Authors

Abstract

Predictions of radionuclide dose rates to freshwater organisms can be used to evaluate the radiological environmental impacts of releases from uranium mining and milling projects. These predictions help inform decisionson the implementation of mitigation measures. The objective of this study was to identify how dose ratemodelling could be improved to reduce uncertainty in predictions to non-human biota. For this purpose, wemodelled the activity concentrations of 210Pb, 210Po, 226Ra, 230Th, and 238U downstream of uranium mines andmills in northern Saskatchewan, Canada, together with associated weighted absorbed dose rates for a freshwaterfood chain using measured activity concentrations in water and sediments. Differences in predictions of radionuclide activity concentrations occurred mainly from the different default partition coefficient and concentrationratio values from one model to another and including all or only some 238U decay daughters in the dose rateassessments. Consequently, we recommend a standardized best-practice approach to calculate weighted absorbed dose rates to freshwater biota whether a facility is at the planning, operating or decommissioned stage. At theinitial planning stage, the best-practice approach recommend using conservative site-specific baseline activityconcentrations in water, sediments and organisms and predict conservative incremental activity concentrationsin these media by selecting concentration ratios based on species similarity and similar water quality conditionsto reduce the uncertainty in dose rate calculations. At the operating and decommissioned stages, the best-practiceapproach recommends relying on measured activity concentrations in water, sediment, fish tissue and wholebody of small organisms to further reduce uncertainty in dose rate estimates. This approach would allow formore realistic but still conservative dose assessments when evaluating impacts from uranium mining projects andmaking decision on adequate controls of releases.