Density functional theory calculations of self- and Xe diffusion in U₃Si₂

Journal Article · Fri Dec 21 00:00:00 EST 2018 · Journal of Nuclear Materials

DOI:https://doi.org/10.1016/j.jnucmat.2018.12.021· OSTI ID:1489979

Andersson, D. A. ^[1]; Liu, X. -Y. ^[1]; Beeler, B. ^[2]; Middleburgh, S. C. ^[3]; Claisse, A. ^[4]; Stanek, C. R. ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Idaho National Lab. (INL), Idaho Falls, ID (United States)
3. Bangor Univ. (United Kingdom)
4. Westinghouse Electric Sweden, Vasteras (Sweden)

Uranium silicide, U₃Si₂, has been proposed as an advanced nuclear fuel to be used in light water reactors (LWRs). Development of this alternative to the predominant current fuel, UO₂, is motivated by enhanced accident tolerance as a result of higher thermal conductivity as well as improved fuel cycle economics through increased uranium density. In order to accurately model the fuel performance of U₃Si₂, the diffusion rate of point defects, which is related to self-diffusion, and of fission gas atoms must be determined. DFT calculations are used to predict the U and Si point defect concentrations, the corresponding self-diffusivities, the preferred Xe trap site and the Xe diffusivity. Effects of irradiation are not considered. A low defect formation energy and a high entropy for Si interstitials give rise to Si-rich non-stoichiometry at elevated temperatures. Both U and Si self-diffusion and Xe diffusion are anisotropic as a consequence of the tetragonal crystal structure of U₃Si₂. Si diffusion occurs by interstitial mechanisms in both the a-b plane and along the c axis, while the U c axis diffusion rate is controlled by a vacancy mechanism. Interstitial diffusion of U is very fast in the a-b plane of the U₃Si₂ crystal structure. Xe atoms prefer to occupy U vacancy trap sites. The highest Xe diffusion rate occurs by a vacancy mechanism in both the a-b plane and along the c axis. The diffusion rate is similar in the a-b plane and along the c axis. U and Si self-diffusion and Xe diffusion are all faster in U3Si2 than intrinsic U and Xe diffusion in conventional UO₂ nuclear fuel.

• 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: 1489979
• Alternate ID(s): OSTI ID: 1507802
• Report Number(s): LA-UR-18-28448
• Journal Information: Journal of Nuclear Materials, Vol. 515, Issue C; ISSN 0022-3115
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

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