Durable, Low-Cost Sorbents for Iodine Capture

Nuclear fission produces iodine-129, a volatile fission product that comprises 78% of the radiological impacts from atmospheric emissions released during reprocessing, and 65% of the solid waste; the capture of radioactive iodine must produce a waste form that may be safely and legally disposed. This project will develop non-silver based sorbents to capture iodine under prototypical off-gassing conditions, and result in a waste form that does not produce mixed waste. This project uses high-throughput x-ray fluorescence to identify a set of sorbents that meet a set of published performance criteria, followed by development of the most promising sorbents into scrubber filters for capturing radioactive iodine. The data from the high-throughput analysis will also be used as a training set for machine learning / artificial intelligence analysis of sorbents, to allow the use of artificial intelligence to predict the chemical features of improved sorbents. Phase I work included a high-throughput screen under prototypical off-gas conditions to identify sorbents that minimized the filler to active sorbent ratio, followed by individual testing of sorbents in a flow cell system. Phase I also included development of a proof of concept scrubbing filter, which was tested with both gas phase and aqueous phase iodine to determine iodine capture kinetics. Additional aspects were characterized, including radiation stability and pressure drop. Phase II work will include sequencing the sorbent libraries to build a training dataset for sorbents. Phase II will also include scale up synthesis of the sorbents identified in Phase I, followed by extensive testing of these sorbents in a filter housing, for the following criteria: capture performance, sorbent kinetics, performance under relevant environmental conditions, filter properties such as pressure drop, and sorbent stability and disposition pathways. There is a large unmet need for iodine sorbents for nuclear fuel disposition. There are about 277,000 spent assemblies in storage in the United States. Waste management is typically 2-4% of the cost of a nuclear process. In addition to the existing base of nuclear reactors, there are advanced nuclear reactors under development. Nuclear materials separations are included in ôSeven chemical separations to change the worldö as published in the journal Nature. Current sorbents are based on silver, which is expensive, and more importantly produces mixed hazardous and radioactive waste which has no pathway for disposal.