Identification and tracing of radionuclides in low- and medium-activity liquid radwaste sources of G.A. Siwabessy reactor

Abstract The liquid radioactive waste generated by the G.A. Siwabessy reactor (RSG-GAS) is categorized into low-activity liquid radwaste (LALR) and medium-activity liquid radwaste (MALR). The radionuclide content of both LALR and MALR can use as an indicator of the structural integrity of the reactor’s systems, structures, and components (SSC). To evaluate the degradation of the reactor SSC, the radionuclide species were identified, and their activities were measured using gamma spectroscopy. Based on the identified radionuclides, the process of their formation can be traced. The radionuclides identified in LALR were 24Na, 51Cr, 59Fe, 60Co, 65Zn, and 124Sb, while the radionuclides in MALR were 24Na, 51Cr, 58Co, 59Fe, 60Co, 65Ni, 65Zn, 89Kr, 90Kr, 109Cd, 131I, 132I, 140Ba, 137Cs, 146Ce, and several others. The radionuclides found can be classified into corrosion product activation (60Co, 65Zn, 51Cr, 59Fe, 24Na, 65Ni), topaz impurities activation (51Cr, 59Fe, 60Co, 65Zn), fission product (90Kr, 140Ba, 131I, 137Cs, etc.), and demineralized water impurities activation (51Cr, 59Fe, 65Zn, 60Co, etc.). After comparing the activity value of each radionuclide with the limit value in the safety analysis report document, we can conclude that the activity of each one is below the required level. It can infer that the structural integrity of reactor SSC is still well maintain. During routine monitoring, the radionuclide content in the primary coolant fluctuates depending on the reactor load. The concentration of radionuclides detected varies when a large or small number of research samples are loaded onto the core. Nevertheless, their activities remain within the required safety limits.