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Modeling Solute Transport in Fractured Rocks-Role of Heterogeneity, Stagnant Water Zone and Decay Chain
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.ORCID iD: 0000-0003-2353-6505
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 [en]
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: urn:nbn:se:kth:diva-141778ISBN: 978-91-7595-018-1 (print)OAI: oai:DiVA.org:kth-141778DiVA: diva2:698426
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
List of papers
1. Solute transport in fractured rocks with stagnant water zone and rock matrix composed of different geological layers-Model development and simulations
Open this publication in new window or tab >>Solute transport in fractured rocks with stagnant water zone and rock matrix composed of different geological layers-Model development and simulations
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
Keyword
Tracer Tests, Radionuclide Migration, Performance Assessment, Numerical Inversion, Laplace Transforms, Fluid-Flow, Media, Diffusion, Network
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-123442 (URN)10.1002/wrcr.20132 (DOI)000317829900034 ()2-s2.0-84876729488 (Scopus ID)
Note

QC 20130617

Available from: 2013-06-17 Created: 2013-06-10 Last updated: 2017-12-06Bibliographically approved
2. Solute transport in a single fracture involving an arbitrary length decay chain with rock matrix comprising different geological layers
Open this publication in new window or tab >>Solute transport in a single fracture involving an arbitrary length decay chain with rock matrix comprising different geological layers
2014 (English)In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 164, 59-71 p.Article in journal (Refereed) Published
Abstract [en]

A model is developed to describe solute transport and retention in fractured rocks. It accounts for advection along the fracture, molecular diffusion from the fracture to the rock matrix composed of several geological layers, adsorption on the fracture surface, adsorption in the rock matrix layers and radioactive decay-chains. The analytical solution, obtained for the Laplace-transformed concentration at the outlet of the flowing channel, can conveniently be transformed back to the time domain by the use of the de Hoog algorithm. This allows one to readily include it into a fracture network model or a channel network model to predict nuclide transport through channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant properties. More importantly, the simulations made in this study recommend that it is necessary to account for decay-chains and also rock matrix comprising at least two different geological layers, if justified, in safety and performance assessment of the repositories for spent nuclear fuel.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Radionuclide decay chain, Solute transport model, Rock matrix diffusion, Laplace transform, Simulation
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-141786 (URN)10.1016/j.jconhyd.2014.05.011 (DOI)000340989100006 ()2-s2.0-84903220683 (Scopus ID)
Note

QC 20140919. Updated from manuscript to article in journal.

Available from: 2014-02-24 Created: 2014-02-24 Last updated: 2017-12-05Bibliographically approved

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