Under construction since 2000, the laboratory on the storage of radioactive waste where Bure has been a fatal accident already has 1600 meters of underground galleries.
Before going down by one of the two elevators that sink in 5 or 7 minutes at 500 meters deep, the Bure site visitor is explaining the safety measures to be followed in the underground structure. There are no radioactive waste in the galleries. The first packages of used nuclear fuel should not go down, at the earliest, by 2025 Cigéo in the future, the storage site itself, the final decision is expected around 2017. But the laboratory, built by ANDRA (National Agency for radioactive waste management) to study the conditions of the future storage and extending over 1600 meters of underground tunnels already requires serious security measures. After a presentation of 15 minutes, during which the rules to be observed when meeting with a construction vehicle and the location of survival rooms on the site are indicated, visitors are led above the site itself.
Armed with a suit, helmet, boots and site of a large belt to fit around the waist phones, GPS underground and self-contained breathing apparatus in case of problems, it is then possible to exchange its surface visitor’s badge against the underground visitor. A few meters away, after two security gates, ventilation blowing over the site’s front door which leads to the elevator. This is the sound of the air that is renewed in depth to allow the workers to dig galleries in various sizes.
Check the safety of a deep repository
This project Industrial is extraordinary. The final repository will be operated for 140 years before permanent cementation. Several generations of engineers and workers will succeed to lead the work whose cost was reassessed recently by the Ministry of Environment to 25 billion euros. The cost of the laboratory has been estimated at 1.5 billion euros since 1990.
In the basement, several tests are performed to verify the validity of a deep geological repository, whose option was arrested in 2005. It is planned to store there for millions of years 10,000 m3 of high-level waste from reprocessing of fuels at La Hague and Marcoule, and 70,000 m3 of those medium level and long-lived, which is mainly the rod cladding that have contained nuclear fuel.
To this end, the properties of the clay layer, old 160 million years have been tested . More than 3,000 sensors (pressure, temperature, humidity, etc.) were installed for experiments to verify in particular that the water does not circulate too quickly. This last parameter is indeed crucial to make sure that radioactive waste are unlikely to migrate to the surface too quickly. Natural diffusion of water in the clay is extremely slow. Migration is a theoretical limited to 1 meter every 3.3 million years, and for breach of barrels of radioactive waste.
The tunnel boring machines assembled in depth
Modeling large galleries (over 10 meters in diameter) and monitoring their deformation led to opt for retaining the technique known as “segments” that is to say, to ensure the shape of underground tunnels by prestressed members concrete. The same technique was used for the Channel Tunnel. But given the characteristics of the Bure site, posted TBMs parts are assembled directly in the basement; and descended by the elevators.
In addition, the cells of a little over a meter in diameter were dug to house the barrels of high activity fuels. Their straightness is very dependent on the worker skills that pierce the … What is a major condition for making reversible solution, and possibly remove these barrels, in case of new technical solutions that would be discovered during the next century.
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