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Study of the Uranium Heterogeneous Diffusion through Crystalline Rocks and Effects of the “Clay-Mediated” Transport

Published online by Cambridge University Press:  01 February 2011

U. Alonso ,
T. Missana ,
M. García-Gutiérrez ,
A. Patelli ,
J. Ravagnan  and
V. Rigato
U. Alonso
Affiliation:
CIEMAT, Avda. Complutense 22, Edif. 19, 28040 Madrid, SPAIN
T. Missana
Affiliation:
CIEMAT, Avda. Complutense 22, Edif. 19, 28040 Madrid, SPAIN
M. García-Gutiérrez
Affiliation:
CIEMAT, Avda. Complutense 22, Edif. 19, 28040 Madrid, SPAIN
A. Patelli
Affiliation:
LNL - INFN, Via dell' Università 2, 35020 Legnaro-Padova, ITALY
J. Ravagnan
Affiliation:
LNL - INFN, Via dell' Università 2, 35020 Legnaro-Padova, ITALY
V. Rigato
Affiliation:
LNL - INFN, Via dell' Università 2, 35020 Legnaro-Padova, ITALY
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Abstract

Rock matrix diffusion is one of the possible mechanisms for radionuclide retardation in a deep geological high-level radioactive waste repository, and it is usually considered that radionuclides diffuse as solutes through the rock. Nonetheless, the potential effects that clay, from the bentonite barrier, may induce on the radionuclides migration should be taken into account. Furthermore, transport models generally assume that the whole mineral surface is accessible to transport, whereas transport is highly conditioned by the heterogeneous mineral distribution, since different minerals may act as preferential pathways, while others may present higher sorption capability. It is therefore necessary to determine the actual surface area accessible to transport.

The aim of the present work is the identification of the uranium preferential pathways to the granite, both in presence or absence of bentonite clay. Results showed that uranium as solute diffused in specific mineral areas, indicating that the actual surface area accessible to matrix diffusion, and/or sorption on the surface, is significantly lower than the whole mineral surface. By the other hand, the uranium in presence of the clay was randomly distributed on the surface, and penetrated into the granite mainly through “defects” (as fractures or grain boundaries); its migration being enhanced on specially fractured or disturbed areas.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 807: Symposium Scientific Basis for Nuclear Waste Management XXVII , 2003 , 621
Copyright
Copyright © Materials Research Society 2004

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