An empirical probabilistic approach for constraining the uncertaintyof long-term solute transport predictions in fractured rockusing in situ tracer experiments

摘要

Although radionuclide tracer tests have beencarried out for over 30 years, the role of tracer tests inradioactive waste repository performance assessment (PA)has been questioned due to the differences between thetime scales for tracer tests and PA. The possibility of usingin situ tracer tests to constrain PA time scale (over 10,000years) solute transport has been demonstrated using asystematic "microstructural model" approach to defineadvective and retentive materials. A series of simulationswere conducted of the "TRUE-1" sorbing solute transportexperiments in a well-characterized block of fracturedgranite. These experiments were then used to constrain theuncertainty of long-term transport on the same pathways,using a gradient several orders of magnitude smaller. Thecomparison of uncertainty of this long-term transport, withand without this conditioning step, provided a measure ofthe ability of tracer tests to reduce PA time-scaleuncertainty. Although this approach for quantifyinguncertainty reduction is somewhat empirical, it doesindicate the potential usefulness of tracer experiments inreducing the uncertainty of the key PA time-scaletransport parameters such as the flow wetted surface,provided that immobile zone properties such as sorption(Kd), porosity and diffusivity are available.