Objectif Rock matrix diffusion is an important element in radionuclide migration models: diffusion from water-conducting fractures into the rock matrix provides a potentially important mechanism for the retardation of nuclide migrating from a repository. Recent studies of crystalline rocks have shown, however, that free diffusion of nuclide from fractures into the rock matrix does not always take place and that very little of the rock adjacent to fractures may be available for diffusion. Although mathematical models describing diffusion have been developed in the past, they have never been furnished with complete physical and chemical data from actual sites. The aims of the study are: 1) to observe evidence of past diffusion of uranium and its daughters from fractures into the rock adjacent to fractures; 2) to relate observed diffusion phenomena to the physical properties of the rock; 3) to construct physicochemical profiles across fractures and into the adjacent rock to allow complete characterisation of past diffusion and assess the potential for future diffusion; and 4) to develop a mathematical diffusion model that can be validated by reference to geo-logical evidence and be incorporated reliably into overall radionuclide migration models.Rock matrix diffusion is an important element in radionuclide migration models: diffusion from water conducting fractures into the rock matrix provides a potentially important mechanism for the retardation of nuclides migrating from a repository. Recent studies of crystalline rocks have shown, however, that free diffusion of nuclides from fractures into the rock matrix does not always take place and that very little of the rock adjacent to fractures may be available for diffusion. Although mathematical models describing diffusion have been developed in the past, they have never been furnished with complete physical and chemical data from actual sites. The aims of the study are: to observe evidence of past diffusion of uranium and its daughters from fractures into the rock adjacent to fractures; to relate observed diffusion phenomena to the physical properties of the rock; to construct physicochemical profiles across fractures and into the adjacent rock to allow complete characterisation of past diffusion and assess the potential for future diffusion; and to develop a mathematical diffusion model that can be validated by reference to geological evidence and be incorporated reliably into overall radionuclide migration models. Preliminary studies of the 3-dimensional microfractographic network of granite have been undertaken under laser scanning microscopy in confocal mode (LSM-CM). A preliminary petrographic study has been carried out using 2 different methods: digital image analysis and stereology. Polished thin sections of granite have also been studied under acoustic microscopy. The images obtained make possible the detailed identification of intergranular structures in the rock forming minerals. Thin sections of granite, impregnated with fluorescent resin, have been studied in Besancon using fluorescence optical microscopy. The feldspars appear highly altered; quartz grians show intragranular and intergranular cracks and the mica sometimes shows a loss of cohesion between grains. The data being acquired in the various studies described above will provide the input for a mathematical diffusion model.Work programme: (1) Determination of rock properties and examination of evidence for past diffusion in a series of rock slices at distance of up to 50 cm from hydrogeologically-active fractures;(2) Quantitative petrophysical analysis and the determination of key physical properties (accessible porosity, dry density, void index, kinetic water behaviour, dynamic properties);(3) Quantitative microstructural analysis using optical, fluorescence, acoustic and confocal laser microscopy, digital image processing and stereological techniques;(4) Geochemical analysis (major elements, iron chemistry, uranium and thorium, Rare Earth Elements, selected trace elements);(5) Uranium disequilibrium studies by alpha spectrometry;(6) Uranium microcartography by autoradiographic, fission track and SEM/EDX techniques;(7) The development of a mathematical diffusion model based upon real geological/geochemical data. Champ scientifique social sciencesmedia and communicationsgraphic designnatural sciencesphysical sciencesopticsmicroscopynatural scienceschemical sciencesnuclear chemistryradiation chemistrynatural sciencesphysical sciencesopticslaser physicsnatural sciencesmathematicsapplied mathematicsmathematical model Programme(s) FP2-RADWASTOM 4C - Specific research and technical development programme (Euratom) in the field of management and storage of radioactive waste, 1990-1994 Thème(s) A.4.3 - Radionuclide migration in the geosphere Appel à propositions Data not available Régime de financement CSC - Cost-sharing contracts Coordinateur University of Exeter Contribution de l’UE Aucune donnée Adresse Laver Building North Park Road EX4 4QE Exeter Royaume-Uni Voir sur la carte Liens Site web Opens in new window Coût total Aucune donnée Participants (4) Trier par ordre alphabétique Trier par contribution de l’UE Tout développer Tout réduire Commissariat à l'Energie Atomique (CEA) France Contribution de l’UE Aucune donnée Adresse Centre d'Études de Fontenay-aux-Roses 60-68 avenue du Général Leclerc 92265 Fontenay-aux-Roses Voir sur la carte Coût total Aucune donnée UNIVERSIDAD DE OVIEDO Espagne Contribution de l’UE Aucune donnée Adresse C/. Jesús Arias de Velasco, s/n 33005 OVIEDO Voir sur la carte Coût total Aucune donnée University of Liverpool Royaume-Uni Contribution de l’UE Aucune donnée Adresse Brownlow Street L69 3BX Liverpool Voir sur la carte Coût total Aucune donnée Université de Franche-Comté France Contribution de l’UE Aucune donnée Adresse 16 route de Gray 25030 Besançon Voir sur la carte Coût total Aucune donnée
