Non-Destructive Testing Technique for NPP Containment Concrete Structure Inspection

Large public infrastructure facilities around the world like dams, cooling towers and bridges use concrete as the main building material. Although made from a durable material many of these large assets have begun to age and are in need of periodic inspection to ensure their integrity. Integrity assessment is particularly important in case of containment building in nuclear power plants, since it is a last barrier the between highly contaminated area and the environment in case of hazard event. The inspection process of these structures is not adequately developed yet. Current inspection routine involves setting up scaffolds that have to be moved around for personnel to reach the whole surface. In order to make proper integrity assessment of concrete structure in timely manner, visual inspection manually performed by inspection personnel is not convenient solution. The VortexScan project has developed a vortex robot that is used to autonomously navigate the vertical surfaces of such structures while deploying a combination of non-destructive inspection techniques. Air suction through a nozzle of a specific geometry creates a vortex and initiates a force that attaches the robot to a vertical surface while its wheels move it around. NDT techniques developed for this application are Ground Penetrating Radar (GPR) and low frequency ultrasound (UT). The data fusion is used to diminish the drawbacks of each technique and create an accurate representation of the underlying material and its defects. In this paper, both of these NDT techniques are presented. The prototype system has been tested for the inspection of the concrete sample with known internal structural features, such as reinforcement bars, plastic ducts and post-tensioning tendon. Signals from GPR sensor and UT transducer are documented and the results from the experimental testing of the system follow with discussion and conclusions on them. The testing results verify the feasibility of the developed NDT system for concrete inspection. (author).