Joint Test Plan for the Evaluation of Iodine Retention for Long-Chain Organic Iodides

Abstract

A number of reports have identified four volatile radionuclides that arise from the reprocessing of nuclear fuel ( 3 H, 14 C, 85 Kr, and 129 I) that require controls limiting their environmental release from reprocessing facilities in order to meet US regulatory requirements. Of these, 129 I has the longest half-life and highest potential biological impact.The study of inorganic iodide in aqueous reprocessing facility off-gas systems has been almost exclusively limited to I 2 , and the focus of organic iodide studies has been CH 3 I as a surrogate for various organic iodides that could be present. A study conducted in 2015 focused on those inorganic and organic iodine-bearing species in reprocessing plants that have the potential to be poorly sequestered with traditional capture methods. This study found that even if high decontamination factors (DFs) are achieved for the dissolver off-gas (DOG), losses of iodine to the head-end cell, if greater than about 0.1% of the total iodine inventory, can limit the overall plant DF unless sufficiently high DFs are also achieved for the cell off-gas. The same is true for the losses of iodine to the vessel off-gas (VOG), if those losses are greater than about 0.1%. The study further indicated that high DFs on the VOG may be difficult to achieve as it is the stream where penetrating, or difficult to remove, organic iodide species are most likely. These two factors prompted studies examining organic iodide removal from prototypic VOG streams at both Oak Ridge National Laboratory (ORNL) and Idaho National Laboratory (INL). These studies included an initial evaluation of reduced silver-exchanged mordenite (Ag 0 Z) and silver-functionalized silica-aerogel (AgAerogel) for the capture of CH 3 I and I 2 under VOG conditions by Jubin et al. (2017a) and for the capture of iodobutane under DOG conditions at INL (to be reported in 2018.)The objective of this report is to develop a robust experimental program that will evaluate the adsorption rate of long-chain organic iodides and identify any significant variations in mass transfer zone and byproducts produced during the adsorption on Ag 0 Z and AgAerogel under both DOG and VOG conditions expected for a used nuclear fuel aqueous reprocessing facility. Organic species of interest include both short-chain alkyl iodides such as methyl iodide (CH 3 I) and longer alkyl iodides up to iodododecane (C 10 H 21 I). The primary product of this report is a test plan for the experimental work that could be conducted as part of the ongoing off-gas abatement R&D efforts at both INL and at ORNL.

Organic Iodide Sorption from Dilute Gas Streams

“…Compared with the removal of organic iodine, the removal of inorganic iodine was historically more fully investigated. The primary technical difficulties related to I removal from the DOG are sorbent degradation or capacity loss due to sorbent corrosion, which is sometimes referred to as sorbent aging, and the high level of solid sorbent consumption that occurs if preliminary bulk aqueous I scrubbing is not employed (Jubin et al 2018).…”

“…In 2018, ORNL and INL developed a joint test plan designed to identify remaining knowledge gaps surrounding organic iodide sorption from dilute gas streams and answer them through a collaborative test program (Jubin et al 2018). This test plan addressed some fundamental I sorption questions but also sought to provide more applied data that could be useful in the redesign of a VOG I abatement system.…”

“…Three organic iodides were selected for off-gas studies at INL and ORNL in 2018: CH3I, C4H9I, and C12H25I (Jubin et al 2018). These organic iodides are hypothesized to form in the off-gas due to reactions with the organic solvent and diluent used in a typical PUREX reprocessing scheme.…”

“…Historically, studies of I abatement by Ag-functionalized sorbents have focused on inorganic I in the DOG, but in the last few years, more research attention has been given to organic iodides, especially longer chain species, such as C4H9I, and C12H25I. This report has three main goals: (1) to present new data generated at Oak Ridge National Laboratory (ORNL) in FY21 on the sorption behavior of organic iodides on AgZ, (2) to summarize and synthesize organic iodide data produced by ORNL and Idaho National Laboratory (INL) over the last 4 years to answer questions on organic iodides behavior outlined in the 2018 joint test plan (Jubin et al 2018), and…”

Iodine Retention of Long-chain Organic Iodides on Silver-based Sorbents under DOG and VOG Conditions

“…As listed in the joint test plan, there are seven primary questions under investigation (Jubin et al 2018).…”