The adsorption behavior of molecular iodine is important for understanding the spread of radioiodine in a nuclear accident. Prior experiments indicate that, in addition to the interaction with Fe, molecular iodine [i.e., I-2(g)] also interacts with the next most abundant components of austenitic stainless steel (i.e., Ni, and Cr) at room temperature. In this study, we investigate iodine adsorption on Fe, Ni, and Cr while focusing on understanding the variables affecting adsorption as well as the iodine compounds that are formed during adsorption. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the surfaces of exposed metal particles and aid in the understanding of the morphology and chemistry of iodine interactions with the substrates. Inductively coupled plasma optical emission spectroscopy was used to detect low levels of metal iodides and X-ray photoelectron spectroscopy was used to confirm the formation of the metal iodides. The role of environmental factors (e.g., humidity and oxygen content) for iodine adsorption on metal substrates is addressed. The individual metals demonstrated formation of metal iodides for Fe and Ni particles from interaction with I-2(g). The formation of metal iodides may indicate the affinity of iodine for the respective metal. In this study, the iodine affinities ranked Fe > Ni > Cr as determined by the quantity of chemisorbed iodine. This trend is also supported by the distributions and proportions of metals in the corrosion product of the stainless steels. The exposures without oxygen and humidity indicate the potential of a multistep iodine adsorption process where iodine first attacks the oxide layer and then chemisorbs to the exposed metal.

In order to evaluate the potential impacts to the public from radioiodine in a nuclear event, it is vital to expand our understanding of the interaction of molecular iodine with various surfaces. There are many potential surfaces that iodine could interact with in and around a nuclear facility, including stainless steel. This study, carried out at ambient temperature, pressure and humidity, demonstrates the highly adsorptive nature of molecular iodine on two types of austenitic stainless steel, SS304L and SS316L. By using a novel approach which combines inductively coupled plasma-optical emission spectroscopy (ICP-OES) with surface energy dispersive X-ray spectroscopy (EDS) there is evidence of the formation of metal iodides that have not previously been verified or quantified. Samples exposed to gaseous molecular iodine formed an iodine containing corrosion product visible by scanning electron microcopy (SEM). Evaluation of the metals in the corrosion region using EDS was compared to a water leach of the same samples analyzed using ICP-OES. The combination of techniques provides indication of metal iodide formation with minor stainless-steel constituents including: NiI2, MnI2 and CrI2. (C) 2020 Published by Elsevier B.V.