Environmental Impact Assessment of Liquid Waste Ponds in Uranium Milling Installations

Abstract

A detailed environmental impact assessment is required in many countries when considering the disposal of wastes containing radioactive materials. In this paper we present hybrid numerical-analytical solutions for the subsurface transport of radioactive contaminant decay chains that may be used for such an assessment. The model involves the advective–dispersive transport of multiple radionuclide species within separate but coupled saturated and unsaturated soil domains. The resulting partial differential equations were solved using the Generalized Integral Transform Technique to yield analytical expressions for the concentration distributions versus distance, and analytical or numerical solutions as a function of time. The potential of the hybrid modeling approach is illustrated by means of an environmental impact assessment of an uranium milling liquid waste pond near Caetité, Brazil. Calculated radionuclide concentration distributions were for this purpose used in subsequent radiation dose calculations. Several scenarios were analyzed, including operational, human intrusion, farmer/road builder, and leaching scenarios. Numerical results show that for all scenarios analyzed the total dose is less than the Brazilian regulatory dose limit of 0.3 mSv/year above natural background for a period of 10,000 years.