Prediction of Rn-222 exhalation rates from phosphogypsum-based embankments. Part II: numerical simulation and results

As shown in the first part of this paper, equations for an attempt to simulate 222 Rn activity along the axial distance in phosphogypsum-based embankments were presented. For that, an existing one-dimension diffusive model with source and sink terms was applied. Knowledge of the 222 Rn concentration activity profile enables the assessment of the corresponding exhalation rate. In this second part of the paper, a preliminary version of the corresponding computational simulation program was tested against the analytical solution and steady-state experimental data. The numerical solution method followed a finite volume discretization on a structured orthogonal mesh. Grid points were located according to a cell-centered scheme and variables were stored in a collocated arrangement. The resulting algebraic equation system was relaxed by either the Tri-Diagonal Matrix Algorithm or Gauss-Seidel method. Grid size independence was observed as well. Numerical results are discussed upon and new developments and extensions of this first approach are pointed out. (author)