Abstract
In this study, we discussed distortion of the estimated hydraulic conductivity from a hydraulic test due to excessive injection or extraction of groundwater by evaluating the influence of nonlinear flow. Pulse, slug, and constant head withdrawal tests with various head displacements were conducted in fractured granite rock, and the changes of representative Reynolds numbers (Re) during the tests were calculated. The Forchheimer equation and cubic law were used to evaluate the influence of nonlinear flow on the hydraulic tests, and thus the possibility of distortion of the estimated hydraulic conductivity. Our results showed that there was little possibility that nonlinear flow occurred during the pulse tests in the test zones. In the slug tests at several test zones, however, the estimated hydraulic conductivities were likely to be distorted due to nonlinear flow. Except for the test zones with low permeability, the scale effects of the estimated hydraulic conductivities from different types of tests were observed. These results indicated that the scale effect and distortion of the hydraulic parameters can be evaluated by conducting various types of hydraulic tests.
Highlights
The safety assessment of a subsurface repository for high-level radioactive waste (HLW) is to estimate the dose rates of the nuclides reached to the biosphere from the repository
Slug, and constant head withdrawal tests, the test durations were different as shown in Distortion of the estimated K by excessive injection or extraction of groundwater was discussed by evaluating the influence of nonlinear flow on hydraulic tests
The relations between the maximum Reynolds numbers (Re) during the tests and estimated K from the tests were matched to an equation introduced from the Forchheimer equation and cubic law, and the matching results were used to identify the effects of nonlinear flow on the tests and to evaluate the possibility of distortion of the estimated K
Summary
The safety assessment of a subsurface repository for high-level radioactive waste (HLW) is to estimate the dose rates of the nuclides reached to the biosphere from the repository. One of the major pathways of the nuclides from the repository to the biosphere is groundwater flow, and the reliability of the safety assessment is controlled by the uncertainty in hydrogeological characterization of the disposal site. Crystalline fractured rock is one of the preferred host rocks for HLW disposal repositories. Groundwater flows predominantly through fractures rather than matrix, which makes crystalline rock very heterogeneous and discrete hydraulically. Hydraulic tests for hydrogeological characterization are generally analyzed with the semi-analytical solutions induced from the assumption of a homogeneous and continuous medium, the hydrogeological characterization of a fractured rock is more uncertain than a porous medium. The semi-analytical solutions for the hydraulic test analyses assume the linear relation between the pressure gradient and the flux. Using the results of constant rate injection tests with various rates in a fractured sedimentary rock, Quinn et al [7] analyzed the relation between the imposed injection rates and the resulting stabilized head changes and found that that relation
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