Isotope dilution inductively coupled plasma mass spectrometry for determination of 126Sn content in spent nuclear fuel sample

Abstract

The 126Sn content in a spent nuclear fuel solution was determined by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) for its inventory estimation in high-level radioactive waste. A well-characterized irradiated UO2 fuel sample dissolved in a hot cell was used as a sample to evaluate the reliability of the methodology. Prior to the ICP-MS measurement, Sn was separated from Te (126Te), which causes major isobaric interference in the determination of 126Sn content, along with highly radioactive coexisting elements, such as Sr (90Sr), Y (90Y), Cs (137Cs) and Ba (137m Ba), using an anion-exchange column. The absence of counts attributed to Te at m/z = 125, 128, and 130 in the Sn-containing effluent (Sn fraction) indicates that Te was completely removed from the anion-exchange column. After washing, Sn retained on the column was readily eluted with 1 M HNO3 accompanied with approximately 80% of the Cd and 0.03% of the U in the initial sample. Owing to the presences of Cd and U in Sn fraction, the measurements of 116Sn and 119Sn were affected by the isobaric 116Cd and the doubly charged 238U2+ion, resulting in the positive bias of the determined values. With the exception of the isotopic ratios including 116Sn and 119Sn, 117Sn/126Sn, 118Sn/126Sn, 120Sn/126Sn, 122Sn/126Sn and 124Sn/126Sn were successfully determined and showed good agreement with those obtained through ORIGEN2 calculations. The measured concentration of 126Sn in the spent nuclear fuel sample solution was 0.74 ± 0.14 ng/g, which corresponds to 23.0 ± 4.5 ng per gram of the irradiated UO2 fuel (excluding the presence of 126Sn in the insoluble residue). The results reported in this paper are the first experimental values of 126Sn content and isotope ratios in the spent nuclear fuel solution originating in spent nuclear fuel irradiated at a nuclear power plant in Japan.