Making of the underground scientific experimental programme at the Meuse/Haute-Marne underground research laboratory, North Eastern France

Abstract

In November 1999 Andra began building an Underground Research Laboratory (URL) on the border of the Meuse and Haute-Marne departments in eastern France. The research activities of the URL are dedicated to study the feasibility of reversible, deep geological disposal of high-activity, long-lived radioactive wastes in an argillaceous host rock. The Laboratory consists of two shafts, an experimental drift at 445 m depth and a set of technical and experimental drifts at the main level at 490 m depth. The main objective of the research is to characterize the confining properties of the argillaceous rock through in situ hydrogeological tests, chemical measurements and diffusion experiments. In order to achieve this goal, a fundamental understanding of the geoscientific properties and processes that govern geological isolation in clay-rich rocks has been acquired. This understanding includes both the host rocks at the laboratory site and the regional geological context. After establishing the geological conditions, the underground research programme had to demonstrate that the construction and operation of a geological disposal will not introduce pathways for waste migration. Thus, the construction of the laboratory itself serves a research purpose through the monitoring of excavation effects and the optimization of construction technology. These studies are primarily geomechanical in nature, though chemical and hydrogeological coupling also have important roles. In order to achieve the scientific objectives of this project in the underground drifts, a specific methodology has been applied for carrying out the experimental programme conducted concurrently with the construction of the shafts and drifts. This methodology includes technological as well as organizational aspects and a systematic use of feedback from other laboratories abroad and every scientific zone of the URL already installed. This methodology was first applied to set up a multi-purpose experimental area at 445 m depth. Then the setting up of the experimental programme at the level 490 m was improved from the knowledge acquired during installation of the drift at 445 m. The several steps of the underground scientific programme are illustrated by presenting three experiments carried out in the underground drifts. The first experiment was carried out from the drift at 445 m depth, from end of 2004 to mid 2005. This experiment aimed at setting up an array of about 16 boreholes to monitor the geomechanical changes during and after construction of the shaft between 445 and 490 m. The second experiment was set up in the drift at 445 m depth, and also at the main level at 490 m depth. It consisted in determining the composition of the interstitial water by circulating gas in one borehole and water of a known composition in the other. The evolution of the composition of both water and gases enabled us to test the thermodynamic model of the water/rock interactions. The third example is related to the testing of a concept of interruption of the EDZ through a cross-cut slot technology. The concept, which was tested successfully at Mont Terri (Switzerland), has been transposed and adapted to the URL site conditions. The results will be used for developing a concept for drift sealing.