A look under the ground: GRS researches measurement methods for surface exploration of a repository site

10.09.2018

Techcollector CC By SA 3.0

Germany is searching for a repository site for high-level radioactive waste. A site with the best possible safety conditions needs to be found. The potentially most suitable host rock formations are salt, clay and crystalline rock. Within these host rock formations, the waste is supposed to be safely isolated from the environment.

According to the Repository Site Selection Act, the site selection is phased into three phases. In the first phase, the whole of Germany will be investigated. Regions will be selected which on the one hand have geologically favourable formations and on the other do not have to be excluded in advance (e.g. due to seismic or volcanic activity). In the second phase, surface surveys and comparative analyses will take place. During the third and final phase, underground surveys will be conducted at the remaining sites.

Which measuring methods are suitable for repository site selection?

On behalf of the Federal Office for the Safety of Nuclear Waste Management, GRS is currently conducting a research project to identify measurement methods allowing the surface exploration of potential sites in the second phase of the search. As a first step, GRS experts prepare an overview of the methods usually used for surface exploration for this project. The aim is to provide a catalogue of concrete proposals for exploratory programmes that can be evaluated.

There are different techniques that can be used. These include, for example, surface-based methods such as 3D seismic measurements using an echo sounder (see figure). Another method is gravimetric measurements. Deviations of the earth's gravitational field are recorded, allowing conclusions to be drawn on the subsoil - e.g. on the rock density. In addition to the area-based methods, the spectrum of methods also includes selective investigations of drillings and laboratory analyses of drilled cores.

 All methods have their strengths and weaknesses. This is exactly what GRS will describe in detail in a second step. The approaches are to be compared in terms of goal, significance, limits and effort. Applicability, possible combinations with other methods and possible further developments are also to be evaluated.

Vibrating vehicles generate pressure waves which propagate wave-like through the subsurface and are reflected as echoes by the geological structures in the ground. Geophones on the earth's surface record the echo signals.

"The most exciting step, however, is the third one," says Dr Ingo Kock, head of the project. "We change our perspective and look at the requirements for measurement methods resulting from the Site Selection Act. We translate the abstract legal text into concrete scientific and methodological needs, so to speak. We then compare this need with the existing spectrum of methods. In the end, we would like to find out which methods are most suitable for collecting the required measurement variables."

Project of the Federal Office for the Safety of Nuclear Waste Management

The project is one of several research projects of the Federal Office for the Safety of Nuclear Waste Management (BfE) in which - in preparation of the site selection - measurement and evaluation methods for the surface exploration programmes are investigated.

The procedure for selecting a repository site is carried out by the the federal company for radioactive waste disposal (BGE). Later the BGE will also build and operate the repository. The BfE coordinates and regulates the repository site selection. This includes reviewing the BGE's proposals at the end of each phase and proposing the repository site at the end of the selection procedure. In addition, the BfE ensures the information and involvement of the public during the site selection process.

Find out more

BfE: Research projects for repository site selection have started
Comparing apples and oranges? An interview with GRS repository expert Jörg Mönig on the challenges posed by the site comparison