Sensitivity analysis of a model for the environmental movement of radionuclides

Results are presented from a sensitivity analysis study of a model developed to represent the environmental movement of radionuclides. This model is designated the Environmental Transport Model. The study has three purposes: (1) to develop sensitivity analysis techniques applicable to the Environmental Transport Model, (2) to provide insight and experience with respect to the performance of a sensitivity analysis of this model and (3) to develop understanding of the overall operation of the model and the variables which influence this operation. Two variations of a hypothetical river receiving a radionuclide discharge containing 99Tc, 245Cm, 241Pu, 234U, 230Th and 226Ra are defined. Independent variables of the following types are introduced: variables which define physical properties of the river system (e.g. soil depth, river discharge and sediment resuspension) and variables which summarize radionuclide, the following dependent variables are investigated: (1) radionuclide concentration in soil, (2) dissolved radionuclide concentration in surface-water and (3) total radionuclide concentration in surface-water. The investigation employs sensitivity analysis techniques based on Latin hypercube sampling, rank transformations and stepwise regression. Among the important variables indicated in the analysis are distribution coefficients, river discharge and suspended sediment concentration.