IPSN model for the simplified calculation of atmospheric dispersion of accidental releases

To assess the atmospheric dispersion of accidental releases, the Institut de Protection et de Surete Nucleaire (IPSN) has developed a so called gaussian plume model. It derives from tri-gaussian puffs, characterized by standard deviations parametrized with respect to the transfer time (for only two classes of vertical atmospheric stability). The analytic form of this model makes it possible to take into account the most important phenomena which change the content of the plume during transfer: reflections, radioactive decay, daughter products, dry and wet deposition. Limitations to the use of this plume model are examined. Its field of application is reduced in the case of weak winds, the more so when the release height is great. A limited number of reference meteorological conditions and standard values for dry deposition velocity (iodine and particles) and the washing rate by rain are proposed, and examples of results are given. This model predicts the order of magnitude of the consequences of accidental atmospheric releases over distances from several hundred meters up to several tens of kilometers