Migration of radionuclides in the geosphere : model of the natural analogue of Needle's Eye
The study of the natural analogue of Needle's Eye (Scotland) has covered a three year period. The model is made up of three parts. The first (HYDRODYNAMIC), consisted of the building of a groundwater flow model representative of the whole watershed of which the site (the so-called "Merse area") is a part. This regional model made it possible to determine the boundary conditions of a detailed hydrodynamical local model of the area where migration processes occur. The second (GEOCHEMICAL), essentially relied on four sampling campaigns from BGS: this work consisted of the deduction, from the analyses, of the geochemically active systems which may have a direct impact on uranium transport within the Merse sediments. Two potentially precipitating uranium minerals Ca(2)UO(2)(CO(3)), 10H(2)O (Liebigite) and UO(2) (uraninite or pitchblende), were determined. In the final part (TRANSPORT) several uranium behaviours have been tested. The first of these was the tracer hypothesis which showed clearly the effect of the unusual hydrodynamical context of the site on the dissolved uranium distribution. The second was the K(d) approach (based on experimental data), from which it was concluded that the uranium behaviour cannot be interpreted in terms of instantaneous and reversible linear interaction within the silts. Finally the uraninite precipitation, due to the Eh lowering in the silts (caused by the organic matter oxidation) was tested. The calculated uranium field seems in good agreement with the measured one and the total accumulated solid uranium within the silt has a plausible value. The four codes used for this study are METIS, PHREEQE and CHIMERE and STELE.
Bibliographic Reference: EUR 12840 FR (1990) 87 pp., FS, ECU 8.75
ISBN: ISBN 92-826-1527-8
Record Number: 199011091 / Last updated on: 1994-12-01
Original language: fr
Available languages: fr