Issues for detecting undeclared post-closure excavation at geologic repositories

Following closure, safeguards monitoring will be required for geologic repositories storing spent fuel and other waste forms not qualifying for international safeguards termination. Monitoring for acoustic emission from tunneling machinery, periodic satellite surveillance and site visits are the primary methods proposed for detecting undeclared excavation. Of these, only acoustic monitoring can detect subsurface activity, allowing a fixed monitoring perimeter to be established around a repository. If acoustic monitoring can be defeated, and other subsurface detection methods are unavailable, then surface monitoring must be performed for a larger, more ambiguous radius around the repository. This paper presents a fundamental classification scheme for identifying excavation technologies. The classification allows definition of a spectrum of small-diameter tunnel excavation scenarios. Analysis suggests that even for hard rock, national groups may be able to field compact, modular hydraulic or thermal excavation machinery with acoustic emission below background noise levels. This provides motivation for additional studies of subsurface monitoring methods and diversion scenarios, and suggests that the selection of repository geological media may have important implications for detecting undeclared tunnel excavation.

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