Mineralogical reactions in the Tournemire argillite after in-situ interaction with steels A. Gaudin a, ⁎, S. Gaboreau b, 1 , E. Tinseau b , D. Bartier c , S. Petit d , O. Grauby e , F. Foct f , D. Beaufort d a Faculté des Sciences et Techniques de Nantes, CNRS-UMR-6112, Laboratoire de Planétologie et Géodynamique, 2 rue de la Houssinière, BP 92208, 44322 Nantes Cedex 03, France b IRSN - Institut de Radioprotection et de Sûreté Nucléaire, Av. du Gen. Leclerc BP n°17, 92262 Fontenay-aux-roses, France c Muséum National d'Histoire Naturelle, CNRS-UMR 5143, Bâtiment de Géologie, 43 rue Buffon, 75005 Paris, France d Université de Poitiers, CNRS-UMR 6532, Laboratoire HydrASA, 40 Avenue du Recteur Pineau Poitiers Cedex, 86022, France e Université de Marseille, CNRS-UPR 7251, Laboratoire CRMCN, Case 913, F-13288 Marseille Cedex 09, France f EDF R&D, département matériaux et mécanique des composants, site des renardières, avenue des renardières, Ecuelles, 77818 Moret sur Loing, France abstract article info Article history: Received 17 January 2008 Received in revised form 13 August 2008 Accepted 14 August 2008 Available online xxxx Keywords: Tournemire Argillite Steel Iron Clay I/S Alteration Steels are possible materials for high level radioactive waste containers used in long term geological disposal in argillaceous environments. Under chemical conditions of a deep repository, the release of iron from these canisters could modify the properties of clay minerals. Thereby, many batch experiments have been realized on argillite under disposal conditions. The French Institute of Radioprotection and Nuclear Safety conducts an experimental program on steel/argillite interactions in underground natural conditions in its Tournemire experimental site (Aveyron, France). In order to determine these interaction processes, the present study focuses both on petrography and mineralogy characterization of modifications in the argillite in contact with steel samples. The accurate study of the argillite and steels after 6 years of contact indicates no significant changes for the argillite in contact with the stainless steels. For the argillite in contact with the carbon steels both numerous steel corrosion evidences and clear textural, petrographic, mineralogical and chemical modifications of the initial nature of the argillite are observed. The Fe°/argillite contacts indicate the development of a Fe-rich front within the argillite resulting from the iron diffusion from the corroded steel and which is connected with mineralogical changes of the initial argillite. This Fe-enrichment is accompanied by crystallization of significant amounts of goethite/lepidocrocite (FeOOH) and some traces of magnetite near the steel surface. The formation of Fe-rich phases within the argillite is associated with dissolution– crystallization processes. Thus, after bulk sample XRD and SEM data, these processes consist in dissolution of calcite, phyllosilicate (I/S) and pyrite and crystallization of some traces of gypsum and melanterite. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Multi-barrier disposal concepts for high level radioactive waste involving both steel canister (Fe(0)), engineered barriers (bentonite) and natural geological barriers (clay-rich host-rocks) are considered in several European countries (Belgium, France, Switzerland, …). Deep argillaceous formations (argillite) are potential host-rocks because of their confining properties such as high sorption capacities for radio- nuclides, low permeabilities and swelling capacities allowing the self sealing of eventual cracks. These confining properties can be disturbed by the interaction of exogen materials such as steel, concrete with argillite. Thus, interaction between iron and clay-rich materials has been investigated using different approaches in laboratory experiments (e.g. Guillaume, 2002; Guillaume et al., 2003; Papillon et al., 2003; Perronnet, 2004; Lantenois et al., 2005; Wilson et al., 2006a; Charpentier et al., 2006; Combarieu et al., 2006; Carlson et al., 2007; Perronnet et al., 2007) or by geochemical modelling (Combarieu et al., 2006; Wilson et al., 2006b; Bildstein et al., 2006). Major part of these studies were carried out under disposal reducing conditions on bentonites (FoCa7, MX-80) or purified smectite fractions, while only one was lead on the Callovo–Oxfordian argillite (Combarieu et al., 2006). Until today, no detailed studies have been conducted on the argillite/Fe(0) interaction at in-situ conditions within the host geological formations. Only one in-situ experiment has been performed in Stripa (Sweden) with a bentonite and a metallic plate which were buried during 6 months and 4 years in a granitic massif (Latrille et al., 2001; Habert, 2001). All these previous studies attested that modifications of the clay- rich materials in contact with Fe(0) depend on many parameters such as water/solid ratio, iron/clay mass, pH, temperature, time, mineralogy and crystal chemistry of the initial clay-rich materials. Most of results indicated that, for temperatures up to 200 °C, the Fe(0)/clay interactions destabilize the smectite minerals and promoted the formation of Fe–Al–Si gels which matured into Fe 2+ -rich 7 Å phyllosilicates such as berthierine, cronstedtite or greenalite. At 300 °C, Guillaume et al. (2003) indicated that the reacting dioctahe- dral smectites were replaced by Fe 2+ -rich 14 Å chlorites and saponites. Moreover, crystallization of siderite and magnetite were also often Applied Clay Science xxx (2008) xxx–xxx ⁎ Corresponding author. Tel.: +33251125335. E-mail address: anne.gaudin@univ-nantes.fr (A. Gaudin). 1 Present address: BRGM, 3, avenue Claude Guillemin, 45060 Orléans Cedex 2, France. CLAY-01518; No of Pages 12 0169-1317/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2008.08.007 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay ARTICLE IN PRESS Please cite this article as: Gaudin, A., et al., Mineralogical reactions in the Tournemire argillite after in-situ interaction with steels, Applied Clay Science (2008), doi:10.1016/j.clay.2008.08.007