Abstract
Off-gas from nuclear fuel recycling contains 3H, 14C, 85Kr, 131I, and 129I. Radioactive iodine's
long half-life of over 15 million years, tendency to accumulate in thyroid glands, and ability to
produce toxic, volatile organic compounds such as methyl iodide make it a major concern.
Organic iodides are dangerous even at ppb levels, so capturing 129I is crucial. Research
described herein focused on pretreatment for decomposing organoiodide followed by
adsorption with solid porous iodine adsorbents, particularly for organic iodine in simulated
vessel off-gas (VOG) from a used nuclear fuel (UNF) reprocessing facility. Methyl iodide was
found to decompose quantitatively in a nitrogen environment with dielectric barrier discharge
(DBD). The above hypothesis was supported by methyl iodide, nitrogen, oxygen, and carbon
dioxide experiments. The experiments failed to determine the fate of methyl iodide in the air
environment because N2 and O2 reactions created NOx species, which complicated analysis of
components in the gas stream subjected to pretreatment. Kinetic studies quantified rate
parameters and electric field dependence for the methyl iodide-nitrogen system. DBD
decomposes methyl iodide, which may improve radioactive iodine capture during sorption.
Sorption studies were initially performed with a nanocarbon-coated cordierite matrix that
captured organoiodides in a simulated VOG stream from a UNF reprocessing facility. A
continuous flow column with a constant flow rate and a given inlet concentration of methyl
iodide (CH3I) was used to test coated nanocarbon and nanocarbon pellets with ETS-10
adsorption and desorption. Electron microscopy of adsorbent showed carbon pore size changes
after the experiment, while energy dispersive x-ray spectroscopy (EDS) indicated the presence
of iodine on carbon. Sorption experiments were conducted with presence of moisture and aged
nanocarbon. Other studies have compared nanocarbon adsorption on ETS-10 and cordierite.
The lab-synthesized nanocarbon in this research was found to have higher adsorption capacity
than that reported in literature for other carbons. These findings may help advance the capture
of volatile organic iodine species at lower concentrations in off-gas streams from a UNF.