<p style="text-align: justify">Severe accident at TEPCO’s Fukushima Dai-ichi Nuclear Power Station (FDNPP) occurred due to a strong earthquake and massive tsunami that struck the eastern region of Japan on 11 March 2011. During this accident, reactor core of Unit 1, 2 and 3 of the 1F melted and fuel debris formed in the reactor pressure vessel (RPV) and primary containment vessel (PCV). The Japanese Government has drawn mid- and long-term roadmap towards 1F decommissioning. However, the decommissioning work of the three reactors has faced difficulties due to the lack of realistic information about the damaged cores such as distribution of fuel debris. Since the radiation levels inside the reactor buildings have been too high for human access, the robots and camera have been using to investigate the internal status of PCV. To accelerate the decommissioning process of 1F, determination of fuel debris information and contaminated water leakage are crucial to decide further decommissioning steps and strategies. Therefore, in this study, we are developing an ultrasonic measurement system that can obtain shape of object and velocity around it. Because ultrasonic sensors sensor is robust against high radiation dose and applicable in opaque liquids. Ultrasonic system used in the present study consists with two sectorial array transducers, which can measure object shape and 2D vector flow field. To measure velocity and shape of object that representing fuel debris, Ultrasonic Velocity Profiler (UVP) and Total Focusing Methods (TFM) are employed, respectively. Based on measurement results of the 2D vector field and shape of object, we can predict contaminated water leakage and distribution of object at the bottom of the PCV in 1F. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p><p style="text-align: justify">Key words: Fukushima Daiichi NPP, Decommissioning, Fuel debris, Ultrasound, Sectorial Array Sensors</p>

Development of Ultrasonic Measurement System for Shape and 2d Velocity Field Using Ultrasonic Velocity Profiler and Total Focusing Methods

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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