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Solute transport in fractured rocks with stagnant water zone and rock matrix composed of different geological layers-Model development and simulations
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.ORCID iD: 0000-0003-2353-6505
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.ORCID iD: 0000-0001-6801-9208
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.ORCID iD: 0000-0001-8241-2225
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
2013 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 3, 1709-1727 p.Article in journal (Refereed) Published
Abstract [en]

A model is developed to describe solute transport and retention in fractured rocks. It accounts for the fact that solutes can not only diffuse directly from the flowing channel into the adjacent rock matrix composed of different geological layers but also at first diffuse into the stagnant water zone occupied in part of the fracture and then from there into the rock matrix adjacent to it. In spite of the complexities of the system, it is shown that the analytical solution to the Laplace-transformed concentration at the outlet of the flowing channel is a product of two exponential functions, and it can be easily extended to describe solute transport through channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant geological properties. More importantly, by numerical inversion of the Laplace-transformed solution, the simulations made in this study help to gain insights into the relative significance and the different contributions of the rock matrix and the stagnant water zone in retarding solute transport in fractured rocks. It is found that, in addition to the intact wall rock adjacent to the flowing channel, the stagnant water zone and the rock matrix adjacent to it may also lead to a considerable retardation of solute in cases with a narrow channel.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2013. Vol. 49, no 3, 1709-1727 p.
Keyword [en]
Tracer Tests, Radionuclide Migration, Performance Assessment, Numerical Inversion, Laplace Transforms, Fluid-Flow, Media, Diffusion, Network
National Category
Other Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-123442DOI: 10.1002/wrcr.20132ISI: 000317829900034Scopus ID: 2-s2.0-84876729488OAI: oai:DiVA.org:kth-123442DiVA: diva2:629488
Note

QC 20130617

Available from: 2013-06-17 Created: 2013-06-10 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Modeling Solute Transport in Fractured Rocks-Role of Heterogeneity, Stagnant Water Zone and Decay Chain
Open this publication in new window or tab >>Modeling Solute Transport in Fractured Rocks-Role of Heterogeneity, Stagnant Water Zone and Decay Chain
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A model is developed to describe solute transport and retention in fractured rocks. It accounts for the fact that solutes not only can diffuse directly from the flowing channel into the adjacent rock matrix composed of different geological layers but can also at first diffuse into the stagnant water zone occupied in part of the fracture and then from there into the rock matrix adjacent to it. Moreover, the effect of radioactive decay-chain has also been studied in the presence of matrix comprising different geological layers. In spite of the complexities of the system, the analytical solution obtained for the Laplace-transformed concentration at the outlet of the flowing channel can conveniently be transformed back to the time domainby use of e.g. De Hoog algorithm. This allows one to readily include it into a fracture network modelorachannelnetwork model to predictnuclide transport through channels in heterogeneous fracturedmedia consisting of an arbitrary number of rock units withpiecewise constant properties. Simulations made in this study indicate that, in addition to the intact wall rock adjacent to the flowing channel, the stagnant water zone and the rock matrix adjacent to it may also lead to a considerable retardation of solute in cases with a narrow channel. The results further suggest that it is necessary to account for decay-chain and also rock matrix comprising at least two different geological layers in safety and performance assessment of the repositories for spent nuclear fuel. The altered zone may cause a great decrease of the nuclide concentration at the outlet of the flowing channel. The radionuclide decay, when accounted for, will drastically decrease the concentration of nuclides, while neglecting radioactive ingrowth would underestimate the concentration of daughter nuclides.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. viii, 49 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:4
Keyword
Solute transport model, Fractured rock, Stagnant water zone, Rock matrix diffusion, Radionuclide decay chain, Geological layers, Laplace transform, Simulation
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-141778 (URN)978-91-7595-018-1 (ISBN)
Presentation
2014-03-14, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140224

Available from: 2014-02-24 Created: 2014-02-21 Last updated: 2014-02-24Bibliographically approved
2. Solute transport through fractured rocks: the influence of geological heterogeneities and stagnant water zones
Open this publication in new window or tab >>Solute transport through fractured rocks: the influence of geological heterogeneities and stagnant water zones
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To describe reactive solute transport and retardation through fractured rocks, three models are developed in the study with different focuses on the physical processes involved and different simplifications of the basic building block of the heterogeneous rock domain. The first model evaluates the effects of the heterogeneity of the rock matrix and the stagnant water zones in part of the fracture plane. The second and the third models are dedicated to different simplifications of the flow channels. Both account for radioactive decay chain, but consider either a rectangular channel with linear matrix diffusion or a cylindrical channel with radial matrix diffusion. Not only an arbitrary-length decay chain, but also as many rock matrix layers with different geological properties as observed in the field experiments can be handled.

The analytical solutions thus obtained from these three models for the Laplace-transformed concentration in the flow channel can all be conveniently transformed back to the time domain by use of e.g. de Hoog algorithm. This allows one to readily include the results into a fracture network model or a channel network model to predict nuclide transport through flow channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant properties. The relative impacts and contributions of different processes in retarding solute transport in fractured rocks can easily be evaluated by simulating several cases of varying complexity.

Additionally, a model is developed to study the evolution of fracture aperture in crystalline rocks mediated by pressure dissolution and precipitation. It accounts for not only advective flow that can carry in or away dissolved minerals but also the fact that dissolved minerals in the fracture plane, in both the flow channel and the stagnant water zone, can diffuse into the adjacent porous rocks. The analytical solution obtained in the Laplace space is then used to evaluate the evolution of the fracture aperture under combined influence of stress and flow, in a pseudo-steady-state procedure. The simulation results give insights into the most important processes and mechanisms that dominate the fracture closure or opening under different circumstances.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. x, 53 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2016:15
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-183592 (URN)978-91-7595-906-1 (ISBN)
Public defence
2016-04-26, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160318

Available from: 2016-03-18 Created: 2016-03-17 Last updated: 2016-03-18Bibliographically approved

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