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A miniature solid state galvanic cell was used to measure the oxygen potential of reactor irradiated UO(2) fuel at different burnups in the range of 28 to 150 GWd d/t M. This very high burnup was achieved in the rim region of a fuel with a cross-section average burnup of 75 GWd d/t M. The fuels had different enrichments and therefore different contributions of fission of 235U and 239Pu. The temperature range covered was 900 to 1350 K. None of the fuels showed a significant oxidation. Rather, if allowance is made for the dissolved rare earth fission products and the Pu formed during irradiation, some of the fuels were very slightly substoichiometric and the highest possible degree of oxidation corresponded to UO(2.001). The implication of these results, which are in contrast to commonly assumed ideas that UO(2) fuel oxidises due to burnup, are discussed and the importance of the fission product Mo and of the zircaloy clad as oxygen buffers is outlined.

Additional information

Authors: MATZKE H, JRC Karlsruhe (DE)
Bibliographic Reference: Paper presented: 13th IUPAC Conference on Chemical Thermodynamics, Clermont-Ferrand (FR), July 17-22, 1994
Availability: Available from (1) as Paper EN 38419 ORA
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