Because several questions remain unanswered

It is a railway tunnel as the France has plenty. There are two openings, rails but no train is going for a long time. Tournemire tunnel has managed a brilliant conversion through the rock of the mountain that it crosses. The Institute of radiation protection and nuclear safety (IRSN) offered for a pittance a beautiful slice of 250 metres deep, blue-veined cheese argillite wish of faults, fissures, aquifers. "We are here in the extreme conditions of storage of nuclear waste," provides Karim Ben Slimane, Deputy Head of the LR2 S laboratory. Nearby, the cellars of Roquefort refining are peacefully.

Acquired in 1992, the tunnel has since been equipped experimental galleries whose length has doubled this summer (250 meters). Thanks to them, the new grouping national research "trasse" created by the IRSN and the CNRS has strengthen research on the geological storage of the radioactive waste. Because several questions remain unanswered.

The water issue

This initiative is more that annoy the supporters of geological storage. In particular with the National Agency for the management of nuclear waste (Andra). It is she who built the laboratory in Bure in the Meuse to test such burial in a deep layer of clay at 500 metres below ground. The challenge: persuade the State in 2015 that this storage does not contaminate the environment on several hundreds of thousands of years. Tournemire research attract as much anger of Christian battle, the socialist MP of the North of the eponymous laws of 1991 and 2006 which set storage project schedule. The connoisseur of nuclear estimated Monday in the "Figaro" Tournemire laboratory is mainly there to justify that given activity to a team of scientists.

As an independent expert for his ministerial guardianship, the SNRIS and his partner try to still validate the very sensitive research of Andra, with means 10 times more modest (EUR 6 million). Trasse researchers want to answer two questions: is argillite waterproof Is impermeability preserved in storage Because the question of the disposal of nuclear waste has become that of the water. In a few thousand years, the water contained in clay (3) liquéfiera vitrified or metal packagings releasing radioactive material such as plutonium, the actinides, etc. The isolation of these elements will depend more on the clay layer. Hence the need to verify that no movement of water is migrating these pollutants of groundwater or to the external environment.

Its researchers 20, Tournemire tunnel offers a not expensive replica of Bure and an interesting case. "The layer of 180 million years has almost the same age and same chemical composition," explains Karim Ben Slimane. As to Bure, it undergoes the constraint of the 250 m of limestone over it. Tournemire, scientists have wanted to position themselves in an extreme scenario, one layer fractured and surrounded by two aquifers. In this, the IRSN stands out teams of Andra that Bure clay layer contains no faults. This position defending geologically high stability from the regional shelf is not enough to convince the IRSN. A Tournemire, geologists have shown that some cracks in the clay can escape the best seismic technologies.

But cracks remain today the great question of geological storage according to the researchers. A consensus exists on the impermeability of argillite healthy. A Tournemire, hydrogeologists have been able to reconstruct the migration of water of the aquifer located 50 metres above the tunnel-Lab: 3 centimetres per million years, almost watertight. However, in the fractured areas, water runs 3 kilometres per million years. This permeability was intolerable for nuclear waste.

Control of fractures

For geologists, the presence of fracture would not condemn as the future site of storage. "In this case to ensure that they are distant or that they are non-circulating" says Denise Stammose of the SNRI in a gallery showing a fracture of 2 metres to a few hundreds of metres long: "this fault has moved 10 metres vertically 40 million years ago." "The clay has since been crushed, it is stable."

The second question, Tournemire tunnel brings more answers than the site of Bure. The tunnel, broke at the end of the 19th century, offers one hundred and twenty years of decline. Two phenomena are likely to degrade the impermeability of the storage. Researchers have discovered in 2001 that the digging of tunnels of access and storage crack rock. A Tournemire, with core and chemical and ultrasonic analysis showed that 2 metres around the tunnel ring is damaged. This result was surprising: "with such a mass of rock above the layer, we had not anticipated these cracks. The opening of the tunnel had to degrade the qualities of clay the cutting of the mechanical effects, desaturation in water and oxidation of the rock. "Same measure work conducted on the Gallery breakthrough in 1996. No crack is still was spotted, which makes say to Karim Ben Slimane: "the absence of impact 10 years does not imply that in there is none to 100 years." Clearly, station too hasty conclusions on the site of Bure. Researchers recognize did not understand all the phenomena of the storage. So no modelling pastes with measures of crack of tunnel and galleries. Specialists hope still there a few years.