Thermophysical properties of urania-zirconia (U,Zr)O₂ mixed oxides by molecular dynamics

Journal Article · 04 November 2019 · Journal of Nuclear Materials

DOI: https://doi.org/10.1016/j.jnucmat.2019.151876 · OSTI ID:1574000

Frost, Dillon G. ^[1]; Galvin, Conor O. T. ^[2]; Cooper, Michael William Donald  ^[3]; Obbard, Edward G. ^[1]; Burr, Patrick A. ^[1]

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1. Univ. of New South Wales (Australia). School of Mechanical Engineering; Australia's Nuclear Science and Technology Organisation (ANSTO) (Australia)
2. Univ. of New South Wales (Australia). School of Mechanical Engineering
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Molecular dynamics simulations were used to investigate the thermophysical properties of (U,Zr)O₂ between 300 K and 3500 K. For compositions with <25% UO₂ the tetragonal phase is stable but beyond 25% the cubic fluorite phase becomes stable for all temperatures. Thermal expansion, heat capacity and thermal conductivity have been predicted. The addition of ZrO₂ to UO₂ causes a reduction in thermal conductivity however this effect decreases with increased temperature and, beyond 1000 K, becomes insignificant. Thermal expansion of (U,Zr)O₂ mixtures with >25% UO₂, which are in the cubic fluorite phase, is similar to that of the pure UO₂ end member. A superionic transition is observed in cubic (U,Zr)O₂ at temperatures between 1500 K and 3000 K, occurring at progressively lower temperatures with increasing ZrO₂ content. Here, the heat capacity of these mixed oxides increases from 80 J/mol.K up to 130 J/mol.K at temperatures relevant to accident conditions, possibly retarding heating in fuels with a significant pellet-clad bonding layer.

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 1574000
• Report Number(s): LA-UR--19-25917
• Journal Information: Journal of Nuclear Materials, Journal Name: Journal of Nuclear Materials Vol. 528; ISSN 0022-3115
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English