ICHMT DIGITAL LIBRARY ONLINE
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W. C. H. Kupferschmidt J. C. Wren J. M. Ball ABSTRACT Recent investigations of iodine behaviour under simulated reactor accident conditions in the Radioiodine Test Facility (RTF) have demonstrated that iodine volatility within containment can be appreciably greater than that expected based on thermodynamic considerations alone. Experiments using aqueous CsI as the initial iodine species revealed that iodine volatility is typically one- to two-orders of magnitude higher in the presence of a radiation source as compared to when no radiation source is present. Integrated RTF tests have also demonstrated that iodine behaviour is dependent on the nature of the surfaces present within containment. These experiments revealed that the various surfaces and coatings tested, including polyurethane, vinyl, epoxy, zinc primer, stainless steel and concrete, exhibited differing behaviour regarding the type (physical versus chemical) and location (gas phase surfaces versus aqueous phase surfaces) of iodine adsorption. RTF experiments conducted in the presence of organic-based coatings and radiation also revealed reasonably rapid pH decreases, which in turn resulted in enhanced iodine volatility. This behaviour is attributable to a combination of three separate but related processes: the radiolytic oxidation of aqueous I− to I2 by OH radicals; the radiolytic degradation of organics released to the aqueous phase from the surface coatings, producing carboxylic acids; and the reaction of molecular iodine with the water radiolysis product H2O2, a reaction that exhibits a strong inverse acid concentration dependency in its reaction rate. Key findings from the RTF experimental program are provided and rationalized in terms of the aforementioned processes. |
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