[en] The gas phase decontamination project is investigating the use of chlorine trifluoride (ClF₃) to fluorinate nonvolatile uranium deposits to produce uranium hexafluoride (UF₆) gas. The potential existence of chlorine dioxide (ClO₂) during gas phase decontamination with ClF₃ has been the subject of recent safety discussions. Some of the laboratory data collected during feasibility studies of the gas phase process has been evaluated for the presence of ClO₂ in the product gas stream. The preliminary evidence to date can be summarized as follows: (1) ClO₂ was not detected in the flow loop in the absence of ClF₃; (2) ClO₂ was not detected in the static reactors in the absence of both ClF₃ and ClF; and (3) ClO₂ was detected in a static reactor in the absence of all fluorinating gases. The experimental evidence suggests that ClO₂ will not exist in the presence of ClF₃, ClF, or UF₆. The data analyzed to date is insufficient to determine the stability of ClO₂ in the presence of ClO₂F. Thermodynamic calculations of the ClF₃ + H₂O system support the experimental evidence, and suggest that ClO₂ will not exist in the presence of ClO₂F. Additional experimental efforts are needed to provide a better understanding of the gas phase ClF₃ treatments and the product gases. However, preliminary evidence to date suggests that ClO₂ should not be present as a product during the normal operations of the gas phase decontamination project