Environmental monitoring of actinides and evaluation of the contamination source (nuclear weapons tests, nuclear power plant and nuclear reprocessing plant accidents, etc.) requires precise and accurate isotopic analysis of actinides, especially uranium and plutonium. Double-focusing sector-field inductively coupled plasma mass spectrometry (ICP-SFMS) using a low-flow microconcentric nebulizer with membrane desolvation, “Aridus”, was applied for isotopic measurements of uranium and plutonium at the ultratrace level. The detection limit (3σ) for 236U and 239Pu after chemical extraction was 0.2 pg l−1 in aqueous solution and 0.04 pg g−1 in soil, respectively. 235U/238U, 236U/238U and 240Pu/239Pu isotope ratios were measured in soil samples collected within the 30 km zone around the
Chernobyl nuclear power plant. The average 240Pu/239Pu isotope ratio in contaminated surface soil was 0.396 ± 0.014. The burn-up grade and the portion of spent uranium in the spent uranium/natural uranium mixture in soil were calculated using the iteration method. A slight variation in the burn-up grade of spent reactor uranium was revealed by analyzing 235U/238U and 236U/238U isotope ratios. A relationship between the 240Pu/239Pu isotope ratio and burn-up of spent uranium was observed.
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