LATTICE DISORDER AND METAL SELF-DIFFUSION IN NON-STOICHIOMETRIC UO2 AND U, PuO2Report as inadecuate




LATTICE DISORDER AND METAL SELF-DIFFUSION IN NON-STOICHIOMETRIC UO2 AND U, PuO2 - Download this document for free, or read online. Document in PDF available to download.



Abstract : The predominant defects in the fluorite structure are anion vacancies and interstitials. Cation defects occur at a much smaller rate and are therefore more difficult to study. They are, however, of crucial interest since they are rate-determining for many high temperature matter transport processes. Cation diffusion was therefore investigated in the temperature range ~ 1 400 to 2 200 °C. In stoichiometric and hyperstoichiometric oxides, MO2 and MO2+x M = U or U + Pu, a vacancy mechanism is indicated with diffusion rates increasing roughly proportional to x2. In MO2-x, a decrease in diffusion rates with x is observed for small values of x until a minimum is indicated. On further reduction, diffusion rates increase again. It is argued that this increase reflects a mechanism involving metal interstitials, hence most probably an interstitialcy mechanism of diffusion, though the alternative of a predominant transport via Schottky trios cannot be excluded. The relevant formation energies of point defects in the UO2 fluorite structure, as deduced from the diffusion data, compare favorably with theoretical predictions and measured values for the isostructural earth alkali halides, CaF2 and BaF2. The present diffusion data serve in addition to explain creep measurernents on substoichiometric mixed uranium-plutonium oxides.





Author: Hj. Matzke

Source: https://hal.archives-ouvertes.fr/



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