(258d) Aging Study of Ag-Exchanged Mordenite and Ag-Functionalized Silica Aerogel in Gas Mixture of Water Vapor and NOx Streams

Spent nuclear fuel reprocessing processes generates various volatile radioactive species including ³H, ¹⁴C, ⁸⁵Kr and ¹²⁹I in company with significant amount of water and NO_x vapors into the off-gas streams. ¹²⁹I is one of those radioactive species which has a long half-life (1.6 x 10⁷ years) and negative impacts on the human body and the environment if released to the environment. Many studies have been carried out to capture radioactive iodine from spent nuclear fuel reprocessing off-gas streams. Hydrogen-reduced silver mordenite (Ag⁰Z) and silver functionalized silica aerogel (Ag⁰-aerogel) have been introduced as solid adsorbents which can effectively capture gaseous iodine. However, the impact of the off-gas streams should be considered as it can result in the decrease of the performance of adsorbents due to the chemical and physical changes to the adsorbents when exposed to the off-gas streams. In previous studies, 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 respectively for up to 6 months at 100℃ ~ 200℃, and iodine adsorption experiments on the aged adsorbents were conducted. Results showed that humid air, 1% NO and 2% NO₂ had negative impacts on the performance of Ag⁰Z and Ag⁰-aerogel; especially, 2% NO₂ has the most adverse impact on the iodine loading capacity of the both adsorbents. Iodine loading capacities of the aged Ag⁰Z and Ag⁰-aerogel were decreased with increasing aging time and temperature.

In this study, aging impact of a gas mixture including water, NO and NO₂ on both adsorbents, Ag⁰Z and Ag⁰-aerogel, was investigated to validate the impacts of each gas stream on the adsorbents. At this writing, aging experiments of Ag⁰Z and Ag⁰-aerogel in the gas mixture and adsorption experiments on the aged adsorbents are being conducted. In addition to these experiments, chemical and physical changes on the aged adsorbents through aging process will be observed by conducting characterization study with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD). Also, the kinetic studies of both aged Ag⁰Z and Ag⁰-aerogel in gas mixture will be discussed.