An ultrasonic measurement system and its robotic deployment into vessels for the combined assessment of debris condition and water leakage

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The decommissioning of the Fukushima Dai-ichi Nuclear Power Site (1F) is a high priority for Japan and there are lessons to be learned for decommissioning across the globe. The current situation is that the reactor is flooded with water and the location and distribution of the fuel debris is unknown. A specially designed robot has gained entry to the containment vessel, however, access is severely restricted. This project will investigate the potential of an ultrasonic measurement system and its robotic deployment to assess the conditions within the flooded regions of the primary containment vessel and reactor pressure vessel. Ultrasonic measurements are particularly attractive in this application as they can overcome the problems associated with poor visibility in the water in addition to which the sensors are small and insensitive to radioactivity. We propose the development of three ultrasonic measurement systems integrated into a compact package suitable for robotic deployment. The first two sensor systems will measure flow on a large-scale (meters) and on a smaller-scale (centimetres). This will enable the location and quantification of leakage points. These are known to exist as water is currently being continuously pumped into the reactor. In addition ultrasonic sensor arrays will be developed to image the interior of the vessels and locate and quantify the fuel debris. Attempts will also be made to image inside the debris to discover its structural integrity. This information will ultimately feed into attempts to safely remove the debris. These measurement systems will be built and integrated into a robotic platform and tested on a laboratory-based replica. The project will combine expertise on ultrasonic flow measurement and robotics from Japan with expertise on ultrasonic imaging from the UK. The research will lay the foundation for the decommissioning of the Fukushima Dai-ichi 1F reactor and provide valuable new techniques and expertise for decommissioning activities in the UK and around the world.