Architecture and management of a geological repository - Andra

12 - SynthesisThe study shows from an engineering viewpoint the feasibility of a repository of high-level and longlivedintermediate level wastes in the studied argillite formation. The presented options show thatthere are concrete technical solutions to the questions raised by the feasibility of a repository. Theseoptions were retained at this stage for their simplicity and their robustness.They cover all the existing French high-level and long-lived intermediate level wastes as well as thoseengaged by the total number of nuclear plants. To do this, various assumptions for the production andconditioning of future wastes were made. The diversity of the primary waste packages could be takeninto account by structuring the inventory model using ″reference packages″ representative of all theproblematics introduced by this diversity. It should be noted that not withstanding any managementchoices the study has also explored, beyond the B wastes (medium-level activity and long-lived) and Cwastes (high-level activity), the case of spent fuels if it were decided not to recycle them.The presented options are adapted to the clay formation studied by the underground researchlaboratory of Meuse/Haute Marne. To do this, the study was based on the body of knowledgeprogressively acquired during the extensive work conducted on the site since 1994 (geophysical andbore-hole operations, tests on samples, data acquired during the sinking of laboratory shafts, anexperimental drift at -445 metres). In particular, the repository architecture takes into account thegeometric aspects of this formation (thickness, depth, …), as well as its mechanical and thermalcharacteristics. The presented options stress the favourable properties of the studied formation in termsof containment (very low permeability, low hydrogeological gradients, retention capacity andgeochemical properties).Special attention was paid to the reversibility of the repository in response to the expectations whichwere expressed first in the Law of 30 December 1991, and then at different stages. Reversibility hastherefore significantly influenced the architecture options. It offers great flexibility for themanagement of the disposed packages and the control of the disposal process. Safety also stronglyinfluenced the design choices made. It represents indeed one of the major objectives, aimed ateventually guaranteeing passive safety, ensured by the facility itself.The studied options were compared to those considered in other countries within the framework ofinternational scientific and technical exchanges and cooperations. Many points in common werediscovered, such as the disposal package design, the thermal sizing criteria, or even the structuresinstalled during the closure of a repository. A certain drawing together can be observed over the lastfew years in terms of progressive management and reversibility of a repository, even though there arestill notable differences in the reversibility approach, a particularly developed requirement in France.Generally, differences exist between the proposed technical solutions at the international level, whichare most often explained by the specific geological context of each country (clay or non clayformations, generic approach or specific approach for a particular site), the waste packages and theinventories taken into account as a reference (retreatment wastes or spent fuels, number ofelectronuclear power plants).At the stage of a feasibility assessment, it should be noted that the studied options cannot beconsidered as optimised. Also, without changing the presented design principles, a few studyperspectives can be outlined in view of improving the design.12.1 Simple and robust technical optionsIn order to assess the feasibility of a repository in the studied clay formation, Andra retainedtechnically simple and robust options considering the current limits of knowledge and technology.The simplicity of the studied options favours understanding how a repository works at various timescales. For example, the separation of the various types of wastes in separate zones avoids interactionswhich would complicate this understanding. The assessment of a repository’s performances in termsof reversibility and safety is made easier.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM484/495