Prompt estimation of release rates of gaseous radioactivity from a nuclear plant using an aerial survey

Two methods for estimating release rates of gaseous radioactivity from a nuclear plant using an aerial survey were investigated. In these methods, the release rates are derived from observed spatial distributions of exposure rates through conversion factors. The conversion factors were determined from simulation calculations assuming a Gaussian plume model. First, conversion factors for plumes emitting monoenergetic gamma rays were calculated, then the conversion factors were constructed through convolution for the radionuclides important in a nuclear reactor accident and for mixtures of these radionuclides considering elapsed time after reactor shutdown. Furthermore, these methods were applied to real survey data and the estimated release rates agreed with values from stack gas monitors within a factor of 2-3. (author)