Radon Release at a Rehabilitated Uranium Mine Site and Dose Assessment (Case of the Former Beshtaugorskiy Mine, North Caucasus)

Abstract

The article presents the results of the radon release studies at the rehabilitated uranium mine and an assessment of doses received by the population when using the territory for recreational purposes (the case of the former Beshtaugorsky uranium mine). The measurements of radon flux density from the ground surface, radon concentration in the atmospheric air and groundwater, as well as the gamma dose rate and content of natural radionuclides in soils and bedrocks were performed. It is established that abnormally high radon release associated with both a former uranium adits and natural factors such as tectonic faults. The abnormally high radon release is due to advective radon transport, mainly associated with convective thermally induced air convection in permeable zones of mountain massif; radon transport by groundwater does not affect radon emissions from the surface. The most significant source of radiation risk is the incompletely blocked adit mouths, from which mine air is periodically blown out. Radon concentration and gamma dose rate values many times exceed permissible levels in these locations. A person resting in such an area for 4 hours can lead to a dose exceeding 2 mSv. This is advisable to take measures to prevent or reduce the time people spend in the areas of former adit mouths.