This Safety Report describes an approach for assessing the impact of radionuclide dischages in terms of the resulting individual and collective radiation doses. This is achieved by using screening models which describe environmental processes in mathematical terms, producing a quantitative result. This report supports Safety Standards Series No. WS-G-2.3, Regulatory Control of Radioactive Discharges to the Environment (2000), and expands on and supersedes Safety Series No. 57, Generic Models and Parameters for Assessing the Environmental Transfer of Radionuclides from Routine Releases (1982).