Advanced Distributed Optical Fiber Strain Sensing for Monitoring Radioactive Waste Package Degradation

The safe and effective deep geological disposal of nuclear waste depends on advanced technologies to monitor the degradation of radioactive waste packages. However, long-term monitoring of such facilities presents significant challenges, including restricted access to waste packages and the need to minimize intrusive equipment such as sensors that must pass through protective containment barriers.

This study explores the feasibility and benefits of using high spatial resolution Distributed Optical Fiber Strain Sensing (DOFSS) for the remote detection of package strain evolution and cracks detection, both key indicators of radioactive waste package degradation. DOFSS, widely used in civil engineering for structural health monitoring applications, has been adapted with a novel approach: the integration of optical fiber sensing cables within the concrete walls surrounding nuclear waste packages. This is achieved using 3D additive-printed support structures, which ensure precise installation positioning of the cable and enable high-performance, direct strain measurements. Laboratory experiments simulated package degradation were carried out on reduced scale samples through applying external mechanical force, sulfate attack tests, and CO₂ injection tests. The results demonstrate that DOFSS can effectively map concrete strain and track the evolution of the package shape over time. Furthermore, it can detect concrete cracking, with data analysis providing precise information on the location and width of created fractures.

DOFSS enables the monitoring of both localized and abrupt disruptions such as cracking, and diffuse effects caused by swelling, loading or temperature changes. These findings highlight DOFSS as a promising and effective method for the remote monitoring of radioactive waste package degradation.