Abstract
Addition of zirconia (ZrO2) to nuclear waste glasses, even in small amount, significantly affects physical properties such as chemical durability, density, viscosity, and glass transition temperature. Hence ZrO2 plays an important role in the development of nuclear waste glass compositions. It was found recently that addition of zirconia decreases the initial dissolution rate but increases long-term dissolution by changing the protective properties such as porosity of alteration layers. In this study, the International Simple Glass (ISG) with different amounts of ZrO2/SiO2 substitution was simulated using classical molecular dynamics (MD) simulations and recently developed composition-dependent potential sets. Local structural descriptors such as bond distances, bond angle distributions, and coordination numbers were systematically studied and compared with experimental values. Zr K-edge extended X-ray absorption fine structure spectra were also calculated and compared with experiment to resolve the local coordination environment around Zr. Medium-range structural information (e.g., Qn distribution, network connectivity, and ring-size distribution) showed that ZrO2/SiO2 substitution increases the overall network connectivity and the amount of smaller sized rings, which will decrease the initial dissolution rate by strengthening the glass network and limiting water diffusivity. Finally, diffusion and dynamic properties of the ions were studied and discussed to develop a better understanding of the chemical durability of these glasses.
Highlights
Molecular dynamics (MD) simulation is an effective method of studying structural information in glass materials, and it provides a direct observation of atomic structure, which is difficult to obtain from experimental methods
The calculated structure factor is in including the Zr K-edge extended X-ray absorption fine structure good agreement with the experimental data, indicating an overall reasonable structure model generated from our MD simulation
Selected bond lengths of simulated 0Zr, 2Zr (ISG), 3Zr, and 4Zr glasses obtained from the first peak of pair distribution functions (PDFs) and comparison with values found in literature are listed in
Summary
Borosilicate glasses have been used as one of the vitrification materials of radioactive wastes in many countries. International Simple Glass (ISG) is a simplified model composition for a collaborative study of dissolution/corrosion mechanism of highlevel waste (HLW) glasses. ISG has been intensively researched recently with studies focusing on its dissolution behavior under different conditions, its surface quality, radiation effect, waste loading, mechanical property, and especially on the properties of its alteration layers using diverse techniques such as electron microprobe analysis, Doppler broadening positron annihilation spectroscopy, and atom probe tomography.24due to the lack of long-range periodicity, the structural study of glass materials exhibits many challenges.Detailed information of glass structure provides better understanding of glass physical properties and chemical durability, which helps design glass compositions for different waste types and geological disposals. ISG has been intensively researched recently with studies focusing on its dissolution behavior under different conditions, its surface quality, radiation effect, waste loading, mechanical property, and especially on the properties of its alteration layers using diverse techniques such as electron microprobe analysis, Doppler broadening positron annihilation spectroscopy, and atom probe tomography.. Due to the lack of long-range periodicity, the structural study of glass materials exhibits many challenges. Detailed information of glass structure provides better understanding of glass physical properties and chemical durability, which helps design glass compositions for different waste types and geological disposals. Molecular dynamics (MD) simulation is an effective method of studying structural information in glass materials, and it provides a direct observation of atomic structure, which is difficult to obtain from experimental methods.. With the recent development of modified composition-dependent pairwise potential sets, it is possible to simulate complex glass compositions. ISG was successfully simulated with MD, structural related properties such as the percentage of 4-
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