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<jats:title>Abstract</jats:title> <jats:p>We present the first correlation between South American and African shear zones based on a reconstruction model of SW-Gondwana continental crust, correlating sixty-three Brasiliano-Pan-African crustal scale shear zones that sutured this paleocontinent at ca. 500 Ma. The final amalgamation and consolidation of SW Gondwana continental crust was attained by an anti-clockwise rotation of three cratons (Kalahari, Angola and São Francisco) in relation with the clockwise rotation of the Rio de La Plata craton in the Early Paleozoic Gondwana margin. These relative movements were accommodated by transcurrent shear zones active from 585 Ma to 500 Ma within the Pan-African-Brasiliano belts that surround these cratons. This kinematic interaction resulted in the initiation of a long-term active margin starting with the Cambrian Pampean orogeny and ending with the Permian-Triassic Gondwanide orogeny.</jats:p>

<jats:title>Abstract</jats:title> <jats:p> The heat generated by high-level waste or spent fuel will create disturbances around a deep geological repository (DGR) containing these wastes. Since the 1990s, SCK CEN, EIG EURIDICE and ONDRAF/NIRAS have been characterizing the thermo-hydromechanical (THM) behaviour of Boom Clay and assessing the impact of the thermal disturbances. This research has included laboratory tests as well as <jats:italic>in situ</jats:italic> experiments in the HADES Underground Research Laboratory. The two types of tests have been complementary. Laboratory tests have allowed understanding of the THM behaviour and determination of associated values of the THM parameters of the clay under well-controlled boundary conditions and loading paths. This knowledge and the parameters were then validated and even improved by <jats:italic>in situ</jats:italic> tests which allowed investigation of the effects of temperature on the Boom Clay behaviour at large scales. This paper gives an overview of this research and presents the main findings. It also explains how the knowledge gained supports the design of a possible future DGR and contributes to assessing the extent and impact of the THM disturbances in the Boom Clay around a DGR. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> After decades of RD&amp;D, mature concepts for the geological disposal of long lived and high level radioactive waste exist and some are close to being implemented. Underground Research Laboratories (URLs) have made an essential contribution to this progress. They enable <jats:italic>in situ</jats:italic> characterization and testing of host rocks and the demonstration of technologies and component performances at representative scales and under realistic geological conditions. They also offer a tool for training personnel and show aspects of the geological disposal concepts to stakeholders, including the public. In this paper we will present the different types and roles of URLs and we will discuss how the RD&amp;D role of URLs has evolved and how it is likely to evolve in the near future. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> A wide range of metals have been studied as candidate container material, which is considered in the geological disposal concept of high-level radioactive waste and spent fuel in Belgium. More than 40 years ago, SCK CEN started studies on the corrosion of these metals. The HADES underground research laboratory (URL) played an important role in the corrosion research as it enabled <jats:italic>in situ</jats:italic> corrosion experiments that simulate realistic disposal conditions as closely as possible. These experiments consisted of placing metallic coupons on a steel support tube, heated from the inside, that was installed in the Boom Clay, thereby exposing the coupons to various conditions representative of the disposal concept that was considered at that time. Test durations lasted from 6 months to approximately 7.5 years. This paper summarises the results from the various corrosion studies and discusses their implications on the choice of disposal concept. One of the main outcomes of these experiments was a change of rationale regarding the choice of the container material from carbon steel (corrosion-allowance) to stainless steel (corrosion-resistant). The main arguments for this change were the need to avoid severe pitting corrosion during the aerobic period and to minimise the generation of hydrogen gas during the subsequent anaerobic period. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the 1980s, HADES was the first URL dedicated to the study of the geological disposal of radioactive waste in a deep clay formation, the Boom Clay. It was not until the early 2000s, after a siting process, that Andra implemented the Meuse/Haute-Marne URL, in the Callovo-Oxfordian formation at a depth of about 500 m in order to develop the Cigéo project (French industrial centre for geological disposal). Andra therefore relied heavily on the work carried out in HADES, through numerous cooperation projects (participation in in-situ experiments) both between Andra and ONDRAF/NIRAS &amp; SCK CEN (Euridice) and/or with Mont Terri consortium, and within European projects (CLIPEX, RESEAL, etc.). This was driven by a dual objective: (a) to prepare its own experimental programmes in the Meuse/Haute-Marne underground laboratory (methodology, experimental devices and protocols, etc.), and (b) to have general knowledge on the behaviour of argillaceous rocks, in particular in terms of similarity and differences between the various argillaceous rocks.</jats:p> <jats:p>The paper illustrates the contribution of HADES to the Andra programme. This concerns the characterisation of the claystone behaviour, host rock and swelling clay-based seals (HM, THM, EDZ, etc.), and the design and the behaviour of underground structures and seals in deep clay formation (constructability, lining/support, etc.).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Taconian–Grampian tract was characterized by a diachronous collision of a north-facing oceanic arc–forearc terrane and associated backarc basins with an irregular Laurentian margin with hyperextended segments. Hyperextension produced outboard continental terranes, separated by exhumed subcontinental mantle from the inboard margin. The exhumed mantle facilitated continued subduction of the extended margin after it had entered the trench. Enhanced slab-rollback resulted in spreading in lenticular backarc basins, which gradually transitioned along-strike into extensional arcs where rollback was less. Obduction of the oceanic elements onto the irregular Laurentian margin was followed by diachronous slab breakoff and a subduction polarity reversal, such that south- and north-dipping subduction zones locally were coeval along-strike. The polarity flip changed the convergence obliquity from dextral to sinistral and was accompanied by shallowing of the subducting slab near the end of the Middle Ordovician. Strike-slip movements locally juxtaposed segments where tectonic events occurred at different times, producing conflicting relationships. Slab breakoff produced punctuated magmatism, largely driven by mantle-derived melts, and drove and/or enhanced metamorphism in the overlying and enveloping crustal rocks. Boninite was generated episodically over a time span of 32 myr; the oldest Cambrian phase in the Lushs Bight Oceanic Tract (LBOT) and correlatives was associated with subduction initiation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A seismic array extended from the Grenville Province into the Abitibi and Opatica subprovinces of the Superior Province, Canada. We use P-to-S converted waves in seismograms of distant earthquakes to probe boundaries in seismic properties, and demonstrate the presence of a prominent seismic feature that dips NNW into the mantle beneath the Grenville Front. We use two variants of receiver function (RF) analysis, a common conversion-point (CCP) imaging that combines seismic signals from multiple paths connecting sources and receivers, and harmonic decomposition of RF data that separates signals according to their direction in the cone of paths from which the signals have come. CCP images show the crust beneath the Grenville Province to be thicker than beneath the Superior Province, and identify a NNW-dipping boundary beneath the Grenville Front. Harmonic RF analysis shows that this feature is associated with seismic anisotropy in upper-mantle peridotite, and that this anisotropic feature extends to depths of at least 70 km. We interpret the feature as the result of a NNW-dipping shear zone formed within the mantle lithosphere during the Grenvillian continental collision. It could have accommodated internal deformation within Laurentian lithosphere or, more speculatively, mark the contact with the impacting Amazonian lithosphere.</jats:p>

<jats:title>Abstract</jats:title> <jats:p> Twenty-five years ago, a unique long-term and large-scale <jats:italic>in situ</jats:italic> experiment with <jats:sup>14</jats:sup> C-labelled natural organic matter (NOM) was set up at the HADES underground research facility in Mol (Belgium) to study its migration behaviour. Natural organic matter plays an important role in the mobility of various safety-relevant radionuclides, which is critical in the context of Safety &amp; Performance Assessment (SA/PA) calculations for a possible nuclear waste repository. The objective of this work is to enlarge the confidence in current NOM transport models by validating them with the <jats:italic>in situ</jats:italic> experiment, which is still continued to this day. Stepwise adding more complexity to the model resulted in a 10-parameter model with which excellent fits to the data are obtained. The model considers two different fractions that are transported by advection and diffusion and can be subject to both irreversible and reversible immobilization processes. The associated fitted parameter values compare well with values determined on small-scale migration experiments. This builds confidence in the NOM transport model, which in turn contributes to the confidence in the outcome of the radionuclide migration calculations performed in the context of SA/PA. These results again highlight the incredible value of such long-running experiments at underground research facilities like HADES. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Demonstrating the feasibility of constructing tunnels in deep clay formations is an important goal of the Belgian RD&amp;D programme on the geological disposal of radioactive waste. In 2002 a major achievement was reached when the HADES Underground Research Laboratory (URL) in Boom Clay was extended with the construction of the Connecting Gallery. This demonstrated that it is feasible to construct galleries in poorly indurated clays using industrial techniques. To monitor the mechanical behaviour of the gallery and assess its stability, strain gauges were embedded in the segmental gallery lining and prisms were installed on the segments. These sensors provide valuable information that will support the design of future galleries. This paper presents the acquired 20 years of monitoring data in the Connecting gallery and a first analysis of these data in term of Boom Clay behaviour. In addition, the key findings are compared to those of a similar analysis performed by Andra (the French Radioactive Waste Agency) at the Meuse/Haute-Marne URL. The latter URL is excavated in the Callovo-Oxfordian claystone (COX). The comparison identifies general trends and highlights similarities between the behaviour of tunnels in poorly indurated clay (Boom Clay) and in claystone (COX).</jats:p>

<jats:title>Abstract</jats:title> <jats:p> When assessing a rock formation for its suitability as a potential host rock for the disposal of radioactive waste, knowledge about its pore water chemical composition is essential. When the HADES underground research laboratory became operational in the early 1980s, it offered the possibility of extracting pore water from Boom Clay. At the time, however, there was almost no experience of sampling pore water from deep clay formations. The low hydraulic conductivity of clays makes it difficult to extract pore water and the sampling process itself can induce changes in the observed chemical characteristics due to oxidation and re-equilibration with the ambient air. In the past decades, significant progress has been made in the techniques and protocols to sample and monitor pore water. The use of nitrogen instead of compressed air to drill boreholes and installing piezometers limited the disturbances induced by oxidation of the clay. Furthermore, an advanced system was developed to simultaneously sample pore water and dissolved gases and measure some key geochemical parameters such as pH, pCO <jats:sub>2</jats:sub> and redox potential under <jats:italic>in situ</jats:italic> conditions. This has resulted in a more reliable characterization of the Boom Clay pore water and a better understanding of perturbing processes such as oxidation. </jats:p>