Mathematical Model for Evaluating the Suitability of a Low-Level Radioactive Waste Site.

摘要

A mathematical model intended to study the one-dimensional transport of radionuclides in a non-homogeneous soil system under saturated-unsaturated and isothermal conditions is presented. The model is composed of two modules: the first to calculate the pressure distribution enabling one to compute velocities and soil moisture; the second to calculate the migration of species by considering the major processes associated with the transport phenomena of a dissolved substance in porous media, i.e., advection, mechanical dispersion, molecular diffusion, radioactive decay, and sorption, assuming a linear equilibrium isotherm. The numerical method of solving both flow and solute equations used here is the finite-element method based on the weighted residual technique. The flow equation is solved by the Bubnov-Galerkin method. The solute equation is solved by a Petrov-Galerkin type method. The model allows for a variety of boundary conditions; e.g., infiltration, drainage and/or evaporation. A test case involving the movement of a non-reacting ionic species is used to validate the model. Use of the model is illustrated by the analysis of the movement Sr-90 and Cs-137 and H-3 (as water) from a low-level solid-waste disposal trench subject to a steady rate of rainfall. (ERA citation 08:023119)