Simultaneous Isotopic Analysis of U, Pu, and Am in Spent Nuclear Fuel by Resonance Ionization Mass Spectrometry

Solid samples of spent nuclear fuel were analyzed for actinide isotopic composition by resonance ionization mass spectrometry. Isotopes of U, Pu, and Am were simultaneously quantified using a new method that removes and/ or resolves the isobaric interferences at U-238/Pu-238 and Pu-241/Am-241 without sample preparation other than cutting and mounting small (similar to 10 mu m) samples. Trends in burnup and neutron capture product distributions were correlated with the sampling positions inside the reactor. The results show the skin effect, in which the core and near-edge regions of a fuel pellet exhibit strong differences in actinide concentrations and isotope distributions due to differences in the neutron energy spectra between the pellet rim and the core. While no elemental concentration measurements were made, the ability to measure the Pu-238/Pu-239 ratio in the presence of a 7400x excess of U-238 enabled an estimate of the enhancement in Pu concentration due to the skin effect at the rim of the pellet.

Automated summary

The study analyzed spent nuclear fuel samples for actinide isotopic composition using resonance ionization mass spectrometry, finding differences in actinide concentrations and isotope distributions between the core and near-edge regions of fuel pellets due to the skin effect caused by variations in neutron energy spectra. The ability to estimate the enhancement in Pu concentration at the rim of the pellet was demonstrated by measuring the Pu-238/Pu-239 ratio in the presence of a 7400x excess of U-238.