Nagra (the Swiss National Cooperative for the Disposal of Radioactive Waste) has completed a study to determine the suitability of Opalinus Clay as a host rock for a repository for spent fuel (SF), high-level waste from reprocessing (HLW) and long-livedintermediate-level waste (ILW). The proposed siting area is in the Zürcher Weinland region of Northern Switzerland. A repository at this site is shown to provide sufficient safety for a spectrum of assessment cases that is broad enough to cover all reasonable possibilities for the evolution of the system. Furthermore, the system is robust; i.e. remaining uncertainties do not put safety in question.
The current design of a deep geological repository for high-and intermediatelevel radioactive waste in France consists of a complex system of different underground structures (ANDRA, Dossier 2005 Argile, les recherches de l'Andra sur le stockage géolog-ique des déchets radioactifs à haute activité et à vie longue, collection les Rapports. Châte-nay-Malabry, France, 2005). For a comprehensive understanding of the long-term hydraulic evolution of the entire repository, numerical non-isothermal two-phase flow and transport simulation, taking into consideration the generation, accumulation, and release of hydrogen gas and decay heat, are compulsory. However, a detailed numerical model of the entire repository system would require a tremendous computational effort and pose a laborious task with respect to the operation of the model. To handle these difficulties, we have developed an efficient method for the numerical modeling of a complete repository system and its geologic environment. The method consists of the following steps: (i) subdivision of the repository plane into a large number of "sectors" based on the position of hydraulic seals and on other geometrical considerations, (ii) exploitation of existing symmetries (inside or between sectors), (iii) adoption of the "multiplying concept", and (iv) connection of the individual sectors at the drift interfaces to form the entire repository model. Each sector is modeled as a three-dimensional (3D) block, and the entire model is computed with TOUGH2-MP. The Electronic supplementary material The online version of this article (123 78 A. Poller et al.method allows for a massive reduction in overall finite-volume elements and, at the same time, provides an adequate representation of the small-sized structures in the repository. The main characteristics of the method and its application to an entire deep geological repository system in a clay host rock are presented.
The corrosion of metals contained in intermediate-level long-lived waste (ILW) under reduced chemical condition will lead to the production of hydrogen gas during the post-closure phase of a deep geological repository for radioactive waste. According to previous investigations by Talandier et al. (Proceedings of TOUGH symposium 2006, Berkeley, 2006, the period of concern covers several 1,000 years after closure of a repository in a clay host rock (Callovo-Oxfordian). The limited hydrogen transport efficiency of the host rock will lead to significant saturation of the concrete waste canister pore space and voids with a gas phase and pressure build-up within the emplacement drifts. On the other hand, the water availability is limited as a result of (i) the low permeability of the clay host rock and (ii) the desaturation of the rock mass close to the drift wall due to the ventilation of the drifts during the operational phase of the repository. In former numerical simulations it was assumed that under the reducing chemical conditions prevailing in the repository, the corrosion rate would be a function of the available metal surface and the temperature only. In this paper, simulation results based on new phenomenological functions are presented, which were implemented in TOUGH2. These allow taking into account (i) a water saturation dependency of the hydrogen generation rate, (ii) the water consumption due to the corrosion process, and (iii) the total metal mass available for corrosion. The paper presents results of 1D radial and 2D vertical simulations of a typical cross-section of a waste emplacement drift and the surrounding rock mass. The interactions between water availability from the low permeable clay, the dependency of the hydrogen generation rates from the water saturation of the waste package and the hydrogen migration in the host rock are demonstrated.
Résumé -Essais d'injection de gaz dans les argiles à Opalinus du laboratoire souterrain du MontTerri (Suisse) : données et interprétation -La migration de gaz dans les roches argileuses est un sujet d'intérêt dans le cadre de différents types d'exploitation du sous-sol : que ce soit par exemple dans le domaine du stockage de gaz naturel, de la séquestration du CO 2 , comme éponte imperméable d'un aquifère, ou dans le domaine du stockage de déchets. Une analyse quantitative de la migration de gaz dans ces milieux à très faible perméabilité nécessite l'estimation des propriétés physiques de l'écoulement. Au laboratoire souterrain du Mont Terri (Suisse), dans les argiles à Opalinus, une roche sédimentaire jurassique, une série de tests hydrauliques et d'injection de gaz a été conduite en forages d'expérimentation. Leur but était en particulier de déterminer les propriétés de transfert des gaz dans cette roche. Cet article présente les résultats d'une campagne de tests (sollicitations de type essai hydraulique classique et test d'injection de gaz et récupération de pression de longue durée), conduite dans la roche « intacte », c'est-à-dire non perturbée mécaniquement par le creusement des galeries. Il présente une interprétation détaillée des tests reposant sur l'ajustement des données expérimentales au moyen d'un logiciel de simulation numérique biphasique (eau/gaz) de l'écoulement en milieu poreux (TOUGH2/iTOUGH2). Par analyse séquentielle, il a été possible d'obtenir un set de paramètres hydrauliques mono-et diphasiques cohérent sur l'ensemble de l'expérimentation. L'utilisation d'informations additionnelles et indépendantes sur les caractéristiques pétrophysiques de la roche (porosité et pression capillaire) a permis de mieux contraindre le problème inverse à l'étude. Bien qu'il soit difficile sur la base des différents modèles et ajustements réalisés, d'obtenir une solution unique en terme de courbe de pression capillaire et de perméabilité relative, les résultats indiquent qu'une paramétrisation classique de type Van Genuchten -Mualem serait valide. Enfin, des simulations prospectives sont présentées qui montrent que l'amélioration de la performance des essais en termes de détermination des paramètres biphasiques nécessiterait une augmentation notable de la durée de l'essai (> 1 an). Oil & Gas Science and Technology -Rev. IFP, Vol. 61 (2006) Abstract -Gas Threshold Pressure Test Performed at the Mont Terri Rock Laboratory: Experimental Data and Data Analysis -Migration of gases in argillaceous formations increasingly attracts the attention of various geoscientific disciplines for purposes like CO 2 sequestration, gas storage in
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