Quantification of Iodine-129 in radioactive waste

Separation methods are required to quantify I-129, produced by U-235 and Pu-239 spontaneous fission in nuclear reactors, in radioactive waste, in order to purify and quantify it due to I-129 is a weak beta / gamma emitter difficult to quantify by gamma spectrometry, if other gamma or X emitting radionuclides are present. Therefore, the objective of this work was to develop an iodine separation methodology based on its precipitation as silver iodide (Ag¹²⁹I) on an inert support. Four inert matrices were studied: Kieselgurth (SiO₂), alumina (Al₂O₃), titanium oxide (TiO₂) and Amberlite® XAD4 resin, which were impregnated with silver nitrate (AgNO₃) by two methods: dynamic and static, in order to determine the retention efficiency of Ag¹²⁹I on these supports. The retention of iodine on the supports was determined at three different ph s (2, 6 and 12), using as radiotracer: I-131, also a fission product of U-235, with 8 days of half-life, beta-gamma emitter easily detectable by gamma spectrometry, and that has the same chemical properties as I-129. The retention of I-131 was also determined in the presence of radioisotopes such as ^99mTc, Cs-137 and Co-58. According to the Ag-I Pourbaix diagram, iodine precipitation as Ag¹³¹I is favored at ph less than 10. The highest retention efficiencies of I-131 were obtained in Amberlite XAD4 (96%) impregnated with 1 x 10^-3 M AgNO₃, applying the dynamic method in aqueous solutions at ph 6. Co-58 and Cs-137, also fission products, are not retained in any of the inert matrices treated studied in this work. The inert matrices and treated with AgNO₃ were characterized by: X-ray diffraction, Scanning electron microscopy (Sem), Raman and Infrared spectrometry, in order to determine the structural change of the matrix when AgNO₃ is impregnated. The highest percentage of silver nitrate impregnated over the MIT was obtained in the Amberlite® XAD4 with 5.9%, according to the elemental analyzes of the MIT performed by Sem. The presence of silver nitrate on the inert matrices cause's changes in the crystalline structures of the inert matrices treated, particularly when the dynamic method of impregnation is used; The highest retention of I-131 was presented in the matrix of Amberlite® XAD4 obtaining 96%. (author)