Development of Ag exp 0 Z for Bulk exp 129 I Removal from Nuclear Fuel Reprocessing Plants and PbX for exp 129 I Storage

摘要

Tests were conducted to develop Ag-exchanged mordenite (AgZ) for removal of gaseous exp 129 I from nuclear fuel reprocessing plants. The effects of bed depth and hydrogen pretreatment on the elemental (I sub 2 ) iodine loading of AgZ were examined. The tests indicated that reduced AgZ (Ag exp 0 Z) had about twice the capacity for iodine as AgZ, and at least 15-cm bed depths should be used for loading tests. The effects of H sub 2 O(g), NO, NO sub 2 , and bed temperature on the iodine loading of Ag exp 0 Z were determined. The highest loadings were obtained with NO in the gas stream. Water vapor and bed temperature appeared to have no effect on the iodine loadings. Tests were conducted to develop a dry method for in situ regeneration of iodine-loaded Ag exp 0 Z. A test bed of Ag exp 0 Z was recycled 13 times by loading it with I sub 2 and stripping the I sub 2 (as HI) with H sub 2 . A 20 percent loss in iodine capacity was observed by the fourteenth loading. The iodine loadings of lead-exchanged zeolites, which were used to chemisorb HI during the recycle tests, were measured. The iodine vapor pressures at 20 exp 0 C over the substrates were predicted to be 10 exp -6 , 10 exp -8 , and less than 10 exp -16 atm for Pb-exchanged mordenite, Pb-exchanged faujasite and reduced Pb-exchanged faujasite, respectively. A process-flow diagram was formulated for iodine recovery. Two parallel beds of Ag exp 0 Z are used to permit continuous iodine recovery. While one is being regenerated the other recovers iodine. The iodine is chemisorbed as AgI, stripped as HI, and chemisorbed on the lead bed as a form of PbI sub 2 . The Ag beds were sized for a 30-day operation in a fuel reprocessing plant before regeneration. About 5 days would be needed for regeneration. About 2 m exp 3 of iodine-loaded Pb-exchanged faujasite would be generated each year. The Pb bed would be contained in canisters to permit transfer in and out of the bed holder and storage in 0.2 m exp 3 (55 gal) drums. (ERA citation 03:054681)