Materials Performance in off-Gas Systems Containing Iodine

摘要

During the reprocessing of spent reactor fuel elements, iodine is released to gas streams from which it is ultimately removed by conversion to nonvolatile iodic acid. Under some conditions iodine can produce severe corrosion in off-gas lines; in this study these conditions were established. Iron- and nickel-based alloys containing more than 6% molybdenum, such as Hastelloy G (7%), Inconel 625 (9%), and Hastelloy C-276 (16%), as well as titanium and zirconium, remained free of attack under all conditions tested. When the other materials, notably the austenitic stainless steels, were exposed to gas streams containing even only low concentrations of iodine and water vapors at 25 and 40 exp 0 C, a highly corrosive, brownish-green liquid formed on their surfaces. In the complete absence of water vapor, the iodine-containing liquid did not form and all materials remained unaffected. The liquid that formed had a low pH (usually < 1), and the attack was about the same in either air or nitrogen. The rate of attack increased with increasing temperature at constant relative humidity but decreased with increasing temperature at constant water content. The severity of attack increased with the increasing water content of the gas except under conditions where relatively large amounts of water were present, such as on a condensing surface. Nitric acid and NO sub 2 inhibited attack. (ERA citation 07:003336)