// Waste Management Strategies and Methods, Repository Design

OSMOSS

Operational Safety Monitoring with Fiber Optic Sensing Systems

For several years, fiber-optic sensing devices had been used for straightforward on/off monitoring functions such as presence and position detection. Recently, they are receiving increasing attention as they offer a novel, exciting technology for a multitude of sensing applications. In the deep geological environment most physical properties, and thus most parameters important to safety, can be measured by using fiber-optic technology. The objective of this project has been focused on measurement of physical parameters for thermo-hydro-mechanical monitoring of structures within final repositories as well as the contents of harmful gases for operational safety purposes. The activities performed within this project can be divided in three categories: Development of new sensors addressing the parameters: pH, hydrogen, temperature, porewater pressure, total pressure, fissurization, and high resolution deformation effects; further development and improvement of the interrogation systems for monitoring of complex large scale sensing networks as well as extending the evaluation results of the behavior of the fiber optical monitoring systems in real field installations. The selected sensors have all been developed and tested. Some sensors still require some more fine tuning but the overall goal has been achieved. The interrogation system has completely be redesigned and improved with respect to accuracy and reliability. A couple of field installations have been equipped during the project for evaluating and qualifying the developed fiber optical sensing network systems. A good correspondence with conventional sensors has been demonstrated. After dismantling of the sensing network at the Konrad site, all sensors had been recalibrated and did still show an excellent sensor response. No contamination or malfunctioning could be observed after almost 4 years of operation. From all these field results it can be concluded that fiber optic monitoring systems devoted to operational safety in nuclear waste disposal sites is becoming a very interesting alternative for the conventional electrical sensing systems.