Investigations for determination of Gd and Sm isotopic compositions in spent nuclear fuels samples by MC ICPMS

Abstract

Precise isotopic determination of gadolinium and samarium in spent nuclear fuels is necessary to validate neutronic calculation codes. This study presents an analytical strategy to correct mass bias phenomenon inherent to MC ICPMS for precise and accurate samarium and gadolinium isotope measurements. An external standard bracketing approach to correct for mass discrimination and an exponential law fractionation correction have been applied in this work. Due to the lack of isotopic reference materials for Gd and Sm, the reproducibility of all of the isotopic ratios has been evaluated on the basis of natural spex solution commonly used for ICPMS. These solutions have been analysed for comparison and discussion about their representative isotopic values by thermal ionization mass spectrometry. On the basis of TIMS and MC ICPMS investigations, it was observed that: (1) the choice in representative isotopic values of the elements are essential to obtain accurate isotopic results and (2) the dependence of the mass bias of gadolinium and samarium masses must be taken into account for precise and accurate isotopic results. A reproducibility better than 0.1% was obtained with extensive measurements of Gd and Sm solutions by MC ICPMS. When measured isotope intensities were high enough, standard deviation of Gd and Sm isotopic ratios for purified fractions of Gd and Sm fuel samples were better than 0.2%. From the results obtained in this study, the potential of MC ICPMS techniques for determination of precise and accurate Gd and Sm isotopic compositions was clearly demonstrated for nuclear applications.