Use of CAP88 PC to infer differences in the chemical form of 129I emitted from a fuel reprocessing facility

Emissions of 129I from nuclear fuel separations conducted at the Hanford Site in Washington State have been occurring since the 1940's. Fuel separation on the Hanford Site stopped in 1988, but emissions of 129I have continued as venting of the PUREX Plant occurred. In this study, atmospheric measurements of 129I concentrations were coupled with an EPA approved plume dispersion model (CAP88-PC, Version 3.0) to evaluate the effectiveness of the dispersion model for estimating ambient concentrations at the Hanford Site. This evaluation led to the hypothesis that different chemical forms of iodine were being emitted over the years; this hypothesis was developed as an explanation for the model agreeing with measurements over some time periods, but not over all time periods. The model was then run with modified emissions to simulate the short atmospheric half-life of the suspected reactive chemical form of iodine being emitted. This modification resulted in good agreement between the modeled and measured concentrations over the entire 20 year study period (1986–2005), and provided evidence supporting the hypothesis of a reactive form of iodine being emitted.