Technical Report NTB 00-02
SANTA – Sensitivity Analysis of Nuclide Transport Aspects
The SANTA (Sensitivity Analysis of Nuclide Transport Aspects) program is a simple box model created to simplify understanding of radionuclide or contaminant transport through a fractured medium. SANTA is a teaching tool and allows scoping calculations, interpretation of migration experiments, sensitivity studies, and assists in the development of conceptual models. The processes acting upon a contaminant explored by SANTA include advection in the main channel, dispersion in the main channel, linear/non-linear sorption and desorption in the main channel, diffusion into and out of the rock matrix, sorption and desorption in the rock matrix, radioactive decay and any combination of the above processes.
Conceptually SANTA uses an array of identical boxes (both in physical dimensions and geochemical content) to represent a 1-D homogeneous main channel (fracture), with an optional 1-D homogeneous rock matrix, accessed by diffusion, arranged symmetrically about the main channel and represented by arrays of identical boxes. Transport in the main channel is implemented by simple movement of the aqueous phase from one box to the next during a set time, while diffusion into the rock matrix is governed by a discrete approximation of Fick's first law. The source term, supplying the first box, is limited to a single contaminant input supplied continuously at a fixed concentration, or as a pulse of finite duration. The status in the last box at the end of the fracture is continuously recorded and represents the breakthrough curve.
SANTA contains a built-in grapher to display results such as concentration profiles (fracture and rock matrix) or breakthrough curves, or optionally results can be output to a file.
Code testing focuses on SANTA's implementation of advective flow, diffusion into the rock matrix (within a bounded and unbounded medium), sorption, dispersion and a combined process test, and compares SANTA's results with analytical solutions and results from alternative numerical models. The comparative tests attest sufficient numerical accuracy for the purposes SANTA was designed for. SANTA was programmed in a combination of FORTRAN and VISUAL BASIC, retaining the proven mathematical ability of FORTRAN, while including the user-friendly Windows environment of VISUAL BASIC, with integral graphing and printing capabilities. The program also features a fully illustrated Help file containing an on-line user manual and reference guide, and comes with a selection of example input files. SANTA runs on the following operating systems: Windows 3.x, Windows 95 and Windows NT.