Autonomous 3D Electrical Resistivity Tomography Monitoring For Geologic Repository Safeguards

A recent geophysical analysis technique called Autonomous 3D Electrical Resistivity Tomography (ERT) is available that would be analogous to taking an MRI of a geologic repository. This could be used to continuously monitor for indications of diversion or undeclared access. The technique involves placing electrodes down multiple boreholes or within the repository to autonomously and continuously monitor the 3D electrical conductivity of each region of interest. Electrical conductivity can be used as a proxy indicator to assess the state of the imaged materials over time. Systems using the new technology have been successfully deployed to monitor, for example, the movement of chemicals through the subsurface, alterations in electrical conductivity from underground explosions, leaks from buried piping systems at nuclear power plants, engineered subsurface desiccation, and groundwater migration through the subsurface. Finland and Sweden are preparing deep geological repositories for the permanent disposition of spent nuclear fuel. Repositories pose a significant challenge to verification due to the inability to access the material following emplacement and the very long timeframes involved. There is an opportunity to contribute to the overall effort of geological repository safeguards by providing performance details about 3D ERT that is expected to be cost effective and robust over time. This paper and presentation will describe the modeling work that has been performed to date on various options for deploying 3D ERT in a repository and the costs and benefits of such a system. This work was supported by the US Dept. of Energy, National Nuclear Security Administration, Office of International Nuclear Safeguards. This is PNNL document number PNNL-SA-159921.