Assessing the concrete of Nuclear Power Plants containment by NDT

International audienceThe aging of prestressed concrete containments wall of nuclear power plants is experimentally modelled by a 1/3 scale mock-up of 15 m in diameter and 20 m in high carried out by EDF within the VeRCoRs project. This aging leads to the modification of the concrete properties as well as to possible mechanical damage during a pressurization cycle at 4.2 bars of the containment. This pressurisation carried out annually on the mock up, represents the conditions of the ten-year inspections imposed by the French regulations for Nuclear Power Plants (NPP).On the basis of several previous projects having developed Non Destructive Techniques (NDT) for civil engineering in laboratory and structured their transfer on site, a consortium made up of 9 partners participated in the monitoring of this double-walled containment within the framework of the ENDE project (Non Destructive Evaluation of the NNP containment walls). NDTs have been implemented with two objectives: assessing the physical (water content, porosity) and mechanical (strength, modulus of elasticity) properties of concrete over time and monitoring structure damage (depth and opening closing of cracks) more specifically when the containment vessel is under pressure. The techniques used for characterization are: ultrasonic waves (linear, diffuse and nonlinear acoustics), electromagnetic and electric fields and permeability. A statistical selection of the most efficient measured parameters is associated with a fusion of multi-technical data to assess the concrete properties.To monitor the damage, the NDTs are implemented on an area with cracks. They are surface ultrasounds for deep auscultation, acoustic emission, and diffuse waves.A third approach is developed with a global analysis of the structure by follow of modal analysis and vibration.The article presents the auscultation strategies and measurement methodologies for the three objectives, the proposed innovations, and the results. We focus on the evolution of the water content that we can quantify as well as on the control of cracks length and opening.We intend to propose a strategy of Structural Health Monitoring of the containment walls with a global-local approach based on the modal analysis of the enclosure