(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 100â ~ 200â, 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.