The development of Ag-A for radioactive iodine removal from nuclear fuel reprocessing plants

The solid adsorbents Ag-A for radioactive iodine removal from nuclear fuel reprocessing plants were developed. Ag-A which is prepared by impregnating silver nitrate on the alumina carrier can remove the iodine effectively and reduce the amounts of secondary radioactive waste after the iodine adsorbed. The effect of H2O and NOx impurities, linear gas velocity and temperature on I2 and CH3I adsorption on Ag-A were evaluated in terms of removal efficiency and saturated amounts of adsorption under the simulated dissolver off gas (DOG) stream conditions. The removal efficiency of iodine was more than 103. The saturated amounts of I2 adsorption was about 230 mg I2/g-ad for 24 wt% silver content Ag-A, and which meant 80 % of silver utilization was achieved. Moreover, no effects due to H2O and NOx of up to 1 vol% were observed on I2 and CH3I loading for this adsorbent. The stability of adsorbed iodine on the Ag-A against heat and water were also evaluated. For interim storage, the Ag-A needs to be stored in a dry environment. But alternatively, if the Ag-A is once heated at 450degC, it becomes to hold iodine for a long time even in water. The qualification tests using actual dissolver off-gas were carried out at the WAK-plant (Germany). Ag-A test filter beds were installed in the sampling line separated from the main DOG line. Adsorption distribution of I-129 in Ag-A beds, decontamination factor and adsorption capacity were measured. These data show that the Ag-A can be applied as iodine adsorption material in the dissolver off gas treatment system of the nuclear reprocessing plant. (author)