Instrumentation and monitoring of tunnel plug in ONKALO

Posiva Oy has established a monitoring program that ensures the applicability of the constructed facilities to the final disposal of nuclear waste and the long-term capacities of engineered barrier systems. A monitoring system for a full-scale demonstration is installed to a tunnel end plug being built in a demonstration tunnel in the bedrock of Olkiluoto in Finland. The concrete plug will be instrumented with sensors continuously measuring displacements, strain, humidity, total and pore pressure and temperature. Further sensors will allow for monitoring the pressure being applied in a filter layer behind the plug and the observation and control of the main parameters needed during the pressurization of the structure by pumping water behind the plug. The general idea is to carefully measure the amount and pressure of incoming water in order to analyze the performance of sealing mechanisms of the structure. The out-flowing leakage and in-pumped water will also be determined by a monitoring system.