Variability in dose-equivalent assessments for inhaled U3O8 concentrations

A potentially significant radiological hazard exists in the packaging area of uranium mills through the inhalation of airborne uranium octoxide (U3O8). The Radiation Protection (Mining and Milling Code (1980) requires the measurement and assessment of quarterly, annual and cumulative dose equivalents for employees working in these areas. Arising through differences which exist between the abovementioned Code and ICRP 30, and assumptions of particle size and dust concentration distributions, confusion exists within Australia regarding the methods which can be used to make the required assessments. Exposure data were collected during routine monitoring at an operating mill facility and were interpreted using different methods and a range of assumptions. Results indicated the dust at this facility is characterised by an AMAD greater than 10 μ, and dust concentrations were distributed lognormally. Assumptions of a normal distribution may result in an overestimate of the dose equivalent. The importance of particle size in dose assessments using ICRP 30 techniques was highlighted. Information was masked when employee data was grouped to provide work category dose assessments. The use of ICRP 30 methods were recommended to provide uniformity throughout Australia