School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Silver Adsorbents for Radioactive Iodine Capture in Nulcear Energy Applications

By Ziheng Shen

Advisor:

Dr. Sotira Yiacoumi (CEE)

Committee Members:  Dr. Yongsheng Chen (CEE), Dr. Costas Tsouris (CEE/Oak Ridge National Lab), Dr. Xing Xie (CEE), Dr. Andrew Medford (ChBE)

Date and Time:  Tuesday, December 12th, 2023, at 2pm

Location: Room 4222, Price Gilbert Memorial Library; Zoom: https://gatech.zoom.us/j/93337914447?pwd=MVFuYkVSZXI2VmlQUmIxY2xwZmE0dz09.

Complete announcement, with abstract, is attached.

Nuclear power serves as a pivotal component of the global energy supply, yet managing spent nuclear fuel (SNF) produced during electricity generation remains a challenge. Reprocessing SNF to reuse uranium offers a viable solution in a sustainable fashion, but it releases radioactive iodine (129I), a hazardous byproduct that must be removed from the off gas streams. Silver (Ag) based adsorbents have shown efficacy in iodine capture, whereas further advancement on the material development and the process design relies on a more fundamental understanding of adsorption processes. In this context, the dissertation presented here addresses current knowledge gaps surrounding two prototype Ag adsorbents: reduced silver functionalized silica aerogel (Ag0-aerogel) and reduced silver exchanged mordenite (Ag0Z).
 
One critical challenge with Ag0-aerogel is the diminishment in adsorption capacity after exposure to reprocessing off-gas at elevated temperatures, a phenomenon termed as ‘aging.’ Experiments were designed to evaluate the impact of three potential aging-inducing factors – oxygen, nitrogen dioxide, and temperature – on aerogel’s capacity over time. Through extensive characterization of the aged samples, we deduced plausible mechanisms governing the capacity reduction and employed density functional theory (DFT) calculations for theoretical corroboration. The last part of this thesis focuses on Ag0Z, exploring its capture performance on long-chain alkyl iodides. Synchrotron pair distribution function (PDF) analysis provides insights into the mechanisms underlying the uptake of various iodine species by Ag0Z. A numerical modeling framework was implemented to describe and make predictions on the fixed-bed adsorption process. The methodology established in this study, integrating deep insights into the molecular-level adsorption mechanisms with practical considerations for large-scale applications, is instrumental to the optimization of iodine removal strategies in SNF reprocessing and related fields.