Repository research: How the construction and operation of a repository are related to long-term safety
What requirements must a safe repository fulfil?
These safety cases are tailored to the respective phases, whereby different safety aspects play a role or are weighted differently. For example, special operational features are irrelevant in the post-closure phase since occupational accidents can no longer occur in the drifts and shafts of the repository that are then sealed.
Recent focus of safety research increasingly on construction and operation
In the past, the focus in the development of strategies to demonstrate the safety of a repository was very much on long-term safety, i.e. on the post-closure phase. Accordingly, there are already very advanced safety concepts for the post-closure phase (for example, the concept described in the preliminary safety analysis for the Gorleben site), but no comprehensive concepts for the operational phase. This focus on long-term safety is quite obvious for a repository that is supposed to ensure safety for a million years. However, little attention is paid to the fact that a repository logically cannot be realised without safe construction and operation. Moreover, construction and operation have an influence on long-term safety that should not be underestimated. On the other hand, many requirements for demonstrating long-term safety in turn have an impact on the technical repository concept and on safety during construction and operation of a repository. The operational phase and the post-closure phase thus influence each other – especially when it comes to safety.
Safety can be impaired by internal and external hazards
- What requirements result from having to ensure long-term safety for the evolution of the repository system during the construction and operation of a repository?
- What are the potential hazards for repository operation and what basic measures for avoiding/controlling these hazards can be taken to reduce hazards to operational safety and incidents during operation (e.g. container crash or fire)?
- Which aspects of operational safety and measures to ensure it have an impact on the long-term behaviour of the repository system?
To answer these questions, the researchers identified so-called “hazards”, i.e. impacts that can damage the facility and that can occur regardless of its operating state. Such hazards are not a new invention but are known from the nuclear rules and regulations. They are subdivided into external hazards and internal events.
External hazards, internal hazards and FEPs
The acronym FEPs stands for features, events and processes. Related catalogues are based on the internationally established FEP database of the Nuclear Energy Association and are already available for some disposal concepts discussed in Germany. Examples of such FEPs include metal corrosion, heat flow, radioactive decay, stress changes, microbial processes in the mine workings, solution inflow into the mine workings or sorption.
Making hazards controllable through measures
Finally, they developed organisational and technical measures to prevent potential internal hazards in a repository mine or to make their consequences controllable or mitigate them in order to ensure operational safety. On the one hand, the scientists drew on their own expert knowledge and, on the other hand, on the experience gathered over the years from the Asse, Morsleben and Konrad repositories and the construction of the former Gorleben exploration mine in Germany.
In the research project, based on the systematic compilation of internal hazards and the derivation of associated measures, it was possible to carry out a comprehensive analysis of the effects of internal hazards on long-term safety, which has not been carried out in Germany in this completeness before.
For further work, a more concrete concept should be defined
The observations and results developed from them were limited by the fact that quite general disposal concepts have been considered in BASEL. The advantage of this is that the results can be applied as a starting point for discussion for a variety of possible disposal concepts and can therefore also be used in the next steps of the site selection procedure. Based on this, however, a “customised” safety concept must then be tailored to a specific site.
The project was sponsored by the Federal Ministry for Economic Affairs and Energy (BMWi); the synthesis report is available in the GRS publication database.
Title: "Bewertung der Abhängigkeiten zwischen dem sicheren Bau und Betrieb eines Endlagers für hochradioaktive Abfälle und der Langzeitsicherheit" (Assessment of the interdependencies between the safe construction and operation of a repository for high-level radioactive waste and long-term safety)