[en] The U.S. Department of Energy (DOE) has an ongoing program, the Uranium Mill Tailings Remedial Action (UMTRA) Project, to stabilize piles of uranium mill tailings in order to reduce the potential radiological hazards to the public. Protection of workers and the general public against airborne radioactivity during remedial action is a top priority at the UMTRA Project. The primary occupational radionuclides of concern are ²³⁰Th, ²²⁶Ra, ²¹⁰Pb, ²¹⁰Po, and the short-lived decay products of ²²²Rn with ²³⁰Th causing the majority of the committed effective dose equivalent (CEDE) from inhaling uranium mill tailings. Prior to this study, a default particle size of 1.0 μm activity median aerodynamic diameter (AMAD) was assumed for airborne radioactive tailings dust. Because of recent changes in DOE requirements, all DOE operations are now required to use the CEDE methodology, instead of the annual effective dose equivalent (AEDE) methodology, to evaluate internal radiation exposures. Under the transition from AEDE to CEDE, with a 1.0 μm AMAD particle size, lower bioassay action levels would be required for the UMTRA Project. This translates into an expanded internal dosimetry program where significantly more bioassay monitoring would be required at the UMTRA Project sites. However, for situations where the particle size distribution is known to differ significantly from 1.0 μm AMAD, the DOE allows for corrections to be made to both the estimated dose to workers and the derived air concentration (DAC) values. For particle sizes larger than 1.0 μm AMAD, the calculated CEDE from inhaling tailings would be relatively lower