Isotopic Heterogeneity Imaged in a Uranium Fuel Pellet with Extreme Ultraviolet Laser Ablation and Ionization Time-of-Flight Mass Spectrometry

We use extreme ultraviolet laser ablation and ionization time-of-flight mass spectrometry (EUV TOF) to map uranium isotopic heterogeneity at the nanoscale (<= 100 nm). Using low-enriched uranium fuel pellets that were made by blending two isotopically distinct feedstocks, we show that EUV TOF can map the U-235/U-238 content in 100 nm-sized pixels. The two-dimensional (2D) isotope maps reveal U ratio variations in submicroscale to >= 1 mu m areas of the pellet that had not been fully exposed by microscale or bulk mass spectrometry analyses. Compared to the ratio distribution measured in a homogeneous U reference material, the ratios in the enriched pellet follow a similar to 3X wider distribution. These results indicate U heterogeneity in the fuel pellet from incomplete blending of the different source materials. EUV TOF results agree well with those obtained on the same enriched pellets by nanoscale secondary ionization mass spectrometry (NanoSIMS), which reveals a comparable U isotope ratio distribution at the same spatial scale. EUV TOF's ability to assess and map isotopic heterogeneity at the nanoscale makes it a promising tool in fields such as nuclear forensics, geochemistry, and biology that could benefit from uncovering sub-microscale sources of chemical modifications.

Automated summary

The study used extreme ultraviolet laser ablation and ionization time-of-flight mass spectrometry to map uranium isotopic heterogeneity at the nanoscale, revealing variations in U-235/U-238 ratio at different spatial scales. The results suggest that U heterogeneity in the fuel pellet is due to incomplete blending of the source materials, and the ability of EUV TOF to assess isotopic heterogeneity at the nanoscale makes it a promising tool in various fields.