Capture of Radioactive Iodine and Krypton from Nuclear Off-Gas Streams with a Novel Sorbent

Reprocessing of used nuclear fuel (UNF) is key to making nuclear energy a sustainable, viable part of the world’s energy portfolio. However, during aqueous reprocessing of UNF volatile radionuclides are released in off-gas posing a hazard to health and the environment. Of these radionuclides, iodine 129 and krypton 85 present the biggest threat and are removal priorities. Since the 1960’s, many methods of removing iodine 129 and krypton 85 have been employed, including caustic and acidic scrubbing, fluorocarbon absorption, and cryogenic distillation. The problem with each of these processes is the use toxic and corrosive chemicals and high energy costs. Adsorption provides simpler, safer, and more cost-effective method of removal, and research into new materials for adsorption has been prolific. Nonetheless, much of the existing research is bereft of realistic studies at low concentrations, ambient temperatures, and with multiple components. To further this research, we have developed a novel adsorbent for iodine and krypton capture consisting of Engelhard titanosilicate-10 supported hollow carbon nano-polyhedrons (C/ETS-10), with large-scale synthesis and cost-effectiveness in mind. We investigated the capture of iodine and krypton on C/ETS-10 under single- and multi-component conditions, ambient temperatures, and concentrations similar to actual off-gas. Additionally, we developed a mathematical model based on mass-transfer to assist in scale-up of the process and compared it to the well-known Thomas, Yoon-Nelson, and Adams-Bohart kinetic models. Our investigation found that even in multicomponent conditions, 10 wt% C/ETS-10 has iodine capacity comparable to, and krypton capacity twice that of silver mordenite, a zeolitic sorbent considered to be at the forefront of sorbents for both iodine and krypton. Furthermore, the mass-transfer model fits experimental breakthrough curves better than the kinetic models and had inherent flexibility allowing extrapolation to other operating conditions. Overall, 10 wt% C/ETS-10 has proven to be a competitive sorbent for iodine and krypton at realistic off-gas conditions.masters, M.S., Chemical and Materials Science Engineering -- University of Idaho - College of Graduate Studies, 2017-0