After over a decade of heating: field-scale insights into coupled processes from the Full-scale Emplacement experiment

The Full-scale Emplacement (FE) experiment at the Mont Terri rock laboratory provides crucial in-sights into the coupled thermo-hydro-mechanical (THM) processes governing the near-field evolution of high-level radioactive waste repositories. This contribution presents an analysis of ten years of continuous monitoring data from FE, which features three heaters embedded in bentonite buffer within a full-scale emplacement tunnel in Opalinus Clay. Comprehensive instrumentation enables detailed monitoring of the evolution in the buffer and the near field. Results demonstrate conduction-dominated heat transport with thermal gradients of approximately 80 °C/m established across the buffer. In the geosphere, thermally induced pore pressure changes show clear anisotropic responses. Buffer resaturation progresses slowly with water redistribution showing drying near heaters and condensation in cooler zones. The slow saturation rate, despite significant suction gradients in the bentonite, confirms that resaturation is limited by the low permeability of the host rock rather than buffer properties. Gas monitoring reveals no anomalous compositions that would challenge buffer integrity. The comprehensive dataset validates the conceptual model for bentonite buffer evolution.