The chemistry of iodine in containment

Recent investigations of iodine behavior under radiolytic conditions have demonstrated that kinetics, not thermodynamics, will govern iodine speciation and partitioning under conditions typical of those expected in a reactor containment during an accident. In the presence of radiation, iodine volatility is orders of magnitude higher than that expected based on thermodynamic calculations. Kinetic studies have contributed extensively to the existing database of iodine chemistry and have several implications for modeling iodine behavior for safety analyses. For example, as a result of these investigations, many uncertainties in the iodine database, such as those regarding thermal oxidation of iodine, which were formerly regarded as reactor safety issues, are now considered to be relatively unimportant. In contrast, previously unconsidered factors. such as the effect on aqueous chemistry of impurities originating from surfaces, are now recognized as playing major roles in determining iodine volatility. An updated review of the existing literature regarding iodine behavior is provided, with a focus on recent developments. A critical evaluation of the data in the context of developing a model for iodine behavior under reactor accident conditions is also provided.