MODELING ACCIDENTAL RELEASES TO THE ATMOSPHERE OF A DENSE REACTIVE CHEMICAL (URANIUM HEXAFLUORIDE)

In order to model the atmospheric transport and dispersion of dense re active chemicals such as uranium hexafluoride (UF6), it is necessary t o include algorithms that account for heat exchanges due to chemical r eactions and phase changes. UF6 may be released accidentally at uraniu m-enrichment plants as a warm gas from a pipeline rupture, or as a fla shing liquid from a pressurized tank, or line break. The resulting plu me is initially very dense due to the large molecular weight of UF6, b ut may become lighter-than-air as the UF6 reacts with water vapor to f orm HF, which has a molecular weight less than that of air, and which may cause( )an increase in plume temperature due to the exothermic rea ction. The major chemical and thermodynamic processes related to UF6 h ave been incorporated in a modified version of an existing dense gas m odel, HGSYSTEM. The same general approach could be used to include oth er reactive chemicals in the modeling system. New modules that are app licable to any type of chemical release have also been added to HGSYST EM to account for building downwash, lif-off of warm plumes from the g round, and deposition. The revised HGSYSTEM/UF6 model has been evaluat ed with field data from UF6 tests. The sensitivities of the model pred ictions to variations in input parameters have been assessed. Copyrigh t (C) 1996 Elsevier Science Ltd