Evaluation of Savannah River Lab. atmospheric dispersion models

Evaluation of atmospheric transport and dispersion models using planned releases of chemical tracers is a vital component of atmospheric contaminant modeling. The Savannah River Lab. (SRL) is conducting a continuing series of Mesoscale Atmospheric Transport Studies (MATS). These studies involve the planned release of the tracer sulfur hexafluoride (SF6) to evaluate the performance of SRL atmospheric models, to identify areas for future model improvement, and to gain greater insight into the mechanisms of atmospheric dispersion at the Savannah River Plant (SRP). There are two primary atmospheric transport and dispersion models used at SRL: a simple Gaussian model, Puff-Plume, and a sequential Gaussian model, 2DPUF, still under development. Calculations by these models are used in conjunction with observations from sampling teams to estimate surface concentrations and doses resulting from radiologic and/or chemical contaminants released into the atmosphere. Puff-Plume is used for an initial survey of the plume and to help guide sampler deployment; 2DPUF is used for final evaluation and analysis after a release. Hence, it is important to understand how surface concentrations predicted by these models compare with those observed in an intensive series of surface measurements. The results of 14 daytime MATS, conducted in predominantly convectively unstable conditions, showed that Puff-Plume simulated the plume width well