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  • Rock matrix diffusion as mechanism for radionuclide retardation: natural radio-element migration in relation to the microfractography and petrophysics of fractured crystalline rock


Rock matrix diffusion is a potentially important mechanism for the retardation of radionuclides migrating from a radioactive waste repository. If they are to predict the effectiveness of this retardation reliably, mathematical models describing diffusion need physical and chemical data from actual sites. The purpose of this study has been to provide such data by investigating the petrophysical properties, microstructure, geochemistry and uranium series disequilibrium characteristics of the rock adjacent to fractures in cores collected from depths of between 38 m and 468 m in the El Berrocal granite (Sierra de Gredos, Spain). Evidence for the geologically recent mobilization of uranium has been examined in order to shed light on the potential for diffusive retardation of uranium in the fractured rock environment surrounding a radioactive waste repository. The results presented here suggest that, for most fractures, simple matrix diffusion of uranium has not taken place. The observed migration has resulted, rather, from a complex combination of matrix diffusion and a number of chemical interactions involving different mineral phases and histories. The high uranium concentrations associated with iron oxyhydroxides in the shallow granite (38 m) suggest the potential for important radionuclide retardation in this shallow zone.

Additional information

Authors: HEATH M H, Exeter University, Earth Resources Centre (GB);MONTOTO M (EDITORS), Universidad de Oviedo, Departamento de Geologia (PT)
Bibliographic Reference: EUR 17121 EN (1997) 225pp., FS, ECU 40.00
Availability: Available from the (2)
ISBN: ISBN 92-827-3907-4
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