Measurements of the radiolytic oxidation of aqueous CsI using a sparging apparatus

Radiolytic oxidation is considered to be the main mechanism for the formati on of I-2 from aqueous CsI in the containment of a water-cooled reactor aft er a loss-of-coolant accident (LOCA) in a pressurized water reactor. Despit e the amount of study over the last 60 yr on the radiation chemistry of iod ine, there have, until recently, been few consistent sets of experiments sp anning a wide enough range of conditions to allow models to be verified wit h confidence. The results from a set of experiments carried out to remedy this deficiency are described. In this work the rate of evolution of I-2 from Sparged irra diated berate solutions containing CsI labeled with I-131 was measured onli ne over a range of conditions. This work involved the measurement of the ef fects of pH, temperature, Or concentration, I- concentration, phosphate con centration, dose-rate, and impurities on the rate of evolution of I-2. The range of conditions was chosen to span as closely as possible the range of conditions expected in a LOCA, but also to help to elucidate some of the me chanisms especially at high pH. The pH was found to be a very important factor in determining iodine volati lity. Over the temperature range studied, the extent of oxidation decreased with increasing temperature, but this was counteracted, to a greater or le sser extent, by the decrease in partition coefficient The oxygen concentrat ion was more important in solutions not containing phosphate. The fractiona l oxidation was not particularly dependent on iodide concentration, but G(I 2) was very dependent on [I-]. There was no effect of added impurities, Fe, Mn, Mo, or organics although, in separate work, silver was found to have a very important effect. During attempts to interpret the data, it was found that;it was necessary t o consider the iodine atom as a volatile species with a partition coefficie nt of 1.9 taken from thermodynamic data. The modeling work is described in a separate paper.