Spatially-resolved uranium isotopic analysis of contaminated scrap metal using laser ablation multi-collector ICP-MS

Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) was applied to the detailed investigation of the uranium (U) isotopic composition (234U, 235U, 236U, and 238U) of five contaminated scrap metal samples seized within the European Union. Pressed pellets of the two certified U isotopic reference materials CRM U-020 and CRM U-030 were included in the measurement protocol for mass bias correction, calculation of the gain of the ion counters and for quality assurance. Compared to analysis of pure U compounds such as U ore concentrate (typically >60 wt% U) or UO2 (>80 wt%), the low U content of the investigated scrap metal samples (0.15 wt% - 14.3 wt%) required optimised experimental parameters to be applied for U isotopic analysis. Spatially-resolved (a few µm) U isotopic information was obtained by line scan analysis, generating several thousand individual U isotope ratios for each scrap metal sample. While complementary analytical techniques such as -spectrometry and thermal ionisation mass spectrometry (TIMS) yielded average U isotopic composition of limited significance, LA-MC-ICP-MS provided substantial added value. The latter highlighted the inhomogeneous distribution of U isotopes within various scrap metal samples, giving valuable insights into the history and previous use of the material. Whereas bulk analysis using TIMS revealed an 235U enrichment of ~25.9 wt% in one scrap metal, for example, LA-MC-ICP-MS disclosed an average 235U enrichment of ~37.7 wt% (based on >4500 individual measurements), ranging from 0.52 wt% - 94.4 wt%. Four out of five scrap metal samples contained 236U (~0.05 wt% - ~0.11 wt%), indicating that reprocessed U from a nuclear facility was involved in materialization of these samples. Taken together, LA-MC-ICP-MS analysis provided fast and accurate spatially-resolved U isotopic information without consuming or altering the scrap metal samples, a key feature for nuclear forensic investigations.

KRACHLER Michael;  WALLENIUS Maria;  NICHOLL Adrian;  MAYER Klaus; 

2020-04-29

ROYAL SOC CHEMISTRY

JRC117791

2046-2069 (online),   

https://publications.jrc.ec.europa.eu/repository/handle/JRC117791,   

10.1039/d0ra02899a (online),