A novel approach to determine the local burnup in irradiated fuels using Atom Probe Tomography (APT)

A novel approach is presented to determine the local burnup in irradiated fuels using isotopic quantification obtained by Atom Probe Tomography (APT). Considering the volume of sample used (<100 μm³) for APT experiments using the lift-out process in a scanning electron microscope equipped with a Focused Ion Beam (FIB), the presented method determines the local burnup from a nuclear fuel, where a minimal amount of waste is produced. In this work, three samples were analyzed with different burnup conditions: as received low enriched 19.8% U-235, intermediate burnup (∼52% U-235 fissioned) and high burnup (∼69% U-235 fissioned) U–Mo fuel. APT is used to quantify the isotopes of ²³⁵U, ²³⁶U, ²³⁸U, ²³⁹Pu and ²³⁷Np for burnup calculation in the irradiated metallic U–7Mo dispersion fuel. The equation used to estimate the burnup of fuels is derived by considering that the initial counts of U is equal to the sum of remaining atoms of U isotopes and all the U reactions undergone during irradiation. This method provides U enrichment and local burnup with an unprecedented high spatial resolution based on quantification of isotopic ratios of U.