Thermal conductivity variation in uranium dioxide with gadolinia additions

MJ Qin and SC Middleburgh and MWD Cooper and MJD Rushton and M Puide and EY Kuo and RW Grimes and GR Lumpkin, JOURNAL OF NUCLEAR MATERIALS, 540, 152258 (2020).

DOI: 10.1016/j.jnucmat.2020.152258

By combining experimental observations on Gd doped fuel with a theoretical understanding, the variation in thermal conductivity with Gd concentration and accommodation mechanism has been modelled. Four types of Gd accommodation mechanisms have been studied. In UO2-x, isolated substitutional Gd3+ ions are compensated by oxygen vacancies and 2Gd(U)' : V-O(center dot center dot)(x) defect clusters. In UO2, isolated substitutional Gd3+ ions are compensated by U5+ ions and Gd-U' : U-U(center dot)(x) defect clusters. The results indicate that defect clusters can be considered as less effective phonon scatterers and therefore result in less thermal conductivity degradation. The thermal conductivity predicted for UO2 with Gd-U' : U-U(center dot)(x) defect clusters is in good agreement with experimental data for UO2 with 5 wt% Thermal conductivity variation in uranium dioxide with gadolinia additions . This supports the previous theoretical results that Gd is accommodated through defect clusters Gd-U' : U-U(center dot)(x) in UO2 in the presence of excess oxygen. (C) 2020 Elsevier B.V. All rights reserved.

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