Expert Group on Geological Repositories in Crystalline Rock Formations (Crystalline Club)
The Crystalline Club's fourth meeting held online, June 2021


Deep geological repositories use a combination of engineered and natural barriers to safely contain and isolate radioactive waste from people and the environment. There is a consensus among major nuclear regulatory and monitoring organisations that repositories are the responsible way forward for long-term management of these materials. The area of repository development for long-lived radioactive waste is a strategic area in the work programme of the NEA Radioactive Waste Management Committee (RWMC). Among the different geological formations considered suitable for hosting geological repositories, crystalline rocks are characterised by their high strength, thereby providing cavity stability, low-heat sensitivity, permeability and dissolution properties. Although fractures are common in crystalline rocks, the resulting fracture permeability can be resolved by engineered barriers such as waste containment and bentonite backfill.

Many countries are developing or planning to develop geological disposal facilities for radioactive waste in crystalline rocks. Although an advanced scientific and geotechnical understanding of crystalline rocks has been accumulated by the dedicated research carried out by these countries, there are research areas in which member countries may benefit from joint R&D efforts. Recognising the mutual benefits of joint international research efforts, including the successes of the NEA Clay Club and Salt Club, members of the RWMC Integration Group for the Safety Case (IGSC) requested the NEA to establish a similar group for the study of crystalline rocks.


The key objective of the Crystalline Club is to promote the exchange of information and share state-of-the-art approaches and methods to improve understanding of crystalline rocks as a host rock for high-level radioactive waste repositories.

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Mode of operation

The work programme and modus operandi of the Crystalline Club are co-ordinated by the Crystalline Club Bureau which consists of six experts. Project topics are driven by common interest among members. The mode of co-operation is by plenary meetings, periodic general workshops and the use of electronic media.

Decisions of the Crystalline Club are made in its plenary meetings or through written procedures by mutual agreement.

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