THE DIFFUSION OF URANIUM IN U-3O-8
During oxidation of UO-2 in air, U-3O-8 (for U-3O-(8-x)) is the final product. U-3O-8 is not being used as nuclear fuel, but it is a material of interest for both basic and applied research. For instance, it is used as starting material for various reactions and also as standard for determining O/U ratios of uranium oxides. The motivation for the present study of uranium self-diffusion was a technological problem. While oxidizing (U, Pu)C in air to facilitate solubility in HNO-3, a segregation of Pu between the MO-2 and the M-3O-8 phases formed is observed (M=U and/or Pu). The M-3O-8 is rich in U and the MO-2 phase becomes enriched in Pu, even if the oxidation is performed at relatively low temperatures, say at < 800 degrees C. Since Pu-rich MO-2 is not easily soluble in HNO-3, this causes difficulties in dissolving the oxidation product. Oxygen diffusion is known to be fast in MO-2 and MO-(2+x), but metal atom diffusion is very slow in UO-2 and MO-2. No data exist for U-3O-8. Transport of metal atoms, however, is needed for the observed segregation. To fill this gap, the self-diffusion of uranium in U-3O-8 was measured. Most experiments were performed at constant composition and some attempts were made to study diffusion during oxidation or reduction. 233-U was used as a tracer, applying the thin layer condition and high resolution alpha spectroscopy to measure the U penetration profiles following different annealing steps. This non-destructive method of high resolving power has been described before.
Bibliographic Reference: JOURNAL OF NUCLEAR MATERIALS, VOL. 115 (1983), NOS. 2 & 3, PP. 350-353
Record Number: 1989122040800 / Last updated on: 1987-01-01
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