Objective
IN MOST RADIONUCLIDE TRANSPORT MODELS IT IS ASSUMED THAT RADIONUCLIDES MIGRATING IN SOLUTION ALONG FRACTURES WILL DIFFUSE INTO WATER HELD IN PORES WITHIN THE ROCK MATRIX ADJACENT TO FRACTURES, AND WILL THUS BE RETARDED RELATIVE TO THE FLOW OF WATER. THE POSSIBILITY THAT THERE EXISTS ADJACENT TO FRACTURES A ZONE TO WHICH DIFFUSION MIGHT BE RESTRICTED, OR THAT THE PORES ADJACENT TO FRACTURES MIGHT BE CLOGGED BY THE PRODUCTS OF ALTERATION AND/OR MINERALISATION, HAS NOT GENERALLY BEEN INCLUDED IN RADIONUCLIDE RETARDATION MODELS.
THE OBJECTIVE OF THIS STUDY IS TO ASSESS THE EFFECTIVENESS OF DIFFUSION AS A MECHANISM FOR THE RETARDATION OF RADIONUCLIDES, BY EXAMINING THE MICROSTRUCTURE OF CRYSTALLINE ROCK ADJACENT TO AND REMOTE FROM FRACTURES, AND BY DETERMINING THE EXTENT OF DESEQUILIBRIUM IN THE URANIUM-238 DECAY SERIES IN ROCK ADJACENT TO FRACTURES. THE EFFECT ON POROSITY AND POTENTIAL DIFFUSION OF THE FRACTURES THEMSELVES IS ALSO BEING ASSESSED, WITH PARTICULAR REGARD TO STRESS-RELIEF EFFECTS AND TO PORE-CLOGGING BY THE PRODUCTS OF ALTERATION, MINERALISATION AND PRECIPITATION. IT IS HOPED THAT THE RESULTS OF THE STUDY WILL HELP TO RESOLVE A MAJOR AREA OF UNCERTAINLY IN EXISTING RADIONUCLIDE RETARDATION MODELS.
The possibility that radionuclide retardation by rock matrix diffusion will be limited in granitic rocks by geological factors was studied, as well as the possibility that diffusion would be confined to a narrow zone from water conducting fractures.
Petrophysical measurements, uranium series and geochemical analyses in the rock adjacent to fractures have been performed to establish the extent of fracture related microstructural changes that might influence the potential for diffusion and whether or not there is any record of diffusion of uranium, its daughters, or other elements.
The results obtained from El Berrocal (Spain), Stripa (Sweden) and White-shell (Candad) granites, suggest that: there is a zone adjacent to the fractures (generally less than 100 mm) where microstructural changes and enhanced uranium mobility exist; the evidence for diffusion having taken place in the rock is confined largely to this zone. It appears that diffusivity determinations on rock colllected away from the influence of fractures will not give representative data for diffusion modelling, in addition to the effect of distressing after removing rocks from depth.
It is suggested that diffuison will be of limited efectiveness as a retardation mechanism in many granitic rocks, particularly in water movement confined to narrow channels where access by nuclides to the fracture walls is restricted.
1. MEASUREMENT OF THE POROSITY AND PERMEABILITY OF INTACT ROCK ADJACENT TO AND REMOTE FROM WATER-CONDUCTING FRACTURES; DETERMINATION OF THE PERMEABILITY OF FRACTURE WALLS.
2. EXAMINATION BY OPTICAL, ELECTRON AND ACOUSTIC MICROSCOPY OF THE MICROSTRUCTURE OF ROCK ADJACENT TO FRACTURES AND THE AVAILABILITY OF PORES FOR DIFFUSION, USING DIGITAL IMAGE PROCESSING TECHNIQUES.
3. EXAMINATION OF THE MINERALOGY OF THE ROCK AND OF FRACTURE AND MICROFRACTURE LININGS AND INFILLINGS.
4. INVESTIGATION OF THE PENETRATION OF MODERN WATERS INTO THE ROCK ADJACENT OT FRACTURES BY MEASURING THE STATE OF RADIOACTIVE DISEQUILIBRIUM IN THE URANIUM-238 DECAY SERIES USING ALPHA SPECTOMETRY.
5. DETERMINATION OF THE STATE OF OXIDATION OF IRON IN ROCK ADJACENT TO FRACTURES USING MOSSBAUER SPECTROSCOPY.
6. ASSESSMENT OF THE EFFECT OF IN SITU STRESS CONDITIONS ON THE POTENTIAL FOR DIFFUSION.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- natural sciences chemical sciences electrochemistry electrolysis
- natural sciences physical sciences optics microscopy
- natural sciences earth and related environmental sciences geology mineralogy
- natural sciences chemical sciences nuclear chemistry radiation chemistry
- natural sciences physical sciences optics spectroscopy
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33003 OVIEDO
Spain
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