The scientific consensus today is that deep geological repositories are a safe and effective approach to permanently disposing of spent fuel, high-level and long-lived radioactive waste safely and securely. Among the different geological formations considered suitable for hosting such repositories, rock salts are characterised by their favourable characteristics, such as low hydraulic conductivity, which helps ensure better isolation of the waste from groundwater.
An advanced scientific and geotechnical understanding of rock salt as an appropriate geological material to host repositories has been accumulated since the latter half of the 20th century thanks to research carried out by a number of countries favouring this material. In addition, substantial know-how exists from underground disposal of chemotoxic waste in salt mines as well as the operation of the Waste Isolation Pilot Plant (WIPP) in the United States and Morsleben and Asse-II repositories in Germany. However, there is more work to be done to expand and substantiate knowledge of salt as a repository host rock.
In this context, the NEA’s Expert Group on Repositories in Rock Salt Formations (Salt Club) was established a decade ago to facilitate an exchange of information among member countries on both the favourable and challenging attributes of rock salt as a host rock formation for deep geological repositories. The group held its latest meeting on 11-12 May 2021 to continue its scientific studies for developing geological repositories in rock salts and discuss potential future initiatives.
During the meeting, group members received an overview of the lessons learnt from failure events/processes of conventional salt mines. They reviewed accidents in salt mines worldwide and examined the analysis of the different failure processes, the lessons learnt and implications for safety assessment. The group members noted that public acceptance of safety assessment for future sites can be obtained if the failures of the past are well understood and measures to avoid them are identified and verified numerically. In view of this, in the coming months the Salt Club will focus on lessons learnt from failure events/processes of conventional salt mines.
The meeting also included discussions of scientific analysis of microbial activities in saline systems, the ABC-Salt workshop series and ongoing co-operation with the NEA Thermochemical Database Project (TDB). The meeting concluded with a topical session on the latest technical developments in performance assessment studies of geological repositories.