Update on the deep borehole in Bülach
Radioactive waste will one day be disposed of deep underground in geological repositories. The Federal Government has the lead in the site selection process in Switzerland. Nagra is drilling deep boreholes in all three potential siting regions to complete the overall picture of the underground geological environment. The investigations include studies of the thickness, permeability and composition of the Opalinus Clay host rock in which the repository will eventually be constructed. The rock samples obtained from the Bülach borehole are suitable for determining these properties.
We have spoken to different project managers of the deep borehole campaign.
What insights have been gained?
First of all, I am very pleased that we have already reached a depth of more than 1080 metres of the planned 1350 metres in Bülach without any incidents worth mentioning. We first had to coordinate the work of over 50 subcontractors at the drill site. In geological terms, a deep borehole is challenging and surprises can lie in store. For the boreholes, we have to take precautions to make sure they stay open for the various investigations and do not break out at the sides. In the lower section of the Opalinus Clay in the Bülach borehole, we were not entirely successful in this respect, but we learned several useful lessons that will help us make improvements when drilling the next boreholes. For example, depending on the rock type, we will use different core bits and adjust the composition of the drilling fluid.
What took us by surprise?
Over 2000 people have come to look over our shoulder here at the drill site in Bülach, and many of them also visited the information pavilion. We were surprised at the huge interest generated by the deep boreholes, and we were able to conduct interesting conversations with the visitors and respond to their questions. In this way, we also learned a lot about the concerns of the local population in connection with the boreholes. We were always in close contact with the representatives of the local communities and the authorities, as well as with the residents living near the drill site. The collaboration with everyone concerned went well and together we were able to find solutions to their concerns.
We also appreciate the keen interest shown by the regional and national media. In a contribution to the TV programme “Schweiz aktuell” (Switzerland Today), the process from recovering a drill core to analysing it was documented in detail.
Many visitors to the drill site ask us whether the knowledge gained from this borehole shows that Bülach is the safest site. We are not yet able to answer this question. The significance of the knowledge we gain here must always be evaluated in comparison with that gained in the other siting regions.
The deep borehole in Bülach has provided us with valuable information. We will continue with our deep borehole campaign and remain open for further results and will then carefully evaluate all the information as a whole. We believe that, together with the information gained from the 3D seismic campaign, the deep boreholes will allow us to identify the differences between the three siting regions that are relevant for the safety of a deep geological repository. We will be able to reliably evaluate the siting regions in two to three years.
Our second borehole Trüllikon 1 is proceeding well, and we will soon reach the Opalinus Clay. The preparations for the upcoming boreholes are at an advanced stage, and drill sites are currently being prepared in the communities of Bözberg and Marthalen. We will continue to provide information on any new insights gained.