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Impact of temperature increase on nuclide transport in crystalline rock on the near field scale
KTH, Superseded Departments, Land and Water Resources Engineering.
KTH, Superseded Departments, Land and Water Resources Engineering.
2004 (English)In: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems: Fundamentals, Modelling, Experiments and Applications, Elsevier , 2004, 2, 413-418 p.Chapter in book (Other academic)
Abstract [en]

The TRUE (“Tracer Retention Understanding Experiments”) programme at the Äspö Hard Rock Laboratory (Winberg et al., 2000, 2002) has since 1995 generated a unique database for quantifying retention of radionuclides in crystalline rock on the 5-30m scales. Temperature conditions in the TRUE analysis were about 15°C. In this study, we consider the effect of temperature increase to ca 60°C consistent with conditions after say 1000 years in the rock volume surrounding a KBS-3 type of repository, anticipated to persist over a relatively long time. Temperature elevation will decrease the mean aperture of a conducting fracture by approximately 30%, which in turn will enhance retention. Furthermore, diffusion in the rock matrix will increase at elevated temperatures by approximately factor 4, further enhancing retention. Sorption coefficients are assumed to be unchanged since there is still considerable uncertainty regarding sorption and its change with increasing temperature. We show that elevated temperature on the near field scale enhances nuclide retention, thereby providing an additional safety margin.

Place, publisher, year, edition, pages
Elsevier , 2004, 2. 413-418 p.
Series
Elsevier Geo-Engineering Book Series
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-8792DOI: 10.1016/S1571-9960(04)80076-4Scopus ID: 2-s2.0-77957030590OAI: oai:DiVA.org:kth-8792DiVA: diva2:14221
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-06-24Bibliographically approved
In thesis
1. Hydrodynamic control of retention in heterogeneous aquifers and fractured rock
Open this publication in new window or tab >>Hydrodynamic control of retention in heterogeneous aquifers and fractured rock
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In this thesis, fluid flow and solute transport in heterogeneous aquifers and particularly in frac-tured rock have been investigated using Lagrangian Stochastic Advective-Reaction (LaSAR) framework. The heterogeneity of the aquifer structure or fracture configuration, as well as the various reaction/retention processes have been considered in the modelling approach. Advection and retention processes are considered to be the dominant transport processes. Monte-Carlo simulation results for transport of nonreactive tracers in 2D generic heterogeneous aquifers indicate that the travel time τ can be well approximated by a lognormal distribution up to a relative high degree of heterogeneity of the aquifers. Comparison between the Monte-Carlo simulation results and the results of first-order approximation reveals that the analytical solutions of the statistical moments of τ are valid only when the variability of the aquifer properties is small. For reactive tracers, Monte-Carlo simulations have been conducted by accounting for spatial variability of both hydraulic conductivity and one sorption parameter simultaneously. The simulation results indicate that the reaction flow path μ is a nonlinear function of distance for shorter distance, linear function for longer distance, and also that μ and τ are well correlated over the considered parameter range. The parameter β, which is purely determined by the flow condi-tions, quantifies the hydrodynamic control of retention processes for transport of tracers in frac-tures. Numerical simulations have been performed to study the statistical properties of the pa-rameter β, travel time τ and flow rate Q in a single heterogeneous fracture and in a sequence of fractures. The results of Monte-Carlo simulations indicate that the parameter β and τ are corre-lated with a power-law relationship β ∼ τm. The correlation between β and the flow rate Q have also been studied and an inverse power-law relationship β ∼ Q-m is proposed. The establishment of these relationships provides a link between the parameter β and measurable parameters τ (or Q).

The LaSAR approach has been applied for prediction, evaluation and interpretation of the results of a number of tracer tests (TRUE-1, TRUE Block Scale and TRUE Block Scale Continuation) conducted by SKB at the Äspö site for tracer transport in fractures. The breakthrough curves may be predicted reasonably well, provided that the retention parameters, boundary conditions and hydraulic properties of the domain are given. The evaluation of TRUE tests indicates that the retention occurs mainly in the rim zone on site characterization time scales, while on the per-formance assessment time scale, diffusion and sorption in the unaltered rock matrix are likely to become dominant retention mechanisms.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1025
Keyword
Aquifer, Fracture, groundwater, First-order solution, Monte-Carlo simulation, Nu-clear waste, Heterogeneity, Retention processes, Matrix diffusion, Prediction, Evaluation, Travel time, Flow rate;
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-496 (URN)91-7178-199-4 (ISBN)
Public defence
2005-11-29, Sal M2, Brinellvägen 64, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-06-24Bibliographically approved

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