Defect segregation facilitates oxygen transport at fluorite UO2 grain boundaries

A. R. Symington, M. Molinari, N. A. Brincat, N. R. Williams, S. C. Parker

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Abstract

An important challenge for modelling transport in materials for energy applications is that in most applications they are polycrystalline, and hence it is critical to understand the properties in the presence of grain boundaries. Moreover, most grain boundaries are not pristine stoichiometric interfaces and hence dopants are likely to play a significant role. In this paper, we describe our recent work on using atomistic molecular dynamics simulations to model the effect of doped grain boundaries on oxygen transport of fluorite structured UO 2. UO 2, much like other fluorite grain boundaries, are found to be sinks for oxygen vacancy segregation relative to the grain interior, thus facilitating oxygen transport. Fission products further enhance diffusivity via strong interactions between the impurities and oxygen defects. Doping produces a striking structural alteration in the Σ5 class of grain boundaries that enhances oxygen diffusivity even further. This article is part of a discussion meeting issue 'Energy materials for a low carbon future'.

Original languageEnglish
Article number20190026
Pages (from-to)1-16
Number of pages16
JournalPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Volume377
Issue number2152
Early online date8 Jul 2019
DOIs
Publication statusPublished - 31 Aug 2019

Funding

Data accessibility. Force field parameters, atomic configurations, diffusion coefficients and Arrhenius plots can be found in the electronic supplementary material. Atomic density analysis and the mean squared displacements were carried out using the polypy code [76]. The data supporting the findings of this study are openly available at https://zenodo.org/record/3228371#.XOgEWBZKipo. Authors’ contributions. A.R.S. carried out the simulations, performed the data analysis and wrote the manuscript with contributions from all authors; S.C.P., M.M. and A.R.S. designed the study; M.M. and S.C.P. derived the force fields used in the study. Competing interests. The authors declare that they have no competing interests. Funding. A.R.S. acknowledges AWE and EPSRC (EP/R010366/1) for funding. Computations were run on Balena HPC facility at the University of Bath and the ARCHER UK National Supercomputing Service (http:// www.archer.ac.uk) via our membership of the UK’s HEC Materials Chemistry Consortium funded by EPSRC (EP/L000202, EP/R029431). Acknowledgements. M.M. thanks the University of Huddersfield for access to the Orion computing facility.

Keywords

  • Fission products
  • MO-doped UO
  • Nuclear fuel
  • Oxygen diffusion
  • Segregation
  • Space charge in UO

ASJC Scopus subject areas

  • General Mathematics
  • General Engineering
  • General Physics and Astronomy

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