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Microstructural Characterization of U Coprecipitated Phases Formed in Bentonic-Granitic Groundwater and under Anoxic Conditions

Published online by Cambridge University Press:  19 October 2011

Javier Quinones ,
Eduardo Iglesias ,
Jose M. Cobo ,
Aurora Martinez Esparza  and
Jose Maria Gomez de Salazar
Javier Quinones
Affiliation:
javier.quinones@ciemat.es, CIEMAT, energy, Avda. Complutense 22. E. 12-S1-23, Madrid, 28040., Spain, +34 913466290, +34 913466233
Eduardo Iglesias
Affiliation:
eduardo.iglesias@ciemat.es, CIEMAT, Energy, Avda. Complutense 22, Madrid, 28040, Spain
Jose M. Cobo
Affiliation:
manuel.cobo@ciemat.es, CIEMAT, Energy, Avda. Complutense 22, Madrid, 28040, Spain
Aurora Martinez Esparza
Affiliation:
amav@enresa.es, Enresa, Emilio Vargas, 7, Madrid, 28043, Spain
Jose Maria Gomez de Salazar
Affiliation:
gsalazar@quim.ucm.es, UCM, Materials Science, Avda. Complutense s/n, Madrid, 28040, Spain
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Abstract

For improving the accuracy of the performance assessment studies related to the spent fuel safety under storage conditions it is necessary to develop a new matrix alteration model. These models must be based on laboratory experiences and they should be capable to extrapolate to storing environmental conditions. Most of recently models developed included the oxidation and dissolution process of the spent fuel matrix, but the influence of a possible process of secondary phase formation over the spent fuel surface is not taken into account yet. This is a key process that could produce a reduction of the matrix dissolution rate, radiation shielding behaviour; however, the surface precipitation of the secondary phase could induce a localized corrosion process, which in this case dissolution rate of the spent fuel would be increased. This paper is focussed on microstructural characterization of secondary phases formed in coprecipitation experiments performed under anoxic conditions in granitic-bentonitic simulated groundwater. In order to simulate the influence of the container material, the coprecipitation experiments were performed in absence and presence of iron powder. The solid phases formed were characterized using the following techniques: XRD; SEM-EDX and TEM-EDX. The XRD diffraction pattern showed that under anoxic conditions a mixture of phases were obtained (sodium and potassium uranate and schoepite), whereas uranate phases were detected when only iron was present. The characterization study indicates that the U secondary phase formed (under reducing conditions and presence of iron powder) growth from iron surface. The crystal size of the secondary phase is independent of the presence of iron powder (and it is always less than 3 μm). Furthermore, the microstructural study showed the growing of U phases over iron powder.

Keywords

Usecond phasesmicrostructure
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 985: Symposium NN – Scientific Basis for Nuclear Waste Management XXX , 2006 , 0985-NN02-08
Copyright
Copyright © Materials Research Society 2007

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