Application of the ICRP's New Respiratory Tract Model to an Underground Uranium Mine

Abstract

The ICRP's previous models of respiratory tract dosimetry for inhalation of radon progeny parameterised the effective dose in terms of the median size of aerosol particles with radon progeny attached to them, and the so-called unattached fraction of potential alpha energy. In principle, the new ICRP respiratory tract model allows the radiation dose to be derived as a continuous function of the radon progeny particle size, over the complete size range from about 0.5 to 1,000nm. This paper compares the dose conversion factors derived by applying the old and new respiratory tract models to new size distribution data obtained from an operational underground uranium mine. Methods for measuring the radon progeny activity-size distributions and unattached fractions within the mine are outlined, and the results are summarised. For each respiratory tract model, the exposure-dose conversion factors calculated from our measured radon progeny aerosol size distributions are compared with the values calculated for the 'reference' aerosol conditions assumed by the National Research Council to hold for the 1950s and 1960s uranium miners included in epidemiological studies. In general, the dose conversion factors derived for present-day mining were higher, by a factor of 1.2 to 2, reflecting marked local variations in the radon progeny aerosol size distribution. Both the old and new respiratory tract model predicted similar values for the ratio of exposure to dose conversion coefficients between a modern and an early uranium mine.