Assessment of radon progeny dose conversion factors from measurements in the underground uranium mine at Olympic Dam

The International Commission on Radiological Protection (ICRP) in ICRP Publication 65 (ICRP, 1993) recommended the use of a single conversion factor, determined from uranium mining epidemiological studies, as the preferred method for converting radon decay product inhalation exposure to effective dose. This is the so-called radon decay product 'conversion convention'. In ICRP Publication 115 (ICRP, 2010) the ICRP revised upwards its assessment of risk detriment for inhalation of RDP and indicated its intention to replace the current dose conversion convention with dose conversion coefficients (DCC) or dose conversion factors (DCF) derived from dosimetric modelling. A key parameter used in the ICRP dosimetric modelling of inhalation of radionuclides is the aerosol size distribution of the RDP, particularly particle sizes in the range 0.6 nm to greater than 1 µm. There is very little published data on radon decay products aerosol characteristics in modern uranium mines. Some measurements of this type were carried out in 1992 at the Olympic Dam mine, currently operated by Broken Hill Proprietary (BHP) at Roxby Downs, South Australia. Given the potential regulatory and operational impacts for assessment of doses from inhaled RDP in Australian uranium mines, it was determined that a study of the RDP aerosol characteristics in current Australia mines should be undertaken. In early 2013 the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) formed the Australian Particle Sizing Group (PSG) to advise government, regulatory authorities, industry and other stakeholders on the potential impacts of the proposed change to the dose conversion convention. This report summarises the measurements conducted at the BHP Olympic Dam uranium mine at Roxby Downs, South Australia in December 2013 to characterise the RDP parameters.