When it comes to safety in a nuclear facility, any risk needs to be accounted for, including external hazards such as floods, earthquakes, lightings, explosions, extreme temperatures, etc.

Proper upfront characterisation – through historical data, sampling, etc. – allows the plant designers to carefully design the boundaries of the facility under these hazards. Once facilities are built, the knowledge of the hazard is updated regularly in order to adapt or reinforce installations if needed.

This is why when it comes to earthquakes, prior to starting civil works and also after this work is done, any potential nuclear site has to undergo a lengthy – yet essential – geophysics analysis, with teams both in the office and also on-site. In order to estimate the seismic hazard, on site geology analysis and former seismic activity is reported and analyzed. The fault systems are identified and characterized. Then, site effects can be characterized using different methods detailed thereafter and finally some drillings can be proposed to locally verify geophysical assumptions. With the different drills done across a specific site, the geophysicists collect core samplers showing them layer by layer the different compositions of the subsurface. Among all these geological and geophysical methods used to better understand the subsurface, some of them can be invasive. For example, using active seismic sources – explosions, large trucks, etc. – may not be adapted to urban areas or may disturb the environment. This is also the case for drilling, but the main issue in drilling is that we cannot sample all the area at once, instead drillings are localised discrete information. What can be done when drilling is not an option in an existing operating nuclear site? Or worse, detonating explosive? Or how can we know the composition of the sub-subsurface between the different drills?

 Eventhough seismic methods using active sources are the most used approaches, it comes with some drawbacks: expensive, time consuming, legal permits required, logistics intensive, etc.

With all the new build projects currently planned across the world, any time saved and better data acquisitions are extremely valuable. A novel approach might be considered extremely useful.