APPLICATION OF THE ICRP NEW RESPIRATORY-TRACT MODEL TO AN UNDERGROUNDURANIUM-MINE

The ICRP's previous models of respiratory tract dosimetry for inhalati on of radon progeny parameterised the effective dose in terms of the m edian size of aerosol particles with radon progeny attached to them, a nd the so-called unattached fraction of potential alpha energy. In pri nciple, 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 1000 nm. This pap er compares the dose conversion factors derived by applying the old an d new respiratory tract models to new size distribution data obtained from an operational underground uranium mine. Methods for measuring th e radon progeny activity-size distributions and unattached fractions w ithin the mine are outlined, and the results are summarised. For each respiratory tract model, the exposure-dose conversion factors calculat ed from our measured radon progeny aerosol size distributions are comp ared with the values calculated for the 'reference' aerosol conditions assumed by the National Research Council to hold for the 1950s and 19 60s uranium miners included in epidemiological studies. In general, th e dose conversion factors derived for present-day mining were higher, by a factor of 1.2 to 2, reflecting marked local variations in the rad on progeny aerosol size distribution. Both the old and new respiratory tract model predicted similar values for the ratio of exposure to dos e conversion coefficients between a modem and an early uranium mine.