Assessment of the environmental radiological impact in the emergency exposure phase through the simulation of a uranium mining tailings dam breach

This work is aiming at estimating the radiation doses to members of the public in case of an emergency exposure situation related to a hypothetical uranium mining tailings dam rupture at the UDC - Decommissioning Unit of Caldas, MG, Brazil. The calculations will help to managing the exposures of emergency workers and residents in the region downstream the dam. The computer code chosen to perform the simulations was FLO-2D@ software. Due to the uncertainties involved, mainly regarding the waste rheology and activity concentrations and in parameters values to be used in the dose assessment, considerations were made for the study to present results derived from conservative assumptions. Through the creation of flood maps, it was possible to estimate the extent of the areas affected by the released materials. The results showed that in a scenario of the tailings dam breach, deposition of mud shall extend over 20 km downstream affecting an area of nearly 3 km2. Total dose for a member of the public living in most affected areas would be around 43 mSv/y in the early phase after the accident. Although only shielding would be recommended under current radiation protection regulation, evacuation/relocation is suggested due to the presence of long-lived radionuclides. This protective measure would probably already be indicated by the accident itself, regardless of radiological reasons. More realistic assessment should be performed before returning people, considering long-term environmental transport and uses of the area. It must also be considered that long-term exposures have more restricted recommended acceptable levels than those for the emergency phase.