GRS develops safety case concept for a repository in argillite


By disposing of radioactive waste in deep geological formations, it is to be isolated from the biosphere and from humans over very long periods of time. A so-called safety case has to show whether the necessary prerequisites for doing so are fulfilled. Here, it has to be demonstrated that the radionuclides will be retained in the repository.

A safety case looks at different scenarios that represent possible future evolutions of the repository system. What effects natural developments, such as ice ages, may have on the repository is also included in the considerations, as are possible incidents. The safety case is therefore the crucial element of the licensing procedure for a repository.

The AnSichT project
Together with DBE Technology GmbH and the Federal Institute for Geosciences and Natural Resources (BGR), GRS is currently developing a safety and verification concept for a high-active waste repository in argillite as part of the AnSichT (an acronym from the full German title which translates as: "Methodology and application orientation of a safety and verification concept for repository for heat-generating waste in argillite") project, which is funded by the German Federal Ministry of Economics and Energy (BMWi).
Figure 1: Argillite sample in which a fossil has been shielded from external influences and preserved for over 180 million years (Picture: GRS)Beside rock salt and granite, argillite is one of the three host rock types hat are considered for a repository in Germany. Argillite is characterised above all by the fact that radionuclides stick to it. The experts call this sorption, which is down to the electrically charged surfaces of the argillaceous minerals.

In the AnSichT project, the researchers take recent repository and closure concepts, legal and geological boundary conditions as well as possible repository system evolutions into account. Their studies are based on the state of knowledge that was achieved during the course of previous research projects on repositories in argillite.

Long-term safety analyses as an important tool for a safety case
The long-term safety analysis  is an important component of the safety case. It can additionally be used for support in the site selection process, for steering site exploration activities, or for optimising the technical repository concepts.

Figure 2: Work in the Mont Terri underground laboratory (Picture: Mont Terri Project, swisstopo) The first step of the long-term safety analysis is the compilation of a so-called FEP catalogue (FEP = Features, Events and Processes). The FEP catalogue comprises all features, events and processes that are relevant in connection with the evolution of the repository system. This includes possible climatic developments (e.g. ice ages) in the same way as data about the decomposition of the waste and its interaction with the surrounding rock. One aim of the project is to select the processes that are relevant for a generic argillite site. To describe the processes, the state of the art in science and technology is applied, and the research results obtained from underground laboratories such as Bure (France) and Mont Terri (Switzerland) are used as well.
Development of scenarios for processes in repositories
The FEP catalogue forms the basis for the development of possible scenarios in a repository in argillite. These scenarios are translated into computer models, which in turn form the basis for the development of simulation software with whose help predictions can be made of the behaviour of the repository. Another focus of the project lies on identifying where the largest uncertainties exist in connection with verification and in what areas research will be necessary in the future.
The AnSichT project will run until mid-2016. The results will be published in a series of reports prepared by the three partner organisations involved. GRS has already published the Report on the Safety Concept and the Verification Strategy (report in German language).