Adsorption of iodine on graphite in High Temperature Gas-Cooled Reactor systems: A review

Adsorption of iodine on graphite is of great interest for operation and safety of high temperature nuclear reactors. Graphite can adsorb significant amounts of iodine and retain it for a long period of time. Significant amount of work on this subject has been done in the past. Various types of adsorption apparatus have been designed and data were collected. The types of graphite used in past studies are not available anymore, and as a consequence the data are not applicable for the new type of commercial nuclear grade graphites. However, the past experimental systems, data, and their analysis are useful to design a better experimental system, collect more accurate data, and, provide better understanding of the adsorption process and data. In addition the existing data can be used to generate a framework to understand the types of adsorption processes taking place. In this work, we have conducted an exhaustive literature review and further analyzed the data. Four adsorption isotherms; the Langmuir, the Freundlich, and the two isotherms proposed in the International Atomic Energy Agency (IAEA) Tecdoc-978 were used to correlate the available equilibrium adsorption data. For most of the data, the simple Langmuir and the Freundlich isotherms provided a reasonable fit of the data. The Polyani's potential theory was also used to check the consistency of the data and as indicated by the theory, most of the data set provided a single characteristic curve. The isosteric heats of adsorption calculated using the literature data suggested that iodine-adsorption on graphite could be a chemisorption process.