Application of silver-free zeolites to remove iodine from dissolver off-gases in spent fuel reprocessing plants

The present work dealt with the interaction of zeolite 13X with such organic iodides as CH3I and C2H5I in the presence of NO2 with the intention of applying silver-free zeolites to the iodine removal process of the dissolver off-gas. On the assumption that the dissolver off-gas would be dried for the purpose of removal of tritium, the experiments were carried out under a dry condition. Zeolite 13X removes dilute CH3I from a process gas stream with high efficiencies at approx. 25 deg. C. It was found that NO2 decomposed CH3I on the zeolite. Infrared analysis and mass spectrometry confirmed that this reaction took place on zeolite 13X and also on a silver-exchanged zeolite at approx. 25 deg. C. When a simulated dissolver off-gas (containing approx. 100 ppm-I2, approx. 10 ppm-CH3I and approx. 1%-NO2) was supplied to a zeolite 13X bed, the I2 which was produced by the decomposition of CH3I was absorbed at the same place of the bed as another I2 which was originally included in the gas. At approx. 100 deg. C, the zeolite 13X bed traps only iodine and NO2 passes through the bed without being adsorbed: the zeolite can separate iodine chromatographically from NO2. On the basis of these experimental results, an iodine removal process was discussed