Radiation doses to members of the public from the Olympic Dam uranium mining operation

The Olympic Dam project is a large underground mine with associated processing plant and smelter, producing copper, uranium and precious metals. It operates on the world's largest known uranium resource, and one of the largest copper resources. Current annual mine production is approximately 11 million tonnes of ore, with approximately 250 000 tonnes of refined copper and 4100 tonnes of uranium oxide being produced annually. There is no surface drainage of precipitation and consequently the only significant pathways for radiation exposure for members of the public from project operations are airborne ones: inhalation of radon decay products, and inhalation of radioactive dusts. The most highly exposed members of the public (critical group) are the residents of Olympic Dam village. The radiological aspects of the project are regulated under several pieces of legislation, which include requirements to comply with relevant recommended ICRP and IAEA dose limits: that is, for public exposure an average effective dose of 1 mSv in a year to members of the relevant critical group. A comprehensive program to monitor airborne concentrations of these contaminants and associated meteorological parameters is in place. Radon decay products are measured continuously at four sites, with hourly recording of concentrations. High volume dust monitoring is undertaken at three sites, with subsequent radionuclide analysis of the collected dust. Wind speed and direction is also measured continuously. From these results, estimates of doses to members of the public at Olympic Dam village and at Roxby Downs are made. Standard dose conversion factors are used to convert measured atmospheric concentrations to dose. Atmospheric dispersion modelling has also been used to estimate doses from inhalation of radon decay products. The estimated dose from all radon decay products obtained from atmospheric dispersion modelling was 24 μSv per annum. The annual total dose from inhalation of radioactive dusts (background plus project component) was estimated at 7.5 μSv, with a project related component of 3 micro Sv per annum. It was concluded that the closest residents to the operational area (that is those living at Olympic Dam village) received a total project related annual dose from airborne pathways of the order of 25 μSv. Even under quite extreme worst-case assumptions (all radon decay products measured when the wind direction is from the operational area, and all radioactive dusts, are assumed to be project generated) the annual dose to members of the public is less than 75 μSv