Iodine Capture and Mechanical Stability of Modified Silver-Functionalized Silica Aerogel

Technical Report · Fri Jun 28 00:00:00 EDT 2019

DOI:https://doi.org/10.2172/1570120· OSTI ID:1570120

Bruffey, Stephanie H.  ^[1]; Jubin, Robert T.  ^[1]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Silver-functionalized silica aerogel (AgAero) is a material proposed for use in the removal of iodine from the off-gas streams arising from nuclear fuel reprocessing. This material was developed by Pacific Northwest National Laboratory and has been shown to adsorb up to 300 mg of iodine per gram of AgAero. One of the challenges noted for AgAero as an iodine sorbent is its mechanical stability. Its initial particle size is >0.85 mm, but previous testing has shown that extended exposure to heated gas streams results in the degradation of the material such that the sorbent bed is compacted with a substantial amount of fines produced. The observed mechanical degradation prompted an effort to reengineer the silica aerogel to improve the mechanical stability of the material without compromising its iodine capture characteristics. Pacific Northwest National Laboratory has modified the material with the intention of strengthening the aerogel backbone and improving mechanical durability. This reengineered material was transferred to Oak Ridge National Laboratory for extended testing to assess its mechanical durability. Modified AgAero was continuously exposed to a CH₃I-bearing humid gas stream for 84 days. Testing was performed at 150°C with a superficial gas velocity of 10 m/min., a CH₃I concentration of 554 ppb, and an inlet dew point of 10°C. The density of the AgAero increased by 16% during testing, and the height of the column was observed to decrease by 11%. The fines produced by the material were comparable to that of previously supplied material. Additionally, iodine loading of a thin bed of modified AgAero was performed at 150°C with a superficial gas velocity of 10 m/min. and a CH₃I concentration of 50 ppm (balance dry air) with a total test duration of 1 week. The CH₃I capture capacity of the reengineered material was 225 mg iodine per gram AgAero, as compared to a CH₃I capacity of 250 mg iodine per gram AgAero for the original material. The primary data collected were visual observations, density measurements before and after testing, and the extent of column compaction during testing. Additionally, the material was tested to ensure that the iodine capacity of the material was not adversely impacted by the alternative methods used in the production of the reengineered material. Based on these criteria, no distinguishable improvements were observed between the material produced in fiscal years 2017 and 2019 and the mechanical stability of the aerogel in prototypic off-gas conditions remains a challenge to large-scale deployment.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1570120
• Report Number(s): ORNL/SPR-2019/1206
• Country of Publication: United States
• Language: English