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Within the framework of the research undertaken by the French Atomic Energy Commission on transmutation of long-lived radionuclides, targets of highly enriched actinides and fission products were irradiated in the fast neutron reactor Phenix. Precise and accurate measurements of the isotopic and elemental composition of the enriched elements are therefore required. In order to obtain the uncertainties of several permil and to reduce handling time and exposure to analyst on radioactive material, the on-line coupling of ion exchange chromatography with quadrupole inductively coupled plasma mass spectrometry has been associated with the technique of the double spike isotope dilution. We present in this paper the results obtained on an irradiated sample of Europium oxide powder (enriched at 99.13% in 153Eu). After irradiation of around 5 mg of Eu2O3 powder the theoretical calculations predict the formation of several micrograms of gadolinium and samarium isotopes. In relation to the very high activity of the sample after irradiation and the very low quantity of Sm formed, the on-line ion exchange chromatography separation of Gd, Sm and Eu before Sm isotope ratio measurements has been developed for the quantification of the 152Sm/153Eu ratio. These on-line measurements were associated with the double spike isotope dilution technique after calibration of a 147Sm/151Eu spike solution. The external reproducibility of Sm isotopic ratios was determined to be around 0.5% (2σ) resulting in a final uncertainty on the 152Sm/153Eu ratio of around 1% (2σ). These on-line measurements present therefore a robust and high-throughput alternative to the thermal-ionisation mass spectrometry technique used so far in combination with off-line chromatographic separation, particularly in nuclear applications where characterisation of high activity sample solutions is required.

The measurement of U and Pu isotope ratios is of prime interest in nuclear research fields particularly for the management of radioactive waste. One of the major drawbacks in analysing Pu isotopes is the occurrence of 238U–238Pu isobaric interference. In this work we propose to suppress this interference by adding CO2 as a reactive gas in the collision-reaction cell of the MC-ICPMS. We have demonstrated that the different reactivities of Pu and U towards CO2 gas allow accurate and precise Pu and U isotopic measurements on Pu+ and UO2+ forms, by using two different CO2 gas flow rates: 0.4 mL min−1 for Pu+ and 1.5 mL min−1 for UO2+. Parameters like optimum CO2 gas flow in the cell, oxides isotope abundance, instrumental mass bias and memory blank, were carefully evaluated and corrected. The developed analytical method was validated using a transmutation 235U target sample irradiated in the Phenix French fast neutron reactor. A good agreement between isotope ratios of U and Pu measured with CO2 in the cell and U and Pu measured after chemical separation was obtained. The relative difference of the average isotope ratio values between the chemically purified fraction and the direct measurements using CO2 was found to be 0.38% and 0.11% for U and Pu, respectively.