The Department of Energy (DOE) has performed an evaluation of the technical bases for the default value for the atmospheric dispersion parameter χ/Q. This parameter appears in the calculation of radiological dose at the onsite receptor location (co-located worker at 100 meters) in safety analysis of DOE nuclear facilities. The results of the calculation are then used to determine whether safety significant controls should be established to prevent and/or mitigate the event causing the release of hazardous material. An evaluation of methods for calculation of the dispersion of potential chemical releases for the purpose of estimating the chemical exposure at the co-located worker location was also performed.

The default χ/Q dispersion value and methods for determining atmospheric dispersion are prescribed in Appendix A of DOE Standard (STD) 1189-2008, Integrating Safety into the Design Process. DOE’s evaluation consisted of: (a) a review of the regulatory basis for the default χ/Q dispersion parameter; (b) an analysis of this parameter’s sensitivity to various factors that affect the dispersion of radioactive material; and (c) performance of additional independent calculations to assess the appropriate use of the default χ/Q value. The evaluation also analyzed the appropriateness of the use of the default χ/Q value when calculating the dispersion of chemical releases.