Geophysical Understanding of Coupled Thermal-Hydro-Mechanical Dynamics in Rock Salt During Heating

The distinctive properties of salt, such as low permeability, high thermal conductivity, and self-sealing features, make it a suitable medium for storing heat-generating radioactive waste. Understanding the thermal, hydrological, and mechanical (THM) processes, including permeability evolution and brine migration around the heat source, is crucial for safety. The Brine Availability Tests in Salt (BATS) at the Waste Isolation Pilot Plant were conducted to investigate these processes, employing an array of sensors and techniques like electrical resistivity tomography (ERT), fiber optic distributed temperature sensing (DTS), and strain sensing (DSS). These techniques monitored temperature changes, brine movement, and stress conditions in the salt.

This presentation highlights the results from ERT, DTS, and DSS in controlled heating experiments, focusing on the response differences across various heating events. The analysis, augmented by Discrete Element Models (DEM) simulations, showed that resistivity changes were sensitive to temperature and brine movement. A significant decrease in resistivity, especially beyond temperature effects, indicated brine migration or permeability changes. The DTS and DSS data captured the evolving thermal and mechanical responses of the salt to heating and cooling cycles, including salt deformation, and creeping towards the drift wall.

Joint analysis of ERT, DTS, and DSS data provided an integrated understanding of THM processes in salt during heating. Consistent heating and brine migration patterns were observed across different events. Ongoing work aims to combine all monitoring data for a deeper insight into the coupled behaviors in salt formations, offering valuable calibration and benchmarking for numerical models.