TACK - a program coupling chemical kinetics with a two-dimensional transport model in geochemical systems
The Transport And Chemical Kinetics (TACK) program has been designed to make predictions of the chemistry in the vicinity of a planned repository for nuclear waste, i.e. SFL 3-5, where SFL is the Swedish abbreviation for "Swedish repository for long-lived waste". This implies modelling transport and chemistry in fractured rock. The system concerned in the modelling of SFL is leaching water from decommissioning waste in concrete. The concrete will raise the pH in the water to between 12 and 13.5. So far, only a few calculations have been made on such systems. Coupled transport and chemical reaction programs should be used, since the system is important for safety assessments of the repository. At least two of programs can be used for this kind of problem, for example OS3D/GIMRT and PHAST. As it is also important to consider the uncertainty of the model, the TACK program fills an important purpose here. A slightly different approach to the problem may give significantly different results. Because validation is generally not possible, using several programs is the only key to identifying conceptual uncertainties. To illustrate this point, comparative calculations have been made between TACK and the PHAST program. The calculations gave qualitatively similar result but quantitatively somewhat differing results. The TACK program couples the well known PHREEQC geochemical program with a two-dimensional transport model. The PHREEQC calculations include speciation of solutions and mineral reactions involving kinetics. The reasons for choosing this program are that it is quite a general one and is relatively stable at the high pH values present in the systems used. The transport phenomena taken into account in the model are advection, diffusion and dispersion in two dimensions. (C) 2003 Elsevier Science Ltd. All rights reserved.
coupled two-dimensional transport reaction diffusion dispersion