PNNL

Abstract

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, I2(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 the adsorption on three major constituents of austenitic stainless steel, focusing on understanding the adsorbed species of iodine and the variables affecting 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 adsorption behaviors. 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 surface oxidation and environmental factors (e.g. humidity and oxygen content) on the metal substrates is addressed. The individual metals demonstrated an interaction between I2(g) and the oxygen on the surface of all the metals tested as well as formation of metal iodides for Fe and Ni particles. The formation of metal iodides may be indicating 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 steel. The exposures without oxygen and humidity indicate the potential of a multistep process where iodine first attacks the oxide layer and then chemisorbs to the exposed metal.