)

References 90 publications

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“…Similar to conventional UO 2 -based LWR fuels, spent modern fuels are likely to be disposed of in deep geological repositories, which are considered the most appropriate disposal option for high level nuclear waste [ 12 , 13 , 14 ]. However, knowledge gaps still exist on the stability of the spent modern fuels at conditions of a deep geological waste repository.…”

Section: Introductionmentioning

confidence: 99%

Chromium Doped UO2-Based Ceramics: Synthesis and Characterization of Model Materials for Modern Nuclear Fuels

et al. 2021

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Cr-doped UO2 as a modern nuclear fuel type has been demonstrated to increase the in-reactor fuel performance compared to conventional nuclear fuels. Little is known about the long-term stability of spent Cr-doped UO2 nuclear fuels in a deep geological disposal facility. The investigation of suitable model materials in a step wise bottom-up approach can provide insights into the corrosion behavior of spent Cr-doped nuclear fuels. Here, we present new wet chemical approaches providing the basis for such model systems, namely co-precipitation and wet coating. Both were successfully tested and optimized, based on detailed analyses of all synthesis steps and parameters: Cr-doping method, thermal treatment, reduction of U3O8 to UO2, green body production, and pellet sintering. Both methods enable the production of suitable model systems with a similar microstructure and density as a reference sample from AREVA. In comparison with results from the classical powder route, similar trends upon grain size and lattice parameter were determined. The results of this investigation highlight the significance of subtly different synthesis routes on the properties of Cr-doped UO2 ceramics. They enable a reproducible tailor-made well-defined microstructure, a homogeneous doping, for example, with lanthanides or alpha sources, the introduction of metallic particles, and a dust-free preparation.

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Section: Introductionmentioning

confidence: 99%

Chromium Doped UO2-Based Ceramics: Synthesis and Characterization of Model Materials for Modern Nuclear Fuels

et al. 2021

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“…The unique chemical conditions are characterized by 1) generally reducing conditions due to a significant amount of hydrogen produced due to the anoxic corrosion of metallic waste containers, 2) the presence of locally formed oxidizing conditions caused by radiolytic products such as H 2 O 2 , and 3) complex groundwater chemistry. The radiolytic oxidants evoke locally oxidizing effects at the spent fuel surface leading to an oxidative dissolution of the waste, due to the oxidation of poorly soluble U(IV) to easily soluble U(VI) ( Shoesmith, 2000 ; Eriksen et al, 2012 ; Shoesmith et al, 2013 ; Bosbach et al, 2020 ; Hansson et al, 2021 ).…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

et al. 2021

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Available data on the dependence of the equilibrium chemical potential of oxygen on degrees of doping, z, and non-stoichiometry, x, y, in U1-zLnzO2+0.5(x-y) fluorite solid solutions and data on the dependence of the lattice parameter, a, on the same variables are combined within a unified structural-thermodynamic model. The thermodynamic model fits experimental isotherms of the oxygen potential under the assumptions of a non-ideal mixing of the endmembers, UO2, UO2.5, UO1.5, LnO1.5, and Ln0.5U0.5O2, and of a significant reduction in the configurational entropy arising from short-range ordering (SRO) within cation-anion distributions. The structural model further investigates the SRO in terms of constraints on admissible values of cation coordination numbers and, building on these constraints, fits the lattice parameter as a function of z, y, and x. Linking together the thermodynamic and structural models allows predicting the lattice parameter as a function of z, T and the oxygen partial pressure. The model elucidates contrasting structural and thermodynamic changes due to the doping with LaO1.5, on the one hand, and with NdO1.5 and GdO1.5, on the other hand. An increased oxidation resistance in the case of Gd and Nd is attributed to strain effects caused by the lattice contraction due to the doping and to an increased thermodynamic cost of a further contraction required by the oxidation.

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“…Much effort has been devoted to understanding the properties of a surface-altered layer on borosilicate glasses due to their importance to the long-term chemical durability of nuclear waste glasses. − This is because the surface-altered layer can control the long-term performance of glass dissolution. The amount of boron released into solution can be estimated from a glass dissolution test, and the mass loss is employed to calculate the volume fraction of the altered layer.…”

Section: Introductionmentioning

confidence: 99%

Elucidating the Atomic Structures of the Gel Layer Formed during Aluminoborosilicate Glass Dissolution: An Integrated Experimental and Simulation Study

Furutani

Ohkubo

et al. 2022

J. Phys. Chem. C

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Altered glasses produced during the aqueous dissolution of silicate and borosilicate glasses are among the most complex structures to understand at the atomic level due to their amorphous nature, random porosity, and various levels of hydration. In this study, we gained insights into the complex atomic structures of altered aluminoborosilicate glasses by combining a range of experimental and computational approaches. The altered glasses were prepared by the dissolution of three glasses with varying levels of alumina in an acid for 7 days. A comprehensive set of experimental [elemental analysis, high-energy X-ray diffraction, 29 Si and 27 Al solid-state nuclear magnetic resonance (NMR), and O 1s X-ray photoelectron spectroscopy (XPS)] and modeling (molecular dynamics (MD) simulations using nonreactive and reactive force fields) approaches were used to study the atomic structures of these altered glasses. Elemental analysis showed that most of the B in the pristine glasses was leached into the solution and was not contained in the altered glass. The 29 Si and 27 Al solid-state NMR spectra revealed that the altered glasses have more polymerized silicate networks as compared to those in the pristine glasses due to the reformation of linkages among Si and Al oxygen polyhedral in the altered glasses. The bridging and nonbridging (or hydroxyl O) atoms in the altered glasses were also quantified from their O 1s XPS spectra. Atomic structure models of the altered glasses were constructed using MD simulations using the reactive force field based on the compositional information obtained from experiments. Various pore structures were generated using the charge-scaling (CS) method using different initial densities and CS temperatures; the best CS parameters of each altered glass were then determined by comparing with the experimental structure factors obtained from high-energy X-ray diffraction. Pore and atomic structures and vibrational properties around these pore surfaces were analyzed. These results from this comprehensive study thus provide a realistic insight into the pore morphology, atomic structure, and vibrational properties of altered glasses.

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Research for the Safe Management of Nuclear Waste at Forschungszentrum Jülich: Materials Chemistry and Solid Solution Aspects

Cited by 14 publications

References 90 publications

Chromium Doped UO2-Based Ceramics: Synthesis and Characterization of Model Materials for Modern Nuclear Fuels

Chromium Doped UO2-Based Ceramics: Synthesis and Characterization of Model Materials for Modern Nuclear Fuels

Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

Elucidating the Atomic Structures of the Gel Layer Formed during Aluminoborosilicate Glass Dissolution: An Integrated Experimental and Simulation Study

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