3. DESCRIPTION OF PROGRAM OR FUNCTION
PFPL is an interactive transport and diffusion program developed for real-time calculation of the location and concentration of toxic or radioactive materials during an accidental release. Deposition calculations are included. The potential exists at the Savannah River Plant for releases of either toxic gases or radionuclides. The automated system developed to provide real-time information on the trajectory and concentration of an accidental release consists of meteorological towers, a minicomputer, and a network of terminals called the Weather Information and Display (WIND) System. PFPL which simulates either instantaneous (puff) or continuous (plume) releases is the primary code used at Savannah River for emergency response. In the PFPL model the diffusion process is separated into two phases. In phase I, the Gaussian cloud grows as a function of wind speed and stability class. Near the ground, the vertical concentration becomes logarithmic. Phase II begins when the vertical standard deviation reaches a value of 0.8H, where H is the depth of the atmosphere's turbulent layer. At the horizontal distance from the source where the standard deviation = 0.8H, the material remaining in the cloud is redistributed to a uniform vertical concentration throughout the mixed-layer. The logarithmic surface layer remains. The basic theory of the model assumes that the dry deposition rate is limited by surface deposition processes and by the rate at which turbulence can bring pollutants down to the surface (deposition) layer. The net effect of the two transfer rates determines the cloud depletion rate and surface concentrations. Depletion of the cloud by rain and radioactive decay is treated as an independent process.