Improved plutonium concentration analysis in specimens originating from the nuclear fuel cycle using high resolution ICP-OES

Abstract

An accurate and robust ICP-OES procedure for the reliable determination of the Pu concentration in radioactive samples was developed and subsequently cross-validated using ICP-MS. Method optimisation focused on identifying Pu emission wavelengths that are spectrally not interfered by the occurrence of emission signals of concomitant elements (e.g. Am, Np, Th, and U) in the analyte solution, thereby avoiding an otherwise necessary chemical separation of Pu from the matrix elements. To this end, a total of 43 Pu emission wavelengths were tested for their selectivity and sensitivity. The signal to background ratio of the 27 most prominent Pu emission lines ranged from ∼2 to 20, while relative sensitivities varied only within a factor of two. Peak widths of ICP-OES Pu signals extended from ∼5 pm to ∼11 pm, with the majority remaining <6 pm. Using a desolvating nebuliser, instrumental detection limits (LOD) were lowered by an order of magnitude compared to all previous studies. Among the finally selected, seven worthwhile Pu emission wavelengths, LODs of 2.3 μg L⁻¹, 3.1 μg L⁻¹, and 3.2 μg L⁻¹ were obtained at λ = 299.649 nm, λ = 299.409 nm, and λ = 297.251 nm. Applying external calibration, several radioactive samples originating from pyrochemical separation experiments were analysed for their Pu concentration. Typical relative standard deviations of replicate Pu measurements amounted to ∼1% to 2%. The complementary employment of the standard addition approach confirmed the accuracy of this data as well did comparative in-house sector field ICP-MS analysis. Preliminary experiments with spent fuel solutions revealed promising Pu data highlighting the potential of ICP-OES for reliable Pu analysis in the nuclear field.