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Abstract

Clay formations are being considered in a number of European countries as possible geological host rocks for radioactive wastes. Risk analysis studies have pointed out that fracturing of the formation, followed by water intrusion, could lead to the release of radioactivity. A field study was conducted on samples taken around clay fractures to determine the diffusion profiles of several elements on both sides of the fracture surface and to date existing fractures through which water has percolated. Data collected on samples taken from the face of a clay quarry in central Italy, where oxidized fractures exhibit distinct signs of water percolation, show that: (1) analyses of Fe, Cs, Te, U, and Co are effective in discriminating between perturbed and unperturbed clay in which elements have been diffusing; and (2) the order of magnitude of the active lifetime of the percolation in quarry-face samples ranges between a few tens and a few hundreds of years. Cs, Te, U, and Fe concentration profiles were found to have distribution coefficients strongly dependent on the oxidation-reduction (redox) conditions. A stepwise profile was evident that corresponds to the redox front. The Co profile, however, was apparently not affected by the redox conditions of the medium inasmuch as it shows a more regular trend than those of the other elements.

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