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Mineralogical investigations of the first package of the alternative buffer material test – I. Alteration of bentonites

Published online by Cambridge University Press:  09 July 2018

S. Kaufhold ,
R. Dohrmann ,
T. Sandén ,
P. Sellin  and
D. Svensson
S. Kaufhold*
Affiliation:
BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany
R. Dohrmann
Affiliation:
BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany LBEG, Landesamt für Bergbau, Energie und Geologie, Stilleweg 2, D-30655 Hannover, Germany
T. Sandén
Affiliation:
Clay Technology AB, IDEON Research Center, S-223 70 Lund, Sweden
P. Sellin
Affiliation:
SKB, Svensk Kärnbränslehantering AB, Stockholm, BOX 5864, S-102 40 Stockholm, Sweden
D. Svensson
Affiliation:
SKB, Svensk Kärnbränslehantering AB, Stockholm, BOX 5864, S-102 40 Stockholm, Sweden
*
*E-mail: s.kaufhold@bgr.de
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Abstract

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Bentonite, which is envisaged as a promising engineered barrier material for the safe disposal of highly radioactive waste, was and is investigated in different large scale tests. The main focus was and is on the stability (or durability) of the bentonite. However, most countries concentrated on one or a few different bentonites only, regardless of the fact that bentonite performance in different applications is highly variable. Therefore, SKB (Svensk Kärnbränslehantering) set up the first large scale test which aimed at a direct comparison of different bentonites. This test was termed the ‘alternative buffer material test’ and considers eleven different clays which were either compacted (blocks) or put into cages to keep the material together. One so-called package consisted of thirty different blocks placed on top of each other. These blocks surrounded a heated iron tube 10 cm in diameter. Altogether three packages were installed in the underground test laboratory Äspö, Sweden. The first package was terminated 28 months after installation and the bentonite had been exposed for the maximum temperature (130°C) for about one year.

Almost all geochemical and mineralogical alterations of the different bentonites (apart from exchangeable cations) were restricted to the contact between iron and bentonite. The increase of the Fe2O3 content was attributed to corrosion of the tube. However, the typical 7 or 14 Å smectite alteration product was not found. At the contact of one sample, siderite was precipitated. Some samples showed anhydrite and organic carbon accumulation and some showed dissolution of clinoptilolite and cristobalite. IR spectroscopy, XRD, and XRF data indicated the formation of trioctahedral minerals/domains in the case of some bentonites. Even more data has to be collected before unambiguous conclusions concerning both alteration mechanisms and bentonite differences can be drawn.

Keywords

bentoniteHLRW disposalradwastealternative buffer material testsmectite alterationURL
Type
Research Article
Information
Clay Minerals , Volume 48 , Issue 2 , May 2013 , pp. 199 - 213
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2013 This is an Open Access article, distributed under the terms of the Creative Commons Attribution license. (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2013

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