Cation exchange method for 137Cs radionuclide source fabrication from spent U3Si2–Al reactor fuel of RSG-GAS for radiation portal monitoring systems

137Cs Radionuclide as a radiation source can be applied in portal monitor systems, which play an important role in detecting the movement of radioactive materials. One potential source of 137Cs is spent research reactor fuel of the U3Si2–Al type, which contains strategically valuable fission products. This study aims to develop a methodology for cation exchange and production of a 137Cs radionuclide source from the solution obtained in post-irradiation testing of U3Si2–Al fuel with a density of 4.8 gU/cm3. To determine the 137Cs radionuclide content in U3Si2–Al fuel elements, a separation technique is required to isolate 137Cs from other fission products such as uranium. The separation was carried out using a cation exchange method with modified natural Lampung zeolite, which offers good adsorption efficiency, local availability, and thermal and chemical stability. The homogeneity and activity of the 137Cs–zeolite powder were analyzed using a gamma spectrometer. The 137Cs–zeolite powder was then encapsulated in teflon, and its activity was measured using a dose calibrator. The certified 137Cs radionuclide source was placed in a cylindrical stainless steel container lined with lead (Pb) as shielding. Homogeneity testing at seven sampling positions showed that the 137Cs–zeolite powder samples, each weighing approximately 1.0019 g, had an average specific activity of 2.8932 µCi/g with a standard deviation of 0.0058 and a relative standard deviation (RSD) of 0.1996%. These low SD and RSD values indicate that the activity of the 137Cs–zeolite powder samples is not significantly different from that of 137Cs SRM 4233 from NIST, confirming good homogeneity. The certified activity of the 137Cs radionuclide source in the shielded container was 15.91 ± 0.76 µCi with an uncertainty of 5.0%, and the surface radiation exposure rate was 0.57 µSv/h, meeting safety requirements for occupational environments.