NRC's (Nuclear Regulatory Commission) Limit on Intake of Uranium Ore Dust

摘要

In 1960 the Atomic Energy Commission adopted an interim limit on the intake by inhalation of airborne uranium ore dust. This report culminates two decades of research aimed at establishing the adequate of that limit. The report concludes that the AEC under-estimated the time that thorium-230, a constitutent of uranium ore dust, would remain in the human lung. The AEC assumed that thorium-230 in ore dust like uranium with a 120 day biological half-life in the lung. This report concludes that the biological half-life is actually on the order of 1 year. Correcting the AEC's underestimate would cause a reduction in the permitted airborne concentration of uranium ore dust. However, another factor that cancels the need for that reduction was found. The uranium ore dust in uranium mills was found to occur with very large particles sizes (10-micron AMAD). The particles are so large that relatively few of them are deposited in the pulmonary region of the lung, where they would be subject to long-term retention in the body. The two effects are of about the same magnitude but in opposing directions. Thus the present uranium ore dust intake limit in NRC regulations should provide a level of protection consistent with that provided for other airborne radioactive materials. The report recalculates the limit on intake of uranium ore dust using the derived air concentrations (DAC) from ICRP 30.