Assessment of Radioecologically Relevant Radionuclides 14C, 99Tc, and 129I in Vitrified High-Level Nuclear Wastes from Spent Fuel Reprocessing

A method is proposed for quantifying the specific activities of radioecologically significant radionuclides, including 14 C, 99 Tc, and 129 I, in vitrified high-level wastes. The conditions for the separation and purification of these radionuclides from potential interfering components are optimized and the yield coefficients and purification factors are determined. The quantification of 14 C entails a three-fold distillation in CO 2 followed by the measurement of the 14 C counting rate in the purified solution by liquid scintillation spectrometry. 129 I was determined by dissolving a sample in HNO 3 , five-fold extraction, and the subsequent measurement of the 129 I counting rate in the purified solution using liquid scintillation spectrometry. The determination of 99 Тс included dissolving a sample in the presence of ClO – , double extraction-chromatographic separation of 99 Тс with an adsorbent impregnated with methyltrioctylammonium nitrate, followed by the determination of its activity by inductively coupled plasma–mass spectrometry. We have applied this approach to a simulator of vitrified high-level waste, labeled with radionuclides, and achieved satisfactory results. This approach will be instrumental in the analysis of the accumulated vitrified high-level wastes at the “Mayak” Production Association (Mayak PA). The results will be important for modeling the engineering safety barriers of a deep disposal site for radioactive wastes.