Yes
Following the Fukushima accident, the ILL decided to take as reference extreme scenario, the cascade failure of dams located on the same river. Studies show that the scenario that would cause the most serious damage would be the failure of the four dams on the river Drac.
To calculate the height and speed of the water when it reaches the ILL site, we assumed the total and instantaneous collapse of the “Le Sautet” dam when completely full. We also assumed that, on reaching the dams situated below the “Le Sautet” dam, the “wave” created by the initial dam break would cause the total and instantaneous collapse of these other dams (which we also assumed to be completely full):
Dam | Capacity (Mm3) |
|---|---|
Le Sautet | 107.7 |
St Pierre de Cognet | 27.5 |
Monteynard | 275 |
Notre Dame de Commiers | 34 |
It is important to note that this is the worst-case scenario. In fact, as the other big dams, such as Tignes, Roselend and Grand’maison, are located on different rivers and are much further away, it is totally impossible that the dam-break waves caused by their failure would reach Grenoble at the same time as each other and at the same time as the wave on the river Drac.
The ILL commissioned the company Artélia (ex-Sogreah, a specialist in this type of work) to carry out a specific study on the consequences of the cascade failure of all four dams on the river Drac. The study was based on worst-case modelling assumptions and concluded that a wave of almost 6 metres in height would reach the ILL site approximately 50 minutes after the breach of the Monteynard dam.
This hazard, which is assumed to be caused by an extreme earthquake, is used as the design basis for the “hardened safety core” of components of the ILL’s high-flux reactor.
New studies have been carried out on the ability of the reactor's two containment walls to withstand this level of flooding. Similarly, all the openings in the reactor walls (personnel and equipment airlocks, truck door, pipe and cable penetrations, etc.) have been checked and, if necessary, reinforced. The necessary reinforcement work was carried out between 2014 and 2017.