Deep geological disposal is currently the accepted solution for spent nuclear fuel (SNF), aiming to isolate radioactive waste from the environment for extended time spans. In Israel, the feasibility of geological disposal of SNF in the Ghareb formation, within the Yamin Plain is being evaluated. The Ghareb formation is rich in Kerogen. Exposure to decay heat from radioactive waste may lead to kerogen decomposition, releasing gases such as hydrogen, hydrocarbons, and hydrogen sulfide that could compromise the sealing system integrity.
This research focuses on a borehole, at the west of the Yamin plain, penetrating a deep bituminous Ghareb section. This borehole serves as a unique platform to examine gas transport from organic rich sources, not observed in common boreholes in Israel. The primary objective is to characterize the natural baseline gas flow and composition at the borehole, establishing a benchmark to distinguish natural processes from disposal effects.
Unlike standard monitoring methods that rely on discrete sampling and often miss rapid subsurface dynamics, this study developed a continuous, low-cost multi-sensor monitoring system. This design approach allows for the integration of multiple sensors along the borehole profile, thereby increasing data resolution. The method's key innovation lies in its ability to generate high-resolution time series, revealing the borehole's "breathing" mechanisms and natural variations in gas composition in real-time. The experimental setup includes autonomous nodes installed within the borehole at depths of 3 and 50 meters, measuring CO₂, O₂, temperature, and humidity at high frequency. Preliminary analysis reveals that the borehole "breathes," exhibiting sharp and rapid changes in gas concentrations. A clear correlation was observed between increasing CO2 and decreasing O2 concentrations, down to anoxic conditions, indicating distinct outflow events. These findings demonstrate the system's sensitivity and its ability to document natural state changes in real-time, providing a critical tool for future safety monitoring.