Modeling accidental releases to the atmosphere of a dense reactive chemical (Uranium hexafluoride)

In order to model the atmospheric transport and dispersion of dense reactive chemicals such as uranium hexafluoride (UF6), it is necessary to include algorithms that account for heat exchanges due to chemical reactions and phase changes. UF6 may be released accidentally at uranium-enrichment plants as a warm gas from a pipeline rupture, or as a flashing liquid from a pressurized tank or line break. The resulting plume is initially very dense due to the large molecular weight of UF6, but may become lighter-than-air as the UF6 reacts with water vapor to form HF, which has a molecular weight less than that of air, and which may cause an increase in plume temperature due to the exothermic reaction. The major chemical and thermodynamic processes related to UF6 have been incorporated in a modified version of an existing dense gas model, HGSYSTEM. The same general approach could be used to include other reactive chemicals in the modeling system. New modules that are applicable to any type of chemical release have also been added to HGSYSTEM to account for building downwash, lift-off of warm plumes from the ground, and deposition. The revised HGSYSTEM/UF6 model has been evaluated with field data from UF6 tests. The sensitivities of the model predictions to variations in input parameters have been assessed.