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Simultaneous 4D Cross-borehole ERT Inversion to Guide Leak Monitoring in Nuclear Decommissioning
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Near Surface Geoscience 2014 - 20th European Meeting of Environmental and Engineering Geophysics, Sep 2014, Volume 2014, p.1 - 5
Abstract
Nuclear decommissioning efforts at the Sellafield site, UK, are increasingly supported by near-surface geophysical monitoring. Electrical Resistivity Tomography (ERT) is being applied to help manage the increased risk of leakage from the Magnox Swarf Storage Silos (MSSS) during planned waste retrievals.
A full-scale field trial of ERT has been undertaken in the immediate vicinity of the MSSS site. Six borehole electrode arrays were installed to monitor a subsurface volume equal in size to a proposed imaging cell under the MSSS structure. An automated geoelectrical imaging system was used to observe dynamic resistivity changes within the ground caused by simulated leaks.
Controlled injections into the vadose zone of environmentally benign conductive simulants were designed to test a number of realistic leak scenarios. The complex geology and low conductivity contrasts provided a significant challenge for ERT to detect and characterise the simulated leaks.
We show that full, simultaneous 4D ERT inversion successfully resolved the pathways adopted by the tracer fluid; these were found to be compatible with historic contamination detected in cores retrieved from the boreholes. The trial has demonstrated the value of ERT for nuclear decommissioning by enhancing our conceptualisation of likely behaviour of potential future leakage at MSSS.