Parameter sensitivity and importance for radionuclide transport in double-porosity systems

Abstract

A type-curve methodology using four dimensionless parameters is developed for modeling radionuclide transport through a fractured, double-porosity system. A dimensionless velocity and a dimensionless dispersion coefficient characterize transport through the fractures, while a dimensionless solute storage enhancement coefficient and a dimensionless time constant for matrix diffusion characterize the coupling of the matrix to the fractures. Using the dimensionless parameters, parameter-variation curves exhibit the general response of a performance measure, nuclide travel time, with respect to the entire range of parameter variability. Parameter sensitivities are then calculated as the normalized derivatives of the parameter-variation curves for the dimensionless set of base-case values. Parameter sensitivities are recast to find the response of the performance measure in terms of a natural set of dimensional parameters that characterize the double-porosity transport model. Importance coefficients are defined to ascertain the relative ranking of the natural set of base-case parameters. 15 refs., 15 figs., 6 tabs.