Radiological impact assessment of opencast uranium mining for large reservoirs-uncertainty analysis using Wilk´s method

Opencast mining may lead to natural erosion of ore material due to overland flow of water accumulated from rainfall. The overland flow may ultimately reach the nearby surface water body. This process may lead to the release of U-238 and its daughter products into the surface water body. The present study is carried out to assess the radiological impact of the erosion in terms of dose due to U-238 and its progenies in the surface water body and to quantify the uncertainty associated with the dose due to consumption of the reservoir water. The in-growth of progenies is also taken into account. The properties like settling velocity, distribution coefficients etc. are having inherent uncertainty associated with their values. The uncertainty of various parameters involved is propagated to the model output. Hence, the uncertainty analysis becomes important to build confidence in the results. In this paper, Wilk´s method is used to calculate a value greater than 95^th percentile value for the dose rate through drinking water pathway with 95 percent confidence level (95/95 value). In present study, the 95/95 value for the annual effective dose to the public due to U-238 and its progenies through drinking water pathway is found to be 12.5 times lower as compared to the WHO guidelines for drinking water.