Enhanced Oxygen Isotope Determination in Uranium Oxides Using BrF 5 Fluorination

A new method for accurate determination of oxygen isotopes in uranium oxides encountered in the nuclear fuel cycle was developed using the conventional BrF 5 fluorination technique. Laser‐assisted fluorination was tested for comparison. We focused on fine powders of triuranium octoxide (U 3 O 8 ), uranium dioxide (UO 2±x with 0 ≤  x  ≤ 0.25), uranium trioxide (UO 3 . n H 2 O, with 0.8 ≤  n  ≤ 2) and diuranates (M 2 U 2 O 7 . n H 2 O, with M  = NH 4 , Na or Mg 0.5 and 0 ≤  n  ≤ 6). Fluorination at room temperature and heating under vacuum at 150 °C are shown to eliminate both adsorbed and structural water from the powder samples. Precision fit for purpose of δ 18 O values (± 0.3‰, 1 s ) and oxygen yields (close to 100%) were obtained for U 3 O 8 and UO 2 where oxygen is only bound to uranium. A lower precision was observed for UO 3 . n H 2 O and M 2 U 2 O 7 . n H 2 O where oxygen is both present in the structural H 2 O and bonded to uranium and where the extracted O 2(g) can be contaminated by NF 3 and NO x compounds. Laser‐assisted fluorination gave shifted δ 18 O values between +0.8 and +1.4‰ for U 3 O 8 , around −0.8‰ for UO 3 . n H 2 O and between −3.9 and −4.5‰ for M 2 U 2 O 7 . n H 2 O (± 0.3‰, 1 s ) compared with the conventional method.