Optical Fiber for 3D Imaging of Deformations in Concrete Containers Stacked

Abstract

long-term management of all radioactive waste. Andra is developing a 500-metre deep disposal concept for High and Intermediate Level Long Lived Waste (HLW & ILLW). For the ILLW, the primary nuclear waste packages will be enclosed in reinforced concrete containers before final storage. Such kind of concrete waste container must fulfill appropriate specifications. For instance, three containers could be stacked on top of each other. As each container loaded by its primary waste package weights about 15 tons, and in order to verify that this capability reveal very little deformation, a full scale test has been set up. Two samples of concrete containers have been instrumented by two optical fiber sensing cables to provide distributed strain measurements and eight vibrating wire strain gauges. These sensors have been fixed on the reinforcement bars before the concrete pouring. An Optical Backscatter Reflectometer (OBR) connected to the optical fibers provides fast measurements of deformations all along the fiber with a centimeter spatial resolution (inside the container). An adequate positioning of the optical fibers with regards to the vibrating wire strain gauges has revealed not only the little deformations at the stacking step but also when the containers are lifted up. This paper presents tools and methodology of the test. It describes the experimental results and comparison to the data resulting from a modeling (FEM).