Models to Incorporate Reaction Mechanisms into DG-OSPREY: Fixed-Bed Simulations for Organic Iodides Capture Using Ag⁰Z

Technical Report · Fri Sep 30 04:00:00 EDT 2022

DOI:https://doi.org/10.2172/1923171· OSTI ID:1923171

Shen, Ziheng ^[1]; Wiechert, Alexander I. ^[1]; Ladshaw, Austin P. ^[1]; Yiacoumi, Sotira ^[1]; Tsouris, Costas ^[2]

---

1. Georgia Institute of Technology, Atlanta, GA (United States)
2. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

As one of the most potent radioisotopes released during spent nuclear fuel reprocessing, ¹²⁹I is strictly regulated and must be removed before discharge. Organic iodides (primarily alkyl iodides with different chain lengths, i.e., CH₃I, C₄H₉I, and C₁₂H₂₅I) comprise ~2% of the total iodine in the reprocessing off-gases and are primarily present in vessel off-gas (VOG). Reduced silver mordenite (Ag⁰Z) is predominantly considered for the removal of radioiodine; however, its capture performance and underlying interaction processes with long-chain organic iodides are not fully understood. Two major tasks were accomplished in this study. First, to improve upon the previous experimental studies where Ag⁰Z was used to capture CH₃I, C₄H₉I, and C₁₂H₂₅I at different concentrations, we comprehensively investigated the corresponding capture mechanisms by characterizing fully loaded Ag⁰Z samples. Second, computational codes were implemented to perform fixed-bed simulations that account for transport and reaction mechanisms. Scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), powder X-ray diffraction (PXRD), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and thermogravimetric analysis (TGA) were conducted on Ag⁰Z samples that are saturated with I₂, CH₃I, C₄H₉I, and C₁₂H₂₅I), respectively. Results indicate that AgI is the predominant adsorption product regardless of the adsorbed iodine species, yet alkyl iodides with different carbon chain lengths may have different compositions of α- and γ-AgI. Synchrotron pair distribution function (PDF) measurements and TGA coupled with a Fourier transformed infrared detector (TGA FTIR) have been performed, and experimental data are currently analyzed. Results are expected to provide further insights into the adsorption mechanisms. The fixed-bed capture performance for CH₃I was successfully simulated by solving mathematical equations that describe the underlying transport processes and adsorption reactions. The computational framework, Catalytic After Treatment System (CATS), that was originated in our research group, was used to solve the governing equations. Kinetic parameters, including the pore diffusivity and reaction rate constant were obtained by optimization techniques using data from thin-bed experiments performed at Oak Ridge National Laboratory. The performance of a deep bed predicted using the optimized parameters showed promising agreement with the experimental data.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725; NE0008761
• OSTI ID: 1923171
• Report Number(s): ORNL/SPR-2022/2665
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES