(242f) Aging Kinetics of Ag-Exchanged Mordenite and Ag-Functionalized Silica Aerogel in the Presence of Off-Gas Streams

Iodine-129 is one of the volatile radioactive species in the off-gas streams generated from the spend nuclear reprocessing system, and it is essential to remove ¹²⁹I vapor because ¹²⁹I has a long half-life (1.6 x 10⁷ years) and can be fatal to the human body if released to the environment. Radioactive iodine vapor can be effectively captured by silver containing adsorbents such as silver exchanged mordenite (Ag⁰Z) and silver functionalized silica aerogel (Ag⁰-aerogel) used in this study. However, the aging impact of off-gas streams on the adsorbents is one of major issues in the removal of radioactive iodine vapor during off-gas treatment. The iodine loading capacity on the silver containing adsorbents will decrease over time due to the chemical and physical changes to the adsorbents when exposed to off-gas streams. In this study, the aging impacts of off-gas streams on the kinetics of iodine capture on both Ag⁰Z and Ag⁰-aerogel were investigated. The adsorbents were aged in dry air, humid air, 1% NO and 2% NO₂ for up to 6 months at 100℃ ~ 200℃, and iodine adsorption experiments on the aged adsorbents were conducted. Results show that humid air, 1% NO and 2% NO₂ have negative impacts on the performance of Ag⁰Z and Ag⁰-aerogel; especially, 2% NO₂ has the most severe impact on the iodine loading capacity of the both adsorbents. In addition, it was found that iodine loading capacity of the aged Ag⁰Z decreased as aging time and temperatures were increased. Characterization studies were conducted with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and X-ray absorption fine structure (XAFS) to better understand the mechanisms of the aging processes on Ag⁰Z and Ag⁰-aerogel by observing the chemical and physical changes through aging processes. Kinetic models were developed and evaluated to simulate the aging processes in different gases; aging and iodine adsorption experiments on the Ag⁰-aerogel are in progress. Reversible and irreversible reaction models were postulated to describe the reaction of the aging components with the silver adsorbent pellets. The kinetic studies of both Ag⁰Z and Ag⁰-aerogel will be discussed.