Capture of iodine in off-gas streams from aqueous used nuclear fuel reprocessing - Deep bed test results

A long-term (4,372 hr.) test of iodine capture from iodobutane in a simulated vessel off-gas (VOG) stream was performed using a laboratory-scale “deep-bed” test system containing multiple-segmented fixed beds of silver aerogel (Ag Aerogel) sorbent prepared by Pacific Northwest National Laboratory. Iodine concentrations and Ag utilization in the first three sorbent beds reached practical capacity limits of about 22 wt% iodine and 70% Ag utilization. The sorbent in beds 4 and 5 captured some iodine by test end, and so were within the depth of the mass transfer zone (MTZ). No capture of iodine was detected in bed 6. The MTZ depth was estimated to be between 8-11 cm (3-4.5 inches) deep by the test end, which is consistent with previous deep-bed results. As iodine breakthrough occurred, some of the uncaptured gas-phase iodine was in the form of not only iodobutane but also iodine species such as I2 and HI. Up to 60% of the uncaptured iodine was in the form of gas species reported as I2, not iodobutane. Test results showed that the maximum decontamination factor (DF) ranged over 30,000, consistent with the results of prior deep-bed iodine adsorption tests.