Stability and Buffering Capacity of the Geosphere for Long-term Isolation of Radioactive Waste

Application to Crystalline Rock

image of Stability and Buffering Capacity of the Geosphere for Long-term Isolation of Radioactive Waste
Geological settings selected as potential host formations for the deep geological disposal of radioactive waste are chosen for, among other assets, their long-term stability and buffering capacity against destabilising events and processes. These proceedings present the outcomes of a geosphere stability workshop, held in November 2007, that focused on crystalline and other types of hard, fractured rocks. The workshop underscored the fact that many such rocks are intrinsically stable environments that evolve extremely slowly and provide good buffering against external events and processes.

The proceedings show a good understanding of the processes and events that can affect crystalline rocks and, although there is less confidence in predicting exactly when and where such events will occur and the volume of rock that will be affected, the extent of the impacts on a geological repository can be confidently addressed using bounding approaches supported by geological information from similar sites around the world.



Response and Resilience of Crystalline Rock to Natural Perturbations and Geosphere Evolution (Buffering)

Nuclear Energy Agency

The present paper describes a method to calculate fracture shear displacements occurring as a result of the stress waves and the static stress redistribution following a seismic slip on a nearby fault. Such secondary fracture shear displacements can theoretically, if large enough, damage intersected canisters containing spent nuclear fuel. The method is applied to a type of seismic event that is, or may be, of concern for the long term safety of a KBS-3 nuclear fuel repository: namely, endglacial earthquakes of magnitude 6 and larger. The numerical scheme used to simulate rupture initiation and propagation is described and illustrated. Result examples are given that show that secondary shear displacements on 300 m diameter fractures will be smaller than the damage criterion now applied by the Swedish Nuclear Fuel and Waste Management Co (SKB), provided that the fracture center is at a distance of 200 m or larger from the fault plane. The relevance of the rupture representation is discussed based on comparison with slip velocity records from a recent, large and well-documented crustal earthquake and with stress drop estimates made for large endglacial faults observed in Lapland, northern Sweden. 


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