Tome Architecture and management of a geological repository - Andra

3 – Design study of a repository in a granite formationTable 3.2.1in mg/l)Examples of groundwater chemical compositions in various French contexts (contentsType of water Sites pH Na K Ca Mg Li SiO2 Cl SO4 HCO3AlcalineSite 1 8,8 101,16 5,55 5,13 0,02 0,54 50,26 8,05 96,99 109,76Site 2 . 8,86 124,84 4,54 34,07 0,08 0,38 23,87 148,89 129,63 167,70Site 3 6,64 2195,54 170,46 62,92 47,15 9,85 47,73 3725,79 624,16 1798,93CarbogaseousSite 4 6,80 958,68 24,83 142,28 85,07 4,10 21,62 42,54 21,13 3482,02Site 5 6,67 899,91 94,62 605,18 391,31 5,34 58,97 2006,47 249,67 2451,44These differences in composition are not of a type to modify principles for the design optionsproposed. For certain granite massifs, they could lead to adjusting engineered barrier formulations tochemical composition of the water.• Considerations relating to the long-term geological evolution of French granite sitesIn terms of long-term geological evolution of a site, typological analysis of the granite massifs studiedconfirms that most of them are located away from active geodynamic areas, which means unlikelysignificant modifications in the long term to their geological arrangements, especially concerningunderground fracturing [12]. Climatic changes and erosion can also alter the hydro-geological andtopographical context of a site in the long term. Variations exist between massifs mainly due todifferences in morpho-structural context. The analysis has thus identified the main arrangementsencountered within the French context and phenomena which could come into play within a timeframeof 10,000, 100,000 and 1,000,000 years. It should be pointed out that, on a scale of 100,000 years, themodels do not show any significant differences in evolution between the massifs. Beyond 100,000years, the situation of each massif is to be specifically taken into account for the study of a particularsite.3.3 General options for the design of a repository in a granite mediumIn order to fulfil long-term safety functions, the design proposed for a repository in granite mediumconsists of:- using a variety of technical arrangements to make the most of the beneficial properties of the granitemedium, its low permeability and mechanical resistance of granite rock in particular,- designing engineered repository components (disposal packages, engineered barriers, backfills, andseals) so that they contribute to safety functions in terms of complementarity or redundancy with thegranite medium.- adopting design options aiming at limiting granite disturbances by the repository.In addition to the long term and operational safety, design must meet reversibility requirement, closelylinked to application of the principle of precaution provided for in the 30 December 1991 Waste Act.Beyond the possibility of removing emplaced packages (retrievability), reversibility is based oncautious and staged management of a repository, which, given the timeframes under consideration,leaves the options open for future generations.These principles lead to adopting various technical arrangements for repository architecture anddimensioning, choice of materials for engineered components, and disposal processes. Somemeasures, architectural in particular, that are common to different categories of waste (B and C) and tospent fuel are presented below. Others, as for instance design of engineered components for example,that are specific to each waste categories are described in more detail in chapters 5, 6 and 7.Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY41/228