Search results for "kulkeutuminen"
showing 3 items of 3 documents
Modeling mass transfer in fracture flows with the time domain-random walk method
2019
The time domain-random walk method was developed further for simulating mass transfer in fracture flows together with matrix diffusion in surrounding porous media. Specifically, a time domain-random walk scheme was developed for numerically approximating solutions of the advection-diffusion equation when the diffusion coefficient exhibits significant spatial variation or even discontinuities. The proposed scheme relies on second-order accurate, central-difference approximations of the advective and diffusive fluxes. The scheme was verified by comparing simulated results against analytical solutions in flow configurations involving a rectangular channel connected on one side with a porous ma…
Tracer migration in crystalline rock : application to geological barriers of nuclear waste storage
2016
This work deals with transport of radionuclides in the geosphere. The subject is investigated through characterisation of water conducting fractures, determining of rock transport properties and development of new methods for characterising geological samples. Here, as is often the case, radionuclide transport is investigated indirectly by characterising the structures, where the transport takes place, and directly by measuring transport properties in the gas phase. First water conducting fractures of three different types and the rock matrix surrounding them were analysed through rock samples from Olkiluoto. The analysis was done using X-ray tomography, the 14C-PMMA autoradiography techniq…
A method for measuring wetting and swelling of bentonite using X-ray imaging
2022
A non-invasive method based on X-ray imaging for measuring deformation and water transport in wetting and swelling bentonite samples is introduced. Sequential X-ray images taken of the samples were used to calculate the attenuation coefficient and deformation. These results, together with careful calibration, allowed finding the dry density and water content distributions and their temporal evolution in the wetting and swelling samples. A specific correction technique, based on regularly taking reference X-ray images of aluminum plates of varying thickness, was developed and used to take into account X-ray beam instabilities and thus to improve the accuracy of density analysis. Large deform…