Oxygen Isotope Alterations during the Reduction of U₃O₈ to UO₂ for Nuclear Forensics Applications

Abstract

The fabrication of UO 2 from U 3 O 8 is an essential reaction in the nuclear fuel cycle. The oxygen isotope fractionation associated with this reaction has significant implications in the general field of nuclear forensics. Hence, the oxygen isotope fractionation during the reduction of U 3 O 8 to UO 2 was determined in the temperature range of 500−700 °C and for a duration of 2 to 6 h under a high-purity H 2 atmosphere. Three U 3 O 8 samples, possessing a different oxygen isotopic composition, were used to investigate key parameters involved with the fractionation during the reduction process. All UO 2 products did not maintain the original isotope composition of the starting U 3 O 8 under all conditions. The results show that the system UO 2 −H 2 O attains isotope equilibrium at 600 °C, provided the reduction process lasts at least 4 h or more. At 600 °C, UO 2 was isotopically depleted by 2.89 ± 0.82‰ compared to the U 3 O 8 from which it was produced. We find that the H 2 O formed during the reduction plays a major role in determining the final δ 18 O of UO 2 prepared from U 3 O 8. The isotope equilibrium of the system UO 2 −H 2 O at 600 °C was calculated, indicating that δ 18 O of the H 2 O was enriched by about 11‰ relative to the UO 2 due to the uranium mass effect. These findings could potentially have important implications for nuclear forensics, as they provide a new method for determining the history of UO 2 samples and tracing back their production process.

Oxygen Isotope and Fluorine Impurity Signatures during the Conversion of Uranium Ore Concentrates to Nuclear Fuel

“… 17 They also found that the UO 2 products were slightly more depleted in 18 O content than the starting U 3 O 8 materials, while the water vapor formed was around 11‰ more enriched. 17 …”

“…17 They also found that the UO 2 products were slightly more depleted in 18 O content than the starting U 3 O 8 materials, while the water vapor formed was around 11‰ more enriched. 17 Collectively, these experiments provide valuable information about the oxygen isotope fractionation of UOCs during calcination in inert or atmospheric conditions at elevated temperatures. However, knowledge is still lacking with respect to oxygen isotope fractionation and impurity effects for many other UOC conversion pathways.…”

“…From these experiments, they found that the final δ 18 O values of the UO 2 were dictated by the isotopic equilibrium between the water generated during the reduction and the resultant UO 2 . They also found that the UO 2 products were slightly more depleted in 18 O content than the starting U 3 O 8 materials, while the water vapor formed was around 11‰ more enriched …”

“…Expanding this work, they calcined three U 3 O 8 samples of differing δ 18 O values to UO 2 between 500 and 700 °C for 2, 4, and 6 h. 17 From these experiments, they found that the final δ 18 O values of the UO 2 were dictated by the isotopic equilibrium between the water generated during the reduction and the resultant UO 2 . 17 They also found that the UO 2 products were slightly more depleted in 18 O content than the starting U 3 O 8 materials, while the water vapor formed was around 11‰ more enriched. 17 Collectively, these experiments provide valuable information about the oxygen isotope fractionation of UOCs during calcination in inert or atmospheric conditions at elevated temperatures.…”

“… 16 They also found that preferential incorporation of 16 O by U 3 O 8 led to U 3 O 8 attaining δ 18 O values lower than O 2 . Expanding this work, they calcined three U 3 O 8 samples of differing δ 18 O values to UO 2 between 500 and 700 °C for 2, 4, and 6 h. 17 From these experiments, they found that the final δ 18 O values of the UO 2 were dictated by the isotopic equilibrium between the water generated during the reduction and the resultant UO 2 . 17 They also found that the UO 2 products were slightly more depleted in 18 O content than the starting U 3 O 8 materials, while the water vapor formed was around 11‰ more enriched.…”