Refined Analytical Method for 129I in Cement-Solidified Spent Ion Exchange Resins

Gi Yong Kim, Kyunghun Jung, Jai Il Park, Tae-Hong Park^*

Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea

Received 2025-02-21 ; Revised 2025-04-16 ; Approved 2025-06-20

Abstract

Spent ion exchange resins (SIERs) are commonly immobilized in cement, necessitating the reliable determination of radionuclides in cement-based waste forms. This study developed a simple and practical method for quantifying 129I, a key radionuclide in low- and intermediate-level radioactive waste (LILW) disposal. Investigation into iodine behavior during leaching, extraction, and precipitation revealed that iodate (IO3-) readily adsorbs onto cement minerals, reducing chemical recovery in extraction-based methods. To mitigate this, we implemented an in-situ conversion of IO3- to I2, improving chemical yields from 58% to 93% in fine cement samples ( < 0.05 mm). The optimized method was further applied to cement containing anion exchange resins, where increasing resin content led to a decrease in chemical yield, reaching 51% at 10wt% resin loading, close to the practical limit in ordinary Portland cement (OPC) waste forms. This decline was likely attributed to the re-adsorption of iodide (I-) onto the resins during the conversion of IO3- to I2. Despite this, measured 129I activities closely matched expected values, demonstrating its reliability for routine analysis of cement-based radioactive waste.

Key Words : Characterization of radioactive waste, Radiochemistry, Decommissioning, Silver iodide, Ettringite