(477f) Kinetic Study of Ag Mordenite and Ag Functionalized Silica Aerogel Aging in Nuclear Fuel Reprocessing Off-Gases

In the study of spent nuclear fuel reprocessing off-gas treatment, radioactive iodine vapor can be effectively captured by silver containing adsorbents. However, the impact of aging on adsorbents performance is one major issue during off-gas treatment operation due the presence of water vapor and NOx. To better understand the performance of the adsorbent in the off-gas treatment system, it is important to study the aging mechanism and kinetics. In this study, the impact of aging from off gas components on the kinetics of iodine capture on silver exchanged mordenite (Ag⁰Z) and silver functionalized silica aerogel (Ag⁰-aerogel) were investigated, two well recognized adsorbents for capture of radioactive iodine. These adsorbents were aged in dry air, humid air, 1% NO/N₂, and 2% NO₂/air, at 100 ^oC, 150 ^oC, and 200^oC. Consequently, iodine loading experiments with the aged adsorbents were conducted. Results showed that humid-air, 1% NO/N₂, and 2% NO₂/air had strong impacts on the performance of Ag⁰Z and Ag⁰-aerogel. It was also found that the negative aging effect increased as the aging temperature increased. For example, the Ag⁰Z aged in humid air showed 42% , 45% and 58% of iodine loading capacity losses at 100^oC, 150^oC, and 200^oC, respectively. Kinetic models were developed and evaluated to simulate the aging processes in different gases. The models include reversible and irreversible n^th order reaction models to describe diffusion and reaction of the aging gas into the adsorbent pellets. Related parameters such as reaction rate constants and diffusivities were obtained. Work is in progress to incorporate the aging kinetic models into the iodine adsorption models for fixed beds to predict the actual adsorption process in an off-gas stream.