Global variation of oxygen isotope compositions in rain and snow has been well documented. A similar spatial pattern of variation is also likely reflected in the oxygen isotope compositions of waters used in the production of nuclear materials. An oxygen isotope signature may be imparted to uranium oxide materials via exchange with water or an aqueous solvent during reprocessing and/or conversion to uranium oxide. Understanding the relationship between locally derived process waters and uranium oxide materials should allow the use of oxygen isotope abundances as a signature of the provenance (production/ reprocessing site) of samples of unknown origin. We have analyzed the oxygen isotope compositions of 23 fuel pellets from 5 localities using high vacuum fluorination and isotope ratio mass spectrometry to examine the variation in oxygen isotope compositions of UO2 fuel pellets. We also created particle dispersions from powders of two of the fuel pellets and measured the oxygen isotope compositions of individual UO2 particles by secondary ion mass spectrometry (SIMS). We find that UO2 oxygen isotope compositions vary with pellet location and local water isotope compositions, with δ18O-UO2 values being 5 ± 2 per mil lower than local waters on average. The standard deviation of δ18O-UO2 values for different fuel pellet production lots from the same plant ranges from 0.2 to 1.4 per mil and may depend on the variability of local water sources and/or production methods. Our SIMS measurements of individual particles were able to distinguish between two different fuel pellet oxygen isotope compositions (1.2 per mil vs. -18.3 per mil). Taken together, these data demonstrate that UO2 fuel pellets produced at the same facility using the same process result in consistent oxygen isotope compositions over time and can be distinguished from other production localities both on a bulk and particle basis.

Variation of oxygen isotopes in uranium oxide fuel pellets

2019 Spring National Meeting

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