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Development and application of an advection-dispersion model for data analysis of electromigration experiments with intact rock cores
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.ORCID iD: 0000-0001-6801-9208
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
National Category
Other Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-265609OAI: oai:DiVA.org:kth-265609DiVA, id: diva2:1380161
Note

QC 20191220

Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2019-12-20Bibliographically approved
In thesis
1. Solute transport in fractured rocks: Analysis of analytical solutions and determination of transport parameters
Open this publication in new window or tab >>Solute transport in fractured rocks: Analysis of analytical solutions and determination of transport parameters
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In order to facilitate the assessment of the safety and function of deep geological repositories for radioactive waste, several models have been developed to describe water flow and transport of solutes in fractured crystalline rock. The rock around the repository is described and modelled as a network of water-bearing fractures.

The first part of the work concerns analytical solutions of the mathematical models, first developed in the 1980s to describe nuclide transport with seeping water in the fractures where the nuclides can also diffuse in and out of the pores into the rock matrix. A new simple analytical solution is described in which the interaction between matrix diffusion and hydrodynamic dispersion could be decoupled, which makes the interaction between the processes visible while making the solution more manageable. In addition, another dispersion mechanism caused by the presence of independent transport paths is easily handled with the new model. This makes it possible to treat both dispersion mechanisms with the same formalism. This makes the new model more useful in interpreting field experiments with tracer as well as for long-term simulation of nuclide migration in rock.

The second part of the work is about molecular diffusion in the rock matrix itself, which is a central mechanism in the model above. One way to measure diffusion and sorption in rock pieces is to force ions through the pores of the rock by means of electromigration. The method previously used has been improved by adding a potentiostat and a pH buffer. The experimental results become more stable.

To better interpret the results, a general model for transport in the rock matrix was developed. The model includes electromigration, electroosmosis and dispersion in the pore system. The effective pore diffusivity and matrix formation factor can be determined from the experiments. The results show that the developed electromigration method can be used to provide high quality experimental data.

Abstract [sv]

För att underlätta bedömning av säkerhet och funktion hos djupa geologiska förvar för radioaktivt avfall har flera modeller utvecklats för att beskriva vattenflöde och transport av lösta ämnen i kristallint berg med sprickor. Berget kring förvaret beskrivs och modelleras som ett nätverk av vattenförande sprickor.

Den fösta delen av arbetet handlar om analytiska lösningar av de matematiska modellerna, utvecklades på 1980-talet för att beskriva nuklidtransport med sipprande vatten i sprickorna där nukliderna även kan diffundera in och ut ur porerna in bergmatrisen. En ny enkel analytisk lösning beskrivs i vilken samverkan mellan hydrodynamisk dispersion och matrisdiffusion kunnat frikopplas, vilket gör att samverkan mellan processerna synliggörs samtidigt som lösningen är mer hanterbar. Dessutom kan en annan dispersionsmekanism orsakad av närvaron av oberoende transportvägar med lätthet hanteras med den nya modellen. Detta gör det möjligt att behandla både dispersionsmekanismer med samma formalism. Detta gör den nya lösningen mer användbar vid tolkningen av fältförsök med spårämnen liksom för långsiktig simulering av nuklidspridning i berg.

Den andra delen av arbetet handlar om molekylär diffusion i bergmatrisen vilket är en central mekanism i modellen ovan. Ett sätt att mäta diffusion och sorption i bergstycken bygger på att driva in joner i bergets porer av med hjälp elektromigration. Den tidigare använda metoden har förbättrats genom att lägga till en potentiostat och pH-buffert. De experimentella resultaten blir därvid mer stabila.

För att bättre tolka resultaten utvecklades en generell modell för transport i bergmatrisen. Modellen inbegriper elektromigration, elektroosmos och dispersion i porsystemet. Den effektiva por-diffusiviteten och matrisens formationsfaktor kan bestämmas ur experimenten. Resultaten visar att den utvecklade elektromigreringsmetoden kan användas för att ge experimentella data av hög kvalitet.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. p. 49
Series
TRITA-CBH-FOU ; 2020:5
Keywords
Fractured rock, Radionuclide transport, Analytical solution, Dispersion mechanisms, Electromigration., Sprickigt berg, Radionukidtransport, analytisk lösning, Dispersionsmekanismer, Elektromigration.
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-265611 (URN)978-91-7873-412-2 (ISBN)
Public defence
2020-02-27, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Nuclear Fuel and Waste Management Company, SKB, C7241
Note

QC 2020-01-20

Available from: 2020-01-20 Created: 2019-12-18 Last updated: 2020-01-20Bibliographically approved

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