Simple cation-exchange separation for ICP-MS measurement of 79Se in spent nuclear fuel sample

A simple separation using a single cation-exchange column has been developed for the measurement of 79Se in a spent nuclear fuel solution with inductively coupled plasma mass spectrometry (ICP-MS). An irradiated UO2 pellet cut out from a PWR fuel rod was dissolved and used as a standard sample. A known amount of 82Se (20 ng) was added to the sample solution for the determination of the amount of 79Se by isotope dilution mass spectrometry (IDMS). The 82Se-spiked and non-spiked sample solutions were fed to each cation-exchange resin-packed column, followed by 1 M nitric acid for washing. The first 3 mL of the effluent was directly injected to the ICP-MS for obtaining the isotopic ratio of 79Se/82Se. The recovery of Se in the effluent was 92%, while no leakage of Gd3+ (158Gd) and Dy3+ (164Dy) which cause major isobaric interferences on 79Se and 82Se determinations by forming 158Gd2+ and 164Dy2+, respectively, was observed. In addition, the highly radioactive coexisting components e.g., Sr2+, Y3+, Cs+, and Ba2+ were retained on the cation-exchange resin, leading to the decrease in the surface dose rate of the sample solution from 0.3 mSv/h to a background level. The isotopic ratio 82Se/79Se of the non-spiked and the spiked fractions were 5.4 ± 1.0 and 13.7 ± 2.2, respectively. From these isotopic ratios, the amounts of 79Se and 82Se in the sample solution were calculated to be 2.4 ± 0.7 and 13.3 ± 4.6 ng, respectively. (author)