Modelling the dispersion of radon-222 and radionuclides in dust from the Ranger final landform

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South Pacific Environmental Radioactivity Association
The Ranger uranium mine, located in the seasonal wet-dry tropics of Australia’s Northern Territory, is scheduled to cease operating by 2021 and be rehabilitated by 2026. The planned rehabilitation of the mine will result in a final landform covered by low uranium grade waste rock and vegetation. The rehabilitation objective is to establish an environment similar to the World Heritage protected area ot Kakadu National Park, which surrounds the mine. Radiological conditions must also not place significant restrictions on the use of the area. Radon-222 gas, and a range of radionuclides bonded to dust emitted from the waste rock substrate of the final landform represent potential radiation exposure pathways to the public. The inhalation dose rates from 222Rn and dust exposure, together with the dose rates from other potential exposure pathways, need to be assessed to determine what. it any, land use restrictions may be required and demonstrate to compliance with dose limits. This study used RESRAD-OFFSITE 3.2 to model the dispersion of 222Rn and radionuclides in dust from a conceptual landform representing the rehabilitated state of the Ranger uranium mine. The predicted dispersion of 222Rn and radionuclides in dust was primarily governed by wind direction frequency. Contour maps of dry and wet season dispersion were developed to aid estimates of potential dose rates to the public from 222Rn and dust exposure. The maps were used to estimate above-background annual doses to hypothetical receptors at the Aboriginal community at Mudginberri (~10 km NNW) and at the town of Jabiru (~7 l<m W). A ‘worst case’ scenario involving a hypothetical receptor permanently occupying the final landform was also investigated. The estimated doses were generally low, less than the public dose limit of 1 mSv in a year. The 222Rn exposure pathway was the major contributor to the predicted inhalation doses.
Uranium mines, Northern Territory, Australia, Simulation, Radioactivity, Dusts, Seasons, Remedial action
McMaster, S., Doering, C., & Johansen, M. P. Modelling the dispersion of radon-222 and radionuclides in dust from the Ranger final landform. Paper presented to the SPERA Conference 2018, "Bringing environmental radioactivity research to Western Australia, Perth, Western Australia, 6 - 9 November 2018, (pp. 33).