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- Wörman, Anders, et al.
(författare)
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Kinematic analysis of solute mass flows in rock fractures with spatially random parameters
- 2003
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Ingår i: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 60:04-mar, s. 163-191
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Tidskriftsartikel (refereegranskat)abstract
- Field data of physical properties in heterogeneous crystalline bedrock, like porosity and fracture aperture, is associated with uncertainty that can have a significant impact on the analysis of solute transport in rock fractures. Solutions to the central temporal moments of the residence time probability density function (PDF) are derived in a closed form for a solute Dirac pulse. The solutions are based on a model that takes into account advection along the fracture plane, diffusion into the rock matrix and sorption kinetics in the rock matrix. The most relevant rock properties including fracture aperture and several matrix properties as well as flow velocity are assumed to be spatially random along transport pathways. The mass transport is first solved in a general form along one-dimensional pathways, but the results can be extended to multi-dimensional flows simply by substituting the expected travel time for inert water parcels. Based on data obtained with rock samples taken at Aspo Hard Rock Laboratory in Sweden, the solutions indicate that the heterogeneity of the rock properties contributes to increasing significantly both the variance and the skewness of the residence time probability density function for a pulse travelling in a fracture. The Aspo data suggests that the bias introduced in the variance of the residence time PDF by neglecting the effect of heterogeneity of the rock properties on the radionuclide migration is very large for fractures thinner than a few tenths of a millimetre.
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- Wörman, Anders, et al.
(författare)
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Role of the bio- and geosphere interface on migration pathways for Cs-135 and ecological effects
- 2004
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 148:2, s. 194-204
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Tidskriftsartikel (refereegranskat)abstract
- An approach is described for hydrological, geochemical, and ecological process modeling in assessing the migration pathways of radionuclides from a repository for radioactive waste in crystalline bedrock back to the surface environment where dose to individual humans can occur. The approach is based on the characterization residence times in geologic media of a unit pulse of Cs-135 released from the repository. Performance assessment modeling of geosphere transport processes generally focuses on the properties of the host rock (crystalline bedrock in this case). Our approach includes a detailed representation of the quaternary deposits that overlie the bedrock. Although water residence times in quaternary deposits can be short, geochemical reactions, predominantly sorption, can increase solute residence times significantly. Moreover, the quaternary deposits govern the pathways to terrestrial and aquatic ecosystems and are of utmost importance for the assessment of doses to individual humans.
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- Xu, S. L., et al.
(författare)
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Heterogeneous matrix diffusion in crystalline rock - implications for geosphere retardation of migrating radionuclides
- 2001
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Ingår i: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 47:04-feb, s. 365-378
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Tidskriftsartikel (refereegranskat)abstract
- As a basis for an analysis of the effect of rock heterogeneity on radionuclide migration in a single fracture, the geostatistics of the main properties governing solute transport in crystalline rock have been determined experimentally for two granitic rock types. The rock samples were collected at the Aspo Hard Rock Laboratory, Sweden and used to deduce the auto-covariance functions for the porosity, effective diffusivity and partition coefficient, k(d). and adsorption kinetics. One-dimensional analytical solutions for the mean values of the temporal moments of the residence time probability density function (PDF) show that the heterogeneity of the rock properties can have a substantial impact on the transport, A case study of the effect of heterogeneity in matrix diffusion for a single fracture could be performed by decomposing the transport problem into a one-dimensional mass transfer problem and a two-dimensional flow problem using a Lagrangian method of description. Monte Carlo simulations of the flow field indicate that the correlation length of the aperture is much longer along the trajectory paths than along an arbitrary direction. Increasing the correlation lengths and variances of the aperture and matrix diffusion increases significantly the variance of the travel time PDF.
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