Investigation of uranium isotopic signatures in real-life particles from a nuclear facility by thermal ionization mass spectrometry.

An improved method was recently developed for the isotopic analysis of single-reference uranium oxide particles for nuclear safeguards. This method is a combination of analytical tools including in situ SEM micromanipulation, filament carburization and multiple ion counting (MIC) detection, which is found to improve sensitivity for thermal ionization mass spectrometry (TIMS) isotope ratio analysis. The question was raised whether this method could be applied for the detection of nuclear signatures in real-life particles with unknown isotopic composition. Therefore, environmental dust was collected in different locations within a nuclear facility. The screening of the samples to find the uranium particles of interest was performed using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray (EDX) detector. The comparison of the measurement results to reference data evaluated by international safeguards authorities was of key importance for data interpretation. For the majority of investigated particles, detection of uranium isotopic signatures provided information on current and past nuclear feed operations that compared well with facility declarations.