NUFT-C (Nonisothermal, Unsaturated Flow and Transport with Chemistry) is a code designed to simulate coupled fluid movement (multiple liquids and gas) and chemical reactions in saturated or unsaturated porous media. Chemical interactions that modify the physical properties of the porous media are also considered. Applications of the code have primarily addressed simulations of the long-term evolution of rock in the vicinity of deep geological high level nuclear waste repositories, thermal perturbation of sedimentary basins, and mineral and chemical evolution associated with subsurface sequestration of CO2. Installation and use of NUFT-C has included PCs, workstations and massively parallel high performance platforms.
Implementation of the code on massively parallel computers has allowed the first high resolution 3-dimensional simulations of complex chemical and mineralogical interactions around tunnels in which may be placed high level nuclear waste. These simulations are important for predicting where fluid movement will be concentrated, how its chemistry will evolve with time, and where to place sensors for monitoring purposes. The colored cross-sections in the movies shown here are from a 2-dimensional slice through 1 tunnel in a 3-dimensional simulation that considered sampling strategies for a monitoring program. The computational mesh consisted of approximately 2 million nodes, with resolution varying from 10 centimeters to 10s of meters. The movies depict the change in dissolved sulfate in waters that would be sampled in fractures and in the porous rock (matrix) in the near vicinity of a waste emplacement tunnel. The time span represented is the last 15 years of a hypothetical 100 year-long monitoring program. The line graph to the left of each color cross section shows how the concentration of sulfate would change each year (migrating red line) along a hypothetical borehole (red line in cross sections extending from 70 to 75 meters). This particular simulation demonstrates that virtually no measurable change in sulfate concentration would be expected in the matrix during this 15 year period, but measurable change would be expected in fracture waters in a restricted region directly below the waste emplacement tunnel. By providing quantitative, space- and time-resolved descriptions of when and where measurable change would occur, a cost effective and scientifically defensible monitoring and sampling program can be designed that will allow testing of model predictions, as well as key data collection for future refinement of simulations and models.
Click on the images to play the movies.
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