A hundred holes drilled, the digging of several galleries and of new experimental storage cells, the creation of an X crossroads, embankment tests ...
Even if the Covid-19 led Andra to slow down its activity during springtime, 2020 remains a very active year at the underground laboratory of the Andra Center in Meuse / Haute-Marne. Focus on some of the most prominent achievements, and work in progress...
Since its creation in 2000, the experiments carried out at the Underground Laboratory have combined digging activities, technological demonstrations and scientific experiments to prepare the industrial implementation of the Cigeo project. After digging the first galleries and studying the behavior of the rock, testing different embodiments of the galleries and disposal cells for high activity waste (HA), the time is now for new tests and the integration of science and technologies. "With this new project, which started last year, we are getting closer and closer to the industrial reality of Cigeo," explains Émilia Huret, assistant to the director of Research and Development at Andra.
Technical and scientific issues
Several experiments undertaken this year will accompany the assessment of the application of the Cigéo licence. This is the first time that a prototype of a disposal cell for medium-level long-lived waste (MA-VL) at representative size will be constructed. Three new demonstrators of disposal cells for HA waste will also be dug, as will the "four-branch" intersection (see below). "We must show the Nuclear Safety Authority that what we are proposing for Cigeo is doable, with the level of performance that we have announced," adds Olivier Alavoine, manager of the technological testing program at Andra. The scientific program is no less important. A hundred boreholes are planned in 2020 to continue the analyzes of gas exchanges between cells and galleries, on the behavior of rock during the digging of underground structures, on the interactions between rock and other materials used (steels, concrete…). These are all experiments that will strengthen and develop knowledge . Thus, science and technology are advancing together in order to continue to learn and innovate to optimize the Cigeo project.
Three new disposal demonstrators for High Level Waste
A new prototype of an 80-meter-long HA waste disposal cell will be produced and equipped in a configuration close to that expected in Cigeo, especially during the pilot industrial phase. Two other 10-meter-long cells will also be dug to supplement knowledge of the physico-chemical interactions between the cell and the gallery.
A crossroads with four branches (in "X")
There will be many "X" crossroads in Cigeo, especially in the logistical support areas. However, only T-junction (three branches), were built in the underground laboratory. Although feedback from the Laboratory shows that these crossroads are good, as the crossings are areas where mechanical stresses are concentrated, it is important to make an intersection of this type in order to fully understand the effect of a such digging on the rock and the behavior of the support. Even before digging, sensors will be inserted in the rock, in order to follow the evolution of the future structure throughout the digging period, as well as after.
There are plans to backfill the galleries at the end of Cigeo’s operation. Without prejudging the choices that will be made at this time, tests will be carried out on the surface and preparatory work in the galleries of the Underground Laboratory to test, on a representative scale of Cigeo, the realization, the choice of the materials constituting the embankments (sand, clay from laboratory verses *, bentonite, etc.) and the phenomenological behavior of various technical backfill solutions. In addition, following the same logic, tunnel sealing tests will also be carried out in the next two to three years, in particular in preparation for the demonstrators planned for the pilot industrial phase of Cigeo.
* Verses: cuttings from the argillaceous rock excavated during the digging of the galleries and cells of the Laboratory. They are put in the form of a mound on the surface.
A first prototype disposal cell for MA-VL waste
This is one of the first steps in this project: the creation of a prototype disposal cell for Intermediate Level Waste (ILW) on a Cigeo scale. With an excavated diameter close to 10 m, it will take two years to complete the 80 m-long gallery. The digging work started at the end of February, in the extension of a gallery which is today about 5 m in diameter. This prototype will make it possible to test the installation and the behavior of different types of liners, in particular a compressible material. The cell will also be equipped with many sensors to measure deformations in the rock and liners, or the water pressure in the rock (called pore pressure).