Characterisation of pore space geometry and modeling of radionuclide transport in granitic rock

Description

Investigations related to the material properties of geological formations that serve as host rocks for nuclear waste repositories require different methodological approaches. The evaluation of the transport and retardation properties of rock matrices proceeds from thorough rock pore space characterisation. The relevant rock properties to be quantified are (i) the accessible internal pore volume that determines the diffusive transport/retardation of non-sorbing and slightly sorbing radionuclides and (ii) the accessible internal surface area that controls sorption/fixation of radionuclides and chemical interactions. These properties are linked to the spatial porosity distribution of the rocks, which have been studied over the last decade with the PMMA method developed in the Laboratory of Radiochemistry.
The decimetre-sized rock samples are impregnated with 14C labelled methyl-methacrylate (14 C-MMA), which is polymerised by gamma irradiation inside the rock pores. The impregnated rock cores are analysed by autoradiography followed by digital image analysis. Furthermore a new imaging technique was introduced, namely digital photostimulated luminescence autoradiography (FLA 5100 scanner, Fuji). Radioactivities and fluorescent dyes from 2D matrices can be analysed by this method, the sensitivity and linearity of this method is better than by the film autora-diography technique.
I
The heterogeneity of rocks in the scale of the expected transport/interaction distances has to be taken into account when evaluating their retardation parameters. The second goal in the project is to understand the diffusion of radionuclides in a heterogeneous matrix. A modeling tool has been developed which uses cm-scale 2D PMMA autoradiographs as a template for calculating diffusion coefficients of dif-ferent mineral phases of rocks. The modeling is based on the particle tracking methods (time domain random walk) and the inversion techniques. The work is done in co-operation with the University of Poitiers (Prof. Paul Sardini). Within the co-operation projects the development of the PMMA method for characterising clay and bentonite matrices is also in progress.
StatusActive
Effective start/end date01/01/1999 → …