Abatement of radioiodine in aqueous reprocessing off-gas

Abstract

The reprocessing used nuclear fuel (UNF) releases volatile fission and activation products, including 129I, into the off-gas of a processing plant. Mitigation of the release of vapor phase radionuclides is necessary for meeting regulatory requirements in the United States and other countries. In an aqueous reprocessing plant, volatile radioiodine could be present in several forms, depending on the chemistry of the process used. Inorganic iodine will be the predominate species in any shearing or voloxidation pretreatment off-gas and dissolver off-gas (DOG). Organic iodides such as CH3I, C4H9I, and C12H25I have been proposed to be generated during solvent extraction; thus, these species must be captured from the vessel off-gas (VOG). The abatement of inorganic and organic iodide species to meet United States regulatory requirements has been demonstrated in laboratory experiments using Ag-based solid sorbents. The data presented in this paper includes the effect of gas composition (e.g., the presence of water vapor and NOx), iodine speciation (I2, CH3I, C4H9I, C12H25I), and sorbent bed parameters (e.g., temperature, sorbent age) on complete iodine capture on Ag-mordenite in an aqueous reprocessing plant.

Effects of moisture and aging upon decomposition of methyl iodide by reduced silver mordenite

“…These detected hydrogen iodide and diatomic iodine were present in the impingement traps and therefore in the exhaust gases [4]. Greaney et al [16] studied the performance of silver-based sorbents on the removal of various organic and inorganic radioiodine species.…”

Metal-Encapsulated, Polymer-Containing Halide Salt Composites as Potential Long-Term Hosts for Radioiodine: Evaluating Halmets, Polyhalmets, and Halcermets

“…4,5 Also, iodine speciation differs significantly across various streams and processes, including I 2(g) , CH 3 (CH 2 ) x I (e.g., x = 0−11), ICl (iodine monochloride), HI, HOI, I − , and IO 3 − . 2,6,7 This complicates the complete capture process using a single capture technology.…”

“…This paper focuses on the capture and long-term immobilization of radioiodine released from nuclear processes, which includes the high-activity, short-lived 131 I ( t 1/2 = 8.02 days) and the low-activity, long-lived 129 I ( t 1/2 = 1.57 × 10 7 years). Iodine is highly mobile in the environment and can lead to thyroid cancer, so mitigating its release is essential. , Also, iodine speciation differs significantly across various streams and processes, including I 2(g) , CH 3 (CH 2 ) x I (e.g., x = 0–11), ICl (iodine monochloride), HI, HOI, I – , and IO 3 – . ,, This complicates the complete capture process using a single capture technology.…”