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Sensitivity and Probabilistic Analyses of Ground Water Travel Time in a Fractured and Variably-Saturated Geologic Medium

by A. B. Gureghian, Cent for Nuclear Waste Regulatory, Analyses, San Antonio, United States,
Y. -T. Wu, Cent for Nuclear Waste Regulatory, Analyses, San Antonio, United States,
B. Sagar, Cent for Nuclear Waste Regulatory, Analyses, San Antonio, United States,
R. G. Baca, Cent for Nuclear Waste Regulatory, Analyses, San Antonio, United States,



Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993

Abstract:

This paper presents a method for sensitivity and probabilistic analyses of performance of a hypothetical nuclear waste repository located in a layered, fractured, and variably-saturated unconfined aquifer. Groundwater travel time (GWTT) is used as the performance measure. The repository is located in the unsaturated zone, and the sole source of aquifer recharge is steady infiltration impinging uniformly over the surface area that is to be modeled. The equivalent porous media concept is adopted to model the fractured zone in the flow field. The evaluation of pathlines and travel time of water particles in the flow domain is performed based on a Lagrangian concept. The Bubnov-Galerkin finite-element method is employed to solve the primary flow problem (nonlinear), the equation of motion, and the adjoint sensitivity equations. A Gaussian elimination technique using sparse matrix solvers is used to solve the matrix equations. Based on the computed GWTT and the first-order sensitivities, an advanced mean-value method is used to estimate the cumulative distribution function (CDF) of GWTT and evaluate the importance of the system input random parameters. The features of this method are illustrated with a test case that represents a layered, fractured, and variably-saturated, unconfined aquifer.

Subject Headings: Sensitivity analysis | Probability | Groundwater flow | Hydraulic fracturing | Geology | Radioactive wastes | Matrix (mathematics)

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