(280d) Adsorption of Radioactive I2 and Tritiated Water from Spent Fuel Reprocessing Off-Gases By Reduced Silver Mordenite

Adsorption of iodine and water by reduced silver-exchanged mordenite (Ag^oZ) is experimentally and theoretically investigated to support the development of advanced modeling tools for the separation and recovery of radioisotopic gases in off-gas streams of nuclear fuel reprocessing. Single-layer adsorption experiments were performed to obtain both iodine and water adsorption data with Ag^oZ using continuous-flow adsorption systems. The commercial AgZ (IONEX-type Ag-900) used in this study was reduced to Ag^oZ in 4% H₂/Argon at optimal conditions (400^oC, 24 hours) determined in this study. The conditions for iodine adsorption experiments are: temperatures 100–200°C; iodine gas concentrations 1-50 ppmv; and dew points -65 to 20 ^oC. The sorbents are pre-equilibrated in the gas stream with a desired dew point prior to iodine adsorption to study the effect of dew points on the iodine adsorption capacity of Ag^oZ. The conditions for water adsorption experiments are: temperatures 100–200 °C and dew points -65 to 20 ^oC.

The effect of reduction conditions on the capacity of Ag^oZ was studied. The results confirmed the favorable effect of temperature and reduction time on the capacity of Ag^oZ, and suggested optimal reduction conditions: 400^oC, 24 hours. Preliminary results of adsorption experiments indicated that the Ag^oZ had an iodine loading capacity of ~13 wt%, corresponding to a silver utilization of ~90%. Both the adsorption/desorption and equilibrium data indicated that iodine adsorption on Ag^oZ was mostly chemisorption. About 2.4 to 4.7% of the adsorbed iodine was physisorbed. Kinetic data were analyzed with the Shrinking Core model and Linear Driving Force model to determine the intraparticle mass transfer and reaction parameters. Single-component adsorption equilibrium data of iodine and water were also obtained to determine the saturation capacity and evaluate the parameters of isotherm models for modeling of co-adsorption.