Oxygen Isotope Alterations during the Reduction of U(3)O(8) to UO(2) for Nuclear Forensics Applications

[Image: see text] 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.