The short-term radiological impact of some serious reactor accidents may be governed by the release of airborne radioiodine to the environment. The impacts of parameters affecting iodine volatility, including radiation, iodine concentration, and solution pH, were investigated under a range of postaccident chemical conditions expected in a reactor containment structure. A bench-scale apparatus, installed in the irradiation chamber of a Gammacell, was used to measure the rate of iodine volatilization from dilute, 10-6 to 10-4 M, CsI solutions with pH values from 5 to 9. Iodine volatilization dramatically increased in the presence of radiation. The volatilization rates were nearly proportional to iodine concentration over the range of concentrations and pH values examined. Volatilization rate increased significantly with a decrease in pH. A kinetic-based model containing a mechanistic description of iodine chemistry was developed to simulate the radiation chemistry of iodine. The majority of the model prediction and experimental results of iodine volatilization rates were in agreement, although some divergence was evident.